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Origin and Diagenesis of Cryptobiontic Frutexites in the Chapel Island Formation (Vendian to Early Cambrian) of Southeast Newfoundland, Canada
Abstract
The sheet cracks, which formed from expansion of the microbial mat and associated sediment, stayed in communication with sea-water until they became filled with marine cement. Some microfossils show laminae and a fibrous microstructure whereas others consist of cement-filled chambers or hematitic clots devoid of obvious microstructure. -from Authors
... Kazmierczak and Kempe (2006) registered Frutexites-like structures in modern shallow-water stromatolites growing in alkaline environments. A cryptobiontic lifestyle of the organisms originating Frutexites has been proposed by Myrow and Coniglio (1991), Böhm and Brachert (1993) and Cavalazzi et al. (2007). ...
... An abiotic process was first proposed by Wendt (1970) given the superficial resemblance of Frutexites to abiotic dendrites. Nevertheless, the involvement of microbes in mineral precipitation and the number of reports of microbial signatures found in Frutexites (Horodyski, 1975;Lowenstam and Weiner, 1989;Chafetz et al., 1998;Buczynski and Chafetz, 1991;Frankel and Bazylinski, 2003;Rodríguez-Martínez et al., 2011a, 2011bJakubowicz et al., 2014) led to the wide acceptation of the hypothesis that Frutexites grow as a result of microbial activity (Myrow and Coniglio, 1991;Böhm and Brachert, 1993;Reolid, 2011). Their origin was assigned to cyanobacteria (Maslov, 1960;Szulczewski, 1963) and to other phototrophic microbes (Myrow and Coniglio, 1991). ...
... Nevertheless, the involvement of microbes in mineral precipitation and the number of reports of microbial signatures found in Frutexites (Horodyski, 1975;Lowenstam and Weiner, 1989;Chafetz et al., 1998;Buczynski and Chafetz, 1991;Frankel and Bazylinski, 2003;Rodríguez-Martínez et al., 2011a, 2011bJakubowicz et al., 2014) led to the wide acceptation of the hypothesis that Frutexites grow as a result of microbial activity (Myrow and Coniglio, 1991;Böhm and Brachert, 1993;Reolid, 2011). Their origin was assigned to cyanobacteria (Maslov, 1960;Szulczewski, 1963) and to other phototrophic microbes (Myrow and Coniglio, 1991). The presence of Frutexites in deep-water and cryptic habitats is in contrast with this interpretation (Tsien, 1979;Böhm and Brachert, 1993;Reolid and Nieto, 2010;Reolid, 2011). ...
... Kazmierczak and Kempe (2006) registered Frutexites-like structures in modern shallow-water stromatolites growing in alkaline environments. A cryptobiontic lifestyle of the organisms originating Frutexites has been proposed by Myrow and Coniglio (1991), Böhm and Brachert (1993) and Cavalazzi et al. (2007). ...
... An abiotic process was first proposed by Wendt (1970) given the superficial resemblance of Frutexites to abiotic dendrites. Nevertheless, the involvement of microbes in mineral precipitation and the number of reports of microbial signatures found in Frutexites (Horodyski, 1975;Lowenstam and Weiner, 1989;Chafetz et al., 1998;Buczynski and Chafetz, 1991;Frankel and Bazylinski, 2003;Rodríguez-Martínez et al., 2011a, 2011bJakubowicz et al., 2014) led to the wide acceptation of the hypothesis that Frutexites grow as a result of microbial activity (Myrow and Coniglio, 1991;Böhm and Brachert, 1993;Reolid, 2011). Their origin was assigned to cyanobacteria (Maslov, 1960;Szulczewski, 1963) and to other phototrophic microbes (Myrow and Coniglio, 1991). ...
... Nevertheless, the involvement of microbes in mineral precipitation and the number of reports of microbial signatures found in Frutexites (Horodyski, 1975;Lowenstam and Weiner, 1989;Chafetz et al., 1998;Buczynski and Chafetz, 1991;Frankel and Bazylinski, 2003;Rodríguez-Martínez et al., 2011a, 2011bJakubowicz et al., 2014) led to the wide acceptation of the hypothesis that Frutexites grow as a result of microbial activity (Myrow and Coniglio, 1991;Böhm and Brachert, 1993;Reolid, 2011). Their origin was assigned to cyanobacteria (Maslov, 1960;Szulczewski, 1963) and to other phototrophic microbes (Myrow and Coniglio, 1991). The presence of Frutexites in deep-water and cryptic habitats is in contrast with this interpretation (Tsien, 1979;Böhm and Brachert, 1993;Reolid and Nieto, 2010;Reolid, 2011). ...
... 12 microbial signatures found in Frutexites (Horodyski 1975;Lowenstam and Weiner, 1989;Chafetz et al. 1998;Buczynski and Chafetz 1991;Frankel and Bazylinski 2003;Rodríguez-Martínez et al., 2011a, 2011bJakubowicz et al., 2014) led to the wide acceptation of the hypothesis that Frutexites grow as a result of microbial activity (Myrow and Coniglio, 1991;Böhm and Brachert, 1993;Reolid, 2011). Their origin was assigned to cyanobacteria (Maslov, 1960;Szulczewski, 1963) and ...
... to other phototrophic microbes (Myrow and Coniglio, 1991). The presence of Frutexites in deepwater and cryptic habitats is in contrast with this interpretation (Tsien, 1979;Böhm and Brachert, 1993;Reolid and Nieto 2010;Reolid, 2011). ...
... On the contrary, Kazmierczak and Kempe (2006) found Frutexites-like structures in modern shallow stromatolites. A cryptobiontic behavior of the organisms producing Frutexites has been proposed by Myrow and Coniglio (1991) on the surface of the larger cavities and fractures, while Frutexites texture seems to grow from discontinuity surfaces into the surrounding micritic sediment microcavities, possibly widened and hardened during early diagenesis. The arborescent texture seems related to microcavity shapes attained through enlargement of the original micropores by dissolution. ...
Frutexites-like structures were recorded in small bioconstructions from Recent and Pleistocene marine caves. The skeletal/microbialite frameworks hosting Frutexites form in cryptic environments characterized by poor light availability and reduced water circulation leading to confinement, oligotrophic conditions and the development of typical cave communities. Biostalactites and biotic crusts develop in the more confined parts of the both Recent and Pleistocene caves. They are composed of skeletal organisms engulfed in fine micrite sediments deposited in situ via microbial metabolic activity. The Frutexites, composed of Iron and Manganese oxides, are confined to microcavities or microfractures of the bioconstructions. They grow from an original discontinuity surface into the surrounding consolidated micritic sediments. A model based on the increase of the microporosity of micritic sediments due to the dissolution of the original material and precipitation of ferromanganesiferous compounds was proposed. This process occurs during the syndepositional diagenetic stage due to the intrusion in the bioconstruction framework of acidic continental water rich in Iron and Manganese. Mesophilic Fe-Mn autotrophic and chemoheterotrophic bacteria flourish on the microcavities and induce the precipitation of Fe and Mn oxides.
... Frutexites, Figure 4 cracks within stromatolites of the Upper Vendian to Lower Cambrian Chapel Island Formation, Canada (Myrow and Coniglio, 1991). Frutexites have been found in cavities of Devonian deep water mud mounds and grouped with Renalcis-Epiphyton calcimicrobes, and with deep water stromatolites assemblage (Tsien, 1979) as well as in stromatactoid cavities from Viséan microbial limestones where they occur interbedded with marine isopachous crusts of fibrous and botroydal calcite cements (Gischler, 1996). ...
... Some authors (Myrow and Coniglio, 1991;Böhm and Brachert, 1993) have compared the marine records of Frutexites with similar arborescent, dendritic forms found in speleothems, desert varnish, and travertines. Also, continental manganese and iron-rich black shrubs have been compared with the marine Frutexites records (Koban and Schweigert, 1993;Chafetz et al., 1998). ...
... Hofmann and Grotzinger (1985) discussed the affinity of Frutexites to different cyanobacteria and proposed further alternatives (purely physicochemical accretion and/or iron bacteria due to the ferruginous character of stromatolite). The occurrence of Frutexites in cavities, fissures, and dykes was interpreted as a cryptobiont role (Myrow andConiglio, 1991). However, Tsien (1979) was the first suggesting a non-phototrophic character, sometimes linked to chemoheterotrophic cyanobacteria (Gischler, 1996) or to chemohetero and autotrophic bacteria (Cavalazzi et al, 2007). ...
SynonymsFe-oxidizers; Fe(II)-oxidizing prokaryotes/microorganisms; Ferrous iron-oxidizing prokaryotes/microorganisms; Iron-oxidizers; Iron-oxidizing prokaryotes/microorganisms.; Iron(II)-oxidizing prokaryotes/microorganismsDefinitionFe(II)-oxidizing prokaryotes. Diverse species of the prokaryotic domains Bacteria and Archaea have the ability to oxidize Fe(II), ferrous iron, to Fe(III), ferric iron. The electrons obtained from the oxidation of Fe(II) are utilized for energy generation in aerobic or anaerobic respiration and/or for assimilative reduction reactions.IntroductionAerobic neutrophilic Fe(II)-oxidizing bacteria were among the first environmentally relevant prokaryotes that were discovered and studied in the nineteenth century. At that time, eye-catching ochre deposits in ponds and slowly running waters had attracted the attention of microbiologists. Microscopic analyses of such ochre deposits revealed the prevalence of twisted stalks a ...
... Black shrubs also occur in Quaternary travertines found in the vicinity of Belin, north-central New Mexico, and in the Eocene travertines of the Palm Park Formation, southern New Mexico. Similar features have been reported as a component within desert varnish (Krumbein and Jens 1981), and in deep-sea Mn nodules (Sorem and Fewkes 1979), as well as forming the major constituent in the fossil Frutexites (Myrow and Coniglio 1991). ...
... 10b;Walter and Awramik 1979, fig. 10;Myrow and Coniglio 1991, fig. 7). ...
... In addition to the morphological resemblances, other similarities exist between the black Mn-rich travertine shrubs and these other shrubs, such as Frutexites. Frutexites is an Fe-rich fossil with a shrub morphology that has been recognized in shallow marine (Myrow and Coniglio 1991) to deep marine (Bohm and Brachert 1993) deposits and has an age range from early Proterozoic (Hofmann and Grotzinger 1985) to Jurassic (Myrow and Coniglio 1991). Frutexites has formed within voids in the sediment and ''its negative phototactic downward growth is evidence for a non-photosynthetic mode of life and indicative of dark environments. ...
Black shrubs (i.e., arborescent forms) are present within hot-water travertine deposits from Morocco. The shrubs are commonly a few centimeters high and laterally grouped along individual laminae. Other than in mineral composition, the black shrubs closely resemble the calcite shrubs from other hot-water travertine deposits (e.g., Bagni di Tivoli, Italy, and Mammoth Hot Springs, Yellowstone National Park). They are composed of a variety of minerals that are Mn-rich and also have a significant Fe-oxide component. Similar Mn- and Ferich shrub-like forms have been described from desert varnish, deepsea Mn nodules, and marine carbonates (Frutexites). SEM analyses show that bacterial bodies are densely packed within the Mn-rich black travertine shrubs whereas no bacterial bodies are evident within the enclosing aragonite and calcite laminae. The bacterial bodies range in shape and size from rods (commonly 0.8 fini long by 0.1 |im in diameter), to spherical forms (commonly 0.3 fini in diameter) that form chains up to l (im long, to nanobacterial spheres (150 to 200 nm in diameter) that make up densely packed chains commonly 15 n.m in length. It is well documented within the microbiological literature that, not only do bacteria have the ability to induce the precipitation of Mn and Fe, they can concentrate Mn in mineral precipitates from waters with very low to essentially undetectable concentrations of Mn. The black Mn-rich shrubs within the Moroccan travertines, other hot-water travertines, and related features such as desert varnish, deep-sea Mn nodules, and Frutexites are postulated to also be the result of bacterially induced precipitation.
... Generally, Frutexites seem to have preferred low-energy environments, characterized by low sedimentation rates and often limited availability of oxygen; they are consequently commonly found on the bottoms of deep, dysaerobic basins (Playford et al. 1976;Tsien 1979;Böhm and Brachert 1993;Reitner et al. 1995;Mamet and Préat 2006;Woods and Baud 2008;Lazȃr et al. 2012), not uncommonly in association with hardground surfaces (Mišík and Aubrecht 2004;Reolid and Nieto 2010). Where present in shallow-water settings, in turn, Frutexites are typically limited to cryptic environments, such as such as small cavities and sheet cracks (Hofmann 1969;Horodyski 1975;Walter and Awramik 1979;Myrow and Coniglio 1991). Frutexites shrubs are rarely associated with contemporaneous benthic metazoans, although in some cases they encrusted other organisms after their death (Préat et al. 2008;Reolid and Molina 2010), and, occasionally, were overgrown themselves by foraminifera (Reolid and Molina 2010;Rodríguez-Martínez et al. 2011b). ...
... Given the superficial resemblance of Frutexites to abiotic dendrites, it has been proposed that they could have formed due to purely abiotic processes (Wendt 1970). The growing evidence for the involvement of microbes in mineral precipitation (e.g., Buczynski and Chafetz 1991;Frankel and Bazylinski 2003) and the growing number of reports of microbial-associated fossils found in Frutexites and Frutexites-like structures (e.g., Horodyski 1975;Chafetz et al. 1998) have, however, led to the wide acceptation of the hypothesis that Frutexites grew as a result of microbial activity (e.g., Myrow and Coniglio 1991;Böhm and Brachert 1993;Reolid 2011). Yet, the specific types of microbes involved, as well as the primary composition of the shrubs remains a matter of discussion. ...
... Yet, the specific types of microbes involved, as well as the primary composition of the shrubs remains a matter of discussion. Whereas early workers proposed that Frutexites-forming organisms were cyanobacteria (Maslov 1960;Szulczewski 1963;Walter and Awramik 1979;Nicoll and Playford 1993) or other phototrophic microbes (Myrow and Coniglio 1991), others disagreed, pointing at the common presence of Frutexites in deep-water or cryptic habitats (Tsien 1979;Böhm and Brachert 1993;Reolid and Nieto 2010;Reolid 2011). Instead, it has been proposed that Frutexites formed as a result of the activity of iron bacteria (Playford et al. 1976;Chafetz et al. 1998), but the role of various microbes and the exact mechanism of iron precipitation are still poorly understood. ...
Microbially induced Frutexites microstromat-olites developed on corallites of the Givetian rugose coral ''Amplexus'' in the sedimentary cover of a submarine volcanic intrusion in the eastern Anti-Atlas of southern Morocco. The corals lived in proximity to submarine hydrothermal fluid emissions. Frutexites form irregular shrubs encrusting external walls of corallites. The shrubs, consisting of alternations of calcitic and hematitic laminae, grew predominantly on abandoned corallites. Some Fru-texites grew within the sediment, whereas others developed entirely above the seafloor, or started their accretion in water and continued to grow during burial. Three types of Frutexites encrustations have been distinguished. They look similar macroscopically, but differ significantly in their microstructure and mineralogical characteristics, resulting primarily from spatial and temporal variations in redox conditions. Both hematitic and calcitic laminae are primary features of Frutexites. The shrubs accreted as a result of mineralization of microbial biofilms under fluc-tuating environmental conditions, caused by changes in pH, Fe 2? -supply and/or oxygenation, presumably related to discharges of reducing hydrothermal fluids. The calcitic laminae are interpreted to have formed due to activity of heterotrophic (mainly sulphate-reducing) microbes, whereas the hematitic laminae developed as a result of enhanced activity of nitrate-reducers or due to periodical passive mineralization of biofilms with iron. Cathodolu-minescence data provide evidence that the nitrate and sulphate reduction preceded the Mn(IV) and Fe(III) reduction, presumably due to increased accumulation of organic matter and a high stability of the iron oxides present.
... Generally, Frutexites seem to have preferred low-energy environments, characterized by low sedimentation rates and often limited availability of oxygen ; they are consequently commonly found on the bottoms of deep, dysaerobic basins (Playford et al. 1976; Tsien 1979; Böhm and Brachert 1993; Reitner et al. 1995; Mamet and Préat 2006; Woods and Baud 2008; Laza ˘r et al. 2012), not uncommonly in association with hardground surfaces (Mišík and Aubrecht 2004; Reolid and Nieto 2010). Where present in shallow-water settings, in turn, Frutexites are typically limited to cryptic environments, such as such as small cavities and sheet cracks (Hofmann 1969; Horodyski 1975; Walter and Awramik 1979; Myrow and Coniglio 1991). Frutexites shrubs are rarely associated with contemporaneous benthic metazoans, although in some cases they encrusted other organisms after their death (Préat et al. 2008; Reolid and Molina 2010 ), and, occasionally , were overgrown themselves by foraminifera (Reolid and Molina 2010; Rodríguez-Martínez et al. 2011b ). ...
... Given the superficial resemblance of Frutexites to abiotic dendrites, it has been proposed that they could have formed due to purely abiotic processes (Wendt 1970). The growing evidence for the involvement of microbes in mineral precipitation (e.g., Buczynski and Chafetz 1991; Frankel and Bazylinski 2003) and the growing number of reports of microbial-associated fossils found in Frutexites and Frutexites-like structures (e.g., Horodyski 1975; Chafetz et al. 1998) have, however, led to the wide acceptation of the hypothesis that Frutexites grew as a result of microbial activity (e.g., Myrow and Coniglio 1991; Böhm and Brachert 1993; Reolid 2011). Yet, the specific types of microbes involved, as well as the primary composition of the shrubs remains a matter of discussion. ...
... Yet, the specific types of microbes involved, as well as the primary composition of the shrubs remains a matter of discussion. Whereas early workers proposed that Frutexites-forming organisms were cyanobacteria (Maslov 1960; Szulczewski 1963; Walter and Awramik 1979; Nicoll and Playford 1993) or other phototrophic microbes (Myrow and Coniglio 1991 ), others disagreed, pointing at the common presence of Frutexites in deep-water or cryptic habitats (Tsien 1979; Böhm and Brachert 1993; Reolid and Nieto 2010; Reolid 2011). Instead, it has been proposed that Frutexites formed as a result of the activity of iron bacteria (Playford et al. 1976; Chafetz et al. 1998), but the role of various microbes and the exact mechanism of iron precipitation are still poorly understood. ...
Microbially induced Frutexites microstromat-olites developed on corallites of the Givetian rugose coral ''Amplexus'' in the sedimentary cover of a submarine volcanic intrusion in the eastern Anti-Atlas of southern Morocco. The corals lived in proximity to submarine hydrothermal fluid emissions. Frutexites form irregular shrubs encrusting external walls of corallites. The shrubs, consisting of alternations of calcitic and hematitic laminae, grew predominantly on abandoned corallites. Some Fru-texites grew within the sediment, whereas others developed entirely above the seafloor, or started their accretion in water and continued to grow during burial. Three types of Frutexites encrustations have been distinguished. They look similar macroscopically, but differ significantly in their microstructure and mineralogical characteristics, resulting primarily from spatial and temporal variations in redox conditions. Both hematitic and calcitic laminae are primary features of Frutexites. The shrubs accreted as a result of mineralization of microbial biofilms under fluc-tuating environmental conditions, caused by changes in pH, Fe 2? -supply and/or oxygenation, presumably related to discharges of reducing hydrothermal fluids. The calcitic laminae are interpreted to have formed due to activity of heterotrophic (mainly sulphate-reducing) microbes, whereas the hematitic laminae developed as a result of enhanced activity of nitrate-reducers or due to periodical passive mineralization of biofilms with iron. Cathodolu-minescence data provide evidence that the nitrate and sulphate reduction preceded the Mn(IV) and Fe(III) reduction, presumably due to increased accumulation of organic matter and a high stability of the iron oxides present.
... Petrographic examination of the black microbialites reveals a fabric comprised of the microfossil Frutexites surrounded by granular sparry calcite (Fig. 5A, B). Frutexites is a problematic microfossil found in rocks ranging in age from the early Proterozoic (Hofmann and Grotzinger, 1975) to the Jurassic (Böhm and Brachert, 1993), and is typically associated with deep-water, iron-rich stromatolites (e.g., Böhm and Brachert, 1993;Mamet and Préat, 2006), however it has also been documented from cryptic habitats in shallow marine settings (e.g., Myrow and Coniglio, 1991;Böhm and Brachert, 1993). The origin of Frutexites has generated some controversy over the years in terms of the organism responsible for the microfossil, as well as the timing of the iron mineralization of the microfossils, since Frutexites may be comprised of calcite, Fe-Mn minerals, or a combination of both (e.g., Walter and Awramik, 1977;Hofmann and Grotzinger, 1975;Böhm and Brachert, 1993;Chafetz et al., 1998). ...
... As noted previously, Frutexites have been documented in cryptic habitats (e.g., Myrow and Coniglio, 1991), and it might also be expected that they may have formed in voids within the Lower member of the Alwa Formation. Several lines of evidence suggest, however, that the Frutexites-bearing microbialites examined for this study formed on the seafloor, as opposed to within voids, including: 1) the occurrence of scattered ammonoid phragmacones within the microbialites (Fig. 9), suggesting that the microbialites were exposed to the water column; 2) the Frutexites-bearing microbialites do not cut across primary sedimentary features, which would be expected if they formed within voids; and 3) a lack of evidence that the Frutexites were occupying cryptic habitats; specifically, no Frutexites are observed growing downwards from the upper surfaces of the microbialites. ...
... Thrombolites do not require sunlight to form (e.g., Leinfelder et al., 1994), and multiple examples of deep-water or cryptic thrombolites and stromatolites have been described (e.g., Jenkyns, 1971;Massari, 1981;Dromart, 1989;Delamette, 1990;Zankl, 1993;Leinfelder, 1994;Mancini et al., 2004). Frutexites has also been documented from cryptic habitats (e.g., Myrow and Coniglio, 1991;Böhm and Brachert, 1993) as well as pelagic settings (e.g., Szulczewski, 1963;Playford et al., 1976;Massari, 1981;Böhm and Brachert, 1993;Mamet and Preát, 2006 for a review), which further indicates that the lower member of the Alwa Formation accumulated below the photic zone. ...
- The lower member of the Alwa Formation (Lower Olenekian), found within the Ba'id Exotic in the Oman Mountains (Sultanate of Oman), consists of ammonoid-bearing, pelagic limestones that were deposited on an isolated, drowned carbonate platform on the Neotethyan Gondwana margin. The strata contain a variety of unusual carbonate textures and features, including thrombolites, Frutexites-bearing microbialites that contain synsedimentary cements, matrix-free breccias surrounded by isopachous calcite cement, and fissures and cavities filled with large botryoidal cements. Thrombolites are found throughout the study interval, and occur as 0.5-1.0 m thick lenses or beds that contain laterally laterally-linked stromatactis cavities. The Frutexites-bearing microbialites occur less frequently, and also form lenses or beds, up to 30 cm thick; the microbialites may be laminated, and often developed on hardgrounds. In addition, the Frutexites-bearing microbialites also contain synsedimentary calcite cement crusts and botryoids (typically <1 cm thick) that harbour layers or pockets of what appear to be bacterial sheaths and coccoids, and are indicative of biologically mediated precipitation of the cement bodies. Slumping following lithification led to fracturing of the limestone and the precipitation of large, botryoidal aragonite cements in fissures that cut across the primary fabric. Environmental conditions, specifically palaeoxygenation and the degree of calcium carbonate supersaturation, likely controlled whether the thrombolites (high level of calcium carbonate supersaturation associated with vertical mixing of water masses and dysoxic conditions) or Frutexites-bearing microbialites (low level of calcium carbonate supersaturation associated with anoxic conditions and deposition below a stable chemocline) formed. The results of this study point to continued environmental stress in the region during the Early Triassic that likely contributed to the uneven recovery from the Permian-Triassic mass extinction.
... Frutexites, Figure 4 cracks within stromatolites of the Upper Vendian to Lower Cambrian Chapel Island Formation, Canada (Myrow and Coniglio, 1991). Frutexites have been found in cavities of Devonian deep water mud mounds and grouped with Renalcis-Epiphyton calcimicrobes, and with deep water stromatolites assemblage (Tsien, 1979) as well as in stromatactoid cavities from Viséan microbial limestones where they occur interbedded with marine isopachous crusts of fibrous and botroydal calcite cements (Gischler, 1996). ...
... Some authors (Myrow and Coniglio, 1991;Böhm and Brachert, 1993) have compared the marine records of Frutexites with similar arborescent, dendritic forms found in speleothems, desert varnish, and travertines. Also, continental manganese and iron-rich black shrubs have been compared with the marine Frutexites records (Koban and Schweigert, 1993;Chafetz et al., 1998). ...
... Hofmann and Grotzinger (1985) discussed the affinity of Frutexites to different cyanobacteria and proposed further alternatives (purely physicochemical accretion and/or iron bacteria due to the ferruginous character of stromatolite). The occurrence of Frutexites in cavities, fissures, and dykes was interpreted as a cryptobiont role (Myrow and Coniglio, 1991). However, Tsien (1979) was the first suggesting a non-phototrophic character, sometimes linked to chemoheterotrophic cyanobacteria (Gischler, 1996) or to chemohetero and autotrophic bacteria (Cavalazzi et al, 2007). ...
SynonymsColloform limonitic crusts; Frutexites crusts; Frutexites-like forms; Frutexites microstromatolite; Frutexites tuffs; Haematitic/ferruginous/iron microstromatolites; Iron dendritic aggregates; Iron shrubs; Pillar-shaped microstromatolitesDefinitionFrutexites is a problematic microfossil rich in iron. From a taxonomic point of view, only five species have been figured (Frutexites arboriformis, Maslov, 1960; F. microstroma, Walter and Awramik, 1979; Frutexites sp. 1, Frutexites sp. 2, and New gen. 3, Tsien, 1979), although the authors mostly use the term Frutexites sensu lato. The genus Frutexites was coined by Maslov (1960) in order to describe submillimeter-sized, iron-rich, and subordinate calcite microfossils (Figure 1). Frutexites have a dendritic shape formed by divergently branched microcolumns. The height and width of microcolumns as well as their composition and microstructure can vary (Table 1). The preservation of microstructure is strongly controlled ...
... Frutexites are microstromatolitic structures with a purported biological origin, and have been reported from a variety of subsurface environments such as deep-sea basalts (Bengtson et al. 2014), granitic rocks (Heim et al. 2017), and marine carbonate caves (Guido et al. 2016). Frutexites display fine-scale lamination and a directional growth orientation forming columnar structures and are characteristically composed of iron oxides and/or manganese oxides and carbonates (Maslov 1960;Horodyski 1975;Myrow andConiglio 1991, Heim et al. 2017). As noted by Jakubowicz et al. (2014) and Guido et al. (2016), Frutexites are typically restricted to environments with low light availability and low sedimentation, which is consistent within cryptic deep subsurface environments. ...
... The morphology of the microstromatolites is characterized by apparent alternating laminations (Fig. 1il), fractal branching growth (Fig. 1), and a distinct direction of growth, which is consistent with previously reported microstromatolites, which have been interpreted as having a biological origin (Guido et al. 2016;Heim et al. 2017). The size distribution of MS reported in these environments are similar to the structures we describe here (Heim et al. 2017;Böhm and Brachert 1993;Myrow and Coniglio 1991). Similar morphologies to the MSs have been reported by Sjöberg (2019, Fig. 5) in the Ytterby mine in Sweden, where active microbial communities create similar morphologies to the MS and where induced concentration of elements precipitates birnessite-type Mn oxides. ...
Micrometer sized stromatolitic structures called Frutexites are features observed in samples from the deep subsurface, and hot-spring environments. These structures are comprised of fine laminations, columnar morphology, and commonly consist of iron oxides, manganese oxides, and/or carbonates. Although a biological origin is commonly invoked, few reports have shown direct evidence of their association with microbial activity. Here, we report for the first time the occurrence of subsurface manganese-dominated Frutexites preserved within carbonate veins in ultramafic rocks. To determine the biogenicity of these putative biosignatures, we analyzed their chemical and isotopic composition using Raman spectroscopy and secondary ion mass spectroscopy (SIMS). These structures were found to contain macromolecular carbon signal and have a depleted 13C/12C carbon isotopic composition of – 35.4 ± 0.50‰ relative to the entombing carbonate matrix. These observations are consistent with a biological origin for the observed Frutexites structures.
... Frutexites are microstromatolitic structures with a purported biological origin, and have been reported from a variety of subsurface environments such as deep-sea basalts , granitic rocks (Heim et al., 2017), and marine carbonate caves (Guido et al., 2016). Frutexites display ne-scale lamination and a directional growth orientation forming columnar structures and are characteristically composed of iron oxides and/or manganese oxides and carbonates (Maslov, 1960;Horodyski, 1975;Myrow andCoriglio, 1991, Heim et al., 2017). As noted by Jakubowicz et al. (2014) and Guido et al. (2016), Frutexites are typically restricted to environments with low light availability and low sedimentation, which is consistent within cryptic deep subsurface environments. ...
... The morphology of the microstromatolites is characterized by apparent alternating laminations (Fig. 1i-l), fractal branching growth (Fig 1), and a distinct direction of growth, which is consistent with previously reported microstromatolites, which have been interpreted as having a biological origin (Guido et al., 2016;Heim et al., 2017). The size distribution of MS reported in these environments are similar to the structures we describe here (Heim et al., 2017;Böhm et al., 1993;Myrow et al., 1991). Similar morphologies to the MS´s have been reported by Sjöberg (2019, Fig. 5) in the Ytterby mine in Sweden, where active microbial communities create similar morphologies to the MS and where induced concentration of elements precipitates birnessite-type Mn oxides. ...
Micrometer sized stromatolitic structures called Frutexites are features observed in samples from the deep subsurface, and hot-spring environments. These structures are comprised of fine laminations, columnar morphology, and commonly consist of iron oxides, manganese oxides, and/or carbonates. Although a biological origin is commonly invoked, few reports have shown direct evidence of their association with microbial activity. Here, we report for the first time the occurrence of subsurface manganese-dominated Frutexites preserved within carbonate veins in ultramafic rocks. To determine the biogenicity of these putative biosignatures, we analyzed their chemical and isotopic composition using Raman spectroscopy and secondary ion mass spectroscopy (SIMS). These structures were found to contain macromolecular carbon signal and have a depleted ¹³ C/ ¹² C carbon isotopic composition of –35.4 ± 0.50 ‰ relative to the entombing carbonate matrix. These observations are consistent with a biological origin for the observed Frutexites structures.
... Frutexites elsewhere normally forms bush-like growths. Frutexites has been described from a variety of ancient shallow-marine (Myrow & Coniglio, 1991) to deep-marine (Bohm & Brachert, 1993) environments. While most authors agree that Frutexites is a fossil microbe, there is considerable ambiguity about whether the microbes are dominantly bacterial or fungal and thus non-photosynthetic (Bohm & Brachert, 1993) or cyanobacterial, and thus photosynthetic (Walter & Awramik, 1979). ...
... Frutexites is usually described from two marine settings: (1) slowly accumulating and condensed, red nodular limestones (Playford et al. 1976(Playford et al. , 1984Wendt, 1988;Hurley & Van der Voo, 1990;Mamet & Préat, 2006;Reolid & Nieto, 2010) like the Red Chalk, or (2) within cavities in mud mounds or reefs (e.g. Myrow & Coniglio, 1991;Reolid & Molina, 2010). In all cases the Frutexites growths are attributed to microbial fixation of iron in the depositional environment, typically in dysaerobic-anoxic conditions where chemotrophic bacteria might gain energy from iron oxidation (e.g. ...
New petrographic observations and stable isotope data help reinterpret the complex sedimentology of the Albian–Cenomanian boundary exposed in the famous red and white chalks of the cliff section at Hunstanton in Norfolk, UK. Thin-section analysis of a prominent crust at the top of the Hunstanton Red Chalk Formation reveals fossil microstructures attributable to the microbe Frutexites. These Red Chalk microstructures are less bushy that Frutexites sensu stricto, and poor preservation, in part caused by later diagenetic iron migration, means they are identified only tentatively as Frutexites. Stable oxygen isotope values from the crust are similar to those from early diagenetic nodular chalks immediately below the crust, and to partially altered chalks elsewhere in Norfolk. The δ18O data are interpreted as Albian seafloor depositional values albeit slightly altered by subsequent meteoric diagenesis. The microbial affinities of Frutexites are not yet proven; thus, the presence of Frutexites alone is not diagnostic of either photic zone or deep-water sedimentation. However, the presence of Frutexites(?) suggests that the red colour of the Hunstanton Red Chalk is due, at least in part, to the mediation of iron-fixing microbes in the accumulating chalk sediment at a dysoxic–anoxic interface. Centimetre-scale columnar and nodular structures above the ‘Frutexites crust’ that project upwards into the basal Paradoxica Bed of the overlying Ferriby Chalk Formation are sites of localized syndepositional iron staining. These nodules are not stromatolitic or microbial and are not evidence for deposition in shallow-water or intertidal settings.
... Oncoid-like structures resembling the ones described from the veins in the Hollard Mound have been reported from a number of crypto-habitats, especially from deepand shallow-marine settings (Tsien, 1979;Myrow and Coniglio, 1991;Bohm and Brachert, 1993;Chafetz et al., 1998). These structures are morphologically and compositionally similar to the problematic microfossil Frutexites Maslov (1960). ...
... Oncoid laminations containing carbonaceous amorphous surfaces and micro-rods were also loci of Fe-oxide precipitation (Fig. 10B, C). The staining and encrustations of the Frutexites-interpreted oncoids by Fe-oxides could be the final products of the degradation of organic matter by sulfate-reducing bacteria, which precipitate sulfides under anoxic conditions, and their subsequent oxidation (Myrow and Coniglio, 1991). The activity of chemosynthetic bacteria in the narrow veins of the Hollard Mound might represent the agent that generated the Frutexites oncoids. ...
Veins cutting across the Devonian conical mounds of the Hamar Laghdad Ridge (eastern Anti-Atlas, Morocco) were the carriers of geofluids. Although not completely determined, the composition of these fluids seems related to hydrothermal and seepage fluxes that were the primary contributors to the establishment of sub-seafloor (cryptic) environments linking deeper fluid sources to the seafloor. The optical and scanning electron microscope investigation of the laminated carbonate infill of these veins has revealed that they consist of stromatolite- and oncolite-like fabrics. In the Early and Middle Devonian mounds, the laminated carbonates contain morphologies that are attributable to microbially mediated processes that in turn suggest a direct biological contribution to the deposition of the veins infill. Microbial evidence include rod-shaped and cocci clusters embedded in amorphous membranes, iron-rich filaments organized as mat-like and biodictyon filamentous aggregates, or isolated filaments, microbial clotted textures and peloids. Moreover, the oncoids from the veins of the Middle Devonian (Hollard) mound have been interpreted as the mineral replacement of crypto-microorganisms as Frutexites. Other microbial evidence are biominerals and include carbonate with spheroids and pyrite framboids, in which typifying hydrocarbon seep environments.The Hollard Mound, which is the only one with a well-documented origin by hydrocarbon seepage, shares a number of geomicrobiological evidence with other Early Devonian mounds. These evidence, which are supplemented by δ13C-depleted data, suggest that the infill of the veins system in the Hamar Laghdad mounds would be the product of chemotrophic/chemosynthetic microbial communities that are adapted to crypto-habitats sustained by hydrocarbon (and other components) fluid fluxes.
... Centimetre to decimetre-thick mud-mounds are sporadic and mainly related to episodes of low energy. Thromboid structures are locally preserved both as clotted textures within mound cores and distinct calcimicrobes (for example, Frutexites; Myrow & Coniglio, 1991). ...
The characterization of carbonate production on rift basins is critical for understanding the nucleation and demise of reefs in tectonically active areas. A new petrographic and mineralogical analysis of Cambrian strata from the Avalon Zone in Newfoundland, based on scanning electron microscopy – back‐scattered electron detector and Raman spectrometer analyses, facilitates recognition of several episodes of Terreneuvian–Miaolingian carbonate production and associated precipitation of ironstone and phosphorite. These distinct units mainly developed on uplifted rift shoulders and basaltic lava palaeoreliefs, and reflect amalgamated high‐energy events, interrupted by scouring discontinuities (diastems) commonly lined by phosphatized and ferruginized microbial crusts. Mud‐mounds, in contrast, nucleated under calm conditions episodically punctuated by high‐energy episodes, where scattered thromboid structures occur as both clotted textures and distinct calcimicrobes. Precipitation of hematite/goethite versus chamosite couplets, both occluding primary porosities and replacing interlaminae and cortices of oncoids and coated aggregates, point to marine substrates close to the Fe‐redox boundary. Upwelling of phosphate‐rich ferruginous hydrothermal waters contributed to the precipitation of ironstone and phosphate interbeds. Ferruginous waters related to penecontemporaneous hydrothermal activity, reflected by the record of synsedimentary fissuring and stockwork ore bodies, were delivered to confined rift‐related horst‐and‐graben settings, largely controlled by the development of specific Cambrian carbonate and associated ironstone facies. The influence of ferruginous waters necessarily affected the record of climatically sensitive evaporitic pseudomorphs, reefs/mounds and phosphorites, which are then not suitable criteria to discriminate palaeolatitude, as demonstrated by a comparison of low‐latitude to middle‐latitude margins fringing Baltica, and the Avalonian and Atlas – Ossa‐Morena – Northarmorican rift transects of West Gondwana.
... In fact, these waters, infiltrating along the discontinuity of the bioconstruction previously covered with Fe/Mn crusts, could have continuously introduced new mineralizing ions necessary for the growth of the Frutexites. Indeed, Frutexites have been suggested to form through the ionic charge of acidic fluids which feed mesophilic autotrophic and chemoheterotrophic bacteria communities in restricted aphotic and anoxic microenvironments that, in turn, induce the deposition of Fe and Mn oxides (Myrow and Coniglio, 1991;Böhm and Brachert, 1993;Mamet and Préat, 2003;Kazmierczak and Kempe, 2006;Cavalazzi et al., 2007;Jakubowicz et al., 2014;Guido et al., 2016). Allouc and Harmelin (2001) assumed that the mucus (mainly composed of water and exopolysaccharides) induces a local increase in the concentration in dissolved Mn 2+ and acts as an ion exchange resin that allows the retention of Mn 2+ on the functional groups of EPS. ...
The dark and confined conditions of submarine caves allow the development of cryptic bioconstructions. They have been named “biostalactites” due to their distinctive growth from the ceiling and walls. Biostalactites resemble small scale “build-up” and have received increasing attention in recent years since they allow geobiological studies that could clarify the style of growth of the cryptic bioconstructions in the fossil record. The “lu Lampiùne” cave in Apulia represents an example of these natural laboratories where the presence of bioconstructions locally enhances biodiversity. Micromorphological observations, UV-epifluorescence and micro-Raman spectroscopy analyses were applied to investigate the internal structures and growth pattern of the oblique meter-long biostalactite. Two types of building engineers were detected: sessile skeletonized organisms and microbialites. These contribute to the formation of three boundstone frameworks: 1) core, represented by a skeletal-supported boundstone of large Protula tubes; 2) autochthonous micrite (microbialite)/skeletal boundstone on the downward-facing side; and 3) pure microbialite boundstone on the upward-facing side of the biostalactite.
Complex taphonomic and early diagenetic processes suggest variability in seawater chemistry. Phases of carbonate deposition, indicated by skeletal/microbialite growth and early cement precipitation, alternate with phases of carbonate dissolution and the precipitation of ferromanganiferous coatings.
The uniformity of the organisms, microstructures and biochemical signals, from the base to the growing tip of the biostalactite, suggests a uniform growth style from its inception to the present-day.
... In this context it is believed to be fundamental the role of specific Mn(IV)reducing and Mn(II)-oxidizing bacteria biologically driving a closed Mn cycle (Blöthe et al. 2015). In particular, the origin of Frutexites was originally assigned to cyanobacteria (Maslov 1960;Szulczewski 1963) and to other phototrophic microbes (Myrow and Coniglio 1991). The involvement of chemosynthetic microorganisms has been consequently postulated to explain the formation of Frutexites structures in deep marine, aphotic environment, also ascribed to the Jurassic Fe-Mn Frutexites (Böhm and Brachert 1993;Préat et al. 2000;Reitner et al. 2000;Allouc and Harmelin 2001;Mamet and Préat 2003;Mišík and Aubrecht 2004;Reolid and Nieto 2010;Reolid 2011). ...
Fe–Mn concretions and mineralizations, associated with condensed horizons and hardground, are significant archives in ancient carbonate rocks. Their petro-chemical study allows an assessment of the palaeoenvironmental context in which they were formed also connected to their biotic or abiotic origin. At the western side of the Monte Inici (Fornazzo section, north-western Sicily) a well exposed outcrop of condensed pelagic limestones (Rosso Ammonitico facies: Middle‒Upper Jurassic) is well-known and thoroughly studied. In this section, the base of the Rosso Ammonitico facies consists of a very condensed level rich in fossils with a variable thickness deposited from the early Bathonian to the early/middle Callovian. It is characterized, at the top, by the noticeable presence of Fe–Mn concretions, typical of the Tethyan Jurassic and related to very low sedimentation rates. For this study, Fe–Mn crusts and mineralizations from the Fornazzo section were investigated using X-ray diffraction, scanning electron microscopy, X-ray fluorescence, ICP and stable-isotope mass spectrometry. The collected samples, deposited in submarine conditions (as testified by stable oxygen and carbon isotopes), have been subdivided in two typologies with different macroscopic and mineralogical features. The Fe–Mn crusts consist of hematite, todorokite and birnessite and are characterized by a relatively low Mn/Fe ratio. Their content in trace elements, rare earths and yttrium (REY) is compatible with a hydrogenetic origin involving the oxy-hydroxides colloids precipitation directly from seawater. Microbially mediated processes are here testified by the recognition of filamentous and coccoid-shaped microstructures referable to coexistence of chemosynthetic fungi and photosynthetic cyanobacteria and accounting for a deposition in the deep euphotic zone. An average growth rate of ~ 8.5 mm/Myr for the Fe–Mn crusts, estimated by cobalt concentrations, suggests a time elapsed for deposition of ~ 3.5 ± 1 Myr. This value is compatible with the stratigraphic gap embracing the time span from the early/middle Callovian to the middle Oxfordian. In the neighbouring pelagic limestones, Fe–Mn deposits are present in the form of micro-dendrites mainly consisting of pyrolusite, sometimes associated with carbonato-fluorapatite. The geochemical composition gives evidence of a prevalent early diagenetic origin with precipitation, at the sediment/water interface or in the first centimeters of sediments, of metals diffused from the crusts as consequence of fluctuating redox conditions. Although the well-preserved Frutexites texture is commonly related to a microbial activity, other bacterial microstructures have not been recognized, having probably been obliterated during the growth of the dendrites. Nevertheless, it is possible to suppose a deepening in the bathymetry consistent with the involvement of chemosynthetic microorganisms in the formation of Frutexites structures.
... Böhm and Brachert [142] related the record of Frutexites with scarce light availability and aphotic stromatolites and evoked a non-phototrophic behavior in Jurassic examples from Germany. Myrow and Coniglio [161], Böhm and Brachert [142], and Cavalazzi et al. [128] have interpreted a cryptobiontic lifestyle for the organisms producing Frutexites. Bacterial and fungal communities have been recorded related to Fe-Mn crusts in Pleistocene and modern examples from submarine caves in the Mediterranean [134,162,163], and from reef caves at Lizard Island in Great Barrier Reef [164]. ...
The term microbialite is commonly applied for describing carbonate organo-sedimentary deposits that have accreted as a result of the activity of benthic microbial communities (BMC). However, non-carbonate microbialites are progressively well-known and show a great diversity of organisms, processes, and mineralogical compositions. This article reviews three types of Jurassic microbialites from four different environmental contexts from the Betic-Rifian Cordillera (South Spain and North Morocco): marine hardgrounds, submarine caves, hydrothermal vents, and submarine volcanic deposits. The Middle-Late Jurassic transition in the External Subbetic (Betic Cordillera) and the Jbel Moussa Group (Rifian Calcareous Chain) was characterized by the fragmentation of the carbonate epicontinental platforms that favored these different settings: (A) Many stratigraphic breaks are recorded as hardgrounds with surficial hydrogenetic Fe crusts and macro-oncoids related to chemo-organotrophic behavior of BMC that served as a specific trap for Fe and Mn enrichment; (B) Cryptic hydrogenetic Fe-Mn crusts (or endostromatolites) grew in the walls of submarine cavities and fractures mainly constituted by Frutexites (chemosynthetic and cryptobiontic microorganism) locally associated to serpulids; (C) Hydrothermal Mn crusts are mainly constituted by different types of filaments and bacillus-shaped bacteria, whose mineralogy and geochemistry point to a submarine hydrothermal origin; (D) Finally, glauconite laminated crusts, constituted by branched cylindrical filaments, have grown in cryptic spaces among the pillow-lava bodies, probably related to the metabolism of chemo-organotrophic microbes under oxic conditions at temperatures between 30 and 90 °C. In most of the cases described in this work, microbial organisms forming microbialites were extremophiles.
... Within the stromatolites are sheet-crack structures and rare tepee structures, the former of which consist of thin, elongate seams of white sparry calcite. Red-weathering microbial structures, present along the base of these layers, represent some of the earliest known coelobiontic taxa (Myrow and Coniglio, 1991). An important feature, noted within the stromatolites of this unit, is a tepee structure 50 cm wide and 10 cm tall. ...
... In the fossil record, Frutexites occur in rock samples from different environments such as marine stromatolites, microbial limestones, hardgrounds, cavities, cracks, veins, and Neptunian dikes [e.g. 7,8,9,10,11,12,13,14,15,16]. Major occurrences are described from rock cavities and fractures, mainly growing upward, but also radially to the a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 nucleating surface [17].The genus Frutexites with five different species was first described by Maslow [18]. ...
... In the fossil record, Frutexites occur in rock samples from different environments such as marine stromatolites, microbial limestones, hardgrounds, cavities, cracks, veins, and Neptunian dikes [e.g. 7,8,9,10,11,12,13,14,15,16]. Major occurrences are described from rock cavities and fractures, mainly growing upward, but also radially to the a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 nucleating surface [17].The genus Frutexites with five different species was first described by Maslow [18]. ...
Stromatolitic iron-rich structures have been reported from many ancient environments and are often described as Frutexites, a cryptic microfossil. Although microbial formation of such structures is likely, a clear relation to a microbial precursor is lacking so far. Here we report recent iron oxidizing biofilms which resemble the ancient Frutexites structures. The living Frutexites-like biofilms were sampled at 160 m depth in the Äspö Hard Rock Laboratory in Sweden. Investigations using microscopy, 454 pyrosequencing, FISH, Raman spectroscopy, biomarker and trace element analysis allowed a detailed view of the structural components of the mineralized biofilm. The most abundant bacterial groups were involved in nitrogen and iron cycling. Furthermore, Archaea are widely distributed in the Frutexites-like biofilm, even though their functional role remains unclear. Biomarker analysis revealed abundant sterols in the biofilm most likely from algal and fungal origins. Our results indicate that the Frutexites-like biofilm was built up by a complex microbial community. The functional role of each community member in the formation of the dendritic structures, as well as their potential relation to fossil Frutexites remains under investigation.
... El estudio al microscopio de láminas delgadas muestra evidencias de reemplazamiento de los estromatolitos carbonatados laminares y microcolumnares (tipo Frutexites; Fig. 2C) por fosfato y óxidos de Fe, lo que apoya una mineralización original en forma de calcita y un posterior reemplazamiento por fosfato y óxidos de Fe (Myrow & Coniglio, 1991). ...
... Contrariwise Kazmierczak and Kempe (2006) registered Fe-Mn dendrolitic mineralizations (Frutexiteslike) in modern shallow stromatolites. A cryptobiontic life style of the organisms originating Frutexites has been interpreted by Myrow and Coniglio (1991), Böhm and Brachert (1993) and Cavalazzi et al. (2007). ...
Ferromanganesiferous macro-oncoids are distinctive from the External Subbetic Zone (Betic Cordillera, SE Spain) in relation to a major heterochronic unconformity, with a Middle Bathonian-Lower Oxfordian minimum hiatus and a Lowest Bathonian-Lowest Kimmeridgian maximum hiatus. The Fe-Mn macro-oncoids (43 mm mean-size) consist of microbial laminae with planar and arborescent to dendrolitic morphologies. Under petrographic microscopy, the planar morphologies are made up by condensed fibrillar meshworks whereas the dendrolitic ones are similar to Frutexites. Alternation between these two types of laminae reveals a rhythmic growth in the Fe-Mn macro-oncoids. Bacterial and fungal filaments are observed in SEM analyses as microbial mats constituted by a disperse web of filaments exhibiting a branching tube-like morphology with diameters ranging between 2 and 10 μm. Aggregates of coccoid-shaped forms are also registered by SEM analyses. Taxonomical approximation of the microbiota is complex, though in the thin section the condensed fibrillar meshworks look like cyanobacteria, and in SEM images the morphology of the filaments resembles fungal hyphae and green algae, whereas coccoids are assigned to cyanobacteria. The precipitation of Fe-Mn is related to the chemoorganotrophic behaviour of the benthic microbial communities, probably corresponding to the fungal mats and other chemosynthetic microbes. Inorganic precipitation mechanisms are regarded as insufficient for the accumulation of a significant amount of MnO. An efficient precipitation of Mn from natural water largely depended on the presence of Mn-oxidizing microorganisms. Sediment-starved zones of pelagic swells of the External Subbetic, located in the deep euphotic zone, were the best places for microbially mediated authigenesis.
... along the edges of cavities (Woods & Baud, 2008). They are also documented in various environments, ranging from deep-water stromatolites (Böhm & Brachert, 1993; Jakubowicz et al., 2014) and pelagic depositional settings (Woods & Baud, 2008) to cryptic habitats in shallow marine settings (Myrow & Coniglio, 1991; Reolid and Molina, 2010). Frutexites is considered as a problematic microfossil observed from the early Proterozoic (Hofmann & Grotzinger, 1975) up to the Cretaceous (Böhm & Brachert, 1993); it is therefore difficult to interpret in terms of palaeoenvironment. ...
The Lower Triassic Mineral Mountains area (Utah, USA) preserves diversified Smithian and Spathian reefs and bioaccumulations that contain fenestral-microbialites and various benthic and pelagic organisms. Ecological and environmental changes during the Early Triassic commonly are assumed to be associated with numerous perturbations (productivity changes, acidification, redox changes, hypercapnia, eustatism and temperature changes) post-dating the Permian–Triassic mass extinction. New data acquired in the Mineral Mountains sediments provide evidence to decipher the relations between depositional environments and the growth and distribution of microbial structures. These data also help to understand better the controlling factors acting upon sedimentation and community turnovers through the Smithian–early Spathian. The studied section records a large-scale depositional sequence during the Dienerian(?)–Spathian interval. During the transgression, depositional environments evolved from a coastal bay with continental deposits to intertidal fenestral–microbial limestones, shallow subtidal marine sponge–microbial reefs to deep subtidal mud-dominated limestones. Storm-induced deposits, microbialite–sponge reefs and shallow subtidal deposits indicate the regression. Three microbialite associations occur in ascending order: (i) a red beds microbialite association deposited in low-energy hypersaline supratidal conditions where microbialites consist of microbial mats and poorly preserved microbially induced sedimentary structure; (ii) a Smithian microbialite association formed in moderate to high-energy, tidal conditions where microbialites include stromatolites and associated carbonate grains (oncoids, ooids and peloids); and (iii) a Spathian microbialite association developed in low-energy offshore conditions that is preserved as multiple decimetre thick isolated domes and coalescent domes. Data indicate that the morphologies of the three microbialites associations are primarily controlled by accommodation, hydrodynamics, bathymetry and grain supply. This study suggests that microbial constructions are controlled by changes between trapping and binding versus precipitation processes in variable hydrodynamic conditions. Due to the presence of numerous metazoans associated with microbialites throughout the Smithian increase in accommodation and Spathian decrease in accommodation, the commonly assumed anachronistic character of the Early Triassic microbialites and the traditional view of prolonged deleterious conditions during the Early Triassic time interval is questioned.
... Böhm & Brachert (1993) related the record of Frutexites with aphotic stromatolites and evoked a non-phototrophic behaviour in Jurassic examples from Germany. Myrow & Coniglio (1991), Böhm & Brachert (1993) and Cavalazzi et al. (2007) have interpreted a cryptobiontic lifestyle for the organisms producing Frutexites. Böhm & Brachert (1993), in the particular case of Frutexites, interpret a preference for oxygen deficient environments. ...
The Middle-Upper Jurassic transition within the External Subbetic (Betic Cordillera) and the Jbel Moussa Group (Rifian Calcareous Chain) is characterised by numerous stratigraphic breaks recorded as palaeoreliefs, omission surfaces and hardgrounds. One common characteristic is the presence of microbial Fe-Mn crusts and Mn crusts. Three different contexts of microbially mediated Fe-Mn crusts can be distinguished: a) hydrogenetic surficial Fe-Mn crusts and macro-oncoids, b) hydrogenetic cryptic Fe-Mn crusts, and c) hydrothermal surficial Mn crusts. Encrusting foraminifera (Thurammina, Placopsilina, Tolypammina and nubeculariids) and fungi fed on bacteria, while the bacteria and fungi took advantage of the nutrient-rich foraminiferal excretions. The cryptic Fe-Mn crusts are also hydrogenetic crusts developed in the walls of submarine cavities and fractures in the External Subbetic at the time of the hardground development. They are endostromatolites consisting almost exclusively of Frutexites in the case of thin neptunian dykes, or serpulid-Frutexites assemblages in a large neptunian sill. This assemblage reflects the colonization of unfavourable environment (aphotic with low oxygenation) as a response to the photophobic behaviour of chemosynthetic and cryptobiontic microorganisms. Finally, the hydrothermal Mn crusts registered in the Rif are characterised by the record of bacillus-shaped bacteria and different type of filaments. The precipitation of manganese minerals is interpreted as induced by the chemo-organotrophic behaviour of benthic microbial communities, since manganese oxides may form as a result of the direct metabolic activity of bacteria in hydrothermal environments. Very well-preserved fungal hyphae evidence the presence of fungi that probably fed on bacterial communities and their by-products
... The evolving net-like structures feature semi-solid ridges, harbouring a particular, highly diverse physicochemical origin. According to previous publications (Maslov, 1960;Myrow and Coniglio op cit), Böhm and Brachert (1993) explained the ferromanganese or phosphate mineralogy of Frutexites as a replacement of primary carbonate mineralogy. A primary iron mineralization of Frutexites was postulated by Horodyski (1975), Hurley and Van der Voo (1990). ...
... These fractally branching bodies are morphologically identical to the microstromatolitic structures known as Frutexites (Maslov, 1960), characteristic of cryptic habitats and hydrothermal vents through the Proterozoic and Phanerozoic (Walter & Awramik, 1979;Myrow & Coniglio, 1991;B€ ohm & Brachert, 1993;Rodr ıguez-Mart ınez et al., 2011). We will refer to them under this name. ...
The deep biosphere of the subseafloor crust is believed to contain a significant part of Earth's biomass, but because of the difficulties of directly observing the living organisms, its composition and ecology are poorly known. We report here a consortium of fossilized prokaryotic and eukaryotic micro-organisms, occupying cavities in deep-drilled vesicular basalt from the Emperor Seamounts, Pacific Ocean, 67.5 m below seafloor (mbsf). Fungal hyphae provide the framework on which prokaryote-like organisms are suspended like cobwebs and iron-oxidizing bacteria form microstromatolites (Frutexites). The spatial inter-relationships show that the organisms were living at the same time in an integrated fashion, suggesting symbiotic interdependence. The community is contemporaneous with secondary mineralizations of calcite partly filling the cavities. The fungal hyphae frequently extend into the calcite, indicating that they were able to bore into the substrate through mineral dissolution. A symbiotic relationship with chemoautotrophs, as inferred for the observed consortium, may be a pre-requisite for the eukaryotic colonization of crustal rocks. Fossils thus open a window to the extant as well as the ancient deep biosphere.
... El estudio al microscopio de láminas delgadas muestra evidencias de reemplazamiento de los estromatolitos carbonatados laminares y microcolumnares (tipo Frutexites; Fig. 2C) por fosfato y óxidos de Fe, lo que apoya una mineralización original en forma de calcita y un posterior reemplazamiento por fosfato y óxidos de Fe (Myrow & Coniglio, 1991). ...
The record of Jurassic chondrichthyans remains from the Iberian Peninsula is reviewed.
This record is very poor on the entire peninsula, with the exception of the Guimarota site
(Portugal), with several taxa described and properly illustrated. The present paper is the first
bibliographical list of publications dealing with the sharks record from the Jurassic of the Iberian
Peninsula.
... El estudio al microscopio de láminas delgadas muestra evidencias de reemplazamiento de los estromatolitos carbonatados laminares y microcolumnares (tipo Frutexites; Fig. 2C) por fosfato y óxidos de Fe, lo que apoya una mineralización original en forma de calcita y un posterior reemplazamiento por fosfato y óxidos de Fe (Myrow & Coniglio, 1991). ...
The chondrichthyan faunas from the Late Jurassic of Asturias is reviewed in this work.
All the material in this study (teeth, finspines and dorsal spines), currently under preparation, are
part of the Museo del Jurásico de Asturias (Colunga) collections. This record is relatively scarce,
and consists exclusively of hybodontiform sharks: Hybodontiformes indet., Asteracanthus,
Hybodus, and Planohybodus. All specimens come from Tereñes and Lastres Formations
(Kimmeridgian).
... The fact that the Givetian 'Amplexus'-bearing carbonates that contain the microstromatolitic encrustations (C1 and C2 in Fig. 7A) reveal the δ 13 C values of about 1.5‰ to 4.5‰ PDB lower than the contemporaneous associations lacking such encrustations, but having instead a well-developed fibrous cement generation (C3 in Fig. 7A) can be most likely explained by an increased content of carbonate derived from decomposition of organic matter. Accordingly, the dark, dendritic to shrub-like microstromatolites stained by iron minerals, often referred to as 'Frutexites' (e.g., Myrow and Coniglio, 1991;Böhm and Brachert, 1993), are typically interpreted as having formed by encrusting microbes in poorlyoxygenated, stagnant-water environments, which stimulated an increased accumulation of organic matter within the sediment. Nevertheless, these isotopic data show clearly that, as in the case of the majority of carbonate buildups found in the Hamar Laghdad area, hydrocarbons were at best only subordinate components of the locally emitted hydrothermal fluids. ...
The rugose coral 'Amplexus' occurs frequently in the sedimentary cover of the Devonian submarine volcanic intrusion in the eastern Anti-Atlas, southern Morocco. This study elucidates the palaeoecology of 'Amplexus', which forms very rich and mostly monospecific, spot assemblages within the Lower and Middle Devonian carbonates. Geological and isotopic evidences show that these associations developed at hydrothermal vents and at a cold seep site. The assemblages are always spatially associated with micritic carbonate bodies, occurring within bedded, hemipelagic deposits. The 'Amplexus' corals preferred locations in the close proxim-ity of submarine hydrothermal fluid seepage, but they generally avoided places with the most elevated tem-peratures. The corals colonised also a hydrocarbon seep, probably only in its terminal phase of development, when the fluid flow was still at least periodically active. This was only possible as a result of the corals follow-ing a calice-in-calice growth, developed due to the environmental toxicity, which facilitated selective survival of larvae that settled in the shelter of empty calices. The 'Amplexus' corals appear to have constituted ecolog-ical opportunists, thriving in the nutrient-rich, venting-and seepage-affected areas that were hostile for other benthic organisms. It can be suspected that the unusual, extremely simplified morphology of 'Amplexus' made it particularly well adapted to living in environments typified by harsh and unstable conditions.
... Also, calci fi ed cushion-like colonies of rivulariacean cyanobacteria ( Rivularia sp. and Tolypothrix sp.) occur at certain stromatolite levels (Fig. 10e , f) forming a cystous microfabric (Fig. 9c ) similar to those observed in Proterozoic stromatolites (e.g., Bertrand-Sarfati, 1976 , Fig. 2a ). A special kind of stromatolitic fabric is represented by micro-arborescent structures (Fig. 9d ) resembling Proterozoic and Paleozoic fossils described as Frutexites (Maslov, 1960 ;Horodyski, 1975 ;Walter and Awramik, 1979 ;Myrow and Coniglio, 1991 ) . These usually Mn-and F-enriched structures have been often found growing near volcanic hydrothermal vents (Walter and Awramik, 1979 ) . ...
The results of geological, hydrochemical and biosedimentological studies of two main caldera lakes, Vai Lahi and Vai Si‘i, on the volcanic Niuafo‘ou Island (Kingdom of Tonga) are presented. These slightly alkaline lakes support formation of carbonate sediments among which the most spectacular are calcareous cyanobacterial microbialites comparable with ancient, particularly Precambrian, stromatolites. The hydrochemistry of both lakes indicate that they originated and evolved from precipitation-water with some admixture of hydrothermal fluids. The lakes and their microbialites prove to be an excellent model for testing the hypothesis of an early alkaline ocean.
Keywords:Planetary oceans, early ocean chemistry, soda ocean, silicate weathering, Niuafo‘ou Island, Tonga, volcanology, caldera, limnology, alkalinity, carbonate chemistry, stromatolites, stable isotopes
... Contrarily, Kazmierczak and Kempe (2006) found Fe-Mn dendrolitic mineralizations (Frutexites-like) in modern shallow stromatolites. Myrow and Coniglio (1991), Böhm and Brachert (1993), and Cavalazzi et al. (2007) have interpreted a cryptobiontic lifestyle of the organisms producing Frutexites. According to Mamet and Préat (2003) the growth of ferrobacteria and fungi in relatively deep environments below the normal wave base level would entail dysaerobic conditions with weak oxygen gradients. ...
In the Middle-Upper Jurassic boundary of the External Subbetic, there are abundant discontinuities with neptunian dikes and sills composed of Callovian-lower Tithonian deposits. In cavities developed on a slope with escarpments, cryptobiontic communities were preserved in life position.These cavities were excavated beneath a hardground covering the upper surface of Bathonian oolitic limestones deposited in very shallow pelagic carbonate platforms. The biogenic crusts are composed mainly of serpulids and Frutexites—laminated dendrolitic microstructures—and, secondarily, by sessile foraminifera. The serpulids were pioneer organisms during colonization of the walls of small cavities in stressed shadowcryptic environments. Serpulid aggregates then grew downward from the top walls of the cavities. The colonization of serpulid tubes was mainly after the death of organisms, first by microborers, secondly by Frutexites, and later by sessile foraminifera. The preferential colonization of these cryptic environments by serpulids can be interpreted as due to possible photophobic behavior and or the possibility of avoiding space competition or predation.
... (c) Mn-and Fe-enriched microlaminated dendroid structures: These microbialites, which are almost identical with the problematic fossils known as Frutexites, appear occasionally between laminae of the stromatolites mentioned above. Frutexites are described from the Proterozoic and early Paleozoic strata and they are always associated with stromatolite-bearing sediments (see Horodyski 1975;Walter and Awramik 1979;Myrow and Coniglio 1991). Similar structures were found in subfossil, calcareous microbialites from the caldera lake of Niuafo 0 ou Island (South-Pacific, Kingdom of Tonga) (Kazmierczak and Kempe 2006). ...
Remains of silicified microbial mats composed of benthic colonial coccoid cyanobacteria similar to modern entophysalidaceans and/or pleurocapsaleans have been identified in Lower Silurian black radiolarian cherts from central and southwestern Poland. Contrary to widespread views ascribing the genesis of such deposits to permanently anoxic deep-water marine environments, the abundance of benthic mats of phototrophic cyanobacteria suggests that the water-mat interface must have been located at moderate depth, most probably close to the limit of light penetration (dysphotic zone). Depending on ambient sulfide levels, the mats could intermittently perform anoxygenic (PSI) or oxygenic (PSII) photosynthesis, thriving under anoxic, oxic, or dysoxic (microaerophilic) conditions. The open marine (offshore) character of these cherts is consistent with their paleooceanographic location and with the presence of remains of such planktonic organisms as acritarchs, radiolarians, chitinozoans, and graptolites, entrapped by the cyanobacterial mats.
... Also, calci fi ed cushion-like colonies of rivulariacean cyanobacteria ( Rivularia sp. and Tolypothrix sp.) occur at certain stromatolite levels (Fig. 10e , f) forming a cystous microfabric (Fig. 9c ) similar to those observed in Proterozoic stromatolites (e.g., Bertrand-Sarfati, 1976 , Fig. 2a ). A special kind of stromatolitic fabric is represented by micro-arborescent structures (Fig. 9d ) resembling Proterozoic and Paleozoic fossils described as Frutexites (Maslov, 1960 ;Horodyski, 1975 ;Walter and Awramik, 1979 ;Myrow and Coniglio, 1991 ) . These usually Mn-and F-enriched structures have been often found growing near volcanic hydrothermal vents (Walter and Awramik, 1979 ) . ...
The results of geological, hydrochemical and biosedimentological studies of two main caldera lakes, Vai Lahi and Vai Si‘i, on the volcanic Niuafo‘ou Island (Kingdom of Tonga) are presented. These slightly alkaline lakes support formation of carbonate sediments among which the most spectacular are calcareous cyanobacterial microbialites comparable with ancient, particularly Precambrian, stromatolites. The hydrochemistry of both lakes indicate that they originated and evolved from precipitation-water with some admixture of hydrothermal fluids. The lakes and their microbialites prove to be an excellent model for testing the hypothesis of an early alkaline ocean.
... Also, calci fi ed cushion-like colonies of rivulariacean cyanobacteria ( Rivularia sp. and Tolypothrix sp.) occur at certain stromatolite levels (Fig. 10e , f) forming a cystous microfabric (Fig. 9c ) similar to those observed in Proterozoic stromatolites (e.g., Bertrand-Sarfati, 1976 , Fig. 2a ). A special kind of stromatolitic fabric is represented by micro-arborescent structures (Fig. 9d ) resembling Proterozoic and Paleozoic fossils described as Frutexites (Maslov, 1960 ;Horodyski, 1975 ;Walter and Awramik, 1979 ;Myrow and Coniglio, 1991 ) . These usually Mn-and F-enriched structures have been often found growing near volcanic hydrothermal vents (Walter and Awramik, 1979 ) . ...
Summary of Life on Earth and other Planetary Bodies (Introduction of J. Seckbach, § 5)
This volume has gathered 68 expert authors from around the world to discuss questions of life on Earth and elsewhere. Their chapters deal with primeval seas, the origin of the genetic code, panspermia, and terrestrial habitability. The Extremophiles section includes the halophiles, the polar cyanobacteria, and life without water, as well as microorganisms tolerating, surviving, and flourishing in severe environments. The extremophiles are important for practical uses (enzyme production) and extraction of special proteins. In the Extraterrestrial Life section of this volume there are discussions about the search for extraterrestrial intelligent life, terrestrial analogues for planetary oceans, life in terrestrial lava-caves, as implications for life detection on other planets, habitability of Earth-like exoplanets, Mars water and polar dunes, Antarctica as a model for life on Europa, Saturn and its moons, astrobiology of Titan, habitability of extrasolar planets and cosmic catastrophes.
This volume is number 24 of the Cellular Origin, Life in Extreme Habitats and Astrobiology [COLE] series [J. Seckbach (editor) 1999-2013, www.springer.com/series/5775]. The present book complements previous books of this series discussing also topics associated with this volume, namely, the Science of Astrobiology (2011), Stromatolites (2011), Symbioses and Stress (2010), Algae and Cyanobacteria in Extreme Environments (2007), Enigmatic Microorganisms and Life in Extreme Environments (1999). The target audience for this new book comprises scientists, microbiologists working with extremophiles, biology, geology students, teachers and general readers.
... Their presence in stromatolites has been linked with different types of cyanobacteria (Playford et al. 1976(Playford et al. , 1984Scytonematacean -Walter and Awramik 1979;Rivulariacean -Hofmann and Grotzinger 1985;Angulocellularia group -Riding 1991). Their growing in cavities, sheet cracks and Neptunian Dykes have been related with non-phototrophic (heterotrophic) behaviour (Tsien 1979) or cryptobiont role (Myrow and Coniglio 1991), which sometimes were linked with non-phototrophic cyanobacteria (Gischler 1996) as well as with chemosynthetic bacteria (Cavalazzi et al. 2007). The cryptobiont, negative phototactic downward growth and cryptoendopelitic behaviour of Frutexites were interpreted by B€ ohm and Brachert (1993) as a signal of oxygen deficient environments. ...
Foraminifera are the most abundant sessile organisms found on ferromanganese crusts and nodules (Greenslate 1974; Wendt 1974; Dugolinsky et al. 1977; Riemann 1983; von Stackelberg 1984; Mullineaux 1987, 1988; Verlaan 1992;
Resig and Glenn 1997; Toscano and Raspini 2005). In fact, actual ferromanganesecrusts and nodules share numerous similarities with their fossil counterparts.
... Carbonaceous fossils in the Vendian Harlaniella podolica Zone include Sabellidites cambriensis and impressions of vendotaenid algae including Tyrasotaenia gnilovskaya (Narbonne et al., 1987;Landing et al., 1989). The Cambrian portion of the Chapel Island Formation also contains a suite of shelly fossils (Bengtson and Fletcher, 1983;Landing et al., 1989;Myrow and Landing, 1992 ), calcified microbial remains (Myrow and Coniglio, 1991 ), and impressions of the soft-bodied chondrophore megafossil Kullingia delicata (Fedonkin) (Narbonne et al., 1991 ). Microfossils from this section include cyanobacterial sheaths referred to as Eomycetopsis (H. ...
A ca. 15 km thick succession of volcanic and sedimentary Neoproterozoic rocks are exposed within the Avalon Terrane of Newfoundland. Petrologic and geochemical study of volcanic suites and sedimentological analyses indicate that most deposition took place in ensialic rift basins and associated continental arc settings. On the Avalon Peninsula, over 7500 m of volcaniclastic strata include initial submarine fan and slope deposits, which pass upward into a prograded wedge of deltaic and fluvial deposits. This flysch-to-molasse transition, and associated folding and volcanism, mark the Neoproterozoic Avalonian Orogeny. Post-orogenic erosion was followed by deposition of extensive Cambrian siliciclastic deposits.Recent UPb zircon dating of many of the Neoproterozoic volcanic units provides some constraints on both intra-Avalon and global correlations. More precise dates are needed to improve correlation and better constrain the geologic history of this region. Glaciogenic diamictites of the Gaskiers Formation exposed on the Avalon Peninsula may eventually also prove useful for global correlation. Biostratigraphic study of the latest Neoproterozoic-Lower Cambrian deposits has resulted in ratification of the Precambrian-Cambrian Boundary Stratotype in an exposure on the Burin Peninsula. Older Neoproterozoic rocks contain well-preserved Ediacara-type fossils and a low-diversity suite of microfossils including acritarchs and carbonaceous filaments, the latter of which have little biostratigraphic utility. Aside from work on the Precambrian-Cambrian boundary section, little or no chemostratigraphic, magnetostratigraphic or sequence stratigraphic work has been completed on the Neoproterozoic of the Newfoundland Avalon Terrane.
... As these typical dhedgehogsT and derythrospheresT microstructures are recurrent in the other studied series their names have been systematically used. The sedimentological interpretation of the thinsections of the Slivenec Limestone points to an outer ramp setting near the storm wave base level; (2) The Baleas Limestone is characterized by the presence of the controversial Frutexites (Myrow and Coniglio, 1991). dErythrospheresT and dhedgehogsT are rare. ...
Different pathways can be proposed to explain the origin of the red pigmentation present in many Phanerozoic limestones. We investigate three possible models: (1) telogenetic alteration; (2) detrital input and (3) role of iron-bacteria. The third hypothesis is supported by our data for a number of Phanerozoic series. By this hypothesis not only can we highlight the importance of the microenvironments at the dysoxic–anoxic water sediment interfaces for the bacterial Fe-oxidation but also can conclude that the ‘red limestones’ have no particular paleogeographic meaning. The seven studied red successions are rather poor in iron (350 ppm in the Ammonitico Rosso) without large fluctuations. The pigmentation is due to the dispersion of submicrometric (hydro)oxides (now hematite) formed by bacterial mediation during early diagenesis in various microaerophilitic environments. Different ferruginous morphs, e.g., filaments, coccoids, microstromatolites, suggest the presence of iron-bacteria. The limiting factor is the oxygen content which was low in these very quiet and relatively deep environments. The presence of iron-bacteria is also confirmed by iron isotope analysis on the Ammonitico Rosso. Fe isotopic compositions have been analyzed on residues as well as on leachates of red and grey facies of the same interval. δ56Fe values are systematically lower in the red residues (varying from − 1.19‰ to − 0.34‰) compared to the grey ones (0.27‰ to − 0.09‰). This indicates a significant accumulation of lighter isotopes in the red parts suggesting that hematite have been formed via a biological pathway.
Frutexites ‐like microstructures are described from the exhumed Late Devonian reef complexes of the northern Canning Basin, Western Australia. Several high‐resolution imaging techniques, including X‐ray microcomputerised tomography, scanning electron microscopy and X‐ray fluorescence microscopy, were used to investigate morphology and composition in two samples. Three types of Frutexites ‐like microstructures (Types I–III) have been identified. Type I, found lining an early marine cement‐filled cavity in fore‐reef grainstone facies, consists of dendritic structures formed primarily of coccoid bacteria with filamentous bacteria embedded in sheets of amorphous extracellular polymeric substances (EPS). These ferromanganiferous dendrites have laminated to spheroidal textures. Types II and III are from a toe‐of‐slope hardground. Type II grew in a crypt between two corals, is also dendritic and composed of bacilliform and filamentous bacteria embedded in an amorphous EPS sheet. The opaqueness of these ferriferous dendrites precludes more detailed description of textures. Type III grew as branching columnar microstromatolites and is composed of entwined filaments of Girvanella , Rothpletzella and Wetheredella with Fe‐enriched outer walls that generate Frutexites ‐like microstructures. Types I and II resemble Frutexites sensu stricto as defined by Maslov ( Stromatolites , Trudy Instituta geologicheskikh nauk Akademiya nauk SSR, 1960) and are the result of the consecutive growth and permineralisation of biofilms composed of mixed bacterial communities growing in cryptic habitats. Type III superficially resembles Frutexites sensu stricto based on macroscopic field observations, however, detailed microscopic analysis reveals that it is composed of Fe‐enriched tubular walls surrounded by Mn‐enriched calcite.
Masters Thesis, Department of Earth Sciences, University of Oxford (2007)
At the end of the Early Cambrian glacial event occurring on the West African craton, the tillite surface was marked, especially in the northeastern part of the Taoudenni basin, by noticeable topographic relief. After deglaciation, the eustatic rise in sea level led to deposition over all the West African Craton of a thin but widespread carbonate unit containing Lower Cambrian shelly fossils. At the ice-cap periphery, isostatic rebound of the craton resulted in uplift of the topographic highs and weathering of the carbonate. During fluctuations of relative sea level, before the return to marine transgressive conditions, a succession of events took place. First, in the submerged areas, stromatolitic phosphorite in flat-domal to columnar buildups accreted, followed by growth of dolomitic ministromatolites. Laterally, phospharenitic beds (oncolites and phosphatic grains) accumulated under water in the depressions. The stromatolites and oncolites are made of carbonate-fluorapatite, characteristic of coastal environments. Glauconite is closely related to apatite and suggests conditions of a sea-level rise in respect to phosphatization. Precipitation of dolomite, calcite and evaporite postdates phosphatization and glauconitization, indicating a regression and a chemical concentration due to a warm and perhaps arid climate. Apatitic stromatolites and oncolites resulted from in situ precipitation within bacterial mats. This phosphogenesis corresponds to the major Early Paleozoic phosphogenetic event.
The Ombombo Subgroup of the Otavi Fold Belt, Kaokoveld, Namibia preserves a succession of clastic and carbonate sediments with unusual sedimentary features. The stratigraphy of these units is discussed here in detail for the first time since their initial definition, with particular emphasis carbonate sedimentology. Early Neoproterozoic shales of the Beesvlakte Formation, equivalent to the Zambian Katangan Copperbelt’s Lower Roan Formation, host evaporitic lithologies and minor copper mineralisation. The overlying, dolomitic ~ 760Ma Devede Formation contains carbonate platformal lithologies which are in many way dissimilar to Phanerozoic shallow-water carbonates. This includes unusual “curl breccias”, sheet cavities, carbonate shrubs and tepee carbonate lithologies which contain large quantities of fibrous cements. “Curl breccias” are defined here as distinctive, curled intraclasts of laminated dolomite that often have shrinkage cracks in their margins, and are cemented by fibrous dolomite cements. Fibrous cements take on two forms: an early, length-fast fascicular-optic dolomite, and a later length-slow phase with unit extinction. The presence of overlying internal sediments, the fibrous habit of these first-generation cements, as well as their preserved cathodoluminescent and optical character, suggests that these cements originally precipitated as calcite and dolomite marine cements respectively. After this initial marine calcite precipitation, all components of Devede Formation carbonates have been mimetically dolomitised, preserving original depositional fabrics. Combined with the presence of marine dolomite cements, this style of dolomitisation is suggested to be syn-sedimentary, similar to that of some Cryogenian dolomites, suggesting unusual ocean conditions during the Early Neoproterozoic. In particular, the presence of dolomite marine cements, which have been linked to ocean anoxia and high seawater Mg/Ca conditions, suggests that the onset of marine anoxia in the Neoproterozoic may have occurred during the growth of the Devede Formation carbonate platforms, prior to the Sturtian glaciation. This implies that glaciation may not be the sole cause for the development of marine anoxia during the Neoproterozoic. It is possible that marine anoxia in this southern African ocean basin may have contributed to a build-up of metals in seawater, perhaps pre-enriching basinal fluids for large-scale stratabound copper mineralisation.
Despite extensive discussions during the last 20 years stromatolites are still used by many geologists as unequivocal indicators of very shallow-water conditions. We investigated four stratigraphic units from the Lower and Middle Jurassic of southern Germany (Posidonien-Schiefer, Amaltheen-Ton) and of the Northern Calcareous Alps (Adneter Kalk, Klauskalk), which were formerly interpreted as shallow marine sediments by some authors due to the occurrence of stromatolites. Our interpretations of the macro-, micro- and ultrafacies of these sediments are not compatible with shallow-water settings. We therefore propose a deep-marine, aphotic origin of these stromatolites.
Former interpretations of the Posidonien-Schiefer as a shallow-water deposit are mainly based on the occurrence of stromatolites. We favour the model of a temporarily stagnant, deep, aphotic basin for these planktonrich sediments. Particles resembling ooids, but lying within mudstones cannot be taken as evidence for shallow agitated water. They either formed within the mud or are allochthonous.
The deep-water setting of the red limestone of the Alpine Early and Middle Jurassic is indicated by a lack of platform-typical components like coated grains and phototrophic benthos and by shells of plankton and nekton forming a major part of the sediment. Stromatolites occur on the steep slope of a drowned Rhaetian reef with an estimated relief of 50–100 m and immediately below and within radiolarian limestones, deposited below the aragonite compensation depth (ACD).
The aphotic stromatolites show some morphological differences to their shallow water counterparts. In all of our sections they occurred during intervals of reduced sedimentation. They form only thin horizons and probably grew very slowly. Mineralizations by Fe−Mn oxides and phosphate are very common. The presence of a microbial film is evident from binding of sedimentary particles, but the nature of the microbes is not known. Growth habits within the very distinct environments of red limestone and black shales show some common features, but also clear differences.
The microproblematicumFrutexites
Maslov is a very common component in deep-water stromatolites, but may also itself form small crusts or dendrolites. It occurs in two different forms. Opaque, slender forms with indistinct outlines probably grew within the weakly lithified sediment. Thicker, transparent forms with well defined outlines are found in cavities and probably also grew on the seafloor. Well preserved specimens display an internal fabric of radially arranged fibres of Fe−Mn oxides and calcite. It is suggested that calcite or aragonite were one original mineralogy ofFrutexites, which was later replaced by Fe−Mn oxides or phosphate.
It is not certain whetherFrutexites is an organic, biomineralized structure or an inorganic mineralization, but the variable mineralogy and growth forms in different environments point to an organic origin. But even if organic, the occurrence in cryptic habitats and negative phototactic growth-directions make it clear thatFrutexites was not phototrophic.
Organic geochemical methods for conodont analysis have been developed. Coniform elements of the conodont genus Drepanodus from the Ordovician Emanuel Formation and pectiniform elements of the conodont genus Polygnathus from the Devonian Napier Formation both from the Canning Basin, Australia have been shown to contain different organic matter. Both conodont samples have been artificially matured and the structure of organic matter present related to the conodont alteration index (CAI) and maturation temperature (TM). The carbon 1s X-ray photoelectron spectra (XPS) acquired from both sample sets contain six peaks. These peaks are assigned to highly ordered graphitic like carbon (282.9 eV), sp3 hybridised carbon bonded to only carbon or hydrogen (284.7 eV), ether (286.1 eV), alcohol (287.0 eV), carbonyl (287.6 eV) and carboxyl (289.0 eV) functional groups. Alkene and aromatic carbon is also probably present but is difficult to delineate. During artificial maturation, XPS analysis monitors the main chemical modifications expressed by the carbon–oxygen functional groups. The first stage of maturation begins with the removal of carboxyl and alcohol groups before a CAI of 2 (TM 450 °C). Between a CAI of 3–6 (TM 450–800 °C) an increase of sp3 hybridised carbon bonded to only carbon or hydrogen is found, which is accompanied by a decrease in ether and carbonyl functional groups. From a CAI of 6–7 (TM 800–950 °C), sp3 hybridised carbon bonded to hydrogen or carbon and carbonyl decreases while the development of highly ordered graphitic like carbon is observed. The first order laser Raman spectra recorded for both sample sets show a low degree of structural order from a CAI of 2–3, and from CAI 4–6 show a progressive increase in structural disorder of conodont organic matter. The D/G band (band at approximately 1345–1365/band at 1610 cm−1) line width ratio correlates with CAI. Conodont colour during artificial maturation occurs by migration of compounds to the surface. As the nitrogen compounds are volatilised from the surface, colour disappears.
Two iridium anomalies have been identified near the Frasnian-Famennian boundary (Upper Devonian) in the Canning Basin of Western Australia. Both anomalies are associated with the cyanobacterium Frutexites and are located in marginal slope facies. The first was identified in the Virgin Hills Formation on the west flank of McWhae Ridge near the southeastern end of the Devonian outcrop belt. This anomaly, initially identified as being from the Famennian Upper Palmatolepis triangularis Zone, is now known to be from the Early Palmatolepis crepida Zone, on the basis of the presence of Palmatolepsis crepida in the bed. The second anomaly, found in drill core from the Napier Formation just south of the Napier Range, is older than the first and is from the Frasnian Montagne Noire Conodont Zone 12 or 13 of Klapper (1989) = the Palmatolepis rhenana Zone of Ziegler and Sandberg (1990). These two iridium anomalies are thus significantly below and above the Frasnian-Famennian boundary and are not associated with the extinction event in the Palmatolepis linguiformis Zone. In the Canning Basin the association of two iridium anomalies with beds containing abundant Frutexites microstromatolites indicates that the concentrations of iridium are probably associated with a process of organic concentration. There is no evidence that either example is directly associated with an impact event.
A sequence of clastic sediments in southeastern Newfoundland straddling the Precambrian-Cambrian boundary has been investigated for its stable isotope geochemistry of carbon and sulfur and acid-resistant organic-walled microfossils. A detailed study of the Chapel Island Formation, which includes the boundary interval, has revealed fluctuations in the isotopic composition of organic carbon. These are largely interpreted as caused by differences in the depositional environments. Highly variable sulfur isotopic compositions indicate bacterial sulfate reduction as a pyrite-forming process, sometimes under sulfate-limited conditions. Palynological results are quite limited with respect to diagnostic microfossils.
A previously undescribed carbonate-shrub facies has been discovered in the lower member of the Noonday Dolomite-a Neoproterozoic post-glacial cap carbonate. This unusual facies consists of centimeter-scale structures composed of micrite and encased in early-marine cement, and exhibits an overall clotted, mottled appearance. Shrub architecture is characterized by occurrence of a central stalk with diverging branches that are composed of micrite leaves. A combination of biological, environmental, and diagenetic influences contributed to the growth and present appearance of Noonday Dolomite carbonate shrubs. Comparison with modern and ancient known abiogenic and biogenic shrub-like structures indicates that microbial communities were most likely responsible for at least localizing and initiating calcium carbonate growth in the Noonday Dolomite shrubs, although no undisputable microbial fossils have yet been discovered. Diagenetic processes may have obliterated Noonday Dolomite shrub microstructure and obscured any former fossil evidence. Unusual seawater conditions (high alkalinity/extreme calcium carbonate supersaturation) were vital for shrub growth. This research highlights a possible biologic component in Neoproterozoic post-glacial cap carbonates where most studies have focused on abiogenic processes.
The structure, mineralogy, and accretion processes of the modern and subfossil cyanobacterial microbialites from the alkaline crater lake Alchichica (Puebla, Mexico) were studied, along the lake's bathymetry and hydrochemistry. The recent lowering of the lake level had exposed microbialitic carbonate mounds and crusts, which emerged up to 2 m above the water surface, while accreting cyanobacterial microbialites were present down to a depth of ~15 m. Morphological and molecular analysis found that the living cyanobacterial mats were composed of diverse filamentous and coccoid cyanobacteria (Nostocales, Chroococcales, Oscillatoriales, and Pleurocapsales). The emerged subfossil microbialites comprised two generations: "white" (domes and crusts composed mainly of hydromagnesite with an admixture of huntite and calcite, 238U/230Th age of ~2.8 ka BP), and "brown" (chimneys, columns and laminated crusts composed of aragonite with an admixture of Mg-calcite, 238U/230Th age of ~1.1 ka BP). The significant age, structural, mineralogical, and isotopic differences suggest that the two generations were formed in different environmental conditions: the "white" during a dry period, and the "brown" in wet climate associated with high water level and intense inflow of ground water, which lowered the Mg/Ca ratio resulting in formation of aragonite instead of hydromagnesite. The hydromagnesite, replacing the primary aragonite precipitated in the living cyanobacterial biofilm, frequently undergoes silicification, which obliterates both the primary structure of the carbonate and the enclosed remains of cyanobacterial microbiota. This process helps to explain the abundant formation of dolomites and cherts in an allegedly highly alkaline Early Precambrian ocean. Thus, Lake Alchichica represents a modern alkaline environment where biosedimentary structures resembling Precambrian deposits are generated.
In Southern Germany, two examples of travertines of different age and depositional morphology were examined in detail. Travertines
are laminated carbonate rocks formed by precipitation from mineral and/or thermal waters. They include characteristic facies
types, such as bushy layers (‘shrubs’) referred to calcification of branching microbes (‘Dichothrix’-morphotype), laminar microbial mats, peloidal layers, and gas bubble layers formed within the sediment. In travertines,
microbial activity is the most important factor for carbonate precipitation.
Tufas differ from travertines by their abundance of molds of higher plants (leaves, reed, moss, green algae). They may be
associated with travertines, but do not exhibit strict travertine facies types. Tufas are common in normal fresh water environments.
Contrary to travertines and tufas, calcareous sinters usually occur in restricted areas like spring fissures, caves, or in
pores, where microbial activity is not totally absent, but not of paramount importance for precipitation.
Pedogenetic processes, which can alter travertine deposits, are responsible for large-scale features such as tepee-structures,
and some intraclastic layers, and microscopic structures like endolithic borings andMicrocodium. Travertines may also grade into lacustrine limestones with Characeae, ostracods, and aquatic gastropods.
Facies relationshps in the Vendian to Lower Cambrian Chapel Island Formation of southeast Newfoundland are used to establish a sequence stratigraphic framework for this important boundary stratotype section. The formation consists of five members of sandstone, mudstone and minor limestone deposited in a variety of shoreline to shelf environments. Peritidal sandstone and shale units in member 1 are overlain by sandstone and silstone deltaic and shelf deposits of member 2. These make up a transgressive system tract in which small-scale changes in relative sea level are superimposed on autocyclic deltaic processes. The thickness (> 400 m) of nearshore and inner shelf sediments resulted from high sediment accumulation rates which for member 2 nearly kept pace with subsidence.Upper member 3 and member 4 consist of inner shelf mudstone and peritidal limestone that were deposited in a low-energy oxygen-stratified basin. These deposits are arranged in three large-scale shoaling cycles representing three foresteping parasequences of one highstand systems tract. An extensive limestone bed at the tope of member 4 contains a sequence boundary.Associated with, or shortly postdating, development of this surface is a significant epeirogenic event that resulted in basin reorganization, increased subsidence, and progradation of a thick clastic sequence represented by member 5. The deposits of this upper member consist of an upward-coarsening storm-dominated shelf to shoreface succession of sandstone and silstone. Deposits of nearly identical character are also found in New Brunswick, and suggest that these sediments and the underlying sequence boundary could be significant for interregional correlation. Global correlation of the paleobathymetric curve developed for the Chapel Island Formation is considered unfeasible, given the long history of epeirogenic movements during the Vendian and Early Cambrian in this region.
The concretions formed in marine porewaters at shallow depths, influenced by sulfate reduction and methanogenic bacterial action. Carbon becomes progressively lighter toward the concretion margins. Septarian vein-fill of yellow spar calcite and rare, very late dolomite are both interpreted as forming in mixed meteoric-marine porewaters. -from Authors
To understand the patterns of lithofacies, marine faunas, organic-carbon enrichment, isotopes, and trace elements deposited in the early Turonian Western Interior seaway, we conducted circulation experiments using a three-dimensional, turbulent flow, coastal ocean model driven by GENESIS, a climate model developed at the National Center for Atmospheric Research (NCAR). Circulation and chemical evolution of the seaway waters are computed under the following initial and boundary conditions: (1) paleobathymetry according to a new interpretation of the lithostratigraphy and biostratigraphy; (2) temperatures and salinities of the Boreal and Tethys oceans and adjacent drainage basins based on isotopic data, atmospheric temperatures, and precipitation-evaporation magnitudes computed by GENESIS; and (3) mean annual wind stresses over the seaway computed by GENESIS. Results show that the seaway exported freshened water much like Hudson Bay today. Runoff from eastern drainages exited the seaway as a northern coastal jet; runoff from western drainages exited as a southern coastal jet. Both jets simultaneously drew in surface Tethyan and Boreal waters, creating a strong counterclockwise gyre occupying the entire north-south extent of the seaway. The curious stratal and faunal variations of the early Turonian deposits arise from this gyre and its associated water masses.
Petrographic and geochemical data from each concretion have yielded the following diagenetic sequence: 1) bioturbation by marine benthos; 2) partial phosphatization of glauconite, fecal pellets, and shell material; 3) sulfate reduction and pyrite formation; 4) siderite precipitation; 5) radial-fibrous calcite precipitation, and 6) equant calcite precipitation. The transition from marine to freshwater is recorded in concretion paragenesis. -from Authors
The most likely cause of the anomalously depleted oxygen values is a decrease in pore-water δ18O values during early diagenesis - a result, perhaps, of a significant influx of meteoric water into the marine shelf environment, or water-mineral interaction (e.g. precipitation of 18O-enriched minerals). The carbon isotopic field for dolomite is quite different from that for calcite and siderite. Highly positive δ13C values are fairly common only for dolomites. This indicates that, while dolomite concretions often form in sediments where methanogenesis is rapid precipitation of calcite and siderite concretions is restricted to sediments where either no methanogenesis takes place or where methanogenesis is not extensive enough to generate highly positive pore fluidδ13C values. -from Authors
The isotopic and cation chemistry of meteoric waters changes in response to the effects of rock—water interaction, uptake of organically derived CO2, and primary mineralogic differences among carbonate terranes. Moreover, variations in the dominance of these factors produce diverse chemical conditions within the meteoric systems which allow the sub- environments of vadose-phreatic, mixed-water, and spelean diagenesis to be distinguished. Therefore, geochemical patterns within the meteoric water system are examined to provide criteria for recognition of these subenvironments of meteoric diagenesis in ancient carbonate sequences.
The limestone/marlstone bedding couplets of the Bridge Creek Limestone Member, Cenomanian-Turonian Greenhorn Formation, were analyzed by applying spectral techniques to high-resolution lithologic and geochemical data from a core. The results suggest that the Bridge Creek contains a complex record of orbital cyclicity. The dominant signal appears to be obliquity, but signals corresponding to precession and eccentricity were also observed. The development of the bedding couplets is interpreted to have resulted from a combination of factors, including insolation-controlled changes in higher-latitude precipitation leading to dilution/redox cycles, and in lower-latitude evaporation, leading to changes in surface water conditions and productivity cycles in the calcareous plankton. The data interpreted to reflect redox cycles appear to be more strongly influenced by obliquity, and show a weak precessional signal. In contrast, trends in the carbonate record show the opposite response. The complex bedding pattern observed in the Bridge Creek Limestone is interpreted to result from the competing influences of different orbital cycles expressed through different pathways of the depositional system, and was also affected by changes in sedimentation rates related to relative sea level fluctuations, aperiodic dilution by volcanic ash, and changes in organic-matter production and redox conditions related to a global oceanic anoxic event. These factors complicate cycle analysis in the lower part of the member but leave a relatively undisturbed record in the upper Bridge Creek Limestone.
The sulphur isotope ratios of barite in many syngenetic barite deposits are shown to be approximately the same as those of the seawater from which they were deposited. Although the stratiform replacement barite-fluorite deposits of northeast British Columbia are epigenetic, their barite sulphur isotope ratios (δ34S) of +24.2 to +30.1‰ may indicate a late Middle Devonian time of mineralization if the sulphur in these deposits was derived from seawater.A model for barite mineralization is proposed in which mixing of euxinic (i.e., reducing) seawater with meteoric groundwater near the seaward edge of a large coastal aquifer, similar to the present-day Floridan Aquifer, caused solution of the shelf carbonates and induced low-temperature precipitation of barite in the resultant solution cavities. The extensive solution collapse that accompanied mineralization, and the coarse crystallinity and low manganese content (< 65 ppm) of the barite in northeastern British Columbia support this interpretation. The postulated Devonian paleoaquifer in northeastern British Columbia coincided with the regional distribution of solution-collapse breccias in the Stone Formation dolomite. The karsted upper surface of the Sulphur Point Formation may have been the landward recharge area for this aquifer.The variation in the mole percent SrSO4 along barite blades suggests that during precipitation there were changes in the rate of circulation of the mineralizing solution. In some places up to 30% of the barium in solution may have been precipitated. The δ34 values of later formed, strontium-enriched barites tend to be lower suggesting an isotope effect during crystallization favouring 34S in the crystalline phase.
Displacive calcite in the organic-rich, fine-grained carbonates of the "Nordegg Member is characterized by textures, mineralogy and stable carbon isotopic compositions which indicate precipitation in the bacterial sulphate reducing and decarboxylation zones at burial depths less than 1 km. Oxygen isotopic compositions of displacive calcite suggest pore waters had a variable but increasing meteoric influence towards the west/southwest, indicating emergence in that area in the late Early Jurassic (?) to Middle Jurassic, probably in response to terrane accretion along the western margin of ancestral North America. Solid bitumen occurs within displacive calcite zones and also fills vertical and horizontal fractures. These were derived from the "Nordegg Member'. The fracture-filling solid bitumen is more mature than the solid bitumen associated with the diplacive calcite. In situ formation of some of the solid bitumen, from organic-rich rock fragments trapped within the displacive calcite zones, likely occurred during catagenesis. -from Authors
The Codell Sandstone Member of the Carlile Shale in south-central Colorado is a coastal deposit forming the upper part of the regressive phase of the Upper Cretaceous Greenhorn cyclothem. These beds consist of fine-grained sandstones and lesser amounts of silty shale deposited in a system of barrier islands, lagoon fills, tidal deltas, and offshore bars. Barrier-bar deposits display a characteristic vertical succession of facies. Lebensspuren in the Codell include feeding structures, dwelling burrows, trails and escape traces. The Juana Lopez Member of the Carlile Shale disconformably overlies the Codell and is the basal trangressive deposit of the Niobrara cyclothem. It consists of a thin lag deposit composed of reworked Codell sand with admixed shark teeth, and mollusk shells, and an overlying fetid, skeletal limestone. -from Author
The regressive sequence displays a graded, upward-coarsening suite of facies cut by rare disconformities. Cyclically bedded pelagic carbonates (Bridge Creek Limestone Member) grade upward through chalky and calcareous shales (Fairport Member) to dark non-calcareous shales becoming more silty and sandy upward (Blue Hill Shale Member), and the sequence terminates in lower, middle, and upper shoreface sands of the Codell Sandstone Member. The top of the cyclothem is truncated on middle-upper shoreface sandstones of the Codell by a regional transgressive unconformity at the base of the Niobrara Cyclothem. Although the Greenhorn regressive facies sequence generally mirrors that of the transgression (the symmetrical cyclothem model), significant differences were recorded which suggest that the Western Interior Basin was tectonically passive during eustatic fall and regional regression. -from Authors
Describes metre-sized, spherical to subspherical ferroan calcite concretions. Their texturally massive centres are composed of coarsely crystalline pseudospar whereas the margins consist of thick fringes of fibrous calcite. Widespread precipitation of ferroan dolomite and pyrite occurred at shallow burial depths below the sediment-water interface during the early stages of bacterial sulphate reduction. These concretions were initiated within centimetres of the dysoxic to anoxic sediment-water interface and continued to grow to depths of a few hundred metres. -from Authors
The lower member of the Cape Phillips Formation (Late Ordovician - Early Silurian) on northeastern Cornwallis Island is a sequence of interbedded carbonates and shales that preserves a continuous record of diagenesis that started with the formation of early diagenetic, nonferroan calcite concretions and ended with precipitation of late stage nonferroan calcite in vugs and fractures. The petrographic and geochemical evidence from the carbonates of this study is consistent with regional organic maturation data indicating that these rocks reached temperatures within the oil window. Hydrothermal effects, if real, must have been short-lived and were probably restricted to fracture zones. Elsewhere in the region, probably coeval hydrothermal fluids produced economically significant Mississippi Valley-type Pb-Zn mineralization. -from Authors
The carbon and oxygen isotopic compositions of authigenic siderite, dolomite, and calcite from mudstone and siltstone of the Albian Harmon Member indicate mineral formation from fluids with a significant meteoric component. All authigenic carbonates show an 18O depletion in basin margin facies. The magnitude of this depletion varies with time, suggesting a primary isotopic variability in the basinal fluids that was subsequently influenced by meteoric incursion from the west-southwest (basin margin). -from Author
Reveals a record of simultaneous variation in δ18O and δ13C values at the intrazonal scale that is incompatible with compositional change anticipated from the evolution of meteoric fluids in response to progressive water-rock interaction. Regionally extensive mixing between marine and meteoric water along the basal margin of the phreatic lens is the process responsible for the cementation of much of this platform succession. Attributes low Mg and Sr contents to temperature and/or PCO2 effects, or to differences in conditions under which calcite is precipitated. -from Authors
The Upper Albian-Coniacian section cored in the Amoco No. 1 Rebecca K. Bounds well in Greeley County western Kansas, serves as a reference section for the timing of depositional events in the Western Interior Seaway. Chronostratigaphy of this section was calibrated by a multidisciplinary study of nannofossils, dinoflagellates, spores, pollen, foraminifers, and mollusks. Range data of the biota in the Bounds core were compared by graphic correlation to a global composite standard that includes key reference sections in Europe and North Africa.
The basal Upper Albian sequence boundary is overlain by transgressive facies of the Purgatoire Formation dated as 102.8 Ma. The upper Upper Albian sequence boundary between the Purgatoire and Dakota Formations marks a hiatus in deposition from 99.4 to 98.2 Ma. The Albian-Cenomanian intra-Dakota sequence boundary spans from 96.0 to 94.1 Ma. The Turonian-Coniacian sequence boundary between the Carlile and Niobrara Formations spans from 89.9 to 88.3 Ma. Maximum flooding is documented within the Purgatoire at 101.4 Ma and in the Graneros Shale at 93.7-92.8 Ma. The Albian-Cenomanian boundary defined by European ammonites and correlated by dinoflagellates is placed at the intra-Dakota unconformity.
Graphic correlation is an independent method of measuring the durations of Milankovitch-scale depositional cycles and can separate climatic cycles from longer tectono-eustatic cycles. Four orders of depositional cycles are recorded by lithological changes, and their durations are constrained by graphic correlation. The longest cycles range from 2.0 to 3.4 My and are found in the sequences defined by the Purgatoire Formation, the lower part of the Dakota Formation, the upper Dakota and Graneros Formations, and the Greenhorn and Carlile Formations. The next lower order comprises transgressive-regressive subcycles of about 0.5 My long in the Purgatoire. The third-scale cycles include sandstone-mudrock cycles in the Dakota, limestone-marl cycles in the lower part of the Greenhorn, and cyclical strata in the Fort Hays Limestone Member of the Niobrara Formation that are about 100 ka long. The shortest cycles are limestone-marl couplets in the upper Greenhorn that are about 41 ka long.
The oxygen isotope compositions of diagenetic minerals from sandstones and conglomerates have been determined for a Permian to Upper Cretaceous section through the Alberta deep basin. These data have been used to reconstruct variations in the δ¹⁸O values of pore water during diagenesis of intercalated sandstones and shales. The results confirm earlier observations on the oxygen isotope evolution of pore water in the western Canada sedimentary basin. First, meteoric water was abundant during early diagenesis, even in sediments deposited in shallow marine environments. Second, the maximum δ¹⁸O values attained by pore waters during burial diagenesis were generally < + 3%, much lower than in other shale-dominated basins (e.g., Gulf Coast). However, pore waters in sandstones located adjacent to, or intercalated with, carbonates and shales of the underlying Paleozoic section had substantially higher δ¹⁸O values (+ 7 to +9%) at or near maximum burial. Third, late diagenesis was dominated by low-¹⁸O meteoric waters.
Saturation of the sedimentary section by meteoric water during early diagenetic processes probably resulted from infiltration during subaerial exposure associated with sea level fluctuations of the inland sea. Influx of meteoric water probably continued episodically throughout burial diagenesis. Contribution of meteoric water during early diagenesis is reflected in the low maximum porewater δ¹⁸O values that characterize the peak of burial diagenesis. These results also indicate that the smectite-to-illite reaction in Mesozoic shales did not dominate oxygen isotope evolution of sandstone pore waters in the western Canada sedimentary basin. Any increase in the δ¹⁸O value of pore water during burial probably resulted from variable mixing between early diagenetic, meteoric-dominated pore waters and ¹⁸O-rich pore waters that had equilibrated with the underlying Paleozoic carbonate platform. The δ¹⁸O values of late diagenetic minerals and present pore waters reflect both this process and the subsequent, substantial influx of surface-derived meteoric water during post-Laramide uplift and erosion.
Macrofossils were sampled from 650 ft (198.1 m) of core material from the USGS Escalante No. 1 core, consisting mainly of proximal offshore marine calcareous mudstones of the Cretaceous Western Interior Seaway of North America. Samples range in age from Upper Cenomanian (S. gracile ammonite zone) through Upper Middle Turonian (P. hyatti ammonite zone) and include representatives of ammonites, inoceramid bivalves, and oysters. Diagenetically altered carbonates were identified through visual inspection and trace-element (Sr, Mn, Fe, S, K, Na) analysis of shell material. Carbon- and oxygen-isotopic measurements of carbonate shell material were performed on 170 individual shell samples.
In general, δ¹⁸O values of inoceramids are more negative and δ¹³C values are more positive than those of ammonites. Well-preserved oysters are significantly enriched in δ¹⁸O in comparison with inoceramids. Inoceramid shell material is generally more enriched in δ¹³C than the surrounding carbonate matrix. Inoceramid δ¹⁸O is enriched relative to the surrounding matrix in the lower portion of the core, however, this relationship is reversed near the top of the core.
Isotopic compositions of inoceramids and ammonites reflect both variations in primary water column chemistry and biological effects. Overall, oxygen isotopic values appear to vary in concert with patterns of sea level variation reconstructed from basin-scale stratal patterns. Ammonite δ¹⁸O, in particular, appears to mirror regional short-term, base-level cyclicity. The amplitude of oxygen isotope variations in ammonites (2‰–3‰) suggests an interplay of at least two distinct water masses with very different isotopic compositions. The dominance of one water mass over the other may be related to sea level variation; a northern component water depleted in δw probably dominates during regressive intervals.
Organic-rich, shale-hosted septarian and nonseptarian calcite concretions, in the (Givetian) Hamilton Group of central New York State, formed early in the shallow subsurface. Evidence of primary porosity in concretions during growth indicates that early stage diagenetic alteration occurred in an open-marine, phreatic environment that homogenized isotopic and geochemical signatures of metastable carbonate minerals. Preburial condensation of sediments in younger stratigraphic units within the Hamilton Group, possibly caused by increased winnowing, bioturbation, and erosional events during shallowing of the Hamilton sea, has generated stratigraphic variations in concretion lithology and shape. -from Authors
New observations upon cavity-filling radiaxial calcites from Western Australia suggest that most of the features originally considered of neomorphic origin are instead primary.-from Author
Carbonate concretions occur commonly in organic-rich clastic sediments of ancient coastal floodplains and deltas. The mineralogy and chemistry of early cements are dependent on dissolved sulphate concentrations and processes which affect them (notably depositional water composition, microbial sulphate reduction and mixing with waters of different origin). Calcite precipitates from marine-influenced pore waters rich in dissolved sulphate, dolomite from similar waters depleted in sulphate and siderite from meteorically-derived pore waters. -from Authors
Conventional thinking has long held that the abiotic precipitation of calcium carbonate occurs with a causal relationship between fluid Mg/Ca ratios and crystal morphology, crystal composition, and carbonate mineralogy, resulting in the formation of meteoric, equant, low-magnesium calcite and marine, acicular, high-magnesium calcite and aragonite. Problematically, calcites with varying amounts of incorporated magnesium occur either as equant or acicular crystals, and aragonite may coexist with calcite in either environment. Commonly, however, a systematic relation exists between crystal morphology, composition, mineralogy, and rates of reactant supply to growing crystal surfaces. Such relations suggest that crystal morphology, composition, and mineralogy are controlled by the kinetics of surface nucleation and the amount of reactants, principally carbonate ions, at growth sites. Precipitating phases are the ones which can best accommodate such excess reactants; ambient Mg/Ca ratios only indirectly control the nature of inorganically precipitated carbonate phases.-from Authors
Authigenic minerals and diagenetic textures in the marine conglomerates and sandstones of the Cretaceous Cardium Formation in the northeast Pembina area preserve a complex sequence of diagenetic events. Textural relationships observed in thin section and under the scanning electron microscope were used to determine the relative timing of diagenetic events in these marine sediments. Paragenetic sequences are similar for the conglomerate, sandstone, and siderite nodules in the enclosing shales. Extensive cementation by siderite and calcite occurred early in the diagenetic history, before any significant compaction. The geometry and distribution of lithofacies in the Cardium may have influenced the diagenesis and internal stratigraphy of the conglomerate. Overlying shale matrix conglomerate may have trapped upward-migrating fluids increased in buoyancy by dissolved CO 2 produced by decay of organic matter in the enclosing shales. These fluids could have infiltrated the upper portion of open matrix conglomerate, causing cementation. Petrographic evidence shows alternating precipitation of siderite and pyrite, implying fluctuating activities of dissolved carbonate and hydrogen sulfide, probably caused by bacterially mediated processes during early diagenesis. Early sequences of siderite and pyrite precipitation can be related to zones of iron reduction, sulfate reduction, and, possibly, decarboxylation during diagenesis. Carbon and oxygen isotopic data indicate a systematic change in the isotopic compositions of calcite and siderite from -25 to -30 per thousand delta ¹³ C and 0 per thousand delta ¹⁸ O, for cements early in the paragenetic sequence, to 0 to -5 per thousand delta ¹³ C and -15% per thousand delta ¹⁸ O for cements which are interpreted to occur later in the paragenetic sequence. This observation is consistent with the influence of meteoric water on later stages of cement deposition in the Cardium, a unit considered to be marine and deposited well offshore on a shallow marine shelf. The intrusion of meteoric water far offshore may be related to changes in sea level. Many variables must be accounted for, but it is feasible, using the estimated regional dip of the Cardium at the time of deposition (0.005 degrees ), for a 1-m drop in sea level to push the freshwater--seawater interface seaward on the order of 100 km.
Petrographic, chemical and isotopic studies of marine sediment-hosted septarian concretions from Lower Jurassic Whiteaves Formation in the Queen Charlotte Islands, B.C., Canada, reveal a complex diagenetic history that has resulted from bacterially mediated reactions at shallow burial depth as well as hydrothermally modified meteoric waters. The general diagenetic sequence in cement-filled septaria cracks includes: 1) fibrous calcite, 2a) bladed calcite or 2b) ferroan "saddle-like" calcite, 3) blocky calcite with early ferroan and late non-ferroan stages, and 4) barite. Each cement generation has a characteristic chemical and isotopic signature. Oxidation of upward-diffused methane contributed to an extremely negative value ofdelta C (ca. -35 per thousand ) in the early generation of fibrous calcite. The delta O (ca. -3.0 per thousand ) and 87 Sr/ 86 Sr (0.70683) values of these calcites, however, reflect Jurassic seawater composition. Plutonism during Late Jurassic to Early Cretaceous time provided hydrothermal discharge that altered meteoric waters. This process became the main factor for the precipitation of "saddle-like" and bladed calcites. These two generations of carbonate cement are characterized by relative depletion in delta 18 O (-11.5 to -17.4 per thousand ) and less radiogenic 87 Sr/ 86 Sr (0.70532 to 0.70575) signatures. Progressive modification in pore water chemistry and increasing depth of burial occurred during the formation of late ferroan blocky calcite.
A downhole decrease in 18O, Mg 2+ and K
+, an increase in Ca 2+ and a low 87Sr
/86Sr ratio of 0.7067 in the pore fluids of DSDP site 323
were caused principally by the alteration of volcanic material. These
chemical and isotopic patterns were produced by the alteration, in order
of decreasing importance of: a 60-m thick basal layer of volcanic ash;
the underlying basalts; and igneous components in the 640-m thick upper
sequence composed largely of terrigenous material. A significant portion
of the alteration of the ash in the basal sequence must have occurred
before the deposition of the upper sediments, perhaps under the
influence of advecting solutions. The rest of the alteration occurred
during the deposition of the thick upper sediments. Mass balance
considerations and the low δ 18O values of most of the
alteration products suggest that much of the later alteration occurred
progressively over the last 13 Myr. The principal alteration products
were smectite, potassium feldspar, clinoptilolite and calcite.
Isotopic data from exceptionally well preserved foraminifera show that the subtropical North Atlantic had sea surface temperatures (SSTs) between 30 and 31 °C during the late Albian and early Cenomanian. These temperatures were warmer than average modern temperatures in the tropical western Atlantic and support previous inferences based on diagenetically suspect material of Albian tropical SSTs of ˜30 °C. This finding is consistent with basic theories of oceanic thermal response in the tropics to the high atmospheric carbon dioxide levels during the middle-Cretaceous greenhouse. However, our data do not support the concept of a super-Tethyan region of hypersaline waters in the western North Atlantic during late Albian and early Cenomanian time, because seawater salinities substantially higher than modern ones would require significantly higher SSTs than those reported here. Isotopic analysis of mid-Cretaceous planktic foraminifera shows that Planomalina, Ticinella, and Biticinella grew in surface waters and provide isotopic proxies for SST, whereas deeper growing species include Hedbergella, Rotalipora, and Praeglobotruncana. None of these taxa display isotopic indications of photosymbiosis, suggesting that this ecology did not evolve in planktic foraminifera before the Late Cretaceous. Contrary to previous hypotheses, none of these species increased their depth habitat during their life cycles, unlike many extant planktic foraminifera. The rotaliporids may have been preferentially susceptible to extinction during oceanic anoxic events because they lived within or below the thermocline for most of their life cycles.
The idea that carbonate mineral precipitation, by preferentially removing 1S0, can cause isotopic depletion in pore waters and subsequently precipitating minerals has been in the literature for 20 years (Irwin et al. 1977). A numerical model of the process shows that for calcite and dolomite precipitation such a mechanism is not viable for reasonable rates of precipitation. Siderite precipitation in marine environments is also not likely to be able to occur rapidly enough to deplete pore waters in 180.
A previously unreported, coarsely crystalline calcite fills pores and is composed of crystals that possess inclusion-patterns and lattice-curvatures mimetic after bundled acicular carbonate cements. This calcite fabric, named 'fascicular-optic' because of the characteristic divergent optic-axis pattern within each crystal, is possibly widely distributed in certain limestones. It has been found within both shallow-marine and deep-water (pelagic) limestones. The replacement mechanism responsible for generating fascicular-optic calcite is believed to involve the lateral joining together (coalescence) of the former acicular crystals, either directly if the original cement had a low-Mg calcite mineralogy, or by coalescence of acicular aragonite or high Mg-calcite crystals, followed by subsequent stabilization (calcitization or magnesium loss).
The textural evidence in septarian concretions shows that the septa formed as tensile fractures during burial and compaction of the host shale. Comparison of the combinations of vertical and horizontal stresses and pore-fluid pressure required for tensile fracture of cemented concretions and those likely to occur during shale burial indicates that septarian fracturing will be favoured by overpressuring and low horizontal stress, most likely to occur during times of rapid burial. Burial histories of septarian concretions from the Eocene London Clay and the Jurassic Kimmeridge Clay show that fracturing can form under as little as 50 m of sediment. By relating episodes of septarian fracturing to times of rapid burial, the timing of diagenetic cement formation can be constrained. (Author's abstract)-D.J.M.
Upper Cretaceous organic-rich carbonates in Israel contain benthonic foraminifera and varying amounts of early diagenetic infilling of sparry calcite. The sparry calcite has oxygen-isotope values (down to -9.50/00 PDB) that are significantly lower than those of the coexisting skeletal calcite (averaging -20/00 PDB). Low delta18O values are very common in carbonates that are associated with organic matter. These occurrences are conventionally explained as being due to carbonate formation under conditions of low salinity and/or elevated temperature. On the basis of petrographic data and local geologic evidence, however, none of the conventional explanations can be applied in this case. We advance an alternative model that relates the light oxygen compositions of the diagenetic calcite to depletion of 18O in pore water of normal salinity. The proposed operating mechanism is a direct consequence of organic matter decomposition in the sulfate-reducing zone. Being inherent to reducing marine environments, this model can be applied to many organic-rich rock associations.
Large septarian concretions from the Kimmeridge Clay, up to 1.2 m in diameter, have centres comprising anhedral calcite microspar passing into margins of radiating fibrous calcite microspar, with a pyrite-rich zone at the transition. Septarian veins formed and were lined with brown calcite synchronously with fibrous matrix growth, with white calcite precipitated in septarian cavities after concretion growth ceased. Septarian veins, filled only with white calcite, formed later, at the same time as the outermost calcite microspar crystals were enlarged.
The concretions were buried in the Late Jurassic to about 130 m, and in the Late Cretaceous to about 550 m, with uplift between. Oxygen isotopes show that the concretion grew throughout the first burial, with septarian veins forming from about 30 m depth onwards. Later septarian veins formed between about 200 and 500 m during the second burial.
Carbon isotopes show that the compact inner matrix grew in the sulphate reduction zone, the end of which is marked by the pyrite-enriched zone. Dissolving shells, and possibly minor methanogenic carbonate, slowly diluted sulphate reduction-zone carbonate during deeper burial. During early concretion growth, Mg and Sr were depleted in the pore water. During later stages of the first burial, Mg, Sr, Mn and Fe all increased, especially after concretion growth ceased. During the second burial, Fe, Mn and Mg decreased as calcite precipitated, implying relatively closed systems for these elements.
Synchronous formation of septarian fractures and fibrous calcite matrix shows that the Kimmeridge Clay became overpressured during the later stages of both burials.
Carbon, oxygen and sulphur isotope data for transects across two pyrite-bearmg carbonate concretions, and their host sediments, from the Upper Lias of N.E. England show symmetrical zonation. 13 C PDB values of the calcite cement (-12.9 to -15.4%.) indicate that most of it originated from organic matter by bacterial reduction of sulphate, augmented with marine and, to a lesser extent, fermentation derived carbonate. Organic carbon ( 13 C PDB = -26.1 to -37.0%.). reflects the admixture of allochtho-nous terrestrial organic matter with marine material and the selective preservation of isotopically light organic material through microbiological degradation. Two phases of pyrite are present in each concretion. The earlier framboidal pyrite formed throughout the sediment prior to concretionary growth and has 34 S CD values of -22 to -26%. indicating formation by open system sulphate reduction. The later euhedral phase is more abundant and reaches values of - 2.5 to - 5.5%. at concretion margins. This phase of sulphate reduction provided the carbonate source for concretionary growth and occurred in a partially closed system. The 13 C and 34 S data are consistent with mineralogical and chemical evidence which suggest that both concretions formed close to the sediment surface. The 18 O values of the calcite in one concretion ( 18 O PDB = 2.3 to -4.8%.) indicate precipitation in pore waters whose temperature and isotopic composition was close to that of overlying seawater. The other concretion is isotopically much lighter ( 18 O PDB -8.9 to -9.9%.) and large 18 O differences between concretions in closely-spaced horizons imply that local factors control the isotopic composition of pore waters.
Because meteoric water δ¹â¸O (dO) values decrease with decreasing ambient temperature and increasing latitude, dO values of meteoric calcite cement should exhibit a similar relation with paleolatitude and be an indicator of continental paleotemperatures. To test this, the authors compiled isotopic and paleolatitude data for 20 meteoric cements and nine speleothems ranging in age from Devonian to modern and in paleolatitude from 3.5° to 83°. The dO vs. latitude trend for these carbonates is almost identical to that predicted for modern inland environments, but differs from the trend for coastal environments. It is assumed that the modern meteoric water dO vs. temperature relation is valid for the past and that insignificant evaporation occurred prior to carbonate precipitation, then coastal and inland paleotemperatures can be calculated from the dO values of meteoric calcite (dO{sub mcl}) and seawater (dO{sub sw}) by using the equations T{sub coastal} = 13.3 {plus minus} 32.6(-0.231 - 0.0613(dO{sub mcl} + dO{sub sw}))¹² and T{sub inland} = 17.8 {plus minus} 16.2(-0.572 - 0.1233(dO{sub mcl} + dO{sub sw}))¹², where T is temperature °C. Calcite precipitated from coastal meteoric water at temperatures between 0 and 25°C will exhibit a narrow range in dO (-6% to -4%, where dO{sub sw} = 0%). The dO of calcite precipitated from inland meteoric water will be sensitive to paleotemperature, ranging from -14% to -5% (where dO{sub sw} = 0%) for temperatures of 0 to 25°C.
Authigenic ankerite in the gas-bearing mid-Permian Aldebaran Sandstone (Denison Trough, Queensland, Australia) has an anomalously light oxygen-isotopic composition () and exhibits a trend of 18O-enrichment from the base to the top of the unit. Textural relationships, together with burial and thermal modelling, indicate that this carbonate precipitated at temperatures of about 100 to 140°C, when the sequence approached maximum burial during the Late Triassic. This implies that ankerite precipitated from porewater very depleted in 18O with respect to marine water (). The formation of this deep, relatively high-temperature ankerite is difficult to reconcile with downward percolation of meteoric water at that time since the basin was then undergoing its first burial/compactional cycle. We interpret the ankerite to have precipitated from porewater expelled upward from the earliest Permian Reids Dome beds. This thick unit, consisting mainly of high-latitude continental sandstones, mudrocks and coals, was initially saturated with very 18O-depleted meteoric water () partly derived from melted snow and ice, and is likely to have undergone overpressuring during rapid burial (at rates up to 1 km/Ma). Tectonically induced expulsion of “connate meteoric” porewater out of the Reids Dome beds took place as the sequence approached maximum burial prior to Late Triassic basin uplift. This water was flushed upward through the overlying units, retaining a (modified) meteoric isotopic signature, which was recorded by the precipitating ankerite. Computer modelling of heat transport, isotopic mass balance and water mixing quantitatively shows that this interpretation is viable, lending support to the suggested mechanism of upward, cross-formational porewater flow deep in a sedimentary basin.
A conspicuous seaward bulge of the middle to late Turonian shoreline of the Cretaceous seaway in northeastern Utah and southwestern Wyoming has been identified by previous authors as the Vernal delta. Strata of the Frontier Formation and the Ferron Sandstone Member of the Mancos Shale that form the Vernal delta consist largely of fluviodeltaic facies. The delta, however, is not recognizable as a locus of Turonian sedimentation; there is no isopach thick associated with it. The Vernal data is a large feature, encompassing an area of at least 6250 mi/sup 2/ (16,187 km/sup 2/). A comparison between the depositional setting and paleogeography of northeastern Utah during the Late Cretaceous and a present-day area on the east flank of the Andes in Colombia indicates strong similarities. Further comparison suggests that feature the size of the Vernal delta could not have been produced by a single river. The Vernal delta overlies the ancestral Uinta Mountain uplift, an area where Cenomanian marine shales were entirely removed by what appears to have been submarine erosion during early Turonian time. When the shoreline prograded eastward across this area during middle Uronian time, the sediment load caused the area to subside, but at a rate slower than rates of subsidence to the north and south. This differential subsidence is the cause of the shoreline bulge. Although it includes deltaic facies, the Vernal delta is not a delta per se, but a feature produced as the result of interaction between sedimentation and gentle tectonic movement of the ancestral Uinta Mountain uplift.
Chronolithologic units and unconformities in mid-Cretaceous formations of the central Rocky Mountains region indicate widespread marine transgressions and regressions as well as recurrent deformation of the foreland in the Western Interior during Cenomanian, Turonian, and Coniacian times (88-96 Ma). The stratigraphic record of the widely recognized Cenomanian and early Turonian transgression, middle Turonian regression, and late Turonian and Coniacian transgression was modified in several areas by episodes of slight uplift and attendant erosion. The most evident tectonism was in western Montana during the middle to late Cenomanian (93-94 Ma), in western Wyoming and adjoining areas during the early Turonian to earliest middle Turonian (90-91 Ma), in north-central Colorado, eastern Wyoming, and northwestern Wyoming in the early late Turonian (89.8 Ma), and in northeastern Colorado, Wyoming, and southwestern Montana in the late late Turonian (89.3 Ma). Crestlines of most of the swells trend generally either northwest or northeast. The tectonism of the mid-Cretaceous foreland corresponds in age to displacements of thrusts in the Sevier orogenic belt of southwestern Wyoming and southeastern Idaho. Furthermore, much of the foreland deformation probably reflects episodes of eastward thrusting in the thrust belt.
The sedimentology and stratigraphy of the Cretaceous Cardium Formation are generally interpreted as indicating an offshore, shallow-marine environment of deposition; however, geochemical and isotopic data suggest that porewater salinity varied widely during early diagenesis for much of the Cardium. In cases with little of no evidence of subaerial exposure of the sediments, this apparent conflict can be resolved by postulating infiltration of early meteoric water into these nearshore sediments behind a mobile mixing zone. Infiltration of meteoric water and movement of the interface may have been possible during any phase of basin formation, whether transgression, regression or stillstand. Evidence for the presence of this paleoaquifer is found in data from the early-diagenetic siderite cements of the Raven River Allomember and the Carrot Creek Member of the Cardium Formation.
Organic matter is modified by several processes operating at different depths during burial diagenesis: (1) sulphate reduction; (2) fermentation; (3) thermally-induced decarboxylation, and so on. CO2, one common product of each, can be distinguished by its carbon isotope composition: approximately (1) −25‰, (2) +15‰, (3) −20‰ relative to PDB. These values are preserved in diagenetic carbonates of the Upper Jurassic Kimmeridge Clay. Independent corroboration of the relative dominance of each process within specific depth intervals is given by the isotopic composition of incorporated oxygen which is temperature dependent (1) 0 to −2‰, (2) −1.5 to −5‰,(3) −3.5 to −7.0‰.
Fine-Grained Deposits and Biofacies of the Cretaceous Western Seaway: Evidence of Cyclic Sedimentary Processes - This volume emphasizes the influence of cyclic sedimentary processes on the distribution of rock types and faunas in the Cretaceous strata in Colorado. As a whole, the volume provides an interdisciplinary view of the causes and consequences of gradual cyclic, periodic, and catastrophic changes in environmental conditions recorded by strata in the Kiowa-Skull Creek, Greenhorn, and Niobrara Cyclothems.
Paleotemperature and salinity profiles for the Western Interior Seaway are reconstructed by use of oxygen and carbon isotopic signatures of shell material. Data have been gathered on different groups of molluscs distributed in three distinct habitat types. Isotopic variations and inferred environmental tolerances of the organisms were used to determine upper and lower temperature boundaries for each habitat group and therefore water-depth zones. The results clearly show that the water column consisted of denser, more saline, warm bottom layers that were overlain by, and decoupled from, cooler, less saline intermediate layers. This profile originated due to a surface current transporting runoff water from the western highlands toward the eastern shallow border of the seaway where evaporation and heating of surface water in a warm, humid atmosphere caused increased density and sinking, followed by westward return flow of the warm saline bottom water. This model is compatible with known climatic and oceanographic information for the Cretaceous. - from Author
The Cretaceous geological record left by the North American epicontinental sea suggests that the climate of North America was considerably different from the present. The climate was warm and at least seasonally humid. Oxygen isotopic evidence from biogenic carbonate also suggests at least periodic episodes of increased runoff into the seaway and freshening of surface water. One likely cause of paleoclimate change is the latitudinal difference in Cretaceous land-mass distribution. This will affect land-sea air circulation, wind patterns and precipitation. The authors have examined the effects of cyclical insolation variation. Results show that, by intensifying insolation contrast between northern and southern hemispheres during northern hemisphere winter, precipitation intensified over North America, possibly caused by increased cyclonic activity. -from Authors
Modeling of sevier orogeny and development of foreland basin
A high-resolution stratigraphic framework based on macrofossils, microfossils, regional marker beds, radiometric age determinations, inorganic geochemistry, and stable isotopic composition of carbonate and organic matter has been developed for the Upper Cretaceous Greenhorn and Niobrara formations, and equivalent units, in the US and Canada. Use of this framework has allowed characterization of cycles and events in paleoclimatic and paleoceanographic conditions that influenced sedimentation and early diagenesis of fine-grained carbonates in the Western Interior Seaway. -from Authors
Variation in the carbon isotopic composition of organic matter in the Greenhorn Limestone are described for Black Mesa, Arizona; Pueblo, Colorado; Bunker Hill, Kansas; Ponca State Park, Nebraska; and Cone Hill, Montana. Carbon and oxygen isotopic compositions of inoceramid bivalve shells and whole-rock carbonate are reported for the Black Mesa and Pueblo sections. Oxygen isotopic values of whole-rock carbonate generally become more positive upward in the Greenhorn from the lower Lincoln Limestone Member through the Hartland Shale Member and into the lower Bridge Creek Limestone Member. This trend is inferred to reflect generally increasing salinity of Western Interior seawater. Superimposed on this overall trend are intervals with marked isotopic and geochemical fluctuations. A particularly severe and rapid paleoenvironmental change is inferred to have occurred just prior to the Cenomanian-Turonian boundary defined by macrofossil extinctions. -from Author
Three paleobiogeographic divisions characterized the Cretaceous Western Interior Seaway of N America during most of its history: a Cool Temperate N Interior Subprovince; a Mild Temperate Central Interior Subprovince; and a Warm Temperate S Interior Subprovince. To the S lay the Subtropical Gulf and Atlantic Coast Subprovince, and the Tropical Caribbean Province. Stratigraphic data reveal 5 third-order eustatic cycles which inundated the interior of N America during the Cretaceous. In each, the distribution of paleobiogeographic units was dramatically altered within a 1-2Ma interval around peak transgression and eustatic highstand. These peaks were associated with abrupt paleoceanographic changes involving warming and amelioration of climates, normalization of salinity, and rapid fluctuations between well oxygenated waters and anoxic events. During these 1 to 2 Ma intervals, abrupt northward migration of Subtropical organisms as much as 1500 miles into west-central Canada, and of Tropical reef biotas into the southern United States, depict rapid northward incursions of Sub-tropical and Warm Temperate biogeographic units. These were followed rapidly by southward emigration to normal distributions. Major extinction events are commonly associated with these incursions, as are periods of rapid evolution among marine taxa. The major centers of endemism and the most rapid rates of evolution on North Cretaceous molluscs occurred within paleobiographic ecotones.-from Author