Fig 5 - uploaded by Anna Gandin
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Stromatolites and autoclastic breccias (outcrop photographs). (a) Stromatolites with concentrations of iron oxides, probably resulting from the alteration of early diagenetic, organic-derived pyrite (Kuruman Kop section). (b) Finely laminated stromatolites with a very smooth profile. (Kuruman Kop section). (c) Autoclastic breccia associated with a diapir-like, domal structure. Contorted and disrupted mat facies appear to have intruded, pierced and displaced overlying sediment, thinning and breaking dolomitized layers which now appear as broken, corroded rafts (Kuruman Kop section). (d) Prograding of the brecciation front from left to right: chaotic, contorted sediment encroaches on the rusty red dolomitized sediment and associated grey herringbone calcite (black arrow). Associated, planar and vertical fractures in the undeformed rock have been filled by multiple rims of white diagenetic cement (white arrow) (Kuruman Kop section).
Source publication
A detailed sedimentological and petrographic analysis of the Neoarchaean Campbellrand and Malmani carbonates of South Africa provides evidence that collectively indicates the former existence of evaporites and the early replacement of primary sulphate deposits by calcite. Diagenetic disruption of sedimentary structures, solution collapse breccias,...
Contexts in source publication
Context 1
... ( Fig. 4a) to larger (up to 50 cm) Dolomitized, cable-like, crinkled 'stem' of a flower-like structure (see Fig. 3b) resulting from amalgamated and folded filaments. Seen under cathodoluminescence is evident that dolomitization is strictly associated with the partially degraded organic filaments (sample Rau 5.1; Kuruman Kop section). forms (Fig. 5a, b). Some are preserved by silicifica- tion ( Fig. 4a) with superposed, irregular laminae ( Fig. 4b) of dense, microcrystalline former primary sediment (micrite or gypsum mud). Spherulitic length-slow chalcedony is locally associated in the intermound voids (Fig. ...
Context 2
... larger and more developed stromatolites are made from a very regular lamination similar to that of the planar laminites, and commonly exhibit a very smooth profile (Fig. 5a, b). They may be embedded in herringbone calcite and show frequent concentrations of iron oxides, often with yellowish haloes (probably hematite and sulphur after early- diagenetic pyrite) distributed along the laminae (Fig. ...
Context 3
... made from a very regular lamination similar to that of the planar laminites, and commonly exhibit a very smooth profile (Fig. 5a, b). They may be embedded in herringbone calcite and show frequent concentrations of iron oxides, often with yellowish haloes (probably hematite and sulphur after early- diagenetic pyrite) distributed along the laminae (Fig. ...
Context 4
... intrastratal collapse and solution breccias are commonly associated with the diapir- like cones and with planar and vertical fractures filled with multiple rims of white diagenetic cement (Fig. 5c, d). They are composed of matrix- supported sub-rounded or angular clasts of dolomite bordered by parallel, folded, stretched and buckled, sparry veins. The fine-grained, contorted and dis- rupted mat facies, studded with irregularly shaped sublinear calcite blebs, appear to have intruded, pierced and displaced overlying sediment, ...
Citations
... The corresponding relationships among evaporate (halite), Large igneous provinces (LIPs) and Thermal cycle in the geological time (the colour in the figure indicates the relative temperature of Earth's surface layer, with yellow, red, blue and white representing temperature from warm to cool, respectively). a, Temporal distribution of masses of evaporites (redrawn from12,26,27,[31][32][33][34][35][36][37] ). b, Temporal distribution of area of the large igneous provinces (redrawn from1,18 ). ...
Large evaporite provinces (LEPs) represent prodigious volumes of evaporites widely developed from the Sinian to Neogene. The reasons why they often quickly develop on a large scale with large areas and thicknesses remain enigmatic. Possible causes range from warming from above to heating from below. The fact that the salt deposits in most salt-bearing basins occur mainly in the Sinian-Cambrian, Permian-Triassic, Jurassic-Cretaceous, and Miocene intervals favours a dominantly tectonic origin rather than a solar driving mechanism. Here, we analysed the spatio-temporal distribution of evaporites based on 138 evaporitic basins and found that throughout the Phanerozoiceon, LEPs occurred across the Earth’s surface in most salt-bearing basins, especially in areas with an evolutionary history of strong tectonic activity. The masses of evaporites, rates of evaporite formation, tectonic movements, and large igneous provinces (LIPs) synergistically developed in the Sinian-Cambrian, Permian, Jurassic-Cretaceous, and Miocene intervals, which are considered to be four of the warmest times since the Sinian. We realize that salt accumulation can proceed without solar energy and can generally be linked to geothermal changes in tectonically active zones. When climatic factors are involved, they may be manifestations of the thermal influence of the crust on the surface.
... The corresponding relationships among evaporate (halite), Large igneous provinces (LIPs) and Thermal cycle in the geological time (the colour in the figure indicates the relative temperature of Earth's surface layer, with yellow, red, blue and white representing temperature from warm to cool, respectively). a, Temporal distribution of masses of evaporites (redrawn from12,26,27,[31][32][33][34][35][36][37] ). b, Temporal distribution of area of the large igneous provinces (redrawn from1,18 ). ...
Large evaporite provinces (LEPs) represent prodigious volumes of evaporites widely developed from the Sinian to Neogene. The reasons why they often quickly develop on a large scale with large areas and thicknesses remain enigmatic. Possible causes range from warming from above to heating from below. The fact that the salt deposits in most salt-bearing basins occur mainly in the Sinian-Cambrian, Permian-Triassic, Jurassic-Cretaceous, and Miocene intervals favours a dominantly tectonic origin rather than a solar driving mechanism. Here, we analysed the spatio-temporal distribution of evaporites based on 138 evaporitic basins and found that throughout the Phanerozoiceon, LEPs occurred across the Earth’s surface in most salt-bearing basins, especially in areas with an evolutionary history of strong tectonic activity. The masses of evaporites, rates of evaporite formation, tectonic movements, and large igneous provinces (LIPs) synergistically developed in the Sinian-Cambrian, Permian, Jurassic-Cretaceous, and Miocene intervals, which are considered to be four of the warmest times since the Sinian. We realize that salt accumulation can proceed without solar energy and can generally be linked to geothermal changes in tectonically active zones. When climatic factors are involved, they may be manifestations of the thermal influence of the crust on the surface.
... Ancient marine evaporites typically have poorly developed Quaternary counterparts in scale, thickness, tectonics and hydrology (Warren, 2010). 'Vanished' or 'interpretative' sequences that can be inferred as evaporite (Gandin and Wright, 2007) are well represented by HEG. ...
... Ancient marine evaporites typically have poorly developed Quaternary counterparts in scale, thickness, tectonics and hydrology (Warren, 2010). 'Vanished' or 'interpretative' sequences that can be inferred as evaporite (Gandin and Wright, 2007) are well represented by HEG. ...
Megascopic, petrographic and SEM-EDX studies of halite bearing Hanseran Evaporite Group (HEG) of Nagaur-Ganganagar evaporite (NGE) basin were carried out by analysing preserved drill cores at Lakhasar, Bikaner district, Rajasthan. The paper aims to study the various sulfosalts present in HEG and its depositional environment. Megascopic and petrological studies indicate fluctuating environment and climatic conditions of HEG. Stellate growth of anhydrite crystals indicates subaerial exposure as a result of excessive and rapid evaporation of brine. The continuous precipitation of evaporite resulted in progressive enrichment of 'potashites' (potash bearing salts) in brine. These 'potashites' are precipitated in top layers of individual evaporite cycle. Löweite is first time reported from HEG of Nagaur-Ganganagar basin which also implies saline playa deposit and possibly a volcanic sublimate. Sylvinite (KCl.NaCl) and sylvite (KCl) were identified in the cap rock of halite cycles, forming important resource of potash in the area. Unusual clumps of organic bodies (Hairy blobs) found in evaporite minerals, may represent microbial remains.
... Such structures are produced by localized changes in volume after evaporite deposition (cf. Gandin and Wright, 2007). This synto meta-depositional deformation is induced by the chemical transformation of the sulphates, such as the swelling of anhydrite during hydration to gypsum. ...
... This synto meta-depositional deformation is induced by the chemical transformation of the sulphates, such as the swelling of anhydrite during hydration to gypsum. Gypsum and anhydrite nodules form through the capillary system within the upper phreatic zones beneath the sabkha surface, displacing and replacing sediment under pressurized saline fluids that are flowing through pores due to evaporative capillarity (Tucker, 1988;Warren, 1999Warren, , 2006Flügel, 2004;Gandin and Wright, 2007). These intrasediment crystals grow in a matrix of fine sediment (i.e. ...
... The direct relationship between increasing oxygen levels in the Precambrian atmosphere and increased concentrations of bioavailable metals and sulfate in ancient shallow marine setting is due to the weathering of subaerially exposed pyrite-bearing rocks on continents, or the reaction of riverine-transported oxidized metal anions with H 2 S diffused from buried Neoarchean sediments to shallow Paleoproterozoic oceans (El Tabakh et al., 1999;Ojakangas et al., 2001;Kah et al., 2004;Gandin et al., 2005;Gandin and Wright, 2007;Schröder et al., 2008;Konhauser et al., 2011). Such conditions that followed major orogenic pulses (Condie, 2005;Campbell and Allen, 2008), led to more active C, S, and Fe and Mn biogeochemical cycling in coastal areas, potentially under the influence of very active near-surface AOM consortia, which were likely analogue to those now restricted to the deep biosphere. ...
... Additionally, our experiments provide insights into the preservation of photosynthetic mats in a variety of sediments deposited throughout the history of life on Earth. Microbes living in shallow, evaporitic environments can experience extensive silicification and carbonate precipitation (Gandin & Wright, 2007;Renaut, Jones, & Tiercelin,1998),butmayalsobeinfluencedbytheepisodicdeliveryof clays(e.g., Gandin&Wright,2007;Noffkeetal.,2001Noffkeetal., ,2002 ...
Microbial fossils and textures are commonly preserved in Ediacaran and early Cambrian coarse-grained siliciclastic sediments that were deposited in tidal and intertidal marine settings. In contrast, the fossilization of micro-organisms in similar marine environments of post-Cambrian age is less frequently reported. Thus, temporal discrepancies in microbial preservation may have resulted from the opening and closing of a unique taphonomic window during the terminal Proterozoic and early Phanerozoic, respectively. Here, we expand upon previous work to identify environmental factors which may have facilitated the preservation of cyanobacteria growing on siliciclastic sand, by experimentally determining the ability of microbial mats to trap small, suspended mineral grains, and precipitate minerals from ions in solution. We show that (i) fine grains coat the sheaths of filamentous cyanobacteria (e.g., Nodosilinea sp.) residing within the mat, after less than 1 week of cell growth under aerobic conditions, (ii) clay minerals do not coat sterile cellulose fibers and rarely coat unsheathed cyanobacterial cells (e.g., Nostoc sp.), (iii) stronger disturbances (where culture jars were agitated at 170 rpm; 3 mm orbital diameter) produce the smoothest and most extensive mineral veneers around cells, compared with those agitated at slower rotational speeds (150 and 0 rpm), and (iv) mineral veneers coating cyanobacterial cells are ~1 μm in width. These new findings suggest that sheathed filamentous cyanobacteria may be preferentially preserved under conditions of high fluid energy. We integrate these results into a mechanistic model that explains the preservation of microbial fossils and textures in Ediacaran sandstones and siltstones, and in fine-grained siliciclastic deposits that contain exceptionally preserved microbial mats.
... Under these conditions, calcium would be depleted during precipitation of calcium carbonate and would be unavailable for incorporation into gypsum. Increased reporting of gypsum, calcitized gypsum, and gypsum molds in Paleoproterozoic and Mesoproterozoic successions Cook and Ashley, 1992;Gandin and Wright, 2007;Grotzinger and Kasting, 1993;Pope and Grotzinger, 2003), however, indicate that sulfate concentrations may have exceeded ∼2.5 mM -at least in some surface water environments -for much of the Proterozoic. Unfortunately, at present, both our sampling and understanding of Proterozoic depositional environments is insufficient to determine to what extent these occurrences are representative of global marine sulfate concentrations. ...
... Sr concentrations) suggest only limited evaporative concentration in restricted, inner ramp environments. Some recent discoveries of precipitation of sulfate minerals from Neoarchaean and Paleoproterozoic seawater (Gandin and Wright, 2007;Melezhik et al., 2005;Schröder et al., 2008;Zentmyer et al., 2011) appears to indicate that, even in the immediate aftermath of the GOE, the concentration of sulfate in shallow marine environments was high enough to produce evaporites upon extensive (cf. Kah et al., 2001) evaporation. ...
... Shallow-water deposits include widespread stromatolitic carbonate platforms dominated by cyanobacteria (Altermann and Schopf, 1995;Kazmierczak and Altermann, 2002;Kazmierczak et al., 2009;Flannery and Walter, 2012). Local evaporite deposits of calcium sulfates have also been described, together with halite casts (Simonson et al., 1993;Sumner and Grotzinger, 2000;Hardie, 2003;Eriksson et al., 2005;Gandin et al., 2005;Gandin and Wright, 2007). Postdepositional alteration of evaporites to carbonates and chert is ascribed to the activity of bacterial sulfate reduction, the effects of which are preserved as variable δ 34 S values of pyrite (Gandin et al., 2005). ...
This review summarizes and assesses a series of papers presented at the Geological Society of America Annual Meeting in 2011 on the changing composition of Earth's early atmosphere. This is a developing field, with differing views, due largely to the facts of an incomplete rock record and negligible preservation of the gaseous components of the atmosphere. Nevertheless, there are constraints, available through geological proxies in the form of chemical sedimentary rocks that reflect the composition of the hydrosphere, and because the two are directly linked, the atmosphere. A review of the geological constraints on atmospheric conditions is presented for early Earth, from its formation at 4.56 Ga up to 1.8 Ga, followed by a developing model that links changing atmosphere/hydrosphere conditions and biosphere evolution to changes in planetary tectonics, including the evolving supercontinent cycle.
