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The Ammonite Family Hildoceratidae in the Lower Jurassic of Britain
Abstract
In part 2, species of the genera Harpoceras, Ovaticeras, Pseudolioceras, Polyplectus, Osperleioceras, Frechiella, Jacobella, Leukadiella, Leptaleoceras, Canavaria, Hildaites, Orthildaites and Hildoceras are described. The distribution, phylogeny and evolution of the Hildoceratidae are described.
... The former ammonites may correspond to the Harpoceras falciferum Ammonite Zone in the Paris Basin, which indicates an age not younger than the early Toarcian commonly used to infer this age of many black shale intervals in Europe (Chen et al., 2005). In the Yorkshire section of the British Isles, the base of the Harpoceras falciferum Zone is characterized by the common occurrence of age-diagnostic marker ammonites, such as Eleganticeras elegantulum, Cleviceras exaratum and Cleviceras elegans (Howarth, 1992). In the NW European province, the Harpoceras falciferum Zone can be divided into Harpoceras exaratum and Harpoceras falciferum subzones. ...
... In the NW European province, the Harpoceras falciferum Zone can be divided into Harpoceras exaratum and Harpoceras falciferum subzones. In the Suobucha section, the level of 24 m (the first occurrence of Eleganticeras sp.) may correlate to the base of the Harpoceras exaratum Subzone in NW Europe (Howarth, 1992). The level of 79 m (the first occurrence of Harpoceras sp. and the last occurrence of Cleviceras sp.) may correlate to the base of the Harpoceras falciferum Subzone in the NW European province (Howarth, 1992). ...
... In the Suobucha section, the level of 24 m (the first occurrence of Eleganticeras sp.) may correlate to the base of the Harpoceras exaratum Subzone in NW Europe (Howarth, 1992). The level of 79 m (the first occurrence of Harpoceras sp. and the last occurrence of Cleviceras sp.) may correlate to the base of the Harpoceras falciferum Subzone in the NW European province (Howarth, 1992). Moreover, the ammonites Dactylioceras sp. and Dactylioceras cf. ...
The Toarcian Oceanic Anoxic Event (T-OAE) is characterized by significant environmental perturbation and climatic instabilities due to a substantial release of greenhouse gases. Several investigations of the T-OAE were conducted based on reliable and well-developed integration of multi-proxy approaches, revealing the global distribution of this event in the Panthalassic, Boreal, and Western Tethyan regions. However, a few marine shelf T-OAE records are reported from the Eastern Tethys. This study presents high-resolution organic and inorganic and isotope geochemistry, mineralogical, and sedimentological analyses from the marine Suobucha section of the Qiangtang Basin to assess the role of continental weathering and paleoceanographic conditions, including paleoredox and paleoproductivity conditions, and factors that govern organic carbon accumulation during the T-OAE in the Eastern Tethys. The carbon isotope profile of Suobucha displays a long-term negative excursion characterizing the Jenkyns Event, which is recognized in geographically widespread sedimentary archives indicating its global nature. Continental weathering was intensified at the onset of the Jenkyns Event. Increased values of fluvial detrital proxies (i.e., Si/Al and Ti/Al) and the occurrence of coarser-grained sediments (i.e., silty mudstones) at Suobucha indicated enhanced terrigenous input at the onset of the Jenkyns Event, which was driven by accelerated continental weathering at this time. The lower Toarcian interval in the marine shelf environment of the Qiangtang Basin is characterized by fully oxidizing conditions intermittent with minor phases of dysoxic setting, especially during the Jenkyns Event interval. Given that a stratified water column with anoxic bottom water occurred in the proximal and more restricted lagoonal area (i.e., the Bilong Co area), redox conditions were spatially variable and controlled by basin hydrography and water depth during the Jenkyns Event in the Qiangtang Basin. Oxygen-enriched conditions and low marine bioproductivity were responsible for the low organic carbon burial within the Suobucha section.
... It is stratigraphically extremely condensed, containing obvious hardgrounds, and records most ammonite zones and subzones of the Toarcian: it is typically less than a metre in thickness in coastal outcrops. Lithologically, it comprises grey to yellow, pink to red and brown nodular micritic limestone, fossil-rich and heavily mineralized with dark-coloured iron and manganese oxyhydroxides, locally in the form of centimetre-scale nodules, coatings and dendrites (Buckman, 1922;Jackson, 1922Jackson, , 1926Arkell, 1933;Howarth, 1957Howarth, , 1992Hallam, 1967;Sellwood et al. 1970;Cope et al. 1980;Jenkyns & Senior, 1991;Hesselbo & Jenkyns, 1995). ...
... The Junction Bed contains faunas representing all the zones of the Toarcian from the serpentinum (falciferum) to the levesquei. Significantly, however, the presence of the lower part of the exaratum subzone (of the serpentinum zone) has never been proven (Howarth, 1992). The time interval represented by the Marlstone and Junction Bed would have been characterized by environmental events around the Pliensbachian-Toarcian boundary including the Toarcian Oceanic Anoxic Event (T-OAE) and associated hyperthermal episode, although the potential of the condensed and incomplete nature of the sequence to capture the signature of these major phenomena is obviously open to question. ...
... Modified from Hesselbo & Jenkyns (1995). Stratigraphy follows Jenkyns & Senior (1991) and Howarth (1992). The contact between the Middle and Upper Lias (Pliensbachian-Toarcian) was originally thought to lie between the Marlstone and the Junction Bed (hence its name) until discovery of tenuicostatum zone ammonites in the highest parts of the stratigraphically lower unit (cf. ...
Two fallen blocks of the Marlstone and stratigraphically overlying Junction Bed sampled on the beach below Doghouse Cliff in Dorset, UK (Wessex Basin) have been examined for carbon and oxygen isotopes of bulk carbonate as well as for strontium, carbon and oxygen isotopes and Mg:Ca ratios in the contained belemnites. The sequence, which contains most of the Toarcian zones and subzones within a metre or less of grey to yellow to pink, red and brown fossil-rich nodular limestone, is extremely condensed and lithologically similar to pelagic red limestones of the Tethyan Jurassic that are locally mineralized with Fe-Mn oxyhydroxides (e.g., Rosso Ammonitico). Strontium-isotope ratios of the contained belemnites are compatible with existing reference curves and both blocks show a rise to more radiogenic values post-dating the Pliensbachian–Toarcian boundary. The high degree of correlation between the relatively negative carbon and oxygen isotopes of the bulk carbonate is compatible with significant diagenetic overprint, and contrasts with higher carbon-isotope values in coeval condensed coccolith-rich limestones elsewhere. Evidence for the characteristic signature of the Toarcian Oceanic Anoxic Event, as represented by organic-rich sediment, is absent, possibly owing to a stratigraphic gap. Both blocks exhibit abrupt carbon-isotope shifts to lower values, one of which could represent the limbs of an incompletely recorded negative excursion associated with the Toarcian Oceanic Anoxic Event. That the Toarcian Oceanic Anoxic Event was also a significant hyperthermal is illustrated in both blocks by a drop in oxygen-isotope values and rise in Mg:Ca ratios of belemnites close to the base of the Junction Bed in the lowest part of the serpentinum zone.
... The Toarcian succession on Raasay is exposed in and around disused ironstone mine workings at Inverarish Burn in the south of the island (UK Grid Reference NG 573365; Figs. 2 and 3). Here, the section (in ascending stratigraphic order) consists of a ~6 m succession of finegrained sandstones of the uppermost Scalpa Sandstone Formation, dark grey-black micaceous shales of the Portree Shale Formation, and oolitic ironstones of the Raasay Ironstone Formation ( Howarth, 1956Howarth, , 1992. The top of the Scalpa Sandstone Formation and fairly sharp transition to the darker and finer-grained Portree Shale Formation are exposed in a tributary to the northeast of the main ironstone workings (NG 5719 3688; Fig. 3B and C). ...
... Nearby, numerous randomly oriented belemnites occur on a bedding surface (the "belemnite battlefield"), representing the top of the Portree Shale Formation ( Fig. 3D; Doyle and Macdonald, 1993;Price, 2010). An abundant ammonite fauna in the Portree Shale Formation (Howarth, 1992) indicates deposition in a marine environment. A lack of observed sedimentary structures observed within this formation potentially indicates deposition in a quiescent environment. ...
... The Dactylioceras tenuicostatum Zone, marked by the first occurrence of the ammonite genus Dactylioceras, indicates the base of the Toarcian stage (Lee, 1920;Howarth, 1956Howarth, , 1992. Poorly preserved Dactylioceras tenuicostatum fossils occur within the top 2 m of the Scalpa Sandstone Formation on Skye and Raasay, indicating that the base of the Toarcian is within this formation, and the tenuicostatum Zone extends into the lowest part of the overlying Portree Shale Formation (Howarth, 1992;Fig. ...
The early Toarcian (~183 Ma) was characterized by a prominent volcanism-induced warming event associated with a massive addition of ¹²C-enriched carbon to the ocean-atmosphere system. This warming likely contributed to marked ocean deoxygenation during this time, giving the event its name: the early Toarcian oceanic anoxic event (T-OAE). Although the T-OAE has been recognized globally, clear geographic differences in the character of the event and its environmental effects have been noted. Here we present new carbon isotope, element abundance and organic geochemical data from a lower Toarcian succession on the Isle of Raasay, Scotland (Hebrides Basin, Northwest European Shelf). These data provide the first evidence of the T-OAE in Scotland. The succession is generally enriched in organic matter through the T-OAE interval, though redox-sensitive trace element data indicate that oxic-suboxic bottom water conditions prevailed, potentially interspersed with ephemeral anoxic episodes. Our elemental data contrast with evidence for persistent anoxia/euxinia in nearby basins, and emphasizes how deoxygenation was spatially variable and dependent on water depth and basin hydrography. Similarly, the data emphasize how anoxia was not a prerequisite for the deposition of organic-rich lithologies during the T-OAE. Sedimentological evidence, coupled with inorganic geochemical data, indicates increased coarse-grained detrital flux and enhanced chemical weathering during the T-OAE. Our findings support emerging evidence for a marked strengthening of hydrological cycling and increased storminess at tropical and subtropical latitudes globally in response to global warming during the T-OAE.
... The Toarcian 'Junction Bed', or Barrington Member, of the Ilminster district has long been known as a rich source of ammonoid fossils, with species such as Ammonites elegans, now Cleviceras elegans, first being described as long ago as 1815 by J. Sowerby, and detailed studies being published by the local priest, the Reverend Charles Moore in 1866. It was not until the early twentieth century, however, that the rich faunas began to be more systematically studied by the high-resolution ammonoid chronology pioneer, S.S. Buckman (see Page 2017) when new sections were created during new quarrying activities and reservoir construction between Barrington and Stocklinch, as described by Hamlet (1922), Pringle & Templeton (1922) (later reviewed by Howarth 1992). ...
... In contrast, the underlying upper Pliensbachian, developed in Marlstone Rock Formation facies does contain a typical Subboreal fauna dominated by a Pleuroceras (Amaltheiidae) dominated fauna and hence the same chronozonal scheme can be applied as elsewhere in the UK, including North Yorkshire (although refined using sub-subchronozonal 'Horizons' as reviewed by Dommergues et al. 1997). In addition, although the lowest upper Toarcian, as developed in the uppermost part of the Barrington Member, can also be correlated with the same ammonoid chronozonation for the substage as the rest of the UK -now for the North West European Province -the scheme of Dean et al. (1961) as used by Howarth (1992) has been superseded, and that of Elmi et al. (1997) is used here. The terminology and concept of chronozones, subchronozones, sub-chronozonal 'Horizons', and successive faunal 'events' used to correlate 'Biohorizons' herein, is comprehensively reviewed by Page (2017). ...
... It should be noted that although Howarth (1992) established the Barrington section as a 'standard' or reference succession for the Barrington Member of the area, every known section in the unit across the site is different in terms of bed sequence and biochronological record and, furthermore, major changes in thickness are also evident (see Wilson et al. 1958 for instance). Hence, any attempt to comprehensively apply the bed numbering system for Barrington to any other section is simply not tenable, even if certain beds may still apparently be recognisable, or at least correlatable, based on combined lithological and faunal characters. ...
This study focuses on a condensed sequence of alternating carbonate-clastic sediments of the Barrington Member, Beacon Limestone Formation (latest Pliensbachian to early Toarcian) from Somerset (south west England). Abundant ammonites confirm (apart from the absence of the Clevelandicum and Tenuicostatum ammonite subchronozones) the presence of Hawskerense Subchronozone to Fallaciosum-Bingmanni subchronozones. Well-preserved, sometimes diverse assemblages of ostracods, foraminifera, nannofossils and low diversity dinoflagellate assemblages support the chronostratigraphic framework. Stable-isotope analyses demonstrate the presence of a carbon isotope excursion (CIE), relating to the Toarcian Oceanic Anoxic Event (T-OAE), within the early Toarcian. Faunal, geochemical and sedimentological evidence suggest that deposition largely took place in a relatively deep-water (sub-wave base), mid-outer shelf environment under a well-mixed water column. However, reduced benthic diversity, the presence of weakly-laminated sediments and changes in microplankton assemblage composition within the T-OAE indicates dysoxic, but probably never anoxic, bottom-water conditions during this event. The onset of the CIE coincides with extinction in the nannofossils and benthos, including the disappearance of the ostracod suborder Metacopina. Faunal evidence indicates connectivity with the Mediterranean region, not previously recorded for the United Kingdom during the early Toarcian.
Supplementary material at https://doi.org/10.25500/edata.bham.00000574
... In order to collect the necessary data to make the detailed lithofacies Howarth (1992); . The bed numbers were obtained from . ...
... exaratum subzone) (e.g. Howarth, , 1992. Published rock description of these units are summarised below. ...
... The succession at this location was logged and sampled using the published logs of and Table 1. Logs modified from Howarth (1992) and . The bed numbers were defined by . ...
This book is about all factors that control musdtone dispersal and organic carbon preservation......
... Modified from Page (1996). Modified from Howarth (1992a). Figure 34. ...
... Beginning with the myth of Saint Hilda's 'snakestones', the rich ammonite succession of the WMF has since been extensively documented (Howarth, 1973;1992a;1992b) and now provides a biostratigraphical and chronostratigraphical basis for the majority of zones and subzones of the Pliensbachian and Toarcian stages within Northwest Europe (Powell, 2010). ...
... Species morphology was described using several morphometric parameters (Figure 33), which were compiled into a comparative table (Table 1) to calculate the average measurements for each species. Description terminology followed Howarth (1973;1992a;1992b) and the Treatise on Invertebrate Palaeontology, Part L, Mollusca 4. The best example of each species was compiled into photo plates with corresponding descriptions. Microconchs 9-40mm adult diameter, with blunt single ribs. ...
Although the ammonites of the Toarcian Whitby Mudstone Formation (WMF) of the North Yorkshire coast have been central to many significant biostratigraphical studies throughout the 20th century, the taphonomy of these fossils has been rather understudied. Here it is demonstrated that the ammonites of the Grey Shale and Mulgrave Shale members within the WMF possess complex taphonomic histories, which can be attributed to the depositional environments of the encompassing strata. It was found that ammonite preservation moderately varies between individual horizons, ranging from 2D and 3D ammonites to those with periostracal films, preserved as ‘half’ ammonites or encompassed within nodules. Nevertheless, pyritised ammonites are observed to dominate both members, indicating that the oxygen-deficient bottom conditions of the upper Grey Shale and Mulgrave Shale members preferentially favoured this style of preservation, therefore creating a taphonomic bias. Within the Mulgrave Shale Member, ammonites are observed to demonstrate various physical and biological disturbing factors following post-mortem deposition, including hydraulic shell re-orientation, and the presence of Radulichnus and Discinisca. In addition to denoting water depth, this evidence suggests that the stagnant, anoxic bottom-waters were punctuated by periodic oxygenation events, allowing fauna to colonise and graze on the ammonites lying on the substrate. This research establishes the order of taphonomic processes observed on the ammonites of the Toarcian WMF, and provides a taphonomic and diagenetic sequence for these organisms, beginning with post-mortem deposition, and ending with their permanent incorporation in the sediment.
... However, phylogenetic relationships between major groups of the Hildoceratidae are far from being resolved and have never been tested using cladistics. Many hypotheses are contradictory (Wiedenmayer, 1980;Howarth, 1992;Venturi and Bilotta, 2008). The goal of this study is to perform a unique cladistic analysis including most hildoceratid forms to provide the first tested phylogeny of the family as a whole. ...
... The tree shows a divergence between what we call Arieticeratinae s.l. and the rest of Hildoceratidae. This topology confirms the view of Howarth (1992) and refutes the hypothesis of Wiedenmayer (1980), Fantini-Sestini (1977, Braga (1983) and Morard (2004) that put the origin of the Arieticeratinae from the genus Fuciniceras. However, the weakness of Bremer values emphasizes the fragility of this result. ...
... This clade regroups the genus Matteiceras, the Arieticeratinae s.s. and the Bouleiceratinae. The two species of the genus Matteiceras appear monophyletic and to be the sister group of the Arieticeratinae s.s. and Bouleiceratinae as proposed by Howarth (1992). The Arieticeratinae s.s. is a paraphyletic stem group of the monophyletic Bouleiceratinae. ...
Ammonite phylogeny has mainly been established based on a stratigraphic approach, with cladistics underconsidered. The main arguments against the use of cladistics are the supposed large amount of homoplasy and the small number of characters. Resolving the phylogeny of the Hildoceratidae (Early Jurassic) is especially challenging because of its large diversity and disparity. Many forms that have not been determined as closely related in previous studies exhibit very similar shapes. Moreover, some groups are morphologically very different, adding difficulties to building a unique coding scheme at a low taxonomic resolution (i.e. species). Here we propose an integrated coding scheme of the peristome shape and the ornamentation, allowing an increased level of comparison. The shape of the peristome is used as a new reference to locate ornamental features and propose new homology hypotheses. In total, 105 taxa have been analysed for 47 characters. We code continuous characters by their means and ranges ± one standard deviation. We test two weighting schemes: equal weights standardized by unit range and implied weighting with several concavity constants. This work has led to redefinition of the phylogenetic inclusivenesses of all the hildoceratid subfamilies. The new coding scheme based on peristome shapes provides the fewest homoplastic characters. The schemes appear promising to improve phylogenetic analyses in ammonoids as well as molluscs as a whole by creating a general coding framework.
... Hildoceras sublevisoni Fucini, 1922 was established to group the non-grooved morphs, most of which had been previously referred to Hildoceras levisoni (Simpson, 1843), later assigned to genus Hildaites by Buckman (1921) and eventually regarded as junior synonymous to Hildaites murleyi (Moxon, 1841) by Howarth (1992). Because Fucini omitted to designate a holotype for Hildoceras sublevisoni, Merla (1933, p. 51) assumed the specimen figured by Dumortier (1874, Pl. 9, Fig. 3) as type form among those included in the synonymy (Fucini, 1922, p. 182). ...
... However, he considered Hildoceras sublevisoni as a broad-ranging, polymorphic species, which may embrace both Merla's specimens (with more numerous ribs) and Dumortier's type. In contrast with this view, later authors envisaged the possibility that Hildoceras sublevisoni could split into two (Zanzucchi, 1963;Géczy, 1967;Howarth, 1992) or even more than two species (Guex, 1972(Guex, , 1973Gabilly, 1976;Elmi, 1977). ...
... By considering the presence or absence of the periumbilical relief as a more objective character compared to variability in ribbing pattern, no more than two morphotypes can be distinguished within the broadly interpreted Hildoceras sublevisoni. Because, according to Howarth (1992), Hildoceras sublevisoni is a junior synonymous of Hildoceras laticosta Bellini, 1900, the two species into which non-grooved Hildoceras should be grouped are Hildoceras laticosta, lacking the periumbilical relief; and Hildoceras lusitanicum, with periumbilical relief occasionally flanked by marked inflections that confer a somewhat grooved or "pseudogrooved" morphology ( Fig. 4). Nevertheless, a screening of literature data dealing with Hildoceras species reveals the persistence of Hildoceras sublevisoni in classification and biostratigraphic schemes (Neige and Rouget, 2002;Page, 2004;Galácz et al., 2010;Kovács, 2011;Sassaroli and Venturi, 2012). ...
The record of Hildoceras species from the Rosso Ammonitico marls (Toarcian) near Terni (Central Apennines) is analysed in order to outline a possible relationship between ontogenetic and phylogenetic variability. Bed by bed sampling provides evidence of ontogenetic variability in shell morphology that parallels evolutionary change, suggesting a possible control by heterochrony. Specifically, heterochrony is proposed as a potential mechanism by which: 1) discontinuous inflections accompanying rib fading at the inner flank of Hildoceras lusitanicum, initially a character of later growth stages, are progressively anticipated during ontogeny, finally culminating in the spiral groove of Hildoceras bifrons; 2) delayed maturation and inhibition of the adult " uncoiling " stage of Hildoceras bifrons, concomitant to allometric growth of whorl height, result in the overall involute and relatively compressed shell structure observed in Hildoceras semipolitum. Interrelated to heterochrony is also the concept of " developmental polymorphism " , considered as a plausible alternative and more general frame in which to place sexual dimorphism as displayed by Hildoceras bifrons.
... Wright, 1882). Лектотип: [Howarth, 1992, Номенклатура. Предложена Ю.С. ...
... Приравнивается одноименному биогоризонту подзоны exaratum стандарта (K.N. Page, 2005), [Howarth, 1992]. ...
... Номенклатура.Выделена [Дагис, Дагис, 1965] как лона Ovaticeras propinquum. Этот таксон рассматривается[Howarth, 1992] как младший синоним вида Tiltoniceras antiquum.Границы. Нижняя граница определяется появлением Lioceratoides asiaticus Repin. ...
... Genus Hildaites Buckman, 1921 Hildaites murleyi ( Material: 12 specimens (Eötvös University Coll.) Remarks: The species shows remarkable variability in morphology, so Hildaites levisoni (Simpson), H. borealis (Seebach), H. propeserpentinus (Buckman), and Murleyiceras aptum Buckman were considered as synonyms of H. murleyi by Howarth (1992), this arrangement is accepted herein. The species differs in morphology from its NW European congeners Hildaites wrighti (Spath) and H. serpentiniformis Buckman by bearing much stronger and more widely spaced ribs. ...
... Although the preservation of the Toarcian specimens is generally poor to mediocre, the large material (more than 5000 ammonites) is regarded as an exceptionally representative sample for the area and time interval. We found that the diversity of the Toarcian Ammonitina in the Mecsek Mts is significantly lower than at fossiliferous localities in the NW European Province in England, France, Germany, N Spain, and Bulgaria (e.g., Goy & Martínez 1990;Howarth 1992;Schulbert 2001;Fauré 2002;Rulleau 2007Rulleau , 2009Metodiev 2008;Arp 2010;Goy et al. 2010;Lacroix 2011;Rulleau et al. 2013Rulleau et al. , 2015Rulleau et al. , 2020. In the studied material, many genera that are widespread and characteristic elsewhere and are considered zonal or subzonal indices occur rather rarely in this area (e.g., Orthodactylites, Dactylioceras, Nodicoeloceras, Catacoeloceras, Haugia, Esericeras, Phlyseogrammoceras, Phymatoceras, Dumortieria, and Pleydellia) or are missing altogether (e.g., Peronoceras, Paltarpites, Maconiceras, Orthildaites, Paroniceras, Denckmannia, Pseudolillia, Hammatoceras, and Crestaites). ...
... Few additional ammonites recovered by private fossil collectors were taken into account. Ammonite determinations follow the systematic descriptions in Howarth (1958Howarth ( , 1978Howarth ( , 1992, Gabilly (1976a, b), Schulbert (2001a), Rulleau (2007), Hoffmann (2010Hoffmann ( , 2015, Arp (2010), and Di Cencio and Weis (2020). ...
... In addition, Frechiella subcari nata has been reported for this bed 5.5 km ESE of the Ludwigskanal section (Krumbeck 1932a;Weiß and Freitag 1991). No indication of the Ovatum Horizon (Howarth 1992;Page 2003) was found. Within the "Dactylioceras" to "Monotis Bed", however, Dactylioceras athleticum ( Fig. 12: 3) is most abundant. ...
Extensive construction work at the canal cutting of the Ludwigskanal near Dörlbach, Franconian Alb, provided the opportunity to re-investigate a scientific-historical and biostratigraphically important reference section of the South-German Toarcian. The 16 m thick section, described bed by bed with respect to lithology and macrofossils, starts within the Upper Pliensbachian Amaltheenton Formation, covers the Toarcian Posidonienschiefer and Jurensismergel Formation, and ends in basal parts of the Opalinuston Formation. Carbonate contents are high in the Posidonienschiefer and successively decline within the Jurensismergel to basal parts of the Opalinuston. The high carbonate contents in the Posidonienschiefer are associated with comparatively low organic carbon contents. However, organic carbon contents normalized to the silicate fraction are similarily high if compared to other regions in Germany. Only the persistence of high organic carbon levels into middle parts of the Upper Toarcian differs from those of most regions in central Europe.
Ammonite biostratigraphy indicates a thickness of >9 m for the Upper Pliensbachian, 1.15–1.20 m for the Lower Toarcian, 5.04 m for the Upper Toarcian, and >0.5 m for the Lower Aalenian. Despite the low sediment thickness, all Toarcian ammonite zones and almost all subzones are present, except for major parts of the Tenuicostatum Zone and the Fallaciosum Subzone.
On the basis of discontinuities, condensed beds, and correlations with neighbouring sections in Southern Germany, a sequence stratigraphic interpretation is proposed for the Toarcian of this region: (i) The Posidonienschiefer Formation corresponds to one 3 rd order T-R sequence, from the top of the Hawskerense Subzone to a fucoid bed at the top of the Variabilis Subzone, with a maximum flooding surface at the top of the Falciferum Zone. (ii) The Jurensismergel Formation exhibits two 3 rd order T-R sequences: The first ranges from the basis of the Illustris Subzone (i.e., the Intra-Variabilis-Discontinuity) to the top of the Thouarsense Zone, with a maximum flooding surface within the Thouarsense Zone. The “belemnite battlefield” reflects a transgressive “ravinement surface” within the first Jurensismergel Sequence, not a maximum regression surface at its basis. The second sequence extents from the erosive basis of the Dispansum Zone to the top of the Aalensis Subzone, with a maximum flooding surface at the Pseudoradiosa-Aalensis Zone boundary. Finally, the Opalinuston starts with a new sequence at the basis of the Torulosum Subzone. Transgressive system tracts of these 3 rd order T-R sequences are commonly phosphoritic, while some regressive system tracts show pyrite preservation of ammonites. The maximum regression surfaces at the basis of the Toarcian and within the Variabilis Zone reflect a significant submarine erosion and relief formation by seawater currents, while this effect is less pronounced at the basis of the Dispansum Zone and basis of the Torulosum Subzone (i.e., the boundary Jurensismergel-Opalinuston Formation).
... はじめに 三畳紀末の危機を乗り越えたアンモノイド類は，ジュラ紀に再び大発展を遂げる (Donovan et al., 1981) ． ジュラ系の古典的な研究が進められた西欧標準地域( Fig. 1)では，比較的安定した基盤の上に縁海の堆 積相が広がる．そこにはジュラ系最上部を除くほぼ完全なアンモノイド化石層序が記録されており，当時 の彼らの隆勢を偲ばせる (佐藤 , 1967;Kennedy and Cobban, 1976) ．中でもジュラ紀前期のヒルドセラス上科 (Hildoceratoidea)に属するヒルドセラス科(Hildoceratidae)の一群は，下部ジュラ系の古典的な示帯化石種 を数多く含むだけでなく，その世界的な分布から国際層序対比や古生物地理の解明に非常に重要な役割 を果たしてきた (Figs. 2, 3;Arkell, et al., 1957;Donovan et al., 1981;Schlegelmilch, 1992;Howarth, 1992aHowarth, , 1992bHowarth, , 2013Cariou and Hanzpergue, 1997;Schweigert, 2015) ． 一方，地球温暖化が進んだジュラ紀前期には，トアルシアン期前半を中心に汎世界的な海洋貧酸素環 境(oceanic anoxia)が発達し，世界各地に黒色葉理泥岩が堆積した (Jenkyns, 1985(Jenkyns, , 1988Clayton, 1986, 1997;Mailliot et al., 2006) (Hauff, 1921;Brenner and Seilacher, 1978;Seilacher et al., 1985;Bottjer et al, 2002) ．例えば，ヒルドセラス科アンモノイドの化 石は，周期的な酸欠を繰り返す環境下 (Kauffman, 1978;Fig. 2D)で，しばしば付着生物を伴ったまま層理 面と平行な姿勢で埋没し (Seilacher, 1982;Schmid-Röhl and Röhl, 2003) ，住房と気房とで変形が異なる二相の 圧密を受けたことが知られている (Seilacher et al., 1976) ． 他方，日本を代表する下部ジュラ系縁海相である西南日本内帯の豊浦層群・西中山層も，当時の汎世界 的な海洋無酸素事変の影響下で堆積した黒色葉理泥岩相を主体とし，ヒルドセラス科アンモノイドの化石 を多産することが古くから知られている (井上 , 1896;Yokoyama, 1904;小林 , 1931;鳥山 , 1938;松本・小野 , 1947;Hirano, 1971Hirano, , 1973a中田 , 2014;Matsuoka, 2008, 2011;Izumi et al., 2012; 前田・大山 , 2019) ．さ らに，圧密で潰れ，殻が溶脱したアンモノイド化石の保存の成因や過程が論じられている (Shikama and Hirano, 1970;棚部ほか , 1982;Tanabe et al., 1984;Maeda, 1987;Maeda and Seilacher, 1996;前田 , 2001 Howarth, 1955Howarth, , 1980Howarth, , 1992aPowell, 1984;Cox et al., 1999;Simms et al., 2004) の石灰質コンクリーションから産出した Hildoceras bifrons (Figs. ...
... はじめに 三畳紀末の危機を乗り越えたアンモノイド類は，ジュラ紀に再び大発展を遂げる (Donovan et al., 1981) ． ジュラ系の古典的な研究が進められた西欧標準地域( Fig. 1)では，比較的安定した基盤の上に縁海の堆 積相が広がる．そこにはジュラ系最上部を除くほぼ完全なアンモノイド化石層序が記録されており，当時 の彼らの隆勢を偲ばせる (佐藤 , 1967;Kennedy and Cobban, 1976) ．中でもジュラ紀前期のヒルドセラス上科 (Hildoceratoidea)に属するヒルドセラス科(Hildoceratidae)の一群は，下部ジュラ系の古典的な示帯化石種 を数多く含むだけでなく，その世界的な分布から国際層序対比や古生物地理の解明に非常に重要な役割 を果たしてきた (Figs. 2, 3;Arkell, et al., 1957;Donovan et al., 1981;Schlegelmilch, 1992;Howarth, 1992aHowarth, , 1992bHowarth, , 2013Cariou and Hanzpergue, 1997;Schweigert, 2015) ． 一方，地球温暖化が進んだジュラ紀前期には，トアルシアン期前半を中心に汎世界的な海洋貧酸素環 境(oceanic anoxia)が発達し，世界各地に黒色葉理泥岩が堆積した (Jenkyns, 1985(Jenkyns, , 1988Clayton, 1986, 1997;Mailliot et al., 2006) (Hauff, 1921;Brenner and Seilacher, 1978;Seilacher et al., 1985;Bottjer et al, 2002) ．例えば，ヒルドセラス科アンモノイドの化 石は，周期的な酸欠を繰り返す環境下 (Kauffman, 1978;Fig. 2D)で，しばしば付着生物を伴ったまま層理 面と平行な姿勢で埋没し (Seilacher, 1982;Schmid-Röhl and Röhl, 2003) ，住房と気房とで変形が異なる二相の 圧密を受けたことが知られている (Seilacher et al., 1976) ． 他方，日本を代表する下部ジュラ系縁海相である西南日本内帯の豊浦層群・西中山層も，当時の汎世界 的な海洋無酸素事変の影響下で堆積した黒色葉理泥岩相を主体とし，ヒルドセラス科アンモノイドの化石 を多産することが古くから知られている (井上 , 1896;Yokoyama, 1904;小林 , 1931;鳥山 , 1938;松本・小野 , 1947;Hirano, 1971Hirano, , 1973a中田 , 2014;Matsuoka, 2008, 2011;Izumi et al., 2012; 前田・大山 , 2019) ．さ らに，圧密で潰れ，殻が溶脱したアンモノイド化石の保存の成因や過程が論じられている (Shikama and Hirano, 1970;棚部ほか , 1982;Tanabe et al., 1984;Maeda, 1987;Maeda and Seilacher, 1996;前田 , 2001 Howarth, 1955Howarth, , 1980Howarth, , 1992aPowell, 1984;Cox et al., 1999;Simms et al., 2004) の石灰質コンクリーションから産出した Hildoceras bifrons (Figs. 2E, 5) , および (２) ドーセット州イルミンスター(Ilminster)に分布するビーコン石灰岩層(Beacon Limestone Formation; Cope et al., 1980;Callomon and Cope, 1995;Cox et al., 1999;Simms et al., 2004;Huxtable, 2013)から産出した Hildoceras spp. ...
Modes of fossil-preservation of the lower Toarcian (Lower Jurassic) hildoceratid ammonoids were closely examined by lithofacies, i.e., the Whitby Mudstone Formation, UK, the Beacon Limestone Formation, UK, and well-laminated black mudstone of the Nishinakayama Formation, Japan together with the Posidonienschiefer Formation, Germany. All materials occurred from the Serpentinum- or Bifrons zones, or equivalent biozones. Hildoceras bifrons in the calcareous concretion of the Whitby Mudstone Formation is free from shell-collapse and dissolution, and shows almost intact preservation. The vacant body chamber is filled with fine muddy deposits, while the intact air chambers are filled with sparry calcite. Presence of organic-rich siphuncular tube and fragile septal necks reflects consolidation in the very early fossilization stage. Hildoceras spp. in bioturbated limestone of the Beacon Limestone Formation also show 3D preservation, but the inner whorls, siphuncular tubes, and septal necks are almost lost. As a narrow “pathway” penetrating the air chambers was opened, both body chamber and air chambers could be filled with
lime mud by the draught-through current. These features reflect the moderate diagenetic damages. In contrast, various severe damages are overprinted in Cleviceras chrysanthemum in black, well-laminated mudstone in the Nishinakayama Formation. The flattened whorls
suffered two-phase collapse, and the shell tests are mostly dissolved. These reflect the latter stages of diagenetic processes. Preservation-potential of ammonoid shell-parts varies by lithofacies, and the taphonomic histories can be traced from shell-damages. After the death of hildoceratid animals, two contrary trends, i.e., one accelerates degradation (shell-dissolution etc.) and another enhances preservation (mineralization etc.), concerned the fossilization.
Their preservational states are results of compromise of both rtends.
... and 54°27′29.89″N, 00°33′ 25.62″W, respectively) every 2.5 cm between 1.30 m above and 7.81 m below the base of the Harpoceras exaratum ammonite subzone, as defined by Howarth (1992). Samples were collected from the outcrop using a cordless drill with an 8-mm masonry drill bit. ...
... Leco elemental analyzer data and lithology are fromKemp et al. (2011). Lithostratigraphy and biostratigraphy are fromHowarth (1992). ...
Cyclostratigraphic studies are used to create relative and high‐resolution time scales for sedimentary successions based on identification of regular cycles in climate proxy data. This method typically requires the construction of long, high‐resolution data sets. In this study, we have demonstrated the efficacy of portable X‐ray fluorescence spectroscopy (pXRF) as a nondestructive method of generating compositional data for cyclostratigraphy. The rapidity (100 samples per day) and low cost of pXRF measurements provide advantages over relatively time‐consuming and costly elemental and stable isotopic measurements that are commonly used for cyclostratigraphy. The nondestructive nature of pXRF also allows other geochemical analyses on the same samples. We present an optimized protocol for pXRF elemental concentration measurement in powdered rocks. The efficacy of this protocol for cyclostratigraphy is demonstrated through analysis of 360 Toarcian mudrock samples from North Yorkshire, UK, that were previously shown to exhibit astronomical forcing of [CaCO3], [S], and δ¹³Corg. Our study is the first to statistically compare the cyclostratigraphic results of pXRF analysis with more established combustion analysis. There are strong linear correlations of pXRF [Ca] with dry combustion elemental analyzer [CaCO3] (r² = 0.7616) and of pXRF [S] and [Fe] with dry combustion elemental analyzer [S] (r² = 0.9632 and r² = 0.9274, respectively). Spectral and cross‐spectral analyses demonstrate that cyclicity previously recognized in [S], significant above the 99.99% confidence level, is present above the 99.92% and 99.99% confidence levels in pXRF [S] and [Fe] data, respectively. Cyclicity present in [CaCO3] data above the 99.96% confidence level is also present in pXRF [Ca] above the 98.12% confidence level.
... The samples were collected from a composite of the Toarcian exposures at Saltwick Bay, Port Mulgrave, and Hawsker Bottoms along the coast of North Yorkshire in the UK. The T-OAE in Yorkshire is characterized by unbioturbated, laminated marine organic-rich mudrocks with discrete levels of calcite concretions and spans the upper tenuicostatum and lower falciferum Ammonite zones (Howarth, 1992;Kemp et al., 2005). These exceptionally well preserved sedimentary rocks provide a complete record of the T-OAE. ...
... These exceptionally well preserved sedimentary rocks provide a complete record of the T-OAE. The biostratigraphy and lithostratigraphy presented here are from Howarth (1992). The TOC, P, Fe/Al, Mn, Mo, S, V, and Cu data from this location used in this study are from Harding (2004). ...
The Toarcian Oceanic Anoxic Event (T-OAE, ∼183 Myr) was a long-lasting episode of ocean deoxygenation during the Early Jurassic. The event is related to a period of global warming and characterized by major perturbations to the hydrological and carbon cycles with high rates of organic matter burial in shelf seas. Ocean circulation during the Toarcian and its influence on marine biogeochemical cycles are still not fully understood. Here we assess the spatial extent of anoxia in the NW Tethys Ocean during the T-OAE, the relationship with ocean circulation and the impact on organic carbon burial, using new and existing sedimentary records from the European Epicontinental Shelf in combination with general circulation model results. We demonstrate that bottom waters on the southwestern part of the shelf were mainly oxic during the T-OAE, while those in the northeastern basins were mostly anoxic or even sulfidic. Results for two ocean-atmosphere models (Fast Ocean-Atmosphere Model and Massachusetts Institute of Technology general circulation model) suggest the presence of a strong clockwise gyre over the European Epicontinental Shelf, which brought oxygenated equatorial waters from the Tethys Ocean to the southern shelf. The northward limb of the gyre was significantly weakened due to the rough bathymetry of the northern shelf, making this relative small region highly sensitive to local ocean stratification. These sluggish ocean dynamics promoted bottom water anoxia and enhanced burial of organic carbon in the northeastern basins, which accounted for 3–5% of the total carbon extracted from the ocean-atmosphere system as recorded by the positive carbon isotope shift.
... Harpoceras lassum (Buckman, 1927) sensu Bécaud, 2006 = H. soloniacense (Lissajous, 1906) sensu Howarth, 1992 Pl. 2, Fig. 17 1992. Harpoceras soloniacense (Lissajous). ...
... Bien qu'elle ne fasse pas l'unanimité (Neige & Rouget, 2002 ;Morard, 2004), l'hypothèse du dimorphisme est adoptées par de nombreux auteurs qui placent le taxon Maconiceras au rang de genre à part entière (Guex, 1972(Guex, , 1973 ou de sous-genre de Harpoceras (Gabilly, 1976 ;Bécaud, 2006). à la suite de Howarth (1992) Description : Plusieurs fragments d'un Hildoceras micromorphe ont en commun une section subquadratique plus large que haute et une aire siphonale aplatie dont la carène est bordée de sillons profonds. L'ombilic est dominé par une aire oblique lisse, fortement inclinée. ...
The study of a new section around Caylus (Tarn-et-Garonne) allows new biostratigraphic and sedimentological observations on the terms of passage from the Upper Pliensbachian (Formation of the Barre à Pecten) to the Toarcien (Formation de Penne) of the Quercy (France). The Schistes cartons member (Lower Toarcian, Serpentinum zone) is particularly remarquable. Four taxa of brachiopods and eleven taxa of Toarcian ammonites from the Tenuicostatum, Serpentinum and Bifrons zones, sub-zone to Sublevisoni are the subject of the following
paleontological study.
... Ammonite assemblages of the middle Toarcian (Bifrons and Gradata zones) are dominated by Tethyan taxa and contain some Subboreal species testifying to the presence of a marine communication between the Central Atlantic and the Central Unit of the South Riffian Ridges which was already established from the early Pliensbachian. Bécaud, 2002, Brun and Marcelin, 1934, Choffat, 1880, Choffat, 1947, Deslongchamps, 1862-1885, Haas and Pétri, 1882, Howarth, 1992, Meneghini, Meneghini, 1867-1881, Renz, 1909, Reynè s, 1879, Seebach, 1864, Website, Website, Website, Wilmsen et al., 2002 ...
The uppermost lower Toarcian and middle Toarcian succession of the Central Unit of the South Riffian Ridges, particularly in the El Heitouf and Sned sections, is rich in benthic macrofauna and contains rare middle Toarcian ammonites of the Bifrons and Gradata zones. Eleven species and for morphs (one is nov.) of terebratulides arranged into three genera, have been identified, which are: Lobothyris arcta, L. crithea, L.? hispanica, L. punctata morph clevelandensis, Sphaeroidothyris decipiens, S. dubari, S. aff. dubari, S. vari, Telothyris arnaudi, T. jauberti, T. jauberti morph depressa, T. jauberti morph nabanciensis, T. jauberti morph triangularis morph nov., T. monleaui, and T. pyrenaica, as well as eleven species of ammonites, Collina aff. meneghinii, Harpoceras sp. indet., Haugia cf. jugosa, H. cf. navis, Hildaites cf. murleyi, Hildoceras bifrons, H. lusitanicum, H. semipolitum, H. sublevisoni, Phymatoceras cf. formosum and Polyplectus sp. These brachiopod and ammonite taxa are described and illustrated for the first time from the Central Unit of the South Riffian Ridges, Morocco. Most are new occurrence taxa that are common to the most Peritethyan basins of the northern and southern margins of the western Tethys, particularly north Africa, southwest Europe and the Subboreal Domain of western France and southeast England, and the Lusitanian Basin of the Central Atlantic margin of Portugal.
... Outside of Russia, in the stratigraphic chart of the Jurassic deposits of Argentina, representatives of the species Arctotis frenguellii (Damborenea) were cited in the description of beds with Meleagrinella, which correspond to part of the upper Toarcian and Aalenian (Damborenea, 1994;Riccardi et al., 2011). Zones of Jurassic System, 1982 Dean et al., 1961;Howarth, 1992Elmi et al., 1997Repin, 2016, 2017Zakharov et al., 1997Shurygin et al., 2011 This work The study of the collections of bivalve mollusks of the family Oxytomidae Ichikawa, 1958 from the Toarcian-Aalenian deposits of the north of Eastern Siberia and northeastern Russia, begun by O.A. Lutikov in the late 1980s, allowed us to establish the regularities of the evolution of some Jurassic-Cretaceous representatives of the family Oxytomidae Ichikawa, 1958 and to perform a preliminary classification of taxa . ...
Biochronological Scale of the Upper Toarcian–Lower Aalenian
of Eastern Siberia by Bivalve Mollusks
of the Genus Arctotis Bodylevsky, 1960
O. A. Lutikov*
Geological Institute, Russian Academy of Sciences, Moscow, Russia
*e-mail: niipss@mail.ru
Received March 9, 2021; revised April 2, 2021; accepted April 20, 2021
Abstract
On the basis of the study of shell morphogenesis, the classification of the Toarcian–Aalenian representatives of the genus Arctotis Bodylevsky, 1960 was refined. A sequence of species was established in the reference sections of Anabar Bay and Cape Tsvetkov (Eastern Taimyr), traced in a series of Toarcian and Aalenian sections in Eastern Siberia, and correlated with the Boreal ammonite scale. The biochronological scale was developed for the upper Toarcian–lower Aalenian on the basis of bivalve mollusks of the genus Arctotis (family Oxytomidae Ichikawa, 1958). This scale has its own chronological periodization and consists of four so-called oxyto-zones. The scale was used to carry out an interregional correlation of the upper Toarcian–lower Aalenian sections of Eastern Siberia (Anabar Bay, Cape Tsvetkov, Markha, Tyung, Kelimyar, Molodo, and Motorchuna rivers, boreholes drilled in the Vilyui syneclise) and northeastern Russia (Levy Kedon River basin). The chronostratigraphic volumes of oxyto-zones are determined by comparison with ammonite zones of the Boreal Standard: the Praearctotis milovae oxyto-zone corresponds to the Zugodactylites braunianus and Pseudolioceras compactile ammonite zones, the Praearctotis marchaensis oxyto-zone
corresponds to the Pseudolioceras wuerttenbergeri Zone, the Praearctotis similis oxyto-zone corresponds to the Pseudolioceras falcodiscus Zone, and the Arctotis tabagensis oxyto-zone corresponds to the Pseudolioceras maclintocki Zone.
Keywords: Jurassic, Toarcian, Aalenian, bivalves, biochronological scale, Eastern Siberia
DOI: 10.1134/S086959382106006X
... These ammonites may correspond to the Harpoceras falciferum Zone in the Paris Basin, and therefore associated with the Lower Toarcian black shales occurring extensively in Europe (Chen et al., 2005). On the Yorkshire coast in the British Isles, the lower portion of the Harpoceras falciferum Zone is defined by the successive biohorizons of Cleviceras exaratum, Eleganticeras elegantulum, and Cleviceras elegans (Howarth, 1992), and in NW Europe by the successive subzones of Harpoceras exaratum and Harpoceras falciferum. In the Sewa section, the level of 16.0 m (the lowest occurrence of Eleganticeras sp.) may correlate to the base of the H. exaratum Subzone in the NW European province (Figure 4). ...
The Early Toarcian “Oceanic Anoxic Event” (T-OAE) is recorded by marked disruption to both the climate system and marine ecosystems. Here, we present intergraded high-resolution carbon-isotope data (δ13C), bulk geochemistry, mineral characterization from an open-ocean setting in the eastern Tethys. With these data, we (1) construct the high-resolution record of the T-OAE from an open-ocean setting in the eastern Tethys; (2) show that the T-OAE in the Sewa succession was marked by coarser-grained deposits associated with high-energy conditions within the otherwise low-energy claystone deposits that likely linked to a globally increased supply of clastic sediments into marginal and deeper marine basin; (3) propose that the low Corg:Ptotal ratios, in combination with bioturbated structure and depletion or slight enrichment in redox-sensitive trace elements of V, Mo, and U suggest a long-term oxygenation event throughout the T-OAE interval at the Sewa succession, and hence, anoxia may not play a fundamental role during the Toarcian negative CIE in this setting; (4) exhibit that a warming and more humid climate began at the start of the T-OAE, and many episodic changes in sediment provenance throughout the T-OAE interval occurred at this location; and (5) suggest that accumulation of organic-matter sediments during the T-OAE is generally controlled by global climatic changes, but a regional environmental perturbation also might influence the preservation of organic matter.
... Il est bien établi que les Harpoceratinae répertoriées à ce niveau, ici regroupées dans les genres Matteiceras et Fildingiceras, sont représentés par des espèces totalement endémiques à la Province nord-ouest européenne et qu'elles prédominent dans les confins méridionaux du craton européen où leur présence donne un cachet « méridional » aux associations d'ammonites. Au sein de leur aire de répartition maximale, nous citerons les Pyrénées (FAURÉ 2002), les Corbières (FAURÉ 2002 (HOWARTH 1955(HOWARTH , 1992) et l'Allemagne méridionale (FISCHER 1975). Il s'agit alors d'exemplaires peu nombreux, voire d'individus isolés, qui se mêlent à une majorité d'Amalthéidés. ...
Located at the eastern end of the Montagne Noire, the Bédarieux Basin offers a Mesozoïc serie representative of the southern end of the Grand-Causses Basin. The Jurassic is little known here. The Upper Sinemurian (Raricostatum chronozone) and the Pliensbachian (Jamesoni, Ibex and Davoei chronozones) are here calibrated by rich associations of ammonites which are described and illustrated in the paleontolgical appendix. With its particularly condensed facies, the Jurassic of Bédarieux fits perfectly into the system of the Cévennes Threshold, of which it constitutes the southern extension.
... Coastal sections in Yorkshire, UK, expose shales deposited in the Cleveland Basin. The lithology and ammonite zonation of the sediments of Toarcian age given in Howarth (1962Howarth ( , 1992, whose bed numbers are used here. The same ammonite zones are recognised in Peniche and Yorkshire (Page, 2004;McArthur et al., 2020). ...
During the early Toarcian, volcanic gases released by the Karoo-Ferrar large igneous province are widely believed to have caused severe environmental disturbances, including ocean acidification. Here we show records of δ44/40Ca and δ88/86Sr through the early Toarcian, as recorded in three groups of biogenic calcite: Megateuthididae belemnites, Passaloteuthididae belemnites, and brachiopods of the species Soaresirhynchia bouchardi. We evaluate the data to eliminate the influence on isotopic composition of varying temperature, calcification rate, and salinity, through the section that may mask the environmental signals.
Neither δ44/40Ca and δ88/86Sr show negative isotope excursions across the suggested acidification interval as would be expected had acidification occurred. A profile of δ¹¹B, re-interpreted from a published study, shows no variation through the interval. Taken together, these data provide little support for ocean acidification at this time.
Values of δ88/86Sr are independent of temperature or Sr/Ca in our belemnites. For brachiopods, too few data are available to determine whether such a dependence exists. Values of δ44/40Ca show a weak temperature control of magnitude +0.020± 0.004‰/°C (2 s.d.). In belemnites, δ44/40Ca also correlates positively with Mg/Ca and Sr/Ca.
... Scarce fragments of Pleuroceras in Bed 4 and rare Emaciaticeras in beds 23 and 28 (section S1) indicate that Unit 1 belongs at least partly to the uppermost Spinatum Zone (Fig. 3). Although the Tenuicostatum Zone of the lower Toarcian is not documented by in situ ammonites, a single specimen of Dactylioceras (Eodactylites) mirabile indicative of the lower part of the Tenuicostatum Zone was found in the debris, suggesting that this zone is preserved within Unit 2 between the last occurrence of the late Pliensbachian ammonites in Bed 28 and the earliest ammonites of the Exaratum Subzone at the base of Unit 4 (Fig. 3) Howarth, 1992aHowarth, , 1992b or respectively the upper part of the Elegantulum Subzone (Strangewaysi Horizon, see Elmi et al., 1997). The marly interval just above the Bed 69 (section S2) yielded a fragment of Harpoceras sp. with weakly developed lateral spiral groove and falcate ribs. ...
The chemostratigraphic record of the Toarcian Oceanic Anoxic Event (T-OAE) is generally well documented in epicontinental basins; however, the duration of anoxia and recovery remains poorly constrained in the Tethys Ocean owing to limited stratigraphic resolution of oceanic sections with hiatuses. In this paper, we describe a relatively continuous hemipelagic record in the Central Western Carpathians of Slovakia (Skladaná Skala section), which contains the Pliensbachian/Toarcian boundary, the T-OAE, and the subsequent recovery phase. In our section, the Pliensbachian Spinatum Zone is represented by a ~ 7 m thick alternation of spotted, spiculitic marly limestones and limestones of the Allgäu Formation that contain moderately diverse trace fossils including abundant Zoophycos, Lamellaeichnus and Teichichnus. In the uppermost part of the Spinatum Zone, a ~ 0.8‰ decline in δ13Ccarb values marks the carbon isotope excursion (CIE) at the Pliensbachian/Toarcian boundary. This isotope anomaly is overlain by a ~ 3 m-thick interval of spotted marly limestones and marls, which contains a positive CIE that represents the base of the T-OAE. The T-OAE interval comprises a 60 cm-thick pyritic black shale interval that lacks bioturbation and shows a negative CIE (δ13Corg values drop by 4–5‰), coincident with an increase in TOC values (from 0.3% to 2–3%), and a drop in CaCO3 values (from 50 to 80% to 3–7%). The black shale is overlain by ~8 m thick marls with rare intercalations of marly limestones, which show ammonites of the Exaratum Subzone in the lowermost part (~1 m) succeeded by Serpentinum Zone beds. This unit exhibits a second positive CIE (δ13Corg increases by 2.5‰ and δ13Ccarb increases by 1.5‰), significantly more negative δ18O values relative to the pre-T-OAE interval, and a low diversity of trace fossils dominated by Chondrites and extremely thin Zoophycos. Sponge spicules re-appear in the uppermost 6.5 m-thick interval of the section formed by the alternation of spotted marls and limestones, with ammonites of the Falciferum Subzone in the lower part and of the Bifrons Zone in the uppermost parts; however, diversity of trace fossils remains low. Based on these findings, we argue that the 60 cm-thick pyritic black shale that represents the T-OAE is a strongly condensed succession because it includes the onset of the negative CIE and the subsequent rebound, and thereby encompasses the full duration of the anoxic event. Anoxia in basins open to the oceanic Tethys thus coincided not only with reduced carbonate production but also with reduced siliciclastic supply, generating very thin black shale deposits. In contrast to current-swept swells where black shales associated with hardgrounds are thin or missing owing to winnowing, carbonate starvation was induced by a calcification crisis coincident with the T-OAE and siliciclastic starvation was probably induced by rapid sea-level rise. Although bottom waters were not anoxic in the aftermath of T-OAE, bioturbation remained restricted during the Falciferum Subzone in basinal settings, indicating that environmental stress induced by limited ventilation and/or high bottom-water temperatures were persistent. The reduced diversity of trace fossils and the re-appearance of sponge spicules close to the lower/middle Toarcian boundary indicate that the ecological recovery in basins open to the oceanic Tethys was delayed, a pattern similar to the epicontinental seas that experienced anoxia.
... The types of processes discussed above (post-mortem drift, storm transport, and sediment reworking) sometimes leave tell-tale physical signatures in fossil assemblages. However, the work on ammonoids of the Cleveland Basin was largely undertaken many decades ago (e.g., Howarth, 1973Howarth, , 1992, before a modern understanding of cephalopod taphonomy was developed (e.g., Wani, 2004;Wani et al., 2005;Mapes et al., 2010), so the necessary observations to test the taphonomic history of these fossils have not been made to date. ...
We thank Stephen Hesselbo and his colleagues for their thoughtful Comment (henceforth, “Hetal-20”) on our article (Remírez and Algeo, 2020a, henceforth “R&A-20” as in their Comment), which provides us an opportunity to elaborate upon several key issues related to our study. R&A-20 presents evidence for a large decrease in salinity within the Cleveland Basin (U.K.) during the Toarcian Oceanic Anoxic Event (T-OAE). Our study is significant in (1) offering an alternative model to the existing paradigm for observed patterns of geochemical and paleobiological changes during the T-OAE, and (2) demonstrating the importance of applying a combination of salinity and redox proxies in analysis of paleoenvironmental variation in marginal-marine basins. We hope that R&A-20 stimulates further investigations of these issues.
... The studied section is located in the Suobu Cha area of the southern part of SQD (Fig. 1c), and its lithology consists of shallow-ocean mudstone and calcareous mudstone of the upper part of the Quse Formation. The ammonites, including Grammoceras striatulum Sowerby, Renziceras sp., and Polyplectus discoides, were found in the upper part of the Quse Formation (Yin et al. 2006;Wang et al. 2009) (Fig. 3), indicating that the upper part of the Quse Formation belongs to the Middle to Late Toarcian in age (Howarth 1992;Wang et al. 2009). This depositional age is younger than the Early Toarcian organic-rich black shales and marls in the Bilong Co area (Fu et al. 2016b). ...
The Toarcian (Early Jurassic) sediments are regarded as the most significant hydrocarbon source rocks in the Qiangtang Basin, Qinghai–Tibet Plateau. In this study, geochemical and mineralogical data are reported from the Middle to Late Toarcian organic-lean sediments in the Qiangtang Basin, eastern Tethys. Combined with previous studies, the factors that control organic matter (OM) accumulation during the Toarcian are investigated. The Early Toarcian organic-rich sediments were deposited in stratified water column with oxygen-deficient bottom water, which was conducive to OM preservation. A warm and humid paleoclimatic condition favored the growth of organisms, which in turn could enhance the surficial biotic productivity. During the Middle to Late Toarcian, oxic waterbody was widely distributed in the Qiangtang Basin. This condition was unbeneficial to the preservation of OM. During this interval, a cold–arid climate had an adverse effect on organism growth, which in turn would reduce the initial productivity of surface water. The consistently low Ti/Al and Si/Al ratios revealed restricted but rather homogeneous clastic influx conditions during the Toarcian. This may suggest that the dilution of terrigenous material input had a little influence on OM accumulation. In addition, the differential enrichment of OM between shales and marls should attribute to carbonate dilution. These studies emphasize that redox conditions and paleoclimatic conditions were likely responsible for OM accumulation during the Toarcian.
... En España se registra en la Zona Bifrons (Subzona Sublevisoni y parte inferior de la Subzona Bifrons), coincidiendo con un episodio transgresivo que representa el momento de máxima profundización de todo el Jurásico Inferior en éste área (Gómez & Goy, 2000Aurell et al., 2003), y que corresponde a un intervalo de calentamiento según los estudios realizados por Gómez et al. (2008) (Fig. 3). Su posición estratigráfi ca es similar a la que presenta en otras cuencas de Portugal, Inglaterra, Francia y Hungría (Mouterde, 1967;Howarth, 1992;Elmi et al., 1997;Rulleau et al., 2003;Géczy & Szente, 2006;Kovács, 2010). En el género Paroniceras (especie tipo: Paroniceras sternale (v. ...
El registro de las especies de Frechiella Prinz, 1904, Paroniceras Bonarelli, 1893 y Oxyparoniceras Guex, 1974 durante el Toarciense en el E y N de España, se ha relacionado con la evolución paleogeográfica y los ciclos deposicionales reconocidos en la Cordillera Ibérica. Sin embargo, es más evidente su relación con los intervalos de calentamiento relativo y picos térmicos, indicados por distintos autores en el Toarciense del norte y de la parte centro-oriental de la Subplaca Ibérica. Frechiella se ha registrado en la Zona Bifrons, Paroniceras en la Zona Variabilis y Oxyparoniceras en la parte superior de la Zona Thouarsense y parte inferior de la Zona Dispansum. La relación entre el registro de dichos géneros y las paleotemperaturas, parece indicar que sus especies se han desarrollado en medios cálidos y su presencia en las Cordilleras Ibérica y Cantábrica se debe a una migración desde otras áreas, sin que en todos los casos esto implique una colonización efectiva
... Cette ammonite dont la position stratigraphique est inconnue présente une grande ressemblance avec certains Mercaticeratinae. L'espèce n'a ensuite été citée que par Lehman (1968) qui l'attribue au Toarcien inférieur (sous-zone à Elegantulum) et par Howarth (1992) qui la rapproche à la fois des Brodieia sensu Gabilly (1974 ; microconques des Haugia), de Crassiceras bayani (Dumortier, 1874) et de Merlaites gradata (Merla, 1932), concluant malgré tout à la probabilité de l'appartenance de Whitbyiceras pingue au genre Brodieia. Cependant, les auteurs italiens (Sassaroli & Venturi, 2010, 2012 maintiennent cette rare espèce dans les Mercaticeratinae. ...
We here thoroughly compare the middle Toarcian Mercaticeratinae faunas from the NW European and the Mediterranean realms and show that these two fau- nas are significantly different. In turn, we erect a new genus for the Mercaticeratinae from the NW European realm, Pseudocrassiceras. This latter, whose first occurrence is in France and northern Spain at the base of the Variabilis Zone, is a very short-ranging taxon, as it went extinct without descendants before the end of the same zone. Although this new taxon indubitably originates from the Mediterranean Mercaticeratinae, we presently cannot identify the direct ancestor of Pseudocrassiceras bayani (Dumortier, 1874) n. gen., i.e., the most abundant and most cited species of the genus. The Mercaticeratinae occur in the Bifrons Zone both in Italy and Spain and therefore can have reached France from these two areas.
... The aptychi discussed by Riegraf et al. (1984) and labelled e, f, g and h in Figure 9 are of particular interest as they are associated with the genus Harpoceras. In particular, the aptychus labelled 'e' (Fig. 9) is associated with Harpoceras antiquum, which is a synonym of Tiltoniceras (Howarth 1992a), The discussion above highlights the association of Cornaptychus with Harpoceratid ammonites. Other instances have been documented in which a particular type of aptychus is associated with a particular family of ammonites. ...
Ammonite aptychi from the Lower Jurassic of Port Mulgrave near Whitby, U.K., are reported for the first time in association with ammonites of the Family Hildoceratidae, Subfamily Harpoceratinae. The aptychi are preserved in shale, varying in their completeness and exhibiting a range of sizes, but are identified as Cornaptychus sp. and cf. Lamellaptychus sp. Some Cornaptychus specimens are preserved with ammonites identified as Tiltoniceras antiquum. The aptychi, especially Cornaptychus, are comparable with aptychi associated with ammonites of the Harpoceratinae elsewhere, notably in the Posidonia Shale of Toarcian age in Germany. The ammonite aptychi were further analysed using an Environmental Scanning Electron Microscope (ESEM) in order to determine their composition and assess whether this might have implications for their occurrence and preservation potential compared with that of the ammonite shells.
... It gives us the opportunity to establish a framework which will serve as a reference to document the temporal distribution of the belemnite species (Figs 5,6). The systematic description of the ammonite faunas exceeds the scope of the present paper, but the section yields taxa wellknown from the north-west European paleobiogeographical province (Howarth 1992;Dommergues et al. 1997;Page 2003). Therefore, we figured only some stratigraphically important species (Figs 7-9). ...
http://sciencepress.mnhn.fr/sites/default/files/articles/pdf/g2018v40a4.pdf.
The present paper deals with the systematic description of the belemnite assemblages from the Lower Jurassic, collected at the Roche Blain quarry, Fresney-le-Puceux. In spite of the reduced thickness of the succession at Fresney-le-Puceux, 13 successive ammonite chronozones could be documented in this rather unique outcrop situation in mainland Europe. Twelve genera and 26 species of belemnites belonging to the Passaloteuthididae, Hastitidae, Megateuthididae, Salpingoteuthididae, and family incertae sedis are described and illustrated herein. The stratigraphical range of the belemnites is correlated with the standard ammonite zonation, using the chronozone concept: the described specimens range from the lower Pliensbachian (Davoei Chronozone) to the uppermost Toarcian (Aalensis Chronozone) while ammonites indicate the Aalenian (Murchisonae Chronozone) to be present too, but these beds delivered no identifiable belemnites so far. The belemnite diversity from Normandy is compared to data from coeval outcrops in Western and Central Europe.
... The d 13 C org shows cyclicity with a period of ca 75 cm. Bed numbers and ammonite stratigraphy is from Howarth (1992). The interval shown in Fig. 2 is indicated. ...
Mudrocks are the most common rock type at the Earth's surface, and they play a major role in informing current understanding of the palaeoenvironmental history of the planet. Their suitability for this purpose is at least partly underpinned by the assumed stratigraphic completeness of mudrock successions, and the ostensible fidelity with which they record temporal changes in palaeoenvironment. Mud does not necessarily accumulate, however, as a steady, near-continuous ‘rain’ under low energy conditions. Advective modes of mud transport and episodic, ephemeral accumulation have been shown to dominate in many ancient successions. This has implications for the completeness of these records and their suitability for high-resolution sampling and analysis. In this study, a numerical model of mud accumulation, parameterized with data from the Lower Jurassic of Yorkshire (United Kingdom) is presented to explore completeness and resolution constraints on ancient epicontinental mudrock successions. Using this model, stratigraphic completeness of the analysed Yorkshire succession is estimated to be ca 13% and ca 98% at centennial and millennial time scales, respectively. The findings indicate that sub-millennial scale processes and events are unlikely to be accurately resolved, despite the largely unbioturbated and well-laminated nature of the succession. Epicontinental mudrock successions are a crucial archive of ancient environmental changes, and the findings of this study help to define a plausible upper limit on the resolution achievable in these successions. Even with high-resolution sampling, sub-millennial scale records of palaeoenvironmental change may not be attainable in ancient epicontinental mudrocks.
... capillatum are found below and above the boundary. The latter species differs from the Tiltoniceras antiquum of Britain (Howarth, 1992) in having a more open umbilicus, and its stratigraphical range is also different, being confined to the Polymorphum Zone (Dommergues et al., in Cariou and Hantzpergue, 1997). ...
... Callomon (1963) provided detailed account of sexual dimorphism in many Jurassic ammonite families, for example, Graphoceratidae and Hildoceratidae of the Toarcian (Lower Jurassic) and Hammetoceratidae (Lower-Middle Jurassic). Howarth (1992) provided an account of dimorphism in the family Hildoceratidae from the Toarcian of Britain. Page (2008) mentioned the cryptic development of sexual dimorphism in the family Phylloceratidae of Lower Jurassic. ...
The genus Hubertoceras was described under the subfamily Proplanulitinae from the middle to upper Callovian (Middle Jurassic) beds of Kutch. Recently we revisited the Kutch Proplanulitinae and proposed a new endemic subfamily Sivajiceratinae for them. The new subfamily consists of the genera Sivajiceras, Kinkeliniceras, Obtusicostites and Hubertoceras. Development of sexual dimorphism was widespread in Jurassic ammonite families and at the same time, there was a significant increase (especially from the Callovian) of isolated sexual variants, which could not easily be paired up. In the present endeavour, we have explored the status of Hubertoceras in the light of sexual dimorphism. The genus Hubertoceras is characterised by small adult size, evolute shell with biplicate ribs and well-preserved lappets, which speak for its microconchiate nature. We have also made an attempt to identify the probable antidimorph of Hubertoceras from the contemporary large genera with evolute shells described from Kutch.
Detailed morphological and morphometrical analyses indicated that Obtusicostites is likely the macroconchiate counterpart of Hubertoceras. The Hubertoceras-Obtusicostites pair satisfied all the paleobiological as well as geological prerequisites to form antidimorphs. Evolutionary trends between macroconchs and microconchs within the Sivajiceratinae lineage also showed parallelism.
Most of the Callovian ammonite genera of Kutch were strongly dimorphic. Intense competition for food, habitat and mates perhaps forced these genera to undergo character displacement. While the macroconchs remained less diverged being uniformly large, evolute and strongly ornate; the microconchs showed wide interspecific variation in the shape of lappets, some even lacked peristomal modifications. Different types of lappet or absence of it perhaps facilitated easy mate recognition system among other functions.
... ). Ammonite stratigraphy is fromHowarth [1973Howarth [ , 1992, carbon isotopes and TOC are fromCohen et al. [2004] andKemp et al. [2005], and Mo isotopes and concentrations are fromPearce et al. [2008]. Vertical dashed lines highlight the range of the Mo-isotope fluctuations observed byPearce et al. [2008] in the lower falciferum ammonite Zone. ...
Molybdenum (Mo)-isotope chemostratigraphy of organic-rich mudrocks has been a valuable tool for testing the hypothesis that the Toarcian Oceanic Anoxic Event (T-OAE, Early Jurassic, ~183 Ma) was characterized by the spread of marine euxinia (and organic-matter burial) at a global scale. However, the interpretation of existing Mo-isotope data for the T-OAE (from Yorkshire, Cleveland Basin, U.K.) is equivocal. In this study, three new Mo-isotope profiles are presented: from Dotternhausen Quarry (South German Basin, Germany), the Rijswijk core (West Netherlands Basin, Netherlands) and the Dogna core (Belluno Basin, northern Italy). Precise bio- and chemo-stratigraphic correlation between the three sites allows a direct comparison of the data, enabling some key conclusions to be reached: (i) The Mo-isotope composition of seawater during the peak of the T-OAE was probably close to ~1.45 ‰, implicating a greater removal flux of sulphides from seawater, and a larger extent of global seafloor euxinia compared to the present day; (ii) Mo-isotope cycles previously identified in the Yorkshire sedimentary succession are attributed to changes in the degree of local Mo drawdown from overlying Cleveland Basin seawater; (iii) The consistency of the new multi-site Mo-isotope dataset indicates a secular reduction in the burial of sulphides globally in the late stages of the T-OAE, implying a contraction in the extent of global marine euxinia; (iv) Subtle differences in the Mo-isotope composition of deposits formed in different euxinic sub-basins of the European epicontinental shelf were probably governed by local variations in basin hydrography and rates of water renewal.
... ). Ammonite stratigraphy is fromHowarth [1973Howarth [ , 1992, carbon isotopes and TOC are fromCohen et al. [2004] andKemp et al. [2005], and Mo isotopes and concentrations are fromPearce et al. [2008]. Vertical dashed lines highlight the range of the Mo-isotope fluctuations observed byPearce et al. [2008] in the lower falciferum ammonite Zone. ...
... simulans subplanata and mainly R. fallax, as well as Prodactylioceras cf. colubriforme sensu Fucini, indicates a period to be situated in the upper part of Ibex to DEAN et al. 1961;HOWARTH 1992;DOMMERGUES et al. 1997a;CORNA et al. 1997;BLAU & MEISTER, 2000; MEISTER BRAGA 1983;JIMENEZ 1986;GOY et al. 1988 BETIC ZONE APENNINES ZONE DOMMERGUES et al. 1994;FARAONI et al. 1996;MACCHIONI 2001 MEDITERRANEAN EUROPE UPPER, MIDDLE and LOWER AUSTROALPINE HORIZONS DOMMERGUES & MEISTER 1990;MEISTER et al. 1994;BLAU 1998;DOMMERGUES et al. 1995;GECZY & MEISTER 1998, 2007; • Davoei Chronozone Fuciniceras costicillatumdetractum is a good marker for the Davoei Chronozone in the Tethyan realm. ...
This work provides a more precise up-to-date biostratigraphical framework of the Early Jurassic
ammonite succession of the Brescian Prealps with more than seventy taxa for the Sinemurian, Pliensbachian and basal Toarcian corresponding to a about 30 horizons or faunal assemblages rather well correlable with the NW European standard zonation. These results are supported with already published data, new data from recent field investigations, revised contributions of different authors and with the study of the historical collection of the Museum of Natural Sciences of Brescia (Northern Italy). The biohorizons are referred to the Lower Jurassic carbonate series of the Brescian Prealps, cropping out between the eastern surroundings of Brescia (Botticino-Serle), to the East, and the Lake Iseo, to the West. This area was located in the eastern border of the wide Lombardian Basin, a part of the southern continental passive margin subjected to the Jurassic rifting, preceding the Neo-Tethys opening.
... davoei at 410 m and the FO of Amaltheus stokesi at 408.30 m. The latter ammonoid bioevent, together with the following FO of Protogrammoceras sp. at 407.50 m, are characteristic of the Stokesi ammonite subzone (ASz), which corresponds to the lower part of the Margaritatus AZ (Howarth, 1992). The position of the top of the Stokesi ASz is unclear in the original description by Lorenz et al. (1987) and no mention of the Subnodosus Asz is given by these authors. ...
Extreme global warming and environmental changes associated with the Toarcian (Lower Jurassic) Oceanic Anoxic Event (T-OAE, ~ 183 Mya) profoundly impacted marine organisms and terrestrial plants. Despite the exceptionally elevated abundances of fossil insects from strata of this age, only assemblages from Germany and Luxembourg have been studied in detail. Here, we focus on the insect assemblage found in strata recording the T-OAE at Alderton Hill, Gloucestershire, UK, where <15% of specimens have previously been described. We located all known fossil insects (n = 370) from Alderton Hill, and used these to create the first comprehensive taxonomic and taphonomic analysis of the entire assemblage. We show that a diverse palaeoentomofaunal assemblage is preserved, comprising 12 orders, 21 families, 23 genera and 21 species. Fossil disarticulation is consistent with insect decay studies. The number of orders is comparable with present-day assemblages from similar latitudes (30°–40°N), including the Azores, and suggests that the palaeoentomofauna reflects a life assemblage. At Alderton, Hemiptera, Coleoptera and Orthoptera are the commonest (56.1%) orders. The high abundance of Hemiptera (22.1%) and Orthoptera (13.4%) indicates well-vegetated islands, while floral changes related to the T-OAE may be responsible for hemipteran diversification. Predatory insects are relatively abundant ( ~ 10% of the total assemblage) and we hypothesise that the co-occurrence of fish and insects within the T-OAE represents a jubilee-like event. The marginally higher proportion of sclerotised taxa compared to present-day insect assemblages possibly indicates adaptation to environmental conditions or taphonomic bias. The coeval palaeoentomofauna from Strawberry Bank, Somerset is less diverse (9 orders, 12 families, 6 genera, 3 species) and is taphonomically biased. The Alderton Hill palaeoentomofauna is interpreted to be the best-preserved and most representative insect assemblage from Toarcian strata in the UK. This study provides an essential first step towards understanding the likely influence of the T-OAE on insects.
The Bilong Co oil shale is one of the most significant source rocks in the Mesozoic Qiangtang Basin (Northern Tibet); however, its absolute chronology remains controversial. In this study, in situ carbonate U-Pb isotope dating analysis was carried out for the first time. Detailed field geological investigations yielded some age-diagnostic ammonites, enabling a re-evaluation of the stratigraphic age of the Bilong Co oil shale. A total of 61 spots of U-Pb isotope dating from the middle part of the Bilong Co oil shale section suggests an average age of 181 ± 13 Ma. Elemental geochemistry and diagenetic analysis indicate that the proposed age represents the early deposition of the calcite, and the oil shale was deposited during the Early Jurassic time. This estimated age is further supported by the newly discovered ammonite assemblage of Hildoceratidae-Tiltoniceras sp. at the top part of the oil shale section, which confirms the deposition of the oil shale during the Toarcian age of the late Early Jurassic. Consequently, the Bilong Co oil shale can be assigned to the Quse Formation, which is attributed to the Lower Jurassic rather than the Middle Jurassic. The re-assessment of the stratigraphic age of the Bilong Co oil shale is of great significance for regional evaluation and exploration activities of hydrocarbon source rock layers in the Qiangtang Basin as well as for global stratigraphic correlation of the late Early Jurassic Toarcian oceanic anoxic event.
Here, we describe the upper Pliensbachian to middle Toarcian stratigraphy of the Dove's Nest borehole, which was drilled near Whitby, North Yorkshire, in 2013. The core represents a single, continuous vertical section through unweathered, immature Lower Jurassic sedimentary rocks. The thickness of the Lias Group formations in the Dove's Nest core is approximately the same as that exposed along the North Yorkshire coast between Hawsker Bottoms and Whitby. The studied succession consists of epeiric-neritic sediments and comprises cross-laminated very fine sandstones, (oolitic) ironstones, and argillaceous mudstones. Dark argillaceous mudstone is the dominant lithology. These sediments were deposited in the Cleveland Basin, a more subsident area of an epeiric sea, the Laurasian Sea.
Supplementary material: https://doi.org/10.6084/m9.figshare.c.6154436
A specimen of the ammonoid Cleviceras (Hildoceratidae), collected at Port Mulgrave, near Whitby, North Yorkshire, shows an in-situ aptychus in the body chamber. The precise stratigraphic origin of the specimen is unknown, but the lithology and generic identity are compatible with derivation from the Mulgrave Shale Member of the Whitby Mudstone Formation. The specimen is the first in-situ jaw apparatus to be reported for this genus from Britain. A second loose specimen, a Harpoceras sp. with in-situ aptychus was found and photographed at Deepgrove Wyke, but was too friable to be collected. Both specimens reinforce previous observations that the aptychus form type Cornaptychus is characteristic of the ammonite family Hildoceratidae.
A great part of domerian fauna of Blesa (prov. Teruel, Spain) is cited. Some specific annotations are given and also figures.
New ammonoid data prove an early Late Pliensbachian deepening event above the ?Late Hettangian-Sinemurian shallow-subtidal gray-reddish micro-oncoidal-foraminifera grainstone facies and the ?Early Pliensbachian deeper-marine micro-oncoidal-crinoidal-ammonoid wacke- to packstone facies. Based on the presence of Fuciniceras lavinianum (Fucini), Lytoceras ovimontanum Geyer and Arieticeratinae gen. indet. from a hardground above the deeper-water micro-oncoidal limestones in the Mihajlovici section (northeastern Montenegro) a Late Pliensbachian to Early Toarcian condensation horizon is proven. The Middle Toarcian ammonoid-bearing horizon also yielded species not known from previous studies: Calliphylloceras capitanii (Catullo), Harpoceras subplanatum (Oppel) and Furloceras aff. chelussii (Parisch & Viale), also described in the present paper. These new data prove a stepwise deepening of the depositional area during the Early and the Middle Jurassic reflected in detail in four sedimentary members: 1) ?Late Hettangian to Sinemurian/? earliest Pliensbachian open-marine shallow subtital micro-oncoidal limestone; 2) ?Early to Late Pliensbachian open-marine condensed limestones with few micro-oncoids and more open-marine influence; 3) Toarcian openmarine condensed red limestones with hardgrounds; and 4} condensed red nodular Bositra Limestone. These four members are separated by hardrounds representing Stratigraphie gaps in deposition. The stepwise deepening during the Early-Middle Jurassic follows the general trend of deposition as known in the whole Western Tethys Realm above the Late Triassic Dachstein Carbonate Platform.
The genus Nejdia Arkell, 1952 has rarely been cited outside the Arabo-Malgach Province and, few specimens have been recorded outside this province. On the Iberian Peninsula it has been identified in three sites, two of these in the southwest of the Iberian Basin and one in the Lusitanian Basin. Three species are described: N. cf. bramkampi, N. pseudogruneri and N. duartei sp. nov., Following the indications of the journal the new species was recorded in the ZooBank recorded in the interval between the upper part of the Serpentinum Chronozone, where they are associated with Harpoceras falciferum and Orthildaites douvillei and the lower part of the Bifrons Chronozone containing Hildoceras sublevisoni. In all the Iberian outcrops having a record of Nejdia, the fossils constitute ademic or parademic taphonic entities, as there is no evidence to indicate that the known populations inhabited an area close to the southwest sector of the Iberian Range, or the northern part of the Lusitanian Basin, where were recorded. With the specimens obtained in Portugal, the known geographic distribution of the genus Nejdia is extended, currently comprising, apart from the Arabo-Malgach Province, the Iberian Range and the Lusitanian Basin in the Submediterranean Province, and the Middle Atlas and the Apennines in the Mediterranean Province.
url:lsid:zoobank.org:pub:BEE9F42E-92FE-483E-9CC1-B4B8FB927E82
The "Etudes paléontologiques sur les dépôts jurassiques du Bassin du Rhône" constitutes the main work of the paleontologist Dumortier originated from Lyon (1801-1876). The volume IV describes Toarcian and Aalenian faunas. The revision of those faunas, based on the study of Dumortier's collections kept in the Museum of Lyon, has allowed to precise the taxonomic and stra-tigraphical position of the species created by Dumortier. Lectotypes or neotypes have been designated everytimes it was necessary. Among 30 cephalopod or brachiopod new species, 24 have been considered as valid. 17 other species, also
considered as valid, have been created by other authors, one of which in this publication : Cenoceras (Hemicenoceras) thiollieri Tintant. Their acception is based upon the Dumortier's figurations. The localities-types of the South-Eastern France studied by Dumortier, are replaced in their actual geographical and biostratigraphical framework.We hope that the so reactualized Dumortier's work long will constitute a necessary reference for all the
studies dealing with Toarcian and Aalenian Faunas.
We present the biostratigraphical events, ammonites and foraminifera from the Pliensbachian (Spinatum Chronozone) to the Toarcian (Bifrons Chronozone) in San Miguel de Aguayo. We sampled the profile layer by layer for ammonites (400 specimens in 86 successive levels), and we extracted 19 samples for foraminifera (4858 picked specimens). In the Spinatum Chronozone, the Amaltheidae Family dominated, with little presence of the Arieticeratinae or Harpoceratinae. The Tenuicostatum Chronozone presents a good record of Dactylioceratinae, with successive species, from Dactylioceras (Eodactylites) simplex to Dactylioceras (Orthodactylites) semicelatum. The Serpentinum Chronozone is characterised by Harpoceratinae (Eleganticeras, Cleviceras, Harpoceras), Hildoceratinae (Hildaites, Orthildaites) and by the persistence of Dactylioceras (Orthodactylites). The Bifrons Chronozone presents a good succession of Hildoceras. The foraminifera are benthic and autochthonous, and the calcareous hyaline taxa of the Lagenina Suborder, Vaginulinidae Family, are dominant. The most diverse genera are Nodosaria and Lenticulina. The most abundant species is Lenticulina toarcense, which constitutes 55.37% of the total number of specimens. Also represented, albeit as a minority, are the Textulariina, Miliolina, Spirillinina and Robertinina Suborders. The ammonites are typical of the Submediterranean Province and common to the Subboreal Province; the species of the Mediterranean Province are scarce and their record is sporadic in the Pliensbachian–Toarcian transition. The foraminifera are typical of the Atlantic Boreal Domain; two main biotic events were recognised: step-wise extinction of species between the Hawskerense and Semicelatum subchronozones, with a maximum extinction rate in the Semicelatum Subchronozone, and faunal turnover principally in the Elegantulum Subchronozone (Serpentinum Chronozone).
SUMMARY
A number of new dactylioceratid specimens are described from the lowermost Toarcian (Tenuicostatum Zone) of Baden-Wuerttemberg, SW-Germany. The stratigraphically important species Dactylioceras (Orthodactylites) wunnenbergi HOFFMANN, 1968 (formerly mostly known as D. (O.) clevelandicum HOWARTH, 1973) is for the first time definitely recorded from the lowermost part of the Aschgraue Mergel of the Posidonienschiefer-Formation of Baden-Wuerttemberg. Dactylioceras (O.) ernsti LEHMANN, 1968, hitherto mostly known from NW Germany, is also recorded for the first time from the Obere Fukoidenschiefer of the Posidonienschiefer Formation of SW-Germany. D. (O.) crosbeyi (SIMPSON, 1855) is recorded from the Fleins (upper Tenuicostatum Zone). It was before only recorded from horizons much lower in the section and its occurrence therefore represents a slight biostratigraphic anomaly – when compared to the north western European standard zonation of Yorkshire. An incomplete but well-preserved specimen from the Obere Fukoidenschiefer is indistinguishable from the paratype of D. (O.) crassifactum (SIMPSON, 1855) and accordingly cautiously referred to that little known species, of which it is the first record in SW-Germany, as D. (O.) cf. crassifactum (SIMPSON, 1855). Together with comparable material from France, it provides a hint towards the true stratigraphic placement of this little known species. The genus Kedonoceras DAGIS, 1968 is recorded for the first time from SW-Germany, based on a specimen from the top of the Tenuicostatum Zone (lowermost Untere Schiefer) identified as K. cf. compactum DAGIS, 1968. A badly preserved but diagnostic specimen, most probably from the Untere Aschgraue Mergel, is the first definitive record of the zonal index fossil Dactylioceras (O.) tenuicostatum (YOUNG & BIRD, 1822) from SW-Germany. The biochronological significance of these and earlier finds of dactylioceratids and other ammonites from the Tenuicostatum Zone of the Posidonienschiefer-Formation of Baden-Wuerttemberg is discussed. It is concluded that there is sufficient evidence for the presence of the Paltum-, Crosbeyi-, Wunnenbergi- (“Clevelandicum”), Tenuicostatum-, Semicelatum- and Antiquum- biohorizons, that is all nominal biohorizons of the north western European standard zonation. The Paltum Horizon appears to encompass sediments traditionally included in the uppermost Pliensbachian (Top of the Amaltheenton-Formation), as evidenced by several findings of dactylioceratids of the genus Eodactylites.
Key words: Toarcian, Tenuicostatum Zone, ammonites, Dactylioceratidae, Posidonienschiefer-Formation, stratigraphy, taxonomy.
During the Toarcian oceanic anoxic event (OAE) considerable environmental changes occurred that were associated with global warming, perturbations to the C-cycle and ocean deoxygenation which resulted in a mass extinction of marine fauna. Recovery of the biota after the event was protracted and has to date undergone limited study. However, understanding the patterns and processes of recovery are critical to anticipating ecosystem responses to the environmental changes predicted for the near future. Results showed that increases in benthic diversity, and the re-establishment of the Toarcian infauna was gradual and followed the changing redox conditions. Pioneering infauna, such as Dacryomya ovum that dominated the seafloor after the event in the Cleveland Basin, Yorkshire, UK, can modify the physico-chemical environment and thus facilitate ecological succession after disturbance. The length of D. ovum increased >8 mm throughout the bifrons Zone and these body-size changes were linked with total organic carbon (TOC) content suggesting a link to primary productivity, although only at intermediate levels of deoxygenation. Major changes in the phytoplankton, and so food supply, seem to have driven changes in bivalve body size, across trophic guilds, both during and after the event in Yorkshire, and on the mid to lower shelf in Spain and France, respectively. Primary productivity collapse seems then to have been a major driver of biotic change throughout the Toarcian event, as it was during the Permian–Triassic, Triassic/Jurassic and Cretaceous/Tertiary mass extinctions. Further investigation of both the palaeontological and geochemical changes that occurred within early successional Toarcian infaunal communities are required to more fully understand the pattern of recovery after the OAE.
The zonal standart of the Toarcian stage in the North-East Asia represented by a series of parallel autonomous scales for different groups of macro- and microfauna is substantiated in the book. The ammonite zonal standart is based on the evolutionary changes of harpoceratinae and dactylioceratidae. A species succession of harpoceratinae is suggested as the basic ammonite zonal scale. It was found out that the boundaries of Bivalve zones (b-zones), Foraminifer zones (f-zones), Ostracoda zones (o-zones) frequently not coincide with ammonite zones. To draw the boundaries of zones determined in accordance with stages of these fossil organism groups complex methods were used ranging from talezonal separation and epiboles to zones of mutual distribution and sometimes ecozones. It allowed us to distinguish and correlate very narrow levels (intervals of zone overlap, i.e. cointervals) using the whole set of scales (from ammonites to microfauna). The parallel autonomous zonal scales on ammonites, bivalve mollusks (Bivalvia), foraminifera, and Ostracoda were significantly modernized, and their interregional correlation levels which favoured to carry out the circum-boreal correlations were determined. The images of zonal species (indices) are given in paleontological tables.
By 1849, Alcide d'Orbigny had proposed a very modern looking global subdivision of a Jurassique ‘System’, into a sequence of 10 étages. D'Orbigny's stages were based on a basic biostratigraphical framework, but there were still a number of issues with its actual demonstrable applicability internationally. In 1856, Albert Oppel took d'Orbigny's framework and, as stated by W.J.Arkell in 1933, ‘breath[ed] new life into it…placing the whole science of stratigraphical geology on a new footing’. Oppel recognized eight ‘Etagen’, divided into a sequence of ‘zones’ which he considered to be time-related to correlation units of theoretically universal application – a very clear and unambiguous statement of what now would be considered to be chronostratigraphical practice. Subsequently, evolution of Jurassic stratigraphy had, by the end of the 18th century led to S.S Buckman's high-resolution ammonite correlation schemes using hemera – essentially the same as modern biohorizons. Although some of this detail was subsequently lost in his syntheses, from around 1933–1956, W.J. Arkell took many pre-existing ‘zonal’ schemes and began to develop global ‘standard’ ammonite correlation schemes – again explicitly chronostratigraphical. Nevertheless, the potential for very high-resolution ammonite-based correlation schemes – with a resolution of only around 100,000 or less – was soon rediscovered and promoted by J.H. Callomon and by a very active ‘French School’. Despite all this activity, however, we still have not quite realized the ordered stratigraphical dreams of Oppel and his successors. Of the 11 stages now formally recognized within the Jurassic, four still do not have a ratified GSSP, and within the entire system, there still appear to be no formal agreements on what really are the ‘standard’ zones for each stage. Crucially, however, confusion is still widespread as to the ‘meaning’ of these zones – Jurassic ‘Standard Zones’ are chronozones not biozones – they have been explicitly so since Oppel's day, and as the stratigraphical building blocks of all ‘modern’ Jurassic stages, they must still be.
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