Uppermost Bajocian Research Articles

On the Dimorph Pair Lobosphinctes/Planisphinctes (Ammonoidea: Perisphinctidae) from the Uppermost Bajocian–Lowermost Bathonian of the Kuban River Basin (Northern Caucasus, Russia)

On the Dimorph Pair Lobosphinctes/Planisphinctes (Ammonoidea: Perisphinctidae) from the Uppermost Bajocian–Lowermost Bathonian of the Kuban River Basin (Northern Caucasus, Russia)

On Some Parkinsonia (Ammonoidea: Parkinsoniidae) from the Uppermost Bajocian of the Kuban and Urup Rivers Interfluve (Northern Caucasus, Russia)

On Some Parkinsonia (Ammonoidea: Parkinsoniidae) from the Uppermost Bajocian of the Kuban and Urup Rivers Interfluve (Northern Caucasus, Russia)

Ammonite occurrences in North Sea cores: implications for Jurassic Arctic–Mediterranean marine seaway connectivity

The paucity of ammonite recovery from North Sea wells has meant that offshore correlations are largely dependent upon microfossil assemblages. While rare, ammonites have been found in a few boreholes during the course of oil exploration activities. The occurrence of ammonites in ten wells in the UK sector of the Viking Graben and the Moray Firth rift arms provides a new basis by which to demonstrate that there was a distinct separation between Arctic and sub-Mediterranean species that lasted from Bajocian to Early Callovian times. Five wells contain ‘Boreal Bathonian' ammonites from the Arctic Realm. Arctocephalites from the Boreal Arcticus Zone (uppermost Bajocian) correlates basinal partly anoxic mudstones in the Beryl Embayment (9/13b) with both bioturbated siltstones in the southern Viking Graben (9/10b), and calcareous mudstones in the East Shetland Basin (211/21). Upper Bajocian Pompeckji Zone Cranocephalites and younger Arcticoceras from Lower to Middle Bathonian Greenlandicus, Ishmae and Cranocephaloide zones are confined to 211/21 demonstrating that the marine transgression began earlier and lasted longer. A Cadoceras from well 3/3-8 dates to the Lower Callovian Koenigi and Calloviense zones during which renewed extensional faulting re-established ammonite migration routes between the Boreal and sub-Mediterranean realms. A Middle Oxfordian (Densiplicatum Zone) Perisphinctes from well 22/5b-8 confirms an episode of northward migration from the sub-Mediterranean into the Boreal Realm. Upper Oxfordian (Regulare to Rosenkantzi zones) Amoeboceras in wells 211/21-1 and 9/13b-19 are close to Upper Bajocian/Lower Bathonian faunas, suggesting an absence of Upper Bathonian to Middle Oxfordian strata as a result of rift-related footwall uplift and erosion. In four wells from Block 15/21 (-4, -11, -12A and -25) Lower Kimmeridgian ammonites have been documented, including Rasenia , Amoebites , Aulacostephanoides and Zenostephanoides , from the Baylei (?), Cymodoce, Mutabilis and Eudoxus zones, the latter (confirmed at well 13/28b-8) dating a widespread regional marine flooding surface in the Inner Moray Firth. Supplementary material: The detailed measurements of dimensions of the ammonites described are available at: https://doi.org/10.6084/m9.figshare.c.5087313

Oscillating redox conditions in the Middle–Late Jurassic Alpine Tethys: Insights from selected geochemical indices and 57Fe Mössbauer spectroscopy

Abstract: The Middle–Late Jurassic greenhouse conditions included CO2 levels that have been estimated to be four to five times higher than they are presently. By analysing the pattern of selected trace elements as redox proxies (V, U, and Mo) and the variations in the chemical state of iron using 57Fe Mossbauer spectroscopy, we demonstrate the occurrence of major changes in sediment redox conditions from the Late Bajocian through the Late Oxfordian in the pelagic environment of the Alpine Tethys in its Carpathian domain. Our interpretation is based on analysis of siliceous limestones rich in radiolarians intercalated with red nodular limestones of Ammonitico Rosso-type facies from the Križna Nappe in the eastern part of the Tatra Mountains, Poland. The presented redox potential (Eh values) shows its changeable pattern along the section (from −0.74 V to 0.16 V). The low values of Eh (from −0.74 V to −0.4 V) create the long-term (ca. 7 Myr) trend of the medium-scale fluctuations comprising the Upper Bajocian through the Lower Oxfordian interval of predominately grey and green radiolarian siliceous limestones. This interval comprises the three short-term (less than 0.5 Myr) periods of slightly increasing Eh (from −0.35 V to −0.17 V) observed in the uppermost Bajocian, Lower Bathonian, and Lower Callovian, as well as the significant changes in sediment redox conditions from oxic to dysoxic in the Upper Bajocian. The overlying succession corresponding to the Middle–Upper Oxfordian (ca. 4 Myr) is characterized by red radiolarian siliceous limestones with positive Eh values that indicate deposition under more oxic conditions than those during any other period in the study section. The negative values of Eh, attributed to the upwelling periods, coincide with the decreasing sea surface water temperature (SST) and increasing organic matter flux. The largest negative shift is noted in the Upper Callovian, which coincided with the cool climatic phase. The positive Eh values indicate oxic conditions due to the lowering of organic matter input, coinciding with an increased SST caused by surface water stratification. Based on the observed long-term variation in the redox, we postulate thermally driven east–west atmospheric circulation along the equatorial Tethys Ocean, caused by the sharp contrast in sea surface temperature, similar to the Walker Circulation operating across the modern Pacific. This phenomenon would have been the dominant periodical mode over the tropics and subtropics regions of the NW Tethys during the Middle–Late Jurassic. Global warming reduces the long-term strength of the mean tropical atmospheric circulation, leading to sea water stratification near the surface and consequently lowering the organic matter flux. However, additional seaways of heat transport could also exist, as they are associated with the opening/closing of the Hispanic Corridor.

Middle to Late Jurassic carbonate-biosiliceous sedimentation and palaeoenvironment in the Tethyan Fatricum Domain, Krížna Nappe, Tatra Mts, Western Carpathians

The Jurassic of the Alpine-Mediterranean Tethys was characterized by the formation of several interconnected basins, which underwent gradual deepening and oceanization. Sedimentation in each basin was influenced by a specific set of interrelated factors, such as tectonic activity, seawater circulation, climate, chemistry and trophic state of seawater as well as evolutionary changes of the marine biota. This paper deals with the Fatricum Domain (Central Carpathians, Poland and Slovakia), which in the Jurassic was a pull-apart basin on a thinned continental crust. The sedimentation history of this domain during the Bajocian–Tithonian and its governing factors have been revealed. Facies analysis of the Bajocian–Oxfordian deposits evidences considerable relief of the basin-floor topography. Deposits in the Western Tatra Mts represent sedimentation on a submarine intrabasinal high, whereas the coeval deposits of the eastern part of the Tatra Mts accumulated in a deeper basin. The basin succession began with Bajocian bioturbated “spotted” limestones and siliciclastic mudstones (Fleckenmergel facies). These were succeeded by uppermost Bajocian – middle Bathonian grey nodular limestones, affected by synsedimentary gravitational bulk creep. The coeval deposits of the intrabasinal high are represented by well-washed Bositra -crinoidal limestones with condensed horizons. Uniform radiolarite sedimentation commenced in the late Bathonian and persisted until the early late Kimmeridgian. The basal ribbon radiolarites (upper Bathonian – lower Oxfordian), which consist of alternating chert beds and shale partings, are a record of seawater eutrophication, a related crisis in carbonate production and the rise of the CCD, which collectively resulted in biosiliceous sedimentation. The overlying calcareous radiolarites (middle Oxfordian – lowermost upper Kimmeridgian) marked a gradual return to carbonate sedimentation. The return of conditions that were favourable for carbonate sedimentation took place in the late Kimmeridgian, when the red nodular limestones were deposited. They are partly replaced by basinal platy limestones (uppermost Kimmeridgian – Tithonian) in the Western Tatra Mts. This lateral variation in facies reflects a change in the sedimentary conditions governed by a bathymetric reversal of the seafloor configuration, attributed to a further stage in the pull-apart transcurrent tectonics of the Fatricum Domain.

A new homolodromioid crab (Brachyura: Dromiacea: Tanidromitidae) from the Bajocian of central Poland and a review of the stratigraphical distribution and paleoenvironments of the known Middle Jurassic homolodromioids

A new homolodromioid (Brachyura, Tanidromitidae) crab from the Middle Jurassic (uppermost Bajocian) of central Poland is described and a new species, Tanidromites muelleri , is erected. The new species is not only one of the oldest representatives of true crabs, but also the most numerous in the world in terms of collected individuals (46 carapaces, including incomplete specimens) of the Middle Jurassic homolodromioid crabs. Tanidromites muelleri sp. nov. lived in a shallow-water, soft-bottom marine environment around developing oyster patch-reefs, being similar as later during the Late Jurassic when they lived in association with extensive sponge bioherms and coral reefs. The preservation of carapaces of the new species was influenced by a quick burial and rapid mineralization of calcitic concretions in which they are embedded. The stratigraphic distribution, to ammonite subzone level, of homolodromioid Middle Jurassic crabs is reviewed. Analysis of their paleoenvironmental preferences indicated that during the first step in the origin of true crabs they were connected with shallow, marine, high-energy carbonate deposits dominated by oolitic (including ferrugineus-oolitic one) facies, coralliferous reefs, and grey/black clays with carbonate concretions which hosted these crabs.

Ammonite assemblages and chronostratigraphy of the uppermost Bajocian–Callovian (Middle Jurassic) of the Murcia Region (Betic Cordillera, south-eastern Spain)

In this paper the stratigraphy and biostratigraphy of the Bathonian–Callovian rocks of the Murcia Region, based on high-resolution sampling yielding good ammonite dating, is reported. All the ammonites analysed are from four sections located on a pelagic swell (External Subbetic palaeogeographic domain) of the External Zones of the Betic Cordillera, Murcia Region, southern Spain. These represent characteristic Bathonian–Callovian sections of the Subbetic epipelagic swells in the Betic Cordillera. The lithology consists mainly of both nodular limestones and marly limestones. Discontinuities with hiatuses of variable duration, submarine hardgrounds, Fe–Mn macrooncoids, limonite crusts, neptunian dykes, etc., occur in the Middle Bathonian–Callovian interval. Extreme condensation episodes are common, but abundant ammonite faunal records have enabled a consistent and accurate chronostratigraphy. The Parkinsoni Zone, Daubenyi and Dimorphus subzones (uppermost Bajocian), the Zigzag and Aurigerus zones (Lower Bathonian), the Sofanus and Costatus zones (Middle Bathonian), the Orbis Zone (Upper Bathonian), and the Bullatus and Gracilis Zones (Lower Callovian) are recognised and characterised. The ammonite fauna shows a typical Mediterranean character. Phylloceratina and Lytoceratina are the predominant elements within the ammonite fauna, but Lytoceratina is dominant in the Lower Bathonian whereas Phylloceratina predominates in the rest of the Bathonian and in the Callovian. Other ammonites, such as Oppeliidae, Lissoceratidae, Stephanoceratidae, Perisphinctidae, Tulitidae, and Reineckeiidae, are also common throughout the uppermost Bajocian to Lower Callovian interval. Strigoceratidae are present, but scarce.

Strigoceras septicarinatum (Jurassic Ammonoidea) in the Precordillera of North Chile: Paleobiogeographical and paleoenvironmental implications

The first circum-Pacific record of the Bajocian dimorphic ammonite Strigoceras septicarinatum, from the Quebrada San Pedro area, Antofagasta, northern Chile, is described and illustrated. Morphological features of two specimens display macroconch and microconch characters of a single biospecies, usually assigned to separate morphospecies of the West Tethyan genera Strigoceras [macroconch] and Cadomoceras [microconch]. Preservational features of these two specimens, found in situ in the same stratigraphic level at the top of the Torcazas Formation, correspond to resedimented elements of the uppermost Bajocian Dimorphinites Biohorizon, contemporaneous with the sedimentary matrix. These specimens represent dimorphic shells produced by extremely scarce individuals inhabiting the Tarapaca Basin, without evidence of lasting biostratinomic modifications such as sorting by necroplanktic drift or biostratinomic encrusting. In the Tarapaca Basin, the distribution of ammonite shells was taphonomically and ecologically driven by regional changes of relative sea level. Taphonomic, paleoecological and paleobiogeographical observations in the areas of Quebrada San Pedro and Caracoles corroborate the development of an advanced-deepening phase, with episodes of sedimentary starvation, during the uppermost Bajocian, Parkinsoni Zone. This phase characterizes the last episode within a deepening half-cycle of a third order and the maximum deepening of a second-order, transgressive/regressive facies cycle, in the marine, back-arc Tarapaca Basin during the Bajocian–Bathonian interval. These paleontological and paleoenvironmental results represent new criteria to characterize the Dimorphinites Biohorizon in the Tarapaca Basin, allowing the identification the upper Bajocian Parkinsoni Zone in the East Pacific Subrealm, as well as chronocorrelation between the West Tethyan and East Pacific basins at the Bajocian/Bathonian boundary.

Redox conditions during sedimentation of the Middle Jurassic (Upper Bajocian–Bathonian) clays of the Polish Jura (south-central Poland)

Depositional redox conditions of the uppermost Bajocian–Bathonian (Middle Jurassic) ore-bearing clays of the Gnaszyn/Kawodrza area in the Polish Jura have been determined using an integrated geochemical (Th/U and U/Th ratios, degree of pyritisation (DOP), sulphur stable isotopes, biomarker analysis) and petrographic approach (measurements of pyrite framboid diameters, and microfacies analysis). The Th/U and U/Th ratios indicate that oxic conditions prevailed on the sea-floor during this interval, and 34S isotopes suggest open-system conditions. DOP values, however, are rather scattered, and may reflect oxic, dysoxic, or anoxic conditions. We consider that the DOP values result from reducing conditions within the sediment and the chemistry of the pore-waters, rather than true sea-floor redox conditions. Pyrite framboid populations also indicate that dysoxic conditions prevailed within the sediment, beneath an oxygenated water column. Biomarker data did not provide any evidence of water column stratification or anoxia during sedimentation of the Middle Jurassic clays.

Ammonoid succession at the Bajocian-Bathonian transition in the Bas Auran area, Digne district, South-East France.

The uppermost Bajocian to lowermost Bathonian ammonoid succession has been studied in the Bas Auran area in view of choosing one of its sections as the Global Stratotype Section and Point (G.S.S.P.) of the Bathonian Stage. The Bas Auran ammonite assemblages display exceptional values of record quality. The stratigraphic distribution of 629 specimens referred to 63 species and 35 genera, collected during the last forty years from three sections (Ravin du Bes, Ravin d'Auran, Ravin des Robines), is plotted and analyzed, bed by bed. Over 85 stratigraphic levels, through 9 m in thickness, have been studied at the top of the Marno-calcaires a Cancellophycus formation, ranging from the latest Bajocian (Parkinsoni Zone, Bomfordi Subzone) to the earliest Bathonian (Zigzag Zone, Convergens Subzone) and the base of the Macrescens Subzone. Ammonoid assemblages are composed of Northwest European and Mediterranean elements, associated with Sub-Mediterranean ones, allowing chronocorrelation between the Northwest European Convergens Subzone and the Sub-Mediterranean Parvum Subzone. The basal boundary of the Zigzag Zone and of the Bathonian Stage is placed at the base of Sturani's bed 23 in the Ravin du Bes section and is identified by the first occurrence of Gonolkites convergens, and coincides with the loest occurrence of Morphoceras parvum. Features of the ammonoid succession indicate relatively homogeneous and good record quality, gradual biostratigraphic change and high degree of taxonomic similarity between the Bomfordi and Convergens subzones. Palaeontological criteria also indicate relatively high values of palaeontological and stratigraphic completeness at the base of levels RB070-RB071 (= level 23 in Sturani 1967) which corresponds to the Bajocian/Bathonian boundary. The Ravin du Bes Section, with forty-six successive ammonoid fossil-assemblages of the Convergens Subzone belonging to three biohorizons through five metres of thickness, shows maximum values of biostratigraphic and biochronostratigraphic completeness, being one of the most complete in the world. Therefore, the Ravin du Bes Section should be chosen as the Global Stratotype Section and Point for the base of the Bathonian Stage. Two biostratigraphic logs summarize the ammonite content from the uppermost Bomfordi to basal Macrescens subzones. Three plates illustrate the most characteristic ammonoid taxa at the Bajocian-Bathonian passage in the Bas Auran succession.

Ammonite fauna from uppermost Bajocian (Middle Jurassic) calcitic concretions from the Polish Jura—biogeographical and taphonomical implications

Uppermost Bajocian (Parkinsoni Zone, Bomfordi Subzone) calcitic concretions from the epicratonic basin in South-Central Poland (Polish Jura) contain numerous, well-preserved ammonites unique for this area. Characteristic of the assemblages is the presence of small, juvenile specimens. Associated with dominant parkinsoniids ( Parkinsonia ( Parkinsonia) aff. dorni Arkell) are lytoceratids [ Nannolytoceras tripartitum (Raspail)], lissoceratids [( Lissoceras ( Lissoceras) oolithicum (d'Orbigny) and Lissoceras ( Microlissoceras) solitarium Zatoń and Marynowski nov. sp.)], leptosphinctids ( Vermisphinctes sp.) and strigoceratids [( Strigoceras ( Strigoceras) sp. juv. gr. strigifer/ pseudostrigifer)], as well as fragments of phylloceratids ( Phylloceras sp.). Parkinsoniids (the most numerous) are considered here as host fauna. Other ammonites, especially phylloceratids and nannolytoceratids, are supposed migrants from the Mediterranean area into the shallow epicratonic Polish Basin during the Late Bajocian sea-level rise. N. tripartitum, which has a broad geographical range probably drifted as a plankton-feeder in the upper water column and, together with phylloceratids, are considered to be unsuccessful immigrants which did not adapt to the new environment. It seems that the whole fauna, inclusive of plant remains, was accumulated by bottom currents in randomly situated depressions on the sea-floor, where carcasses became ideal nucleation sites for concretion genesis. Early diagenesis, which played an important role, resulted in well-preserved ammonite assemblages close to the original biological assemblage. Most of described ammonites (nannolytoceratids, lissoceratids, strigoceratids and leptosphinctids) are reported from the Upper Bajocian epicratonic deposits of Poland for the first time. This makes the concretions a true “taphonomic window” into latest Bajocian census biocenosis. The organic geochemistry results suggest predominance of terrestrial organic matter in both concretions and surrounding clays, with well oxygenated conditions in the sedimentary basin. The large concentrations of Δ 13(17)diasterenes in the analysed carbonate concretions indicates that these compounds must have been formed by contact with clay minerals before formation of the carbonate concretions. The processes described may have followed early stage of diagenesis, but certainly under tens of cm to even a few meters of burial. The high negative δC 13 values in the inner zone of the concretions suggest that concretion growth began in the sulphate reduction zone and may have continued in the methanogenesis zone.

Middle Jurassic (Bajocian and Bathonian) Dinosaur Megatracksites, Bighorn Basin, Wyoming, U.S.A

Abstract Two previously unknown rare Middle Jurassic dinosaur megatracksites are reported from the Bighorn Basin of northern Wyoming in the Western Interior of the United States. These trace fossils occur in carbonate units once thought to be totally marine in origin, and constitute the two most extensive Middle Jurassic dinosaur tracksites currently known in North America. The youngest of these occurs primarily along a single horizon at or near the top of the “basal member” of the “lower” Sundance Formation, is mid-Bathonian in age, and dates to ∼167 ma. This discovery necessitates a major change in the paleogeographic reconstructions for Wyoming for this period. The older tracksites occur at multiple horizons within a 1 m interval in the middle part of the Gypsum Spring Formation. This interval is uppermost Bajocian in age and dates to ∼170 ma. Terrestrial tracks found, to date, have been all bipedal tridactyl dinosaur prints. At least some of these prints can be attributed to theropods. Possible swim t...

Middle Jurassic record of the limnic ostracode genus <i>Rosacythere</i> (Limnocytheridae, Timiriaseviinae): implications on the origin and evolution of the <i>Kovalevskiella</i> group

Abstract. Two species of the limnic ostracode genus Rosacythere Colin (Limnocytheridae, Timiriaseviinae) have been identified in the uppermost Bajocian (Middle Jurassic) of the southern part of the Paris Basin, France. This record is the earliest for this genus and for the ‘Kovalevskiella group’ of Colin & Danielopol (1978 Colin & Danielopol (1980). This study also confirms that most of the Timiriaseviinae morphological groups really started to diversify during the Middle Jurassic.