Early Tithonian Research Articles

The latest Jurassic–earliest Cretaceous climate and oceanographic changes in the Western Tethys: The Transdanubian Range (Hungary) perspective

AbstractThe Jurassic/Cretaceous transition was characterized by several distinct palaeoenvironmental processes and events, amongst which some of the best known are the late Tithonian–early Berriasian aridization and the late Berriasian tectonic reactivation in the Neotethyan Collision Belt. This study aims to reconstruct the latest Jurassic–earliest Cretaceous palaeoenvironment and its evolution in the area of the Transdanubian Range (Hárskút and Lókút successions, Hungary), and provide new data on the relation between climate changes, palaeoceanography and marine ecosystems. Herein, calcareous nannofossil and geochemical data are presented and put into a geochronological framework in order to evaluate and compare palaeoenvironmental signals recorded in the two studied successions; the resultant scenario is compared with published literature data from both the western Tethyan region and northern Europe. Accordingly, in the Transdanubian Range, the relatively humid climate of the early Tithonian was followed by the late Tithonian–early Berriasian arid phase and the late Berriasian humidification. Besides, two intervals of palaeoceanographic perturbations were documented in the upper Tithonian–lowermost Berriasian (OD I), and the lower/upper Berriasian transition beds (OD II); these are manifested by the record of seafloor hypoxia and elevated accumulations of micronutrients, as well as changes in calcareous nannofossil assemblages. In the view of this study, the most probable trigger of the late Tithonian–early Berriasian aridization was a restriction in the atmospheric circulation (including monsoons), which was forced by climate cooling and lowering thermal gradient between landmasses and the ocean. Under such conditions, the mechanism of a wind‐induced water mixing might become less efficient, driving seawater stratification, seafloor hypoxia and increased burial of nutrients. Although the humid climate of the late Berriasian likely resumed the monsoon‐type circulation, the tectonic reactivation and uplift in the NeoTethyan Collision Belt might have effectively separated the Bakony Basin from the ‘open’ NeoTethys, which hampered the marine circulation and efficient water mixing in the former.

Development and chronology of the Late Jurassic shallow-water carbonate deposits of the Holy Cross Mountains area, central Poland

The Late Jurassic shallow-water carbonates with intervening clayey-marly deeper-water deposits in the Holy Cross Mts. area formed over large bank of the elevated part of the Northern Tethyan Shelf during about 12 myr. They comprise three main successions (I, II and III) deposited partly in different environmental conditions, controlled by tectonic and climatic factors, and still preserved in the north-eastern margin, the north-western margin and the south-western margin of the Holy Cross Mountains. The history of sedimentation is presented according to the concept of the large tectono-stratigraphic units COK, LUK and KVB, which owe their origin to variable rates of tectonic subsidence, as introduced by Kutek (1994) for the area of central Poland. The studied deposits of the COK megasequence corresponding to the Upper Oxfordian and the Lower Kimmeridgian up to the Hypselocyclum Zone consist of coral limestones, various grained (including oolitic) limestones, and micritic limestones formed over the gradually enlarging shallow-water carbonate platform of the Holy Cross Mts. This platform was subsequently subdivided into two elevated areas, separated by a depressed zone in the middle, bounded by the Nowe Miasto–Iłża–Bałtów Fault Zone in the north-east and the Holy Cross Fault System in the south. The younger megasequence LUK with it strongly transgressive character marks the successive stages of the marine transgression which entered the central, lowered part of the area of the Holy Cross Mts. from the west, where it appeared already in the early Hypselocyclum Chron. It successively spread across the Holy Cross Mts. area towards the north-east and south bringing everywhere the deposition of various oyster lumachelles and marls with ammonites at the end of the Hypselocyclum Chron and during the Divisum Chron of the Early Kimmeridgian to the Acanthicum/Mutabilis Chron of the earliest Late Kimmeridgian. The following megasequence KVB is represented by the detrital lumachelles and chalky limestones with nereineids of the Eudoxus Chron of the Late Kimmeridgian marking the development of still younger shallow-water carbonate platform in the uplifted areas in the north-eastern and possibly the south-western margins of the mountains, allegedly subdivided by a deeper area of sedimentation of marly deposits. The youngest Late Jurassic deposits of the Holy Cross Mts., are very fragmentarily preserved, mostly because of Early Cretaceous uplift and erosion. They suggest an initial episode of complete drowning of the carbonate platform which became covered by marly deposits during the Early Tithonian, and the subsequent restoration of shallow-water carbonate sedimentation at the end of the Early Tithonian.

Hiatuses and redeposits in the Tithonian-Berriasian transition at Le Chouet (Les Près, La Drôme, SE France): Sedimentological and biostratigraphical implications

Our new study of the Tithonian and lower Berriasian succession of Le Chouet (Les Près, La Drôme, France) better characterizes the lithological succession, the macro- and microfacies, and the stratigraphic ranges of some microfossils mostly calibrated on the calpionellid biozonation. On the lithological side, the Tithonian strata are dominantly characterized by thick-bedded breccias representing debris flows and related calciturbidites whereas the Berriasian strata are typically white limestones that also comprises scattered intercalations of thin-bedded breccias and calciturbitides (including cryptic mud calciturbidites). In thin sections, these white limestones display mud- to wackestone textures and their allochems are mostly tiny bioclasts (e.g., radiolarians, calpionellids, saccocomids). Breccias are lithoclastic rudstones and/or floatstones with a matrix similar to the calciturbidites. Their lithoclasts are either extraclasts sensu stricto (i.e., material derived from updip shallow-water areas) or pseudointraclasts, representing reworked subautochthonous material (i.e., mud- and wackestone lithoclasts with radiolarians, saccocomids and/or calpionellids). In addition to the erosional features observed at the bases of the gravity flows, these pseudointraclasts document the intensity of submarine erosion. Locally they help to estimate the depths of erosion updip of the deposit. A number of bioclasts are reworked from updip shallow-water areas; among them, it is worth mentioning the foraminifer Protopeneroplis ultragranulata (Gorbatchik), the first occurrence of which is dated to late early Tithonian. Saccocomids are part of the dominating pelagic biota reported from the lower and lower upper Tithonian interval whereas calpionellids replace them in the uppermost Tithonian to lower Berriasian interval. Intervals with saccocomids characteristic of zones 4-5 and zones 6-7 are respectively ascribed here to the lower Tithonian (4-5) and pro parte to the upper Tithonian (6-7). The biozonation of the calpionellid group sensu lato allows identification of the Boneti Subzone of the chitinoidellids, the Crassicollaria Zone with its four subzones (A0-A3), and the Alpina Zone with its first subzone (B1). On the basis of biostratigraphical and sedimentological data (including the rates of sedimentation), most zonal boundaries are located at the erosional bases of breccia or turbidite layers and thus coincide with hiatuses.

Finding a VOICE in the Southern Hemisphere: A new record of global organic carbon?

Variations in the carbon isotopic composition of carbonate and organic carbon (δ13Ccarb and δ13Corg) are generally used to record perturbations in the global carbon cycle, which are in turn closely linked to changes in climate. However, because of climate gradients on Earth, assignment of the “global” signal in ancient records is not straightforward. Here, we report the δ13C values of organic material in the Upper Jurassic to Lower Cretaceous sedimentary record of the Vaca Muerta Formation, situated in the Neuquén Basin, Argentina, which show similar patterns to those observed in several northern latitude basins. This record of δ13C values in the organic material differs from those measured in the early Atlantic Ocean, a record previously considered to be representative of the global values of organic carbon. As a result of the global synchronicity observed in the δ13C values of organic material from both northern and southern latitudes, we suggest that these patterns may represent the global record of δ13C values in organic material rather than those measured in the proto−Atlantic Ocean. The δ13C values of the organic components show a slight initial decrease of ∼2‰ in the early Tithonian (149−145 Ma) and then another decrease of ∼2‰ before reaching a minimum of −30.29‰ in the late Tithonian (145−143 Ma), followed by a gradual increasing trend throughout the Berriasian (143.1−137.7 Ma). The early Valanginian (137.7−135.5 Ma) was marked by a more substantial increase in δ13C values up to −23.46‰. These changes mirror those seen in Northern Hemisphere locations during the Late Jurassic and Early Cretaceous, where this perturbation has been termed the Volgian isotopic carbon excursion (VOICE). This difference in the Late Jurassic and Early Cretaceous δ13C values between the early Atlantic Ocean and the Neuquén Basin is interpreted to be the result of the climate gradient at the time, which was characterized by more humid conditions in high latitudes compared to dry conditions in the Atlantic Ocean basin.

Tough to digest: first record of Teleosauroidea (Thalattosuchia) in a regurgitalite from the Upper Jurassic of north‐eastern Italy

AbstractPostcranial remains of a small teleosauroid from the Upper Jurassic of north‐eastern Italy are described in detail. The specimen, discovered in 1980 on a slab of Rosso Ammonitico Veronese (RAV Fm.; Bajocian–Tithonian), is represented by partially articulated thoracic, sacral and anterior caudal vertebrae, fractured and displaced osteoderms and pelvic girdle elements. Additional bone elements overlap one another in a densely packed cluster. The peculiar arrangement of this specimen is here interpreted as the result of regurgitation of the animal carcass from a pelagic predator or scavenger. Microstructural and geochemical evidence from bone and surrounding matrix support this hypothesis. A dearth of phosphorus in the matrix near the bone mass corroborates the interpretation of the specimen as a regurgitalite rather than a coprolite. Calcareous nannofossil and stratigraphic data allow us to assign the fossil to the latest Kimmeridgian or earliest Tithonian. The specimen is here tentatively referred to the teleosauroid subfamily Aeolodontinae based on the alternating pattern of the osteoderm ornamentation; this attribution is supported by stratigraphical and palaeoenvironmental evidence. If confirmed, this represents the first occurrence of Aeolodontinae in Italian outcrops of the western Tethys margin and represents the first marine crocodylomorph described as a bromalite.

Negative δ13Ccarb values at the Jurassic-Cretaceous boundary – Vaca Muerta Formation, Neuquén Basin, Argentina

The stable carbon isotopic compositions of carbonate sediments (δ13Ccarb) have been widely used to reconstruct the global carbon cycle and as a stratigraphic correlation tool. This work investigates a δ13Ccarb record of marine organic-rich, mixed siliciclastic‐carbonate mudstones accumulated from the Tithonian (late Jurassic) to the early Valanginian (early Cretaceous) in a retro-arc basin connected to the Proto-Pacific Ocean (Neuquén Basin, Argentina). The high-resolution record of δ13Ccarb values of these strata from outcrops at various locations in the basin differ from those in the coeval pelagic strata of the Tethys. The δ13Ccarb profile in the Puerta Curaco area shows an overall increasing trend from average values of −7‰ (early Tithonian) to approximately 0‰ (early Valanginian). The negative δ13Ccarb values occur in a ~ 400 m thick TOC-rich succession (TOC > 2%) and are arranged in 3 large-scale increasing-decreasing cycles. Although absolute values are offset, main trends are similar in other outcrops and in subsurface wells. The co-occurrence of the highest U/Th (>1.4) and the most negative δ13Ccarb values suggests that the major trends in the δ13Ccarb profile might be modulated by oscillations in oxygen content within the basin probably driven by sea-level changes. Clastic-dominated transgressive hemicycles have higher TOC and more negative δ13Ccarb values while the opposite occurs in carbonate-rich regressive hemicycles. A trend from “normal” Tithonian surface-water values (avg. +2‰) in the southern shelf to increasingly negative δ13Ccarb values towards the basin center indicates a mixing between platform-derived carbonate material unaffected by diagenesis and carbonate precipitated or altered in a dysoxic/anoxic basin. The δ13Ccarb profile in the Tethyan realm does not record this episode of high burial of organic carbon occurred in the Neuquén basin during the Tithonian and Berriasian but display a slightly decreasing trend between +2.5 and +1.5‰.

Environmental changes across the Jurassic–Cretaceous boundary in the western proto-Gulf of Mexico — Chemo- and biostratigraphic correlation of NE Mexican sections

Late Jurassic–earliest Cretaceous (Kimmeridgian–earliest Berriasian) marine shelf sediments in northeastern Mexico reveal repeated temperature-related oceanic and biotic turnovers in the northwestern proto-Gulf of Mexico. Our detailed geochemical analysis of four sections crossing the Jurassic-Cretaceous (J/K) boundary is based on chemostratigraphic correlation and repeated mollusk assemblage changes reflecting significant environmental fluctuations, including sea level and marine redox conditions. The present study confirms tectonic tilting and rapid drowning of shallow-water environments in the early Kimmeridgian, associated with the near-synchronous spread of bottom-water anoxia in shelf areas bordering the proto-Gulf of Mexico. Boreal cold-water faunal elements are associated with a sea-level drop in the late Kimmeridgian, while a transient transgressive-regressive phase is interpreted for the shelf transect in the earliest Tithonian. A general transgressional trend is reported for the Tithonian and across the J/K boundary, while the migration into the area of boreal and austral high-latitude faunal elements marks specific intervals. We hypothesize that oscillations in the oceanic current system were responsible for the intermittent establishment of cold-water boreal and austral faunal assemblages in the northwestern proto-Gulf of Mexico. • Integrated correlation of Jurassic–Cretaceous marine successions in northeastern Mexico. • Significant environmental changes including sea-level and marine redox conditions. • Repeated temperature-related oceanic and biotic turnovers. • Evidence for cold-water indicative belemnites occupying shallow-water habitats. • Diachronous spread of bottom-water anoxia during Early Kimmeridgian transgression.

Magnetostratigraphy and magnetic properties of the Jurassic to Lower Cretaceous Girón Group (northern Andes, Colombia)

AbstractWe report paleomagnetic results from the Jurassic to Lower Cretaceous continental sedimentary succession exposed in the eastern limb of the Los Yariguíes anticlinorium, Eastern Cordillera, Colombia. About 820 m of a stratigraphic section of the upper part of the Girón Group (Angostura del Río Lebrija and Los Santos Formations) was sampled to construct a magnetic polarity stratigraphy. A total of 199 independent samples that yield interpretable and acceptable data have a characteristic remanent magnetization component (ChRM) isolated between 400 °C and 680 °C in progressive thermal demagnetization. Demagnetization behavior and rock magnetic properties are interpreted to indicate that hematite is the principal magnetization carrier with a possible contribution by magnetite in some parts of the section. After tilt correction, 123 samples are of normal polarity (declination [D] = 44.9°, inclination [I] = +9.7°, R = 110.64, k = 9.87, and α95 = 4.3°), and the other 76 accepted samples are of reverse polarity (D = 216.4°, I = −6.1°, R = 68.29, k = 9.72, and α95 = 5.5°). The statistical reversal test conducted on virtual geomagnetic poles is positive (class B). Based on paleontologic age estimates for the Cumbre and Rosablanca Formations, we assume a Berriasian age for the Los Santos Formation. The magnetostratigraphic data from the Girón Group strata are interpreted to suggest an age for the sampled part of the section between early Kimmeridgian and early Valanginian (ca. 157–139 Ma). The age of the Angostura del Río Lebrija Formation is estimated as between early Kimmeridgian and early Tithonian (ca. 157–146.5 Ma). The age of the Los Santos Formation is estimated between early Tithonian and early Valanginian (146.5–139.3 Ma). With our proposed, but nonunique, correlation with the Geomagnetic Polarity Time Scale, the Jurassic-Cretaceous boundary is interpreted to be located within the Los Santos Formation. The Girón Group is characterized by two periods of high (>8 cm/k.y.) and two periods of low (< 2 cm/k.y.) sedimentation rates. An inferred clockwise rotation of ∼44°, based on paleomagnetic declination data from the Girón Group, is similar to rotation estimates reported in some previous studies in the general area, and this facet of deformation could be related to local and regional response to displacement along regional-scale strike-slip faults.

Kimmeridgian and early Tithonian cephalopods from the Kisújbánya Limestone Formation, Zengővárkony (Mecsek Mountains, southern Hungary), their faunal composition, palaeobiogeographic affinities, and taphonomic character

A new collection at Zengővárkony (Mecsek Mountains, Hungary) provided a rich and diverse but poorly preserved cephalopod-dominated fossil assemblage representing the Kimmeridgian and the lower Tithonian. The material came from mixed scree, soil, and amongst roots affected by weathering processes having been exposed to the elements for a long time. The nautiloid Pseudaganides strambergensis is the first record from the Mecsek Mountains. Due to the weathering, the ammonite fauna consists of mainly fragmentary and dissolved individuals that comprises 528 specimens belonging to 34 species and 30 genera out of which 20 species and 15 genera are reported for the first time from the Mecsek Mountains. The fauna includes specimens of known taxa. No new taxa are introduced. Based on the comparison with other faunas, this assemblage most closely resembles the fauna of the Venetian Alps (Italy). Additional faunal elements include aptychi (Laevaptychus latus, Lamellaptychus murocostatus), belemnites (Hibolithes semisulcatus), and an indetermined brachiopod. The first record of Spiraserpula spirolinites, an encrusting fossil polychaete preserved on the internal mould of a Taramelliceras shell fragment indicates favourable bottom conditions for the epifauna. The presence of Aspidoceras caletanum, Gravesia aff. gigas, and Pseudowaagenia inerme indicates faunal connections with the Submediterranean Province of the Tethys, which is in line with the tectonic and palaeogeographical position of the Mecsek Zone during the Late Jurassic. The ammonite assemblage represents elements of five Tethysian ammonite zones of the Kimmeridgian and Tithonian. The lower Kimmeridgian Herbichi Zone is indicated by Streblites tenuilobatus and Praesimoceras herbichi. The upper Kimmeridgian Acanthicum Zone is indicated by Aspidoceras acanthicum, and the Cavouri Zone by Mesosimoceras cavouri and Aspidoceras caletanum. The upper Kimmeridgian Beckeri Zone is suggested by Hybonoticeras pressulum and Pseudowaagenia inerme. Whereas Gravesia aff. gigas, Lithacoceras aff. siliceum, and Malagasites? denseplicatus are faunal elements characterising the Early Tithonian Hybonotum Zone. Phylloceratid and lytoceratid specimens account only for 12% of the fauna, while the majority of the specimens belong to the Oppeliidae and Ataxioceratidae (60%).

The Vaca Muerta transgression (Upper Jurassic), Neuquén Basin, Argentina: Insights into the evolution and timing of aeolian–marine transitions

AbstractConsidering the evolution of aeolian to marine transitions for the geological record, either catastrophic or gradual transgressive scenarios showing high or low rates of coastal migration have been proposed. A critical evaluation of modern analogues suggests that a catastrophic transgression shares many characteristics with Holocene transgressions, yet they are caused by different rates of sea‐level rise. The present study provides insights into the evolution of aeolian to marine transitions in order to discuss these alternative scenarios of sea‐level rise. For this purpose, a sedimentological and ichnological analysis was carried out on ten stratigraphic sections of the Picún Leufú area, Argentina. There, marine deposits of the Vaca Muerta Formation accumulated over the aeolian deposits of the Quebrada del Sapo Formation during the early Tithonian. The sedimentary evolution of the transition can be summarized in: (i) a shutdown of aeolian dune field deposition, generating a planation surface in somewhat elevated areas and reworked megadunes in lowlands; (ii) beach sedimentation caused by episodic marine flooding that contributed to megadune reworking; and (iii) deposition in an embayed marginal‐marine setting at the coast, recorded by bay margin bindstone, proximal bay and distal bay sedimentation. This transition indicates very rapid coastline migration and a condensed Transgressive Systems Tract succession throughout the study area. Rates of sea‐level rise similar to Holocene ones (millimetres to centimetres per year) may have produced the transition between the Quebrada del Sapo and Vaca Muerta formations. The Late Jurassic represents a non‐glacial time, and the global sea‐level maximum highstand pre‐dated the Vaca Muerta transgressive event. Thus, part of the sea‐level rise has to be attributed to tectonic/thermal subsidence and compaction of underlying strata, which may have generated these atypical rapid rates of sea‐level rise.

Ophiolite derived material as parent rocks for Late Jurassic bauxite: evidence for Tithonian unroofing in the Northern Calcareous Alps (Eastern Alps, Austria)

In shallow-water limestones of the Plassen Formation in the Tirolic nappe of the Northern Calcareous Alps, bauxite was formed on karstified and tilted platform margin grainstones to boundstones around the ?Kimmeridgian/Tithonian boundary, or in the Early Tithonian as proven by Protopeneroplis striata Weynschenk, Labyrinthina mirabilis Weynschenk, and Salpingoporella pygmaea Gümbel. The platform established on top of the obducted ophiolite nappe stack. The onset of unroofing at the Kimmeridgian/Tithonian boundary exposed ophiolites to weathering, forming laterites, and bauxites. The weathered ophiolitic material was shed on the tilted, emerged, and karstified platform, where the bauxite accumulated. Continued subsidence led to flooding, and a Tithonian transgressive carbonate sequence sealed the bauxites. XRD analysis of the bauxite yields a composition of mainly boehmite with hematite and some berthierine, kaolinite, and chromite. SEM analysis verified magnetite, hematite, rutile, chromite, zircon, ferropseudobrookite, ilmenite, monazite, xenotime, and garnet distributed in pisoids and within the matrix. The pisoids reach a millimeter in size and partly show cores of older, larger pisoids. The composition of the chromites indicates an ophiolitic origin. Geochemical examination using major- and trace elements points to a mafic andesitic to basaltic parent material contaminated with highly fractionated rocks from an island arc. Formation of Early Tithonian bauxites in shallow-water limestones confirms Middle to Early Late Jurassic ophiolite obduction. This was followed by uplift and unroofing of the orogen from the Kimmeridgian/Tithonian boundary onwards after a period of relative tectonic quiescence with an onset of carbonate platforms during the Kimmeridgian on top of the nappe stack and the obducted Neo-Tethys ophiolites.

Upper Kimmeridgian to Lower Tithonian foraminifers and ostracods of the Boulonnais region, Northern France. Stratigraphic and palaeoenvironmental implications and inter-regional correlations with the Siberian arctic

The well-exposed Upper Kimmeridgian to Lower Tithonian sequences of the Boulonnais Region (Northern France) are revisited with an integrated litho-, bio- and chemostratigraphic study of the Cran du Noirda (CDN) and Pointe de la Crèche (PDC) sections. Three foraminiferal and two ostracods zones are identified and tied to the ammonite zones previously established in the Boulonnais. The Upper Kimmeridgian Pseudolamarckina pseudorjasanensis foraminifera Zone is of particular interest, as we establish that it may be recognized in very distant regions throughout the Subboreal, Boreal, and Arctic provinces. The comprehensive analysis of the TOC content and Rock Eval pyrolysis allows to underline the deposition of a Lower Tithonian Organic-Rich Interval (ORI) associated with the scitulus (p.p.), wheatleyensis ammonite zones. Furthermore, the palaeoecological analysis of the identified foraminiferal assemblages suggests the occurrence of four dysoxic events during the Late Kimmeridgian to Early Tithonian. Foraminiferal assemblages with genera adapted to low-oxygen conditions are present in intervals with high values of δ13CTOC. During the Late Kimmeridgian to Early Tithonian, organic-rich deposits are widespread across the Western European Archipelago and the Laurasian Seaway. The establishment of hypoxic conditions above the sea-floor was favoured by high marine productivity and stratification of the water column. Conversely, periods of low relative sea-level resulted in the redeposition of sediments from the margins into the basin, while water depth was insufficient to allow the development of reduced conditions.

Morphology and anatomy of the Late Jurassic Mayrocaris bucculata (Eucrustacea?, Thylacocephala) with comments on the tagmosis of Thylacocephala

Known from at least the Silurian (c. 435 Ma) up to the Late Cretaceous (c. 85 Ma), thylacocephalans are among the most intriguing fossil euarthropods. They are characterized by a prominent shield enveloping most of the body, hypertrophied compound eyes, three pairs of large, raptorial appendages and a trunk with 8–22 stout segments bearing appendages. Despite this knowledge of their anatomy, the phylogenetic affinities of Thylacocephala are controversial due to a lack of knowledge on their body organization and tagmosis. This study focuses on Mayrocaris bucculata Polz, 1994 from the Solnhofen Lagerstätte, Germany (c. 150 Ma, early Tithonian, Jurassic). We document new specimens of Mayrocaris bucculata from the Solnhofener Plattenkalke sensu lato and provide new descriptions for previously reported specimens. We demonstrate that the raptorial appendages of Thylacocephala are most probably maxillulae, maxillae and maxillipeds. Additionally, we report new details on the posterior trunk appendages, including the description of a paddle-like proximal part and of a rod-like distal part, but also of a specialized terminal trunk appendage. These new findings, in addition to the reinterpretation of a cephalic appendage of Clausocaris lithographica as a possible mandible, are essential for a better understanding of the body organization in thylacocephalans and their phylogenetic affinities within Eucrustacea.

A new species of Cricosaurus (Thalattosuchia: Crocodylomorpha) from southern Germany: the first three-dimensionally preserved Cricosaurus skull from the Solnhofen Archipelago

Cricosaurus represents one of the most important radiations within Metriorhynchidae, a specialized marine clade of Crocodylomorpha that flourished in marine environments from the Middle Jurassic until the Early Cretaceous. Here, we describe a new species of Cricosaurus, Cricosaurus rauhuti sp. nov., from the Mörnsheim Formation (lower Tithonian) of southern Germany. The specimen is the first three-dimensionally preserved Cricosaurus from this realm, and it is represented by a partially preserved cranium and lower jaw that has autapomorphic characters that distinguish it from any other species of Cricosaurus. The phylogenetic analysis shows that the new species is more closely related to some non-European forms from the Late Jurassic and one taxon from the Valanginian of Germany (all 3D-preserved) than to other Late Jurassic Cricosaurus from southern Germany (all 2D-preserved). Our exploratory analyses confirm that this is not a preservation bias. For the first time, this shows that there are two clades of Cricosaurus present during the Late Jurassic in Germany. Furthermore, it provides additional evidence of a close faunal relationship between Europe and South America in the Late Jurassic, as also evidenced by the fossil record of other marine reptiles. Finally, the distribution of metriorhynchids in localities of the Solnhofen Archipelago suggests a change in the taxic diversity of the region during the early Tithonian, which might be the result of environmental changes in the Solnhofen Archipelago. http://zoobank.org/urn:lsid:zoobank.org:pub:488705BF-AEAD-4F02-BB4E-429E3117BCD1

Failed prey or peculiar necrolysis? Isolated ammonite soft body from the Late Jurassic of Eichst\xe4tt (Germany) with complete digestive tract and male reproductive organs

Ammonoid soft parts have been rarely described. Here, we document the soft parts of a perisphinctid ammonite from the early Tithonian of Wintershof near Eichstätt (Germany). This exceptional preservation was enabled by the special depositional conditions in the marine basins of the Solnhofen Archipelago. Here, we document this find and attempt to homologize its parts with various organs such as the digestive tract, reproductive organs, the mantle cavity with gills, and the hyponome, with differing degrees of reservation. Alternative interpretations are also taken into account. We suggest that the soft parts were separated from the conch either taphonomically (following necrolytical processes affecting the attachment structures) or during a failed predation, where a predator (fish or coleoid) removed the soft parts from the conch but then dropped them. This find is interesting because it adds to the knowledge of ammonite anatomy, which is normally hidden in the conch. The reproductive organs show traces of what might have been spermatophores, thus supporting the hypothesis that the microconchs represented the males.

Late Jurassic temperatures for the southern Tethyan margin based on belemnites δ18O from the Ouarsenis Mountains, northwestern Algeria

This study presents the first record of stable carbon and oxygen isotopes of well-preserved belemnites and bulk sediment from the Upper Jurassic pelagic carbonates of the Ouarsenis Mountains (northwestern Algeria), which were deposited at the southern margin of the Tethys ocean. Cathodoluminescence and scanning electron microscopy was used to eliminate potentially diagenetically altered specimens (brachiopods, aptychi, and some belemnites). Ultimately, 55 belemnite specimens were used to reconstruct water temperatures for the Middle Oxfordian to the Early Tithonian. Their δ18Ocarb values ranged from −0.35‰ to −3.88‰, suggesting warm and mostly stable temperature conditions during the Late Jurassic. Using a δ18Osea value of 0‰ for the tropical palaeolatitude of 15–20°N, the δ18Ocarb values of the well-preserved belemnite rostra translate into average temperatures of 27.8 °C in the Middle Oxfordian (Gregoryceras transversarium Zone), 27.0 to 27.5 °C in the Late Oxfordian (Epipeltoceras bimmamatum and Idoceras planula zones, respectively), 26.2 °C in the Early Kimmeridgian, and 27.3 °C in the Early Tithonian (Hybonoticeras hybonotum Zone).

Mineralogy and geochemistry of deeply-buried marine sediments of the Vaca Muerta-Quintuco system in the Neuquén Basin (Chacay Melehue section), Argentina: Paleoclimatic and paleoenvironmental implications for the global Tithonian-Valanginian reconstructions

The Vaca Muerta-Quintuco (VM-Q) system of Tithonian-early Valanginian age was studied in the Chacay Melehue section of the Neuquén Basin (western Argentina) by means of sedimentological, mineralogical and geochemical analyses in order to determine the main driving factors that triggered the paleoenvironmental change from a carbonate ramp (Vaca Muerta Formation, VMFm) to a mixed siliciclastic/carbonatic marine environment (Quintuco Formation, QFm). The VMFm was divided into two stratigraphic intervals: Lower VMFm (LVMFm) and Upper VMFm (UVMFm), whereas the QFm is subdivided into the Puesto Barros Member (PBMb) and the Cerro La Visera Member (CVMb), which can be correlated to other sections in the basin (e.g., Puerta Curaco). Isolated, turbiditic sandstone beds, correlated to the Huncal Member, are included in the QFm.The LVMFm (Tithonian) and the UVMFm (Berriasian) are constituted by dark, well-laminated marls, mudstones, calcite concretions and tuffs. The PBMb (earlier early Valanginian) is constituted by marls and sandstones, whereas the CVMb (later early Valanginian) is constituted by marls, mudstones, siltstones, sandstones and coquinas. The LVMFm (Total organic carbon, TOC ~ 1–4 wt%) is characterized by the enrichment of redox sensitive trace elements (RSTE), where the enrichment of Ni and Cu suggest high productivity in the water column, and the enrichment of Mo, U, V points to sea bottom anoxia, with periods of increased oxygenation as deduced from higher P concentrations in marls and mudstones. The clay mineral association is constituted by mixed-layer illite/smectite formed by the transformation of smectitic layers. The predominance of smectite in coeval sucessions, less overprinted by burial diagenesis, suggests a temperate and semi-arid climate in the adjacent continent. The UVMFm (TOC ~ >1 wt%) is characterized by a gradual decrease of the RSTE pointing to a decrease in productivity and a slight increase in the oxygenation of the sea bottom. In addition, a change towards more humid conditions in the continent is inferred by both the increase in the Chemical Index of Alteration and the Al2O3/TiO2 ratio. The PBMb (TOC ~1 wt%) has even lower content of RSTE indicating diminished sea water productivity and a gradual rise of the oxygenation of the sea bottom. In this interval, increased illite contents suggest periods of enhanced physical weathering, probably related to the tectonic uplift of the Huincul Ridge. The RSTE in the CVMb (TOC <1 wt%) documents a fully oxygenated sea bottom, where the productivity of the water column was negligible. The presence of kaolinite and the increment of the detrital sedimentation in the CVMb indicate a change towards more humid conditions in the hinterlands. The enhanced runoff caused by this paleoclimatic change towards more humid conditions that started in the early Berriasian and increased during the later early Valanginian triggered the change from carbonate ramp to mixed siliciclastic/carbonatic to siliciclastic marine paleoenvironments. The organic carbon isotope composition (δ13Corg vs. VPDB) of the VMFm ranges between −30.0 and −23.4‰, whereas in the QFm values range between −29.0 and −23.9‰. Two positive carbon isotope excursions (PCIE) are recorded in the system: PCIE-A in the lower part of the VMFm (early Tithonian) with δ13Corg values ~ −25‰, and PCIE-B in the upper part of the QFm (later early Valanginian) with δ13Corg values ~ −24.5‰. The shift in δ13Corg at PCIE-B is up to +4.2‰ and marks the onset of the Weissert Event. This is the first time that the onset of this event is recorded in the Neuquén Basin, within the Lissonia riveroi ammonite zone. The results of our study confirm that clay mineralogy, trace elements and stable isotopes are valuable proxies of past ocean-climate variability even in sediment deposits that underwent near-surface and deep burial diagenesis.

A new ophthalmosaurid ichthyosaur from the Upper Jurassic (Early Tithonian) Kimmeridge Clay of Dorset, UK, with implications for Late Jurassic ichthyosaur diversity.

A new ophthalmosaurid ichthyosaur, Thalassodraco etchesi gen. et sp. nov., from the Upper Jurassic Kimmeridge Clay Formation of Dorset, UK is described. The specimen, a partial, articulated skull and anterior thorax in the Etches Collection of Kimmeridge, Dorset, is exceptionally well preserved on a slab of laminated coccolith limestone and has been expertly prepared. It comprises a near complete skull in articulation with associated anterior vertebral column and dorsal ribs, complete pectoral girdle, fully exposed left forelimb, and some elements of the right forelimb. Other elements present, including an ischiopubis are preserved on separate slabs. Presumed rapid burial of the anterior portion of the specimen in the coccolith substrate has preserved a number of ossified ligaments lying across the vertebral column and associated ribs as well as stomach contents and decayed internal organs. Aspects of the dentition, skull roof bones and the forelimb configuration distinguishes the new specimen from previously described Late Jurassic ichthyosaurs. Autopmorphies for T. etchesi include a large rounded protuberance on the supratemporal bone; a thin L-shaped lachrymal, with a steeply curved posterior border; ~ 70 teeth on the upper tooth row, and deep anterior dorsal ribs. A well resolved phylogenetic analysis shows T. etchesi as a member of a basal clade within Ophthalmosauridae comprising Nannopterygius, Gengasaurus, Paraophthalmosaurus and Thalassodraco. The new specimen adds to the diversity of the Ichthyopterygia of the Kimmeridge Clay Formation and emphasises the important contribution of amateur collectors in palaeontology.

A late Jurassic carbon-isotope record from the Qiangtang Basin (Tibet), eastern Tethys, and its palaeoceanographic implications

An Upper Jurassic succession of deep-marine limestones, marls and claystones preserved in the Ambo section of the Qiangtang Basin (Tibet) contains information concerning the response of the eastern Tethys Ocean to multiple carbon cycle perturbations and to palaeoceanographic changes. Three positive δ 13 C excursions (P-CIE 1–3), dated as latest Callovian, middle Oxfordian and early Late Kimmeridgian, respectively, are observed in our section and related to high organic carbon burial episodes; they are correlatable with profiles from the Atlantic, western Tethys and western Paleo-Pacific regions. A significant decrease in δ 13 C values in our section in late Oxfordian to early Kimmeridgian times is attributed to the onset of upwelling of 13 C-depleted watermasses caused by the opening of new seaways during the progressive collapse of Pangaea. A fourth positive δ 13 C excursions (P-CIE 4), dated as Late Kimmeridgian-Early Tithonian, is unlikely to be due to accelerated burial of organic carbon, but may be associated with the establishment of a stable low-latitude thermohaline circulation that replaced the upwelling zones. Due to the oceanic changes linked to the breakup of Pangaea, incursions of cold Arctic waters and associated changes in water mass density triggered a collapse in thermohaline circulation in the Tethys Ocean during the middle Early Tithonian (ca. ~151–150 Ma). As a consequence, an upwelling cold bottom current was formed, triggering global cooling and a significant reduction in the δ 13 C values. This study is the first to show continuous carbon isotope profiles for the eastern Tethys Ocean, and provides an inter-regional correlation and new paleoceanographic information. • The first high-resolution carbon isotope record of the Upper Jurassic from the Tibet, eastern Tethys. • Remarkable P-CIEs during the earliest Tithonian are associated with the major reorganization of Tethys oceanography. • A collapse in thermohaline circulation likely occurred in the middle Early Tithonian.

Jurassic – Cretaceous boundary record in Carpathian sedimentary sequences

An integrated study of micro- and nannoplankton distribution, O and C isotopes and palaeomagnetic record of nine Carpathian sections provided a key interpretation tool to characterize the Jurassic–Cretaceous (J/K) boundary transition. Biostratigraphy supported by saccocomids, radiolarians, calpionellids, dinoflagellates and nannofossils helped to distinguish biostratigraphic zones which could have been correlated both with stable isotopes and with magnetostratigraphy. The Alpina Event (lorica size change) accompanied by Nannoconus wintereri and N. steinmannii minor FO's designates the J/K boundary.Sedimentary model in N Mediterranean Tethys margin consists of elevated blocks with slow (1–2 mm/ka) Rosso Ammonitico carbonate sedimentation separated by dysoxic depressions. Tectonic instability has been indicated by Upper Jurassic fluxoturbidites.Late early Tithonian (M21n to M20r) saccocomid abundance increases with positive δ18O isotope ratios, similar excursion between M20n and M19r accompanied late Tithonian crassicollarian boom. The δ13C variation (>0.2‰) confronted with microplankton quantity variations: positive excursion occurred both during early Tithonian Saccocoma sp., and during late Tithonian calpionellid and nannoconid blooms. Higher up in the Berriasian “Maiolica” sequence, lighter δ13C values prevailed.During late Tithonian (Praetintinnopsella-to earliest Crassicollaria zones; M20n1n to M19r), Saccocoma microfacies has been substituted by a calpionellid one. Reorganization of Tethyan oceanic currents during opening of the Hispanic corridor started planktonic carbonate particle „rain“ resulting in the Maiolica facies dominance. Sedimentary rate raised ten times. Calpionella alpina lorica size change event was synchronneous with FO's of Nannoconus wintereri and N. steinmannii minor and with negative δ18O trend of latest Tithonian (Colomi Subzone) warming. Expressiveness of eccentricity and obliquity cycles indicates climatic optimum conditions.