The Jurassic (∼201-145 Myr ago) was long considered a warm 'greenhouse' period; more recently cool, even 'icehouse' episodes have been postulated. However, the mechanisms governing transition between ...so-called Warm Modes and Cool Modes are poorly known. Here we present a new large high-quality oxygen-isotope dataset from an interval that includes previously suggested mode transitions. Our results show an especially abrupt earliest Middle Jurassic (∼174 Ma) mid-latitude cooling of seawater by as much as 10 °C in the north-south Laurasian Seaway, a marine passage that connected the equatorial Tethys Ocean to the Boreal Sea. Coincidence in timing with large-scale regional lithospheric updoming of the North Sea region is striking, and we hypothesize that northward oceanic heat transport was impeded by uplift, triggering Cool Mode conditions more widely. This extreme climate-mode transition provides a counter-example to other Mesozoic transitions linked to quantitative change in atmospheric greenhouse gas content.
Konservat-Lagerstätten-deposits with exceptionally preserved fossils-vary in abundance across geographic and stratigraphic space due to paleoenvironmental heterogeneity. While oceanic anoxic events ...(OAEs) may have promoted preservation of marine lagerstätten, the environmental controls on their taphonomy remain unclear. Here, we provide new data on the mineralization of fossils in three Lower Jurassic Lagerstätten-Strawberry Bank (UK), Ya Ha Tinda (Canada), and Posidonia Shale (Germany) -and test the hypothesis that they were preserved under similar conditions. Biostratigraphy indicates that all three Lagerstätten were deposited during the Toarcian OAE (TOAE), and scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) show that each deposit contains a variety of taxa preserved as phosphatized skeletons and tissues. Thus, despite their geographic and paleoenvironmental differences, all of these Lagerstätten were deposited in settings conducive to phosphatization, indicating that the TOAE fostered exceptional preservation in marine settings around the world. Phosphatization may have been fueled by phosphate delivery from climatically-driven sea level change and continental weathering, with anoxic basins acting as phosphorus traps.
Exceptional fossil preservation is required to conserve soft-bodied fossils and even more so to conserve their behaviour. Here, we describe a fossil of a co-occurrence of representatives of two ...different octobrachian coleoid species. The fossils are from the Toarcian Posidonienschiefer of Ohmden near Holzmaden, Germany. The two animals died in the act of predation, i.e. one had caught the other and had begun to nibble on it, when they possibly sank into hypoxic waters and suffocated (distraction sinking). This supports the idea that primitive vampyromorphs pursued diverse feeding strategies and were not yet adapted to being opportunistic feeders in oxygen minimum zones like their modern relative
Vampyroteuthis
.
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.
Impact ejecta formation and emplacement is of great importance when it comes to understanding the process of impact cratering and consequences of impact events in general. Here we present a ...multidisciplinary investigation of a distal impact ejecta layer, the Blockhorizont, that occurs near Bernhardzell in eastern Switzerland. We provide unambiguous evidence that this layer is impact-related by confirming the presence of shocked quartz grains exhibiting multiple sets of planar deformation features. Average shock pressures recorded by the quartz grains are ~ 19 GPa for the investigated sample. U-Pb dating of zircon grains from bentonites in close stratigraphic context allows us to constrain the depositional age of the Blockhorizont to ~ 14.8 Ma. This age, in combination with geochemical and paleontological analysis of ejecta particles, is consistent with deposition of this material as distal impact ejecta from the Ries impact structure, located ~ 180 km away, in Germany. Our observations are important for constraining models of impact ejecta emplacement as ballistically and non-ballistically transported fragments, derived from vastly different depths in the pre-impact target, occur together within the ejecta layer. These observations make the Ries ejecta one of the most completely preserved ejecta deposit on Earth for an impact structure of that size.
The contribution records and illustrates one new and nine other nautiloid species from six sections of southern Poland (Wysoka, Zalas, Ogrodzieniec, Przybynów, Rzędkowice and Żarki) spanning in age ...from the early Callovian to the late Oxfordian (Middle to Late Jurassic). This contribution also provides the first precise age-constrained record of nautiloid occurrences based on co-occurring ammonites, and refines the biostratigraphy of the six studied sections from southern Poland. Based on the ammonite data, the study sections are assigned to the lower Callovian Koenigi Zone (Zalas and Wysoka), lower Oxfordian Cordatum Subzone, Cordatum Zone (Ogrodzieniec and Przybynów) and upper Oxfordian Stenocycloides Subzone, Bifurcatus Zone (Rzędkowice and Żarki). A new species, Cenoceras
polonicum sp. nov. (Wysoka) is reported from Poland, along with the first records of Eutrephoceras rotundum (Crick) (Zalas), Paracymatoceras cf. mondegoense Tintant (Wysoka), Pseudaganides helveticus Loesch (Ogrodzieniec) and with better stratigraphy of Xenocheilus krenkeli (Loesch) (Ogrodzieniec and Żarki), Pseudaganides aganiticus (Schlotheim) (Ogrodzieniec), P. aff. aganiticus (Schlotheim) (Przybynów and Rzędkowice), Pseudaganides sp. (Żarki), 'Paracenoceras' calloviense (Oppel) and Paracenoceras blakei Jeannet (Zalas). New middle Bathonian occurrence of 'P'. calloviense (Oppel) associated with Micromphalites (Clydomphalites) clydocromphalus Arkell is also reported from Kachchh (western India).
Konservat-Lagerstätten—deposits with exceptionally preserved fossils of articulated multi-element skeletons and soft tissues—offer the most complete snapshots of ancient organisms and communities in ...the geological record. One classic example, the Posidonia Shale in southwestern Germany, contains a diverse array of fossils preserved during the ∼183 Ma Toarcian Oceanic Anoxic Event. Seminal work on this deposit led to the hypothesis that many Konservat-Lagerstätten were preserved in stagnant basins, where anoxic conditions limited soft tissue degradation. To date, however, no studies have thoroughly investigated the geomicrobiological processes that drove fossil mineralization in the Posidonia Shale. As a result, the role of anoxia in its exceptional preservation remains uncertain. Here, we address these issues by reviewing the geology of the Posidonia Shale; describing the mineralization of its fossils; and synthesizing novel and existing data to develop a new model for the paleoenvironment and taphonomy of the Lagerstätte. Although shells and carbonate skeletal elements were preserved as pyritized and carbonaceous fossils, non-biomineralized tissues were primarily preserved via phosphatization (transformation of remains into calcium phosphate minerals). Unambiguous examples of phosphatization include ammonite shells, crustacean carapaces, ichthyosaur remains, coprolites, and coleoid gladii, mantle tissues, and ink sacs. Phosphatized crustaceans and coleoids contain cracks filled with pyrite, sphalerite, and aluminosilicate minerals. Such cracks were likely generated during burial compaction, which fractured phosphatized tissues, exposed their organic matter to focused microbial sulfate reduction, and thereby led to formation of, and infilling by, sulfide and clay minerals. These observations indicate that phosphatization happened early in diagenesis, prior to burial compaction and microbial sulfate reduction, beneath (sub)oxic bottom water, and corroborate the hypothesis that the animals were preserved during ephemeral pulses of oxygenation in the basin and/or within environments located along boundaries of anoxic water bodies. Overall, our findings support the view that anoxic bottom water does not directly promote exceptional preservation; in fact, it may impede it. Konservat-Lagerstätten, particularly “stagnation deposits”, tend to form in (sub)oxic depositional environments with steep redox gradients and/or high sedimentation rates. Under these conditions, organisms are rapidly buried below the redox boundary, where their mineralization is promoted by focused geomicrobiological processes, and degradation is limited by the supply of oxidants in the microenvironments around them.
•The geology and taphonomy of the Posidonia Shale Konservat-Lagerstätten are reviewed.•Non-biomineralized tissues of Posidonia fossils were preserved via phosphatization.•Onset of phosphatization was early and occurred beneath suboxic bottom water.•Posidonia Shale fossils were preserved during ephemeral pulses of oxygenation.•New assessment of the role anoxia plays in ‘stagnation deposits’ and Lagerstätten.
A new forma type of palaeopathy, Forma malaspina (growth of additional double spines instead of the regular pairing with no exogenous injury) in Peltoceras schroederi Prieser M recorded from a ...condensed section (upper Callovian-lower Oxfordian) from the Ogrodzieniec Quarry (southern Poland) is reported and attributed to genetic abnormality. Microtomographical analysis of P. schroederi did not reveal any internal structures or density changes that would otherwise be suggestive of parasitism. Previous mentions by other authors of a similar duplicated spine palaeopathy in P. schroederi M from the Mediterranean region is also suggestive of a genetic abnormality rather than parasitism. The other palaeopathy recorded includes a transitional example of Forma juxtasulcata Géczy ‒ juxtacarinata Hölder, where the ventral region is marked by a row of single ventro-lateral tubercles rather than the usual two rows in the upper Callovian Peltoceras athleta M recorded from Arçay, near Loudun (western France). This palaeopathy is attributed to parasitism and also does not show any signs of exogenous injuries.
The rare Middle Jurassic ammonite Oecoptychius refractus is revisited based on material collected in southern Poland (Ogrodzieniec quarry) and France (St.-Laon near Loudun, western France). Based on ...available data and an evaluation of the literature, O. refractus ranges from the middle Callovian Kosmoceras jason Zone to the upper Callovian Quenstedtoceras lamberti Zone. Additionally, two specimens from Kachchh (western India) were re-evaluated and are now assigned to the lower part of the upper Callovian Peltoceras athleta Zone, similar to specimens from southern Germany. In the present study, O. refractus displays large morphological variation in the shape of the body-chamber, with a gradation from V- to U-shape. Additionally, the smaller upper Callovian specimens from Poland are morphologically closer to the lectotype (more evolute and compressed) and form a separate grouping as compared to the much larger middle Callovian specimens from France. Based on available data, the authors tentatively propose Phlycticeras polygonium var. waageni M as the dimorphic partner of O. refractus m; both dimorphs have similar morphology (ribbing pattern and striations), suture line and co-occur from middle to upper Callovian. Oecoptychius refractus maintains its morphological variability throughout the middle and upper Callovian, before its final dissapearance in the Q. lamberti Zone. Oecoptychius refractus is better documented from western Tethyan localities (Poland, Germany and France) as compared to those from the eastern Tethys (Madagascar and India). Recurrent sea level rises in the Middle Jurassic might be one of the plausible factors for its extensive palaeobiogeographic range. Key words: Ammonoidea, Oecoptychius, morphological variation, Callovian, Jurassic, Tethys, Poland.
Although the calcitic hard parts of belemnites (extinct Coleoidea) are very abundant fossils, their soft parts are hardly known and their mode of life is debated. New fossils of the Jurassic ...belemnitid Acanthoteuthis provided supplementary anatomical data on the fins, nuchal cartilage, collar complex, statoliths, hyponome and radula. These data yielded evidence of their pelagic habitat, their nektonic habit and high swimming velocities. The new morphological characters were included in a cladistic analysis, which confirms the position of the Belemnitida in the stem of Decabrachia (Decapodiformes).
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