Posidonia Shale
The Posidonia Shale is an Early Jurassic geological formation of southwestern Germany, northern Switzerland, western Czech Republic, northwestern Austria, southeast Luxembourg and the Netherlands, including exceptionally well-preserved complete skeletons of fossil marine fish and reptiles. The Posidonienschiefer, as German paleontologists call it, takes its name from the ubiquitous fossils of the oyster-related bivalve Posidonia bronni that characterize the mollusk faunal component of the formation.
The formation comprises finely laminated layers of oil shales formed of fine-grained sediments intercalated with bituminous limestones and crops out in a number of locations in southwestern Germany, although most remains are from near the village of Holzmaden. The European oil shales deposited on a sea floor during the Early Toarcian in the ancient Tethys Ocean are described as being deposited in an anoxic, or oxygen-depleted, deep water environment, although the details of the depositional environment are the subject of debate by researchers of the formation.
Geology & lithology
The Posidonia Shale is part of the so-called Southern German Cuesta Landscape, with the strata referred to being the principal representative of the Lower Jurassic layers in the foreland area of the Swabian and Franconian Alps, where it is one of the dominant layers of the Liassic deposition. The lithology consists mostly of carbonate concretion layers, mixed with abundant pyrite and euhedral crystals. Detrital clay, with a fine grain depositional exposure forms the bulk of the Posidonia, along with the presence of siltised quartz, being a component found on the lower layers of the formation. The black shales are the main component of the lithology of the Posidonia Shale, with different ratio of thickness, being more exposed on the southern German realm, specially near Ohmden. Studies of the shales have shown that the rise and fall of the sea level was one of the main effect of change on the Chemofacies present on the Posidonia. Posterior changes set environments for Chlorobiaceae and antiestuarine deposition. It was deposited on the Central European Basin, whose was connected on the Toarcian period with the Proto-Athlantic realm, under the sedimentary influence of the Fennoscandian deltas & sedimentation, along with several massif deposition, such as the Renic and the Bohemian, being the main representative emerged lands on the central European margin. its characterised by and abundant content of organic matter, with a presence of an up to 16% TOC, caused by anoxic to euxinic bottom water conditions. Most of the depositional margins of the German realm were on Pelagic marine settings, where the oxygen was the object of different changes along the layers, due to climate conditions and sea current effects. Outside the Shales, there are other types of lithology present, such as the light grey marls of the Aschgraue and Blaugraue Mergel that occur at the base of the Posidonia Shale section, which are related to sea bottom environment with a large period of well and suitable oxygen conditions, reflected on the presence of organic matter. The Black Shales are the opposite, with anoxic bottom effect and a detailed negative effect on the biota. Other elements of the Formation are the presence of Pyrites on the Black Shales. The effects of the changes to oxygen and depositions have had visible effect, with diagenetic and syngenetic pyrite forms, being the second ones deposited in oxygenated or dysoxic bottom waters, with pores and effects of biotic interaction, and the diagenetic pyrite needing high contents of transition metals. The Posidonia Shale is also one of the Environments where the Methane release on the Toarcian is better exposed. Related to worldwide effects, rapid and large-scale emissions by dissociation of methane hydrate in Europe and worldwide was driven by astronomical forcing superimposed and ending on a longer-term global warming.Dating
According to sedimentologic and palynologic features, a tidally influenced transgressive development within the Lower Toarcian is inferred. It is the reference formation for this interval. The Posidonia Shale of Dotternhausen and Schesslitz is well dated on the basis of ammonite and microfossil biostratigraphy. The Lower Toarcian sections are subdivided into three ammonite biozones and several subzones. The Posidonia Shale is considered to be the reference formation for the Lower Toarcian section. On the other hand, Black shale formation in the Toarcian of NW Germany is associated with a major turnover in phytoplankton assemblages interpreted as the response to lowered salinities in surface waters of the epicontinental sea. The presence of the Turnover is essential for the datation and the preservation of the fauna of the formation, with detailed index ammonites preserved. The study of the different layers and strata of the Posidonia Shale has given different data about the chronology of the formation. Dormettingen shales have been calculated biochronologically and with isochron data, giving and approximate age of 183.0 million years old, being close to the Pliensbachian boundary based on the recent revisions of the Early Jurassic Subperiods. The Toarcian and the Pliensbachian are considered as strongly constrained in terms of chronology, although that doesn't imply that all the formations labelled to one of the two periods have to be limited; for example Lithuanian Neringa Formation whose upper strata matches with the lowermost Toarcian. The rich Shale of the foreland area of the Swabian and Franconian Alb have been recovered as part of the Posidonia, with samples that expose an age between 183.0 and 181.1, thus recovering the Lower Toarcian strata. Although the east margin of the formation has yield strata with an age of 179.7 m.a, showing the presence of the depositional environment on Middle Toarcian times.History
The Posidonia Shale has been a focus of scientific interest for the last 100 years. There have been several types os research locally, ranging from the predominant study of the geology and sedimentology on the formation and associated layers, along with the geochemical, climatic, and ecosistemic research to set the different changes that have been documented along the formation. Paleogeography, paleontology, palynology, tectonics, and several other kinds of works have been done along the Formation. The most studied section has been the German, with the other being found as part of the Posidonia on late 1960-80s works, and most of them not covered yet.1800s
The first related studies with the Posidonia Shale Strata where done on the Early 1800. At the first the Formation was not identified as a separated unit. The first fossils where recovered on several Collections, some since the Modern Age, present on localities like the pits near the Banz Abbey. Among the oldest examples of fossils found on the formation is included the crocodrylomorph Steneosaurus on 1824, but being identified as a Gharial. Was on the 1820s when major studies of the fossil finds where done. Boué did in 1829 a study of the general geology of the Jurassic along Germany, recovering Limestone and Shale Facies, with a superficial assignation of what he considered most of the main Jurassic Strata, without classify the layers on a concrete subperiod. And in 1830 the pterosaur Dorygnathus was described, being the first one from the Formation. On the 1830-40s more works where done, becoming more concrete a recovering different data, setting the firsy assignations for the Lias & Dogger strata along Germany. Buch did a large study about the evolution of the jurassic on the German realm, identified that most of the layers where associated to marine facies & sedimentation, interpretating a change of the emerged lands, with epicontinental deposits on the Southern German Realm. The found facies where compared with ones from the Baltic Sea deposits. The Posidonienschiefer and the Black Jurassic facies where recovered on a 1837 work that studied the deposition on the Rhenish Transitional Mountains, altrougth it was left as a group os strata related to Lias-Dogger transition. A second edition recovered that the facies where similar of those deposited on tropical settings, like Tanzania & other similar settings, specially on near fluvial deposits. Quenstedt do a major recopilation of the Jurassic on 1843 focused on Würtemberg, covering the Black Shales and the Black Jura as only Liassic in age. The first insight on the Flora was done in 1845, with partial leaf fragments. After that, several works where done searching on the Posidonienschiefer, such as Roemer in 1844, returning to the Rhenish Transitional mountains, with the previous works revisited, with a mineral research study for the Posidonia Layers. That was complemented with paleotological studies along other parts, such as Thuringia. The fish genus Lepidotes was recovered on various layers assigned to the Black Jura, being the first main fish Genus identified related to the strata. After 1850, the amount of studies grown, from general studies recovering the petrology, comparing it to other deposits found several parts of Germany petrified small animals, composition in terms of minerals present, chemistry of the procecess recovered on the strata, applications for the mineralogical industry, the Foraminiferans present on marine rocks with its affinities and ecological implications, the Crinoids associated to rafting woods, resemblances with the other liassic strata know on central Europe amd implications for the general lias sedimentology or for the geology and sedimentology respect to other units along Germany. with research on North Germany, where new deposits where found. And finally, recopilations of the previous discoveries along the last decades, compared to the finds on new pits and its layers.1900s
While there are paleontological works since 1880, the formation itself gets a deeper view on the 1900s. One of the first main discoveries at the start of the century was the description of the ichthyosaur Stenopterygius in 1904. With also renovated data about the different minerals present of the rocks of the formation. The changes on the deposits of the formation where also recovered, where the thickness changes from North to South deposits become know, and was vinculated mostly to influence of the Glacial erratics. The influence of the Cuaternary events on the strata was compared and proved on latter studies. On 1921, Hauff do the main research of thefound fossils from Holzmaden on the previous decades, finding exquisite specimens, some of them nearly complete, including Ammonites, Fish and Marine reptiles, such as Plesiosaurs and Icthyosaurs. It also recovered that the chemology and know most of the sedimentation of the formation was marine, with pelagic fauna, influenced by marginal marine to deep basin deposits. All with the implications for the Industry, updated from previous works. Hauff described in 1938 "Acidorhynchus", the latest surviving of the Saurichthyiformes. The stratigraphical works where done after 1930 to corroborate the Pelagic affinities of the locations, along with comparations with other Middle and Late Juarssic deposits. As a result of those works on the strata, organic substances, related to carbonate particles, where found and studied on the late 40s. Also fragments of metallic particles where studied. The Posidonienschiefer was studied after the 60s focusing on some points bituminous shales, and the nature of them, due to the finds on the 30s-50s. The study of the Shales led to recover data and compare to similar settings to the objective of find similar sedimentation settings, being found that the Pelagic depostits where influenced by changes on the Oxygen composition, that led to decrease the presence of scavengers, and let excepcional preservation of vertebrates and invertebrates to happen. On 1978, Wild described the First and only know Dinosaur Fossil from the formation, what he named Ohmdenosaurus, a small sized Sauropod. As the setting and the importance of the Oxygen levels get important to study the ecological boundary of the formation, new data was provided to expose the influence of the deposits, the fauna, minerals, and other components. The Ecological perspective of the formation had change, being seen as a Stagnant Basin Model, influeced by paleocurrents from the North and the South of the Central European Basin. The newest studies of the Black Shale recovered that its formation was related to anoxic changes, with temporal changes on the fauna, led by the oxygen levels. Due to that, the major fossil collections where re-observed, looking for traces of the new discovered data about the Shale.
Also proliferate works recovering all the history of the formation, the previous studies and the changes seeing trought the reexamination, with a retrospective of the new knowledge about the changes on the deposition. That included the revision of older specimens, and historical finds on the formation.
2000s
Recent work has recorded and rewritten data from previous works, and focused more on the appearance of the environment and the study of earlier found specimens, distribution of the sediments and its implication to the Sea currents during the Toarcian. New Flora Fragments where reported from the layers near Holzmaden and along the strata on the seashore sections on the Bohemian region, implying terrestrial deposits nearby. The Hauff Museum, where mostly of the specimens where housed, was revisited for the study of some of the forgotten fossils on the collection. The Black Shales where recovered as a Biomaker for the lower Toarcian subperiod of the Lower Jurassic, where it retained the age-referenced Foramifers and Algae microfossils. Using Gamma-Ray measurements was found the deposition started on the lowermost Toarcian stage, around 182.5 million years ago, where on some pits the lower layers start with the presence of index Ammonites and Bivalves. Along with the data and the North German Facies, where recovered new Facies on Austria and the Netherlands. The main works referred to the sedimentation where done on relationship with the Toarcian Anoxic Event. The nannofacies show that the anoxic changes where the main reference to follow to see the changes on the bottom of the seas along the Toarcian Boundary, being discovered irregualities along the different regions of the Posidonia Shale. That find also that the deposition of the Shales was restricted on some parts of the formation, what led to changes on the currents, and thus influenced the different stratification on series of layers. Also, Posidonia Shale was present on abundant works relating the impact of the Anoxic event with another formations of same age. Or even changes of the behaviour of the fauna. The most recent finds have been related to old specimens, where fossil Icthyosaurs have reported preserved skin or pathologies. Also the recover of considered synonymous taxa, such as Mystriosaurus.Paleogeography
The Posidonia Shale was a mostly marine unit, influenced by various highs and emerged lands that provided most of the terrestrial matter found along the Formation. The Main structure of the formation was dispossed along the modern southern Germany, recovering the locations of Holzmaden, Ohmden, with Niedersachsen facies at the north, and others appearing along the east, such as the related to the Banz Abbey strata or the near-Bohemia facies. The Formation was divided on various sections, including the Southwest German Basin, the main unit, where the most detailed fossils have been found, including the Icthyosaurus and Plesiosaurs housed at the Hauff Museum. The SW German Basin was a pelagic deposit, with influence of open sea currents from the North and the South, with an estimated water depth of 500 m to 1.5 km. Abyssal depression sedimentation has not been found for now. Connected to the SW German basin where the Paris Basin, that recovered central France, with correlated sedimentation to the Shale deposition on Germany. The Paris Basin was also mostly a Pelagic to open-shelf deposit, without a major abbysal sedimentation. At the North, the Wenzen Well provide a deeper basinal setting for facies coming from the main continental land present anywhere nearby the formation, Fennoscandia. The main terrestrial units present along the main Posidonia Body, where the Rhenish High at the west, being an small land of the size of Sicily, and on the east the Bohemian Massif with the Vindelician High, the major units present on the Central European basin on the Toarcian. The Tophography of the Massif is believed to be hereditary of the Paleozoic Transgressions that happened on the central European margin, with possible elevated facies, where the major tophograpical accidents would be situated along the southern coast. The Vindelician Land/High has been represented as a peninsula to the Bohemian Massif, or an isolated landmass, that is due its connections that hadn't been recovered in depth, being considered a mostly plain emerged sedimentary structure. Finally, the southernmost part of the Formation, the Bern High recovered the modern north of Switzerland, a small terrestrial setting with similar conditions to Sardinia. Out of the main basin, The layers of the formation extend to the Danish Central Graben, that deposited on the Baltic coast of Germany and Denmark. The Danish Central Graben was a depositional shelf basin, with depths around 1–2 km maximum, with abundant facies related to Volcanic deposits, coming mostly from the southern Fennoscandia Central Skåne Volcanic Province. The extension of the Facies of the Posidonia Shale come near the London-Brabant Massif, with a similar Tophography to modern Creta. At the northern shores of the Massif was present the West Netherlands Basin, a seashore to epicontinental deposit, with abundant terrestrial facies.Oil
Recent studies have shown that the petroleum generation potential of the PS is high in all studied regions due to the high TOC and Hydrogen Index. However, differences exist which can be expressed by SPI values. The latter are highest for northern Germany, where the PS is richest in TOC and has the highest HI values combined with a thickness of 30 to 40 m at most places. Since the first serious evaluations in the 2000s, different organic samples were extracted to revise the changes and potential presence of the Shale Oil on the main quarries of the southern realm. Based on several core samples with abundant organic material different thermal maturity has been found, specially on the samples from the Hils Syncline strata. The maturation of this strata has implied losing organic carbon and loss of hydrogen index values. Beyond that, the status of the samples has been stable during at least 40 measured years.Ecology
The Lower Toarcian is characterized by the widespread occurrence of organic-rich mudstones, termed black shales, in western Europe and other parts of the world. It is considered to represent mostly marine units, including Pelagic, epicontinental and on a more less presence, deltaic and seashore environments. Near Shore sections are filled with algal fragments and pollen, that suggest interceded dunar environments with proximal water and Halophile flora, and probably water flooded forests. Most of the fossilized environments are open sea and marine settings, with abundance of shells and coral fragments. The relation between the sea environments and the less present terrestrial match with the paleogeography of the Lower Toarcian of Europe, where a main sea covered most part of the modern countries, with emerged lands such as the Amoricanian Massif or the Bohemian Massif.Marine environments
The early Toarcian stage was characterized with the presence of a general deposition of mudrocks along with organic matter mostly on marine strata, showed by different kind of succession in marine strata, that can be observed nowadays worldwide. The Black shales present in the Posidonia Formation are related to deposits present on Lithuania, Canada and several other countries & Continents. This suggests the presence of a general deposition of organic matter, driven by several global events and changes present on the surface. This caused changes on the bottom of the seas, with abundant deposition of organic matter. It is related to a change in carbon-isotope excursion in marine and terrestrial life, and was probably a perturbator of the carbon cycle. Global seawater has been proved to be approximately, for the interval of the negative carbon-isotope excursion, close to 1.45‰, less than modern values, with estimated 2.34‰. Waters interchange were on of the major effects on the paulatine de-oxygenation showed on most of the Lower Toarcian Layers around the word, with the connection with the Viking Corridor as one of the main effects, due to the arctic waters freshening and breaking the oceanic circulation. The effect was consequently negative on the German realm, where the environments expose a tropical fluctuation, with conditions similar to the modern Caribbean Sea, which hosted a high variety of sea fauna, except on the bottom layers, where only a few genera where able to survive when oxygen conditions get slightly better. The changes on the bottom floor oxygen where common, with most of the animals dying without being scavenged by bottom-dweller organisms, and sessile life. Posterior facies of the middle Toarcian show changes on the Environments, getting more oxygen and different depositional settings with the presence of trace fossils such as Chondrites and Phymatoderma granulata, surfacing deposit-feeding animals, being adapted for effective nutrient searching, becoming more common on the uppermost layers. The sea levels where transgressive, as it is shown on layers across Bavaria where major events set the fate of the nearshore environments. One example is the case of the Monotis–Dactylioceras beds, that had an extent of +500 km, that has been linked with a possible Tsunami. There is not major indicative of synsedimentary faulting in South Germany, but is present on the western Tethyan Shelf, with breccias created from earthquakes, present on Toarcian levels of the Austrian Adnet Formation. It would start as an initial wave propagation affecting the Altdorf High aiming for the south, where it would have hitten the shoreline of the Bohemian Island.Marine Animal Behaviour Frozen in Time
Several animal behaviours have been recovered on the Posidonia Shale. The Monotis-Dactylioceras bed is one of them, as it shows an agrupation of the bivalves Meleagrinella substriata and the Ammonite Dactylioceras, that were the most abundant representatives of its group on the Altdorf region, and were probably washed to near epicontinental waters by a rapid event, or as result of a large succession of events. Related to the Ammonite fauna, on Holzmaden there have been found several empty shells of this cefalophods, with associated crustaceans inside. The original specimen was reported in 1995 and consisted on a possible member of the genus Paleastacus inside a chamber of a Harpoceras. Other epizoans are found related to the decayed Ammonite shells, such as Serpulid Annelids and Bivalves, creating what was denominated as "benthic islands" as reference at be isolated benthic units that attracted fauna. The Decapod is related to the family Erymidae, that are considered as possible bottom dweller carnivorous or carrion feders. The associated fossil has several spherical structures that had been iterpreted as decapod coprolites, impliying that the animal lived for a long period on the shell, and maybe changes on the bottom oxygen stopped the process. More recent studies had recovered new data about the inquilinism of decapods inside Ammonites, this time hovewer recovering three Eryonoidea lobsters together within a body chamber. The lobsters most likely used the ammonoid as some kind of shelter, where was excluded the possibility of transportation into the body chamber by bottom currents. There are several teories about the gregarious inquilinism showed by this specimens, such asthat the shell was and ideal location to molt, as hasn't been proved to be corpses or molts; that the shell provided protection against predators; the
decomposing soft body of the ammonoid was a sorurce of food that attracted the decapodans or that was used as a long-term shelter. One key aspect foun was that the muddy bottom was not suitable for burrowing, impliying that the decapodans look for a different shelter due to be unable to made its own.
Other of the frozen relationships related to cefapophods includes the genus Clarkeiteuthis and its predatory behaviour, found associated with fishes of the genus Leptolepis. Based on the position of prey and predator, was suggested that the coeloid cephalopods caught and killed the fishes while the schools still in well-oxygenated waters and then descended into oxygen-depleted water layers where the cephalopod suffocated and died attached to its prey. The fish measured 12 cm, while the coeloid 21 and it was measured by the fossilized arms of 14 specimens of coeloids that the hunting specimens arms where contracted over the fish, probably quickly killing it by cutting its spine. Other coeloid, Geotheutis has been reported with eumelanin preserved along with its ink sacs.
Maybe one of the most complex organism interactions on the Posidonia Shale where the Crinoid Megarafts, that agroup a wide variety of animals, creating large floating ecosystems, being the longest surviving communities to exist in the fossil record. The Largest Megaraft found measures 18 m, and is based on an Araucarioxylon trunk, where different animals where attached. The first attached animals would have been the growing community of Oysters, Bivalves and Crinoids, that would suppose and small weigth to the raft. The rafts would be after colonized by another organisms, such as thoracic cirripedes of the genus Toarcolepas, that become the oldest epiplanktonic cirripede known on the fossil record, probably motivated by the appearance of the rafts. Other genera can be related, such as the possible oldest pelagic representative of the Sea Cucumber family, Uncinulina parvispinosa. The weigth of the colony would have ended being up to 15.000 kg at the end. The presence of this megarafts was in part possible due to the absence of marine wood worms, that destroy tree logs on less than 3 years along without the presence of modern raft wood predators those rafts can last up to 5 years, being that the main reason the crinoids attached were able to reach huge sizes. Probably where also essential to distribute animals along the sea basins. Seirocrinus, Pentacrinites & Isocrinus where various of the main crinoid colonizers of the floating rafts. Seirocrinus is the main representative of the pelagic crinoids, being among the tallest animals know, with a size of 26 m the largest documented specimen. The ecology of the genus is widely known, where is known that the smallest stems were among the first animals to colonize the rafts, with at least 2 generations of crinoids found per raft, where the hydrodynamic changes of the log influenced the settlement of the Crinoids. It is believed that Seridocrinus had a seasonal reproduction, linked to the Moosonal conditions that sent new logs to the sea. The large crinoids would have feed on pelagic micronutrients, and afer fall on the bottom, all the colony would have died.
The Shark Hybodus includes specimens with the gastric contens, being full of Belemnnite fragments. That implied active predatory behaviour by the genus of several kinds of belemnnites, such as Youngibelus. It isn't the only trace of predatory behaviour on vertebrates, as a Spienballen, a regurguitated mass composed of indisguestible stomach contents had been found on the Holzmaden quarry. The Speinballen measures 285 mm length with a diameter of 160 mm, and consists of 4 members of the genus Dapedium and a jaw identified as Lepidotes. The animals capable of it had been suggested as Sharks like Hybodus, Actinopterygians and several marine reptiles. Hybodus, being was able to reach nearly 3 meters long and with a dentition suitable to hunt fish, although its stomach contents suggest it is a mostly invertebrate hunter. Actinopterygians like Saurostomus grew up to 2 m long, and have been found with fishes, coeloids and ammonites in its stomach contents, hovewer, not the fishes present on this Spienballen. Marine reptiles included marine crocodriles, such as Platysuchus or Pelagosaurus, associated to the fishes of the Speinballen, altrougth are proven to have eaten gastroliths to improve buoyancy and digestation. Ichthyosaurs, whose diet is among the best studied of the Posidonia Shale, with Dapedium Specimens in juvenile stomachs, along with coeloids. Temnodontosaurus, measuring between 8 and 13 m, would have been able to do such a large Speinballen. Plesiosaurs where desacredited due to the study of its teeth, that proves a diet based on soft-body prey, such as fishes of the genus Leptolepis and coeloids. Dapedium and Lepidotes, with a heavy and solid squamation can be excluded.
One of the Most emblematic finds of the formation its that of a mother Stenopterygius giving birth living young, like the modern Dolphins and marine mammals, being born with the tails first. Other specimens have been found with Embryos inside, but with the bones of them scattered, partly beyond the body limits of the mother. There have been various teories about this scenario: the bones of embryos had been deposited before the body of the adult went to the sea floor, covering the embryo bones and impliying that the adult would not be the mother of the embryos. Other option is that a pregnant ichthyosaur on its last moments sank to the bottom and may have struggled for life, given untimely birth to some of the foetuses. Other option follows the presence of foetus bones outside the mother body, where a dead female sank to the bottom, with the water warm enough, helping to the putrefaction gases to start to develop while the hydrostatic pressure was too high to be prevented by the body. Scavengers must have started eating from the dead body, until the chamber retaining the pressure was to thin and exploded. This teories where hovewer contested after the study, where it was criticised the absence of the presence of the bottom-current activity in the epicontinental sea covering Central Europe during the Toarcian, pointing that the mother carcass should have been translated after it sank to the bottom floor, probably exploding or expulsing its embryos first, that would be transported along.
Terrestrial environments
The main Terrestrial environments of the Posidonia Shale are the near emerged lands, mostly of Paleozoic Origin that include the London-Brabant Massif at the west, the French Central Massif at the south, the Vindelician High and Bohemian Massif at the east, with minor lands present whose emerged nature on the Toarcian is controversial, including the Vlotho Massif at the northwest, the Swedish Bern high at the south, Rhenish Massif on the Center and the Fuenen High in the north. The Fennoscandian province was the major continental realm, that provide most of the freshwater for the nearshore environments. The Bern high was characterised with being one of the southernmost environments on the formation, with a terrestrial setting characterised by tropical climate, with the presence of enhanced rainfall and river freshwater inputs together with recurrent discharges of northern waters. Is compared with a modern Bahamian setting, with relative humid flora and the presence of abundant rivers, although it is believed to have a more vertical topography. The Vlotho Massif is one of the most interesting cases on the realm, being capable of generate a thermal influence on nearshore waters. With a high deposition of metals, the layers of the High show instead a climate varied between 21° to 26° and a more dry climate, being a Mediterranean climate zone. Same is applied to the Bohemian Shores, populated by large Araucarian and Cycadales. The Environments were influenced by monsoonal conditions, and large scale rains that hit most of the nearshore settings, causing the large accumulation of Insect remains found on the epicontinental layers. Southern summers with humid south-west monsoonal conditions occur on most of the emerged lands, getting a winter with dry north east trade winds. Those were related to the seasonal occurrence of wood rafts on the formation and linked to the life cycle of the stem crinoids. On the land, probably where the main source of seeds and help to interchange species between landmasses.Paleontological significance
In addition to their Posidonia bronni, the shales contain some spectacularly detailed fossils of other Jurassic sea creatures—ichthyosaurs, and plesiosaurs, spiral-shelled ammonites and crinoids, or sea-lilies. The best-preserved fossils found on the Early Jurassic can be the ones from the Posidonia Shale. There are also abundant fish fossils. Most of the fauna is marine, with several terrestrial specimens, and some of them being semiaquatic, such as the sphenodont Palaeopleurosaurus.Flora has been found, especially the genus Xenoxylon, but also Otozamites, Equisetites and Pagiophyllum.