Epicontinental Sea Research Articles

Provenance of heavy minerals to the Middle and Upper Jurassic epicontinental deposits of NW Poland

The source of clastic material supplied to the epicontinental sea during the Middle and Late Jurassic in the Pomeranian Segment of the northern part of the Mid-Polish Trough is analysed, using deposits from the Rzeczyn PIG-1 borehole that represent the Łyna, Chociwel, Brda, Pałuki, Kcynia and Rogoźno formations. Heavy mineral analysis, including weathering indices (ZTR, GZI, RZI and Q) and standardised scores for each mineral species, shows that each formation is characterized by a different heavy minerals association. In each association, transparent minerals include both ultrastable minerals (zircon, tourmaline and rutile), occurring in various proportions, and unstable minerals. This indicates that deposits subject to earlier multiple reworking were eroded from the surrounding landmasses. Most probably these deposits represented Triassic rocks, although fresh weathering covers were also eroded. The main direction of clastic material supply was from the N and NW, and to a lesser degree from the NE. The main reasons for changes in the source areas were probably sea level oscillations, while during regressions, exposed parts of the seabed became source areas of clastic material. Conversely, during transgressions, parts of the seabed became cut off from the supply of clastic material from eroded landmasses.

Siliceous microfossils as a potential age marker for the early Hirnantian Mass Extinction horizon in South China

Abundant cone-shaped siliceous microfossils have been recovered from Upper Ordovician black shales of the Wufeng Formation in South China. They occur in the Hirnantian Metabolograptus extraordinarius Biozone. An investigation of their internal structure conducted using focused ion beam-scanning electron microscope (FIB-SEM) and transmitted light microscope shows that the specimens are possibly composed of three parts: cephalis, thorax and foot. Robust, longitudinal costae are developed, sometimes branching at the thorax. The geological distribution of these microfossils in South China indicates that they occurred in a restricted epicontinental sea on the Upper Yangtze Platform, which was connected to the open ocean in the north. It seems likely that these microfossils have a limited temporal range relative to the Late Ordovician Mass Extinction (LOME) in the early Hirnantian. In the absence of coeval graptolites or other index fossils, their occurrence therefore provides an age marker for the LOME, and has utility for future shale gas exploration in the Wufeng Formation. Xuejin Wu [xjwu@nigpas.ac.cn], State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing, 210008, PR China; University of Science and Technology of China, Hefei, 230026, PR China; *Hui Luo* [huiluo@nigpas.ac.cn], State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing, 210008, PR China; *Yuandong Zhang [ydzhang@nigpas.ac.cn], State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing, 210008, PR China; University of Chinese Academy of Sciences, Beijing, 100049, PR China; Chao Li [chaoli@nigpas.ac.cn], State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing, 210008, China; University of Chinese Academy of Sciences, Beijing, 100049, PR China.

A summary of the Jurassic System in North and East-Central Iran

The rocks of the Jurassic System in North and Central Iran are represented by very thick sedimentary successions reflecting the deposition during two tectono-stratigraphic megacycles, bounded by three important unconformities. The older (Early to early Middle Jurassic) cycle starts, after the Late Triassic closure of the Palaeotethys and the collision of the Iran Plate with the southern margin of Eurasia (Turan Plate), with an abrupt uplift of the Cimmerian Mountains around the Triassic–Jurassic boundary (Main-Cimmerian Event) and is terminated by the Mid-Cimmerian Tectonic Event in the mid-Bajocian. The predominantly siliciclastic sediments of this tectono-stratigraphic cycle are accommodated in the Ab-e-Haji Subgroup of the (upper) Shemshak Group. The Ab-e-Haji Subgroup consists of thick and widespread, partly coal-bearing siliciclastic strata and also records some important marine ingressions, especially in the Toarcian and Aalenian. The younger tectono-stratigraphic cycle starts with an extensive marine transgression in the Late Bajocian and ends around the Jurassic-Cretaceous boundary with the Late Cimmerian Tectonic Event. In the aftermath of the Mid-Cimmerian Tectonic Event, the Iran Plate was dissected into several structural units, the geological histories of which differed and so did their facies patterns. Thus, in North Iran two main sedimentary areas developed, namely the Alborz and Koppeh Dagh basins, which show moderate diffe-rences in lithology and thicknesses. However, the differentiation is much more pronounced on the Central-East Iranian Microcontinent, which comprises three N–S-oriented and independent structural units, i.e., from east to west the Lut, Tabas and Yazd blocks. During the Jurassic Period, the sea mostly covered the Tabas and Lut blocks, whereas the Yazd Block remained largely emergent. The lithologically diverse and numerous formations of the area are combined in the Magu and Bidou groups. Early to Early Middle Jurassic ammonite fau-nas of North and Central Iran are palaeobiogeographically closely related to Northwest European (Subboreal) ammonite faunas, allowing a similar biozonation. Concurrent with the Late Bajocian transgression, there is an abrupt change in faunal composition and the Middle and Late Jurassic ammonite faunas of North and Central Iran are much more similar to those of epicontinental seas bordering the nort-hern margin of the western Tethys and occupy an intermediate position between the Mediterranean and the Submediterranean Province. The results of the studies on ammonoid palaeobiogeography are in line with Early Jurassic palaeogeographic reconstructions that place the Iran Plate at fairly high palaeo-latitudes of about 45°N, followed by a rapid southward shift throughout the Middle and Late Jurassic to a position of about 30°N.

Late Cenomanian-Turonian isotopic stratigraphy in the chalk of the Paris Basin (France): a reference section between the Tethyan and Boreal realms

A chemostratigraphic study (δ13C and δ18O) of the Late Cenomanian and Turonian chalk succession from the “Craie 701” Poigny borehole (near Provins in the Paris Basin, France) provides new high-resolution stable carbon and oxygen isotope data. Correlation of the bentonite horizons and the isotopic trends from Poigny with its English Chalk equivalent allows the development of a precise stratigraphic framework. δ13C and δ18O variations are synchronous and widespread throughout the European epicontinental seas and Tethyan Ocean. In the Poigny borehole, the Oceanic Anoxic Event 2 (OAE 2) is marked by a large and brief positive excursion of carbon isotopes (a carbon isotope excursions: CIE of 3‰ amplitude) without any apparent anoxia in the Late Cenomanian Chalk. Comparisons between different key sections on a North-South transect from the Anglo-Paris Basin to the Umbria-Marche Basin (Gubbio Section, Italy) and the Vocontian Basin (South-East France), suggests that the OAE 2 is linked to an increase in marine organic matter production, modulated by a regional effect on the organic carbon burial rate. Thus, the large positive carbon isotope increase spanning the Middle Cenomanian through to the Middle Turonian, including the salient CIE associated with the OAE 2, reflects a global scale increase in marine productivity that would be concomitant with a major long-term sea level rise. The stratigraphic position of the Turonian-Coniacian boundary can also be better defined by this isotopic study. A comparison of δ18O data between the Anglo-Paris Basin and Tethyan Basin shows high-amplitude, long-term synchronous variations reflecting primary paleo-environmental changes which are independent of local facies, sediment thickness and diagenesis. In particular, a negative shift (−1‰ of amplitude) reflects a warmer climate regime, marking the onset of OAE 2. Two colder phases (+1‰ amplitude each) occurred in the Early Turonian and the beginning of the Late Turonian.

Timing and forcing mechanism of the final Neotethys seawater retreat from Central Iran in response to the Arabia-Asia collision in the late early Miocene

The Iranian Plateau lies in the middle of the Neotethys tectonic domain; to the east it connects with the Tibetan Plateau, and to the west with the Anatolian Plateau and the Alpine orogenic belts. In the Cenozoic it underwent land/sea changes and tectonic uplift in response to the Arabia-Asia plate collision. One of the most prominent geological consequences of the collision was the disappearance of an epicontinental sea in Central Iran, which was a northeastern branch of the Neotethys seaway in the Oligocene-early Miocene. The timing of the final seawater retreat from Central Iran and its forcing mechanism are important for understanding the effects of Arabia-Asia plate collision as well as global eustatic sea-level changes. In this paper we present new magnetostratigraphy, UPb ages of one tuffaceous bed, and stable isotopic records of carbonates. The results of this multidisciplinary study indicate that a shallow open sea in the Qom back-arc basin ended at 17 Ma, but the final seawater retreat from a restricted marine environment was at 16.8 Ma. The final regression was just before the Middle Miocene Optimum, implying that it was not related to a climatic factor, but driven by the Arabia-Asia plate collision. Moreover, the δ18O record of fine-grained lacustrine carbonates indicates an isotopic shift towards more positive isotopes after 13 Ma, suggesting an enhanced aridification in Central Iran. This climatic deterioration was a response to reduced transport of moisture by westerlies from a retreating Neotethys Sea driven by a global eustatic sea-level drop in response to the East Antarctica ice-sheet expansion after the middle Miocene Optimum.

A new reptile from the lower Permian of Brazil (Karutia fortunata gen. et sp. nov.) and the interrelationships of Parareptilia

A new parareptile from the Cisuralian Pedra de Fogo Formation of north-eastern Brazil is described. Karutia fortunata gen. et sp. nov. is the first Gondwanan member of Acleistorhinidae, a clade previously known only from North America but thought to be closely related to the Russian Lanthanosuchidae. A re-examination of parareptile phylogeny indicates that lanthanosuchids are not closely related to acleistorhinids. These results are more congruent both stratigraphically and biogeographically than the previous ‘lanthanosuchoid’ position for acleistorhinids, as they eliminate a 15 Ma ghost lineage within parareptiles, leaving Acleistorhinidae as an exclusively Pennsylvanian/Cisuralian clade from western Pangaea. Karutia fortunata contributes to our knowledge of the early Permian diversity of Parareptilia in Gondwana, a clade previously represented only by the mesosaurid inhabitants of the Irati-Whitehill epicontinental sea in the southern portion of the supercontinent. The new parareptile joins captorhinids in the amniote record of the Pedra de Fogo Formation, improving our picture of the inland tetrapod fauna of the southern hemisphere during the Cisuralian. http://zoobank.org/urn:lsid:zoobank.org:pub:79D59764-4DA0-4C28-B4D3-C517BBF64D81

Assessing anoxia, recovery and carbonate production setback in a hemipelagic Tethyan basin during the Toarcian Oceanic Anoxic Event (Western Carpathians)

Abstract The chemostratigraphic record of the Toarcian Oceanic Anoxic Event (T-OAE) is generally well documented in epicontinental basins; however, the duration of anoxia and recovery remains poorly constrained in the Tethys Ocean owing to limited stratigraphic resolution of oceanic sections with hiatuses. In this paper, we describe a relatively continuous hemipelagic record in the Central Western Carpathians of Slovakia (Skladana Skala section), which contains the Pliensbachian/Toarcian boundary, the T-OAE, and the subsequent recovery phase. In our section, the Pliensbachian Spinatum Zone is represented by a ~ 7 m thick alternation of spotted, spiculitic marly limestones and limestones of the Allgau Formation that contain moderately diverse trace fossils including abundant Zoophycos, Lamellaeichnus and Teichichnus. In the uppermost part of the Spinatum Zone, a ~ 0.8‰ decline in δ13Ccarb values marks the carbon isotope excursion (CIE) at the Pliensbachian/Toarcian boundary. This isotope anomaly is overlain by a ~ 3 m-thick interval of spotted marly limestones and marls, which contains a positive CIE that represents the base of the T-OAE. The T-OAE interval comprises a 60 cm-thick pyritic black shale interval that lacks bioturbation and shows a negative CIE (δ13Corg values drop by 4–5‰), coincident with an increase in TOC values (from 0.3% to 2–3%), and a drop in CaCO3 values (from 50 to 80% to 3–7%). The black shale is overlain by ~8 m thick marls with rare intercalations of marly limestones, which show ammonites of the Exaratum Subzone in the lowermost part (~1 m) succeeded by Serpentinum Zone beds. This unit exhibits a second positive CIE (δ13Corg increases by 2.5‰ and δ13Ccarb increases by 1.5‰), significantly more negative δ18O values relative to the pre-T-OAE interval, and a low diversity of trace fossils dominated by Chondrites and extremely thin Zoophycos. Sponge spicules re-appear in the uppermost 6.5 m-thick interval of the section formed by the alternation of spotted marls and limestones, with ammonites of the Falciferum Subzone in the lower part and of the Bifrons Zone in the uppermost parts; however, diversity of trace fossils remains low. Based on these findings, we argue that the 60 cm-thick pyritic black shale that represents the T-OAE is a strongly condensed succession because it includes the onset of the negative CIE and the subsequent rebound, and thereby encompasses the full duration of the anoxic event. Anoxia in basins open to the oceanic Tethys thus coincided not only with reduced carbonate production but also with reduced siliciclastic supply, generating very thin black shale deposits. In contrast to current-swept swells where black shales associated with hardgrounds are thin or missing owing to winnowing, carbonate starvation was induced by a calcification crisis coincident with the T-OAE and siliciclastic starvation was probably induced by rapid sea-level rise. Although bottom waters were not anoxic in the aftermath of T-OAE, bioturbation remained restricted during the Falciferum Subzone in basinal settings, indicating that environmental stress induced by limited ventilation and/or high bottom-water temperatures were persistent. The reduced diversity of trace fossils and the re-appearance of sponge spicules close to the lower/middle Toarcian boundary indicate that the ecological recovery in basins open to the oceanic Tethys was delayed, a pattern similar to the epicontinental seas that experienced anoxia.

Age, provenance and tectonic setting of metasedimentary sequences of the Gurupi Belt and São Luís cratonic fragment, northern Brazil: Broadening the understanding of the Proterozoic-Early Cambrian tectonic evolution

Geological, U-Pb (detrital zircon), whole-rock Nd isotopes, and geophysical information constrain the timing, provenance, and depositional and tectonic settings of sedimentary successions from the Gurupi Belt (GB) and São Luís cratonic fragment (SLCF) in northern Brazil. The results, along with published information about the magmatic events are used to discuss the crustal framework and regional correlations. We defined the following stages of sedimentation related to the Rhyacian and Neoproterozoic-Early Cambrian evolution. (1) 2240–2160 Ma –metavolcano-sedimentary sequences formed in arc- (SLCF) and back-arc (GB) basins. (2) 2165–2120 Ma – two syn-orogenic, siliciclastic (turbidite) sequences; the oldest (>2149 Ma) formed in a forearc or intra-arc setting, the youngest (>2116 Ma) formed in forearc or distal intra-arc system. (3) 2120–2088 Ma – post-collisional, continental, siliciclastic basin(s) formed in fluviatile setting, and representing a foreland system, which was split into two sub-basins in more recent times. These Rhyacian sequences correlate with similar successions in the West-African and Amazonian cratons, and formed during the agglutination of a continental block in pre-Columbia times (>2000 Ma), which remained joined through the assembly (~1800 Ma) and breakup (~1300 Ma) of Columbia, being only fragmented during Rodinia breakup (~750 Ma). This breakup produced, probably distal, intracontinental effects that led to the deposition of (4) 1130–740 Ma – siliciclastic sequences formed in rift and passive margin basins; no evidence of oceanization is observed, and the sequences correlate in time with sedimentary formations of the Rokelide Belt in West Africa. The closure of the epicontinental sea took place during intracontinental orogeny, which represents a distal effect of the collisional orogenies that assembly West-Gondwana at the Neoproterozoic-Early Cambrian boundary. The last sedimentation event comprises (5) < 591 Ma – a post-orogenic/post-collisional siliciclastic basin formed in a rift that might also have been acted as a precursor rift of the Phanerozoic intracratonic basins.

Early Jurassic (middle Hettangian) marine gastropods from the Pogibshi Formation (Alaska) and their paleobiogeographical significance

A middle Hettangian marine gastropod assemblage is reported from the Kenai Peninsula of south-central Alaska supplying new paleontological evidence of this group in Lower Jurassic rocks of North America. Pleurotomaria pogibshiensis sp. nov. is described from the middle Hettangian marine succession informally known as Pogibshi formation, being the first occurrence of the genus in the Kenai Peninsula and the oldest occurrence of the genus in present-day Alaska and North America. One species of the genus Lithotrochus, namely Lithotrochus humboldtii (von Buch), is also reported for the first time from the Kenai Peninsula. Lithotrochus has been considered as endemic to South America for a time range from the early Sinemurian to the late Pliensbachian. The newest occurrence of Lithotrochus in rocks of the Pogibshi formation extends the paleobiogeographical and chronostratigraphical distribution of the genus into the present-day Northern Hemisphere. However, the Southern Hemisphere affinities are consistent with the hypothetical interpretations (although supported both by paleobiogeographical and paleomagnetic data) that the Peninsular terrane of south-central Alaska is far-traveled and may have originated at much more southerly paleolatitudes than its present-day position. Two other Early Jurassic caenogastropods typical of the Andean region of South America and of the Tethyan epicontinental seas are described for the first time in the Pogibshi formation, and these are Pseudomelania sp. and Pictavia sp. The new gastropod assemblage reported here shows close affinities with coeval South American and European gastropod faunas, supplying new evidence to interpret their distribution during the Early Jurassic.

PALEODICTYON IN SHALLOW-MARINE SETTINGS – AN EVALUATION BASED ON EOCENE EXAMPLES FROM IRAN

ABSTRACTThe graphoglyptid trace fossil Paleodictyon, characterized by stratiform hexagonal meshes, typically occurs preserved at the base of deep-marine turbidites. There is, however, a growing number of occurrences of Paleodictyon in shallow-marine deposits as evidenced by new finds in the Eocene of Iran. The Paleodictyon-containing Asara Shale Member of the Karaj Formation accumulated in a shallow backarc basin. Parallel-crested wave-ripple marks and microbially induced sedimentary structures occur closely above and below the Paleodictyon-bearing strata. Shallow-marine Paleodictyon have so far been reported from morphologically structured, extensive, epicontinental seas, rift basins, and young, prograding passive continental margins, but mainly from foreland and backarc basins. In the two latter cases, the Paleodictyon producers appear to represent adaptive survivors. Initially they settled in abyssal to bathyal turbiditic settings that rapidly aggraded and/or became tectonically uplifted with slight changes to depositional conditions. Finally, the Paleodictyon producers lived in rather shallow water and became preserved by tempestites. This scenario argues against the continuous presence of Paleodictyon producers in shallow-marine settings, suggesting instead they appeared there recurrently.

Late Jurassic – earliest Cretaceous prolonged shelf dysoxic–anoxic event and its possible causes

AbstractThe Late Jurassic – earliest Cretaceous time interval was characterized by a widespread distribution of dysoxiс–anoxiс environments in temperate- and high-latitude epicontinental seas, which could be defined as a shelf dysoxic–anoxic event (SDAE). In contrast to black shales related to oceanic anoxic events, deposits generated by the SDAE were especially common in shelf sites in the Northern Hemisphere. The onset and termination of the SDAE was strongly diachronous across different regions. The SDAE was not associated with significant disturbances of the carbon cycle. Deposition of organic-carbon-rich sediment and the existence of dysoxic–anoxic conditions during the SDAE lasted up toc.20 Ma, but this event did not cause any remarkable biotic extinction. Temperate- and high-latitude black shale occurrences across the Jurassic–Cretaceous boundary have been reviewed. Two patterns of black shale deposition during the SDAE are recognized: (1) Subboreal type, with numerous thin black shale beds, bounded by sediments with very low total organic carbon (TOC) values; and (2) Boreal type, distinguished by predominantly thick black shale successions showing high TOC values and prolonged anoxic–dysoxic conditions. These types appear to be unrelated to differences in accommodation space, and can be clearly recognized irrespective of the thickness of shale-bearing units. Black shales in high-latitude areas in the Southern Hemisphere strongly resemble Boreal types of black shale by their mode of occurrence. The causes of this SDAE are linked to long-term warming and changes in oceanic circulation. Additionally, the long-term disturbance of planktonic communities may have triggered overall increased productivity in anoxia-prone environments.

Sedimentary characteristics and interactions among volcanic, terrigenous and marine processes in the Late Permian Kuishan Member, Eastern Block of the North China Craton

Understanding the variability of depositional environment and depositional processes of the Late Permian Kuishan Member, North China Craton, is crucial for unraveling the evolution of sedimentary basin and epicontinental sea in Shandong tectonic domain. The Kuishan Member in the Eastern Block of the North China Craton, formed in association with general regression of an epicontinental sea, is composed of abundant volcanic deposits and nearshore sedimentary deposits. Three lithofacies assemblages together with eleven lithofacies are identified in the study area, including volcanic deposits of the turbidity lithofacies assemblage, epiclastic deposits of the nearshore lithofacies assemblage, and mixed volcaniclastic and epiclastic sedimentary deposits of the terrestrial lithofacies assemblage. These alternating volcanic-epiclastic lithofacies assemblages illustrate the depositional environments induced by volcanic activities and nearshore wave influence. Syn-eruptive lithofacies, in the shallow water area, were formed by high density turbidity currents and ash fall into water introduced by rising sea levels and high rainfall due to volcanic eruptions to the north, whereas thin-bedded shallow marine silty mud developed in the distal area. Inter-eruptive lithofacies were represented by tuffaceous mudstone deposited in an exposed and oxidized setting due to falling sea level, whereas epiclastic nearshore deposits accumulated by wave or current flow regimes. Paleocurrent measurements show that the predominant regression direction changes from uniform southwest to divergent southwest and southeast during volcanic inter-eruptive periods. The Kuishan succession therefore can be regarded as a volcano-related sequence, in which the input of volcaniclastic and epiclastic deposits were significantly modulated by controls of volcanism, with frequently changing coastline position of the epicontinental sea and alternating depositional environments.

Comments on “Paleosalinity determination in ancient epicontinental seas: A case study of the T-OAE in the Cleveland Basin (UK)” by Remirez, M. N. and Algeo, T. J.

Comments on “Paleosalinity determination in ancient epicontinental seas: A case study of the T-OAE in the Cleveland Basin (UK)” by Remirez, M. N. and Algeo, T. J.

A Miocene Phreatoplinian eruption in the North-Eastern Pannonian Basin, Hungary: The Jató Member

A Middle Miocene, ~8 m thick pyroclastic succession, reported from the Bükk Foreland Volcanic Area (BFVA) in Northern Hungary (Central Europe) specified here as the Jató Member, was produced by silicic phreatomagmatism (Phreatoplinian sensu lato). Two well-preserved outcrops ~8 km apart and inferred to be within ~10–50 km from source represent the discontinuously exposed, layered, paleosol-bounded, phreatomagmatic Jató Member. They show an identical phenocrystal assemblage of feldspar, biotite and amphibole without weathered zones or signs of erosion, that suggest deposition in one eruption phase lasting hours to months. The succession contains three subunits: 1) subunit A, 1.8 m thick, a series of well-sorted fine to coarse ash or lapilli tuff layers with constant thickness; 2) subunit B, 2.1 m thick, a series of normal-graded layers with an upper fine-grained zone containing abundant ash aggregates with a coarser-grained core and distinctively finer-grained outer rim; 3) subunit C, 4.5 m thick, a massive, poorly to well-sorted coarse ash with gas escape structures and ash aggregates at its base. The upward change of these lithofacies implies an initially sustained dry fallout-dominated deposition of ash and pumice lapilli resulting in subunit A. Subsequently, multiple wet and dilute Pyroclastic Density Currents (PDCs) dispersed subunits B and C. The general abundance of PDC-related ash aggregates in the middle-upper part of the succession (particularly in subunit B), and the transformation of a fall-dominated to a collapsing depositional regime producing wet dilute PDCs, imply the increasing influence of water during the eruption (Phreatoplinian sensu lato). The presence of water is related to an epicontinental sea during Middle to Late Miocene in the Carpatho-Pannonian region. The transition from an initial dry magmatic phase generated fallout activity followed by the emplacement of wet PDCs' rich in ash aggregates, when external water infiltrated from a surrounding lake or sea water entered the vent.

Research on Sedimentary Facies and Sedimentary System of Permo-Carboniferous Strata in Xin’an Coal Field

In this paper, through rock core, logging curve, plane shape, distribution and other characteristics in the research area, combined with regional data, the Permo-Carboniferous Strata in the research area experienced tidal flat sedimentary system, delta sedimentary system and river sedimentary system, flood-overlake sedimentary system from bottom to top, it is proved that basin filling evolution of the epicontinental sea basin from occurrence, development to extinction.

Palynomorphs in surface sediments of the North-Western Black Sea as indicators of environmental conditions

Most previous Black Sea palynology studies have used pollen-spore assemblages as proxies for climate and landscape changes, and dinocyst assemblages as proxies for surface water salinity. However, there are few data on within-region variations in these assemblages using large sets of surface samples and a full suite of palynomorphs, including terrigenous pollen + spores, freshwater algal spores, and organic remains of marine microplankton, micro- and meiobenthos. Here we fill this knowledge gap, using results from a palynological study of 43 surface samples from water depths of 71–905 mbsl on the Ukrainian Shelf and adjoining continental slope, NW Black Sea. The palynology samples were collected in conjunction with water and sediment chemistry data, grain-size, micropaleontological and meiobenthos data from the EU-FP6 project HERMES “Hotspot Ecosystems Research on the Margins of European Seas”. This dataset uniquely covers shelf and upper slope areas east and west of the Odessa-Sinop Fault Zone (OSFZ) that delimits areas of lower and higher hydrocarbon gas contents, respectively.The new data show that on the wide shelf with a shallow (ca. 80 m) oxycline, pollen assemblages differ from classical models for marine pollen transport. On the Ukrainian Shelf, pollen concentrations are extraordinarily high far offshore and the grains are often pyrite-infilled. These features apparently reflect high pollen preservation potential in low oxygen sediments, probably enhanced by cross-shelf transport of land-derived particulate organic matter. The new data have important consequences for accurate modelling of carbon burial and storage in epicontinental seas, and they provide a baseline for evaluating marine pollen concentrations expected to reflect the early Neolithic farming on the Ukrainian shelf. Furthermore, although large concentrations of dinocysts comprise more than half of the total Non-Pollen Palynomorphs (NPP), the high pollen concentrations skew the P:D index (pollen:dinocyst ratio) commonly used to evaluate changes in paleo-shoreline (proxy sea-level) positions. Despite the discharge of several large rivers to the Ukrainian Shelf, there are negligible traces of freshwater algae in the HERMES samples except at Sta. 15 where Pediastrum is abundant. Overall, palynomorphs of terrestrial origin make up about half (52%) of the acid-resistant organic-walled particles on the outer NW Black Sea Shelf and adjacent slope.The abundances of the major micro- and meiobenthic palynomorph groups show the same trends east and west of the OSFZ as the micropaleontological data reported for the HERMES samples taken at the same sites. The combined microzooplankton and zoobenthos surface assemblage data provide an important new baseline for evaluating historical and past changes in biodiversity and aquatic foodweb structure in the now polluted NW Black Sea. Comparison can also be made with foodweb reconstructions for Permian black shales.

Phosphorites, glass ramps and carbonate factories: The evolution of an epicontinental sea and a late Palaeozoic upwelling system (Phosphoria Rock Complex)

AbstractThe Permian Phosphoria Rock Complex of the western USA contains an enigmatic assemblage of bioelemental rocks (i.e. phosphorites and cherts) that accumulated in a depositional system with no modern analogue. This study utilizes detailed sedimentological, stratigraphic and petrographic examination to evaluate the genetic relations of phosphorites, spiculitic chert and carbonates of the Ervay cycle (depositional sequence) and propose a unified oceanographic model for their deposition. The Ervay cycle contains three marine and one terrestrial facies association, each of which composes the bulk of a single lithostratigraphic unit. The marine facies associations include: (i) granular phosphorites (Retort Member); (ii) spiculitic cherty dolostones (Tosi Member); and (iii) marine to peritidal carbonates (Ervay Member). Red beds and intercalated gypsum (Goose Egg Formation) accumulated in the vast desert adjacent to the sea. The three marine members are chronostratigraphically distinct, successive and conformably stacked. They are not coeval facies belts. They reflect the progressive evolution of the epicontinental sea from the location of: (i) authigenic phosphogenesis (lowstand to transgression); to (ii) a glass ramp with biosiliceous (sponge) deposition (transgression); to (iii) a carbonate ramp (regression). This succession of switching biochemical sediment factories records the evolution of sea‐level, nutrient supply, upwelling, oxygenation and dissolved Si. Intense upwelling, potentially coupled with aeolian input, led to sedimentary condensation and phosphogenesis. Decreased upwelling intensity during transgression increased oxygenation sufficiently for a siliceous sponge benthos. Sponges were favoured over biocalcifiers due to elevated dissolved silica and a low carbonate saturation state. The cessation of sponge dominance and transition to a carbonate ramp occurred due to decreasing upwelling intensity, Si drawdown and an increased carbonate saturation state. These results provide insight into the role of Si loading in faunal turnover on glass ramps and highlight how differences in dissolved Si utilizers in pre‐Cretaceous versus post‐Cretaceous upwelling systems influence the resultant deposits.

Linking Western Tethyan Rhynchonellide morphogroups to the key post-Palaeozoic extinction and turnover events

Genetic control undoubtedly plays the most decisive role in the development of characters in rhynchonellides, especially in those structural features such as shell microstructure and brachidial architecture. However, considering the relationship between shell microstructure and type of crura in post-Palaeozoic rhynchonellides supported by recent growing research, the present study links this striking matching to the distribution of rhynchonellide morphogroups around the main post-Palaeozoic mass extinction and diversification events, innovatively introducing the ribbing pattern as a feature widely argued as indicator of deeper/shallower habitats and particular ecological conditions. The analyses performed on the Western Tethys rhynchonellide database and, directly on 28 species from the peri-Iberian margins around selected post-Palaeozoic extinction/diversification episodes, reveal a recurrent distribution pattern according to the habitat considered (epicontinental vs. epioceanic). The smooth, eurinoid, septifal/arcual body plan is the distinctive inhabitant of deeper epioceanic environments, also being the last to withdraw from the epicontinental platforms when the environmental conditions were adverse, and the pioneers or opportunistic taxa conducting repopulation of these epicontinental habitats when the conditions were re-established after crises. The ribbed, eurinoid, falciform morphogroup seems to be the more resilient stock on epicontinental platforms in relation to ecological crises. Conversely, the ribbed, leptinoid, raducal group is typical inhabitant of epicontinental seas when normal conditions prevail and shows an uneven distribution unlinked to critical events, suggesting a more specialist pattern with a diversification related with a secondary differentiation. It is suggested that this distribution dynamic of morphogroups was controlled by the availability of requirements to generate each type of crura and microstructure in epicontinental/epioceanic habitats, such as metabolic or oxygen restrictions, or the filter-feeding efficiency of the lophophore. A research line starting-point is thus herein introduced which can lead to shed light into the adaptive strategies of rhynchonellides, relating particular morphotypes with potential triggering factors of mass extinction events.

The Unconformity That Isn’t: A Sequence-Stratigraphic Reinterpretation of the J-5 Unconformity and the Redwater–Windy Hill–Morrison Transition in Wyoming, USA

The J-5 unconformity was originally described as occurring in Wyoming at the base of the Upper Jurassic Windy Hill Sandstone, where it separates the underlying Redwater Shale from the overlying Morrison Formation. The existence of this unconformity has been questioned, as has the closely coupled issue of the depositional environment of the Windy Hill Sandstone. In this article, we document the facies and architecture of the Redwater–Windy Hill–Morrison transition. Facies analysis indicates that the Windy Hill Sandstone represents a tide-dominated deltaic system that prograded northward across the shelf mudstones of the Redwater Shale, followed by the coastal plain of the Morrison Formation. The modern Han River Delta of Korea is a close analog to the Windy Hill Sandstone. The base of the Windy Hill Sandstone is not an unconformity; instead, it is conformable and time transgressive, becoming younger northward along depositional dip, implying that portions of the Redwater Shale and Morrison Formation are coeval. This reinterpretation of the J-5 unconformity in Wyoming, along with a greater appreciation of how abrupt stratigraphic contacts are formed stratigraphically, how they are recognized, and how unconformities are generated eustatically and tectonically, all suggest that a broader reappraisal of the Pipiringos and O’Sullivan unconformities is warranted. In addition, the recognition of a prograding tide-dominated delta in the highstand systems tract underscores the growing rejection of a sequence-stratigraphic paradigm that wave-dominated coasts form primarily during periods of progradation, with tide-dominated coasts being limited or favored during periods of transgression. Finally, tide-dominated deltas have been much more poorly recognized in the rock record than wave-dominated coasts and river-dominated deltas, but the previously unrecognized presence of one in the Windy Hill Sandstone suggests that other tide-dominated deltas might be similarly unrecognized in the rock record of epicontinental seas.

Lepisosteiform fish (Holostei) ganoid scales from the middle jurassic deposits of Ukraine

Gars (Lepisosteiformes) flourished in epicontinental seas throughout the world during the second half of Mesozoic and early Cenozoic. Cretaceous and Paleogene remains of these fishes are common in Europe while their Jurassic fossils are still relatively scarce. Here we re-describe in detail a series of ganoid scales from the latest Middle Jurassic (Callovian) deposits of&nbsp;Pekari (Cherkasy Region, Ukraine). These fossils were identified by&nbsp;Professor O.&nbsp;S.&nbsp;Rogovich in 1861 as those that belong to Lepidotus mantellii and L.&nbsp;fittoni. The referral of these scales to a certain species should be considered with caution because the described material lacks characters sufficient for identification it even to the genus or family. We consider to&nbsp;identify these fossils as Lepisosteiformes gen. et sp. indet. An overview of currently known Jurassic occurrences of lepisosteiform fishes is also presented in the paper. Lepisosteiformes, museum collection, morphology, Callovian, Europe.