Limestone Member Research Articles

A New Late Cretaceous Marine Vertebrate Assemblage from the Lincoln Limestone Member of the Greenhorn Limestone in Southeastern Colorado

The Lincoln Limestone Member of the Greenhorn Limestone is a mid-Cenomanian (94.7–95 Ma) deposit of the Late Cretaceous Western Interior Seaway in North America. Fossiliferous rock samples from the Lincoln Limestone were collected at a new locality (‘Table Mesa locality’) in southeastern Colorado. Acid treatment of the rock samples yielded at least 29 vertebrate taxa, including 13 chondiichthyan and 14 osteichthyan fishes as well as two reptilian (squamate) taxa. The taxonomic composition of the fauna broadly resembles previously described mid-Cenomanian localities in North America that further demonstrates the high taxonomic homogeneity of vertebrates in the Western Interior Seaway. Although the occurence of a terrestrial lizaid is noteworthy, proportions of common taxa at the Table Mesa locality are particularity similar to another Lincoln Limestone locality situated about 100 km to the west where remains of bony fishes also dominate.

Bombers and Bivalves: First North American Occurrence of the RudistDuraniasp. (Bivalvia: Radiolitidae) in the Upper Cretaceous (Cenomanian) Greenhorn Limestone of Southeastern Colorado

A colonial monospecific cluster of rudist bivalves from the lowermost Bridge Creek Limestone Member, Greenhorn Limestone (Upper Cenomanian) are attributable to Durania cf. D. cornupastoris. This discovery marks only the eighth recorded pre-Coniacian occurrence of rudist bivalves in the Cretaceous Western Interior and the only Cenomanian record of rudist Durania in North America. Discovered in 2011, the specimen was unearthed by aerial bombing at a training facility utilized during World War II. The appearance of rudist bivalves at mid-latitudes coincident with marked change in marine sediments likely represents the onset of mid-Cretaceous global warming.

Late Wenlock sequence and bentonite stratigraphy in the Malvern, Suckley and Abberley Hills, England

The Late Wenlock Series (Homerian Stage) of the central Midland Platform occupies an area stretching from Ledbury to the Malvern, Suckley and Abberley Hills. Based upon the establishment of a sequence stratigraphic framework for the Much Wenlock Limestone Formation, and the immediately under- and over-lying Coalbrookdale and Lower Elton Formations, comparisons can now be made with key sections across the northern Midland Platform and beyond. These correlations have been strengthened by the determination of apatite rare earth element (REE) geochemical signatures obtained from four volcanic ash layers (bentonites) at Whitman's Hill Quarry (Herefordshire), which allow for comparisons with published coeval sections at Wren's Nest Hill (West Midlands) and Wenlock Edge (Shropshire), as well as with bentonites described from the Island of Gotland (Sweden).Across the study area fifteen parasequences associated with two pronounced regressive episodes, separated by a marked transgression, can be identified. The lithological responses to these relative sea-level changes are the same as those reported from the West Midlands, including the threefold division of the Much Wenlock Limestone Formation into Lower Quarried Limestone, Nodular Beds and Upper Quarried Limestone Members. Apatite REE geochemical signatures from Whitman's Hill Quarry identify three bentonites which probably originated from a granodiorite magmatic source, while a fourth bentonite has a distinctively mafic composition, more akin to that of a gabbro or syenite. This distinctively mafic bentonite is preserved on a marked flooding surface within the Nodular Beds Member and appears compositionally and stratigraphically equivalent to a bentonite at Wren's Nest Hill (West Midlands). Furthermore in both sections this bentonite is of notable thickness (120–200mm) allowing for its identification in other sections across the region. Comparisons with Gotland identify three closely spaced bentonites of a similar mafic composition to the bentonite described from the Midland Platform. While similarities in stratigraphic position and composition do not, at present, allow for the identification of a single ash fall event covering both the Midland Platform and Gotland, they are indicative of a shared source region, which may offer the possibility for future bentonite correlation between these regions.

Carbon and sulfur isotopic fluctuations associated with the end-Guadalupian mass extinction in South China

Concentrations of total organic matter (TOC), carbon isotopic compositions of carbonate and organic matter (δ13Ccarb, δ13Corg), and sulfur isotopic compositions of carbonate associated sulfate (δ34Ssulfate) across the Guadalupian–Lopingian (G–L) boundary were analyzed from identical samples of Tieqiao section, Laibin, Guangxi province, South China. The δ13Ccarb values show a positive excursion from −0.45‰ to the peak of 3.80‰ in the Laibin limestone member of the Maokou Formation, followed by a drastic drop to −2.60‰ in the lowest Heshan formation, then returned to about 1.58‰. Similar to the trends of the δ13Ccarb values, Δ13Ccarb–org values also show a positive excursion followed by a sharp negative shift. The onset of a major negative carbon isotope excursion postdates the end Guadalupian extinction that indicates subsequent severe disturbance of the ocean–atmosphere carbon cycle. The first biostratigraphic δ34Ssulfate values during the G–L transition exhibit a remarkable fluctuation: a dramatic negative shift followed by a rapid positive shift, ranging from 36.88‰ to −37.41‰. These sulfate isotopic records suggest that the ocean during the G–L transition was strongly stratified, forming an unstable chemocline separating oxic shallow water from anoxic/euxinic deep water. Chemocline excursions, together with subsequent rapid transgression and oceanic anoxia, were likely responsible for the massive diversity decline of the G–L biotic crisis.

Calcareous plankton bio-chronostratigraphy of the Maltese Lower Globigerina Limestone member

Abstract Baldassini, N., Mazzei, R., Foresi L.M., Riforgiato, F. and Salvatorini, G. 2012. Calcareous plankton bio-chronostratigraphy of the Maltese Lower Globigerina Limestone member. Acta Geologica Polonica, 63 (1), 105-135. Warszawa. The planktonic foraminifera and calcareous nannofossil biostratigraphy of the Maltese Lower Globigerina Limestone member has been investigated. The member was dated to early planktonic foraminiferal P22 Zone and nannofossil NP25 Zone (upper Chattian). A climate-stratigraphic approach, based on the quantitative analyses of calcareous nannofossils, was used additionally to achieve a more precise chronology. The species Coccolithus pelagicus (diameter £11 μm) and the genus Umbilicosphaera were selected for the recognition of cold and warm surface waters intervals respectively. The ratio of their percentages enabled the construction of a Climatic Factor (CLF) curve. The CLF values were consistent with a warm climatic phase, which is probably represented by the portion of the oxygen stable isotope curve of Miller et al. above the Oi2c event and below the beginning of the cooling trend that culminates in the Mi1 event. Considering these two climatic events and the upper boundary of the NP25 Zone, it can be inferred that the deposition of the Lower Globigerina Limestone member took place between 25.1 and 24.3 Ma.

Bivalves from the Olenekian (Early Triassic) of south-western Utah: systematics and evolutionary significance

The recovery from the end-Permian mass extinction event was a key interval in the history of life, but few modern studies provide systematic data on benthic marine faunas from the epoch immediately following the crisis. Here, the bivalve fauna from the early Spathian (Olenekian, late Early Triassic) Virgin Limestone Member of the Moenkopi Formation is comprehensively documented for the first time. The new genus Sementiconcha (Myophoricardiidae), type species Sementiconcha recuperator sp. nov., and the new species Leptochondria nuetzeli, Eumorphotis ericius, E. virginensis and Pleuromya prima, are described. Leptochondriidae is placed in synonymy with Asoellidae, which is revised. With 27 species belonging to 18 genera, the Virgin Limestone Member records the highest bivalve diversity reported so far from this time interval, questioning previous claims that the recovery from the end-Permian mass extinction was delayed until the Middle Triassic. The two bivalve subclasses (Pteriomorphia and Heteroconchia) that are present in the Virgin Limestone Member clearly differ in their evolutionary contexts. Pteriomorphs of the Virgin Limestone are nearly exclusively composed of genera that survived the end-Permian mass extinction event, whereas heteroconchs are highly dominated by genera that evolved in the Early Triassic. This contrasting evolutionary background probably reflects differential effects of the end-Permian mass extinction event and subsequent crises on these two subclasses, possibly related to differences in filter feeding efficiency and shell mineralogy. The high proportion of infaunal heteroconchs, including deep-infaunal Pholodomyoida, is an additional indicator of a relatively advanced recovery stage, further corroborating that recovery of benthic organisms was well underway during the late Early Triassic. http://zoobank.org/urn:lsid:zoobank.org:pub:EC9802EA-F1D5-4066-A608-2B8DECE7C10D

Enrichment of uranium in the uppermost Al-Hisa Phosphorite Formation, Eshidiyya basin, southern Jordan

The Al-Hisa Phosphorite Formation (AHP) in the Eshidiyya basin of south Jordan consists of three members, the lower member accommodates the main high grade commercial phosphorite deposits, followed upwards by the coquinoidal limestone member which is overlain by the uppermost member, the A0 member. The phosphorites in both member are granular (peloidal) type deposits. Uranium (U) and Vanadium (V), in the main phosphorites of the lower member, are 75 and 70ppm respectively as analyzed in a previous work.The distribution of the analyzed elements in this work is governed by three factors: the phosphorite (P, Ca, Na, U, V, Cd, Zn, and Sr) decreasing upwards from the lower A0 unit to the topsoil, detritals (Al, Si, Fe, Mg, K, Ga, Hf, Nb, Rb, Th, and Zr) increasing upwards, and minor carbonates (Ca, and Sr) with no obvious trend. Uranium is three times more enriched in the upper phosphorite member, the A0, relative to the lower or main phosphorite member, 234ppm versus 75ppm respectively. Vanadium is likewise enriched several times in the A0. Both elements, U and V are worth further exploration in the A0 in northern Eshidiyya basin. Thorium, Zr and Hf are relatively low.

Palaeogeographic, palaeoclimatic, palaeohydrological and chemical/biochemical controls on accumulation of late Eocene coastal lacustrine–palustrine limestones, Southern England

The shallow-lacustrine to palustrine Hatherwood Limestone Member of the late Eocene Headon Hill Formation, Southern England, is in a succession of fluvio-estuarine and laguno-lacustrine siliciclastic sediments. It is up to 8.0m thick and is subdivided by metric-scale palaeotopographic erosion surfaces, one of which underlies lenticular humic siliciclastic mudstones. The limestone lithologies are (1) biocalcilutites/biocalcisiltites, (2) biocalcarenites, (3) calcirudites, and (4) laterally-discontinuous laminar and fenestral crusts. Lithology (1) accumulated in a low-energy shallow-lacustrine depositional environment, indicated by the predominance of pulmonate pond-snails in the mollusc assemblage. In contrast, lithologies (2) and (3) are the coarse-grained fills of shallow palaeotopographic lows, and also form basal lags and palaeokarst-fills. Lithology (3) comprises remnant autochthonous lags that resulted from selective erosion during lacustrine transgressions. Brecciation and proto-intraclast to nodular differentiation in lithology (2) suggests derivation of the intraclasts from subaerially- and pedogenically-modified shallow-lacustrine muds. Laminar crusts (4), 0.5–6.0cm in thickness, display irregularly undulose and anastamosing laminations 150–400μm thick, that display differential staining by iron oxide. The abundance of rootlet traces and calcitised parenchymatic root tissues in the fenestral crusts suggests a palustrine depositional environment for these lithologies. The siliciclastic mudstone lithologies are (1) black humic muds and (2) blue-green silty muds and marls. The high C/N molar ratio of the black muds suggests derivation of the humic content mainly from vascular plants in local wetlands. The mollusc assemblage of the blue-green siliciclastic muds resembles floodplain lake assemblages from the regional Palaeogene succession. Mean stable isotopic values for limestone samples, of −4.75±1.53 for δ13C and −2.77±1.47 for δ18O, indicate a relatively heavy tendency within published spectra for Tertiary lacustrine carbonates. The δ18O isotope results agree with published subtropical surface-water palaeotemperatures for this succession. The total characteristics of the Member therefore suggest a shallow-lacustrine to palustrine depositional environment. Pedogenic overprinting and mechanical reworking displayed by the limestones are attributable to seasonal fluctuations of water level during lake highstands, but in this marine-influenced setting, major long-term lake lowstands, resulting in deep erosion and palaeokarsting of the limestones, may be attributable to falls in relative sea-level. The biocalcilutites and humic muds accumulated during the ensuing lake transgressions.

The Okcheon Supergroup in the Lake Chungju area, Korea: Neoproterozoic volcanic and glaciogenic sedimentary successions in a rift basin

The Okcheon Belt in southern Korea is an NE-SW trending fold-and-thrust belt consisting of two sedimentary basins of different origins: namely, the Chungcheong Basin and the Taebaeksan Basin. The Chungcheong Basin was a Neoproterozoic rift basin belonging to the South China Craton, while the Taebaeksan Basin was a Paleozoic shallow marine to non-marine sedimentary basin fringing the Sino-Korean Craton. These two basins merged to form the Okcheon Belt in the early Triassic by the collision of Sino-Korean and South China cratons and their boundary is currently demarcated by the South Korean Tectonic Line. The Okcheon Supergroup is herein refined to include the Neoproterozoic volcanic and glaciogenic sedimentary successions deposited in the Chungcheong Basin and is divided into the two groups: the Chungju Group consists of the Gyemyeongsan Formation, Hyangsanni Dolomite, and Daehyangsan Quartzite and the Suanbo Group is proposed to include the Munjuri, Hwanggangni, Myeongori, and Gounni formations in ascending order. The Myeongori Formation is emended to comprise the Geumgang Limestone and the Seochangni members. This lithostratigraphic scheme is correlatable with that of the Nanhua Basin in South China, suggesting that the Chungcheong Basin was an eastward extension of the Nanhua Basin during the Neoproterozoic. The geological structure of the Okcheon Supergroup in the Lake Chungju area is characterized by a number of isoclinal to tight, frequently overturned, anticlines and synclines. No major thrust faults were recognized within the study area, except the constraining bend of the South Korean Tectonic Line. Three deformational phases are empirically differentiated: D1 deformation most strongly affected the rocks of the Okcheon Supergroup; D2 deformation was produced by the collision between the Sino-Korean and South China cratons; and D3 deformation is represented by normal to strike-slip faults. D1, D2 and D3 deformational phases are referred to the Okcheon (mid-Paleozoic), Songnim (Triassic) and/or Daebo (Jurassic) orogenies, and post-Jurassic events, respectively. The Chungcheong Basin was initiated as a part of an intracratonic rift basin (Nanhua Basin) within the South China Craton in association with early Neoproterozoic break-up event of the supercontinent Rodinia. The bimodal volcanic succession of the Gyemyeongsan Formation corresponds to the initial rift episode of the Chungcheong Basin, and was succeeded by shallow marine Hyangsanni Dolomite and Daehyangsan Quartzite. The second phase of rifting at ∼750 Ma accumulated a thick bimodal volcanic succession of the Munjuri Formation which is overlain by the diamictites of the Hwanggangni Formation representing the Cryogenian global glacial event, snowball Earth. The immediately-succeeding cap carbonate, Geumgang Limestone Member of the Myeongori Formation, recorded the deglaciation event. The Seochangni Member of the Myeongori Formation is characterized by dark gray slate/phyllite facies indicating a poorly-oxygenated basin during the Ediacaran. No stratigraphic unit overlying the Gounni Formation, the youngest Neoproterozoic formation of the Okcheon Supergroup, occurs in the Lake Chungju area, and thus little is known on the Paleozoic tectonic evolution of the Chungcheong Basin. It is inferred that the medium-pressure type regional metamorphism and the predominance of ductile deformation of the Okcheon Supergroup can be attributed to the mid-Paleozoic Okcheon Orogeny which would have been in line with the Wuyun Orogeny of South China. The South China and Sino-Korean cratons should have been drifted away from the Gondwana sometime during the mid-Paleozoic and collided to form the East Asian continent at ∼250 Ma.

Geochemistry of carboniferous shales of the Sardar Formation, east central Iran: Implication for provenance, paleoclimate and paleo-oxygenation conditions at a passive continental margin

The Sardar Formation (Carboniferous) has a lithological variation that is characterized by sandstone, shale and limestone members. Shales of the Sardar Formation from the east central Iran have been analyzed for major elements and a number of trace elements. The shales of Sardar Formation are rich in quartz minerals and clay minerals of the bulk minerals. Clay minerals of shales are composed of illite, kaolinite and slightly montmorillonite. SiO2 versus K2O/Na2O diagram shows these shales plotted in the passive continental margin or cratonic field. Geochemical data suggest high acidic source rocks similar to granite and intermediate igneous rocks. CIA and ICV suggest semi-humid climatic conditions during depositions and indicate high chemical weathering in the source area. The geochemical parameters such as V/Cr, Ni/Co and Cu/Zn ratios indicate that these shales were deposited in oxic environment.

Paleoecology and geochemistry of Early Triassic (Spathian) microbial mounds and implications for anoxia following the end-Permian mass extinction

Large microbialite mounds (1–2 m in height) have previously been reported from two units within the Spathian section of the Virgin Limestone Member of the Moenkopi Formation at Lost Cabin Spring, Nevada (United States). Previous investigations led to the interpretation that the mounds were formed under anoxic and alkaline conditions that suppressed metazoan grazers and delayed the biotic recovery from the end-Permian mass extinction. Here we report low organic carbon and total sulfur abundances throughout the section that suggest that anoxia was not prevalent during deposition. We also report that the upper mound-bearing unit contains stromatolitesponge patch reefs in which mutual encrustation between stromatolites and sponges contributed to the building of a reef framework. The stromatolite-sponge patch reefs contain discrete burrows within stromatolitic laminations, suggesting that there was suffi cient oxygen for grazing during the formation of the upper unit mounds. The enhanced ecological complexity of the upper unit mounds leads us to conclude that the mounds represent the transition to biotic recovery following the end-Permian mass extinction.

Of Bombers and Bivalves: North American Cenomanian Occurrence of the Rudist Durania sp. (Bivalvia: Radiolitidae) in the Upper Cretaceous Greenhorn Limestone of Southeastern Colorado

A colonial monospecific cluster of rudist bivalves from the lowermost Bridge Creek Limestone Member, Greenhorn Limestone (Upper Cenomanian) are attributable to Durania cf. D. cornupastoris. This discovery marks only the eighth recorded pre-Coniacian occurrence of rudist bivalves in the Cretaceous Western Interior and the only Cenomanian record of rudist Durania in North America. Discovered in 2011, the specimen was unearthed by historic aerial bombing during World War II. The appearance of rudist bivalves at mid-latitudes coincident with marked change in marine sediments likely represents the onset of mid-Cretaceous global warming.

The Carboniferous Archerbeck Borehole, near Canonbie (Dumfriesshire, southern Scotland): biostratigraphic revision of the late Asbian to early Pendleian succession using foraminiferans and regional correlations

ABSTRACTThe upper half of the Archerbeck Borehole contains a continuous Mississippian succession from the late Asbian (late Viséan) to the Pendleian (early Serpukhovian), with numerous limestone horizons. The borehole sequence lies within the Solway Basin (western end of the Northumberland Trough) and bridges the successions between the Midland Valley of Scotland and the Pennines (northern England). The rich foraminiferal and algal assemblages are compared to those described by previous authors, and genera as well as species are updated as far as is possible. In addition, some other overlooked or underestimated taxa have been identified and illustrated, which improve notably the biostratigraphic resolution of the Archerbeck Borehole succession. Within the abundant foraminiferal assemblages can be highlighted the richness and diversity of representatives of the family Archaediscidae. In general, the succession developed in the Archerbeck Borehole is closely comparable with that in the Alston Block of northern England. The Asbian/Brigantian transition mimics that observed in the Janny Wood boundary stratotype section, with clear late Asbian horizons (lower part of the Archerbeck Beds), transitional beds (middle and upper parts of the Archerbeck Beds), and Brigantian limestones (from the Cornet Limestone upwards). The base of the early Brigantian is placed at the base of the Cornet Limestone (equivalent to the Lower Peghorn Limestone in the Alston Block). The base of the late Brigantian is placed at the base of the Gastropod Limestone (equivalent to the Scar Limestone Member in northern England), and the base of the Pendleian is repositioned at the base of the Under Limestone (equivalent to the Four Fathom Limestone Member in northern England). Throughout, the borehole, protista and microfloral elements are abundant, which allows the recognition of Assemblages 4 to 10, previously recognised in northern England and the Midland Valley of Scotland. Furthermore, other local assemblages are recognised and related to palaeoecological controls, although they do not represent any improvement in biostratigraphical resolution.

The late Barremian Halimedides horizon of the Dolomites (Southern Alps, Italy)

A new trace fossil marker level, the Halimedides horizon, is proposed for the Lower Cretaceous pelagic to hemipelagic succession of the Puez area (Southern Alps, Italy). The horizon occurs in the middle part of the late Barremian Gerhardtia sartousiana Zone (Gerhardtia sartousiana Subzone). It is approximately 20 cm thick and restricted to the uppermost part of the Puez Limestone Member (marly limestones; Hauterivian–Barremian; Puez Formation). It is fixed to the top 20 cm of bed P1/204. The grey–whitish limestone bed of the G. sartousiana Zone is penetrated by Aptian red marls–siltstones of the Redbed Member. The horizon is documented for the first time from the Southern Alps, including the Dolomites, and can be correlated with other Mediterranean localities. The trace fossil assemblage of this marker bed with the co-occurrence of Halimedides, Spongeliomorpha and Zoophycos sheds light on the Lower Cretaceous sedimentological history and current system of the Puez area within the Dolomites. It also highlights the palaeoenvironmental evolution of basins and plateaus and provides insights into the late Barremian interval.

Fifth-order cyclicity and organic matter contents relationship (Lower Eocene, Pyrenees)

The Upper Limestone Member of the Corones Formation of the Spanish Pyrenees consists of various units (Lower and the Upper Foraminifera Units, Shale Unit, Cherty-ostracode Unit, Ostracode Unit and Chara-ostracode Unit) and offers strong facies and lateral thickness (20 to 80 m) variations. Detailed facies analyses, fifth-order cycles and organic geochemical determinations in the central domain of the Corones platform carbonates (Cherty-ostracode Unit), lower Eocene in age, were carried out to establish a case of close relationship between variations in organic matter productivity and cyclicity with annual period. The Cherty-ostracode Unit displays a continuous and pervasive fifth-order cyclicity, represented by 5 cycles. Each cycle consists of a lower part (mollusc facies) and an upper part (laminated ostracode facies). The calculated fifth-order cycle period ranges from about 17,000 to 28,000 years, which falls within the Milankovitch Band. Variations in organic matter content related to these carbonate cycles have been established. The lower mollusc facies members show a low organic carbon content and Hydrogen Index (HI) below 0.6% in weight and 261, respectively. By contrast, the upper laminated ostracode facies members show high organic carbon contents (up to 2% in weight) and high HI (between 164 and 373), and are also characterized by important silicification processes (the content in chert is up to 30%). The organic geochemistry resulting from these organic rich levels reflects a contribution of algal marine input.

Recognition of algal rich facies from the Umlatdoh Limestone of Shella Formation, Jaintia Group, Meghalaya

The carbonate rocks of the Shella Formation (Middle Eocene) belonging to the Jaintia Group in the Jaintia Hills of Meghalaya are represented by two sandstone units in alternation with three limestone units, viz. Lakadong Limestone, Umlatdoh Limestone and Prang Limestone respectively in chronological order. Umlatdoh Limestone, the middle limestone unit of Shella Formation is conformably underlain by the Lakadong Sandstone and overlain by Narpuh Sandstone. Samples from the Umlatdoh Limestone were collected from the outcrop on the Jowai-Badarpur Road, about 1 km southwest of Lumshnong. Calcareous algae have been recovered from four samples and two distinct facies have been recognized. One of the facies is dominated by non-geniculate coralline red algae and benthic foraminifera. The non-geniculate corallines are represented by Lithothamnion and Mesophyllum (Family Hapalidiaceae), Lithoporella (Family Corallinaceae) and Sporolithon (Family Sporolithaceae). The other facies is rich in calcareous green algae along with benthic foraminifera. The green algal genera belong to families Dasycladaceae, Udoteaceae and Halimedaceae. Previously, a green algal assemblage was recorded from the Umlatdoh Limestone Member of Shella Formation exposed in the low lying hills between Sutnga and Litang valleys of Jaintia Hills. However, this is the first report on the occurrence of non-geniculate coralline red algae from the Umlatdoh Limestone Member of the Shella Formation. Based on the algal-foraminiferal assemblages, interpretation has been made on the palaeoenvironment and palaeobathymetry.

Strontium isotopic ages of the Torinosu-type limestones (latest Jurassic to earliest Cretaceous, Japan): Implication for biocalcification event in northwestern Palaeo-Pacific

The ages of the Late Jurassic to the Early Cretaceous shallow marine limestones in Japan (the Torinosu-type limestones) were evaluated by Sr isotopic stratigraphy. The 87Sr/86Sr ratios of 17 brachiopods collected from three sections revealed ages that are consistent with the previous assumption based on biostratigraphy. The age of the upper horizon of the Koike Limestone Member (the Soma-Nakamura Group, NE Japan) ranges from 150.6Ma to 149.2Ma (the latest Kimmeridgian to the early Tithonian). The limestones from two sections (the Torinosu and Imaidani Group) on Shikoku Island of SW Japan yield the younger ages, which evaluate the depositional rate of the two limestones 6.3–14.5m/m.y. By applying these rates, the depositional period was estimated for the whole limestone of each section; from 151.1Ma (the latest Kimmeridgian) to 140.3Ma (the latest Berriasian) for the Torinosu Group, from 151.5Ma (the late Kimmeridgian) to 143.0Ma (the early Berriasian) for the Imaidani Group. These results confirm active carbonate deposition in the shallow fore-arc platform in SW Japan from the Tithonian to the Berriasian. The biocalcification event recognized in relevant age in the Tethyan region was likely expanded to the Palaeo-Pacific. The carbonate deposition in the platform was terminated by sea level fall during the early Valanginian.

Lower Miocene oyster shells from the Southeast Zagros Basin (Zade Mahmud area, Iran) and their paleoecology

The Guri limestone Member of the Mishan Formation in the Zagros Basin consists of thick bedded limestone bearing benthic foraminifera and oyster shells. Seven species of Ostreidae and Gryphaeidae were identified as belonging to four genera (Crassostrea, Cubitostrea, Ostrea, and Hyotissa), i.e., Cubitostrea frondosa, Ostrea (Cubitostrea) dubertreti, Cubitostrea digitalina, Crassostrea gryphoides, Hyotissa virleti, Ostrea vesitata, and Ostrea plicatula. These fossils are reported for the first time from Iran. Miocene deposits in the studied area contain a rich benthic foraminiferal fauna dominated by Pseudotaberina, Meandropsina, Miogypsina, Flosculinella, Borelis, and other larger benthic foraminifera. We assign these sediments to a Burdigalian age based on Borelis melo curdica–Borelis melo melo Assemblage Zone. Paleoecological considerations also revealed that the beds were deposited in a near-shore non-agitated and shallow-water environment with moderate to low sedimentation rate. The studied oysters are located in one of more important paleogeographic settings in the world and very similar to many other Tethyan regions. The presence of these oysters suggests that the Zade Mahmud area located at margins of a sea way that connected the north and south of Zagros Basin during Burdigalian.

Planktic Foraminiferal Biostratigraphy of the Cretaceous Oceanic Red Beds in Kangmar, Southern Tibet, China

Abstract:The planktic foraminifera of the Chuangde Formation (Upper Cretaceous Oceanic Red Beds, CORBs) as exposed at Tianbadong section, Kangmar, southern Tibet has been firstly studied for a detailed for a detailed biostratigraphy elaboration. A rich and well‐preserved planktic foraminifera were recovered from the Chuangde Formation of the Tianbadong section and the Globotruncanita elevata, Globotruncana ventricosa, Radotruncana calcarata, Globotruncanella havanensis, Globotruncana aegyptiaca, Gansserina gansseri and Abathomphalus mayaroensis zones have been recognized. The planktic foraminiferal assemblage points to an early Campanian to Maastrichitian age for the CORBs of the eastern North Tethyan Himalayan sub‐belt, which also provides a better understanding of the shifting progress of the Indian Plate to the north and the evolution of the Neotethyan ocean. The lithostratigraphy of the Chuangde Formation of the Tianbadong section comprises two lithological sequences observed in ascending succession: a lower unit (the Shale Member) mainly composed of purple (cherry‐red, violet‐red) shales with interbedded siltstones and siliceous rocks; and an upper unit (the Limestone Member) of variegated limestones. The strata of the Chuangde Formation in the Tianbadong section are similar to CORBs in other parts of the northern Tethyan Himalaya area of Asia (Gyangze, Sa'gya, Sangdanlin, northern Zanskar, etc.). The fossil contents of the Chuangde Formation in the sections (CORBs) studied provide a means of correlation with the zonation schemes for those of the northern Tethyan Himalayan sub‐belt and the Upper Cretaceous of the southern Tethyan Himalayan sub‐belt. Paleogeographic reconstruction for the Late Cretaceous indicates that the Upper Cretaceous Chuangde Formation (CORBs) and correlatable strata in northern Zanskar were representative of slope to basinal deposits, which were situated in the northern Tethyan Belt. Correlatable Cretaceous strata in Spiti and Gamba situated in the southern Tethyan Belt in contrast were deposited in shelf environments along the Tethyan Himalayan passive margin. CORBs are most likely formed by the oxidation of Fe(II)‐enriched, anoxic deep ocean water near the chemocline that separated the oxic oceanic surface from the anoxic.

New biostratigraphic data on an Upper Hauterivian–Upper Barremian ammonite assemblage from the Dolomites (Southern Alps, Italy)

A biostratigraphic subdivision, based on ammonites, is proposed for the Lower Cretaceous pelagic to hemipelagic succession of the Puez area (Southern Alps, Italy). Abundant ammonites enable recognition of recently established Mediterranean ammonite zones from the upper Hauterivian Balearites balearis Zone (Crioceratites krenkeli Subzone) to the upper Barremian Gerhardtia sartousiana Zone (Gerhardtia sartousiana Subzone). Ammonites are restricted to the lowermost part of the Puez Formation, the Puez Limestone Member (ca. 50 m; marly limestones; Hauterivian–Barremian). Numerous ammonite specimens are documented for the first time from the Southern Alps (e.g., Dolomites). Ammonite abundances are clearly linked to sea-level changes from Late Hauterivian to mid Late Barremian times. Abundance and diversity peaks occur during phases of high sea-level pulses and the corresponding maximum flooding surfaces (P. mortilleti/P. picteti and G. sartousiana zones). The ammonite composition of the Puez Formation sheds light on the Early Cretaceous palaeobiogeography of the Dolomites. It also highlights the palaeoenvironmental evolution of basins and plateaus and provides insights into the faunal composition and distribution within the investigated interval. The intermittent palaeogeographic situation of the Puez locality during the Early Cretaceous serves as a key for understanding Mediterranean ammonite distribution.