Normal Marine Environment Research Articles

Geochemical, mineralogical, and petrological analyses for the interpretation of the sedimentary environment of the Middle-Late Ordovician Majiagou Formation (northern China) as a tool for more effective gas exploration

Core samples from the deeply buried Ordovician Majiagou Formation below the Huainan Coalfield (E China) have been investigated for their carbonate types, major and trace elements (including rare earth elements) and C and O isotopes. The objective was to get a better insight into the possible occurrences of gas (and possibly oil) derived from Carboniferous coals. It was found that the carbonates are dolomites with strongly varying amounts of CaO and MgO. The low concentrations of SiO 2 , Al 2 O 3 , and Fe 2 O 3 indicate deposition in a normal marine environment with little terrigenous input. The Na 2 O/K 2 O, Fe/Mn and Sr/Ba ratios, as well as the Ga values indicate mainly a marine salinity and a hot and humid climate. The slight depletion of Ce and Eu, the depletion of heavy REE and the enrichment of light REE indicate deposition in a reducing environment. It thus appears that the Majiagou Formation below the Huainan Coalfield closely resembles that in the eastern part of the Ordos Basin, where several gas reservoirs are present, so that the Majiagou Formation under the Huainan Coalfield represents a promising target for hydrocarbon exploration.

Carbon and oxygen isotopes of the Lianglitage Formation in the Tazhong area, Tarim Basin: Implications for sea‐level changes and palaeomarine conditions

Carbon isotopes can be used to interpret sea‐level changes during deposition, but the accuracy of sea‐level changes indicated by shallow‐water carbonates remains unclear. We carried out sedimentary microfacies and stable isotope analysis of carbonate rocks in Upper Ordovician Lianglitage Formation in Tazhong area, Tarim Basin, to examine the response of isotopes to high‐frequency cycles of shallow‐water carbonate rocks. The Lianglitage limestones can be divided into four types of microfacies that were deposited in reef and shoal environments on a platform margin. A total of sixty‐one (61) selected limestone samples have the δ13C value varying from 0.5993‰ to 1.6228‰ (average 1.1364‰). The extremely low correlation coefficient of carbon and oxygen isotopes indicate that the samples can represent the deposition seawater, thus the estimated Z value and temperature show that the Lianglitage Formation was deposited in the normal marine environment in a tropical to subtropical zone. The Lianglitage Formation shows a clear deposition trend from tidal flat to reef shoal and then to an open platform. The sedimentary environment controls the difference in carbon and oxygen isotopes of shallow‐water carbonates through the rate of burial of organic carbon, and thus the δ13C tend to increase when sea level rise. Hence the carbon isotopic composition of shallow‐water carbonate rocks can reflect sea‐level changes. The δ13C of Lianglitage Formation in well TZ72 shows four sedimentary cycles (20–40‐meters‐thick) controlled by sea‐level changes, which were also recorded in this Formation from other parts of the Tarim Basin.

Catastrophic event sequences across the Permian-Triassic boundary in the ocean and on land

This review forms the preface of a special issue dealing with Environmental stresses and biotic responses during the Palaeozoic-Mesozoic transition, and develops an improved understanding of the sequence of catastrophe events associated with the Permian-Triassic (P–Tr) transition in particular. The 16 papers that comprise this special issue mostly focus on the Paleo-Tethys and Panthalassia regions, and enable us to recognize seven distinct phases of biotic and environmental evolution that may be precisely correlated between marine and terrestrial environments. Phase 1 represents the normal marine environments and biota that existed at 252.104 Ma, prior to the onset of major environmental perturbation. Phase 2 is marked by the onset of a negative carbon (δ13Ccarb) isotopic excursion, and coincides with a significant decline in radiolarian diversity, the collapse of communities in shallow metazoan reefs and deep-water settings, and the loss of rainforests on land (including the disappearance of Gigantopteris flora). Phase 3 is characterized by a pulse of biodiversification on the eve of the end-Permian extinction (EPE). Phase 4 comprises the EPE event itself, dated to 251.941 Ma, and coincides with an extreme episode of widespread anoxia, biodiversity loss, community structural collapse, and volatile volcanic eruptions. Phase 5 is marked by the renewed onset of oxic conditions in all oceanic environments except those in microbialite-rich shallow platform settings where abundant pyrite framboids signal dysoxia. Phase 6 includes the earliest Triassic extinction (ETE) event, dated to 251.880 Ma, and associated with euxinic to anoxic conditions and ocean acidification. An extended phase of deoxygenation and acidification returned to the marine settings during Phase 7, possibly driving a calcium crisis. The terrestrial extinction event (Phase 2) probably commenced c. 60 kyrs (in South China) or 370 kyrs (in Sydney basin) before the marine P–Tr extinction, the latter consisting of two distinct events (Phases 4 and 6), spaced c. 60 kyr apart, each being marked by both a carbon isotope excursion and ecologic collapse. The environmental changes associated with these three extinction phases in the ocean and on land can be attributed to the effects of volcanic emissions (e.g., CO2, SO2, halogens and metals) during the eruption of the Siberian Traps Large Igneous Province and convergent margin volcanism related to Tethyan tectonics.

FISH OTOLITHS AND FORAMINIFERA FROM THE BORSKÝ MIKULÁŠ SECTION (SLOVAKIA, MIDDLE MIOCENE, UPPER BADENIAN, VIENNA BASIN) AND THEIR PALEOENVIRONMENTAL SIGNIFICANCE

Thirty-eight otolith-based species of fishes and 41 foraminifera species have been recorded in the Borský Mikuláš-Vinohrádky section in the upper Badenian deposits in the eastern part of the Vienna Basin, in West Slovakia. Two new species of otoliths are introduced here: Thorogobius antirostratus n. sp. and Gerres mlynskyi n. sp. Among the foraminifera Biasterigerina planorbis and Elphidium crispum associated with other elphidiids, Lobatula lobatula and Cibicides crassiseptatum prevail. Overall, the family of Gobiidae dominate in the assemblage of otoliths (>90 % of specimens). Meso- and epipelagial fishes or diversified gadids and sciaenids are missing. From the molluscs, the first record of Aturia sp. in the Borský Mikuláš section is observed. Otoliths and foraminifera document a normal marine environment of well-aerated shallow water with a depth of 30-50 metres, with muddy to sandy bottoms of marine meadows and plenty of light in the subtropical climatic conditions. Several fish genera (for example Gerres) give evidence for the nearness of reef structures. There are no species (excepting Lesueurigobius vicinalis) in common with the known Lower Serravallian otolith fauna from the Eastern Paratethys. Some species from the Borský Mikuláš-Vinohrádky section can also be found in the Mediterranean Langhian-Serravallian interval and are interpreted as a relic of the lower Badenian (Langhian) fish assemblages.

MARINE LIFE IN THE MEDITERRANEAN DURING THE MESSINIAN SALINITY CRISIS: A PALEOICHTHYOLOGICAL PERSPECTIVE

Almost fifty years after the first definition of the Messinian salinity crisis (MSC), the events that occurred in the Mediterranean during the terminal portion of the Miocene still attract the attention of a large and diverse scientific community. Although fossils are relatively common in the deposits that accumulated during the MSC, their significance for the interpretation of the latest Miocene paleoenvironmental evolution of the Mediterranean has been underevalued. In this paper, we summarize the marine paleoichthyological record of the three stages of the MSC based on both articulated and isolated skeletal remains and otoliths, the latter almost exclusively known from the Lago-Mare phase. We focus on the composition of the marine ichthyofauna of the Mediterranean during the three main stages of the MSC, showing the persistent continuity of marine stenohaline taxa throughout most of the interval between 5.97 and 5.33 Ma. While the record of articulated fish skeletons is unquestionably autochthonous, thereby providing unambiguous evidence of the occurrence of open marine environments in the MSC preceding the Lago-Mare phase, the autochthonous nature of the otolith record has often been questioned. For this reason, the otolith record of marine fishes has been examined in detail from a taxonomic and paleoecological point of view. Three species, Bellottia verecunda n. sp., Benthosema taurinense n. sp., and Bostrychus marsilii n. sp., are described as new and a thorough discussion about the possible origin of the otoliths is provided. Alternative explanations for the occurrence of otoliths of marine fish during the Lago-Mare phase, such as reworking, contamination from overlying Pliocene sediments or import from outside the Mediterranean through aquatic birds are considered unlikely. In our assessment, the occurrence of marine fish otoliths in the Lago-Mare phase can be explained with the presence of normal marine environments in the Mediterranean, at least temporarily. Therefore, we suggest that the paleoichthyological data provided herein should be integrated in the future evolutionary paleoenvironmental reconstructions of the MSC.

CHARACTERISTICS AND ORIGIN OF THE DOLOSTONES OF THE EDIACARAN DENGYING FORMATION IN THE EASTERN SICHUAN BASIN, SOUTH CHINA

The Ediacaran Dengying Formation dolostones were the crucial carrier of the co-evolution between the biota and environment before the Cambrian Explosion and the solid mineral and petroleum resources. Based on the petrological and mineralogical analyses, the Dengying Formation at the Liaojiacao Section consists of micritic, fine-crystalline and medium-crystalline dolostones and algal-bonded or algal-clastic dolostones. Moreover, the micritic and algal-bonded dolostones mostly retain the original sedimentary structure with widespread microbial mats, algal spots, algal traces, and other microbial fossils. Recrystallization, dissolution, and other diagenetic alterations occurred in the fine-crystalline and medium-crystalline dolostones as well as algal-clastic dolostones, and their original sedimentary structures had been significantly altered. Furthermore, in situ geochemical analysis shows that the micritic and algal-bonded dolostones of the Dengying Formation, which retain the original sedimentary structure, have Mg/Ca ratios close to the ideal primary dolomite; Na, Fe, Mn, and Sr concentrations located in the distribution range of calcites and dolomites formed in a normal marine environment, negative Ce anomaies and positive Eu anomaies with the patterns of light rare earth element depletion and medium and heavy rare earth element enrichment. In addition, the whole-rock stable isotopic analyses show that the δ13Cdol values of dolostones that retain the original sedimentary structure are consistent with the distribution range of the original marine carbonate rocks, but the δ18Odol values are slightly lower than those of the original marine carbonate rocks. Therefore, we infer that the dolostones of the Dengying Formation at the Liaojiacao Section with original sedimentary structure are the products of mimetic dolomitization and formed in an environment with extensive microbial activity, calcite as the preexisting mineral, normal salinity, and oxidized seawater as the dolomitization fluid. Moreover, the fine- and medium-crystalline dolostones were the results of recrystallization that retained the original sedimentary structures during diagenesis.

Geochemical characteristics and organic matter enrichment mechanism of Permian black mudstone in the South Yellow Sea Basin, China

The middle Permian organic matter-rich mudstone in the South Yellow Sea Basin has been considered the most important source rock for Paleozoic reservoirs in the basin. However, information on the variation in depositional environment within the Qixia Formation to lower Longtan Formation interval is lacking, and the formation mechanism of these organic matter-rich mudstones is unclear. Based on a series of geochemical analyses of borehole CSDP-2, the paleoclimatic conditions, nature of the watermass, paleoproductivity and terrestrial detrital influx of the different intervals in the middle Permian of the South Yellow Sea Basin were assessed to determine the main factors controlling organic matter enrichment. All three intervals (from the Qixia Formation to the lower Longtan Formation) were deposited under a relatively warm and humid paleoclimate with moderate terrestrial detrital input. The Qixia Formation was deposited under oxic paleoredox conditions in a normal marine environment. During deposition of the Gufeng Formation, the paleoredox conditions changed to suboxic with intermittent anoxia associated with paleoproductivity higher than that in the other studied intervals. The lower Longtan Formation was characterized by a brackish watermass, suboxic paleoredox conditions and low paleoproductivity. The covariant relationships among paleoproductivity, paleoredox conditions, watermass salinity indicators and TOC content indicate that paleoproductivity was the critical factor controlling organic matter abundance. High primary productivity not only provided organic matter but also enhanced organic matter preservation by consuming oxygen in the watermass, which resulted in the formation of the organic matter-rich source rock in the Gufeng Formation. • The Gufeng Formation exhibits higher paleoproductivity than other two intervals. • Higher paleoproductivity resulted in relative reducing redox condition. • Paleoproductivity level controls the deposition of OM-rich source rock.

Analysis of dolomite reservoir characteristics of Lower Permian Maokou Formation and dolomite origins in Chuanzhong Area

Dolomite of Lower Permian Maokou Formation has a strong heterogeneous formation in-plane and vertical in Chuanzhong Area. Its formation mechanism is not yet fully understood. Thus, this study focuses on the Maokou Formation core and conducts thin section analysis, isotope analysis, cathodoluminescence, and data analysis of fluid inclusion using a combination of geological and chemical analysis methods to summarize the characteristics of dolomite reservoir layer of Maokou Formation and its formation mechanism. The Maokou Formation is believed to be the result of a deformity of dolostones, medium–fine grained dolomite, and a few gray dolomites, with the exception of gypsum layer. In the reservoir space of dolostones, pore type occupies the first layer, and dissolved seam and particle-dissolved pores are in the second layer. The dolomite value of δ 13 C was distributed in the range of 1.78‰–3.95‰(PDB), and the value of δ 18 O was distributed in the range of −7.39‰ to −3.8‰(PDB) with above 120 salinity. Thus, the dolomite reservoir was formed in a normal marine environment. Inclusions show that dolomite in the study area have a multi-phase fluid filling and a homogenized temperature of the maximum value of above 160 °C, which is not within the value that the normal temperature gradient can reach. Thus, buried dolomitization, seepage flow, Penesyndiagenesis, and Sabha genetic model are ruled out from the study area of Maokou Formation. The fault development that connected the basal layer with the stratum of Maokou Formation was distributed in the G3 well area, which provides a channel for the upper channeling of the basal hydrothermal fluid. In the Chuanzhong Area, the dolomite of the Lower Permian Maokou Formation is considered to be mainly of tectonic-hydrothermal origin.

Stratigraphic architecture of a mixed clastic-carbonate succession and 87Sr/86Sr-based chronostratigraphy along the margin of a synorogenic extensional basin (Hochmoos Formation, upper Santonian, Northern Calcareous Alps)

Abstract The Gosau Group (Turonian to Ypresian) of the Eastern Alps is a synorogenic wedge-top succession that accumulated in active depocenters in an oblique-convergent plate tectonic setting. Due to high morphological differentiation of depocenters by tectonism, the Gosau Group displays a wide range of facies as well as marked facies heteropy and thickness variations over short lateral distances. In the area of the locations Gosau and Russbach, the Hochmoos Formation along the SE basin margin near Gosauschmied comprises coastal to shallow-marine deposits and small rudist bioconstructions and was investigated by way of field mapping, profile descriptions, microfacies analysis, isotope measurements and assessment of fossil content. Strontium isotope ratios (87Sr/86Sr) from 0.707485 (oldest) to 0.707549 (youngest) indicate a latest Santonian age, with the youngest parts of the Hochmoos Formation possibly extending into the Campanian. On the west side of the study area, the succession of lithologies and fossil content record transgression of a fan-delta to marginal-marine environment (lowstand to transgressive systems tract), followed by shallow neritic deposition (part of the transgressive systems tract) and, finally, by progradational stacking of limestone beds in the highstand systems tract, culminating in growth of rudist thickets in an inner shelf and partially protected ‘lagoonal’ milieu. Eventually, at the inception of the following falling stage systems tract, input of large clasts of Dachstein Limestone, quartz and chert record a recurrence of the subaqueous part of a fan-delta. On the east side of the study area, a preponderance of rudist-clastic limestones over a few rudist biostromes preserved in situ indicate a normal-marine environment punctuated by high-energy events, such as storms or tsunami. The scarcity of benthic foraminifera and the presence of only isolated specimens of colonial corals underscore a habitat with a calcarenitic substrate frequently shifted by currents. Several lines of evidence indicate that the western part of the study area was more proximal relative to the eastern one. With a maximum thickness of 68 m, the Hochmoos Formation at Gosauschmied is slightly thicker and more distal than outcrops located nearer to the basin margin and farther towards the SE (Schmiedsippl, Katzhofgraben), but significantly thinner than the nearly 300 m at Gosau Pass-Gschütt, or the thickness of 170 m observed in the area of Rigaus-Abtenau farther in the West. These thickness variations are interpreted as a result of extensional syndepositional tectonism. At Gosauschmied, the vertical arrangement of facies records a cycle of relative sea-level change that may have been tectonically enhanced.

The distributions and geochemical implications of methylated 2-methyl-2-(4,8, 12-trimethyltridecyl)chromans in immature sediments

Methylated 2-methyl-2-(4,8,12-trimethyltridecyl)chromans are salinity-sensitive biomarkers that have been detected in immature – early mature petroleum and sediments. In this study, the occurrence and distribution patterns of 2-methyl-2-(4,8,12-trimethyltridecyl)chromans were investigated in a set of lacustrine sediments from Nördlinger Ries of southern Germany and marine sediments from the South China Sea. Among all of the 2-methyl-2-(4,8,12-trimethyltridecyl)chroman isomers detected, 8-Me-2-methyl-2-(4,8,12-trimethyltridecyl)chroman presented with high abundance in sediments deposited in hypersaline environments, while absent in samples from normal marine environments. In contrast, 5,7,8-triMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman was more enriched in sediments from marine environments. This study also showed that the ratio of 5,7,8-triMe-/5,8-diMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman can be applied as a potential salinity indicator on account of a positive correlation with other 2-methyl-2-(4,8,12-trimethyltridecyl)chroman salinity indicators. This ratio can be an alternative indicator of paleosalinity when 8-Me-2-methyl-2-(4,8,12-trimethyltridecyl)chroman is absent or present in quite low abundance. The content of 2-methyl-2-(4,8,12-trimethyltridecyl)chroman isomers may be affected by freshwater supply and lithology. Molecular simulations showed that 5,8-diMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman has a higher thermal dynamic stability than 7,8-diMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman. Thus, the ratio of 5,8-diMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman/7,8-diMe-2-methyl-2-(4,8,12-trimethyltridecyl)chroman may be a potential maturity parameter for sediments at a low thermal mature stage.

Acritarchs and prasinophytes from the Lower Devonian (Lochkovian) Ross Formation, Tennessee, USA: stratigraphic and paleogeographic distribution

A diverse and abundant organic-walled microphytoplankton assemblage is reported from two measured sections of the Lower Devonian (Lochkovian) Ross Formation in Benton and Decatur counties, Tennessee, USA. The palynoflora comprises 24 genera and 34 species of acritarchs, including one new genus and species (Caulissoma gordonii); and five genera and 11 species of prasinophyte phycomata (excluding Leiosphaeridia and Tasmanites). Other components include chitinozoans, miospores, and scolecodonts. This is the first Early Devonian acritarch/prasinophyte assemblage to be described from Tennessee, and it is assigned a Lochkovian age based on marine invertebrate faunas, stratigraphic relationships, and the palynomorph assemblage. A high degree of similarity (67% commonality) exists between this palynoflora and that from the stratigraphic and age-equivalent Haragan and Bois d’Arc formations of Oklahoma. Appreciable numbers of the microphytoplankton taxa identified herein are common to the Haragan and Bois d’Arc formations and are, moreover, restricted to the Lochkovian and endemic to Laurentia. Additionally, a number of species are widely distributed and confined to the Early Devonian, and three species, Demorhethium lappaceum, Riculasphaera fissa, and Thysanoprobolus polykion – all cosmopolitan – are constrained to the Lochkovian. With increasing knowledge of Early Devonian palynofloras, the apparent degree of provincialism is progressively declining as seemingly endemic taxa are reported from more regions in both hemispheres. The Ross Formation sediments were deposited in a low-energy, offshore, normal marine environment, punctuated by intermittent episodes of shallow-water current and storm deposition.

The biostratigraphy of the Upper Devonian and lowermost Carboniferous of the Khoshyeilagh area, northeastern Alborz, Iran

Diverse and well-preserved marine palynomorphs occur in the Padeha, Khoshyeilagh, and Mobarak formations in the Khoshyeilagh area, northeastern Alborz, northern Iran. The marine palynomorph assemblages consist of acritarchs, prasinophytes, and chitinozoans, comprising 27 genera and 46 species. In addition, the studied sediments contain 20 species of algae, foraminifera, and corals allocated to 11 genera. The vertical distribution of acritarchs and chitinozoans allows the erection within these sediments of three local assemblage zones. Biozone I occurs in the upper part of the Padeha Formation and the basal part of the Khoshyeilagh Formation, suggesting a Frasnian–early Famennian age; Biozone II is present in the Khoshyeilagh Formation and indicates a Famennian age. Biozone III, which occurs in the basal part of the Mobarak Formation, suggests a Tournaisian age for this interval. Many of the palynomorph species, such as Crassiangulina tessellita, Daillydium pentaster, Deltotosoma intonsum, Gorgonisphaeridium discissum, Helosphaeridium microclavatum, Horologinella horologia, Papulogabata annulata, Somphophragma miscellum, and Veryhachium downiei, are closely comparable with coeval assemblages recorded from Australia, Ireland, Portugal, Saudi Arabia, North Africa, South America, and North America. This indicates the close relationship of the Iranian Platform to other parts of the northern Gondwana and southern Laurentian domain during the Late Devonian–Early Carboniferous. Moreover, results of similarity indices of marine microphytoplankton indicate a relatively high degree of similarity between the assemblages of the Khoshyeilagh area and those elsewhere in the Alborz Mountains and the Kerman Basin. Palaeontological evidence indicates that the Khoshyeilagh Formation was deposited in a low-energy, somewhat offshore, normal marine environment within the Alborz Basin, along the Palaeo-Tethys Ocean during this time interval. Furthermore, based on palynological data gathered from Iran, it can be concluded that Iran was an island during this interval of time.

LATE MIOCENE–EARLY PLIOCENE EVOLUTION OF MEDITERRANEAN GOBIES AND THEIR ENVIRONMENTAL AND BIOGEOGRAPHIC SIGNIFICANCE

The Lago Mare phase at the end of the Messinian Salinity Crisis (MSC) in the Mediterranean has long been known for the Paratethyan affinities of its biota. The taxonomic level of these affinities and their origin, however, is subject to divergent interpretations. Here, we have studied otoliths of the Gobioidei from late Miocene and early Pliocene deposits from Italy and Greece and revised earlier studies including time-equivalent data from Romania and NW Turkey. Nowadays, gobies constitute the most speciose marine fish family in Europe and the most diverse endemic family in the Ponto-Caspian region. Furthermore, they are highly adapted to nearshore shallow marine, brackish, and freshwater environments, which makes them excellent candidates to explore short-term connections of waterways of different nature. The normal marine late Tortonian and pre-evaporitic Messinian deposits of the studied Italian and Greek locations contained a rich and diverse goby assamblage, but species with Paratethyan affinities were very rare and possibly originated from connections during the early Serravallian (late Badenian) and early Messinian (early Meotian). A rare fauna from a paralic environment from Cessaniti, Calabria, similar to the mangrove environments found in the present-day Guinea coastal area, revealed two species of the family Eleotridae and no gobies with Paratethyan affinities. Cessaniti provides a unique opportunity to recognize the presence of this type of environmental context with a unique gobioid assemblage in the Neogene of Europe. The shallow-water brackish-influenced sediments of Strada degli Archi just below the MSC show an increasing influence of Paratethyan gobiid taxa (Proterorhinus yigitbasi, Zosterisessor exsul n. sp.), which are not present in time-equivalent normal marine environments, but have also been identified in the Dacic Basin of Romania. Sediments of the stage 3 ot the MSC, especially those that accumulated during the Lago Mare event, were dominated by a diverse goby assemblage with Paratethyan affinities, while indigenous Mediterranean goby taxa disappeared probably because of the lack of suitable conditions for neritic demersal stenohaline fishes, except for the nektonic Aphia minuta. The sediments of the stage 3 of the MSC also included in one particular location and level the unusual Enigmacottus socialis n. gen., n. sp., a putative member of the family Psychrolutidae of uncertain origin, which constitutes about 70% of all otoliths obtained from that interval in Italy. Beginning with the Zanclean, the goby assemblage of the Mediterranean shows an almost exclusively Atlantic-Mediterranean composition. A total of 15 new species are described, 12 in the family Gobiidae, two of the Eleotridae, and one putative Psychrolutidae. The new taxa are: Eleotris omuamuaensis n. sp., Eleotris tyrrhenicus n. sp., Lesueurigobius stazzanensis n. sp., Gobius peloponnesus n. sp., Proterorhinus cretensis n. sp., Zosterisessor exsul n. sp., Benthophilus aprutinus n. sp., Benthophilus labronicus n. sp., Caspiosoma lini n. sp., Caspiosoma paulisulcata n. sp., Thorogobius petilus n. sp., Buenia pisiformis n. sp., Hesperichthys gironeae n. sp., Knipowitschia etrusca n. sp., and Enigmacottus socialis n. gen. et n. sp.

Depositional environments of limestones from the Taiyuan Formation in the North China Block interpreted from REE proxies

The predominantly calcareous Taiyuan Formation was formed during the Late Paleozoic period in the southern part of the North China block in the eastern Palaeotethys. We present the rare earth elements (REE) and petrography data from nine limestone beds in the Zhangji mine of the Huainan coalfield as proxies to interpret the depositional environment of Taiyuan Formation. Thin-section petrography indicates that the limestones are mainly bioclastic, in-situ and are characterized by matrix-supported cementation. The REE concentrations and elemental patterns in the limestones reflect deposition in a normal marine environment. The REE analyses show the depletion of light rare earth elements, positive La anomalies, and negative Gd anomalies. Moderately negative δCe anomalies indicate that the limestones are most likely formed in an oxidized setting, typically a shallow marine environment. The positive Eu anomaly suggests deposition in a coastal environment with influx of clastics and terrestrial organic matter, thus indicating a more southerly provenance. Results from this study highlight the utility of REE and trace-element analyses of carbonate rocks for the reconstruction of depositional environments.

Dinoflagellate cysts stratigraphy and paleoecology from some Lower Miocene rocks, GS9-1X well, northern Gulf of Suez, Egypt

Palynological analysis of a Lower Miocene section from the GS9-1 well, northern Gulf of Suez, Egypt, has yielded significant dinoflagellate cysts of stratigraphic significance such as Exochosphaeridium insigne, Sumatradinium soucouyantiae and Hytrichokolpoma rigaudiae, which enabled age dating of the well section as Lower Miocene. Two distinct palynofacies are recognised. Palynofacies “A” was recovered from the basal part of the section from the Nukhul Formation. It is dominated by amorphous organic matter (AOM) and contains frequent translucent and opaque phytoclasts indicating a kerogen type II. Palynofacies “B” was recovered from the overlying interval of the well from the Rudeis Formation. It shows an inverse pattern, where phytoclasts are the main components and AOM declines markedly indicating a kerogen type III. Palynomorphs (mostly dinoflagellates) occur in both facies but with lesser percentages than palynodebris. Paleoenvironmental implications are inferred in the light of the recently established information from the distribution of modern-day dinoflagellate cysts (e.g. Zonneveld et al. 2013) since many of the recovered dinoflagellate cysts from the investigated well section still thriving today. A normal (shallow) marine environment is generally inferred for the studied Miocene section, with more peridinioid dinoflagellate cysts than gouyaulacoids. Higher up in the section, terrestrial palynomorphs dominate the dinoflagellate cysts; the latter are rare or missing. This suggests development of a marginal basin that is probably connected to local uplift or sea regression.

Early Jurassic protobranch bivalves from Chubut, Argentina

AbstractKnowledge on Early Jurassic marine fossil invertebrates from Argentina is very uneven. Particularly, faunas from Chubut Province received less attention and were thought to be poorer than those from the Neuquén Basin. Nevertheless, an updated revision of bivalves shows that some groups, such as the Protobranchia, were relatively more diverse in Chubut than in Neuquén during late Pliensbachian–early Toarcian times. Only four species are known from the southern areas of the Neuquén Basin, while seven species (three of them new) are here described from Chubut, belonging to the families Nuculidae, Nuculanidae, Polidevciidae, and Malletiidae. The new species are:Palaeonucula feruglioin. sp.,Ryderia tehuelchanan. sp., andPhaenodesmia?piatnitzkyin. sp. The material is well preserved and allows a detailed analysis of their hinge regions and other internal characters. The presence in Chubut ofPalaeoneilo?patagonidica(Leanza) is confirmed, which, along withPraesaccella ovum(Sowerby), are the only two species in common with the Neuquén Basin. The new speciesRyderia tehuelchana, belonging to a genus that had a wide global distribution between Rhaetian and Toarcian times, but which was known from South America only for upper Triassic deposits, is of special paleobiogeographic interest. These bivalves are restricted to normal marine environments, and due to their detritivorous feeding habits they only live in organic-rich bottoms as very active shallow burrowers.UUID:http://zoobank.org/41225cf2-b7de-4ff0-ad20-ce0d738799a9

Foraminifera from gas hydrate-bearing sediments of the northeastern South China Sea: Proxy evaluation and application for methane release activity

Anomalously low δ13C values of foraminifera in the stratigraphy are usually interpreted to reflect activities of paleo-methane seepage. The application of this proxy, however, requires to understand the cause of anomalously low δ13C signals in foraminifera. Here we present stable carbon and oxygen isotopes (δ13C and δ18O), Mg/Ca ratios and accelerator mass spectrometry (AMS) radiocarbon data from Cores GMGS2-08B (∼0–5.5 m below the seafloor [mbsf]) and 08C (2–23 mbsf) at ∼798 m water depth, recovered from the gas hydrate-bearing sediments in the northeastern South China Sea (SCS). The main objectives are to investigate the primary versus secondary signals of extremely negative δ13C values of foraminifera and further recognize the methane emission events (MEEs). The δ13C values of benthic (Uvigerina peregrina and Cibicidoides spp.) and planktonic (Globigerinoides ruber and Pulleniatina obliquiloculata) foraminifera in these two cores show distinct intervals with negative values (as low as −15.85‰) that indicate the shift of the sulfate methane transition zone (SMTZ) and the change in methane release flux in the past. The δ13C records of U. peregrina by a more exhaustive cleaning procedure designed to remove authigenic carbonate coatings show that most δ13C values are still lower relative to those in the normal marine environment. The Mg/Ca ratios of Uvigerina spp. by this exhaustive cleaning procedure display higher values and more variable for anomalous tests (as high as 13.40 mmol/mol) than normal ones. These observations indicate the 13C-depleted signals of foraminifera are mainly originated from diagenetic alteration of authigenic carbonate precipitates with extremely negative δ13C values. Furthermore, the mass-balance approach is adopted to assess the relative contribution of methane-derived authigenic carbonate in the low-δ13C signals in foraminifera and reveals the maximum contribution can be as high as ∼30% among the δ13C anomalies. Additionally, several major MEEs with distinct characteristics can be recognized according to remarkable δ13C excursions of foraminifera in these two cores.

The sedimentary succession of the last ~ 3.50 Myr in the western South Yellow Sea: Paleoenvironmental and tectonic implications

The South Yellow Sea (SYS) Basin, which is part of the West Pacific Continental Margin, began to form in the late Mesozoic to early Cenozoic as a result of regional tectonic activity in Asia. The pre-Middle Pleistocene sedimentary history of the area remains poorly understood or controversial, mainly due to a lack of long borehole cores penetrating pre-Quaternary strata. Borehole core CSDP-1 (300.10m long), the longest sediment core recovered thus far from the SYS, was drilled in 2013 in the western SYS. Recently, a reliable timescale for the core for the last ~3.50Myr was obtained by magnetostratigraphy (Liu et al., 2016a). Here we report the results of integrated analyses of the core, including sedimentary characteristics, downcore changes in environmental proxies (benthic foraminifera and ostracods), and accelerator mass spectrometry 14C and optically stimulated luminescence dates. In addition, we analyze 546km of single-channel seismic profiles and ~50km of a boomer seismic profile around the core site, and correlate the regional stratigraphy. The core sedimentary succession contains 17 depositional units (lithofacies associations) corresponding to three major seismic units, reflecting a variety of depositional environments during the last ~3.50Myr. Our results show that fluvial environments prevailed in the western SYS from ~3.50 to 1.66Ma, followed by alternations of tidal-flat to shallow-subtidal environments with fluvial environments from ~1.66 to 0.83Ma, and alternations of modern-like marine environments and fluvial environments from ~0.83Ma to the present-day in response to glacio-eustatic sea-level cycles. The depositional succession during the last ~3.50Myr was dominantly controlled by tectonism and glacio-eustatic sea-level cycles. The presumed first marine transgression since the Neogene in the western SYS at ~1.66Ma is interpreted to suggest that sea water could partially flood the Zhe-Min Uplift (ZMU) into the SYS due to tectonic subsidence, and further subsidence of the ZMU and the SYS shelf is inferred to have resulted in establishment of normal marine environments in the SYS during the highstands of glacio-eustatic sea-level cycles since ~0.83Ma. The average subsidence rates in the western SYS were ~120–165m/Myr during the last ~1.66Myr. The sedimentary succession comprises fifth- and fourth-order sequences, which are interpreted to have been driven by the 20-kyr or 41-kyr and by the 100-kyr glacio-eustatic sea-level cycles, respectively, since the late Pliocene. The sequences deposited since the Late Pleistocene are relatively complete, recording deposits from MIS 5 to MIS 1. However, the pre-Upper Pleistocene sequences show significant stratigraphic hiatuses, presumably caused by fluvial erosion during the glacial sea-level lowstands and subsequent transgressive erosion. This type of significant discontinuity in the sedimentary record can be considered to be diagnostic of shelf sequences controlled by glacio-eustatic sea-level cycles.

Bathymetric trend of Late Cretaceous southern Tethys upwelling regime based on benthic foraminifera

Benthic foraminifera are one of the most commonly used indicators to infer paleodepth. The information on depth distribution of fossil benthic foraminifera is generally obtained from normal marine environments. However, a significant gap exists with respect to implications of benthic foraminiferal distributions in unique sedimentary successions, such as those deposited under upwelling regimes. In such settings, the paleobathymetric signal is somewhat obscured by the extreme food fluxes and oxygen depletion at the seafloor that cause changes in benthic foraminiferal assemblage composition. Nevertheless, the dynamics of upwelling systems, and as a result the sediment and organic matter accumulation, are known to be directly influenced by eustatic changes, making paleobathymetric reconstruction highly valuable for understanding these systems.The Upper Cretaceous high productivity marine succession of southern Israel, with its variable lithologies, provides a unique opportunity for addressing this issue. Through this succession, a significant turnover in the benthic foraminiferal assemblages is observed associated with a sharp change in lithology from phosphate (Phosphate Member) to organic rich carbonates (Oil Shale Member; OSM). Statistical nMDS analysis distinguished four groups of species indicative of distinct depth habitats: <200 m, 100–300 m, 300–500 m, and >500 m. Each one of these groups corresponds to different parts of the sequence. According to our analysis, the shift in the benthic foraminiferal assemblages is attributed to a distinct regional deepening from shelf environment (<200 m) in the Phosphate Member (upper Campanian) to upper bathyal (200–500 m) at the base of OSM (base Maastrichtian), and deeper to middle bathyal (>500 m) during the Maastrichtian. While taking into account other factors affecting benthic foraminiferal distribution, this study demonstrates that depth distribution models based on normal marine settings might also be applicable as proxies for paleobathymetry in high productivity environments.

The discovery of Eifelian ammonoids in the Central Kyzylkum Desert (Aristantau Mountains, Uzbekistan)

Eifelian ammonoids are described for the first time from the Central Kyzylkum Desert (Uzbekistan, Navoiy Region, Aristantau Mountains). The ammonoid assemblage includes the typical Eifelian genera Fidelites, Subanarcestes (a new species S. aristanensis Nikolaeva sp. nov. is described), and Cabrieroceras, found in association with brachiopods, conodonts, and dacryoconarids. The ammonoid assemblage is similar to that from the Chotec beds of Barrandien and their equivalents in the Urals, Salair, Germany, and Morocco (Subanarcestes macrocephalus Zone), suggesting a connection between the Eifelian Kyzylkum Basin, which was part of the Turkestan Paleoocean, and European, North African, Siberian, and Uralian basins. The ammonoids studied are not associated with black shale and apparently existed in normal marine environments.