Transgressive Events Research Articles

Age constraints on the fossil fishes (Mesoclupea-Paraclupea assemblage) from the Lower Cretaceous of Zhejiang Province, South China

Fossil fishes (Mesoclupea-Paraclupea assemblage) are well known in the Upper Mesozoic volcano-sedimentary strata in the coast of South China, but the precise age remains uncertain. In this study, we provide LA-ICP-MS UPb zircon ages (ca. 120 Ma) for the volcaniclastic layers overlying the fossil-layer in the Chawan Formation at Linhai City, Zhejiang Province, Southeast China. Our results imply that the Mesoclupea-Paraclupea assemblage lived in the early Aptian. The Chawan Formation in Southeast China and Jiufotang Formation in Northeast China are coeval strata, while their fish faunas are taxonomically different because of possible physical barrier. Considering the fact that Paraclupea chetungensis may have broad salinity tolerance, the discovery of the fossil fishes implies the study area was once affected by the transgressive events or close to the sea during the early Aptian.

Evolution of the paleo-Daesan Bay (Nakdong River, South Korea) as a result of Holocene sea level change

AbstractTo explore sea level transgression in low-lying inland areas and its possible influence on prehistoric cultures, we investigated the physical and geochemical features of 20-m-long sedimentary cores from the previously seawater-filled Daesan Basin located in the middle reach of the present Nakdong River in Korea as proxies for seawater transgression deep inland areas due to Holocene sea level rise. Based on the relationships among grain size, total sulfur content (TS%), and carbon/sulfur (C/S) ratio, the first transgressive event was detected at ca. 8500 cal yr BP, caused by seawater influx along the present Nakdong River. Higher TS% (0.8–1%) and interbedded fossil oysters at 8000–6000 cal yr BP indicate marine environments, supporting a paleo-Daesan Bay with water depth of ~10–8 m. The common peaks in TS%, in both inland paleo-Daesan Bay and a present coastal area (Suncheon Bay) in southern Korea (e.g., at 3200 and 4700 cal yr BP), may indicate intervals of higher salinity, which suggests simultaneous responses to changes in sea level or hydroclimate. The duration of marine environment (paleo-Daesan Bay) in the remote inland from ca. 8000–3200 cal yr BP provides an analog for inland paleo-bay studies in East Asia.

First records of extinct kentriodontid and squalodelphinid dolphins from the Upper Marine Molasse (Burdigalian age) of Switzerland and a reappraisal of the Swiss cetacean fauna.

The Swiss Upper Marine Molasse (OMM) documents a transgression event dated to around 21 to 17 million years in which dolphin and other vertebrate remains have been reported. We revised the whole cetacean (whales and dolphins) OMM assemblage available in main collections, focusing on the identification and interpretation of periotics (bone that contains the inner ear). Periotics are rare, but they provide the richest taxonomic information in the sample and hint to environmental associations. Micro-computerized tomography allowed the reconstruction of bony labyrinths for comparisons and environmental interpretations. Three families are represented by periotics: Kentriodontidae, Squalodelphinidae and Physeteridae. The cetacean taxonomic composition of the Swiss OMM reinforces biogeographical patterns reported for the Mediterranean and Paratethys during the Burdigalian at a regional scale and the Calvert cetacean fauna of the northwest Atlantic at oceanic scale.

Bored log-grounds by teredinid bivalves in marine deposits from the Monos Formation (Upper Cretaceous) in central Cuba

Abstract Borings of Apectoichnus longissimus and Teredolites clavatus are described from wood fragments preserved in sandstone deposits of the Maastrichtian (Upper Cretaceous) Monos Formation in central Cuba. In addition, palaeobiological, palaeoecological and taphonomic implications of these are inferred. The borings are interpreted as mainly produced by Teredinid marine bivalves, which inhabited driftwood substrates. The taphonomic features such as mode of occurrence, density and position of the borings within the relict log-grounds suggest: (i) post-burial compaction of the xylic substrates by the surrounding sediments during burial, (ii) different ontogenetic stages and colonization episodes of teredinids on the studied wood fragments and (iii) different residence time of the wood fragments floating or near the sediment–water interface. Furthermore, the accumulation of wood fragments with A . longissimus and T . clavatus in the shallow marine deposits of the Monos Formation was probably the result of a marine transgression event in these deposits, thus leaving them exposed to attack by teredinid larvae. This study explores the life histories and taphonomic histories of teredinid bivalves and wood fragments in the Monos Formation, adding to the literature on ichnofossils in this lithostratigraphic unit.

Biomarkers and PAH chemostratigraphy in the study of the Frasnian anoxic event in the Pimenteiras Formation outcrop of the Parnaíba Basin, Brazil

The Late Devonian is characterized by episodes of sea-level rise and expansion of dysoxic to anoxic paleoenvironments, resulting in a global abundance of organic-rich sedimentary rocks. These changes have been well documented in biostratigraphic studies of Euroamerica basins. However, the relationship between sea-level rise and marine anoxia in Western Gondwana sedimentary rocks is not completely understood. Here, biomarker and PAH diagnostic ratios were applied to investigate changing depositional paleoenvironment and organic matter inputs of the Pimenteiras Formation along the western edge of the Parnaíba Basin. First, 24 shale samples collected from 16 regionally distributed outcrops were analysed, revealing variability in depositional paleoenvironment conditions. Secondly, for detailed study a 15-m thick outcrop was chosen, from which 11 shale samples were collected. These samples were submitted to chemostratigraphic and palynostratigraphic analyses and their records were highlighted. Two sample groups were identified, one sample group containing mixed organic matter, predominantly terrigenous and with fresh-brackish water organisms, deposited under dysoxic conditions. The other sample group comprised mixed organic matter containing a high contribution of marine organisms, preserved under anoxic conditions. Results indicated a marine flooding surface in the Pimenteiras Formation Outcrop 1, associated with a Devonian transgressive event related to sea-level rise and probably to global anoxic conditions during the Frasnian in the Parnaíba Basin. In addition, it was possible to correlate the abundance of miospores Verrucosisporites genus with high Retene/Chrysene values, suggesting that these miospores can be associated with a biological precursor of retene.

Middle to Late Jurassic stable isotopes and element ratios of fossils from western India: Developing a reference temperature curve for northeastern Gondwana

The stable isotope (δ13C, δ18O) and element (Mg/Ca, Sr/Ca) composition of 374 well-preserved belemnites, bivalves, and brachiopods of the Kachchh and Jaisalmer basins in western India were used to reconstruct climatic changes in the Middle and Late Jurassic time interval. Absolute water temperatures reconstructed from δ18Oshell values depend on the used δ18Osea value and equation, but indicate a long-term temperature decrease of around 8–9 °C in the study area from the Bajocian to the Tithonian. Measured Mg/Ca ratios also point to decreasing temperatures, but additionally reflect species-specific factors and a lower Mg/Ca ratio of Jurassic seawater compared to today. The recorded cooling in western India agrees with previous results from neighbouring Madagascar and the Indian Himalayas and can be connected to a drift of Eastern Gondwana into higher latitudes. This palaeogeographic shift is accompanied by changes in sedimentation indicating an increasingly humid climate and in the composition of ecosystems reflecting increasingly cooler water temperatures. High-resolution stable oxygen isotope analyses of three oyster shells point to seasonal temperature changes of 4–5 °C in the Kimmeridgian. The recorded δ13C values reflect sea-level changes with a positive excursion in the Oxfordian connected to a major transgressive event. Sr/Ca ratios are observed to follow changes in global ocean chemistry.

Occurrence and origin of glauconite in the Cambro-Ordovician Bliss Formation of southern New Mexico and West Texas (U.S.A.)

ABSTRACTIn southern New Mexico and West Texas, USA, the Late Cambrian–Early Ordovician Bliss Formation is a relatively thin and dominantly siliciclastic succession that was deposited on the Proterozoic basement during a major global transgression. The Bliss Formation can be divided into two members: 1) a lower, coarser-grained member composed mostly of sandstone (quartz arenite and subarkose) that lacks glauconite and calcite cement, and 2) an upper, finer-grained member that includes glauconitic sandstone, arkosic sandstone, and mixed siliciclastic–carbonate siltstone to fine-grained sandstone, intercalated with thin carbonate beds of grainstone, packstone, and rudstone. Iron oolite and oolitic sandstone are locally exposed at the base of the upper member. Sandstone of the lower member represents upper-shoreface to foreshore deposits, whereas sedimentary structures in the upper member indicate deposition in a middle- to lower-shoreface setting, and locally in a tidal-flat environment. Intercalated carbonate beds are storm layers (tempestites). Glauconite grains are abundant in the upper member as mostly rounded to well-rounded, spheroidal to ovoidal pellets. Two types of glauconite grains are present: homogeneous, dark green grains with high K2O contents (> 8 wt.%; stage 4) and mottled pellets composed of a mixture of glauconite and apatite. Glauconite of the Bliss Formation is not autochthonous as proposed by earlier workers, but of allochthonous (parautochthonous) origin. Thus, the glauconite grains were reworked from deeper shelf environments in northern Mexico to the south and were transported and deposited under regressive–transgressive conditions. Mottled glauconite grains formed by the reworking of phosphatized and glauconitized micritic sediments during regression and were transported and deposited by storm-induced currents, particularly in storm layers during transgressive events. Homogeneous, mature glauconite grains probably were derived from the reworking of glauconitized fecal pellets or completely glauconitized micritic sediments during regressive–transgressive cycles. The world-wide occurrence of glauconite in Cambrian–Early Ordovician sediments indicates that glauconite formation during that period can be considered as a “global event.”

The mechanism of iodine enrichment in groundwater from the North China Plain: insight from two inland and coastal aquifer sediment boreholes.

As an element relevant to human health, iodine is highly worthy of researchers' attention, especially the mechanism of iodine migration and enrichment in groundwater systems. A total of 43 groundwater, 1 seawater, 107 sediment, and 111 pore water samples from two boreholes (toward to Bohai Sea: BT, HH) were collected along a groundwater flow path at the North China Plain to investigate hydro-geochemical processes controlling groundwater iodine. High iodine groundwater (> 100μg/L) was characterized by Na-Cl type, with high TDS values (827-2,400mg/L) and high Cl (110-705mg/L) and Br (416-1,180μg/L) concentrations, which may be related to marine influence. Borehole BT and HH had pore water I concentration ranges of 1.4-132μg/L and 3.6-830μg/L, with high level that occurred near to coastline and corresponded to ancient transgression events. The results of sequential extraction of borehole sediments indicate that the fractions of sediment inorganic iodine mainly consisted of exchangeable, carbonate, and Fe-oxides associated fractions. Fe-oxides associated iodine was the main occurrence state in borehole BT far from the coastline, but high exchangeable iodine fractions (up to 92% of total extracted iodine) were observed in a high salinity borehole HH located near Bohai Bay, corresponding to the occurrence of high iodine pore water and groundwater. The analysis of iodine species indicates that iodide with strong migration ability dominated high iodine groundwater, pore water, and exchangeable sediment iodine, reflecting the occurrence of adsorption/desorption processes of iodine in groundwater system. High iodine groundwater and pore water exhibited iodine enrichment relative to Cl and Br, which suggests that iodine adsorbed on sediment desorbed under suitable pH and high solution ionic strength and subsequently released to pore water and aquifers. Inverse geochemical modeling stressed that ion exchange plays an important role in iodine enrichment of groundwater system.

Paleoecology of a Lower Cretaceous (lower Albian) marine community of Cerro de Oro, central Sonora, Mexico

The Early Cretaceous time is characterized by regression and transgression events in the oceans, which impulsed the radiation processes of species. In particular, these oscillation events controlled the distribution of marine invertebrates because they generated geographical barriers and the geographical connection between the different ecological niches. These events promote speciation of which there is a limited record in the state of Sonora. This work is the first quantitative paleoecological study of Early Cretaceous marine invertebrate fauna from central Sonora. The Mural Limestone exposed at the El Caloso Hill, located in the Cerro de Oro area, comprises 28 invertebrate taxa belonging to several groups such as corals, bivalves and gastropods, cephalopods, and echinoderms. These paleocommunities are part of the Early Cretaceous Mexican Sea, which covered the southwestern United States and Mexico during regressive/transgressive events. To evaluate and compare the diversity and richness of these paleocommunities, paleoecological indexes like the Simpson Dominance and Evenness index, Shannon index, Menhinick Species Richness, Total Chao Richness, and Pielou's Evenness index have been applied. In addition, the distribution described for these paleocommunities was defined as a clumped type. The limestone textures described for these environments comprises wackestone, and floatstone, typical of a shallow lagoon environment with low energy. Finally, the dominant guilds were represented by epifaunal sessile suspension, infaunal sessile suspension, and semi-infaunal facultative vagile suspension feeders.

Trans-Atlantic correlation of Late Cretaceous high-frequency sea-level cycles

Previous studies of Cretaceous sedimentary rocks have used multi-proxy correlation methods to suggest eustatic change, modulated by the c. 400 kyr long eccentricity rhythm. Although numerous authors have inferred eustatic changes on shorter timescales, none have demonstrated synchronous sea-level changes in separate basins on different plates, thousands of kilometres apart. Our study integrates basin-scale, three-dimensional sequence architecture, molluscan biostratigraphy, and carbon-isotope chemostratigraphy to demonstrate synchronous sea-level changes in upper Turonian to lower Coniacian shallow-marine clastic successions in the Western Canada Foreland Basin, and the Bohemian Cretaceous Basin. Depositional sequences in both basins are plotted in a common time domain using an astronomically calibrated age model, allowing direct comparison. In both basins, at least seven major transgressive events can be shown to be synchronous within the limits of combined biostratigraphic and chemostratigraphic resolution. ‘Major’ and ‘minor’ sequences of late Turonian age appear to have been paced, respectively, by the long (c. 400 kyr) and short (c. 100 kyr) eccentricity cycles. In contrast, early Coniacian sequences evidence pacing by the c. 38 kyr obliquity rhythm. Stratal architecture suggests that sequences developed in response to eustatic changes of c. 14–20 m at average rates ranging 0.08 to >1.3 m/kyr. At a time of ‘warm greenhouse’ climate, sea-level change of this magnitude and timescale may not be explicable entirely as a result of thermal- and aquifer-eustasy, and hence glacio-eustasy may also have been a contributing factor.

Planktonic foraminiferal quantitative analysis across the Campanian/Maastrichtian boundary at the Pondicherry area, Cauvery Basin, Southern India

The late Campanian/Maastrichtian succession exposed at Pondicherry area affords one of the finest exposed marine sections in Cauvery Basin is examined for their foraminiferal contents. The biostratigraphic distribution of 71 species of planktonic foraminifera has been used to diagnose 11 planktonic zones and subzones and correlated to the worldwide bioevent. During the late Campanian, a great transgression event occurred associated with the global warming (CF8b zone) trend indicated by large double‐keeled foraminifera (Globotruncana aegyptiaca Nakkady) of oligotrophic conditions. The latest zone CF4 records a sharp decrease in Planktonic/Benthic (P/B), globotruncanids, rugoglobigerinids and heterohelicids implying a fall of sea level.

Ordovician conodont biofacies of the upper La Silla and San Juan formations (middle Tremadocian-lower Dapingian) at Cerro La Silla, Argentine Precordillera

Conodonts from the upper La Silla (9.6 m thick) and San Juan formations (264.7 m thick) at the Cerro La Silla section are analyzed for the identification of faunal dynamics, biofacies and sea-level changes. The conodont collection of 11 388 specimens was recovered after digestion of 41 samples of carbonate rocks, totalizing 88.155 kg. Conodont total abundance and generic diversity graphs, as well as cluster analysis, reveal seven biofacies. The Colaptoconus, Tropodus-Reutterodus, Oepikodus-Prioniodus, Juanognathus-Bergstroemognathus, Juanognathus-Oepikodus-Protopanderodus, Juanognathus-Protopanderodus, Juanognathus-Semiacontiodus biofacies are determined. These biofacies represent middle to outer carbonate ramp environments for the San Juan Formation. The associated analysis of biofacies and lithology allow for the recognition of two transgressive events in the San Juan Formation at the Cerro La Silla section, which could be related to transgressive systems tracts (TST) that occurred during the Early and Middle Ordovician (middle Tremadocian-early Dapingian).

The influence of paleoclimate and a marine transgression event on organic matter accumulation in lacustrine black shales from the Late Cretaceous, southern Songliao Basin, Northeast China

Lacustrine black shales are widely developed within the Late Cretaceous Nenjiang Formation (k2n) of the Songliao Basin. These black shales provide an ideal natural laboratory for reconstructing the paleoclimate and paleoenvironment during the Late Cretaceous in Northeast China and have great significance in the exploration for potential oil and gas resources. According to the systematic analysis of organic carbon isotopes, elemental geochemistry and clay mineral composition, the organic matter (OM) source, paleoenvironment, paleoclimate, paleoproductivity and marine transgression event of the Nen 1 member (k2n1) were investigated, and the influence of the paleoclimate and marine transgression event on OM accumulation in lacustrine black shales was revealed. Black shales in the lower unit are characterized by a high OM abundance (max. 4.19 wt%, avg. 3.02 wt%), I-II1 kerogen (with abundant lamalginite) and low maturity. The element ratios (Fe/Mn, Mg/Ca and Sr/Cu), paleoweathering indexes (CIA and PIA), δ13Corg values and clay mineral composition together indicate a warm paleoclimate in the Late Cretaceous. The humid paleoclimate promoted the flourishing of lacustrine microalgae and surrounding terrestrial vascular plants and enhanced the lake level, conducive to favorable sources and preservation conditions for OM accumulation. Based on paleontological and radioisotope dating, the global paleotemperature rise in the Late Santonian stage probably led to the marine transgression event. It can be explained by the high lake level and sea-level conditions under the global humid climate background that resulted in the Songliao paleolake connecting with the paleo-Pacific Ocean. Alkaline and saline seawater incursion into the paleolake increased the salinity of the lacustrine water column and further aggravated the anoxic conditions of the lake, and abundant marine nutrient inputs promoted the primary bioproductivity and contributed to the accumulation of OM. The discovery of the OM accumulation mechanism under the influence of the warm-humid paleoclimate and intermittent marine transgression will add critical geological constraints on further studies of geological events in the deposition of late Cretaceous black shale.

A New Insight of Talang Akar Formation in the Ridho Field, North Palembang Sub-basin, Indonesia: An Integrated Approach

The synrift sandstone deposits of Eo-Oligocene Lemat (LMF) and Oligo-Miocene Talang Akar Formations (TAF) are the most well -known hydrocarbon reservoirs in the South Sumatra Basin, Indonesia. However, only limited studies on TAF in the North Palembang Sub-Basin have been published. In the Ridho field, TAF is characterized by fining-up sequences of inter bedded, fine to medium-grained sandstones and shales overlain by a coal layer as the top marker, while LMF comprises of continuous blocky-shaped, medium to coarse-grained, conglomeratic sandstones.Previous lithostratigraphy-driven sand to sand correlation between wells has created difficulties in understanding the geology and in producing consistent correlation, especially within the TAF. In order to define chronostratigraphy-based correlation and interpret the depositional environment of TAF and LMF, an integration between palynological, core study and petrophysical analysis was performed. The result of this integrated approach demonstrates aligned hypotheses. The occurrence of pollen Meyeripollis naharkotensis and Florschuetzia trilobata along the studied wells suggest Late Oligocene age. The palynology study subdivides TAF into three backmangrove-intertidal sand units with an increase of marine influence defining a transgression to the top of the TAF. The transgressive event is identified in core sample by lesser tidal influx sedimentary structures such as ripple, mudlayer, flaser and also finer grained sandstone at the top of TAF. Furthermore, based on petrophysical evaluation, better sand quality with lower NTG (net -to gross) near top TAF confirms the retrogradational event in this formation.The new sand unit definitions from the current study provide more consistent correlation in terms of sand thickness and characteristics for future modeling purposes.

Distribution of Mid‐deeply Buried Sand‐bodies and their Hydrocarbon Significance at Basin Margins: Case Study of the Paleogene in the Eastern Liuzan Area of the Nanpu Sag, Bohai Bay Basin, China

AbstractThe current research aims to unlock the temporal and spatial distribution of sand‐bodies and their relationship with hydrocarbon accumulation in the mid‐deep layer of basin margins, located in the eastern part of the Liuzan area of the Nanpu Sag, Bohai Bay Basin, China. Through this study, the main target interval of the area was divided into two fourth‐order sequences. The lean sand mixed sedimentary belt with great importance in controlling hydrocarbon accumulation was identified through the comprehensive use of 3D seismic data, logging data, lithological data and seismic inversion data. A detailed analysis of sand‐body development characteristics and their role in controlling hydrocarbon accumulation was conducted. The results reveal that the study area mainly develops two distinct fan‐delta lobes from the NE‐trending sediment supply direction. Due to the relatively high influence of the lacustrine transgression event, the scale of the lean sand mixed sedimentary belt within the SQ1‐1 (the lacustrine transgressive systems tract) is relatively small, showing a relatively continuous distribution of sand bodies in the plane. Conversely, due to the relatively high impact of the lacustrine regression event, the scale of the lean sand mixed sedimentary belt developed within the SQ1‐2 (the highstand systems tract) is relatively large, the two east sets of fan‐delta sedimentary systems being clearly separated. The lean sand mixed sedimentary belt formed a good lateral occlusion belt in favor of hydrocarbon accumulation. Through composite analysis of structural interpretation results, sand‐body distribution and well test data, it is evident that the lean sand mixed sedimentary belt located in the structural high is not a favorable zone for hydrocarbon accumulation. In contrast, the wing of the high part of the structure is the zone of sand‐bearing bodies and is a favorable zone of hydrocarbon accumulation.

Neogene calcareous nannofossil biostratigraphy of the northern Indian Ocean: Implications for palaeoceanography and palaeoecology

Neogene sediments of the Andaman and Nicobar Islands in northern Indian Ocean, specifically the lower Miocene (Burdigalian) to lower Pliocene (Zanclean) sequences, were analysed for calcareous nannofossils that yielded well-preserved and diverse assemblages. The majority of samples contained stratigraphic marker taxa that allowed us to identify successions within the Burdigalian-Langhian (uppermost lower Miocene to lowermost middle Miocene) on the Havelock Island, Tortonian (upper Miocene) on the Neil Island and Zanclean (lower Pliocene) on the Car Nicobar Island. The nannofossil assemblages of uppermost lower Miocene to lowermost middle Miocene sediments reflect strong preference for warm tropical climate and nutricline condition i.e., depth dependent high variation of nutrient content. The presence of relatively unusual assemblage compositions, especially the presence of abundant sphenoliths and small reticulofenestrids, in conjunction with rare discoasters and alongside common diatoms, are indicative of high-productivity surface waters and probably upwelling conditions in the late Miocene. In the Tortonian (upper Miocene), low abundance of discoasters and high abundance of small reticulofenestrids (<3 μm) indicate eutrophic condition. The high-productivity surface-water environments can be linked with the intensification of the Indian Summer Monsoon. Well-preserved calcareous nannofossils have been also been recovered from the Zanclean (lower Pliocene) sediments on Car Nicobar Island. During the Zanclean warm water condition prevailed and from marginal to deep water setting i.e., transgressive event was recognised in the northern Indian Ocean.

The effectiveness of cognitive instructions when children provide true and false eyewitness reports of another’s transgression

ABSTRACT Children’s non-disclosures of another’s wrongdoing, particularly in cases involving alleged maltreatment, is a notable concern among forensic professionals. The current study was designed to provide these professionals with much needed information about the efficacy of a range of interviewing strategies, namely free-recall, cognitive instructions and closed-ended questions, when children are asked to conceal the transgression of an adult. After being asked to falsely deny a theft they witnessed, children (ages 8 to 13; N = 104) were interviewed using either the cognitive instructions (n = 52) or a Standard Interview (n = 52). Two raters coded the children’s: (1) report honesty; (2) number of words used; (3) number of Transgression Details disclosed; (4) number of events recalled; (5) temporal order accuracy; and (6) number of theft disclosures made. Children produced longer testimonies with more Transgression Details, disclosures and events on the interview with the cognitive instructions, without compromising temporal order accuracy. However, there were no interview differences in overall report honesty. Overall, the free-recall reports had the most words, along with more Transgression Details, theft disclosures and events recalled. The reverse-order recall was the most effective cognitive instruction for increasing the amount of events recalled. Overall, the cognitive instructions increased the amount of information and disclosures about the theft, but they did not discourage false reporting.

Nitrogen isotopes as paleoenvironmental proxies in marginal-marine shales, Bohai Bay Basin, NE China

Nitrogen isotopes have been widely used as indicators of depositional conditions in studies of ancient sediments. Bohai Bay Basin is a major continental hydrocarbon province in NE China, but nitrogen isotopic signatures of this lacustrine system (connected with the open ocean occasionally) have barely been investigated. We report a study of paleoenvironmental information recorded by N isotopic variations in the lower third member (Es3L) and upper fourth member (Es4U) of the Eocene Shahejie Formation in the Jiyang Sub-basin, southern Bohai Bay Basin. Paleosalinity (B/Ga, Sr/Ba, and S/TOC) and paleoredox (Corg/P, DOP, UEF, and Fe/Al) proxies and δ13Corg values were used to elucidate paleoenvironmental factors that affect N isotopic signals in the study core. Results indicate that δ15N values are positively correlated with paleosalinity proxies in the Luo-69 and Niu-1 drill-cores. Two possibilities may account for this: (1) a paleosalinity surge caused by marine transgression events led to stratification of the water column, creating an anoxic–suboxic deep-water layer and promoting denitrification in sediments; or (2) strong stratification of the water column impeded the upwelling process that brought nutrients to the upper water layer, weakening nitrogen fixation there. In marginal-marine intervals such as the Eocene Shahejie Formation, water-column salinity may play a critical role in regulating the δ15N signal. This study indicates that nitrogen isotopic compositions may aid paleoenvironmental and paleoclimatic interpretations of marginal-marine shale, particularly when applied together with multiple paleoenvironmental proxies to improve the understanding of ancient sedimentary conditions in marginal-environment.

Integrated stratigraphy from a transgressive upper Oligocene section in NW Italy

ABSTRACT: The Oligo-Miocene Transition (OMT) is one of the most important climatic transitions of the last 30 million years. This short period of climate warming coincides with a few biotic turnovers, which are well known in deeper marine settings where stratigraphic successions yield a detailed record; in shallowmarine environments they have been proved difficult to recognize as the occurrence and absence of certain taxa due to ecological preferences hamper the study. This study focuses on the Case Cné section in the late Oligocene of the Tertiary Piedmont Basin (TPB) as it represents a gradual transgressive event, which shows the drowning of a locally developed reef complex and development of a deeper marine sedimentary setting influenced by gravity flow mechanics. Larger foraminifera biostratigraphy was used to date the section to the late Oligocene (SBZ23); preliminary strontium isotope data confirms this result. Using sedimentological, semi-quantitative microfacies and geochemical analysis the sedimentary history of the section was reconstructed and divided into four major phases: the drowning of the reef complex, a short prograding phase of the fluvial system, the onset of gravity flow mechanics and a final transgressive phase with an initial turbiditic influence which continues regionally into the Miocene.

Paleoenvironmental conditions of the late Miocene “Entrerriense” epicontinental sea: A case study of the Camacho Formation, SW Uruguay

Marine sediments deposited during late Miocene transgressive events are recorded over large onshore areas in southeastern South America, characterizing the “Entrerriense Sea”. In Uruguay, these deposits crop out at the coast of the Department of Colonia, and are assigned to the Camacho Formation, which is well-known by its abundant fossil content. Nevertheless, high-resolution geochemical proxy records within the Camacho Formation succession are not yet available. Our goals are: (1) to assess in high-resolution the paleoenvironmental changes recorded by the marine and/or marine-influenced strata of the Camacho Formation in Uruguay; (2) to explore possible links between local responses and global climate shifts that occurred during the late Miocene. To achieve these goals, we applied a multi-proxy approach, in which sedimentary facies and trace fossil occurrences were compared with geochemical and physical properties records measured in high-resolution within the exposed succession of the Camacho Formation. Our results suggest that these strata record a shallowing-upward trend, also characterized by deposition in gradually more proximal settings [increasing-upward trends in log(Zr/Rb) and log(Ti/Rb)], coupled to increased influence of freshwater input in the upper half of the studied sedimentary succession (decreasing-upward Sr/Ba trend). Considering previously published ages for the Camacho Formation, we infer that this shallowing-upward trend was related to the high latitude cooling and/or ice volume expansion occurred between 7.2 and 6.9 Ma, and the associated long-term sea level fall from 7.2 to 6.5 Ma. These trends occurred in tandem with the onset of more humid climate conditions (recorded by the uppermost strata of the studied succession), which were likely related to the latitudinal migration of climatic belts.