Marine Transgression Research Articles

Marine Transgression in Modern Times.

Marine transgression associated with rising sea levels causes coastal erosion, landscape transitions, and displacement of human populations globally. This process takes two general forms. Along open-ocean coasts, active transgression occurs when sediment-delivery rates are unable to keep pace with accommodation creation, leading to wave-driven erosion and/or landward translation of coastal landforms. It is highly visible, rapid, and limited to narrow portions of the coast. In contrast, passive transgression is subtler and slower, and impacts broader areas. It occurs along low-energy, inland marine margins; follows existing upland contours; and is characterized predominantly by the landward translation of coastal ecosystems. The nature and relative rates of transgression along these competing margins lead to expansion and/or contraction of the coastal zone and-particularly under the influence of anthropogenic interventions-will dictate future coastal-ecosystem response to sea-level rise, as well as attendant, often inequitable, impacts on human populations.

Unraveling the sedimentation environment of Marajó island: Insights from geochemical studies and implications for the origin of potentially toxic element in soils

Marajó Island, located at the mouth of the Amazon and Tocantins rivers, is the largest fluvial maritime island on Earth. Its unique location within the Amazon biome and its complex sedimentary dynamics makes it a region of great ecological and socio-economic importance. However, the island is facing significant challenges due to climate change, with projections suggesting permanent flooding of its floodplains in the coming decades. Despite numerous studies on soil geochemistry in the Amazon biome, there is a lack of research specifically focused on Marajó Island. Our study aims to investigate the soil's geochemical properties on the major parent materials in the eastern portion of Marajó Island, seeking to unravel the nature of its complex sedimentary environment, elemental relationships, origin and implications of potentially toxic elements. Samples from seven soil profiles representative of the eastern portion island were collected in a chronosequence, to conduct physical and chemical analyzes: selective dissolution of Fe oxides by sodium citrate-bicarbonate-dithionite and ammonium acid oxalate; quantification of major, trace and rare earth elements (REE) performed by multi-acid digestion and determination in ICP-OES/MS; characterization of weathering intensity by the chemical index of alteration (CIA), chemical weathering index (CWI), plagioclase index of alteration (PIA), chemical proxy of alteration (CPA), and index of compositional variability (ICV); and assessment of potentially toxic elements using enrichment factor and geoaccumulation index. The results indicated that the geochemical variation of soils reflected particularities of the parent material influenced by marine transgression events, and by the current conditions of water table oscillation and humid tropical climate. Holocene Sediments (HS) revealed enrichment by light REE. In soils on Post-Barreiras (PB), Laterite Formation (LF) and Lateritic Debris (LD), the main elements were Al, Fe, and Ti. Due to intense weathering and leaching, negative anomalies were observed in nearly all elements, including the REE. Arsenic enrichment in HS soils was due to the past estuarine influence and the current hydromorphic conditions, while soils on PB, LF and LD are naturally enriched by the parent material.

Pollen from the K–Pg boundary of the La Colonia Formation, Patagonia, Argentina

The La Colonia Formation, outcropping in northern Chubut Province (Patagonia, Argentina), is a Maastrichtian–Danian sequence deposited during a marine transgression of the South Atlantic Ocean. Its fine-grained sediments are associated with lagoon systems that preserved a very rich and diverse biota composed of invertebrates, vertebrates, plants, algae, and fungi. A palynological study was carried out based on 157 samples collected from four representative stratigraphic sections of this geological unit. The plant communities were dominated in terms of richness by ferns and angiosperms, but algae and gymnosperms were also well-represented. About 250 palynomorphs are recognized. The gymnosperms comprise 20 species including representatives of Araucariaceae, Cheirolepidiaceae, Ephedraceae, and Podocarpaceae while the angiosperms include 67 species within the families Araceae, Arecaceae, Aristolochiaceae, Asteraceae, Cannabaceae, Chlorantaceae, Cunoniaceae, Ericaceae, Gunneraceae, Juncaceae, Liliaceae, Malvaceae, Nelumbonaceae, Nothofagaceae, Proteaceae, and Typhaceae and several taxa of uncertain affinities. Here, we present the systematic study of the gymnosperm and angiosperm pollen components of the flora. Two new gymnosperm species and 22 new angiosperm species are erected. Additionally, we introduce the southernmost records of Triprojectacites and Normapolles groups even though their botanical relationships and origin remain unknown. The highly diverse palynoflora of the La Colonia Formation provides critical evidence for understanding the evolution of Southern Hemisphere floras and of certain clades and families and support the hypothesis that the effect of the mass extinction event was less significant at the southernmost portion of South America than in other parts of Earth.

Future scenarios in the former oil capital: coastal flooding and social vulnerability in Macaé, RJ.

The accelerated urban growth in Macaé had important consequences on socio-spatial organization, especially about housing spaces that became increasingly difficult to be accessed by the low-income population. The most devalued lands, such as mangroves and floodplains, were occupied by the low-income population. The proposal highlighted in this project focuses directly on the problem of rising sea levels and flooding in the urban space of Macaé, which is of social interest. A simulation of future scenarios with sea level rise above the current one, allowing the identification of areas flooded by marine transgression on a time scale of 100years (for the year 2100). For this, the rate was chosen for the simulation: the greenhouse gas scenario RCP8.5, as given in IPCC's Fifth Assessment Report (AR5) of 2014. A radiative forcing that corresponds to more than 700ppm CO2-eq, but less than 1500ppm, the projected increase is 1m to more than 3m (medium confidence) and more than 3m (medium confidence). This assessment is based on the average confidence in the contribution from thermal expansion and low confidence in the modeled contribution modeled contribution of the ice sheets. Therefore, the climate change-induced global mean sea level rise is caused by thermal expansion of ocean water and ocean mass gain, the latter being mainly due to a decrease in land ice mass. The estimated sea-level rise used for the projection of this study is 2.15, as proposed by Grinsted et al. in 2009.

Dinosaur and tree-line invasion of southeastern Australia during Cretaceous greenhouse spikes

The paleosol record of the Early Cretaceous Wonthaggi and Eumeralla formations of Victoria reveals a suite of non-calcareous Histosols and Ultisols, as well as stump casts, indicative of humid temperate ecosystems. At some stratigraphic levels, frigid temperatures are indicated by clastic dykes (ice wedges), load casts of mud (periglacial convolutions), and coal-mantled stone rolls (aapamires). The largest tree stumps and thickest paleosols correspond to known Early Cretaceous greenhouse spikes, as revealed by stomatal index of fossil ginkgo leaves, by black shales of oceanic anoxic events, and both marine and non-marine carbon isotopic anomalies. Temperature and CO2 spikes coincide with appearance of broadleaf deciduous forests, including Ginkgo australis, with dinosaurs, monotremes, placentals, early birds and angiosperms. In contrast, permafrost paleosols represent fern-lycopsid tundra and coniferous taiga vegetation. Early Cretaceous CO2 greenhouse spikes allowed southward migration of tree lines and polar biomes several times during the Cretaceous, which was not continuously a hothouse period. The same greenhouse spikes are recorded by maximal marine transgressions in the Great Artesian Basin of Queensland, and the frigid intervals by dropped pebbles and glendonites in South Australia, New South Wales and Arctic regions.

Design of preliminary groundwater monitoring networks for the coastal Tra Vinh province in Mekong Delta, Vietnam

Study RegionThe study region is the coastal Tra Vinh province located in Mekong Delta, Vietnam Study FocusThe objective of the study is to design preliminary monitoring networks for groundwater level and salinity monitoring in the three heavily abstracted aquifers in the Tra Vinh province. Since data from the existing monitoring were insufficient to explore variogram analysis and subsequent Kriging interpolation for the network design, groundwater flow and saltwater transport models were constructed to create groundwater level and salinity distributions. An iterative procedure was adopted to select monitoring well locations based on the contour maps of groundwater levels and total dissolved solids (TDS) constructed from the groundwater models. The standard deviation of Kriging interpolation error was used as the criteria to assess the quality of the designed monitoring networks. Priorities for the locating groundwater level monitoring wells were targeted in areas with cones of depression and boundaries, while priorities for salinity monitoring were given to coastal zone and inland fresh/saltwater interfaces. New Hydrological Insights for the RegionGroundwater overexploitation has resulted in storage depletion and saltwater intrusion in the Tra Vinh province. Simulations from the numerical models determined the cones of the depression and predicted intrusion from inland saltwater trapped in clays from past marine transgressions and from seawater in the coastal zone. A limited number of monitoring wells is operated and is insufficient to delineate the cone of depression and fresh/salt water interfaces. This study combined the numerical model simulation results and Kriging interpolation method and designed preliminary groundwater level and salinity monitoring networks for the Tra Vinh province. Once the designed networks are implemented, observed data from the networks will provide valuable information for sustainable groundwater resources management in Tra Vinh province. Data availabilityAll data generated or analyzed during this study are available upon request from the corresponding author.

Revealing the Extent of Submarine Permafrost and Gas Hydrates in the Canadian Arctic Beaufort Sea Using Seismic Reflection Indicators

AbstractThe Canadian Arctic Southern Beaufort Sea is characterized by prominent relict submarine permafrost and gas hydrate occurrences formed by subaerial exposure during extensive glaciations in Pliocene and Pleistocene. Submarine permafrost is still responding to the thermal change as a consequence of the marine transgression that followed the last glaciation. Submarine permafrost is still underexplored and is currently the focus of several research projects as its degradation releases greenhouse gases that contribute to climate change. In this study, seismic reflection indicators are used to investigate the presence of submarine permafrost and gas hydrates on the outer continental shelf where the base of permafrost is expected to cross‐cut geological layers. To address the challenges of marine seismic data collected in shallow water environments, we utilize a representative synthetic model to assess the data processing and the detection of submarine permafrost and gas hydrate by seismic data. The synthetic model allows us to minimize the misinterpretation of acquisition and processing artifacts. In the field data, we identify features along with characteristics arising from the top and base of submarine permafrost and the base of the gas hydrate stability zone. This work shows the distribution of the present submarine permafrost along the southern Canadian Beaufort Sea region and confirms its extension to the outer continental shelf. It supports the general shape suggested by previous works and previously published numerical models.

Positive and negative effects of marine transgression on the quality of lacustrine source rocks in the Upper Cretaceous Songliao Basin, China

The linkage between marine transgression and lacustrine source rock development has been highlighted for decades. Here, improved understandings were obtained on this challenging issue based on valuable comprehensive profiles from the Upper Cretaceous Songliao Basin, NE China (Qingshankou Formation, brief as K2qn1). 48 shale samples from the Central Depression in the northern Songliao Basin were analysed to establish three geochemical profiles of K2qn1. Multiple biomarkers suggested that organic matter in the source rocks of K2qn1 was mainly sourced from aquatic organisms. Systematic organic and inorganic geochemical analyses reveal that at least five transgressive events occurred during the sedimentary period of K2qn1, denoted as TI, TII, TIII, TIV, and TV from bottom to top. In the context of multiple transgression events, the quality of K2qn1 source rocks was primarily controlled by lacustrine primary productivity. Importantly, transgression events have both positive and negative effects on the quality of lacustrine source rocks. During earlier transgressive events (e.g., TI and TII), the quality of source rocks was negatively correlated with transgression intensity, which is likely due to the difficulty of freshwater organisms adapting to salinity, resulting in a decline in primary productivity. In the later transgression events (e.g., TIII and Tv), the quality of source rocks was positively correlated with transgression intensity, which is probably due to the gradual dominance of salt-tolerant or halophilic organisms during multiple stages of salinization. This study provides a comprehensive research approach for evaluating the influence of transgression events on lacustrine source rocks.

Paleo‐Hydrogeological Modeling to Understand Present‐Day Groundwater Salinities in a Low‐Lying Coastal Groundwater System (Northwestern Germany)

AbstractGroundwater abstraction and drainage are considered to be the main drivers for the salinization of low‐lying coastal groundwater systems, while the role of past boundary conditions is less clear. In this study, 3‐D paleo‐hydrogeological variable‐density groundwater flow and salt transport modeling (“paleo‐modeling”) is applied to reconstruct the evolution of groundwater salinities during the Holocene, that is, the last 9,000 years, in Northwestern Germany. Novel aspects of this study include the consideration of highly resolved time‐variant boundary conditions in a 3‐D paleo‐modeling framework, for example, sea‐level rise, surface elevation and coastline changes, development of drainage networks and groundwater abstraction, as well as the quantification of isolated processes impacting salinization. Results show that salinization was a function of sea‐level rise from 9000 BP until 1300 CE. The creation of the dike line ∼1300 CE set the starting point for increasing anthropogenic control of the hydro(geo)logical system: changes in surface elevation and drainage of low‐lying marshes have become main drivers for salinization after 1600 CE when peat was artificially degenerated. Moreover, changes in the dike line caused by storm floods impacted the salinities. Model results for 2020 CE match well with present‐day salinity observations. Yet, salinization will continue in the future, as the hydro(geo)logical system has not reached an equilibrium. The presented paleo‐modeling framework can be viewed as a blueprint for similar low‐lying coastal groundwater systems, influenced by marine transgression and human development. Thereby, it enables the reconstruction of meaningful present‐day salinity distributions, serving as a vital basis for modeling future groundwater systems in a changing climate.

New understanding and exploration direction of hydrocarbon accumulation in Termit Basin, Niger

Based on the seismic and drilling data, casting thin sections, geochemical analysis of oil and rock samples, and hydrocarbon generation history simulation, the hydrocarbon accumulation characteristics and exploration direction of Termit superimposed marine—continental rift basin are discussed. The Termit basin is superimposed with two-phase rifts (Early Cretaceous and Paleogene). The subsidence curves from two wells on the Trakes slope in the east of the basin show high subsidence rate in the Late Cretaceous, which is believed to be high deposition rate influenced by transgression. However, a weak rift may also be developed. The depositional sequences in the Termit basin were controlled by the Late Cretaceous marine transgression cycle and the Paleogene lacustrine transgression cycle, giving rise to two types of superimposed marine—continental “source-sink” deposits. The marine and continental mixed source rocks developed universally in the whole basinduring the marine transgression period, and are overlaid by the Paleogene Sokor 1 reservoir rocks and Sokor 2 caprocks developed during the lacustrine transgression period, forming the unique superimposed marine—continental basin in WCARS. The early low geothermal gradient in the Termit basin resulted in the late hydrocarbon generated by the source rock of Upper Cretaceous Yogou in Paleogene. Mature source rock of Upper Cretaceous Donga developed in the Trakes slope, so that the double-source-supply hydrocarbon and accumulation models are proposed for the Trakes slope in which formed the oil fields. Due to virtue of the newly proposed hydrocarbon accumulation model and the exploration activities in recent years in the Termit superimposed marine—continental rift basin, an additional effective exploration area of about 2500 km2 has been confirmed in the east of the basin. It is believed that potential domains such as Sokor 1, Donga and Upper Cretaceous lithologic traps in the southeast of the basin are key expected targets for exploration and frontier evaluation in future.

The sedimentological expression of transgression–regression cycles upon aeolian–marine margins

AbstractWhen compared to their temperate coastal counterparts, sediments deposited and preserved along arid aeolian to shallow‐marine margins remain relatively poorly understood, particularly at the scale of lithofacies units and architectural elements. These systems often record evidence for relative sea‐level change within sedimentary basins. This work focusses on the Entrada–Curtis–Summerville formations that crop out in central eastern Utah, USA, and provides a detailed analysis of the aeolian Moab Member of the Curtis Formation (informally known as the Moab Tongue) that was impacted by cycles of marine transgressions and regression in the late Jurassic. This study utilises photogrammetry, sedimentary logging and sequence‐stratigraphical analysis techniques. Results indicate that four short‐lived transgressive‐regressive cycles are preserved within the Moab Member, followed by a broad regressive event recorded at the transition between the Curtis and Summerville formations. These cycles relate to changes in the relative sea level of the Sundance Sea and the deflation and expansion of the neighbouring aeolian dune field. During periods of normal regression, marine sediments displayed evidence of tidal and wave action, whereas the continental domain was characterised by growth of the aeolian system. However, when regression occurred within optimal physiographic conditions such as a restricted, semi‐enclosed basin, and at sufficient magnitude to outpace erg expansion, this acted to shut‐down bedform development and preservation. A rapid restriction of aeolian sediment availability and the inability of the dune field to recover resulted in the formation of deflationary sandsheets, arid coastal plain strata and contemporaneous shallow‐marine deposits that are starved of wind‐sourced sediments. This study highlights how a rapidly developing high‐magnitude regression can lead to the overall retraction of the erg. Deciphering the evolution and sequence stratigraphical relationships of arid aeolian to shallow marine margins is important in both understanding environmental interactions and improving the characterisation of reservoir rocks deposited in these settings.

Late Quaternary marine transgressions inferred from the pyrite sulfur content and isotopes within core sediments from the southeast coast of China

Paleoenvironmental reconstructions of coastal areas during geological history are critical for understanding past responses to marine transgression. Identifying transgressive layers in sedimentary strata is therefore of great importance. To this end, we examined the content and isotopic composition of pyrite sulfur, in combination with classical organic geochemical indicators (e.g., C/N ratio and the δ13C of organic carbon), to trace the marine transgressions along the southeast coast of China since Marine Isotope Stage (MIS) 5. Our results suggest that the mass ratio of total organic carbon and pyrite sulfur (C/S ratio) is sensitive to seawater intrusion. Three transgressive layers were identified by low C/S ratios in core NDGK2, which correspond to sea level rise during MIS5, MIS3, and MIS1. Sediments deposited during MIS1 are represented by low C/S ratios with an average of 2.31, while those deposited during MIS5 and MIS3 have slightly higher C/S ratios, indicating a less extensive influence of seawater. Pyrite production in sediments deposited during MIS5 and MIS3 may have been limited by sulfate supply, as reflected by more positive values of δ34Spyr, whereas pyrites deposited during MIS1 were likely formed without sulfate limitation, as reflected by more negative values of δ34Spyr. The isotopic signals of pyrite sulfur thus further confirm the inference based on the C/S ratio. The magnitude of the transgression increased from MIS5 to MIS1, which is in agreement with the findings from classical organic geochemical indicators examined in this study, as well as geochemical and micropaleontological salinity indicators from previous studies. Our findings provide a promising method for identifying marine transgressions and their magnitude from the depositional record, especially when sedimentary strata lack diagnostic micropaleontological and sedimentological characteristics.

Late Pleistocene and Holocene transgression inferred from the sediments of the Gulf of San Jorge, central Patagonia, Argentina

ABSTRACTThis study presents the first detailed description of the upper sedimentary succession of the late Pleistocene and Holocene deposits in the Gulf of San Jorge (Patagonia) based on several hundred kilometers of high‐resolution seismic (sparker) profiles and numerous sediment cores. High‐resolution seismic stratigraphy confirms the existence of a paleo‐fluvial network formed during sea‐level lowstands and buried by central basin estuarine deposits during the last marine transgression. Analyses of lithostratigraphy and radiocarbon ages indicate the onset of subtidal sedimentation at ~14 cal ka bp. Before the onset of subtidal conditions, the first steps of marine incursion seem to have led to the development of lagoonal/wind–tidal flat environments, advocating for a sea‐level stillstand. An abrupt increase in the log(Ti/Ca) ratio in a distinct multi‐centimeter‐thick layer and the identification of a wave‐ravinement surface suggest rapid sea‐level rise in the gulf prior to ~14 cal ka bp, consistent with Meltwater Pulse 1A. Overall, this study highlights the significant impact of sea‐level rise on sedimentation in the gulf from the onset of marine incursions to the mid‐Holocene, as well as the reduced contribution, as currently observed, of riverine inputs due to the progressive diminution and withdrawal of glacial drainage starting before the Holocene.

Microbe‐mediated, marine authigenic formation of ooidal chamosite: Insights from upper Ordovician carbonates of the South‐Western Yangtze platform (China)

AbstractChamosite is a common marine authigenic mineral and microbial involvement has been often assumed during its formation. However, the fossil record of such microbial activity is ambiguous. Chamosite oolitic ironstones widely occur in the Upper Ordovician of the Yangtze Platform, but their origin remains unclear. In this study, detailed sedimentological and mineralogical investigations on ironstones from the Haima section (south‐western Yangtze Platform) helped unravel the critical role of cyanobacterial activity during marine chamosite authigenesis. Stratigraphically, deposition of the Haima oolitic ironstones corresponded with an early Katian transgression, temporally equivalent to many other early Palaeozoic counterparts worldwide. Petrographic observations revealed that different chamosite forms (ooids, peloids and matrix) all developed in close association with calcified cyanobacteria, suggesting that cyanobacteria‐involved chamosite formation existed across a wide range of hydrodynamic conditions from above fair‐weather wave base to below storm wave base. Further mineralogical characterization (backscatter imaging and electron‐microprobe analyses) at single‐grain scale revealed clear mineral zonation from the matrix (dispersed iron oxide and microquartz) through the calcified cyanobacterial sheaths (dispersed chamosite) to the ooid (chamosite). This zonation is best explained by cyanobacterial microbial mats that created benthic reducing and high‐pH conditions. These conditions drove near‐seafloor, dispersed iron oxide and microquartz (primary precipitates formed in oxic seawater) to form chamosite. The authigenic chamosite, originally dispersed within and surrounding the microbial mats, could be reworked to develop other chamositic grains. It is proposed here that the early Katian transgression was responsible for the chamosite–oolitic–ironstone development. The marine transgression submerged earlier‐exposed lands and likely supplied Fe‐Al‐rich colloidal materials to an open marine setting for the chamosite authigenesis. Moreover, transgression likely triggered upwelling, delivered ferruginous deeper water as an extra Fe source and provided nutrients for the cyanobacterial microbial‐mat development, which was essential for the widespread chamosite authigenesis across the south‐western Yangtze Platform.

Evolutionary history of the groundwater system in the Pearl River Delta (China) during the Holocene

Abstract Coastal groundwater reservoirs are sensitive to the complicated evolution of marine transgressions and regressions in river delta regions. We integrated hydrogeological investigation and hydrogeochemical data with numerical modeling to assess the evolution of the groundwater system in the Pearl River Delta’s aquifer system (in southeastern China). We studied the effects of flow dynamics and redox conditions on the biogeochemical processes of nutrients in the regional groundwater flow systems in response to the transient states related to variable paleoprecipitation and seawater salinity decline from the late Pleistocene to the Holocene. The results from paleo-hydrogeological reconstruction of the aquifer-aquitard system showed that the saline groundwater formed by paleo-seawater intrusion was still present in the old marine aquitard and affected groundwater salinity and chemicals in the adjacent aquifers, while most of the groundwater in the shallow young marine aquitard has been freshened by infiltrated old/fresh rainwater. Consequently, total ammonium and carbon stored in the Pearl River Delta were estimated to be (1.91 ± 1.13) × 107 mol m–1 and (5.74 ± 4.05) × 107 mol m–1, respectively, and the ammonium and bicarbonate fluxes derived from groundwater discharge to the sea were calculated as (90.6 ± 55.9) mol m–1 yr–1 and (301.02 ± 196.23) mol m–1 yr–1, respectively. If the buried ammonium in the delta is released to the sea, it would be equivalent to nearly 205 ± 123 yr of Pearl River fluvial loading. These findings suggest that the chemicals trapped in the deltaic aquifer system during the Holocene could contribute to future ocean eutrophication and acidification.

Remnant peat deposit provides clues to the inundated cultural landscapes of Kepa Kurl, southwestern Australia

In early 2021 several tree stumps embedded in a remnant peat deposit were found in the intertidal zone of Wharton Beach, southwestern Australia by Esperance Tjaltjraak Rangers. Attempts were made to identify the tree using both dendrochronological and anthracological methods but were limited by the lack of reference information from tree species in the southwestern Australia. Radiocarbon dates from one stump indicates the tree lived for approximately 200 years, growing into the peaty sediments sometime before ca. 7340 cal yrs BP and died directly or indirectly as a result of marine transgression. The peat deposit is dated to 7608–7429 cal yrs BP but its exposed seaward edge was unconformably underlain by younger sand, dated by OSL to around 3550 years, which may have intruded as a result of a storm event. An OSL age of 12,600 years was obtained from the base of a laminated dune sequence behind the exposed peat deposit, and is significant given a similar age for a previously documented infant burial site in the area. Together these records provide a rare insight into the former wetland landscape and a cultural and scientific link to the drowned coastal plain. A need for more integrative research along this cultural corridor is clear but this preliminary study has demonstrated the value of combining Cultural Knowledge Systems and Western Science, for Tjaltjraak Healthy Country Program and analogous Aboriginal ‘caring for country’ programmes throughout Australia.

Near equatorial paleoclimatic evolution and control on organic matter accumulation during the Cenomanian in the Abu Gharadig Basin, southern Tethys: Insights from palynology, organic petrography, and geochemistry

The beginning of the Late Cretaceous (Cenomanian) attested to a major marine transgression interrupted by sea level falls in north Africa, which led to significant environmental perturbation and widespread accumulation of organic matter-rich sediments. During this period, northern Egypt was located at the southern edge of the Tethys Ocean and deposition of thick siliciclastic alternations between shales, siltstones, and sandstones of the Bahariya Formation took place in the BED2 gas field of the Abu Gharadig Basin, north Western Desert. An integrated approach of palynofacies analysis and palynomorph composition, organic petrography, and geochemical analysis of total organic carbon (TOC)/Rock-Eval pyrolysis, carbonate content, XRD analysis, and clay mineralogy of thirty-nine cutting samples obtained from the lower-middle Cenomanian Bahariya Formation was conducted. This approach was used to characterize organic matter and possible occurrence of source rock intervals, paleoenvironmental and paleoclimatic conditions and their role in organic matter accumulation. Moderate to high proportions of pteridophyte and water fern spores and pollen grains of Araucariaceae (Araucariacites), Cheirolepidiaceae (mainly Classopollis), and Gnetalean (Elaterate pollen) and Afropollis versus the sparsely recorded xerophilous ephedroids (Ephedripites) indicate prevalent conditions of a warm and humid climate. This is consistent with clay mineral composition that is dominated mainly by kaolinite and smectite compared to low illite and the lack of chlorite, which indicated a predominantly warm-humid climate state. Palynofacies analysis showed two assemblages; the first one is dominated by phytoclasts and indicates gas-prone Type III kerogen and deposition in a fluvio-deltaic environment. The second palynofacies assemblage is characterized by moderate abundance of phytoclasts and AOM mostly of terrestrial origin, suggesting a mixed Type III/II kerogen and deposition in a marginal to shallow neritic shelf environment. The organic geochemical characterization showed relatively low average values of TOC, S2, and HI, indicating that the Bahariya Formation is characterized by Type III gas-prone kerogen. Thermal maturity of the Bahariya Formation ranges from immature to the early stage of the oil window. Additionally, organic matter characteristics of the Bahariya Formation are qualitatively and quantitatively similar to their equivalents from nearby basins. Low TOC contents are attributed to a high sedimentation rate and an increased terrestrial input of sand- and silt-sized fractions at shallow water column settings that controlled strong dilution and decomposition versus low burial efficiency of the organic matter.

The Mamfe Basin in the southern Benue trough extension between Cameroon and Nigeria: Gem origin and problem of litho-stratigraphic nomenclature and marine transgression

The Mamfe Basin in the southern Benue trough extension between Cameroon and Nigeria: Gem origin and problem of litho-stratigraphic nomenclature and marine transgression

Different Microsatellite Mutation Models May Lead to Contrasting Demographic Inferences through Genealogy-Based Approaches: A Case Study of the Finless Porpoise off the East Asian Coast

Understanding the population history of wide-ranging species, especially those ranging over varying landscapes, helps in deciphering the evolutionary force (s) that shaped the present genetic diversity/structure of regional fauna. In the shelf region, evolution of coastal morphology through glacial oscillations played an important role in shaping the contemporary genetic structure of coastal marine organisms, although the type and extent of such influence may differ between ecologically dissimilar species, such as marine mammals vs. other marine vertebrates. We reconstructed the demographic trajectories of four populations of the finless porpoise (Neophocaena spp.), covering a wide latitudinal range in the western Pacific and using coalescent-based techniques. Subsequently, we compare the findings with the evolution of suitable ecological niche by reconstructing historic sea level fluctuations with a maximum entropy method. Our results indicate that the finless porpoise was distributed along the continental slope during the low stand of sea level, while the post-glacial marine transgression enabled the porpoise to re-colonize a vast region of the shelf, leading to the most recent expansion of the genus in east Asia. We underscore that inferences of past demographic events are sensitive to the evolutionary model of microsatellite loci and the proportion of multi-step mutation. For coastal cetaceans inhabiting complex coastal habitats, caution has to be exercised when examining demographic parameters to prevent biased inferences due to historic gene flow during marine transgression. Systematic sampling scheme should be encouraged for rigorous quantification of demographic parameters, which may be further applied to more adaptable methods such as approximate Bayesian computation.

Taphonomy of fish, invertebrates and plant remains in the first Tethyan-South Atlantic marine ingression along Cretaceous rift systems in NE-Brazil

The Aptian–Albian Amargosa Bed, Tucano Basin, which was recently considered as a Konservat-Lagerstätten, is a relatively thin, siliciclastic-dominated succession of yellowish and grayish papyraceous shales. We analyzed the taphonomy of fishes, gastric ejecta, freshwater shrimps and conchostracans, euryaline ostracods, and plants. Fish biostratinomic signatures indicate point to changes in water alkalinity/salinity as their causa mortis, occasionally subject to weak currents. The preferential preservation of flexed shrimps and isolated pleons corroborates this interpretation. Conchostracans, recorded in distinct levels, indicate episodes of mass mortality, variable transport and temporal mixing, and at least one faunal change. During the fossilization, primary P and Ca from shrimps and fishes probably generated phosphates, which finally altered to Fe oxy-/hydroxides, yielding a mixed elemental composition, not expressed in other mineralogies than Fe oxy-/hydroxides. The original calcite of ostracod valves likely has been dissolved/replaced by a K-rich aluminosilicate, or by a precursor phase. Plants were preserved by Fe oxy-/hydroxides or by kerogenisation. Previous studies show that marine ingression of Tethyan waters into the central segment of the proto-South Atlantic gulf flooded the continental scale axial river system captured by the Tucano rift basin, affecting base level up to the Araripe Basin. Here it is interpreted that tributary river systems with relatively steeper stream gradients were less affected by marine transgression than the axial system, resulting in local freshwater riverine influx across the elongated epeiric sea developed over the interior rift basins of NE-Brazil, resulting in a mixed biota of distinct water salinities that alternate in the Amargosa Bed type-section.