Marine Shelf Research Articles

Critical evaluation of trophic discrimination factors using compound-specific stable isotopes in a Northwest Atlantic shelf marine food web

Critical evaluation of trophic discrimination factors using compound-specific stable isotopes in a Northwest Atlantic shelf marine food web

Depositional evolution in response to long-term marine transgression in the northern South China Sea

Research on the interaction between depositional evolution process and marine transgression is critical to understanding the transform mechanism of sedimentary systems and guiding hydrocarbon exploration. The early Miocene witnessed the most significant sea-level rise since the Cenomanian, which resulted in extensive marine-influenced deposits worldwide. However, the relationship between the process of depositional evolution and long-term marine transgressions (>1 Ma) remains poorly understood. The Pearl River Mouth Basin in the South China Sea offers a comprehensive deposition record of the early Miocene marine transgression. This study employs high-quality 3D seismic, well-logging, and core data to investigate the impact of the early Miocene transgression on the evolutionary dynamics of the sedimentary system. The regional sea level exhibited a prolonged rise of at least 100 m during the deposition period of the Miocene Zhujiang Formation, corresponding to the long-term marine transgressive in the South China Sea. Throughout this marine transgression, depositional systems developed in the study area include tidal flats, fan deltas, meandering river deltas, and shallow marine shelf sand bodies. The marine transgression process resulted in a significant change in depositional system types, which can be divided into seven units from Unit 1 at the bottom to Unit 7 at the top. The predominant deposition environment transitioned from tidal flats in Units 1-3 to meandering river deltas in Units 4-5, and finally to shallow marine shelf systems in Units 6-7. In the early stage (Units 1-3), the regional uplifts hindered sea level transgression and caused erosion, leading to the development of small-scale proximal fan deltas. In the middle stage (Units 4-5), these regional uplifts submerged, and meandering river deltas dominated with sediments derived from distant extrabasinal sources. During the late stage (Units 6-7), regional sea levels reached their peak, transforming the entire basin into a shallow marine shelf system. Additionally, this marine transgression significantly influenced the distribution of hydrocarbon resources. Notably, the shallow marine shelf sand bodies in Units 6-7 warrant substantial attention for future exploration. This study outlines the complicated transitional processes within depositional systems during long-term marine transgression events, holding relevance for the global evolution of marginal sea basins.

Transgression–regression cycles drive correlations in Ediacaran–Cambrian rock and fossil records

AbstractStrata of the Ediacaran Period (635–538.8 Ma) yield the oldest known fossils of complex, macroscopic organisms in the geologic record. These “Ediacaran-type” macrofossils (known as the Ediacaran biota) first appear in mid-Ediacaran strata, experience an apparent decline through the terminal Ediacaran, and directly precede the Cambrian (538.8–485.4 Ma) radiation of animals. Existing hypotheses for the origin and demise of the Ediacaran biota include: changing oceanic redox states, biotic replacement by succeeding Cambrian-type fauna, and mass extinction driven by environmental change. Few studies frame trends in Ediacaran and Cambrian macroevolution from the perspective of the sedimentary rock record, despite well-documented Phanerozoic covariation of macroevolutionary patterns and sedimentary rock quantity. Here we present a quantitative analysis of North American Ediacaran–Cambrian rock and fossil records from Macrostrat and the Paleobiology Database. Marine sedimentary rock quantity increases nearly monotonically and by more than a factor of five from the latest Ediacaran to the late Cambrian. Ediacaran–Cambrian fossil quantities exhibit a comparable trajectory and have strong (rs > 0.8) positive correlations with marine sedimentary area and volume flux at multiple temporal resolutions. Even so, Ediacaran fossil quantities are dramatically reduced in comparison to the Cambrian when normalized by the quantity of preserved marine rock. Although aspects of these results are consistent with the expectations of a simple fossil preservation–induced sampling bias, together they suggest that transgression–regression and a large expansion of marine shelf environments coincided with the diversification of animals during a dramatic transition that is starkly evident in both the sedimentary rock and fossil records.

Response of Siliceous Marine Organisms to the Permian‐Triassic Climate Crisis Based on New Findings From Central Spitsbergen, Svalbard

AbstractSiliceous marine ecosystems play a critical role in shaping the Earth's climate system by influencing rates of organic carbon burial and marine authigenic clay formation (i.e., reverse weathering). The ecological demise of silicifying organisms associated with the Permian‐Triassic mass extinction is postulated to have elevated marine authigenic clay formation rates, resulting in a prolonged greenhouse climate during the Early Triassic. Yet, our understanding of the response of siliceous marine organisms during this critical interval is poor. Whilst radiolarians experienced the strongest diversity loss in their evolutionary history and perhaps also the greatest population decline of silica‐secreting organisms during this event, only a small number of Griesbachian (post‐extinction) localities that record siliceous organisms are known. Here, we report newly discovered latest Changhsingian to early Griesbachian (Clarkina meishanensis ‐ Hindeodus parvus Zone) radiolarians and siliceous sponge spicules from Svalbard. This fauna documents the survival of a low‐diversity radiolarian assemblage alongside stem‐group hexactinellid sponges making this the first described account of post‐extinction silica‐secreting organisms from the Permian/Triassic boundary in a shallow marine shelf environment and a mid‐northern paleolatitudinal setting. Our findings indicate that latitudinal diversity gradients for silica‐secreting organisms following the mass extinction were significantly altered, and that silica productivity was restricted to high latitude and deep water thermal refugia. This result has potential to further shape our understanding of changes in marine dissolved silica levels and in turn rates of reverse weathering, with implications for our understanding of carbon cycle dynamics during this interval.

Study on the release of microplastic particles with different particle sizes in sediments caused by wave-induced liquefaction

Every year, almost 1.15–2.41 million tons of plastic from terrestrial rivers undergo fragmentation under certain conditions and settle in the estuarine delta and shallow marine shelf areas, making this region a “sink” for land-based microplastics. Owing to its fast deposition rate, relatively soft sediment bed, and shallow water depth, the estuarine delta region is prone to liquefaction under high wind and wave conditions. This could potentially release deeply buried microplastic particles during the liquefaction process, posing further threats to marine ecology and human health. To investigate this phenomenon, laboratory experiments were conducted using a water tank to simulate wave-induced liquefaction of sediment beds. The results showed that under the influence of wave-induced liquefaction, 56.2 % of microplastic particles were released back into the sediment surface, with larger particles being released to a greater extent. Based on these experimental results, this study also analyzed and discussed the release rate and mechanisms of microplastic particles from sediment during wave-induced liquefaction, estimating that the maximum release rate of microplastic particles under the experimental conditions could reach 0.34 mm/min.

Sequence Stratigraphy of the Jurassic Strata and Occurrences of Potential Sandstone Reservoirs in the ST Gas Field, Northern West Siberia Basin

Jurassic strata in the ST gas field of the northern West Siberia Basin have been regarded as a potential exploration target with undiscovered hydrocarbon resources. However limited research has been performed on the sequence stratigraphy of the Jurassic strata, as well as its sandstone distribution controlled by variable sea level change and sediment input. In this paper, four third-order sequences (SQ1, SQ2, SQ3, and SQ4) and nine fourth-order sequences for the Jurassic strata are interpreted based on seismic facies analysis and the lithology stacking patterns of seven wells. SQ1 is characterized by the special Bazhenov Formation which is featured by regionally distributed deep marine shales. SQ2 (J1) is composed of a coarsening upward sequence, the base of which is an unconformable surface that can be recognizable in both seismic profiles and well logging data. SQ3 (J2-J8) is composed of a complete fining-upward and coarsening-upward sequence, showing a series of transgressive and regressive successions. A complete SQ4 has not been drilled through by all the seven wells, only showing a coarsening upward succession on its top (J9) which evolves into a fining upward succession at the base of SQ3. Combined with the seismic inversion result, which predicts sandstone distribution, a sequence evolution model was built for SQ3 showing a full unit of transgressive system tract and highstand system tract (TST-HST) which often occurs in shallow marine shelves. During sequence development, most reservoir sandstones are deposited in the shelf and tidal delta environment at the bottom of the TST and the top of HST, and mudstones are deposited as shelf mudstones, especially at maximum flooding surface. That is controlled by both accommodation and sediment input. Generally, under this sequence framework, the depositional architecture can be further analyzed with implications for source rock, reservoir sandstones, and sealing rock, which may guide future gas exploration and exploitation in this area.

Cross-basin chronostratigraphic correlation of carbonate succession (Llandovery, Michigan Basin, USA) using global carbon δ13Ccarb isotope excursions

Correlating shallow shelf carbonates and their deep basin equivalents is a perennial challenge in the geosciences, with wide-ranging implications. This hurdle is well illustrated in the Llandovery succession of the Michigan Basin, USA, a 40- to 265-m-thick carbonate interval represented by three lithostratigraphic units: the Cataract, the Burnt Bluff, and the Manistique groups. Although extensively studied at various localities within the basin and across the region, the chronostratigraphic relationships between these units remain unknown. The current study presents a cross-basin chronostratigraphic framework for the Llandovery succession utilizing globally documented carbon (δ13Ccarb) isotope excursions (CIEs). From 10 drill cores and three quarry sites throughout the Michigan Basin, five CIEs were identified and chronostratigraphically constrained using conodont biostratigraphy and conodont 87Sr/86Sr data. The five excursions are interpreted to be the global CIEs: the (1) Hirnantian Isotope Carbon Excursion (HICE; Hirnantian Stage), (2) Early Aeronian, (3) Late Aeronian (Aeronian Stage), (4) Valgu (Telychian Stage), and (5) Ireviken (Sheinwoodian Stage). Most importantly, the HICE and the Ireviken CIEs bracket the Llandovery strata preserved in the basin. The new high-resolution δ13Ccarb data suggest that CIEs can be effectively used to correlate among shallow marine shelf carbonates and their deeper water equivalents. The new chronostratigraphic framework shows that CIE-based time horizons across the Michigan Basin cut across lithostratigraphic unit boundaries, which indicates that these lithostratigraphic units are diachronous in the Michigan Basin. In addition to refining the stratigraphy of the Llandovery succession of the Michigan Basin, particularly the timing of various key sedimentary deposits, the new chronostratigraphic framework can be used to: (1) constrain the timing of various regional tectonic phenomena, (2) identify multiple tectonically driven siliciclastic sediment pulses in the basin, and (3) predict various stratal relationships that may result in previously unknown stratigraphic traps and, therefore, new hydrocarbon plays within the basin. The results of the current study also show that δ13Ccarb trends across the shelf-to-basin transect are spatially and temporally variable and do not match those reported in Modern carbonate settings, which possibly suggests that such δ13Ccarb trends, to some extent, reflect variations in water circulation and water mass heterogeneity during deposition.

Rare earth element and yttrium (REY) geochemistry of 3.46–2.45 Ga greenalite-bearing banded iron formations: New insights into iron deposition and ancient ocean chemistry

Finely laminated cherts enclosing nanoparticles of greenalite and apatite are ubiquitous in Archean-Paleoproterozoic (3.46–2.45 Ga) ferruginous cherts, jaspilites and Banded Iron Formations (BIFs) and the greenalite and apatite are considered to be primary deposits. The cherts and BIFs are chemical sedimentary rocks interpreted to have been precipitated in marine settings prior to the first permanent rise in atmospheric oxygen at the Great Oxidation Event (GOE) ca. 2.45–2.32 M.y. ago. As chemical sediments, they are potential archives of the solutions from which they precipitated, incorporating signals from hydrothermal fluids and ambient seawater. Previous studies of rare earth elements and Y (REY) in pre-GOE BIFs have mostly found an “Archean seawater signature” with positive Eu anomalies, attributed to the influence of high-temperature hydrothermal processes, and positive anomalies for La, Gd and Y, ascribed to seawater. REY abundances determined by in situ LA-ICP-MS are presented for well-preserved, laminated greenalite-bearing cherts from ten formations of pre-GOE ferruginous cherts and BIFs from Western Australia. The samples come from a wide range of depositional environments, e.g., submarine proximal volcanic environments, basin floor, slope and deep marine shelf, and are between 3.46 Ga to 2.45 Ga in age. Five groups with different REY patterns are identified, namely (i) mafic-volcanic-influenced vent-proximal chert from the Marble Bar Chert Member of the Duffer Formation of the Warrawoona Group; (ii) felsic volcanic- and sediment-associated chert from the Kangaroo Caves Formation of the Sulphur Springs Group and the Wilgie Mia Formation of the Murchison Supergroup, (iii) ferruginous cherts in shelf sediments from the Bee Gorge Member of the Wittenoom Formation of the Hamersley Group, (iv) BIFs from the Nammuldi Member of the Marra Mamba Iron Formation and Joffre Member of the Brockman Iron Formation, Hamersley Group, and (v) BIFs from the Dales Gorge Member of the Brockman Iron Formation. Of these, only the Dales Gorge Member BIF has a typical Archean seawater signature while the others have REY patterns likely reflecting differing source fluids and environments of deposition but not necessarily global ocean chemistry. Analyses of chert containing sub-micron-sized particles of greenalite and apatite indicate that the likely hosts of the REEs are apatite, siderite and possibly greenalite. The REY patterns of the greenalite-bearing cherts may differ from those of bulk samples of the same formations, perhaps reflecting a diagenetic overprint in the bulk samples, whereas the greenalite-bearing cherts likely preserve their depositional compositions, locked in by early silicification.

Mollusca collected by Agassiz trawl from the 2016 SO-AntEco (JR15005) expedition to the South Orkney Islands, Antarctica - data.

This dataset contributes to the knowledge of macro- and megafaunal Mollusca associated with a range of benthic habitat types in the South Orkney Islands, Antarctica, an exceptionally diverse region of the Southern Ocean. The information presented is derived from Agassiz trawl samples collected on the archipelago's shelf plateau and slope, within and outside of the South Orkney Islands Southern Shelf Marine Protected Area (SOISS MPA). Sampling was conducted in the framework of the British Antarctic Survey/SCAR "South Orkneys - State of the Antarctic Ecosystem" (SO-AntEco) project aboard RRS James Clark Ross during expedition JR15005 in Austral summer 2016. This dataset is published by the British Antarctic Survey under the licence CC-BY 4.0. We would appreciate it if you could follow the guidelines from the SCAR Data Policy (SCAR 2023) when using the data. If you have any questions regarding this dataset, do not hesitate to contact us via the contact information provided in the metadata or via data-biodiversity-aq@naturalsciences.be. Issues with the dataset can be reported at https://github.com/biodiversity-aq/data-publication/. This dataset is part of the Biodiversity, Evolution and Adaptation Project of the Environmental Change and Evolution Program of the British Antarctic Survey. The cruise report of the expedition is available at https://www.bodc.ac.uk/resources/inventories/cruise_inventory/reports/jr15005.pdf. We report occurrences of Mollusca from individual samples taken with a 2 m-wide Agassiz trawl (AGT) in the framework of the February - March 2016 research expedition JR15005 of RRS James Clark Ross to the SOISS MPA and adjacent shelf and slope areas. Of 78 successful AGT deployments, 44 trawls at depths ranging from 235-2194 m yielded living Mollusca, totalling 2276 individuals, 67 morphospecies and 163 distributional records. One hundred and fifteen empty shells were also collected and recorded in the dataset. Three morphospecies (one Bivalvia and two Gastropoda) were sampled exclusively as empty shells, yielding a total of 70 morphospecies and 2391 specimens represented in the dataset. All specimens were preserved in 96% undenatured ethanol and are stored as vouchers in the collections of the British Antarctic Survey (BAS), Cambridge, United Kingdom. The publication of this dataset aims at increasing the knowledge on the biodiversity, abundance and geographical and bathymetric distribution of larger-sized epi- and shallow infaunal Mollusca of the South Orkney Islands.

Uplift, deflation and marine onlap of a Jurassic rift dome, illustrated by a backstepping Middle–Upper Jurassic shelf‐to‐slope succession, Geographical Society Ø, East Greenland

Abstract“Doming–rifting–spreading” constitute the main phases of classical plate tectonics. The Middle–Upper Jurassic succession of East Greenland is interpreted as reflecting formation, deflation and onlap of a rift dome, similar to contemporaneous rift domes in the North Sea, Denmark and southern Sweden. The succession forms a northwards backstepping and onlapping early rift succession in the N–S oriented basin. Deposition ranged from coastal over shallow marine and slope sands, through offshore siltstones to deep basinal mudstones. An outlier on the island Geographical Society Ø fills an important gap in the documentation of the doming, deflation and progressive onlap. Bajocian deposition took place in a shallow marine shelf. This was followed in the late Oxfordian by slope and base‐of‐slope deposition. The backstepping succession onlaps progressively older rocks towards the north, illustrating the gradual deflation, erosion and onlap of the dome, constituting the early part of the doming–rifting–spreading phases of classical plate tectonics.

The Toarcian Oceanic Anoxic Event in a shelf environment (Eastern Tethys): Implications for weathering and redox conditions

The Toarcian Oceanic Anoxic Event (T-OAE) is characterized by significant environmental perturbation and climatic instabilities due to a substantial release of greenhouse gasses. Several investigations of the T-OAE were conducted based on reliable and well-developed integration of multi-proxy approaches, revealing the global distribution of this event in the Panthalassic, Boreal, and Western Tethyan regions. However, a few marine shelf T-OAE records are reported from the Eastern Tethys. This study presents high-resolution organic and inorganic and isotope geochemistry, mineralogical, and sedimentological analyses from the marine Suobucha section of the Qiangtang Basin to assess the role of continental weathering and paleoceanographic conditions, including paleoredox and paleoproductivity conditions, and factors that govern organic carbon accumulation during the T-OAE in the Eastern Tethys. The carbon isotope profile of Suobucha displays a long-term negative excursion characterizing the Jenkyns Event, which is recognized in geographically widespread sedimentary archives indicating its global nature. Continental weathering was intensified at the onset of the Jenkyns Event. Increased values of fluvial detrital proxies (i.e., Si/Al and Ti/Al) and the occurrence of coarser-grained sediments (i.e., silty mudstones) at Suobucha indicated enhanced terrigenous input at the onset of the Jenkyns Event, which was driven by accelerated continental weathering at this time. The lower Toarcian interval in the marine shelf environment of the Qiangtang Basin is characterized by fully oxidizing conditions intermittent with minor phases of dysoxic setting, especially during the Jenkyns Event interval. Given that a stratified water column with anoxic bottom water occurred in the proximal and more restricted lagoonal area (i.e., the Bilong Co area), redox conditions were spatially variable and controlled by basin hydrography and water depth during the Jenkyns Event in the Qiangtang Basin. Oxygen-enriched conditions and low marine bioproductivity were responsible for the low organic carbon burial within the Suobucha section.

Identification of depositional features in the Albian and Aptian sections over the hydrocarbon exploration block M2 on the Mannar Basin, Sri Lanka

The Mannar Basin extends over 45,000 km2 off the western coast of Sri Lanka. It has evolved due to the multiphase rifting between Indo-Lanka landmasses during the Barremian-Paleocene time. The sediment thickness of the basin ranges from about 4 to 10 km. The northern part of the basin is a targeted area for hydrocarbon exploration in Sri Lanka. Though two natural gas discoveries were made in 2011, the basin remains a frontier due to lack of well penetration and 3D seismic coverage. As a result, the depositional features of sediment in the basin are little known. This study focuses on identifying paleo depositional features in the Albian and Aptian strata using 650 km2 3D seismic data from the Mannar Basin. Root Mean Square (RMS) amplitude was used to characterize the depositional features in three-time windows on IHS Kingdom software (v.8.3). The results show the existence of a multi-level paleo submarine fan system in the Albian and Aptian strata. They are located relatively close to the western coastline compared to the fan system in the Eocene strata. The deposition of this paleo submarine fan system has taken place in a shelf marine environment and has been influenced by relatively high sea levels during the Albian and Aptian compared to the relatively low sea levels in the Paleocene and Eocene.

The southern Wyoming Laramide basin: implications for long-term tectonic control on uplift and subsidence

ABSTRACTAn evolving tectonic setting during the Late Cretaceous and Paleocene drove the dramatic transformation of southern Wyoming from a broad marine shelf setting to a series of lacustrine basins. Early dominant control of depositional patterns by flexural tectonics gave way to control by dynamic topography and Laramide-style deformation. The southern Wyoming region demonstrates how progressive partitioning by Laramide movements exerted increasingly dominant control on regional depositional patterns. It did this by creating a long-lived, Laramide uplift-bounded fluvial catchment and basin largely controlled by Laramide-driven subsidence. The Rock Springs and Rawlins uplifts underpinned the basin and exerted their influence in the subsurface. Episodes of Laramide-driven subsidence produced a series of embayments, including the large Rusty–Allen Ridge embayment and the very large deepwater Lewis embayment. The degree of eustatic control in the region would have been greatest at short time scales in the low coastal–shallow-marine settings, causing shoreline oscillations. Several long transgressive episodes followed relatively punctuated progradational periods of coastal-plain construction when supply was generally high from the thrust belt and surrounding uplifts. Laramide activity in the Paleocene led to enclosure of the fluvial basin and the development of a series of smaller marine embayments that mark the end of influence in the region by open and coastal marine processes.

Carboniferous marine deposits of the Tontal section suggest that no Protoprecordillera existed along the Western Gondwana margin

We present new palaeontological and stratigraphic data from a poorly known section located in the Tontal Range, Argentina, whose importance is key to defining the character of a hypothetical Carboniferous mountain chain, the Protoprecordillera. The Tontal Range composed the core of the hypothetical Protoprecordillera, also called the Tontal arch. The section described here comprises Mississippian and Pennsylvanian marine and mixed marine–terrestrial units that were deposited within a proglacial (non-fjord) environment. A new correlating scheme of Tontal section units is brought based on new biostratigraphic data plus the recent development of a stratigraphic order of Carboniferous units cropping out only 15 km away. The lowermost unit in the Tontal section is Del Ratón Formation conglomerate, which passes upwards into glaciomarine shales correlated with the El Planchón Formation that bears marine bivalves and palynomorphs suggesting a Serpukhovian (Upper Mississippian) age. El Planchón is overlain by the barren Churupatí Formation, with lower units of shallow marine, fan-deltaic conglomerate, passing to fluvial redbeds. The overlying Del Salto Formation has intense intraformational folding due to slumping at its base, and consists of sandstone, organic-rich shale, and shelf carbonate, the latter containing marine invertebrates and palynomorphs that suggest a Bashkirian (Lower Pennsylvanian) age. The Tontal section represents a marginal position within a previously defined strike-slip basin (Milana and Di Pasquo, 2019) that was active during most of the Carboniferous. It was deposited in a shallow marine shelf beside a hummocky coastal landscape, the erosion of which provided rounded gravels deposited in Gilbert-type deltas with associated slumps. We found no indication this area hosted any kind of glaciers, and most of the time it was below sea level. These observations, along with the lack of any mountain-side complex or any alpine-valley glacio-related depositional features remain at this, or any neighbouring sections; suggest that there was no Protoprecordillera mountain chain. Correlation with nearby sections also suggests this margin was not influenced by any prominent topographic highs during the depositional time of the Tontal section (upper Mississipian to Pennsylvanian), but rather that this area was located near sea level, potentially with emergent and positive areas along both margins of the strike-slip basin that allowed preservation of the oldest Carboniferous units of this region. On the other hand, the tendency for generalised subsidence during the Upper Carboniferous over most of the Precordillera, may respond to the development of a volcanic arc westwards over the present Cordillera, associated with the activation of a subduction zone in the present-day Chile, turning most of the area into retroarc basins.

BENTHIC FORAMINIFERAL MORPHOGROUPS AND TRACE FOSSILS FROM ALBIAN SHALLOW-MARINE MUDSTONE FACIES OF THE VIKING FORMATION, WESTERN INTERIOR SEAWAY, CANADA

ABSTRACT This study assesses the foraminiferal morphogroup concept as a quantitative tool for interpreting environments of deposition in the geological record. This was achieved by first establishing a solid paleoenvironmental framework based on assessment of trace fossils (Zoophycos, Cruziana, and Phycosiphon ichnofacies, and the unnamed brackish-water association), sedimentology, and facies analysis of shallow-marine siliciclastic units of the upper Albian Viking Formation of the Western Interior Seaway, Canada. Foraminiferal morphogroups were integrated into a framework of six well-defined marine mudstone-dominated facies—estuarine, embayment, prodelta, upper offshore, lower offshore, and marine shelf. Seven morphogroups were recognized, quantified, and labeled using alphanumeric codes—A (tubular), B1 (globular), B2 (coiled, flat), B3 (lenticular), C1 (elongate), C2 (quinqueloculine), and D (trochospiral). Tubular forms (A, Bathysiphon) occur rarely in these shallow-marine facies. Globular forms (B1, Lagenammina) are common in estuarine (33%) and embayment (23%) facies, but also occur elsewhere in low numbers (7–14%). Coiled planar forms (B2, Ammodiscus) occur only rarely (1–8%), but have a minor presence in embayment facies (8%). Lenticular forms (B3, Haplophragmoides) are dominant in estuarine facies (43%) and occur commonly in other environments (9–29%) as well. Elongate forms (C1, Ammobaculites, Reophax, Verneuilinoides) dominate all shallow-marine facies (43–80%), except estuarine (10%). Quinqueloculine forms (C2, Miliammina) have a minor presence in prodelta and marine facies (5%) but are generally rare. Trochoid forms (D, Trochammina) occur rarely, but are relatively common in the prodeltaic facies (15%). Albian foraminiferal morphogroups of the Viking Formation are comparable to those of modern-day offshore environments from water depths of 13 to 160 meters. Foraminiferal morphogroups are objective entities independent of taxonomic determinations. Analysis of their form and function is applicable not only in the shallow-marine facies of the Albian Western Interior Seaway, but in similar facies throughout the geologic record.

Elliptical body fossils from the Fortunian(Early Cambrian) of Normandy (NW France)

Body fossils have been discovered in the Fortunian deposits of the Rozel Cape, in Normandy (NW France). The material consists of about 80 specimens preserved on a shale surface, recently observed at the base of a cliff at the Cap Rozel, in the Cotentin region. The fossils, centimetric in size, have an elliptical outline, with a peripheral bulge, generally without other conspicuous ornamentation, but showing sometimes concentric or radial lines possibly of taphonomic origins. In addition, these body fossils are preserved parallel to the bedding plane, locally rich in horizontal trace fossils (e.g. Archaeonassa Fenton & Fenton, 1937, Helminthoidichnites Fitch, 1850, Helminthopsis Heer, 1877) and also complex treptichinids burrows (e.g. Treptichnus pedum (Seilacher, 1955)) sometimes associated with microbial mats. The sedimentological characteristics of these deposits (ripple marks, syneresis cracks) correspond to a shallow marine shelf environment, with a variable hydrodynamism in the intertidal zone, low for surfaces showing elliptic fossils and syneresis cracks, higher for surfaces with ripple marks. These new discoveries unravel the potential of the Fortunian strata from Normandy and provide new information about the early Cambrian biocenoses.

Biological processes in seagrass beds of coastal lagoons to maintain estuary-dependent marine fisheries

Following the planned FAO Ecosystem Restoration Programme for estuarine habitats to support estuarine fisheries and early life stages of estuary-dependent marine fish, direct relationships of total seagrass and eelgrass Zostera m. capricorni areas and biomass with fish harvest were derived for a range of slightly to highly urbanized coastal lagoons that are expected to support the larvae and juveniles of estuary-dependent marine fisheries. Fish harvest and seagrass area and biomass in the lagoons increased with moderate catchment total suspended sediment and total phosphorus loads due to lagoon flushing rates directing excess silt and nutrients out to sea via the lagoon entrances. Well managed, sewered catchment management works are shown that could assist estuary managers maintain seagrass for estuarine and offshore estuary-dependent fisheries by maintenance of seagrass and fishery ecological processes. Further research is suggested to investigate estuary-dependent post-juveniles leaving estuaries and lagoons migrating to nearshore, offshore and shelf marine fisheries.

Ichnology of a Middle Devonian regression: Environment, terrestrialization and true substrate controls on trace fossils of the Hangman Sandstone Formation, SW England

The Eifelian-aged Hangman Sandstone Formation of southwest England is a unit of the ‘Old Red Sandstone’ that has traditionally been considered relatively barren of trace fossils. Following recent investigations, we here show it to contain the most diverse Middle Devonian non-marine ichnofauna known globally. The fluvial-lacustrine facies of its constituent Trentishoe Member contain representatives of 21 ichnogenera including Archaeonassa, Arenicolites, Beaconites, Bifungites, Circulichnis, Cruziana, Diplichnites,?Gluckstadella, Gordia,?Halimededes,?Lockeia, Merostomichnites, Palmichnium, Petalichnus, Planolites, Polarichnus, Rusophycus, Siskemia, Spirophyton, Steinsfjordichnus, and Taenidium, as well as several microbially induced sedimentary structures. The transitional marine-influenced facies of the underlying Hollowbrook Member are less extensively exposed but contain four additional unique ichnogenera in the form of Cochlichnus, Halopoa, Phycodes, and Teichichnus, as well as further examples of Cruziana, Planolites and Taenidium. A revised ichnological assessment of the unit reveals several notable features, including the youngest known example of the arthropod refugia trace, Polarichnus, as well as a transitional trace fossil form of Diplichnites-Beaconites, demonstrating that the latter was produced by arthropods. As the Hangman Sandstone Formation records the culmination of a marine regression, its ichnofauna can be compared with that of the conformably underlying Lynton Formation, which was deposited in a sandy marine shelf setting. The ichnological differences between these units are acute, with 88% of the Hangman Sandstone Formation trace fossils being exclusive to non-marine or transitional facies. This observation sheds light on the terrestrialization process and indicates that the segregation of marine and non-marine trace fossil communities had accelerated by the Middle Devonian. Internal variability in ichnological signatures within the Hangman Sandstone Formation is also pronounced, with greater ichnodiversity and ichnodisparity in distal fluvio-lacustrine facies than in proximal fluvial facies. By viewing the depositional environment of the unit as a regionally extensive distributive fluvial system, this variability can be partly explained by a bias arising from the distribution of true substrates (bedding planes that demonstrably preserve an ancient sediment-air interface) in the unit, with such phenomena being more readily preserved in the lower energy outer reaches of the depositional system.

Fault structure and segmentation of the Punta Montalva Fault in southwestern Puerto Rico using high-resolution digital elevation models

The Punta Montalva Fault is an active fault that slipped during the 2019–2023 Puerto Rico seismic sequence. It lies in southwestern Puerto Rico within the ∼250-km-wide deformation zone of the North American-Caribbean plate boundary. The fault cuts Miocene limestone and contains surface features that suggest left-lateral displacement. Previous work suggested that the fault connects with the North Boquerón Bay Fault for a length of 33 km and poses a large seismic hazard. However, not much is known about the structure, segmentation, and spatial extent of the fault as it is obscured under thick vegetation. This study used high-resolution topographic data to map the structure, segmentation, and spatial extent of the fault. The results would allow us to better assess the seismic potential of the Punta Montalva Fault by constraining its spatial extent and how strain has been accommodated. A 0.5 m resolution bare-earth digital elevation model (DEM) derived from a 2018 airborne LiDAR survey and another 1 m resolution 2018 DEM showing shallow bathymetry were used to map the Punta Montalva Fault. High-resolution mapping revealed that the Punta Montalva Fault is comprised of three main fault segments on land, a possible additional scarp, and three fault scarps on the seafloor to the SE. No evidence suggests the Punta Montalva Fault extends further NW of Punta Montalva into La Parguera in Lajas. The DEM revealed that the fault cuts a shallowly dipping sedimentary sequence of the Ponce Limestone that has karst topography in places. On land, the fault is conspicuous where it forms scarps, drags and cuts sedimentary layers, and forms a duplex structure with a predominantly left-lateral offset. A left-lateral offset of an intermittent stream has been refined to 133.6 ± 7.3 m. The fault scarps along a marine shelf strike E-W and show a maximum normal offset of 4.8 m. Another sub-parallel fault scarp in the seafloor strikes NW-SE and displays a left-lateral offset of 98.3 m. The total length of the fault segments is ∼2.67 km long. The surface segmentation suggests that the fault would have a lower seismic hazard than if it were continuous and connected to the North Boquerón Bay Fault. However, if the Punta Montalva Fault is continuous beneath the surface, its total fault length would be approximately 7.97 km long and would pose a larger seismic hazard than that suggested by the surface segmentation. Strike-slip, folding, and normal offset suggest that the area is being deformed by transtentional deformation, which supports seismic analyses and tectonic models.

Paleoclimate and Paleoenvironment Reconstructions from Middle Eocene Successions at Beni-Suef, Egypt: Foraminiferal Assemblages and Geochemical Approaches

The Eocene deposits of Egypt provide a wide variety of shallow marine facies and fossil assemblages, allowing paleoenvironmental reconstructions in this warmhouse climate interval. Forty-three rock samples have been collected from two middle Eocene sections, exposed at southeast Beni-Suef area in northern Egypt. The studied outcrops are lithologicsally subdivided into two rock units named from base to top as follows: (1) the Qarara Formation (Lutetian) and (2) the El Fashn Formation (Bartonian). Most investigated rock samples showed richness in benthic foraminiferal assemblages and only rare occurrences of index planktonic foraminifera. They yielded 160 foraminifera species which belong to 4 suborders, 19 superfamilies, 34 families, and 59 genera. The stratigraphic distribution of the identified species allowed us to define four local benthic bio-ecozones: (1) Bolivina carinata Lowest Occurrence Zone (Lutetian), (2) Cibicides mabahethi/Cancris auriculus primitivus Concurrent-Range Zone, (3) Nonion scaphum Lowest Occurrence Zone, and (4) Brizalina cookei/Nonionella insecta Concurrent-Range Zone (Bartonian). These biozones are described and discussed in detail and correlated to stratigraphic equivalents in Egypt. The rareness of index planktonic foraminifera through the studied sections does not allow a precise biostratigraphic and chronostratigraphic correlation. The shale samples show low TOC values, which may be related to low productivity, high sediment influx, and/or prevailing oxic conditions. Bulk rock geochemistry, consistent with the benthic foraminifera ecological preferences, indicated that the studied sections were deposited in moderate to high oxygen levels and warm climatic conditions in a typical shelf marine setting. The identified species showed strong similarities with nearby southern Tethys areas, reflecting migration via the trans-Sahara seaway, and minor similarities with those identified from the northwestern Tethys and the North Atlantic province attributed to the change in the environmental and climatic conditions, such as cooler, latitudinal zoned climatic conditions along the northwestern Tethys, which was unsuitable for their biological demands. The warming trend identified from Lutetian to Bartonian intervals corresponds to the onset of the Middle Eocene Climatic Optimum (MECO).