Systematics of Modern Benthic Foraminiferal Assemblages From the Deltaic Mangrove Ecosystem of Sundarbans

The contemporary intertidal foraminifera and estuarine environment information were collected from the four sites adjoining the deltaic mangrove environment in the Sundarbans. The marsh zones of the south-western coastal region of Bangladesh were examined for modern benthic foraminifera and to expound on the relationship of the foraminiferal assemblages with the environment. Due to high inaccessibility and remoteness, the taxonomic study of foraminifera and its depositional environment remains largely overlooked in the Sundarbans of Bangladesh. This study includes a detailed survey of depositional environment of these fluvio-deltaic to shallow marine sediments. The seventeen species belonging to fourteen genera representing nine families were recorded from surficial sediment of supratidal, intertidal, and dune environment of Kotka, Jamtala, Kochikhali, and Dimer char area. In the present study, these foraminiferal assemblages are characterized calcareous and agglutinated foraminifera. The Kotka beach is recognized as Nonionina assemblage zone, Jamtala beach designated as Ammonia assemblage zone, Kochikhali as Nonionina assemblage zone and Dimer char as Rosalina-Nonionina-Nonionella assemblage zone. The deposition of foraminifera is restricted to Sundarbans’ low to high marsh zone. J. Asiat. Soc. Bangladesh, Sci. 47(2): 121-136, December 2021

Iron-Coupled Anaerobic Oxidation of Methane in Marine Sediments: A Review

Anaerobic oxidation of methane (AOM) is one of the major processes of oxidizing methane in marine sediments. Up to now, extensive studies about AOM coupled to sulfate reduction have been conducted because SO42− is the most abundant electron acceptor in seawater and shallow marine sediments. However, other terminal electron acceptors of AOM, such as NO3−, NO2−, Mn(IV), Fe(III), are more energetically favorable than SO42−. Iron oxides, part of the major components in deep marine sediments, might play a significant role as an electron acceptor in the AOM process, mainly below the sulfate–methane interface, mediated by physiologically related microorganisms. Iron-coupled AOM is possibly the dominant non-sulfate-dependent AOM process to consume methane in marine ecosystems. In this review, the conditions for iron-coupled AOM are summarized, and the forms of iron oxides as electron acceptors and the microbial mechanisms are discussed.

Structures in Shallow Marine Sediments Associated with Gas and Fluid Migration

Geological structure changes, including deformations and ruptures, developed in shallow marine sediments are well recognized but were not systematically reviewed in previous studies. These structures, generally developed at a depth less than 1000 m below seafloor, are considered to play a significant role in the migration, accumulation, and emission of hydrocarbon gases and fluids, and the formation of gas hydrates, and they are also taken as critical factors affecting carbon balance in the marine environment. In this review, these structures in shallow marine sediments are classified into overpressure-associated structures, diapir structures and sediment ruptures based on their geometric characteristics and formation mechanisms. Seepages, pockmarks and gas pipes are the structures associated with overpressure, which are generally induced by gas/fluid pressure changes related to gas and/or fluid accumulation, migration and emission. The mud diapir and salt diapir are diapir structures driven by gravity slides, gravity spread and differential compaction. Landslides, polygonal faults and tectonic faults are sediment ruptures, which are developed by gravity, compaction forces and tectonic forces, respectively. Their formation mechanisms can be attributed to sediment diagenesis, compaction and tectonic activities. The relationships between the different structures, between structures and gas hydrates and between structures and authigenic carbonate are also discussed.

South-Central Barents Sea Composite Tectono-Sedimentary Element, offshore Norway and Russia

The south-central Barents Sea today comprises a shallow continental shelf with water depths mainly in the 200-400m range, straddling the Norway-Russia marine boundary. Geologically it consists of a stable platform (the Bjarmeland Platform), dissected by rifts of probable Late Carboniferous age, with a significant and geologically persistent basement high (the Fedynsky High) in its south-eastern part. The rifts are the ENE-WSW trending Nordkapp Basin, the similarly-trending but less clearly demarcated Ottar Basin, and the NW-SE Tiddlybanken Basin. The varying rift trends appear to reflect the orogenic grain patchwork of the basement (Caledonide and Timanide), and these basins were infilled with a variable facies assemblage including substantial Carboniferous-Permian halites.Massive sedimentary influx of fluvio-deltaic to shallow marine sediments took place in the Triassic, from the E and SE (Urals, Novaya Zemlya and western Siberia) and south (Baltic Shield), resulting in doming and diapirism in the areas of thickest salt, particularly in the rifts. The succeeding Jurassic, Cretaceous and Cenozoic successions are generally thin, locally thickening in rim synclines and in the NE of the area towards the deep basins flanking Novaya Zemlya. Reactivation of the halokinetic structures took place in the early Cenozoic, probably associated with the development of the NE Atlantic-Arctic Ocean linkage.Marine source rocks of Triassic and Late Jurassic age are present in the area, along with Carboniferous and Permian source rocks of uncertain effectiveness. Petroleum has been found in Jurassic and Triassic clastic reservoirs, including recent shallow Jurassic oil and gas discoveries. Although none are currently in production, near-future oil development is likely in Wisting discovery, on the western margin of the area. New exploration, including drilling, is currently taking place in the east of the area as a result of recent Norwegian and Russian licensing.

The Late Miocene Rifian corridor as a natural laboratory to explore a case of ichnofacies distribution in ancient gateways

Oceanic gateways have modulated ocean circulation and have influenced climatic variations throughout the Earth´s history. During the late Miocene (7.8–7.35 Ma), the Atlantic Ocean and the Mediterranean Sea were connected through the Rifian Corridor (Morocco). This gateway is one of the few examples of deep ancient seaways with a semi-continuous sedimentary record. Deposits comprise turbidites intercalated between deep-sea mudstone (i.e., hemipelagites and drift deposits), channelized sandstone contourite facies, and shallow marine sandstone. Herein an ichnological analysis was conducted in these upper Miocene sediments to improve characterisation of palaeoenvironmental conditions. In addition, ichnofacies were analysed to elucidate how bottom currents control ichnofacies distribution and can modify their attributes. Turbidite deposits are typified by vertical trace fossils (i.e., Ophiomorpha), conforming the Ophiomorpha rudis ichnosubfacies. Contouritic sandstone exhibits high density and low diversity trace-fossil assemblage, with predominant Macaronichnus and Scolicia, resembling a proximal expression of the Cruziana ichnofacies. Shallow marine environments are dominated by vertical trace fossils (e.g., Conichnus, Ophiomorpha, Skolithos), allowing an assignation to the Skolithos ichnofacies. This study reveals for the first time a variability in ichnofacies attributes and distribution at the Rifian Corridor, associated with turbidites, contourite and shallow marine sediments. Hydrodynamic energy reveals as the major factor controlling trace maker communities in the studied seaway. Highly energetic conditions typical of shallower settings are present in deeper-water environments (i.e., slope), contributing to ichnodiversity impoverishment in ichnofacies.