Deep Marine Environment Research Articles

CHARACTERIZATIONS AND CLASSIFICATION OF FORMATION WATER PRODUCED IN OILFIELDS

Formation water known as oilfield wastewater, produced water, associated water and brine; which generated in great volumes in onshore and offshore oil and gas production. As more and more world major oilfields mature, more water begins to be produced from oil producers because of aquifer encroachment and/or water injection. The evaluated characteristics of offshore oilfield produced water in oilfields is very important for petroleum engineering industry from both upstream and downstream activities, as well as is essential for both environmental assessment and reservoir management. This study has been conducted on two oilfields namely Sarir and Nafora for oil producing wells to distinguish the characterizations of the produced water. Also, the water characteristics are investigated in five gathering centers in Sarir oilfield. The study included the analysis of sixty water samples to determine the physiochemical characterizations. The data obtained from the chemical analysis were used to classify formation water and to determine the environmental deposition using Sulin's system. The results revealed that the type of formation water in both two fields are belonging to CaCl2 type and deep marine environment. The Stiff diagrams of the studied formation water of Sarir field were constructed for five gathering centers and compared with different patterns of Stiff diagrams. Most of the studied water exhibits a similarity of these patterns, but some of them show slightly deviation, this may be attributed to the type of formation and the source of brine.

Transformation of dense shelf water cascade into turbidity currents: Insights from high-resolution geophysical datasets

Dense shelf water cascade (DSWC) is a common oceanographic phenomenon on many continental shelves. Previous studies indicate that the DSWC could shape seabed physiography and carry seawater, sediment, and organic carbon a long distance from the continental shelf to the basin floor. However, it remains enigmatic how these DSWC's interact with seabed geomorphology and travel long distances from the shallow to deep marine environments. In this study, we employed high-resolution multibeam bathymetry, 2D and 3D seismic reflection, core description, and sediment grain size data from the Gippsland Basin, southeast offshore Australia. The continental shelf of the central Gippsland Basin stores sediment supplied by the along-shelf transported DSWC. By calculating the sediment motion threshold, we demonstrate that the DSWC is capable of entraining sediment from, and forming dense bottom nepheloid layers above, the seabed. Seismic reflection data reveal that cyclic steps are common on the shelf and slope, indicating a downslope-transported, supercritical current-dominated environment. Core observation and grain size analyses reveal that coarse-grained, Ta-typed turbidites are the major facies, indicating the presence of high-intensity downslope-traversing turbidity currents. Thus, supercritical turbidity currents are the dominant sedimentary process in the central Gippsland Basin. We illuminate that DSWC can interact with pre-existing seabed bathymetry created by a buried submarine landslide, resuspending sediment and igniting downslope-transported turbidity currents. The presence of numerous cyclic steps indicates that the turbidity current can evolve into a supercritical regime upon ignition, leaving complex seabed geomorphology and allowing the forming currents to travel across the shelf and extend more than 80 km down the lower slope. As revealed by our literature review, we imply that the transformation of DSWC into turbidity currents should be a common sedimentary process on outer continental shelves globally, significantly sculpting the seabed morphology and facilitating sediment and other marine particles transportation from shallow to deep sea.

Deep-sea Ordovician lingulide brachiopods and their associated burrows suggest an early colonization of proximal turbidite systems

Trace fossils from Ordovician deep-marine environments are typically produced by a shallow endobenthos adapted to live under conditions of food scarcity by means of specialized grazing, farming, and trapping strategies, preserved in low-energy intermediate to distal zones of turbidite systems. High-energy proximal zones have been considered essentially barren in the early Paleozoic. We report here the first trace and body fossils of lingulide brachiopods in deep-marine environments from an Upper Ordovician turbidite channel-overbank complex in Asturias, Spain. Body and trace fossils are directly associated, supporting the interpretation of a lingulide tracemaker. Ellipsoidal cross-section, cone-in-cone spreite, and spade morphologies suggest the specimens belong to Lingulichnus verticalis. The oblique orientation in both trace and body fossils is the result of tectonic deformation. The organisms were suspension feeders showing escape, dwelling, and equilibrium behaviours controlled by sedimentation rates associated with turbidite deposition. These trace fossils and their in situ producers represent the oldest evidence of widespread endobenthos colonization in high-energy, proximal areas of turbidite systems, expanding the bathymetric range of Lingulichnus and the variety of behaviours and feeding styles in early Paleozoic deep-marine environments.

Porosity Evolution and Sequence Stratigraphy of Khasib Formation (Late Turonian-Coniacian) in Selected Oilfields, Central Iraq

The evolution of porosity and sequence stratigraphy study of the Khasib Formation (Late Turonian-Coniacian) in two wells, in central Iraq were conducted. In the first well EB-X, the Khasib Formation sequences are confined to a depth of 2182-2285 m, with a thickness of about 103 meters, and in the second well Hf-Y, the Khasib Formation sequences are confined to a depth of 2941-2860 meters, with a total thickness of 81 meters. The lithology of the formation is predominantly dark chalky limestone rich in planktonic fossils, with a few thin layers of black shale. The formation lithology progressively shifts higher to shaley limestone rich in planktonic fossils and Calcispheres. On the other hand, the depositional environment of the formation was established by diagnosing six mudstone submicrofacies, five wackestone submicrofacies, and a packstone microfacies, which indicate the formation depositional settings in deep marine environments. Furthermore, the formation is split into three zones based on porosity values: A, B, and C, which are characterized by productive reservoir rock, low-yielding reservoir rock, and medium-productive reservoir rock, respectively. The Khasib formation sequences formed during the Late Turonia to Early Coniacian. As a result, the overall sedimentation period reached 3.1 million years, and the stratigraphic sequence is of the third order.

Characteristics of Stratigraphy and sedimentation of the Phu Khanh Basin and adjacent area

The Phu Khanh Sedimentary Basin is situated in the deep-water offshore area, east of the continental shelf of Central Vietnam. This area is said to have quite good oil and gas potential, but very few geological and petroleum research projects have been carried out in the past. In this article, the authors update new research results based on new seismic interpretation and well data conducted in recent years. The obtained results show that: Stratigraphy of the Phu Khanh Basin was subdivided into 5 large sequences, including: a. Eocene(?)/Oligocene unit is mainly clastic sediments of fluvial/lacustrine, delta plain and marine environments, b. Lower Miocene stratigraphy: Includes deltaic clastic sediments and shelfal carbonates; c. Middle Miocene stratigraphy: includes delta-plain, shallow marine terrigenous sediments and shelfal carbonate, d. Upper Miocene and Pliocene - Quaternary units include continental shelf and deep-sea terrigenous sediments. Each unit of stratigraphy and corresponding sedimentary environment is related to each stage of the geological and tectonic evolution of the basin. In general, the trend changes from the fluvial/lacustrine environment to the deltaic, shelfal and deep marine environments upward. Establishing the names of the formations and the presence of the Eocene sedimentary rocks in the Phu Khanh Basin is still an open issue. More detailed data, especially well data, are needed to obtain a more convincing interpretation.

Long-term carbon sequestration in the Eocene of the Levant Basin through transport of organic carbon from nearshore to deep marine environments

This study addresses a specific component associated with mass transport complexes in marine systems: the role of hyperpycnal flows, dense shelf water cascading, submarine canyons, distributary channels, and other transport mechanisms in transferring organic matter from continental and shallow marine settings into deep-marine environments. We speculate that during the Eocene, allowing for only 0.1‰ of shelf carbon to be preserved through transport mechanisms would account for up to 13.7% of all organic carbon burial. As such, the potential to mobilize through this mechanism large quantities of organic carbon is significant.Our case study focuses on a 150 m Eocene sequence composed of organic-rich chalks interleaved with displaced neritic limestones. TOC values range between 1.5 and 14%, averaging 4.5%. Displaced limestones are composed of a variety of poorly cemented mud- and wackestones, with low-diversity assemblages of large benthic foraminifera associated with planktonic foraminifera, suggesting deposition under low-energy conditions within the oligophotic zone on the outer ramp. Transport overprints include soft-sediment deformation, partially lithified rip-ups, folds, small diapirs, bed-scale imbrication, brecciation and syn-sedimentary shear. These features indicate detachment, movement and emplacement following initial sedimentation, in some cases more than once. Emplacement occurs into a chalk facies that can vary in appearance from darker (higher TOC) and lighter (lower TOC) lithofacies.Combination between the sedimentological, petrophysical, and elemental analyses indicates shifts between autochthonous and allochthonous sedimentation, whereas the organic geochemical analysis reveals a correlation between modes of sedimentation and preservation/composition of organic matter. Organic richness seems to increase within intervals of allochthonous sedimentation, with lower TOC values within intervals of autochthonous sedimentation. Organic matter preservation is enhanced due to poor oxygenation of the sea floor, further depleted by rapid burial beneath mass-transport deposits, increasing sedimentation rates and thus organic matter preservation. Horizons rich in organic matter may be derived from three different sources: organic matter with a fingerprint of terrestrial sources (e.g., enhanced contribution of plant leaf waxes) transported from nearshore environments; an allochthonous marine fingerprint with sulfurized hopanoids, which seem to be reworked from pre-existing Cretaceous organic-rich carbonates entrained within fined-grained micro-turbidites in the para-autochthonous facies; and productivity-derived organic matter deposited on the seafloor of the deep marine environment.This study demonstrates how transport mechanisms allow for the long-term burial of organic carbon in marine systems. When taking into consideration similar processes reported to occur in the world oceans today, it is clear that sediment transport and long-term burial of organic carbon is a fundamental part of the global carbon cycle.

Global distribution and diversity of antimicrobial genes across subsurface bacterial and archaeal metagenome assembled genomes

Microorganisms have the capability to produce antimicrobial compounds through secondary metabolism, which are not essential within their natural environments, but have been found to have many effects on the ecosystem. Antimicrobial production genes have been identified in a wide range of microorganisms; however, research into natural ecosystems has historically been limited to continental soil environments. Antimicrobial production research has been limited in the deep continental subsurface and marine environments, especially deeply buried marine sediments. We analyzed 466 high-quality metagenome assembled genomes (MAGs) collected from continental and marine subsurface environments through the Deep Carbon Observatory’s Census of Deep Life. A total of 383 MAGs contained biosynthetic gene clusters, namely Type I and Type III polyketide synthase genes, non-ribosomal peptide synthetase genes, and other unspecified ribosomally synthesized and post-translationally modified peptide products. All of these genes were found across continental mines, subglacial lakes, hotsprings, and serpentinizing environments. These environments have previously not been investigated via metagenomics for antimicrobial gene diversity, which may be produced for competition or communication purposes. All other biosynthetic genes identified in this study were less than 50% similar to reference biosynthesis genes indicating the novelty of secondary metabolism in subsurface microorganisms. The majority of predicted antimicrobial products were found to be produced exergonically, which could indicate microbial populations use energy-conserving mechanisms to produce compounds that could offer a competitive advantage.

Depositional Environment Characteristic of The Late Miocene Kerek Formation in Kendeng Basin: A Case from Cipluk Area, Kendal Regency, Central Java

This study focused on the Late Miocene Kerek Formation in Cipluk, Kendal Regency, Central Java, which belongs to the Kerek Formation, a lithostratigraphy unit characterized by Early Miocene - Late Miocene turbidite deposits. The research aims to comprehensively interpret the depositional environment characteristics of the Late Miocene Kerek Formation based on lithofacies, thin section analysis, and micropaleontological analysis. Gaining insights into facies characteristics and the depositional environment will offer novel perspectives for the exploration and development of oil and gas resources in the Kendeng basin. The methodology consists of data collection, analysis, and synthesis. Results indicate that the study area is dominated by classical turbidite facies, suggesting a distal zone with slow sediment settling. The analysis reveals that the Late Miocene Kerek Formation was deposited in a deep marine environment within the inner bathyal—outer bathyal bathymetry zone, specifically in the lower fan section of a submarine fan system. Based on the characteristics of existing deposits and facies, the deposition environment is identified as a fine-grained, mud-rich complex in an elongated submarine fan. These findings contribute to a better understanding of the Late Miocene depositional environment in the Kendeng Basin, Central Java.

Geochemistry of the Albian to Upper Maastrichtian formations of the K1 oil well (East of the Côte d’Ivoire offshore basin): Depositional environment and implication of provenance

The studies were carried out on 93 samples of cuttings from the K1 oil well. These samples were processed using the Fluorescence Spectrometer (XRF) method. Chemical analyses contributed to the determination of depositional environments and origin of the sediments. Albian sediments deposited in an environment proximal to the continental characterize the MS1 mega-sequence. In contrast, the MS2 mega-sequence (Cenomanian to Maastrichtian) was deposited in a shallow to deep marine environment marked by a decrease in detrital flow. The ratio Ti/Y, with values below 0.017 in the MS1, means that the sediment source of the mega-sequence MS1would therefore be richer in phosphates, with a contribution from mafic volcanic rocks (rich in illite, iron and magnesium). In contrast to MS1, MS2 is characterized by ratio Ti/Y values above 0.017. This decrease in Yttrium content in this mega-sequence is consistent with Th/Al values below 1.588. This would suggest a richer source of titanium oxides, which could be rutile, sphene or anatase.

A new isochron for stratigraphic correlation in the Permian Delaware Basin and beyond

Altered volcanic ash, preserved as bentonite clay within sedimentary depositional units, can facilitate regional stratigraphic correlation. While many bentonite ash beds have been documented in core extracted over decades of hydrocarbon exploration in the Delaware Basin, a particular ∼1 cm-thick bentonite has been identified at a distinct stratigraphic position, at a sedimentary facies transition from thin-bedded calciclastic turbidites to thick-bedded siliciclastic turbidites, in the compositionally-mixed upper Wolfcamp formation. A comparison of geochemical analyses of the ash from two cores and petrophysical correlations across eight wells was conducted to test the regional correlation of the ash. Despite diagenetic alteration since seafloor deposition ∼280 Ma, nearly identical geochemical trends between incompatible elemental subsets, including light and heavy rare earth elements, large ion lithophiles, and high field strength elements, suggest that these two ash deposits originated from the same volcanic center. Detailed sedimentologic analyses and lithostratigraphic correlations across three cores spaced tens of km apart confirm that the ash bed is bound by correlative quiescent deepwater strata. Based on the chemical composition, probable timing of deposition, and proximity, we speculate that the Las Delicias Arc produced this ash, and it was transported by wind and deposited as a hemipelagite into the Delaware Basin deep marine environment. This discovery implies the existence of the ash marker in other cores within Late Paleozoic western equatorial Pangea, e.g. in compositionally-mixed deep marine deposits of the Midland Basin and outcropping deposits around the Greater Permian Basin and beyond, which would facilitate regional chronostratigraphic correlation for a critical time in Earth's history.

The Sommerodde (Telychian, Silurian) positive carbon isotope excursion: why is its magnitude so variable?

The Sommerodde positive organic carbon isotope excursion (SOCIE) within the Oktavites spiralis graptolite Biozone (Telychian, Silurian) was first identified in the Sommerodde-1 core, Bornholm, Denmark, where it is the largest positive excursion within the Upper Ordovician–lower Silurian part of the core. Other published occurrences of the SOCIE are discussed here, including new δ 13 C org data from the Jabalón River section, Corral de Calatrava, central Spain, where the SOCIE is only a very minor positive excursion. Very unusually, the SOCIE is best developed in deeper water settings, contrary to the typical pattern of declining excursion magnitude offshore. In the Sommerodde-1 core (Bornholm), and where it has been tentatively identified in the Vežaičiai-2 core (Lithuania), the SOCIE is developed in pale, organic-poor mudstones. It is considered likely that the magnitude of the SOCIE has been enhanced in the Sommerodde-1 core record by a change in organic matter composition in the deep-marine environment that did not have such a significant effect in shallower marine environments. Supplementary material: A table of organic carbon isotope data from the Jabalón River section, Corral de Calatrava, central Spain is available at https://doi.org/10.6084/m9.figshare.c.6769514 Thematic collection: This article is part of the Chemical Evolution of the Mid-Paleozoic Earth System and Biotic Response collection available at: https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system

Facies association and Paleo depositional environment of the exposed Neogene succession in the Sitapahar Anticline of Rangamati Area, Chittagong Tripura Folded Belt (CTFB) region, Bengal Basin, Bangladesh

Neogene sedimentary rocks are exposed in the Chittagong Tripura Folded Belt (CTFB) Region in Bengal Basin. Sitapahar anticline is situated in the middle part of the CTFB Region. In this structure, eleven litho-facies have been identified in fluvial, overbank, shallow marine, deltaic, and deep marine depositional environments. Surma Group is composed of Bhuban and Boka Bil formation during Miocene time and was deposited in shallow marine, deltaic, and deep marine environments and characterized by the identification of interbedded shale facies (ShI), fine sandstone facies (SFs), lenticular laminated silty shale to shale facies (Zw), wavy bedded sandstone siltstone facies (Slsh), flaserbedded sandstone siltstone facies (Sxhs), ripple laminated sandstone facies (Sr), black Shale facies (Shb) and nodular shale facies (Zn). While, Pliocene Tipam group and Plio-Pleistocene Dupi Tila Formations were deposited in fluvial intervention and characterized by crossbedded sandstone facies (Sxbt), mudstone facies (Mf), interbedded mudstone and sandstone facies (MI).

Microfacies Analysis and Depositional Environment of the Mishrif Formation at Selected Wells in E Oilfield, Southren Iraq

The Mishrif Formation is an important succession that was deposited during the Cenomanian–Early Turonian. More than 79 thin sections of core in addition to well log data for the Mishrif Formation from 2 boreholes within the E oilfield (E-1, and E- 2) were used to determine the different associations facies to interpret the depositional environment of the Mishrif Formation. Six major microfacies were diagnosed the Mishrif Formation, Mudstone, Wackestone, Packstone, Grainstone, Boundstone, and Rudstone and ten submicrofacies include: Bioclastic Packstone submicrofacies with rich Echinodermat, Coral and Rudist fragment and high Dolomitization, Rudstone submicrofacies with large Rudist fragment and vug porosity , Boundstone submicrofacies with very large coral, Plankton Foraminiferal Packstone submicrofacies withe Globigerinelloides and Calcispheres, Bioclastic Wackestone to Packstone submicrofacies with dolomite and calcareous algae, Peloidal Packstone with coral, pillites, pieces of Rudist and Separate-Vug pore, Bioclastic Packstone to Grainstone submicrofacies, Peloidal to Bioclastic Packstone submicrofacies, Benthonic Foraminiferal Mudstone submicrofacies, Rudist fragmented Mudstone. These microfacies were deposited in restricted, shoal, shallow open marine, rudist bioherm, and deep marine environments.

Depositional Setting of the Shiranish Formation (Campanian-Maastrichtian) in Selected Sections from Northern Iraq

The Shiranish Formation (Campanian-Maastrichtian) was studied in two surface sections (Diana and Garuta) in Erbil Governorate. Both sections lie within the High Folded Zone of Zagros Fold-Thrust Belt in Iraq. Stratigraphically, the formation is divided into three lithostratigraphic units depending on the field characteristics with varied thicknesses of the formation in both sections. The lower unit (Unit A) consists of blue to grey well-bedded marly massive limestone, the middle unit (Unit B) is composed of blue to grey marl, marly limestone and stratified shale, and finally, the upper unit (Unit C) is composed of grey limestone and blue marly limestone. The lower contact of the formation is unconformable with the Bekhme Formation in the Diana section and conformable with the Kometan Formation in the Garuta section, while the upper contact is conformable with both Tanjero and Kolosh formations in Diana and Garuta sections respectively. X-ray diffraction analysis has revealed that calcite is the main mineralogical component with less of quartz and clay minerals as represented by chlorite and illite. Four lithofacies were distinguished (Marl facies (Sml), Shale facies (Ssl), Conglomerate limestone facies (Scl)) and red clay layers (Srl), whereas, three main microfacies were recognized; Fossiliferous Lime Mudstone Microfacies (Sml), Lime Wackestone Microfacies (Sw) and the Packstone Lime Microfacies (Sp), which in turn were subdivided into seven secondary facies, according to their components, which are; Planktonic Foraminiferal Lime Wackestone Submicrofacies (Sw1), Keeled Planktonic Foraminiferal Lime Wackestone Submicrofacies (Sw2), Calcispheres Lime Wackestone Submicrofacies (Sw3), Bioclastic Lime Wackestone Submicrofacies (Sw4), Benthonic Foraminiferal Lime Wackestone Submicrofacies (Sw5), Keeled Planktonic Foraminiferal lime Packstone Submicrofacies (Sp1) and Planktonic Foraminiferal Globular Chamber Packstone Submicrofacies (Sp2 ). Based on these facies, the formation was deposited in a relatively deep marine environment and within two secondary environments; the outer shelf and upper bathyal environments as a result of the widespread transgression in the beginning of the Campanian.

Ichnological analysis of the Messinian-Zanclean (Miocene-Pliocene) transition at Eraclea Minoa (Sicily): Tracemaker response to the Terminal Messinian Flood

A detailed ichnological analysis has been conducted, for the first time, of the Arenazzolo and Trubi formations of the Caltanissetta Basin in Sicily. Aim of this analysis is to evaluate paleoenvironmental changes affecting macrobenthic tracemaker communities during the re-flooding of the Mediterranean at the end of the Messinian Salinity Crisis. The uppermost Messinian Arenazzolo Formation is characterized by a scarcity of trace fossils, probably related to high energy depositional conditions, and perhaps no fully normal salinity level yet, resulting in an unfavourable habitat for macrobenthic tracemaker communities. The exclusive presence of small traces (Chondrites) sparsely distributed in several horizons is associated to intermittent phases of lower energy conditions facilitating colonization by opportunistic tracemakers. A significant change in trace fossil assemblages is observed at the transition to the Zanclean Trubi Formation. Here the ichnofossil assemblage consists of?Arenicolites, Chondrites, Halimedides, Palaeophycus, Planolites, Thalassinoides, Trichichnus and Zoophycos, assigned to the Zoophycos ichnofacies, revealing an abundant, diverse, well-developed, multi-tiered, tracemaker community. This change observed at the Messsinian/Zanclean boundary is related to the rapid establishment of normal, full-marine, conditions with well oxygenated bottom- and pore-waters, and food availability in a deep marine environment. Comparison with previous micropaleontological studies supports the magnitude of the paleoenvironmental change affecting both pelagic and benthic environments.

Late Miocene biostratigraphy and paleoenvironment of the Sais Basin (southern Rifian Corridor, Morocco): New insights from the Moulay Yakoub area

During the Late Miocene, the Rifian Corridor was one of the two main corridors allowing exchanges between the Atlantic and the Mediterranean Seas. Sedimentary records accumulated along this corridor and specifically, in the Sais Basin, constitute case-study material for understanding the impact of the South Rifian Corridor on the evolution of the fauna, phytoplankton and environment during the Late Miocene. In order to reconstruct the evolution of marine paleoenvironments in the Moulay Yakoub region and to compare this evolution with other areas of the Sais basin, we conducted an integrated biostratigraphic and palynological study of the Upper Miocene of borehole KA 102. High-resolution biostratigraphy based on planktonic foraminifera revised and defined the chronostratigraphic framework of the Upper Miocene sedimentary series of the Moulay Yakoub region providing an age of 7.8 Ma to 6.52 Ma (Late Tortonian to Early Messinian). In the Late Tortonian, the planktonic foraminiferal assemblages suggest an open and relatively deep marine environment. At the Tortonian/Messinian boundary, planktonic foraminiferal and dinoflagellate associations, as well as distal indices, suggest a relatively deep and neritic distal marine environment with a decrease in diversity and an increase in reworked taxa. Surface waters are warm with a minor cooling trend observed just below this boundary. In comparison to previously studied sections in the Sais Basin, the Lower Messinian is characterized by a deeper and more distal marine environment. However, proximal trends and warm surface water conditions persisted in all studied areas from the basin during this period.

Clastic carbonates in the South Sistan Basin (SE Iran): implications for subduction vergence and timing of collision

ABSTRACT The N–S-trending Sistan Suture Zone in East Iran results from the collision of the Lut and Afghan continental blocks. The southern Sistan Basin hosts Eocene terrigenous deep-marine turbiditic sequences with carbonate olistoliths, debris-flow sheets and calcareous turbidites. These carbonates represent one or several early to middle Eocene carbonate platforms fragmented and redeposited in a deep-marine environment. Palaeocurrent measurements on the terrigenous and calcareous turbidites show that the source carbonate platform was located on the Afghan active margin. Volcanic debris in the limestone and surrounding turbidites corroborate an active magmatic margin on the Afghan side. The formation of limestone debris-flow sheets is attributed to increased erosion and retreat of the carbonate platform, potentially triggered by the closure of the Sistan Basin and continental collisions in the late middle Eocene, after subduction of the Sistan Ocean beneath the Afghan Block.

Depositional Facies and Palynofacies Provenance of Clastic Deposits: Insight from Paleocene Strata in Southeast Region, Nigeria

Detailed sedimentary facies and palynofacies provenance studies were carried out on clastic deposits outcropping around the Awka area within the Imo Formation (Paleocene) of the Niger Delta Basin. Seven facies were systematically recognized based on the textural parameters, sedimentary structures and palynological constituents. Interpretation of the prevailing paleoenvironments, palynofacies provenance and depositional mechanisms were derived from the hydrodynamic controls. The sedimentary facies include shales, mudstones, siltstones, heteroliths, cross-bedded sandstones and matrix-supported conglomerates. The palynofacies showed preponderance of amorphous organic matter, marine taxa, opaque particles, with few structured phytoclasts and terrestrial microflora. These palynological microflora constituents are grouped into palynofacies association A and B based on the composition and proportion of the organic particles, stratigraphic position and paleoenvironments of the strata. Facies analysis indicates that the mudrock facies (e.g. shale, mudstone and siltstone) are deposits of deep marine depositional settings with terrestrial input while the sandstones mimic deposits associated with tidal sand waves in shallow sandy seas, braided river and tidally influenced distributary channels. The facies and palynofacies provenance model suggest dominance of terrestrially influenced shallow to deep marine environment evidenced from the abundance of amorphous organic matter and presence of gonyaulacacean dinoflagellate species, Glaphyrocysta ordinata, G. exuberans, and pollen of Proxapertites operculatus, Retitricolporites irregularis with other accompanying marine forms. In addition, the presence of texturally mature coarse- to fine-grained sandstones, variable sedimentary structures, internal bed geometries and nature of bedding are suggestive of tidally dominated shallow marine settings including distributaries channel network deposits.

Protracted oxygenation across the Cambrian-Ordovician transition: A key initiator of the Great Ordovician Biodiversification Event?

Fluctuations in marine oxygen concentrations have been invoked as a primary driver for changes in biodiversity throughout Earth history. Expansions in reducing marine conditions are commonly invoked as key causal mechanisms for mass extinctions, while increases in marine oxygenation are becoming an increasingly common causal mechanism invoked for biodiversification events. Here we utilize a multiproxy approach to constrain local and global marine paleoredox conditions throughout the late Cambrian-Early Ordovician from two drill core successions in Baltoscandia. Local paleoredox proxies such as manganese concentrations and iron speciation reveal that both sites in the Baltic paleobasin had persistently anoxic and predominantly euxinic (anoxic and sulfidic) bottom water conditions throughout the study interval. Corresponding trace metal datasets indicate nuanced contraction and expansion of global anoxic and euxinic conditions along continental margins during the late Cambrian-Early Ordovician. Lastly, thallium isotope data from these locally reducing sections suggest a global expansion of oxygenated shelf and deeper marine environments from the late Cambrian into the Early Ordovician. This evidence for increasingly oxic marine environments coincides with increases in burrowing depth and tiering in marine animals, as well as diversification of body fossils throughout this ~8-million-year interval. The collective geochemical datasets provide some of the first direct paleoredox evidence for an increase in marine oxygen concentrations as a key mechanism for the Ordovician radiation of marine life.

Impact of meteoric water flushing on diagenesis of deep-marine turbidite sandstones: A case study from the Tertiary sandstones of Frigg and Grane fields, northern North sea

Meteoric water flushing into deep-marine environments is a topic of debate since the actual transport mechanism remains elusive. In order to evaluate the potential impact of meteoric water on early diagenesis of deep-marine sandstones, two submarine fan sandstone reservoirs, the Eocene Frigg (Frigg oilfield) and the Palaeocene Heimdal (Grane field) that have the same source area, were compared and contrasted. Petrographic studies reveal that both sandstone reservoirs are at the eodiagenesis stage (<70 °C) at the present day. However, the Eocene Frigg sandstones are characterized by geological features suggestive of potential meteoric water diagenesis, such as dissolution and kaolinization of the silicate grains, whereas the Palaeocene Heimdal sandstones show negligible alteration. The δ13CV-PDB and δ18OV-PDB values of siderites in the Eocene Frigg sandstones range from +5.2‰ to +16.7‰, and from −8.2‰ to −6.6‰, respectively, indicating siderite formation during methanogenesis in meteoric pore water. Results from generic hydrogeochemical modelling scenarios lend further support to the hypothesis of meteoric water flushing. Thus, we suggest that massive meteoric water might have been brought into the Frigg turbidite sands by basinward migration of the meteoric water. This occurred because the East Shetland Platform experienced two stages of relative sea-level fall (during and at the end of the Eocene, Priabonian), and flushing might have taken place via connected incised canyons. The location of the Frigg sands deposited immediately below the Shetland escarpment and the narrow palaeo-shelf area may have facilitated such meteoric water incursions. Our study suggests meteoric water intrusions as a possible diagenetic control of deep-marine sandstones, and, therefore, meteoric water diagenesis should be considered in the prediction of properties of deep-marine sandstone reservoirs.