Marginal Marine Research Articles

Palynofacies analysis and depositional environments of Upper Cretaceous sediments in the ST‐9H well, offshore South Tano Basin, Western Ghana

Palynofacies analyses were carried out on 43 cutting samples from the ST 9H well in the Tano Basin, with the view of reconstructing the palaeoenvironment of the Upper Cretaceous sediments in the well. The stratigraphic distribution of the palynofacies assemblages defined four palynofacies units. Palynofacies PA reflects deposition in near shore/shallow marine (inner neritic) environment under distal dysoxic‐anoxic shelf condition. Palynofacies PB was deposited in an inner–middle neritic environment under mud‐dominated oxic shelf conditions, Palynofacies PC in an open marine (outer neritic) environment under distal suboxic‐anoxic basin conditions, and Palynofacies PD in a proximal–marginal marine environment under dysoxic‐anoxic basin conditions. These palynofacies assemblages (PA–PD) are characterized by kerogen types II (oil prone), III‐IV (gas prone), II > I (oil prone), and III (gas prone), respectively. Marker dinoflagellate and miospore assemblages recovered from the sediments –are indicative of a Campanian–Maastrichtian age. The palaeofloral association and the perideanacean dinocysts assemblage are typical of Senonian Palme Province and the Malloy suite, respectively. These assemblages are indicative of a warm and humid tropical‐subtropical climatic condition.

Sedimentology and sequence stratigraphy of the Early Cretaceous Centenario Formation (upper member) in the north-eastern border of the Neuquén Basin, Argentina

The Centenario Formation is a unit known in literature by the content of oil reservoirs in the Productive Trend Río Colorado (PTRC) situated in the north-eastern border of the Neuquén Basin. The formation is composed of a lower and upper member, the latter being the object of this study. The analysis of five wells distributed in a cross section of 10 km length, allowed the analysis of 150 m of cored succession that cover almost all the stratigraphic extent of the upper member. Facies analysis allowed defining ten of them (A–J), recording storm, tidal, and fluvial processes, as well as trace-fossils mainly of the Cruziana and Cruziana-Skolithos ichnofacies and microbialites distributed in different parts of the succession. Nine Facies Associations (I–IX) were defined and them account for marine, marginal-marine and fluvial environments. The marine record documents deposits from the offshore to shoreface that form part of a first and thickest stratigraphic sequence (Sequence I) dominated by a starved transgression (TST), followed by a shallow and wave-dominated delta system (HST) evidencing multiple directions of progradation, and showing quartz dominated composition derived from old sedimentary units. An erosive sequence boundary denotes the beginning of a new depositional cycle (Sequence II). It starts with estuarine facies (TST) containing the coarsest deposits in the entire succession (conglomerates) that are probably correlatable with incised valleys and fluvial deposits documented in outcrops and subsurface. A remarkable change to a lithic composition with abundant volcaniclastic fragments evidences a supply from younger units than the underlying sequence; additionally, tidal action is amplified by a non-lineal coast. A marine interval records the end of the transgression (MFZ), and later a coarsening upward arrangement (HST) product of bay head deltas grading laterally into mud flats. The uppermost part of the unit records the change in the coast line with the advance of fluvial deposits denoting the new sedimentary change with the reorganization of the depositional system (Sequence III). It starts with unconfined fluvial deposits (LST) that present the peculiarity of bimodal grain-size deposits and well-sorting as a result of reworking of previous eolian deposits. The abundant kaolinite contrasts with the underlying sequence and indicates meteoric water input. The fluvial deposits, oil reservoirs, are sealed by marginal marine deposits on top (TST). The succession is incomplete by erosion of the intra-Senonian unconformity, but the stacked sequences exhibit a similar staking trend as in the outcropping Agua de la Mula Member of the Agrio Formation. The last one is a good surface analog unit for comparing sedimentary processes, sequence stratigraphy and ichnology. Taking into account previous studies and outcrops and subsurface correlations, this study restricts the upper member of the Centenario Formation time-equivalent to the Agua de la Mula Member of the Agrio Formation; a post-earliest Barremian age is disregarded. The integration of all available information confirms that conglomerates recorded in subsurface, and also outcrops are the result of incised valleys related to sea level drops. In this sense the Chachauén volcano outcrops are probably the exposed records of the Centenario Formation, rather than the Agrio Formation. Finally, this study confirms a complex sedimentary evolution of the north-eastern basin border, with tectonic controls and a variable coastal line that allows explaining short distance facies changes. This study demonstrates the usefulness of ichnological approaches with sedimentology, particularly in intervals completely oil-impregnated where sedimentary features are frequently difficult to analyze for paleoenvironmental interpretations.

Palaeogeographic implications of ichnotaxa assemblages from early Permian fluvio-marine Barakar Formation, Raniganj Basin, India

The sandstone-shale-coal succession of the Barakar Formation (early Permian) of the Raniganj Basin, India hosts low-diversity ichnoassemblages, containing ichnogenera Arenicolites, Chondrites, Diplocraterion, Monocraterion, Ophiomorpha, Palaeophycus, Planolites, Skolithos, Taenidium, and Thalassinoides, produced by shallow marine infaunal invertebrates. Sedimentary facies architecture depicts a transgressive, fluvio-tidal (with a minor wave) interactive estuarine depositional setting. The fluvial deposits, lying beyond the zone of tidal encroachments, record absence of trace fossils, which is attributed to a low colonization window caused by high fluvial discharge and frequent channel migrations. Tidal interactions with high fluvial discharge led to bay-head deltas in the inner-middle estuary with the dominance of suspension-feeding and deposit-feeding ichnotaxa in coarser- and finer-dominated sediments, respectively, suggesting a mixed Skolithos–Cruziana ichnofacies. Increasing tidal influence with very less fluvial input allowed opportunistic colonizers and deposit feeders of the Cruziana ichnofacies to flourish in the central estuarine setting. Intermittent low-oxygenated restricted conditions marked by the chemosymbiotic ichnoassemblages of the Zoophycos ichnofacies indicate very low energy conditions. The outer estuary with increasing wave dominance is inhabited by suspension-feeding, domicile ichnotaxa of Skolithos ichnofacies, frequently mixed with the ichnotaxa of the Cruziana ichnofacies. The recurrent juxtaposition and lateral distribution of the Seilacherian marginal marine ichnofacies is attributed to complex sediment–organism interaction patterns in response to prevalent energy conditions, sediment discharge and substrate conditions in different zones of the fluvio-tidal estuarine setting. The integrated sedimentological-ichnological model signifies marine transgressions that affected the palaeogeography of the Permian continental Gondwanaland.

Palynostratigraphic and palynofacies analysis of x and y wells, offshore Niger Delta, Nigeria

A detailed palynostratigraphic and palynofacies study was carried out on two shallow offshore wells, codenamed Well X and Well Y, from the Niger Delta Basin, Nigeria. The study is aimed at establishing the age and palaeoenvironment of the sedimentary sequences penetrated by the wells. Standard palynological/palynofacies laboratory procedures were used to free the palynomorphs and palynomacerals from the embedding matrices.Prepared palynological slides were studied using the Leitz Ortholux II transmitted light microscope. The palynofloral assemblages recorded from the two well sequences include well-preserved palynomorphs such as Zonocostites ramonae, Monoporites annulatus, Retitricolporites irregularis, Cyperaceaepollis sp., Echitricolporites spinosus and Nymphaeapollis clarus among others. The recognition of diagnostic pollen of Cyperaceaepollis sp. and Nymphaeapollis clarus as well as the associated palynomorph assemblage aided the delineation of the well sequences into the P830, P840-P850 and P860 subzones of the P800 palynological zone in the late Miocene. The relative abundance of particulate organic matter (Amorphous Organic Matter (AOM), Phytoclasts and Palynomorphs) revealed the delineation of three palynofacies assemblages, PF-A, PF-B and PF-C, suggesting three distinct paleoenvironments of deposition. These paleoenvironments range from distal shelf through marginal to proximal with varying conditions from oxic, suboxic to anoxic, thus suggesting marginal marine to coastal deltaic environments of deposition for the sedimentary sequences penetrated by the two wells.
 Keywords: Late Miocene, Niger Delta, Paleoenvironment, Palynostratigraphy, Palynofacies.

Recent benthic foraminiferal distribution in the Elbe Estuary (North Sea, Germany): A response to environmental stressors

For the past 200 years, estuarine environments experienced intense and rapid environmental degradations due to human interventions. In addition, Global Changes are modifying the estuarine physiography, leading to a re-structuration of marginal marine benthic communities. The aim of this study is to document, the modern assemblage composition and the species-environment relations of benthic foraminifera upstream the Elbe Estuary (southern North Sea) and to observe what has changed since the first survey in 1981. For this purpose, a surface sampling was carried out from 22 stations along the transitional area of the Elbe Estuary. Living (rose-Bengal stained) and dead foraminiferal assemblages were analysed as well as hydrological and sedimentological parameters (such as salinity, pH, grain-size, and organic matter). Living faunas are characterized by very low densities and largely dominated by Ammonia species. Dead assemblages are more diverse and dominated by Ammonia aomoriensis, Haynesina germanica, and Cribroelphidium selseyense. Salinity and grain-size seem to be the major factors influencing foraminiferal distributions in the transitional area. Under the ongoing climate changes, future strategies will be taken to foster the application of benthic foraminifera as biomonitoring tool in the Elbe Estuary, via this baseline investigation.

Mixed carbonate–siliciclastic sedimentation at the margin of a late Miocene tidal strait, lower Colorado River Valley, south‐western USA

AbstractThe processes and deposits of tide‐dominated river deltas and estuaries are well‐understood, but the sedimentary dynamics of tide‐dominated straits and seaways are relatively little studied. Although recent depositional models have started to fill this gap, many aspects of tidal strait sedimentation such as interaction with strait‐margin alluvial fans and marginal marine systems remain poorly understood. This paper presents a study of the late Miocene basal carbonate member of the Bouse Formation exposed along the lower Colorado River, where prior studies have suggested a tidal influence on deposition. This study explores the applicability of tidal strait models in a continental oblique‐rift setting, and tests hypotheses for depositional processes and environments through detailed analysis of sedimentary facies, cross‐bedding architecture and palaeocurrent data. Mixed carbonate–siliciclastic facies on the west margin of the southern Blythe Basin record sedimentation in alluvial fans and fan‐fringing tidal flats at the retreating margin of a transgressive tidal strait. Pre‐Bouse normal faults established a narrow, tectonically confined basin architecture that led to amplification of tidal currents. Basin‐margin deposits pass laterally and up‐section into high‐energy cross‐bedded grainstone facies that record southward migration of compound dunes in the dune‐bedded strait zone of a shallow (ca 25 m) tidal strait. These findings provide the basis for recognition of strait‐margin facies in other settings where complex facies associations result from along‐strike variations in palaeobathymetry and current velocity. The results support a tidal origin for the southern Bouse Formation and provide new evidence for post‐Miocene uplift of the lower Colorado River Valley and adjacent areas.

Timing of hydrocarbon entrapment in the eastern foothills of the Eastern Cordillera of Colombia

The eastern foothills in the Colombian Eastern Cordillera have been an important oil-producing region since the discovery of the Cupiagua and Cusiana fields. Three organic-rich units are considered to be the main source rocks. The Aptian Fómeque and the Cenomanian-Coniacian Chipaque Formations comprise a siliciclastic to locally carbonate shallow marine shelf succession with type-II kerogen, whereas the Paleocene Los Cuervos Formation consists of marginal marine to nonmarine siliciclastic rocks with type-III kerogen. We modeled the petroleum systems of these three source units to characterize the hydrocarbon generation-accumulation processes within the basin. The structural record of the Eastern Cordillera shows that the most important tectonic event began in early Oligocene with contractional deformation along the Soapaga through Guaicaramo faults during early Miocene, culminating during the Pliocene with the Cusiana and Yopal faults. These variable rates of burial and exhumation resulted in contrasting time-temperature histories for each of the source rocks. The Fómeque Formation reached the oil window during the Paleocene in the south and the Eocene to the north. In contrast, the Chipaque Formation generation started during Early Oligocene in the south and by Late Oligocene to the north. Conversely, maturation for the Los Cuervos Formation was uniform along the foothills, reaching the oil window during Late Oligocene. Charge history modeling suggested that the Albian sandstones reservoirs were filled between Oligocene to Miocene. In contrast, the proven reservoirs in the area (the Upper Cretaceous, Paleocene, and Eocene sandstones) were filled by late Miocene, with a second episode of recent charge in the Eocene reservoirs, and perhaps active, from the Los Cuervos Formation. The results of this work proved that petroleum system modeling is useful not only to characterize generation-migration processes but it also can be used as a prediction tool in structurally complex areas such as the Colombian foothills.

Asymmetrical wave-dominated siliciclastic shorelines with evidence of along-strike variability of sedimentary processes: A revised interpretation for the Toarcian Marrat red beds, central Arabia

Marine siliciclastic red beds are common in the geological record; however, distinguishing them from continental red beds can be challenging without detailed sedimentological and stratigraphic analyses. Owing to the common tendency in the geological literature to relate the reddish color to the oxidization processes within the vadose zone, siliciclastic red beds of marine genesis can be misinterpreted as continental deposits. Unlike the other Toarcian successions in the Tethyan basins surrounding Arabia, the sedimentological and stratigraphic characteristics of the Marrat Formation of Arabia in general and its middle unit's red siliciclastic beds, in particular, have not been well constrained. For more than 50 years, the red siliciclastic beds of the Toarcian Marrat Formation have been interpreted as continental to marginal marine deposits based on their reddish color and the absence of fossils. The lack of supporting sedimentological and stratigraphic evidence to this interpretation raises critical concerns regarding its validity.Along the Jurassic outcrop belt in central Arabia, three outcrop localities of the middle Marrat reddish siliciclastic deposits (with a total thickness of more than 120 m) demonstrate sedimentological and ichnological features that are contrary to the non-marine to marginal marine interpretation. The integration between sedimentology and ichnology reveals the existence of asymmetrical wave-dominated shorelines with evidence of river hyperpycnal flows and tidal processes during the middle Marrat time. A total of seventeen facies are identified and grouped into four facies associations: mixed wave and river-dominated delta front to prodelta mudstone (FA1), shoreface (strandplain) and underlying shelf mudstone (FA2), tidally-influenced distributary channel (FA3), and offshore carbonates (FA4). Stratigraphically, six major parasequences (each with a thickness of ~ 3–13 m) were mapped and correlated between the three measured sections with clear overall progradational to retrogradational stacking patterns.To the best of our knowledge, this study is the first to document the presence of Toarcian shallow-marine siliciclastic red beds on the Arabian Plate. It displays an example of a case study where ichnology and process-based sedimentology were integrated to constrain the depositional environment of these red beds. This study provides new insights into the depositional settings of the Toarcian red siliciclastic beds of the Marrat Formation, with implications to the stratigraphy of Arabia and the Early Jurassic paleogeography of the western Tethys and, in particular, the Arabian Plate.

Late Permian–Early Triassic depositional history in the southern Bonaparte Basin: new biostratigraphic insights into reservoir heterogeneity

The upper Permian to Lower Triassic sedimentary succession in the southern Bonaparte Basin represents a marginal marine depositional system that hosts several gas accumulations. Of these, the Blacktip gas field has been in production since 2009, while additional gas resources are under consideration for development. The sedimentary succession extends across the Permian–Triassic stratigraphic boundary, and shows a change in lithofacies from the carbonate dominated Dombey Formation to the siliciclastic dominated Tern and Penguin formations. The timing, duration, distribution and depositional environments of these formations in the Petrel Sub-basin and Londonderry High is the focus of this study. The sedimentary succession extending from the Dombey to the Penguin formations is interpreted to represent marginal marine facies which accumulated during a long-lasting marine transgression that extended over previous coastal and alluvial plain sediments of the Cape Hay Formation. The overlying Mairmull Formation represents the transition to fully marine deposition in the Early Triassic. Regional scale well correlations and an assessment of biostratigraphic data indicate that marginal marine depositional systems were initiated outboard before the end-Permian extinction event, and migrated inboard at about the Permian–Triassic stratigraphic boundary. Marginal marine deposition across the southern Bonaparte Basin continued through the faunal and floral recovery phase as Triassic species became established. The depositional history of the basin is translated to a chronostratigraphic framework which has implications for predicting the character and distribution of petroleum system elements in the Petrel Sub-basin and Londonderry High.

Assessing the effect of riverine discharge on planktic foraminifera: A case study from the marginal marine regions of the western Bay of Bengal

Planktic foraminifera are amongst the most widely used paleoclimatic proxies. The application of foraminifera for paleoclimatic reconstruction requires knowledge of the ecological preference of species. Here, we report the surface distribution and ecology of planktic foraminifera from 99 core top samples collected from the riverine influx dominated western Bay of Bengal. The riverine influx reduces the planktic population on the shelf, in its immediate vicinity. Incidentally, the population increases on the slope in front of the major river mouths. A total 30 species belonging to 14 genera were found. Globigerinita glutinata is the most abundant species in the western Bay of Bengal, followed by Globigerina bulloides. Globigerina bulloides is abundant on the outer shelf, a region influenced by upwelling during southwest monsoon. The negative correlation of Neogloboquadrina dutertrei with sea surface salinity is attributed to the chlorophyll maximum due to the density gradient created by the hyposaline surface water. Globigerinoides ruber were abundant (>10%) at stations with higher salinity (>32 psμ). The mixed layer dwelling Trilobatus sacculifer are abundant on the slope. The increased relative abundance of Globigerinella siphonifera in shallow waters is attributed to the low salinity freshwater plume. The negative correlation of Globorotalia menardii with thermocline temperature and positive correlation with thermocline salinity suggests its cold water, high salinity habitat. We conclude that the freshwater and sediment influx and associated changes strongly modulate planktic foraminiferal distribution. The findings will help in better application of temporal changes in planktic foraminiferal population to reconstruct past environmental conditions from the Bay of Bengal.

Unravelling depositional setting, age and provenance of the Simlipal volcano-sedimentary complex, Singhbhum craton: Evidence for Hadean crust and Mesoarchean marginal marine sedimentation

The Singhbhum craton of eastern India preserves an extensive record of basin formation spanning the Paleoarchean to Neoarchean. Although spatially extensive and well exposed, the absolute age, depositional environment, and regional correlations of many of the purportedly Archean basins of this craton remain poorly resolved. We present a detailed lithostratigraphic analysis of siliciclastic strata in the (lower) Simlipal volcano-sedimentary succession and report the first detrital zircon U-Pb ages from this succession. The studied section is dominated by fine- to medium-grained, quartz-rich sandstones, which preserve herringbone stratification, tidal bundles, soft sediment deformation structures along with ubiquitous trough cross-stratification. Petrographic study confirms these sandstones as quartz arenites and reveal their high textural and mineralogical maturity. These features are consistent with deposition of the lower siliciclastic succession of the Simlipal volcano-sedimentary complex within a tidally-influenced marginal marine setting. The new detrital zircon data support a ~3.08 Ga maximum depositional age for the succession and reveal a provenance with age peaks at ca. 3.55–3.45 Ga, 3.38–3.24 Ga, and 3.10–3.08 Ga. These ages likely correspond to local basement sources including the Older Metamorphic Tonalite Gneisses, the Singhbhum Granitoid Complex, and the Mayurbhanj Granite Suite. Two detrital zircons from our dataset have concordant ages of ~4.02 Ga and ~4.03 Ga. They represent the first Hadean detrital zircons recovered from any Archean strata in the Singhbhum craton, documenting the involvement of Hadean crust in the early development of the craton. The detrital zircons show prominent Pb-loss at ~1.2–1.0 Ga that exemplifies the tectonothermal imprint of a late Mesoproterozoic to early Neoproterozoic orogeny (likely related to the assembly of Rodinia) on the Singhbhum craton. Our findings further support the interpretation that the lower siliciclastic strata in the Simlipal succession are the lateral facies equivalents of alluvial fan deposits at the base of the Dhanjori Formation, exposed to the north.

Reinterpretation of the Neogene sediments of the Bree Uplift, NE Belgium

The present geological map of the Flemish Region shows a small lens-shaped isolated outcrop of the Miocene Bolderberg, Diest and Kasterlee Formations, surrounded by younger formations, in an area that coincides with the tectonic Bree Uplift segment, on the southwestern border of the Roer Valley Graben in NE Limburg. The fault, bordering the segment at its SW side, had been interpreted to be tectonically active throughout the Neogene. Now, it is argued that an erroneous lithostratigraphic interpretation of the outcropping strata supported that view. Field observations of some of the outcrops and sampled drill holes show that the sediments do not belong to an Opitter member of the Bolderberg Formation, a Gruitrode Mill member of the Diest Formation and a Dorperberg member of the Kasterlee Formation, but most probably to the lower, latest Miocene or early Pliocene part of the Mol Formation and an unknown Pliocene marginal marine deposit not unlike and at about the stratigraphic position of the Poederlee Formation. That glauconiferous sand deposit, which has always been interpreted as consisting of two successive sedimentary cycles, is now accommodated in a single cycle, using the sedimentary model of deposition in a confined, backbarrier tidal basin subject to marine sand input and local stages of flow constriction and intraformational incision. Like already proposed by Rossa (1986) and Demyttenaere (1989), reprocessed seismic sections show only minor movements along the southwestern fault of the Bree Uplift since the Paleocene, and no inverse tectonic movements at all since the Middle Miocene.

Presence of the large aquatic snake Palaeophis africanus in the middle Eocene marine margin of the Congo Basin, Cabinda, Angola

Ten isolated snake vertebrae from Landana and Sassa-Zao, Cabinda Exclave, Angola, present a “primitive” grade morphology with a weak lateral compression and do not belong to Palaeophis aff. typhaeus as originally referred to. They well belong to a single taxon and are here attributed to Palaeophis africanus for which the intracolumnar variation is described and illustrated. This species is Lutetian (middle Eocene) in age and originates from a marine coastal environment confirming again the aquatic capabilities of palaeophiid snakes. It represents the third largest species of Palaeophis with P. colossaeus and P. maghrebianus to which it is closely related in our tentative phylogenetic analysis, indicating that these three taxa could belong to an African clade. This study also contributes to the debate on the existence of primitive and advanced grades among palaeophiid snakes. Palaeophis presents laterally compressed anterior trunk vertebrae that could have been often erroneously considered as representing advanced grade species and potential parataxonomy.

Latitudinal variability in the Quaternary development of the Eurasian ice sheets—Evidence from the marine domain

Abstract Here we present the first compilation of sediment volumes, sedimentation rates, and chronology of Quaternary sediment packages along the entire marine margin of the Eurasian ice sheets (EurIS; British–Irish, Kara–Barents Sea–Svalbard, and Fennoscandian). This compilation allows for a subdivision of the EurIS development into three phases (2.6–1.5 Ma, 1.5–0.78 Ma, and 0.78–0 Ma). At the start of the Quaternary, sedimentation rates increased, relative to pre-Quaternary rates, by an order of magnitude. This abruptness in rate change excludes tectonic raising of landmasses as the main factor, but more likely reflects climate change through increased glacial erosion. The sediment distribution data suggest that the Kara–Barents Sea–Svalbard Ice Sheet (KBSIS) already was quite large at the beginning of the Quaternary, and well before 1.5 Ma it extended to the shelf edge and coalesced with the Fennoscandian Ice Sheet (FIS), which prior to 1.5 Ma most likely was located near the coast. Large ice streams and intense glacial erosion characterized the KBSIS in the 1.5–0.78 Ma time period, whereas the FIS at that time extended farther out on the continental shelf. After 0.78 Ma, a north-south change in EurIS development occurred. In the FIS and the British–Irish Ice Sheet (BIIS), large ice streams developed and shelf-edge glaciations occurred nearly 1 m.y. later compared to the KBSIS. The FIS and BIIS also repetitively coalesced in the North Sea. A significant drop in sediment input along the KBSIS marine margin, to the lowest Quaternary level, suggests a less erosive KBSIS.

Actuotaphonomic model of the mollusk fauna of Laguna de Mandinga, Veracruz, Mexico

Introduction: The taphonomic attributes of a faunal assemblage provide information about which agents affect both, the distribution and preservation of ancient or newly-formed biogenic materials, during their depositional and post-depositional processes.
 Thus, actuotaphonomy is a valuable tool to the reconstruction of fossil communities, as it establishes analogies between observable processes in the present and those that happened in the past.
 Objective:The taphonomic attributes of a marginal marine environment were analyzed, in order to assess the origin of fragmentation, bioerosion and incrustation processes and the role of these characteristics in the deterioration of current sediment accumulations of mollusks (gastropods and bivalves), to generate an actuotaphonomic model that could be applyable to analogous ecosystems to Laguna de Mandinga (Mandinga Lagoon), in Veracruz, Mexico.
 Methods: The material came from a shell-remain accumulation called "El Conchal". A batch of 1,697.9 g was processed, selecting 1,165 complete specimens, of which 5 genera of bivalves and 4 genera of gastropods were identified. Results: The taphonomic analysis showed that fragmentation and bioerosion have a medium attribute, which may be due to energy, constant rework and exhumation of the remains at the lagoon's water-sediment interface; three biogeneous agents were identified: Entobia isp, Oichnus and Caulostrepsi, being Caulostrepsi the less abundant. The incrustation showed of poor degree since the ecosystem intrinsic conditions did not allow many encrusting organisms to grow properly, however, these organisms are represented by calcareous tubes of serpulid polychaetes, bryozoans with calcareous skeleton and barnacles.

X-RAY FLUORESCENCE AND STABLE ISOTOPES ANALYSES OF IKPESHI MARBLE, SOUTH SOUTHERN NIGERIA

Integration of X-ray fluor escence and stable isotope spectrometric techniques for quality assessment and provenance study of exposed marble deposit at Fakunle Quarry, Ikpeshi, South Western Nigeria constitute the fundamental aims of this research. Fourteen fresh (14) marble samples obtained at different localities within the quarry were subjected to geochemical and isotopic analyses to ascertain the quantitative abundance of major oxides and stable isotopes using X-Ray Fluorescence and Thermo Fisher mass spectrometer respectively. The major oxides revealed by XRF analysis of the marble samples are CaO, MgO, SiO2, Al2O3, Fe2O3 and Na2O with percentage composition ranging between 11.66 – 13.25, 7.75 – 9.65, 41.36 – 47.55, 12.36 – 15.23, 7.79 – 10.55 and 1.44 – 1.75respectively. Na2O + K2O value ranges between 1.48 and 1.78.The classification of marble in relation to percentage of calcite-dolomite indicate a percentage range of -5 to 4% and 93-103% for Calcite and Dolomite respectively. Chemical Index of Alteration (CIA) ranges from 45.16 to 51.59 % and Chemical Index of Weathering (CIW) ranges from 46.19 to 52.30 %. Stable isotope ( ? –180) of marble ranges from -10.50 to -7.00 with a corresponding value from 25.50 to 55.33.Interpretation of the overall results indicates an impure quartz-rich dolomitic marble; metamorphosed from a low carbonate sedimentary/meta sedimentary protolith which shallowly precipitated within a passive marginal marine environment under humid condition. The high silica impurity can however be attributed to the inordinate influx of terrigenous sediments during the precipitation process. Weathering effect is minimal on the marble deposit. Conclusively, strong correlation is apparent between the obtained geochemical result and the basement geology of the study area.

Foraminiferal biostratigraphy and paleoenvironmental analysis of the sediments penetrated by Sahaiawei-1 well in the Northern Delta Depobelt, Niger Delta Basin

Foraminifera biostratigraphy and paleoenvironmental analysis of the sediments penetrated by Sahaiawei-1 Well in the Northern Delta Depobelt, Niger Delta Basin was carried out in order to determine the foraminifera biozonation, age, paleobathymetry, depositional environment and paleo-oxygen condition of the well. The total foraminifera population recovered was two thousand, three hundred and sixty five (2365), with planktic foraminifera constituting one hundred and fifty four (154) forms, while calcareous benthic and agglutinated benthic foraminifera recovered accounted for two thousand, one hundred and sixty two (2162) and fourty nine (49) of the total foraminifera population respectively. The total foraminifera species recovered was fifty nine (59); planktic accounted for twenty (20) foraminifera species, while calcareous and agglutinated benthic foraminifera accounted for thirty one (31) and eight (8) foraminifera species respectively. Five benthic foramineferabiozones were identified: lumped P7-P13, P5-P6/P7, lumped P3-P4, lumped P1-P2 and M18 Zones of Blow (1969, 1979). The result of the analysis indicates that the entire analysed interval (1800ft – 10680ft) was deposited during the Late Maastrichtian to Late Eocene epoch. The depositional environments of the Well varied from littoral, marginal, shallow and deep marine environments.
 Keywords: Biozonation, Calcareous, Arenaceous, Agglutinated, Hyposaline Marshes, Hyposaline Shelf Sea

Cenozoic tectonic evolution of the Ecemiş fault zone and adjacent basins, central Anatolia, Turkey, during the transition from Arabia-Eurasia collision to escape tectonics

Abstract The effects of Arabia-Eurasia collision are recorded in faults, basins, and exhumed metamorphic massifs across eastern and central Anatolia. These faults and basins also preserve evidence of major changes in deformation and associated sedimentary processes along major suture zones including the Inner Tauride suture where it lies along the southern (Ecemiş) segment of the Central Anatolian fault zone. Stratigraphic and structural data from the Ecemiş fault zone, adjacent NE Ulukışla basin, and metamorphic dome (Niğde Massif) record two fundamentally different stages in the Cenozoic tectonic evolution of this part of central Anatolia. The Paleogene sedimentary and volcanic strata of the NE Ulukışla basin (Ecemiş corridor) were deposited in marginal marine to marine environments on the exhuming Niğde Massif and east of it. A late Eocene–Oligocene transpressional stage of deformation involved oblique northward thrusting of older Paleogene strata onto the eastern Niğde Massif and of the eastern massif onto the rest of the massif, reburying the entire massif to >10 km depth and accompanied by left-lateral motion on the Ecemiş fault zone. A profound change in the tectonic setting at the end of the Oligocene produced widespread transtensional deformation across the area west of the Ecemiş fault zone in the Miocene. In this stage, the Ecemiş fault zone had at least 25 km of left-lateral offset. Before and during this faulting episode, the central Tauride Mountains to the east became a source of sediments that were deposited in small Miocene transtensional basins formed on the Eocene–Oligocene thrust belt between the Ecemiş fault zone and the Niğde Massif. Normal faults compatible with SW-directed extension cut across the Niğde Massif and are associated with a second (Miocene) re-exhumation of the Massif. Geochronology and thermochronology indicate that the transtensional stage started at ca. 23–22 Ma, coeval with large and diverse geological and tectonic changes across Anatolia.

Genetic diversity of Hilsa kelee collected from the Bay of Bengal and the Arabian Sea

The Kelee shad (Hilsa kelee) is currently considered as the only representative species in the genus Hilsa (Clupeidae, Clupeiformes) with a wide distribution in almost all coasts of the Indian Ocean. Two marginal marine water bodies of the Indian Ocean, the Bay of Bengal and the Arabian Sea, are important fisheries areas for this fish. In this study, a comparison of genetic diversity of Kelee shad of these two important fisheries areas was conducted by applying a cross-species gene enrichment method. This was also the first challenge to discover the genetic diversity of this fish. Analysis of molecular variance results showed that the variation between groups is 10.85% and among individuals within populations contributed 89% variation. Nucleotide diversity results showed that Kelee shad populations are in almost stable condition and have a moderate population size. Nucleotide diversity of the Bay of Bengal and the Arabian Sea were almost similar; these were 0.012138 and 0.010831, respectively. Network, structure, and PCA results suggested that Kelee shad of the Bay of Bengal and the Arabian Sea have significant genetic differences. These two populations were separated from each other by a FST value of 0.10955 (p < 0.05). It is speculated that Southern India along with Sri Lanka and Ram bridge together with ancient climatic differences acted as means of isolation concerning Kelee shad populations between these two water bodies. Furthermore, from the maximum likelihood phylogenetic tree, it is established that the Arabian Sea can be regarded as the major stock of this species.

New record of podocopid ostracods from Cretaceous amber.

Burmese Cretaceous amber (∼99 Ma, Myanmar) is famous for the preservation of a wide range of fauna and flora, including representatives of marine, freshwater and terrestrial groups. Here, we report on three ostracod specimens, that came visible as syninclusions to an aquatic isopod. The three specimens represent three different taxa, that were found preserved in a single piece of amber. One of the described specimens was studied using µCT scanning data. On the basis of general carapace morphology we assign all three to the group Podocopida, and (tentatively) its ingroup Cypridocopina. A lack of visibility of more particular diagnostic features such as adductor muscle scars and details of the marginal zone precludes a further identification, but we discuss possible affinities with either the marine-brackish group Pontocypridoidea or the non-marine group Cypridoidea. The taphonomy indicates that the studied ostracods had been subject to limited (if any) post-mortem transport, which could be consistent with marginal marine environments.