Marginal Marine Depositional Environment Research Articles

Micropaleontological and sedimentological analyses of carbonates rocks in parts of Sokoto Basin, Nigeria: implications for paleoecological interpretation and exploration efforts

This study presents a detailed analysis of the Paleocene and Maastrichtian marine sediments in the Sokoto Basin, Nigeria, using boreholes GSN – BH – 2051 and GSN – BH – 4051, respectively. This study is aimed at integrating sedimentological, micropaleontological and petrographic data in paleoecologic interpretation of depositional environments of the Sokoto Basin. The methods adopted in this research involved the examination of ditch cuttings, carbonate thin sections, and microfossils analyses from the boreholes drilled in Sokoto Basin. The sedimentological data from the borehole showed that the studied stratigraphic unit comprises mainly fine to medium-grained limestone facies, sparitic intraclastic packstone and oolitic-elmicrite wackestone facies. The microfacies obtained from petrography data revealed micro-fossils abundance and diversity associated with the onset of shallow marine transgression which resulted in the deposition of the Dange and Kalambaina Formations, respectively. The assemblages of the larger foraminifera (Opercullnoides bermudezi) and the larger ostracod (Bairdia iIaroensis) in the borehole sections further suggested marginal marine depositional environment for the Kalambaina and Gamba Shale Formations. The paleoecological interpretation suggests varying salinities and dysaerobic conditions during deposition, with implications for understanding basin evolution. The study concludes by highlighting the importance of integrating multiple methods for a detailed understanding of paleoecological and depositional environment of Sokoto sedimentary basin.

Late Albian-Cenomanian paleoenvironmental and paleoclimatic reconstructions in northeastern Gondwana: Palynological perceptions

The late Albian-Cenomanian (100.5–93.9 Ma) is considered a greenhouse world without permanent ice caps and with high eustatic sea levels. The high sea-level led to the flooding of low-lying coastal plains and the formation of extensive shallow shelf seas. Depositional conditions and ecosystems at these marginal and shallow shelf settings were affected by changes in environmental conditions, such as climate and vegetational ecosystems in surrounding regions. This study conducts palynomorph and palynofacies and lithofacies analysis of fifty-nine cutting samples from the North Qarun-1x well in the Gindi Basin (North Western Desert, Egypt) to assess the evolution of depositional and paleoenvironmental conditions as well as paleo-vegetation pattern in response to changes in climate and sea level. The sediment succession comprises the upper Albian to Cenomanian upper Kharita and Bahariya formations and Abu Roash G Member. Biostratigraphic analysis of palynomorph composition led to define seven interval zones of upper Albian-Cenomanian. At this time, Egypt was inundated by the southern margin of the Tethys Ocean, which led to the deposition of thick siliciclastic and carbonate facies in a marginal marine depositional environment. Statistical cluster analysis of particulate organic matter (POM) allowed three palynofacies assemblages (PFA-1 to PFA-3) to be recognized, indicating oscillating depositional conditions that shifted between fluvio-deltaic to marginal shallow marine, proximal, and distal inner neritic shelf environments. PFA-1 comprises the highest proportions of total phytoclasts, indicating fluvio-deltaic to marginal shallow marine conditions. PFA-2 is dominated by moderate abundances of AOM and phytoclasts, characterizing a proximal inner neritic shelf environment. PFA-3 consists of a slightly higher concentration of AOM compared to phytoclasts, indicating a distal inner neritic shelf environment with diminished terrestrial input and increased abundances of marine microplankton. Organic palynomorphs are abundant in mid-Cretaceous strata of northern Egypt. Abundant records of humidity indicators, mainly fern spores, along with other gymnosperms (mainly Taxodiaceae and Araucariaceae) compared to low aridity indicators of gnetalean Elaterates and Ephedroids along with non-gnetalean Classopollis suggest predominantly warm and humid conditions. Two intervals in the lower part of the Bahariya Formation and in the middle part of the Abu Roash G Member showed moderate to high abundances of aridity indicators and thus, warm arid to semi-arid climate events during the early and late Cenomanian.

Molecular fossil chronicles and geochemical probes of Paleogene coals from Meghalaya, India

The Paleogene coals from the Jaintia, Khasi, and the Garo hills of Meghalaya, India, are studied for biomarker distributions, carbon isotope signatures (δ13Cbulk), and Rock-Eval pyrolysis (REP) to elucidate their organic matter (OM) source, depositional environment, thermal maturity, and hydrocarbon generation potential. Sulfur-rich OM (1.52 wt%–24.57 wt% S dry-basis) with Hydrogen Index (HI) values ranging from 172 mg HC/g TOC – 353 mg HC/g TOC suggest the presence of type IIS-IIIS admixed kerogen. Mixed gymnosperm – angiospermous OM input to the peatland is implied by δ13Cbulk values spanning from −26.7‰ to −25.5‰, −27.4‰ to −25.1‰, and −27.0‰ to −25.2‰ in the Jaintia, Khasi, and Garo coals, respectively. Further, the presence of pimarane, isopimarane, labdane, rimuane, phyllocladanes, and ent-beyerane, mark the conifer OM input, substantiated by the 1,7-dimethylphenanthrene (1,7-DMP), 1,6-dimethylnaphthalene (1,6-DMN), and 1,2,5- trimethylnaphthalene (1,2,5-TMN) compounds. The abundances of these gymnosperm markers decline from the Garo to the Jaintia coals implying plausible shifts in paleovegetation. Compound A from the oleanoid skeleton and subordinate amounts of oleanane indicate variable contributions from angiosperms. The oleanane index declines from the Garo to Jaintia coals suggesting a lower contribution of angiospermous OM from Garo to the Jaintia samples, which may also indicate a shift in the OM depositional environment towards the Jaintia Hills. Dibenzothiophene isomers increase while dibenzofuran isomers decrease from the Garo to Jaintia coals suggesting shifts from terrestrial to marginal marine depositional environment. Additionally, the gammacerane index increases from the Garo to Jaintia coals implying a transition from a stratified brackish water column or marine transgression to the peatland of the Jaintia Hills. Moreover, the studied coal samples exhibit variable thermal maturity. The mean random vitrinite reflectance of the Garo coals (R¯r=0.48%–0.61%) indicates subbituminous to bituminous rank, while the Khasi (R¯r=0.44%–0.60%) and Jaintia coals (R¯r=0.26%–0.75%) belong to subbituminous to bituminous D, and lignite to bituminous C rank, respectively. Tmax of these coals ranges from 414 °C to 446 °C, indicating the samples span from pre-catagenetic to catagenetic stages of maturation. Saturated C32-bishomohopane epimer and C30 βα-moretane/αβ-hopane ratios, along with aromatic MPI-3 and 3-MP/retene ratios, exhibit an increasing maturity trend from the Garo Hills to the Jaintia Hills samples.

Authigenic Fe Mineralization in Shallow to Marginal Marine Environments: A Case Study from the Late Paleocene—Early Eocene Cambay Shale Formation

The late Paleocene–early Eocene warm greenhouse conditions, characterized by elevated pCO2 levels in the atmosphere and a dramatic increase in sea surface temperature, prompted abundant authigenic glauconite formation within the shallow marine sediments worldwide by lowering the net sedimentation rate, increasing organic productivity and expanding the oxygen minimum zones to shallow oceans. The early Eocene marginal marine Cambay Shale Formation experienced episodes of marine inundation represented by limestone–green shale alternations. The shales host abundant authigenic light-green, dark-green, and brown pellets. A detailed characterization of the pellets of the Valia and Vastan lignite mines, integrating the sedimentological, petrographical, mineralogical, and mineral geochemical data, suggests two distinct varieties of Fe–silicate formation, viz. glauconite and chamosite. While the glauconitic green pellets are ubiquitous to Valia and Vastan mines, brown chamosite pellets are confined within the basal part of the green shale facies alternating with fossiliferous limestone in the Vastan mine. The glauconites of the Valia mine manifest a ‘nascent’ to ‘slightly evolved’ maturation stage of glauconitization, whereas the glauconites of the Vastan mine represent the ‘evolved’ type. The limestone–green shale alternation in the Valia mine is overlain by a ~4 m-thick spherulitic mudstone facies comprising monomineralic sideritic spherulites, reflecting a pure FeCO3 composition. The glauconites in the Cambay Shale Formation transformed from kaolinite-rich clay pellets under dys-oxic depositional conditions. The increasing anoxicity within the microenvironment, possibly amplified by the rapid oxidation of continent-derived organic matter, facilitated chamosite formation instead of glauconite. The increased freshwater influx into the marginal marine depositional environment resulted in immature, K-poor glauconites of the Valia mine. The formation of siderite spherulites overlying the limestone–green shale alternation relates to the beginning of the regressive phase of sedimentation.

Characterization of reservoirs and depositional study of J-P Field, shallow offshore of Niger Delta Basin, Nigeria

Well log data interpretation was carried out over J-P Field in the Niger Delta, Nigeria. This was done with a view to characterizing the reservoirs based on the estimation of petrophysical parameters and to assessing the environment of deposition in J-P Field. Seven reservoirs were mapped and correlated across the four drilled wells in J-P Field. Petrophysical parameters such as porosity, volume of shale, water saturation and hydrocarbon saturation were estimated. In addition, depositional environments of each reservoir in J-P Field were determined based on the gamma ray responses. This study reveals that the range of petrophysical parameters across the delineated reservoirs; for porosity varies from 19 to 21%, thickness varies from 24 to 122 m, volume of shale varies from 15 to 29%, water saturation varies from 22 to 60% and hydrocarbon saturation varies from 40 to 78%. The depositional environment was interpreted as comprised of prograding deltas, transgressive marine sands, fluvial channels and deltaic settings. It is concluded that J-P Field has a porosity range varying from good to very good in quality and high hydrocarbon saturation of oil. Furthermore, the study revealed that J-P Field falls within the marginal marine depositional environment.

The geochemical signatures of the Silurian–Devonian succession in eastern Saudi Arabia

This study was performed on 663 sandstone core and cutting samples taken from the Silurian?Devonian succession in five wells, located in eastern Saudi Arabia. This study aimed to correlate the Tawil Formation in the study wells, defining the lower Qalibah/ Tawil and upper Tawil/Jauf boundaries. The Tawil Formation is mostly characterized by clastic-dominated fluvial to marginal marine depositional environments. A chemostratigraphic correlation workflow was established using key element ratios and comprising four zones (C1 to C4) and five subzones (C2-1 to C2-3 and C3-1-C3-2). The chemostratigraphic zonation allowed robust characterization of stratigraphy in the uppermost Qalibah, Tawil, and lower Jauf Formations. Zone C1 is associated in most cases with the Sharawra Formation. Zones C2 and C3 are generally linked with the Tawil Formation, and Zone C4 broadly defines the lower part of Jauf Formation. In detail, the chemostratigraphic zonal boundaries do not precisely match the biostratigraphical and lithostratigraphic boundaries, indicating that the C1-C2 and C3-C4 boundaries are probably time-transgressive. The ratio Zr/Nb was used to model sequence stratigraphy. This ratio can vary in proportion to grain size, in which the element Zr is known to be concentrated in the heavy mineral zircon; while Nb-bearing heavy minerals along with clay minerals, likely illite, produce Nb. The increasing Zr/Nb ratio values are considered to define the coarsening upward or regressive sequences while decreasing Zr/Nb trends can mark fining upward or transgressive sequences.

Latest Maastrichtian palaeoclimatic and depositional environmental perturbations, a record from Micula prinsii Zone of Meghalaya, northeastern India

A significant latest Maastrichtian calcareous nannofossil assemblage is recorded from the exposed section near Syndai Village, Meghalaya. A total of twenty two samples from sedimentary succession consisting of shales and sandy shales, calcareous at places, were studied; out of which ten samples were found productive in terms of calcareous nannofossils recovery. The presence of Micula prinsii in all the productive samples along with the other latest Maastrichtian nanno taxa suggests that the assemblage belongs to Micula prinsii Zone and well correlates with the CC26b Zone of Perch Nielsen and UC20dTP Zone of Burnett which are an amalgamation of old and new biozonation schemes from a range of palaeolatitudes and biogeographic provinces from both oceanic and shelf palaeoenvironments. Micula prinsii Perch–Nielsen, the latest Maastrichtian marker all over the globe, is recorded from both deep–sea sections and shelf areas. It is most evolved form of the genus Micula and got extinct just before K– Pg boundary. The Micula prinsii Zone is marked by the first occurrence of Micula prinsii to the last occurrence of unreworked, non–survivor Cretaceous taxa. In the present study, cluster analysis envisaged the palaeodepositional environmental changes within the Micula prinsii Zone in northeastern India. In the lower part of the section, the abundance of Micula concava and Micula staurophora with the increased numbers of Watznaueria barnesiae indicates environmentally stressful conditions with low productivity in surface water. However, in the upper part the increased numbers of Calculites obscurus with the decrease in Micula concava and Micula staurophora abundance indicates relatively increased productivity in surface water in marginal marine depositional environment.

Palaeobiogeographic and metric analysis of the Mesozoic fern Weichselia

Eighty-three publications have been examined to recover information on the palaeogeography, the chronostratigraphy and the presence of the fossil fern genus Weichselia Stiehler in different depositional environments. This fossil fern foliage was reported in 72 localities worldwide. Its fossil record ranges from the Bathonian to the Cenomanian, predominating from the Berriasian to the Barremian, but still common during the Aptian to Cenomanian. Weichselia mostly occurred in continental depositional environments in Europe, whereas it has been mostly related to marginal marine depositional environments in Africa, North America, and India. Three species have been described: W. reticulata, W. peruviana, and W. negevensis. We analyse the measurements on specimens collected from sixteen localities as well as published data from twelve others. Our results suggest that: (i) the climate changes during the Aptian might have affected the pinnule size of Weichselia, as the Aptian-Cenomanian pinnules are larger than those from the Berriasian-Barremian; (ii) some differences might be explained by the metric variation of the frond parts; (iii) there are no clear differences in size between remains collected from different depositional environments; (iv) there is no sufficient evidence to determine how many species of Weichselia have existed.

Paleoenvironment of Eocene lignite bearing succession from Bikaner-Nagaur Basin, western India: Organic petrography, palynology, palynofacies and geochemistry

Lignite and associated shale samples from the Matasukh mine of western India have been studied by petrographic, palynofacies, palynological and organic geochemical parameters. The objective is to understand the floral (organic) composition, and palaeo depositional conditions (ecology and climate) of the lignite-bearing sequence. Petrographically, the low rank B lignites are dominantly composed of huminite macerals, followed by moderate liptinite and low inertinite macerals. The predominance of detrohuminite (attrinite+densinite) with respect to telohuminite (textinite+ulminite) suggests that the woody vegetation has undergone higher degree of degradation during the peat accumulation, as is also indicated by the frequent occurrence of funginite. The TPI, GI, GWI and VI indices point towards limno-telmatic condition of the palaeomire during the deposition of lignite-forming peat under mesotrophic to rheotrophic basin conditions. The reducing conditions in the depositional site are evident from the frequent pyrite content. The studied samples had a high organic matter yield, which showed a co-dominance of phytoclasts and AOM. This nexus is indicative of a marginal marine depositional environment, also evident from Tyson's APP diagram. The palynofloral assemblage is dominated by angiosperm pollen, especially those having affinity with the family Arecaceae. The presence of palynomorphs of the family Dipterocarpaceae indicates the existence of rain-forest vegetation in the vicinity of the depositional site. The degradation products of oleanane and 23-norlupane in the sediment extracts also suggest that the angiosperm dominant higher plants served as the source for the peat-forming biomass. The presence of hopanes indicates high microbial activity during the formation of lignites. The high CPI and TAR values also indicate the large input of terrigenous higher plant materials.

Fossil Cetaceans (Mammalia, Cetacea) from the Neogene of Colombia and Venezuela

There are significant geographic gaps in our knowledge of marine mammal evolution because most fossils have been found and described from Northern Hemisphere localities and a few other high-latitude areas in the Southern Hemisphere. Here, we describe fossil cetacean remains from five geological units in the South American tropics (Urumaco, Codore, Castilletes, Cantaure, and Querales formations) generally representing marginal marine depositional environments (estuaries, deltas, and tidal flats). While fossil cetaceans from Venezuelan Neogene localities have been previously studied, this paper includes the first descriptions of fossil cetaceans from Colombia, including a diverse assemblage of mysticetes and odontocetes. We identified and provisionally referred fragmentary remains to the iniid Ischyrorhynchus vanbenedeni and to the platanistid Zarhachis flagellator. The latter suggests the presence of Platanistidae in the eastern coast of South America during the early-middle Miocene, representing the second record of Platanistidae in South America and the first record of Platanistidae in eastern South America. Other less-diagnostic specimens are characterized by features commonly seen in longirostrine odontocetes such as Iniidae, Platanistidae, Pontoporiidae, Lipotidae, Eoplatanistidae, and Squalodelphinidae.

Reservoir characteristics and palaeo depositional environment of Duski Field, onshore, Niger-Delta, Nigeria

The Niger Delta is a prolific hydrocarbon producing belt in the southern Nigeria sedimentary basin on the continental margin of the Gulf of Guinea. This study used well log suites to delineate the hydrocarbon reservoirs, depositional environments and lithostratigraphy of the Duski Field, Onshore Niger Delta, Nigeria. A comprehensive interpretation of the three wells revealed five (5) reservoir units with low volume of shale and thickness variations between 24m and 60.20m. The average porosity values ranged from 12% to 34%, with high hydrocarbon saturation in all the reservoir sands. Generally, porosity and permeability values decrease with depth in all the wells. Cross-plots of water saturation (Sw) and porosity ( o ) (Buckles plot) revealed that some reservoirs were at irreducible water saturation; hence producing water-free hydrocarbons. Therefore the hydrocarbon accumulation of this field is commercially viable and promising. This study revealed that the reservoir sand units were deposited within marginal marine depositional environment which include fluvial channel, transgressive marine, progradational and deltaic settings. Keywords: Reservoir characteristics, depositional environment, Niger Delta

Habitat and C-14 ages of lignitic terrace deposits along the northern Sarawak Coastline

The young terraces fringing the Miri coastline from Miri to Bekenu are formed by lignitic sands, fossil wood, and conglomeratic beds that contain reworked quartz pebbles derived from the older Tukau Formation. The sequence can be subdivided into four sub-units: I. Basal Conglomerate, II. Sandstone with fossil wood and Ophiomorpha, III. Cross- bedded lignitic sandstone, and IV. Bleached and weathered palaeosol. These sediments are indicative of a transgressive near-shore, fluvial to marginal marine depositional environment, as water energy peaked in cross-bedded sandstone of Sub- unit III. Radiometric C-14 based age determination in ten coastal locations indicates an age range from Late Pleistocene to Early Holocene (28,570 + 230 to 8,170 + 50 years BP). Given the terraces were formed in the same environment, but are now located at different elevations and appear to be block-faulted, it might imply significant tectonic movements in the Holocene.

COMPARISONS BETWEEN PALAEOCENE–EOCENE PARATROPICAL SWAMP AND MARGINAL MARINE POLLEN FLORAS FROM ALABAMA AND MISSISSIPPI, USA

Abstract: Climate warming at the Palaeocene/Eocene boundary (c. 55.8 Ma) had significant permanent affects on paratropical and warm‐adapted vegetation types. Pollen and spore records which document vegetation turnover from the eastern US Gulf Coast have all been taken from sediments of marginal marine depositional environments. Pollen and spores (sporomorphs) are preserved excellently in these marginal marine depositional environments but these assemblages contain grains transported from many different vegetation types and over huge geographic distances. Currently it is unclear whether the turnover from important paratropical areas like the US Gulf Coast is a reflection on actual vegetation change in the local region or from source areas far away in the continental interior. Sporomorph data from 20 former swamps (lignites) from the Nanafalia, Tuscahoma and Hatchetigbee formations in Mississippi and Alabama, USA, are used to test the fidelity of the marine sporomorph record across the Palaeocene–Eocene transition. Data show that extinction is noted in the swamp record (≥7 per cent of Palaeocene taxa) and that swamps were susceptible to immigration in the Early Eocene with the first occurrences of Brosipollis spp. (Burseraceae), Dicolpopollis spp. (Palmae), Nuxpollenites psilatus (Loranthaceae) and Platycarya spp. (Juglandaceae). Swamps have higher within‐sample diversity in the Eocene but higher among‐sample diversity in latest Palaeocene–earliest Eocene samples, which parallels exactly diversity trends estimated from marine sporomorph assemblages. Palms also increase in abundance in the Eocene. The swamp data demonstrate that the flora growing in these ancient paratropical forests was diverse (c. 120 taxonomic groups) but incorporated an unusual admixture of plants with modern tropical affinities together with those that now live in modern temperate to subtropical North America.

Dinoflagellate cyst stratigraphy and palaeoenvironment of the marginal marine Middle and Upper Miocene of the eastern Campine area, northern Belgium (southern North Sea Basin)

AbstractA stratigraphical and palaeoenvironmental analysis with organic‐walled palynomorphs of the Bolderberg and Diest formations provides new insights in the depositional history during Miocene times at the southern border of the North Sea Basin. The Neogene transgression invaded Belgium from a north–northwestern direction and fully marine sediments were deposited in the northern part of Belgium. The age and the palaeoenvironment of the deposits at the very border of the southern North Sea Basin remained till a few decades ago incomplete. The recovered dinoflagellate cysts, acritarchs and green algae from the Bolderberg Formation in the Wijshagen Borehole indicate a marginal marine depositional environment during late Burdigalian and Langhian times in the eastern Campine area, in contrast to the deeper marine conditions prevailing to the north–northwest. The relative dating of the Bolderberg Formation confirms that maximum flooding occurred during Langhian to early Serravallian times. Deposition apparently took place during the Middle Miocene Climatic Optimum, and ended when the climatic deterioration set in at around 14 Ma. A hiatus spanning ca. 2 Ma separates the Middle Miocene Bolderberg Formation from the Upper Miocene Diest Formation in the eastern Campine area at the border of the North Sea Basin. Copyright © 2007 John Wiley & Sons, Ltd.

Carbon Isotope Composition of Raialo Carbonates and Its Equivalents, Mesoproterozoic Delhi Supergroup, India: Implications for Stratigraphic Correlation

Carbon isotopic studies are useful not only for reconstruction of palaeoenvironment, but have also been used successfully for chronostratigraphic purposes. The marine limestones and even dolostones faithfully record the carbon isotopic composition of the ocean water in which they formed (Schole and Arthur, 1980; Gao and Land, 1991; Wang et al., 1996). Saltzman et al. (1998) investigated the carbon isotope stratigraphy of the welldated carbonates of the Phanerozoic part of geological record and confirmed that large perturbations in the carbon isotope ratios of common carbonate rocks may be used as a precise measure of time. The Mesoproterozoic Delhi Supergroup of Aravalli Mountain Range, Rajasthan, India (Fig. 1) is mainly comprised of quartz arenite, conglomerate, felds arenite, phyllite, limestone, marble and calc-gneiss. These rocks have undergone polyphase deformation and suffered greenschist to amphibolite facies metamorphism. A marginal marine depositional environment has been envisaged for the sedimentary sequences of the Delhi Supergroup (Deb, 1980; Singh, 1982a). The Raialo Group (type area is Raynahalla town) of Delhi Supergroup, is exposed on the northern extremity of the fold belt and is characterized by the frequent presence of dolomitic carbonates. Carbonates have also been reported on the western limits of the Delhi Supergroup but are significantly calcitic in composition (Heron, 1953). The stratigraphic status of calcitic carbonates occurring on the western margin of the Delhi Fold Belt and its correlation with carbonates from the Raialo Group is a matter of debate. Heron (1953) correlated the carbonates on the western margin of the Delhi Supergroup with the Raialo carbonates. Sen (1983), on the other hand, suggests that these should belong to a younger sequence. Roy and Sharma (1999) advocated for the correlation of these carbonates with the younger Sirohi Group sediments. To resolve the issue we have carried out sampling of carbonates from the Raialo Group and its equivalents occurring on the western margin of the Delhi Supergroup for analysis of carbon and oxygen isotope composition. The whole-rock carbonate samples were collected at close intervals along a stratigraphic profile in the Raialo Group around the Rayanhalla town. Representative samples were however, collected from the different carbonate occurrences occurring on the western margin of Delhi Supergroup and included in the ambit of the Raialo Group. The preliminary isotope results are provided in table 1.

Geochemistry of Early Siderite Cements from the Eocene Succession of Whitecliff Bay, Hampshire Basin, U.K.

ABSTRACT Siderite cements in the Eocene of Whitecliff Bay (Hampshire Basin, U.K.) occur in a range of depositional facies and morphological associations. Most siderites are associated with in situ glaucony or occur beneath conspicuous lithological breaks. These associations illustrate the importance of slow deposition for early diagenetic carbonate precipitation. Siderite in the Eocene sediments of Whitecliff Bay is impure and in many cases comprises zoned crystals, with an overall decrease in substitution of Ca, Mg, and Mn for Fe from crystal core to rim. Trends in Ca, Mg, and Mn from early to later siderite vary between samples, with no evident environmental control. Siderite concretions without calcite cement occur only beneath lithological breaks where meteoric water may have been introduced. Precipitation temperatures have been calculated from siderite 18O data and are based on the assumption that precipitation occurred from seawater. These temperatures are reasonable for typical microbial siderite precipitated in marine sediment but are slightly low for marine siderite where there may have been meteoric overprinting. If the precipitation temperature for siderite cements is assumed (from 18O data for time-equivalent biogenic carbonate) rather than the composition of the precipitating fluid, the calculated isotopic composition of the precipitating fluid is generally compatible with the inferred marginal marine depositional environments.

Sedimentology and Ichnology of Paleozoic Estuarine and Shoreface Reservoirs, Morrow Sandstone, Lower Pennsylvanian of Southwest Kansas, USA

Integration of facies and trace-fossil evidence tests and refines depositional models constructed solely on the basis of physical sedimentology. In recent years, the petroleum industry has increasingly used trace-fossil analysis of cores as an aid in reservoir characterization. In particular, ichnologic data have been instrumental in the recognition of estuarine deposits and their distinction from open-marine facies (e.g., MacEachern and Pemberton, 1994). Previous ichnologic analyses of cores, however, have concentrated on post-Paleozoic reservoirs (e.g., Bockelie, 1991; Pemberton, 1992; Taylor and Gawthorpe, 1993; Howell et al., 1996; Martin and Pollard, 1996; MacEachern and Pemberton, 1997). The present study represents one of the first attempts to apply trace-fossil analysis to cores from Paleozoic reservoirs.
 The Lower Pennsylvanian Morrow Sandstone contains oil and gas reservoirs in a wide variety of shallow and marginal-marine depositional environments. Delta-front, shoreface, and estuarine valley-fill reservoir sandstones are encased in offshore and estuarine mudstones (Sonnenberg, 1985; Krystinik and Blakeney, 1990; Sonnenberg et al., 1990; Wheeler et al., 1990). An integrated stratigraphic, sedimentologic, and ichnologic study provides a more accurate characterization of reservoir facies and geometry. This study allows distinction between marine-shoreface and estuarine valley-fill sandstones from four cores of the lower Morrow in southwestern Kansas. Core analysis subsequently was integrated with well-log information. Previous studies have emphasized the presence of estuarine valley-fills in the upper Morrow (Wheeler et al., 1990). Our integrated approach extends the estuarine valley interpretation into the lower Morrow. Within the midcontinent, trace fossils are useful in distinguishing different facies in estuarine incised valleys and marine shorefaces. Detailed study of biogenic structures provides high-resolution information to solve problems in facies, stratigraphic, and reservoir modeling. In some cases, they represent the only evidence available to develop a reasonable picture of depositional conditions and to estimate reservoir heterogeneity. The present study provides a detailed analysis of the sedimentary facies, documents the associated trace fossils, and illustrates how trace fossils are used to refine environmental interpretations of the lower Morrow sandstone reservoirs.

Controls on sedimentation in distal margin palaeovalleys in the Early Tertiary Alpine foreland basin, south‐eastern France

The influence of palaeodrainage characteristics, palaeogeography and tectonic setting are rarely considered as controls on stratigraphic organization in palaeovalley or incised valley systems. This study is an examination of the influence of source region vs. downstream base level controls on the sedimentary architecture of a set of bedrock‐confined palaeovalleys developed along the distal margin of the Alpine foreland basin in south‐eastern France. Three distinct facies associations are observed within the palaeovalley fills. Fluvial facies association A is mainly dominated by poorly sorted, highly disorganized, clast‐to‐matrix‐supported cobble‐to‐boulder conglomerates that are interpreted as streamflood deposits. Facies association B comprises mainly yellow siltstones and is interpreted as recording deposition in an estuarine basin environment. Estuarine marine facies association C comprises interstratified estuarine siltstones and clean, well‐sorted washover sandstones. The sedimentary characteristics of the valley fill successions are related to the proximity of depositional sites to sediment source areas. Palaeovalleys located proximal to structurally controlled basement palaeohighs are entirely dominated by coarse fluvial streamflood deposits. In contrast, distal palaeovalley segments, which are located several kilometres downstream, contain successions showing upward transition from coarse fluvial facies into estuarine central basin fines, and finally into estuarine‐marginal marine facies. Facies distributions suggest that the fluvial deposits form wedge‐shaped, downstream‐thinning sediment bodies, whereas the estuarine deposits form an upstream‐thinning wedge. The vertical stacking of fluvial to estuarine to marginal marine depositional environments records the fluvial aggradation and subsequent transgression of relatively small bedrock‐confined river valleys, which drained a rugged, upland terrain. Facies geometries suggest that a fluvial sediment wedge initially prograded downvalley, in response to high bed load sediment yields. Subsequently, palaeovalleys became drowned during the passage of a marine transgression, with the establishment of estuarine conditions. Initial fluvial aggradation and subsequent marine flooding of the palaeovalleys is a consequence of the interaction of high local rates of sediment supply and relative sea‐level rise driven by flexural subsidence of the basin.

Palynology of the Maastrichtian/Danian boundary at Savannah River Site, South Carolina

Sixty-three core samples bracketing the Maastrichtian/Danian boundary were collected from wells at Savannah River Site near Aiken, South Carolina for palynological investigation. The samples were collected from the Steel Creek Member of the Peedee Formation (Maastrichtian) and the base of the Ellenton Formation (Danian). Analysis of the Steel Creek Member samples indicates that sedimentation took place in an upper delta-plain to lower delta-plain freshwater environment. The pollen and spores are predominantly terrestrial in origin and no marine dinoflagellates were encountered. The top of the Peedee Formation is heavily oxidized in most areas and underlies deposits of the Ellenton Formation (Danian) with similar lithologies. The base of the Ellenton Formation contains abundant marine dinoflagellates, glauconite, and substantially lower concentrations of pollen and spores along with a decrease in the number of species encountered. There are two distinct groups of pollen and spores in these samples. Danian age species such as Intratriporopollenites stavensis and Subtriporopollenites nanus were encountered with Maastrichtian age species such as Rugubivesiculites reductus and Proteacidites retusus. These Maastrichtian palynomorphs are highly fragmented as a result of a high-energy influence during transport and represent sediments of Maastrichtian age that were reworked and redeposited in the Danian. The presence of marine dinoflagellates and glauconite in these samples is typical of a change from an upper delta-plain to a lower delta-plain or marginal marine depositional environment. The lithology of these units in conjunction with this palynologic study suggests that the paleo-shoreline in the Maastrichtian was located just southeast of Savannah River Site. With the onset of the Danian, a marine transgression migrated the paleo-shoreline to the northwest, partially covering the Savannah River Site with marine waters.

Abstract: Interrelationship of Marginal-Marine Depositional Environment Classifications 

Abstract: Interrelationship of Marginal-Marine Depositional Environment Classifications