Depositional Environment Conditions Research Articles

Sedimentology and geochemistry of Carboniferous-Permian marine-continental transitional shales in the eastern Ordos Basin, North China

A continuously cored well covering the Carboniferous-Permian Benxi, Taiyuan, and Shanxi formations in the eastern Ordos Basin provides a rare window into environmental conditions of the marine-continental transitional strata. Integration of petrographic, mineralogical, and high-resolution geochemical data allows marine-continental investigating the depositional environment, organic abundance, detrital influx, paleoclimate, paleo-water salinity, and paleoredox conditions of transitional facies. The marine-continental transitional strata in the Upper Carboniferous to Lower Permian consist of complex interbedding of sandstone, shale, coal and limestone. TOC contents display a considerable change in the vertical direction, with high TOC content in coal, moderate TOC in shale, low TOC content in limestone and no noticeable TOC enrichment in sandstone. The Upper Carboniferous Benxi Formation is dominated by marine facies then changing into transitional facies. The Lower Permian Taiyuan Formation is characterized by multiple alternation of marine and transitional facies. Marine limestones are characterized by low detrital influx proxies, whereas transitional shales show high detrital influx input and oxic environment. The Lower Permian Shanxi Formation is a typical marine-continental transitional depositional system, which is characterized by complex interbedding of shales, sandstones and coals. Sandy intervals were deposited in deltaic and tidal flat environment and characterized by high Ti and Al content, low TOC (0.09–0.97%, avg. 0.31%), relatively low U/Th (0.11–0.32, avg. 0.17), showing limited influence of seawater. Shale intervals were deposited in a lagoonal environment with high TOC (0.94–40.64%, avg. 5.43%), Sr/Ba and trace elemental proxies values (U/Th, 0.18–3.27%, avg. 0.44%; MoEF, 0.95–32.3, avg. 8.56; UEF, 0.67–15.17, avg. 2.53). This study shows that high-resolution geochemical characteristics of elements could be reliable indicators for sedimentary facies analysis, and hence could provide broader implications for utilizing trace element geochemistry from marine-continental transitional periods in which sedimentary environment changes frequently and organic-rich sediment accumulated under varied conditions.

Three‐Dimensional Morphometry of Ooids in Oolites: A New Tool for More Accurate and Precise Paleoenvironmental Interpretation

AbstractThe prevalence of ooids in the stratigraphic record, and their association with shallow‐water carbonate environments, make ooids an important paleoenvironmental indicator. Recent advances in the theoretical understanding of ooid morphology, along with empirical studies from Turks and Caicos, Great Salt Lake, and The Bahamas, have demonstrated that the morphology of ooids is indicative of depositional environment and hydraulic conditions. To apply this knowledge from modern environments to the stratigraphic record of Earth’s history, researchers measure the size and shape of lithified ooids on two‐dimensional surfaces (i.e., thin sections), often assuming that random 2D slices intersect the nuclei and that the orientation of the ooids is known. Here, we demonstrate that these assumptions rarely are true, resulting in errors of up to 35% for metrics like major axis length. We present a method for making 3D reconstructions by serial grinding and imaging, which enables accurate measurement of the morphology of individual ooids within an oolite, as well as the sorting and porosity of a sample. We also provide three case studies that use the morphology of ooids in oolites to extract environmental information. Each case study demonstrates that 2D measurements can be useful if the environmental signal is large relative to the error from 2D measurements. However, 3D measurements substantially improve the accuracy and precision of environmental interpretations. This study focuses on oolites, but errors from 2D measurements are not unique to oolites; this method can be used to extract accurate grain and porosity measurements from any coherent, granular sample.

Depositional environment and source rock quality of the Woodbine and Eagle Ford Groups, southern East Texas (Brazos) Basin: An integrated geochemical, sequence stratigraphic, and petrographic approach

X-ray fluorescence chemostratigraphy of the Cenomanian–Turonian Woodbine and Eagle Ford Groups in the southern parts of the East Texas Basin highlights significant mudstone chemical heterogeneities that commonly are difficult to observe or quantify at the macroscale. Several key elements, namely, Ca, Si, Mo, Mn, and Ni, were correlated to depositional conditions and used in a hierarchical cluster analysis to characterize five chemical facies (i.e., “chemofacies”) across 10 cored intervals of the Woodbine and Eagle Ford Groups: (1) argillaceous, organic-matter poor; (2) transitional, organic-matter poor; (3) transitional, organic-matter moderate; (4) calcareous, organic-matter rich; and (5) calcareous, organic-matter moderate. Characterizations of organic matter richness, mineralogy, and environmental conditions of deposition were established by correlating between key element abundances, total organic carbon measurements, x-ray diffraction measurements, and petrographic observations of lithologic composition, bioturbation, and sedimentary textures. Combined analysis of elemental geochemistry, stratigraphy, and petrographically observed sedimentary textures indicates that all chemofacies were deposited in an intrashelf basin above storm wave base. The most organic-rich chemofacies was deposited on a dominantly dysoxic distal shelf. Mudstone organic matter enrichment is driven dominantly by the minimization of siliciclastic dilution and secondarily enhanced by oxygen restriction. Regional correlations of chemofacies within a sequence stratigraphic framework developed from previous outcrop and subsurface work indicate a clear relationship between interpreted stratigraphy and chemofacies deposition. Generally, the highstand sequence sets of the Woodbine Group and upper Eagle Ford formation are dominated by mineralogically clay-rich, organic matter–lean, siliciclastic sedimentation and contain poor-quality source rock. Conversely, the transgressive sequence set of the lower Eagle Ford formation is dominated by organic matter–rich pelagic carbonate accumulation and contains excellent-quality source rock.

Facies characterisation of sediments from the East Frisian Wadden Sea (Germany): new insights from down-core scanning techniques

AbstractSediment facies provide fundamental information to interpret palaeoenvironments, climatic variation, archaeological aspects and natural resource potentials since they are summary products of depositional processes, environmental conditions and biological activities for a given time and location. The conventional method of facies discrimination relies on macroscopic and/or microscopic determination of sediment structures combined with basic physical, chemical and biological information. It is a qualitative measure, depending on observer-dependent sedimentological descriptions, which cannot be reanalysed readily by further studies. Quantitative laboratory measurements can overcome this disadvantage, but are in need of large sample numbers and/or high temporal resolution, and are time-, labour- and cost-intensive. In order to facilitate an observer-independent and efficient method of facies classification, our study evaluates the potential of combining four non-destructive down-core scanning techniques: magnetic susceptibility (MS), X-ray computed tomography (CT), X-ray fluorescence (XRF) and digital photography. These techniques were applied on selected sections of sediment cores recovered around the island of Norderney (East Frisian Wadden Sea, Germany). We process and integrate the acquired scanning measurements of XRF elemental intensities, represented by principal components, MS, CT density and lightness of eight sediment facies previously recognised by conventional facies analysis: moraine, eolian/fluvial, soil, peat, lagoonal, sand flat, channel fill and beach-foreshore. A novel type of density plot is introduced to visualise the digitised sediment information that allows an observer-independent differentiation of these facies types. Thus, the presented methodology provides the first step towards automated supervised facies classification with the potential to reproduce human assessments in a fully reproducible and quantitative manner.

Inoceramid bivalve and dinoflagellate cyst integrated biostratigraphy of the topmost Campanian–Maastrichtian in a part of the Western Fore-Balkan Mountains, northwest Bulgaria

We present the inoceramid and dinoflagellate cyst record from the topmost Campanian–Maastrichtian strata of three key sections of the Western Fore-Balkan Mountains, northwest Bulgaria. The following inoceramid zones were recognized: “Inoceramus” redbirdensis Zone, Endocostea typica Zone, Trochoceramus radiosus Zone and “Inoceramus” ianjonaensis Zone. The Campanian/Maastrichtian boundary was tentatively drawn slightly below the first occurrence of Endocostea typica. The uppermost inoceramid assemblage was confined to the lower part of the upper Maastrichtian. Dinoflagellate cyst ranges, as well as the first and the last occurrence events of dinocysts, provided valuable markers for the stratigraphic subdivision of the Maastrichtian. The first occurrence of Microdinium carpentierae was documented in proximity to the Campanian/Maastrichtian boundary. The Cerodinium diebelii Zone was recognized with a stratigraphical range from the lower Maastrichtian to the lower upper Maastrichtian. The last occurrence of Alterbidinium acutulum was recorded in the lower Maastrichtian and used as aid for tracing the lower/upper Maastrichtian substage boundary. The marked domination of delicate chorate dinocysts in all sections and the encountered low P/G ratio values are indicative of stable low-energy depositional environment and oligotrophic conditions, with normal marine productivity and nutrient availability in the basin during the Maastrichtian.

Palaeontological and sedimentological characteristics of the Changhsingian (Late Permian) platform−margin sponge reef and intraplatform skeletal mound in NE Sichuan Basin, South China: their palaeoenvironmental implications

Well-preserved fossil reef/mound-building communities and shallow microfacies have been recovered from Changhsingian platform−margin sponge reef at the Panlongdong Section and intraplatform sponge skeletal mound at the Yanggudong Section in NE Sichuan Basin, South China. The present contribution focuses on the palaeoenvironmental implication of the differentiated development processes on the platform−margin reef and intraplatform skeletal mound based on the palaeontology and sedimentology. Precise field assessments and macroscopic/microscopic qualitative observations led to the identification of five reef/mound-building community and 14 reef/mound-related microfacies in the 2 sections of Changxing Formation. In the Panlongdong platform−margin sponge reef, reef-building communities are recognized into Amblysiphonella Community, Preperonidella−Amblysiphonella Community, and Preperonidella–Sollasia Community in ascending order. The reef-related microfacies are mainly classified into calcisphere−pelletoid wackestone to packstone, crinoidal wackestone to packstone of shallow water bank environment, hypercalcified sponge bafflestone, calcareous algae−hypercalcified sponge binding framestone, hypercalcifed sponge−calcareous algae bindstone, and calcareous algae−hypercalcifed sponge rudstone of reef environment, and benthic foraminifera−calcareous algae wackestone to packstone of shallower water lagoon environment. Two mound-building communities can only be found in the Yanggudong intraplatform skeletal mound, including Preperonidella−Intrasporeocoelia Community of lower part and Preperonidella−Sollasia Community of upper part. The mound-related microfacies include calcisphere−calcareous algae wackestone to packstone, crinoidal wackestone to packstone and crinoidal packstone to grainstone of shallow water bank environment, hypercalcified sponge bafflestone and cyanobacteria−hypercalcified sponge binding bafflestone of skeletal mound environment, benthic foraminifera−calcareous algae packstone grainstone of shallower water bank environment and benthic foraminifera−calcareous algae wackestone to packstone of shallower water lagoon environment. These palaeontological and sedimentological analysis results have facilitated the classification of sponge reef and skeletal mound sections corresponding to a solitary shallow benthic zone into multiple microfacies attributed to variable environmental depositional conditions. The differentiated evolutional process of multiple reef/mound-building stages at the Panlongdong and Yanggudong sections clearly demonstrate a general shallowing-upward trend from an inner shelf setting to a supratidal and low energy lagoon environment.

Characterisation of heteroatomic compounds in free and bound bitumen from different source rocks by ESI FT-ICR MS

Catalytic hydropyrolysis (HyPy) has been widely used in the study of covalently bonded biomarkers from macromolecular organic matter. Current HyPy studies mainly focus on nonpolar aliphatic biomarkers, whereas studies of polar non-volatile heteroatomic compounds are lacking. In this study, heteroatomic compounds in free and bound bitumen released via HyPy of kerogen from three different source rocks were characterised and compared by electrospray ionisation (ESI) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). These analyses suggest that heteroatomic compounds in bound bitumen are better proxies of the original biogenic sources and contain more aromatic structures than in heteroatomic compounds occurring in the free bitumen. From studies of three source rocks, we found that differences in the maturity, depositional environment, and diagenetic conditions seem to have significantly influenced the composition and distribution of heteroatomic compounds in free and bound bitumen. Nitrogen-containing compounds (N1 and N1OX species) in the free bitumen were mainly affected by maturity – only being detected in the rock of highest maturity – although they occurred in similar composition in the bound bitumen of all three rocks. With increasing maturity, nitrogen compounds were partitioned from bound to free bitumen, resulting in compositional differences between these two bitumen types (especially for basic nitrogen compounds). Sulfur-containing compounds (mainly S1, OXS1, and OXS2 species) were mainly influenced by the depositional environment and were abundant in the two rocks from a reducing depositional environment. Their composition was more complex and less saturated in bound bitumen. Oxygen compounds were common to all three rocks, but of highest abundance in the one source rock deposited in a freshwater environment.

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

Infrared spectroscopy refines chronological assessment, depositional environment and pyrolysis conditions of archeological charcoals

Based on infrared spectral characteristics, six archeological sample sets of charcoals from German (5) and Brazilian (1) sites, covering the time span from the nineteenth century CE to 3950 BCE, were compared to a chronological (present to the fifteenth century BCE) series of Austrian charcoals. A typical chronological trend of several bands (stretch vibrations: O–C–O of carboxylates at 1,585–1,565 and 1,385–1,375 cm−1, C–O carboxylic acids at 1,260–1,250 cm−1) that indicate oxidation and subsequently increasing hydrophilicity (O–H stretch vibration at about 3,400 cm−1) was also contained in the archive samples. Three sample sets fit in the typical band development according to their age. For three sample sets this conformity was not observed. Despite the age of two sample sets (3950–2820 BCE), most charcoals were assigned to the Modern Period. Apart from the high degree of carbonization, anaerobic depositional conditions over a longer period of time seem to contribute to the surprising conservation. Non-removable mineral components in charcoals, as observed in a third sample set, strongly influence infrared band intensities and positions of organic compounds. The role of inorganic components in terms of charcoal aging, and the information we can obtain from spectral characteristics in an archeological context, are discussed.

Environmental conditions of deposition of the Lower Cretaceous lacustrine carbonates of the Barra Velha Formation, Santos Basin (Brazil), based on stable carbon and oxygen isotopes: A continental record of pCO2 during the onset of the Oceanic Anoxic Event 1a (OAE 1a) interval?

This study presents new stable carbon and oxygen isotope data from Lower Cretaceous lacustrine carbonate rock samples recovered from a well drilled in the Santos Basin, offshore southeast Brazil. These samples represent a record of a continental environment just prior to the opening of the South Atlantic Ocean and the ultimate break-up of Gondwanaland. The geochemical data, along with carbonate mineralogy, indicate repeated cycles of lake level variation that could be attributed to climatic oscillations. Despite the absence of correlations between δ13C and δ18O values, facies analysis and the isotopic and mineralogical data suggest that lake hydrology was essentially closed for most of the depositional interval studied here. The existence of persisting trends of nearly constant δ13C values with a spread in δ18O values though, suggests long water residence times in the palaeolake, equilibrium between atmosphere and lake water CO2, as well as significant evaporation of water. The overall geological model that emerges unveils a more comprehensive picture of the depositional conditions that favoured the continuity of a significant carbonate factory in the middle of the Gondwanan continent, corroborating previous studies that suggested the lasting existence of a large and somewhat shallow endorheic lake in the area during the Early Cretaceous. As a result of this recorded trend strongly suggesting equilibrium between lake waters DIC (dissolved inorganic carbon) reservoir and atmospheric CO2, the data are most consistent with lacustrine deposition rather than precipitation of travertine, contrasting with some suggestions for the genesis of the carbonates of the Barra Velha Formation. Finally, this apparent equilibrium with the atmosphere likely left a preserved record in the continental carbonates of the final stages that preceded a major global environmental disturbance associated with an increase in atmospheric CO2, known for this time as the Oceanic Anoxic Event (OAE) 1a. If this is correct, it also helps to put further time constraints on this studied interval, which should not be younger than Barremian age, and to provide a regional continental perspective on a global event.

A geochemical investigation into the resource potential of the Lawn Hill Platform, northern Australia

The Lawn Hill Platform (LHP) is a sedimentary province in north-eastern Northern Territory and north-western Queensland that hosts a significant Paleoproterozoic–Mesoproterozoic sequence, often referred to as 'the ‘Isa Superbasin’, and includes the overlying South Nicholson Group. Shale gas resources and base-metals mineralisation are known in north-west Queensland, but the larger basin is underexplored. The Australian Government’s Exploring for the Future (EFTF) 2016−2020 program aims to boost resource exploration in northern Australia. New precompetitive geochemical data obtained in this program includes source rock geochemistry, kerogen kinetics, bitumen reflectance, biomarker and δ13C n-alkanes for understanding the petroleum potential, organic geochemistry of source rocks and fluids, stratigraphic correlations and mineralogy to determine the brittleness of shales. All data and derived reports are accessible on the EFTF portal (www.eftf.ga.gov.au), providing a central location for informed decision making. The results in this study demonstrate fair to excellent source rocks in multiple supersequences that are brittle and favourable to hydraulic stimulation. A comparison to the greater McArthur Basin demonstrates, that although there are many similarities in bulk geochemistry, LHP mudstones are largely heterogeneous, reflecting local variations that may be inherited from variations in contributing biomass, microbial reworking, depositional environment, sediment input and paleoredox conditions.

Grain size distribution and environmental implications of Rosetta beach, Mediterranean Sea coast, Egypt

Grain-size analysis of beach sediments along Rosetta beach of the Nile delta coast has been carried out to reveal the depositional environment condition, energy and hydrodynamic conditions, as well as the mode of transportation along the study area. In total 56 beach samples were collected, distributed along 3 profiles parallel to the shoreline and covering the shoreline, semi-wet area, and the dry backshore area. The study showed the great sensitivity of the interrelationships of various grain size statistical parameters (mean size, sorting, skewness, and kurtosis) to the slight variations in the compositional formula of the sediment mixture. Distribution of the textural parameters revealed the dominance of unimodal pure sand sediments, mainly Nile sand sources. The fluctuation between moderately well-sorted to well-sorted sediments and from coarse skewed to fine skewed under leptokurtic to platykurtic nature was distinguished at different localities and relevant environmental implications. Different discrimination tools as bivariate cross plot of grain size parameters, Linear Discrimination Functions (LDF), skewness and kurtosis relationship as a non-dimensional expression of sediment/energy simulation, Energy Process diagram, and mode of transportation (C-M diagram), indicates the marine signature followed the riverine input as a function of the sediments locality. Depositional processes were mainly hydraulically controlled through active energy processes of the marine environment. The fluvial nature of sediment demonstrated the graded suspension and saltation modes as the prime factors for transportation, influenced by marine and turbidity environment actions, within a shallow agitated marine environment.

Ecostratigraphic implications of a Late Palaeocene shallow-marine benthic community from the Jaintia Hills, Meghalaya, NE India

Moderately preserved shallow-marine extinct, fossil benthic community has been recovered from a sub-surface Late Palaeocene limestone cave section near Lumshnong in the Jaintia Hills, Meghalaya, NE India. The present contribution focuses on the ecostratigraphic implications of the carbonate microbiofacies based on the evaluated facies gradients. Precise field assessments and microscopic observations led to the identification of three microbiofacies: benthic foraminiferal–algal grainstone, coralline algal framestone and oolitic grainstone–packstone. The microbiofacies distinguished in the study suggest a general shallowing-upward trend from an inner shelf setting to a lagoonal–shoal environment depicting the distinct changes in the benthic community. Presence of coralline alga Distichoplax biserialis and benthic foraminifera Idalina sinjarica, Daviesina khatiyahi, Miscellanea primitiva, Rotalia trochidiformis and Vania anatolica assign the studied carbonates to Early Thanetian (SBZ 3) corresponding to the lower part of the Lakadong Limestone. In this study, ecostratigraphy has facilitated the classification of a single carbonate section corresponding to a solitary shallow benthic zone into multiple microbiofacies attributed to variable environmental depositional conditions. This clearly demonstrates its potential in improving the applicability of biostratigraphy worldwide.

Leaching Behavior of As, Pb, Ni, Fe, and Mn from Subsurface Marine and Nonmarine Depositional Environment in Central Kanto Plain, Japan

The leaching behavior of arsenic (As), lead (Pb), nickel (Ni), iron (Fe), and manganese (Mn) was investigated from subsurface core sediment of marine and nonmarine depositional environments in central Kanto Plain, Japan. A four-step sequential extraction technique was adopted to determine the chemical speciation, potential mobility, and bioavailability of metals under natural conditions in variable depositional environments. In addition, a correlation of these properties with pore water and total metal content was carried out. The concentration of As in pore water was found to be 2–3 times higher than the permissible limit (10 µg/L) for drinking water and leachate in fluvial, transitional, and marine environments. The trend of potential mobile fractions of As, Pb, and Ni showed Fe–Mn oxide bound > carbonate bound > ion exchangeable bound > water soluble in the fluvial environment. However, in the marine environment, it showed Fe–Mn oxide bound > water soluble > carbonate bound > ion exchangeable bound for As. The leaching of As in this fluvial environment is due to the organic matter-mediated, reductive dissolution of Fe–Mn oxide bound, where Mn is the scavenger. The amount of total content of As and sulfur (S) in transitional sediment reflects an elevated level of leachate in pore water, which is controlled by S reduction. However, the leaching of As in marine sediment is controlled by pH and organic matter content.

Provenance, tectonic setting, and weathering of sediments in Tumaco-1 ST-P well, Tumaco forearc basin, Colombia: Insights from petrography, heavy minerals, X-ray diffraction, and whole-rock chemostratigraphy

A chemostratigraphic evaluation based on major and trace elements (including the REE group), heavy minerals, and whole rock petrographic analysis is applied on 300 samples from the Tumaco-1-ST-P well located in the Tumaco forearc basin, Colombia. The aim of the study is to gain a better understanding of the provenance, tectonic, and paleoweathering conditions of the succession, which contains three formations (Tumaco, Tangareal del Mira, and Cascajal) ranging in age from the late Oligocene to late Pliocene.SiO2 has the highest concentration of all major elements (mean at 52%), followed by Al2O3 (mean at 14.6%), Fe2O3, MgO, and CaO are in the range of 3.2–5.3%, Na2O and K2O oscillate between 1 and 2%, and TiO2, P2O5, MnO, and Cr2O3 are <1%. Out of trace elements, Ba, Sr, V, Cr, Cu, Zn, Ni and Zr are the most abundant; their enrichment is probably due to the marine/deltaic depositional environment conditions. Th, Cs, and Nb have the highest concentrations of all trace elements. In general, concentrations of light rare earth elements are greater than high rare earth elements (LREE > HREE). Both positive and negative Eu anomalies are present in Tumaco and Tangareal del Mira formations, suggesting that rocks have two sources, mafic and felsic; the presence of both is consistent with petrographic and heavy mineral analyses.Paleoweathering indices, such as the chemical index of alteration (CIA), plagioclase index of alteration (PIA), and index of compositional variability (ICV) in the Tumaco-1-ST-P well suggest that the source of these rocks experienced initial stages of weathering compared with Post-Archean Average Australian Shale (PAAS) and Upper Continental Crust (UCC) values, indicating that the Tumaco formation samples have undergone major alteration. The clay mineral assemblage is dominated by the occurrence of illite and illite/smectite mixed layers; when coupled with the CIA index and the Al2O3-CaO-Na2O-K2O (ACNK) plot this indicates post-depositional K-enrichment. The distribution of Al2O3, TiO2, and Zr suggests a limited recycling effect.The presence of first cycle mafic-to-intermediate igneous detritus, together with felsic to intermediate igneous and metamorphic minerals, suggest that the Tumaco forearc basin detrital material was supplied by two locations. One location corresponds to the orogenic island arc system of the Western Cordillera, which is dominated by mafic and intermediate extrusive rocks (basalt and andesite). The other source, which is volumetrically less important, is the Central Cordillera, which comprises intrusive felsic rocks and metamorphic rocks (skarn, marble, and quartz-micaceous schist). This subsidiary source represents a continental arc setting and is observed mainly in the Tumaco Formation.

Organic geochemistry of the Early Cretaceous shales, Saar Formation in the East Shabwah oil fields, onshore Masila Basin of eastern Yemen

The early Cretaceous Saar Formation includes potential petroleum-bearing source rocks in the onshore Masila Basin, eastern Yemen. The organic matter input, depositional environment conditions and petroleum generation potential from the Saar Formation shales were investigated using geochemical and organic petrological methods.The shales of the Saar Formation contain total organic carbon of 0.5–3.5 wt percent. The geochemical analysis of the organic matter indicated that these shales have fair to very good hydrocarbon source potential. The kerogen of the organic matter is dominated by Type II/III and Type III, referring to both oil- and gas-prone source rocks. The biomarker and bulk carbon isotope analyses of the organic matter suggested that the kerogens were constituted from a combination of marine and high land plant organic matter, and were preserved under suboxic depositional conditions.The geochemical and petrographic analyses of the shales (e.g., vitrinite reflectance (VRo), pyrolysis Tmax and biomarker maturity ratios) lead to the conclusion that the shales are generally immature to very early mature, particularly in shallower locations where the thermal alteration level of the organic matter is not strong enough to generate petroleum. Therefore, this work suggests that the mature source shale intervals of the Saar Formation existed in the deeper parts of the basin could reach a good maturity level that can produce potential hydrocarbons. Prediction of the potential migration pathways for hydrocarbons produced by deep shales could significantly aid in the future of petroleum exploration in the Masila Basin of Eastern Yemen.

Using soil survey data as a predictive tool for locating deeply buried archaeological deposits in stream valleys of the Midwest, United States

AbstractIn stream valleys of the US Midwest, most of the existing record of prehistoric cultures is deeply buried. Therefore, there is a need for understanding the age and distribution of different landform sediment assemblages (LSAs) in these settings to adequately evaluate the landscape for buried archaeological materials. In this study, we show the applicability of US Department of Agriculture Natural Resources Conservation Service soil survey data to (a) provide information on the spatial distribution and characteristics of different LSAs and (b) determine the associated geologic potential for buried cultural deposits. We considered four factors in our assessment, including the age of sedimentary deposits, soil stratigraphy, depositional environment, and drainage conditions. These data were used to develop a GIS‐based predictive model that was verified with data from a large volume of geoarchaeological research conducted throughout the region. The spatial scale of soil survey data, the uncertain nature of soil mapping, and the ability to detect the presence or absence of buried soils were found to be important limitations. Nevertheless, our results show that soil survey data can be useful as each of the four factors is considered to discriminate particular LSAs and appropriately evaluate buried‐site potential. Our approach can be broadly applied to fluvial systems where cultural deposits are deeply buried, particularly in other countries where soil survey databases exist.

Geochemical characteristics of shales in the Mamfe Basin, South West Cameroon: Implication for depositional environments and oxidation conditions

Field and laboratory studies were carried out with the aim of characterizing the depositional environment and oxidation conditions during accumulation of shales in the Mamfe basin. Field studies denoted that the shales were black to dark grey in color, sub-tabular to tabular in occurrence, with some (n = 20) reacting vigorously with dilute HCl, while others did not (n = 5). Due to the carbonate content of the samples both whole rock dissolution and partial dissolution, using dilute acetic acid to target the carbonate fraction in the samples, were employed. The seven shale-rich units investigated have average whole rock Ni/Co, V/Cr, U/Th and Th/U ratios of 1.68–2.0, 1.13–2.95, 0.24–0.51 and > 2, respectively. PAAS normalized rare earth elements in the whole rock samples display an enrichment of light rare earth elements (LREEs) over heavy rare earth elements (HREEs), middle rare earth elements (MREEs) over HREEs, positive Gd, Eu anomalies, no Ce anomalies, and an average Y/Ho ratio of 29.7 ppm. The carbonate fraction of the samples displays two different REE pattern types. Sites 1 and 6 have typical hat-shaped patterns with extensive MREE enrichment. The other locations are slightly HREE depleted and have weak MREE enrichment with negative Y anomalies. The trace element ratios and the REE patterns of the whole rock and carbonate fractions indicate that the sediments deposited in the Mamfe basin accumulated in non-marine environments. Furthermore, their coloration, MREE enrichment and lack of Ce anomalies in the carbonate fractions infers that the depositional area was in a vegetated, low-land lacustrine setting with limited oxygenation of the sediment, whereas the negative Ce anomalies in the whole rock shale samples is probably due to particulate scavenging of REEs from the fluid during transport. This would require the water to be deficient in Ce and, thus reflect oxidizing conditions in the source area and along the transport system.

Jarosite and Alunite in Ancient Terrestrial Sedimentary Rocks: Reinterpreting Martian Depositional and Diagenetic Environmental Conditions.

Members of the alunite group are precipitated at low pH (<1 to ~4) in oxidizing environments, are unstable in circumneutral conditions, and are widespread on Mars. At Mollies Nipple in Kane County, Utah, USA, jarosite and alunite are abundant as diagenetic cements in Jurassic sandstones. This research characterizes the jarosite and alunite cements with the goal of determining their origin, and tests the hypothesis that jarosite and alunite may be more stable than the current understanding indicates is possible. Previous studies have placed the jarosite- and alunite-bearing caprock at Mollies Nipple in the Navajo Sandstone, but the presence of water-lain deposits, volcanic ash, volcanic clasts, and peloids show that it is one of the overlying Middle Jurassic units that records sea level transgressions and regressions. A paragenetic timing, established from petrographic methods, shows that much of the cement was precipitated early in a marginal marine to coastal dune depositional environment with a fluctuating groundwater table that drove ferrolysis and evolved the groundwater to a low pH. Microbial interaction was likely a large contributor to the evolution of this acidity. Jarosite and alunite are clearly more stable in natural environments than is predicted by laboratory experiments, and therefore, the Martian environments that have been interpreted as largely acidic and/or dry over geologic time may have been more habitable than previously thought.

Facies characterisation of a shallow-water deltaic succession: the Upper Jurassic Wagad Sandstone Formation of Kachchh, western India

AbstractAncient deltaic facies are difficult to differentiate from tidally influenced shallow-marine facies. The Wagad Sandstone Formation of the Wagad Highland (eastern Kachchh Basin) is typified by offshore and deltaic facies with sedimentary characteristics that represent different conditions of hydrodynamics and related depositional processes. The study area, the Adhoi Anticline, constitutes a ~154-m-thick, shale-dominated sequence with progressive upward intercalations of bioturbated micritic sandstone and quartz arenite. Two thickAstartebeds (sandy allochemic limestone), with an erosional base and gravel blanketing, illustrate tidal amplification and high-energy stochastic events such as storms. Sedimentological characteristics document three depositional facies: an offshore, shale-dominated sequence prograding to proximal prodeltaic micritic sandstone and quartz arenite with sandy allochemic limestones, further prograding to mouth bars and abandoned channel deposits. The Wagad Sandstone Formation displays depositional environmental conditions that are dissimilar from those of coeval deposits in Kachchh sub-basins as well as on regional and global scales. This is attributed to a reactivation of the Kachchh Mainland and South Wagad faults which resulted in detachment and uplift of the Wagad block which then experienced prograding deltaic conditions.