Fluvial Facies Research Articles

New interpretation of the Gran Dolina-TD6 bearing Homo antecessor deposits through sedimentological analysis

Gran Dolina is a cavity infilled by at least 25 m of Pleistocene sediments. This sequence contains the TD6 stratigraphic unit, whose records include around 170 hominin bones that have allowed the definition of a new species, Homo antecessor. This fossil accumulation was studied as a single assemblage and interpreted as a succession of several human home bases. We propose a complete stratigraphic context and sedimentological interpretation for TD6, analyzing the relationships between the sedimentary facies, the clasts and archaeo-palaeontological remains. The TD6 unit has been divided into three sub-units and 13 layers. Nine sedimentary facies have been defined. Hominin remains appear related to three different sedimentary facies: debris flow facies, channel facies and floodplain facies. They show three kinds of distribution: first a group of scattered fossils, then a group with layers of fossils in fluvial facies, and third a group with a layer of fossils in mixed fluvial and gravity flow facies. The results of this work suggest that some of these hominin remains accumulated in the cave by geological processes, coming from the adjacent slope above the cave or the cave entry, as the palaeogeography and sedimentary characteristics of these allochthonous facies suggest.

Climate and landscape reconstruction of the Arroyo Chijuillita Member of the Nacimiento Formation, San Juan Basin, New Mexico: Providing environmental context to early Paleocene mammal evolution

The sedimentologic, stratigraphic, and paleopedologic attributes of a laterally continuous outcrop exposure of the basal portion of the lower Paleocene Arroyo Chijuillita Member of the Nacimiento Formation located in the Bisti/De-Na-Zin Wilderness Area was examined to provide paleoenvironmental context for the Puercan North American Land Mammal Age (NALMA) terrestrial ecosystems of the San Juan Basin, New Mexico. The studied outcrop spans the middle and late Puercan (Pu2-Pu3) NALMA, and thus is an ideal location to assess the potential causes of faunal turnover between Pu2 and Pu3. The stratal succession consists of fluvial channel and laterally continuous sandstone and associated fine-grained floodplain deposits, including paleosols that document variability in drainage and maturity. Quantitative and qualitative reconstructions of paleoclimate from paleosols, supplemented by analyses of fossil floras, indicate no change in climate through the studied interval. Further, there is no evidence that regional tectonics relate to changes in depositional environments. Given the lack of evidence for climate change or regional tectonics, and the characteristics of the fluvial facies and the paleosols across the study locality, we interpret the spatial and temporal variability in paleopedologic and sedimentologic characteristics to be the result of autocyclic channel avulsion and migration. Additionally, the stable climatic conditions and lack of tectonic influence between the Pu2 and Pu3 biozones suggest that mammalian turnover is unlikely to have been caused by extrinsic environmental changes (i.e. climate or tectonics) and is instead probably the result of rapid evolution following the K-Pg boundary and/or competition from the migration of new mammalian species into the basin.

Depositional environment reconstruction of the Maragheh Formation, East Azarbaijan, Northwestern Iran

The Maragheh Formation is an important deposit, which yields the savanna-type large mammal assemblage known as the “Pikermian Fauna.” Our high-resolution facies analysis of the interval between the Lower Pumice and the White Tuff demonstrated that debris-flow deposits and paleosols are dominant in the studied sequence. Fluvial channel-fill and small pond facies are the subordinate components in this interval. Most of the channel-fill deposits are interpreted as having been accumulated from ephemeral streams. The wide distribution of the Middle Pumice, the fact that it contains grains with older ages than those of the Lower Pumice, and the presence of “traction carpet” deposits allow the interpretation of the pumice interval as having been deposited from a hyperconcentrated flow probably caused by crater-lake destruction around the peak of Mt. Sahand, which supplied older rocks to the flow. The internal architecture of fluvial channel-fill deposits and the structures of paleosols (rhizoliths, cracks and slickensides: probable Vertic Inceptisols) imply a seasonal climate during deposition of the studied interval. This is consistent with previous environmental reconstructions based on mammal fossils (woodland-dominated savannah) as well as the results of phytolith analysis and δ18O data obtained from northern Iran. However, flood deposits covering the paleosols, showing sheet-like geometry, may not have been affected by large trees on the flood plain: the extent of woodland around the study site appears to have been limited.

Hydrocarbon generation characteristics, reserving performance and preservation conditions of continental coal measure shale gas: A case study of Mid-Jurassic shale gas in the Yan’an Formation, Ordos Basin

Shale gas in nonmarine facies has attracted less interest compared with the marine facies. The Ordos Basin is one of the Jurassic nonmarine continental coal basins in northern China. Several exploration wells have revealed the existence of shale gas resources in the Middle Jurassic Yan’an Formation in this basin. The Yan’an Formation is the coal-measures in this basin, dominated by an intercalation of siliciclasitcs and thick coals, and the shales were mainly developed in the fluvial, lacustrine and lacustrine delta environments. The shales are multi-inerlayered with sandstones and coals, and have an unstable horizontal distribution. characterized by a small thickness of individual layer (ranging between 0.1m and 34.77m), and large thickness of the total cumulative layers (up to 380m). The shales have intermediate to high contents of total organic carbon (ranging from 0.24% to 5.82%) and low thermal evolution degree in an immature-mature stage. The gas is mainly of biogenic origin, with relatively small fraction of thermogenic origin. The mineralogy investigation revealed that the shale have a lower content of brittle minerals and a high content clay minerals. The pore types are dominated by dissolution pores, intergranular pores, intragranular holes and micro cracks, and few organic holes can be seen. The porosity and permeability are low, with significant reservoir heterogeneity. The gas content in this nonmarine shale is low, dominated by adsorption phase. The shale gas in this basin were generally/enclosed within the groundwater flow closure zones, where the groundwater salinity is relatively low. The development characteristics of the shale and shale gas were also controlled by the depositional facies, and the conditions for hydrocarbon generation, reservoir performance, and gas preservation, can be favorably developed in the lacustrine facies, followed by the lacustrine delta facies, while the conditions in the fluvial facies are relatively poor. Although the resource potential of shale gas in the nonmarine continental coal-measures is lower than that of the marine facies, the shale gas, coal, coalbed methane, and tight sandstone gas often coexist in the continental coal basins which may support a more prospect energy scenario. Therefore, comprehensive exploration and collaborative development of the shale gas, coalbed methane and tight sandstone gas in the continental basin may be an ideal way to synthetically utilize the continental coal-measure gases.

Sedimentary response to ignimbrite emplacement across a fluvial–shallow‐marine transition: Ordovician Mweelrea Formation, South Mayo Trough, Western Ireland

AbstractThe Ordovician Mweelrea Formation is part of the basin fill of the South Mayo Trough in western Ireland and records progradation of alluvial facies northwestward across shallow‐ and marginal‐marine Mweelrea ‘passage beds’ to marine Glenummera Formation facies. Early in Mweelrea Formation sedimentation, the first of a series of ignimbrites was emplaced, causing a disruption in this progradation. The preserved thickness of the ignimbrite is up to ca. 12 m, and the sedimentary response varied depending on the environment that was affected. Eastern exposures of the Mweelrea Formation are coarse grained and represent fluvial facies. Emplacement of the ignimbrite caused overlying sediment to become richer in feldspar as well as coarser grained; heavy‐mineral laminations are common here and in many supra‐ignimbrite exposures, but the depositional style was unchanged. The ignimbrite overlies decreasing thickness of fluvial sandstone towards the west to where it directly overlies shoreline and shallow‐marine passage beds. Here, sandstone that overlies the ignimbrite is fluvial, indicating that emplacement of the ignimbrite brought about an abrupt progradation. At the westernmost outcrops of Mweelrea Formation, the ignimbrite lies at the contact with the underlying marine Glenummera Formation. Marine sedimentation continued after emplacement of the ignimbrite, although a coarse conglomerate horizon immediately overlying the ignimbrite together with development of a delta suggests that sediment input was vastly increased. Copyright © 2016 John Wiley & Sons, Ltd.

Composition and Architecture of Braided and Sheetflood-Dominated Ephemeral Fluvial Strata In the Cambrian–Ordovician Potsdam Group: A Case Example of the Morphodynamics of Early Phanerozoic Fluvial Systems and Climate Change

Abstract: Two fluvial facies associations, braided and ephemeral fluvial, are recognized in strata of the Cambrian–Ordovician Potsdam Group in the Ottawa Embayment and Quebec Basin in northeastern North America. Braided fluvial sedimentation was dominated by the migration of coarse-grained sandy dunes and rare unit bars and local gravels that built up low-relief 0.4–5-m-thick downstream-accreting compound bars in very wide and shallow braided channels. Rare meter-scale confluence scours, incision, and filling of decimeter-thick bypass channels, and thin (≤ 7 cm) overbank deposition also occurred. Ephemeral fluvial sedimentation was dominated by the progradation of lobate terminal splays, most of which were deflated and/or reworked into thin (10–95 cm) sheets by eolian processes during the long recurrence intervals between floods. These strata were locally incised by rare, 0.3–1.9-m-thick scour-filling high-energy supercritical bedform strata and decimeter-thick bypass channels. Both braided and ephemeral fluvial deposits consist of meter-scale stacked, high-order stratal units separated by horizontal, laterally extensive surfaces recording the recurring buildup, avulsion, and finally abandonment of channel belts. In braided fluvial strata of the Potsdam the dominance of thin (≤ 2 m) elongated compound bars with low-relief (≤ 5°) bar margins and internal accretion surfaces (≤ 15°) suggest that braided channels and in-channel compound bars expanded laterally with negligible increase in flow depth during periods of increased discharge in the absence of bank-stabilizing vegetation, similar to other examples of the pre-vegetated “sheet-braided” style. However, in areas where bedrock topography inhibited the lateral expansion of channels, thicker compound braid bars (1.2–3.5 m) with higher-relief accretion surfaces (up to 35°), like those observed in post-Silurian and modern systems, preferentially formed in relatively deep channels. Ephemeral fluvial deposits here are similar to ephemeral examples throughout geologic history in that they mostly comprise poorly confined sheet-like terminal splays that accumulated in topographic lows. However, compared to several post-Silurian examples, strata in the Potsdam exhibit considerably more eolian reworking of splays and preservation of supercritical-bedform strata, a manifestation of greater rates of surface-water infiltration due to a lack of sheltering by rooted plants and propensity for unconfined flooding. Finally, in the upper part of the Potsdam two regional ephemeral fluvial units are interstratified with two braided fluvial units, providing evidence for shifts in regional climate. The sharp, areally extensive surfaces that separate these fluvial systems are interpreted to approximate time lines, and therein provide a means for relative and absolute chronostratigraphic correlation. These changes are correlated with documented Late Cambrian to Earliest Ordovician global climate fluctuations, with semiarid conditions and related ephemeral fluvial systems corresponding to global cooling events at ca. 491 and 487 Ma.

The Lower Cretaceous Atzompa Formation In South-Central Mexico: Record of Evolution From Extensional Backarc Basin Margin To Carbonate Platform

Abstract: Lower Cretaceous depositional systems of southwestern Oaxaquia, in south-central Mexico, were influenced by initiation of a continental arc on mainland Mexico and subsequent accretion of the Guerrero composite arc terrane to mainland Mexico. The Atzompa Formation, defined herein, which crops out in the Sierra de Tentzo, constitutes a succession of conglomerate, sandstone, siltstone, and limestone with Early Cretaceous fauna and detrital zircon maximum depositional ages that range 126–123 Ma (late Barremian to early Aptian). The lower part of the Atzompa records a transition from alluvial to deep lacustrine depositional environments, suggesting the early stages of an extensional basin; overlying deposits of anabranching axial fluvial systems that flowed to the NE–SE accumulated after a period of rapid subsidence in the Tentzo basin, also formerly undescribed. Fluvial facies grade up-section to tidal deposits overlain in turn by a carbonate ramp succession that contains late Barremian to early Aptian fossils. The ramp deposits of the uppermost Atzompa Formation are overlain on a sharp contact by basinal carbonates of early Albian age.The Tentzo basin, formed due to crustal extension of the overriding plate in a backarc setting, was characterized by very high rates of sedimentation (3.6 mm/yr) during the early stages of basin formation (rift initiation and rift climax), and slower rates during the development of tidal systems and the carbonate ramp (post-rift stage). Regional and local subsidence took place in the backarc region of the Zicapa magmatic arc, which was established in the western margin of Mexico by Hauterivian time. Abrupt deepening following Atzompa Formation deposition is attributed to flexural subsidence related to collision of the Guerrero composite volcanic terrane with the western margin of Mexico. Following late Aptian accretion of the Guerrero terrane to Oaxaquia, the carbonate basin eventually shallowed to become a carbonate platform that faced the Gulf of Mexico.

Similarity and differentiation between the East China Sea Shelf Basin and Cenozoic basins in the northeast South China Sea

The East China Sea Shelf Basin (ECSSB), the Pearl River Mouth Basin (PRMB) and the Taixinan Basin (TXNB) in the northern continental margin of the South China Sea (SCS) are important oil‐ and gas‐bearing basins on the Western Pacific Continental Margin. During the Paleocene to Late Miocene, their strata can be compared, and the lithofacies were continuous from the TXNB, via the Taixi Basin (TXB) to the ECSSB. The lithologies mainly consist of interbedded shale, sandstone and mudstone layers. In addition, these basins have similar tectonic and sedimentation features. The three basins had similar marine‐terrigenous facies in the Paleocene and marine–lacustrine–fluvial facies during the Eocene and Late Miocene. The basins experienced several coeval tectonic movements and episodes, and they developed a series of NE‐ and NNE‐trending faults during the Paleocene and Eocene, which controlled the structure of the basins. During the Early Oligocene and Middle Miocene, they developed a series of NW‐ and WNW‐trending strike‐slip faults, reverse folds and flower‐like strike‐slip faults. However, there were obvious differences in sedimentary and tectonic evolution since the Late Miocene. The TXNB and TXB developed marine facies after the Late Miocene, while in the Quaternary, open marine facies replaced the Pliocene terrigenous facies in the ECSSB. Since the Late Miocene, the south of the ECSSB developed into a subsidence stage, and fault activity stopped. The TXB and TXNB developed some inverse structures and then developed into a thermal subsidence episode after the Dongsha Movement. Thus, this paper proposes that the ECSSB and the Cenozoic basins in the SCS were originally a unified basin and then subsequently separated into two basins as a result of the indentation of the Philippine Sea Plate (PSP) and the arc–continent collision between the Luzon Arc and the Eurasian Plate. Copyright © 2016 John Wiley & Sons, Ltd.

Sequence development, depositional filling evolution, and prospect forecast in northern Aryskum Depression of South Turgay Basin, Kazakstan

Jurassic to Cretaceous clastic rocks of the South Turgay Basin were deposited in the typical Mesozoic rift basin formed during the late Triassic collision between the Kazakstan and Siberia plates. In this study, we used more than 140 wells and 2400 km2 of 3D seismic data in the northern Aryskum Depression to produce a detailed sequence stratigraphic interpretation of the South Turgay Basin. Guided by sequence stratigraphy, sedimentology, and structural geology, lower Jurassic-lower Cretaceous strata of the northern Aryskum Depression in the South Turgay Basin, Kazakhstan were subdivided into 10 third-order sequences based on geological and geophysical data. Combined with tectonic evolution characteristics, sequence developments in the basin can be divided into four stages: early rift stage (SQ1–SQ3), late rift stage (SQ4–SQ6), fault to depression transition stage (SQ7–SQ8), and depression stage (SQ9–SQ10). Through comprehensive analysis of seismic sequence configuration, sequence stacking pattern, and depositional filling characteristics, we established the depositional model of the Aryskum Depression in the South Turgay Basin. It is indicated that there are differences in depositional compositions of sequences formed in different stages. Four stages can be clearly identified: filling stage of fan delta facies–lacustrine facies (Stage I) corresponding to the rapid filling in the early rift stage, filling stage of fan delta facies–lacustrine facies–normal delta facies (Stage II) corresponding to trichotomous characteristics of internal systems tracts in the late rift stage, filling stage of braided river delta facies–normal delta facies–lacustrine facies (Stage III) corresponding to the development of high-stand systems tracts in the fault to depression transition stage, and filling stage of fluvial facies–normal delta facies–lacustrine facies (Stage IV) corresponding to binary characteristics of internal systems tracts in the depression stage. Finally, optimization of favorable exploration strata and prospects in the Aryskum Depression are proposed.

Lateral accretion of modern unvegetated rivers: remotely sensed fluvial–aeolian morphodynamics and perspectives on the Precambrian rock record

AbstractModern unvegetated rivers flowing through aeolian-dune fields demonstrate potential as analogues for pre-vegetation fluvial landscapes. A prominent example is contained in the Lençóis Maranhenses of Brazil, a coastal aeolian system hosting the semi-perennial Rio Negro. Remotely sensed images covering c. 45 years display the rhythmic expansion and wind-driven shift of single-threaded and sinuous fluvial trunks alternating with wider braided plains. Sinuous tracts feature mid-channel and bank-attached bars, including expansional point bars with subdued relief. The morphology, accretion and sediment transport of unvegetated point bars in the Rio Negro are compared to the morphodynamics of vegetated meandering rivers. Unvegetated point bars are composed of large coalescent unit bars, lack apparent scroll topography and are preferentially attached to channel banks located on the windward side of the river course. Unvegetated meanders have expansional behaviour related to downwind channel trailing. Point bars maintain an expansional planform despite spatial confinement induced by aeolian dunes. Channel-flow impingement onto cohesion-less banks favours scouring of deep pools along the bar tails, which host bank-collapse deposits subsequently reworked into new bars. Analogies to Precambrian rivers suggest that ancient unvegetated fluvial landscapes were not unequivocally featured by low sinuosity, especially if characterized by a low gradient and stable discharge. This inference is supported by ongoing studies on Proterozoic fluvial–aeolian systems in the Canadian Shield. Lack of scroll topography introduces overlap with low-sinuosity fluvial facies models, underscoring the value of observing ancient fluvial deposits in planform, or along 3D sections where the palaeodrainage of channel bodies and attached bars can be compared.

The magnetic properties of sediment and sedimentary environment in the Huanghe Delta area after the last glacial maximum

On the basis of measuring the magnetic parameters of sediment in Core YDZ1, combined with a grain size analysis and Carbon-14 dating, the magnetic properties of sediment and sedimentary environment in the Huanghe (Yellow River) Delta area after the last glacial maximum have been studied. The results show that the ferrimagnetic minerals of a pseudo single domain and multi domain particles dominate the magnetic properties of sediment in Core YDZ1. The imperfect anti ferrimagnetic minerals have more contribution on sediment in a depth of 24.0–22.1 m, and more stable-single domain and pseudo single domain particles exist. The susceptibility of anhysteretic remanent magnetization and the ratio of the susceptibility of anhysteretic remanent magnetization to saturation isothermal remanent magnetization show a decrease trend below depth of 24 m, a marked increase trend in a depth of 24.0–13.5 m, and a rapid decrease at depth of 13.5 m, then a fluctuation trend upward. The above two magnetic parameters and the ratio of the susceptibility of anhysteretic remanent magnetization to the mass susceptibility can be regarded as the proxy indicators for the content of clay (<4 μm) and the fine-grained size (<32 μm). The sedimentary environment after the last glacial maximum in the Huanghe Delta area has experienced the fluvial facies, the tidal flat facies, the neritic facies, the pro delta facies, the delta front facies and the floodplain facies. Thickness of the Holocene transgression layer is 10.5 m and the depth of substrate is about 24 m according to the YDZ1 core. The sedimentary dynamic has a variation trend with strongweak- strong, which has been proved by the Flemming triangular schema.

Sedimentary response to the intracontinental orogenic process: insight from the anatomy of a small Mesozoic basin in western Yanshan, northern North China

ABSTRACTThe intra-continental orogeny and tectonic evolution of the Mesozoic Yanshan fold-thrust belt (YFTB) in the northern North China Craton (NCC) have been strongly debated. Here, we focus on the Shangyi basin, located in the centre of the YFTB. An integrated analysis of sedimentary facies, palaeocurrents, clast compositions, and detrital zircon dating of sediments was adopted to determine the palaeogeography, provenance, basin evolution, and intra-continental orogenic process. The Shangyi basin comprises the well-exposed Early–early Middle Jurassic Xiahuayuan Formation and the Longmen Formation, and the Late Jurassic–Early Cretaceous Tuchengzi Formation. Based on the 18 measured sections, five facies associations – including alluvial fan, fluvial, delta, lacustrine, and eolian facies – have been identified and described in detail. The onset of the Shangyi basin was filled with fluvial, deltaic, and lacustrine deposits controlled by the normal fault bounding the northern basin, corresponding to the pre-orogeny. In the Middle Jurassic, the cobble–boulder conglomerates of alluvial fan, as molasse deposits, were compatible with the syn-orogeny of the Yanshan movement, which played a critical role in northern North China and even East Asia. After the depositional break in the Middle–Late Jurassic, the Shangyi basin, controlled by the normal fault present in the north of the basin, re-subsided and quickly expanded southward with thick sedimentation, which is correlative with the post-orogeny. Combined with A-type granites, metamorphic core complexes, mafic dikes, and rift basins of the Late Jurassic–early Early Cretaceous present in the northern NCC and Mongolia, significant extension was widespread in the northern NCC and even in northeast Asia. Moreover, vertical changes of provenance indicate that the Taihang Mountain and the Inner Mongolia palaeo-uplift (IMPU) present at the west and north of the basin, respectively, experienced uplift twice in the Middle–Late Jurassic and Early Cretaceous, resulting in a regional depositional break.

Climatic and tectonic controls on Late Triassic to Middle Jurassic sedimentation in northeastern Guangdong Province, South China

Stratigraphic analyses document climatic and tectonic controls on the filling of a Late Triassic to early Middle Jurassic (T3–J2) basin that developed on top of a young orogenic belt in southeastern South China. About 2700m of Carnian to Bajocian sedimentary rocks is documented in the Meizhou region, Guangdong Province. The Carnian to Rhaetian sequence is characterized by deltaic facies that are succeeded by Hettangian fluvial, shallow marine and volcaniclastic facies, and by Sinemurian to early Toarcian interdistributary bay and floodplain facies. The late Toarcian to Bajocian sequence comprises proximal alluvial to lacustrine facies that changed upwards to fluvial facies. Fossil assemblages indicate that climatic conditions changed from tropical/subtropical warm humid, to temperate humid, and then to hot arid through the Late Triassic to the Middle Jurassic. Climatically induced changes (e.g., in precipitation, vegetation and erosion) exerted a strong influence on sediment supply, whereas tectonics played a dominant role in stratigraphic evolution, accommodation generation, sedimentation pattern and volcanism. Tectonostratigraphic analysis shows that the T3–J2 basin was initiated on an orogenic belt during late-stage orogeny, and evolved into shallow-marine and volcanic environments and then back to terrestrial facies during the post-orogenic stage. This was followed by regional uplift and the development of a basin-and-range province. The order of these events is similar to that of the central Rocky Mountains, western North America during the Palaeogene. The Mesozoic basin of South China and the Eocene basins of the central Rocky Mountains highlight the importance of subduction-related subsidence above young and broad orogens.

Seismites in Permian Barakar Formation, Raniganj Basin, India: implications on Lower Gondwana basin evolution

Fault-bound half-graben-type Raniganj Basin in eastern peninsular India hosts thick sedimentary succession of the coal-bearing Barakar Formation (Early Permian), which constitutes a part of the Lower Gondwana Supergroup. Sedimentological attributes of the upper Barakar succession are portrayed in two predominant facies associations, viz., (i) the lower part characterized by meandering fluvial facies association with distributary channel systems and (ii) the upper part represented by a transgressive, tide-wave-influenced, fluvio-estuarine facies association. Distinct beds with various soft-sediment deformation structures (SSDSs) manifesting paleoseismic events are reported as seismites from the upper Barakar succession. The SSDSs include convolute laminae, complex deformations with folded strata, syn-sedimentary growth faults, pseudonodules, loop bedding, and various water-escape structures including sand–silt flows/dikes. The seismites are restricted at two distinct stratigraphic horizons (S1 and S2) within the upper Barakar succession, separated by undeformed beds in between. The seismites record episodes of paleoearthquake events triggered by syn-sedimentary reactivation of basin marginal faults in the half-graben-type Raniganj Gondwana Basin. These demarcate phases of significant shift in the depositional conditions from fluvial-dominated to a transgressive tide-wave-influenced estuarine system, caused by post-glacial basinal adjustments in the peninsular Indian Gondwanaland.

Conchostracans in continental deposits of the Zechstein–Buntsandstein transition in central Germany: Taxonomy and biostratigraphic implications for the position of the Permian–Triassic boundary within the Zechstein Group

The end-Permian mass extinction marks the largest biotic crisis in the geologic record. The stratigraphic position of this boundary in continental deposits is still under discussion. In the present study, conchostracans from the Zechstein–Buntsandstein (Late Permian to Early Triassic) transition in central Germany have been taxonomically reinvestigated in order to better understand their utility for fine-scale biostratigraphy in continental Permian–Triassic boundary sections. The studied material was obtained from both collections and recent sampling activities in classical key sections and new outcrops of the Zechstein and Buntsandstein Groups. The sedimentary environments of the conchostracan occurrences are interpreted as lacustrine to fluvial facies depending on the paleogeographic position within the basin of the respective sections. The conchostracan fauna in the Zechstein–Buntsandstein transition consists of Euestheria gutta, Palaeolimnadiopsis vilujensis, Cornia germari, Estheriella marginostriata, Estheriella costata, Estheriella nodosocostata, Magniestheria mangaliensis, and Euestheria nordvikensis. Based on comparison with the Early Triassic conchostracan record in the Moscow syncline, the Palaeolimnadiopsis vilujensis–Euestheria gutta association in the upper part of the Fulda Formation indicates both its Early Triassic age and a position of the continental Permian–Triassic boundary within the Zechstein Group.

Applications of 3D seismic attribute analysis in hydrocarbon prospect identification and evaluation: Verification and validation based on fluvial palaeochannel cross-sectional geometry and sinuosity, Ness County, Kansas, USA

Due to their high resolution and established success rates, the analysis of geometrical and stratigraphic 3D seismic reflection data attributes have become one of the most important tools in many hydrocarbon exploration and development programs. In areas with high drilling risk as a result of the lack of spatial continuity and lithological variation of potential prospects, analysis of relevant seismic attributes is essential to successful placement of wells. This study of the York field, Ness County, Kansas, presents a corroborative finding, based on the analysis of a set of 3D seismic attributes, revealing a meandering fluvial channel system incised on the Mississippian stratigraphic unconformity north east of a previously interpreted Weirman field palaeoshoreline and submarine channels. The York field prospect identification and appraisal program targeted the Cherokee sands where reservoir properties are favorable and where it was thought that thick Cherokee sands correlate with structural Mississippian highs. We produce evidence that Cherokee sand-prone fluvial facies is mappable based on synergistic analysis of seismic arrival time, amplitude, spectral decomposition, acoustic impedance, and waveform attributes. Seismic amplitude highs and relative acoustic impedance lows showed moderate conformance with Mississippian-horizon time lows. Controls exerted by channel post-confluence water and sediments supply provide corroborating hydraulic geometry aspects for the interpreted fluvial system.Time-structural maps, in addition to time and horizon slices of several 3D seismic attributes including amplitude, spectral decomposition components, and relative acoustic impedance all seem to indicate that five previously drilled dry wells within the study area were outside the boundary of a meandering, Cherokee fluvial system of potential reservoir quality. Additionally, comparisons of the results of this research to previous studies conducted in the south west of Ness County have provided an opportunity to support and contribute to, interpreted paleodepositional setting established by Raef et al, 2015 where a palaeoshorline was interpreted. The results of this study support a broadly NE–SW trending meandering channel system with SE flow direction.

A Middle Pleistocene intense monsoonal episode from the Kapthurin Formation, Kenya: Stable isotopic evidence from bovid teeth and pedogenic carbonates

Carbon and oxygen isotope values of bovid tooth enamel and pedogenic carbonates were used to reconstruct the paleoenvironments associated with Middle Pleistocene archeological and paleontological sites from the Kapthurin Formation, Kenya. Fossil teeth and pedogenic carbonates were collected from lacustrine and fluvial facies (K3 and K3’) of the Kapthurin Formation (~543–509ka). Twenty teeth from six bovid tribes and twenty four pedogenic carbonates were sequentially sampled for stable oxygen and carbon analysis. The primary aims of this work are to reconstruct the vegetative habitats of bovids and environmental landscapes from the Kapthurin Formation, assessing the presence of C3, C4, or mixed vegetation and foragers. We also assess general paleoclimate factors, such as overall aridity, seasonal shifts in water availability, and broad habitat reconstructions. Carbon isotope values suggest a wide range of foraging strategies were available to bovids, and are characterized by both C3 dominated and C4 dominated diets, with little evidence for mixed feeders, while pedogenic carbonates suggest the landscape combined a mix of C3 and C4 vegetation sources, structurally similar to wooded grasslands. Paleoclimatic conditions, based on the reconstructed mean annual water deficit from δ18Oenamel values suggest a hyper mesic environment, most comparable to the modern Ituri rainforest, indicating a much wetter climate than the modern Lake Baringo Basin. This environment coincides with an intensified Middle Pleistocene African monsoonal system at the onset of Marine Isotope Stage 13 (~533ka). The Middle Pleistocene Lake Baringo regional habitat appears to have been one dominated by woodland areas, perennially active streams, marsh and sumpland environments, and a surrounding grassland ecosystem. This lush basin would have provided hominins with a diverse and productive ecosystem. Perhaps not surprisingly, archeological sites are found in all habitats, including wet, forested, and grassland environments.

Fluvial facies reservoir productivity prediction method based on principal component analysis and artificial neural network

Abstract It is difficult to forecast the well productivity because of the complexity of vertical and horizontal developments in fluvial facies reservoir. This paper proposes a method based on Principal Component Analysis and Artificial Neural Network to predict well productivity of fluvial facies reservoir. The method summarizes the statistical reservoir factors and engineering factors that affect the well productivity, extracts information by applying the principal component analysis method and approximates arbitrary functions of the neural network to realize an accurate and efficient prediction on the fluvial facies reservoir well productivity. This method provides an effective way for forecasting the productivity of fluvial facies reservoir which is affected by multi-factors and complex mechanism. The study result shows that this method is a practical, effective, accurate and indirect productivity forecast method and is suitable for field application.

Paleo-environmental evolution based on high-resolution phytolith since 26 ka B. P. in Huanghe River Delta

The Huanghe River Delta is one of the world's large rivers, the Huanghe River Delta paleoenvironmental evolution in the Huanghe River has been a hot issue since the Last Glacial. Based on the core time series established by combining AMS 14C dating of Core DYZK1 sediments in submerged of Huanghe River Delta and acoustic sequence on sub-bottom profile, phytolith analyses are carried out on 96 sediment samples. The grain size parameters, magnetic susceptibility are combined with the vertical changes of biostratum to reconstruct the paleo-sedimentary and climatic conditions in the Huanghe River Delta. The study results show that there is a significant vertical change law in the index parameters, and that sedimentary environment of Huanghe River Delta experienced an evolutionary process of fluvial facies-sealand transition facies-tidal flat facies-neritic faciesdelta facies since 26.0 ka B. P.. The phytolith analyses results are as following. Firstly, The phytoliths are divided into lanceolate, smooth-elongated, spiny-elongated, rondel, long rectangular, bulliform and other types. In different sedimental environment, the phytolith content changes regularly, indicating that the phytolith assembles in the same sedimentary environment has a certain degree of stability. Secondly, The lanceolate, smooth-elongated and spiny-elongated categories of phytoliths have greater contents in the tidal flat facies and delta deposition, while have a smaller contents in the neritic facies and fluvial facies environment. Thirdly, Through comparative analysis of variation coefficient, the content of major phytolith categories in the sediment has a greater change amplitude in the sealand transition facies and fluvial facies deposition, while being more stable in the tidalflat facies and delta facies deposition.

Seismic Stratigraphy and Development of Deep Fluvial Channel Incisions in the Middle Miocene Deposits, Ewan and Oloye Fields, Northwestern Niger Delta, Nigeria

Seismic interpretation of depth converted three-dimensional seismic survey from Ewan and Oloye fields; onshore northwestern Niger Delta has helped in the identification of incised valleys (up to 350 m) deep. This study evaluated their morphologies, evolution and the local controls that influence their development. The seismic reflections of the incised valleys are characterized by low-moderate amplitude, variable internal reflections, aggradational, chaotic and progradational-sigmoid reflection patterns overlying by parallel to sub-parallel reflections configuration. The seismic reflection characteristics are probably due to variable sedimentation processes within the valleys which were affected by mass wasting. Asymmetry morphology of the valleys suggests fluvial origin while low sinuosity of the channel may indicate high gradient and high discharge. The occurrence of incised valleys landward of the shelf edge suggests and partially reflects underlying structural control. This might be caused by uplift due to shale diapirism (shelf instability). The magnitude of incision is difficult to explain in terms of sea-level fall alone because ecstaticallydriven sea level variations during the Miocene are generally reported to be less than 100 m. This suggests that the character of fluvial incisions development and depositional facies preserved within the study area is locally controlled by growth faults, rapid relative sea level changes, basin physiography (shelf edge), shelf instability, variation in sediment input, slope collapse (mass flow depositional processes and downward cutting by downslope sediment flow). The incised valleys within the study area probably serve as conduits for sediment transport to the deep water. Seismic delineation of the distribution and morphology of these incised valleys may also provide critical input for reservoir modeling and volumetric analysis.