Sedimentary Units Research Articles

Geologi Daerah Buyat Dan Sekitarnya, Kecamatan Kotabunan, Kabupaten Bolaang Mongondow Timur, Provinsi Sulawesi Utara

This research focuses on the eastern part of the northern arm of Sulawesi to understand the geological conditions, including geomorphology, lithology, stratigraphy, and geological structure. The goal is to determine the geological history and map the geological conditions to identify potential mineral resources. The research methods include a qualitative approach through field observations such as morphology, outcrop descriptions, lithology, geological structure measurements, stratigraphic relationships, as well as an inventory of natural resources and geological disaster risks. The quantitative approach involves calculations and analyses, including geomorphological analysis, petrography, paleontology, geological structure, stratigraphy, and the reconstruction of geological history. The research results identify four geomorphological units (karst, denudational, volcanic, alluvial) and six geological units at the research site. Andesite and volcanic breccia are the oldest units dating back to the Miocene. At the end of the Miocene, uplift and subsidence formed intrusive hills of diorite and limestone. Volcanic activity ceased in the Miocene. In the Pliocene, sandstone formed due to river transport. The rock formation process continues to the present, with alluvial deposit units resulting from the breakdown of rocks around the lake. Geological structure analysis reveals fault lines with the main stress direction from northwest to southeast. Relative fault data indicates fault inclination values suggesting the main stress direction is northwest-southeast. The geological history in the research area began in the Miocene with magmatism and tectonic activities, forming andesite and volcanic breccia units. This history extends to the formation of alluvial deposit units in the present. The research provides in-depth insights into the geological history and potential mineral resources in the region, serving as a foundation for further research.

Paleoenvironmental changes during the Late Pleistocene in Buenos Aires province (Argentina), using foraminifera fauna as proxy data

This paper describes the lithological and micropaleontological characteristics of a new record corresponding to the last interglacial for Buenos Aires province. Foraminifera were analyzed from an artificial outcrop 4 m thick (36°34′0.97″ S and 57°22′54.43″ W), from the quarry situated in the town of General Conesa, Buenos Aires province at an approximate elevation of 4 m a.s.l. Benthic foraminifera fauna was constituted by a predominance of calcareous forms represented mostly by the species Buccella peruviana and Ammonia parkinsoniana. The micropaleontological and lithological characteristics of all the sedimentary units involved in this locality suggest deposits associated with a transition from a low-energy shallow intertidal or subtidal zone to a higher-energy beach or supratidal environment. Although, the topographic height does not enable conclusive assignment of the age of this coastal deposit (>79.500 kyr), the environmental conditions could be correlated with the penultimate transgressive event that occurred at the beginning of the Late Pleistocene (MIS 5), which would have occurred in a shallow environment with changes in the marine influence. These findings provide new information that contributes to better understanding of the paleoenvironmental evolution of this region where two marine transgressions and two wind deposits have been recognized.

A Novel VS30 Prediction Strategy Taking Fluid Saturation into Account and a New VS30 Model of Türkiye

ABSTRACT The averaged shear-wave velocity of the top 30 m (VS30) is widely used in earthquake engineering as a proxy to represent site responses. However, the spatial availability of measured VS30 is rather limited, and, so far, a region-specific VS30 model that would aid prediction of strong ground motions is not yet developed for Türkiye. In this study, a new strategy for predicting VS30 is developed using data from Türkiye and California. At first, VS30 measurements are classified into four sedimentary classes according to their ages (Quaternary–Pliocene, Miocene, Paleogene, and Pre-Paleogene) and three nonsedimentary classes (Intrusive, Extrusive, and Metamorphic). Observations from Quaternary–Pliocene deposits are most abundant and characterized by large data scatter, thus further divided into two major landform groups. Because the reduction of VS with saturation is pronounced in soils due to capillary forces, Quaternary–Pliocene deposits are also differentiated as wet if the water table depth is less than 30 m and dry otherwise. In California, available groundwater measurements are utilized while flat areas with elevation differences less than 30 m from water bodies (sea, lake, and major rivers) are mapped out as wet zones throughout Türkiye. After the elimination of outliers, slope and elevation-based VS30 prediction equations are developed separately for subclasses of Quaternary–Pliocene, Miocene, and Paleogene-aged sedimentary units using multivariable linear regression, whereas VS30 values of Pre-Paleogene sedimentary and nonsedimentary units are fixed to the mean of each subclass. Resultant model misfits and comparisons with measurements from the microzonation study conducted across İstanbul clearly indicate that our proposed VS30 prediction strategy is performing better than the competing models tested, especially in the youngest sedimentary units, and thus provides a new, accurate VS30 model of Türkiye.

New frog crabs (Brachyura, Raninoidea) from the early Maastrichtian of Paredón (Coahuila, NE Mexico)

We report several raninoid specimens collected from the lower Maastrichtian Lower Siltstone Member of the Potrerillos Formation (Difunta Group), NE Mexico. These specimens were collected from fine-grained sandstones that crop out at the NE edge of the Parras Basin, Coahuila. This outcrop is very close to a structural feature that has been active since Late Jurassic times (San Marcos Fault) and has affected depositional lithostratigraphic units from the Upper Jurassic to Upper Cretaceous. The studied specimens are assigned to Bournelyreidus paredonensis n. sp. (Lyreididae Guinot, 1993) and Coahuilanina difuntaensis n. gen., n. sp. (Raninidae de haan, 1839). A new subfamily, Coahuilanininae is described to accommodate the new genus and species, Coahuilanina difuntaensis. The new frog crabs represent the first formally described raninoids from the lower Maastrichtian portion of Difunta Group, adding to an already diverse assemblage of raninoids from Mexico.

Quartz Grain Microtextures in the Paleogene Sosnov Formation: Implications for Sediment Provenance in the Eastern Russian Platform

The purpose of the research. The chief task of the research is to examine the microtextures of quartz grains in the Paleogene Sosnov Formation, which is a sedimentary unit located in the Ulyanovsk-Syzran Volga Region of the Russian Platform. By examining the microtextures, which include mechanical, chemical and mechanical/chemical features, it becomes possible to find out the mechanisms by which grains were transported and subsequently modified. The relevance of the research. The relevance of this research lies in the fact that the analysis of quartz grain microtextures provides valuable insights into sediment provenance of sedimentary deposits is crucial for reconstructing past geological environments and unraveling depositional histories. Research methodology. Twenty quartz grains were collected from sands of the Paleogene Sosnovka Formation, exposed by the Eastern-Tashlinsky and the Kuchurovsky quarries to a depth of 5 and 7.5 m, respectively. The research methodology involved scanning electron microscopy (SEM) to investigate the microtextures of quartz grains. Results and conclusions. The study reveals 19 microtextures types, which were categorized into mechanical, chemical, and combined mechanical/chemical microtextures. An analysis of SEM indicated that chemical microtextures are present in the Paleogene Sosnov Formation, which made it possible to suggest that the sands passed through a low-energy phase during their transition. The data obtained enables us to reconstruct the diverse depositional paleoenvironments, including eolian, subaqueous, mixed subaqueous-eolian, and pedological settings.

Evaluasi Aspek Teknis Kualitas Air Membran Ultrafiltrasi dalam Pengolahan Air Minum (Studi Kasus: IPA Krian Perumda Air Minum Sidoarjo)

The Sidoarjo Regional Public Company (Perumda) is a regionally owned business entity that participates in managing and providing clean water which will be distributed to the people of Sidoarjo Regency. The Sidoarjo Drinking Water Company, especially the Krian IPA, uses the main channel to supply raw water from the Mangetan Canal which passes through seven sluice gates to irrigate 17,583 Ha of rice fields. The series of air treatment installations at Perumda Air Minum Sidoarjo are coagulation units, flocculation units, sedimentation units and ultrafiltration membranes. However, not all technology can be implemented optimally due to considerations of costs and Perumda personnel. The problem is that the ultrafiltration membrane unit at Perumda Air Minum Sidoarjo is not activated. Therefore, the aim of the research is to determine the ineffectiveness of ultrafiltration membranes at Perumda Air Minum Sidoarjo in terms of technical aspects, namely the quality of water resulting from membrane processing in 2016-2020. The results of the research on the technical aspect, namely data on water quality parameters for turbidity and color for 2016-2020, have complied with Minister of Health Regulation Number 2 of 2023 for drinking water quality standards, the rejection percentage for turbidity parameters was 69.39%. - 95.48%; the percentage of color parameter rejection was 43.60% - 61.6% with the resulting flux value decreasing.

End-Mesoproterozoic (ca. 1.08 Ga) epeiric seaway of the Nonesuch Formation, Wisconsin and Michigan, USA

Abstract The Nonesuch Formation and related sedimentary units of the Oronto Group, southern Lake Superior region, midwestern United States, are commonly held to have been deposited in a lacustrine rift basin within interior continental Laurentia. Here, we present new sedimentologic and stratigraphic evidence that shows a marine influence on deposition. Tidally influenced shallow-marine sandstone and evaporitic, sandy and muddy tidal flat facies pass upward into fine-grained estuarine and sandy turbidite deposits, which are sharply overlain by mixed sandy and muddy tidal flat and floodplain deposits. These observations are evidence that the lower Oronto Group was deposited in an epeiric seaway, one of several such seaways that developed during the final amalgamation of Rodinia at a time of globally high sea level. Retrogradational-aggradational-progradational-degradational stratal architecture records changes in the relative balance between generation of accommodation space and sedimentation rates, which we interpret to reflect the combined influence of Grenvillian Ottawan phase tectonic subsidence and thermal subsidence from earlier Midcontinent Rift magmatism. We use this revised stratigraphic framework to show that the geochemical proxies of the Nonesuch Formation are tied closely to sedimentary facies and reflect intrabasinal redox heterogeneity rather than global anoxia at the end-Mesoproterozoic. Further, our sedimentology shows that the microfossils recovered from the Nonesuch rocks are primarily associated with tidal flat facies. The combined influence of marine and local nonmarine conditions must be considered when invoking the Nonesuch Formation, or similar marine-influenced interior basin deposits, as global analogues.

Arc Sediments are a Major source of Juvenile Sr in the Northern Cordillera's Taku River Basin: Potential Implications for the Global Sr Cycle

Dendritic network models have proven valuable in predicting variation in strontium concentrations [Sr] and isotope ratios (87Sr/86Sr) across large river systems. These models also support inference about sources and processes controlling Sr fluxes from such systems, although this capacity has not been exploited in previous work. Here, we apply these methods to model [Sr] and 87Sr/86Sr values of a large river draining accreted volcanic arc terranes of the northern Cordillera of North America. The [Sr] and 87Sr/86Sr river models have excellent fit to measured river waters with RMSE = 0.05: r2 = 0.67 and RMSE = 0.0004: r2 = 0.87, respectively. The results strongly indicate that mixed siliciclastic sedimentary units dominate the Sr weathering flux within these systems. Extrapolation using global arc sediment distributions suggests arc sedimentray units could source ∼30% of the modern riverine Sr flux, constituting a major source of juvenile Sr to the ocean. Because the weathering of arc sediments can lag arc growth and may persist over 100's of millions of years, we suggest that the preservation and accretion of mixed siliciclastic units formed in these settings should be considered when scaling arc weathering contributions through geologic time. Contributions from such sediments could amplify or smooth the arc-derived rock weathering and 87Sr/86Sr flux over long timescales, altering interpretations of biogeochemical cycles and the silicate weathering feedback.

Characterizing the Seafloor Sediment Layer Using Teleseismic Body Waves Recorded by Ocean Bottom Seismometers

AbstractThis study presents an approach to better characterize the P‐wave and S‐wave velocity structure of the seafloor sediment layer using ocean bottom seismometers. The presence of low‐velocity seafloor sediment layers influences the observed seismic record at the seafloor over a broad frequency range, such that detailed knowledge of this sediment structure is essential to predict its effect on teleseismic records. We use the radial component of teleseismic P waves and autocorrelation functions of the radial, vertical, and pressure components of teleseismic P and S waves to obtain sediment layer models using the Markov chain Monte Carlo approach with parallel tempering. Synthetic tests show that the body waves constrain the P‐ and S‐wave impedances and travel times and the P‐ to S‐wave velocity ratio of the sediment layers. The proposed method resolves thin layers at a high resolution, including the uppermost thin (∼50 m to a few hundred meters) low S‐wave velocity layer. Real data applications at sites across the Pacific Ocean that are coincident with previous in situ studies demonstrate the effectiveness of this method in characterizing the seafloor sediment unit. The sediment models characterized by this new approach will allow us to more accurately predict and correct the effects of sediment layers in generating P‐ and S‐wave reverberations.

KAOLIN FORMATION IN YATAĞAN (MUĞLA) LIGNITE DEPOSIT

The 30-km-long and 10-km-wide, coal-bearing Yatağan Basin is located in SW Anatolia, close to the eastern coast of the Aegean Sea, Türkiye. The basement consists of Menderes Massif metamorphics in the NW part of this intermontane basin, c. 80-km2-large area (Turgut lignite deposit). The Neogene and Quaternary sedimentary filling comprises fluvioterrestrial, limnic and telmatic sediments which contain a mineable coal seam up to 15 m thick, unconformably overlain the basement. Two fresh and six weathered samples were picked up from the Menderes Massif gneiss outcrops of the catchment area. Eight sedimentary rocks, inorganics over and underlying the coal seam, were obtained from four borehole cores. All samples were examined under the optical microscope; XRD, SEM-EDX and ICP-MS analyses were later performed. This study aims to examine the mineralogical content and geochemical processes of the sedimentary rocks from different formations, namely Sekköy and Turgut Formations, which are over- and underlying the lignite horizon, to assess the clay mineral formations and transformations. Gneiss samples contain mainly quartz, plagioclase, K-feldspar, muscovite and biotite with a lesser amount of tourmaline, chlorite, garnet, apatite, zoisite, zircon and Fe-oxides. The -2 µm fraction consists mainly of illite, with fewer smectite and kaolinite. Sericitizitation of feldspar is the main product in gneisses. Coal over-and underlying sedimentary rock samples contain mainly quartz, plagioclase, K-feldspar, muscovite, and biotite with less pyrite and iron oxides. The -2 µm fraction of the sedimentary rock samples consists of variable clay mineral contents. Kaolin content is higher in acidic conditions with an opposite correlation to smectite occurrences. The geochemistry of Menderes Massif gneisses shows that it gave felsic material to the catchment area, whereas the geochemistry of sedimentary rocks is not coherent in all cases. Geochemical parameters like CIA and PIA proved that weathering processes of the source materials prevailed during the generation of these sedimentary units.

Diffusion of HTO, 36Cl and 22Na in the Mesozoic rocks of northern Switzerland: I. Effective diffusion coefficients and capacity factors across the heterogeneous sediment sequences

Argillaceous rocks are currently being examined worldwide as potential host rocks for repositories for radioactive waste and spent fuel due to their favourable characteristics such as the self-sealing ability or limited diffusive transport of fluids, solutes or gases. In this study, through-diffusion experiments focused on rock samples with different mineralogical compositions taken from deep boreholes in the Mesozoic rock sequence of northern Switzerland, to determine diffusion parameters of HTO, 36Cl− and 22Na+ perpendicular to the bedding plane. Both effective diffusion coefficients and accessible porosities were calculated from the data obtained. In the Opalinus Clay, the primary selected host rock of the repository, the effective diffusion coefficients (De) and accessible porosity values (ε) of the neutral species HTO within and across all study areas are relatively consistent (De = 8.8 ± 1.9 × 10−12 m2 s−1; ε = 0.12 ± 0.02), indicating that the material can be considered homogeneous in terms of diffusion properties. Importantly, the chemical composition of the pore water has no effect on the values of the effective diffusion coefficients of HTO. On the other hand, the rocks above and below the Opalinus Clay, up to the next aquifer, consist of tight sedimentary units (carbonates, siliciclastics including argillaceous rocks) with a wider range of diffusion coefficients, indicating a higher level of heterogeneity. The diffusion coefficients of anions, such as 36Cl−, tend to be smaller due to anion exclusion effects, while those of cations, such as 22Na+, tend to be larger due to surface enhanced diffusion. The extent of these effects is largely determined by the composition of the pore water, and – in the case of cations – by the extent of sorption which depends also on the sorption capacity – indicated by the cation exchange capacity - of the solid. As a result, variations in the effective diffusion coefficient of 36Cl− and 22Na+ can be observed firstly between different rock types (i.e. composition, fabric), and secondly between the different study areas due to differences in the chemical composition of the pore waters in contact with the solid phase.Based on the analysis of around 130 samples, it has been observed that the diffusion coefficients of the Mesozoic units in northern Switzerland exhibit a significant correlation with the total clay content of the rocks. These findings pave the way for the establishment of a diffusion database for the relevant elements under consideration in the Swiss radioactive waste programme and the Safety Case.

The pyramid builders' waterways: Reconstructing the ancient topography of Khufu’s Pharaonic Harbour at Giza, Egypt

This article describes the location and sedimentary environments of the Khufu harbour in Giza, Egypt, with the aim of reconstructing its palaeoenvironmental evolution during the Old Kingdom (2686–2160 BCE). We use chronostratigraphy and sedimentology to elucidate the site’s Holocene sedimentary units and compare and contrast the results with previous studies. Our research provides new insights into the palaeogeography of the Giza floodplain during the 4th Dynasty (2613–2494 BCE), including its impacts on the settlement patterns and cultural practices of the ancient Egyptians and their interactions with the natural environment. The findings provide valuable information for understanding the history and archaeology of the Giza area and contribute to ongoing efforts to preserve and interpret the cultural heritage of ancient Egypt.

Seismic slip zone characteristics in near-surface unconsolidated sediments: Low-angle reverse paleo-rupture in Central Korea

Fault materials and deformed sediments formed by coseismic rupturing events in the near-surface region show various deformation characteristics. To gain insights into rupture propagation and termination processes close to the surface, we analyzed the slip zone and deformed sediments/granite of a paleoearthquake rupture in central Korea. Here, we list our structural and mineralogical findings of the low-angle reverse rupture. (1) The slip zone mainly contains microbreccia and intercalated illuvial clay. The kaolinite-rich illuvial clays migrated downward with water, accumulate in spaces, and have a distinct texture and color. They show strong alignments and injection structures indicating that seismic slip occurred after clay infiltration in the open spaces along the pre-formed rupture. (2) The dip angle of the slip zone where it cuts unconsolidated strata tends to decrease, showing a branching geometry and termination. The slip zone changes in thickness where it goes through the different alternating sedimentary units (sands and clays) due to their physical properties. Based on these features, we conclude that the type and distribution of infilling materials in the slip zone and of surrounding materials transected by ruptures are related to the interruption and termination of the propagating rupture within the unlithified strata at near-surface depths.

Salt tectonics along the High Zagros Fault in Iran, faulting through welded salt walls

In salt-bearing foreland fold-thrust belts, precursor salt structures affect deformation and accommodate fault zones during orogenic shortening. The complex structure and the halokinetic history of these belts, including the spatiotemporal relationship between diapirism and thrust faulting, have yet to be fully understood. The well-exposed Ediacaran–Early Cambrian Hormuz salt diapirs and the Cambrian–Pliocene overburden stratigraphic sequences along the High Zagros Fault (HZF) in Iran are interesting examples in this regard. The detailed field investigation of the diapirs, the halokinetic deformations, and the thickness variations of the sedimentary units toward the flanks of eight salt structures along the fault show that the first movement of the Hormuz salt could be as old as the Middle Cambrian, occurring long before the initiation of regional folding in the early Miocene. This marks the first field-based and the oldest proposed time for the onset of Hormuz salt diapirism in the Zagros fold-thrust belt. Our field and remote-sensing mapping show the presence of precursor linear salt structures like salt walls. The Hormuz salt diapirs likely began to rise as elongated salt walls above extensional basement faults coeval with the Neo-Tethyan rifting in Early Mesozoic. The squeezing of the salt walls during Zagros shortening from Miocene resulted in the partial accommodation of the HZF as thrust welds. This spatiotemporal evolution, showing the interplay between salt diapirism and late thrusting, can be considered as an analog for other fold-and-thrust belts with pre-orogenic diapiric systems.

The aggradation of alluvial fans in response to monsoon variability over the last 400 ka in the Hajar Mountains, south-east Arabia

The preservation and interpretation of past external forcings within sedimentary archives can be complicated. Marine proxy records show that, throughout the Mid-Late Quaternary, monsoon rainfall in south-east Arabia has varied at precessional timescales (∼ 23 ka). By contrast, terrestrial environmental records from the region, such as speleothems and palaeolake sequences, generally only capture rainfall variability at eccentricity (∼ 100 ka) timescales and geomorphological archives rarely record events over multiple glacial cycles. Previous work has suggested that the alluvial fan systems of the Hajar Mountains record aggradation coincident with precessional peaks because of more northerly Indian Ocean Summer Monsoon (IOSM) rainfall, relative to present. However, the alluvial record is complex: there is a growing body of ‘anomalous’ aggradation age data from periods of precessional minima and it is spatially uneven, mainly being derived from fans at either the northern- or southern-most extents of the western side of the mountains.We present optically stimulated luminescence (OSL) ages of alluvial aggradation from new sites in the central portion of the western and eastern sides of the Hajar mountains. Sedimentary units that show evidence of more sustained flow conditions, such as coarse conglomerate deposition and the development of thick floodplain deposits, typically date to periods of higher IOSM rainfall at precessional timescales. Sites where there is evidence of deposition under more ephemeral flow conditions, like today, yield ages corresponding to precessional minima. We synthesise these data with similarly interpreted alluvial and lacustrine deposits from across the region, employing a hierarchical clustering approach to generate clusters of ages representing periods of increased hydrological activity. This objective approach to regional chronological data suggests that ten periods of more sustained hydrological activity are evidenced across the Hajar region, broadly aligning to precessional and eccentricity peaks over the last 400 ka. These clusters show that Hajar fans predominately aggrade because of increasing rainfall over their catchments, with the central ages of clusters often aligning with the onset of precessional forcing. Hajar alluvial systems preserve important records of Quaternary climate variability over long timescales in an arid region where terrestrial records are scarce due to preservation issues.

Detrital zircon and tourmaline unravel polycyclic provenance of sedimentary infill of the Cretaceous Tupanciretã formation, southern Brazil

The recognition and evaluation of polycyclic processes in sedimentary units are critical for proper provenance analysis and sedimentary system interpretation. The chemical composition and textural maturity of detrital tourmalines and zircons allow identification of sediment source areas, transport, and deposition. This study investigates the origin and history of post-Gondwanan sediments of the Tupanciretã Formation in southern Brazil, which lacks provenance studies. The Tupanciretã Formation is in a similar setting of the Bauru Supersequence at the uppermost portion of the Paraná Basin. Detrital zircon ages indicate sediment provenance from the Transamazonian, Grenvillian, and Brasiliano orogenic cycles of the Rio Grande do Sul Shield and younger grains (280-128 Ma) record contribution from the Choiyoi and Serra Geral igneous events, with a maximum deposition age of 127 Ma. Detrital tourmaline chemical analyses points to the Sul-riograndense Shield as the ultimate source, with metapelitic, metapsamitic and granitic origins. The predominant degrees of roundness are well rounded to rounded suggest evidence of sediment recycling from sedimentary units of the Paraná Basin, with important aeolian reworking involved. Zircon U–Pb signatures are compatible with the eastern sector of the Botucatu Formation in Rio Grande do Sul as the immediate source and the northeastern Sul-riograndense Shield as the ultimate source. Intermediate sources between the Sul-riograndense Shield and the Tupanciretã Formation were Gondwanan sedimentary units of the Paraná Basin, with possible participation from the Camaquã Basin.

Lithological and diagenetic variation of mixed depositional units in the middle permian saline lacustrine deposition, Junggar Basin, NW China

Mixed depositional reservoirs are widely distributed in Junggar Basin, NW China. These reservoirs are featured by complex lithology, ultra-low permeability and extremely heterogeneous pore structures that markedly impact field development efficiency. This study illustrated the distribution of lithological combinations within a single sand bar in the Middle Permian Lucaogou Formation, Jimsar Sag, Junggar Basin and revealed the diagenetic control on the reservoir quality of a single sand bar based on thin sections, scanning electron microscopy (SEM), helium porosity and air permeability measurement, pressure-controlled mercury injection (PMI), rate-controlled mercury injection (RMI), X-ray computed tomography (CT), and collected and published data. The results show that the heterogeneity of microscopic pore structures within a single sandbar is controlled by the distribution of various lithological combinations and different levels of diagenetic alteration. The results show that there are mainly three types of lithology developed in a single sand bar. The reservoir quality of dolomitic siltstone reservoirs is the best, followed by silty dolomite reservoirs. The reservoirs quality of dolomicrite reservoirs is the worst. Three main lithological combinations can be identified within a single sand bar. Controlled by climate, lake level fluctuation and provenance, lithological combination A, characterized by blended mixing of dolomitic siltstone, silty dolomite and dolomicrite, is mainly developed in the middle of single sand bar. Lithological combination B, characterized by saltatory mixing of interbedded dolomitic siltstone and dolomicrite, and lithological combination A developed on the side of the sand bar near the shallow lake, while lithological combination C with blended mixing of interbedded dolomitic siltstone and silty dolomite developed on the side near provenance. Strong compaction is the main factor of the decrease of reservoir quality of sand bar reservoirs. Carbonate cementation promotes the densification of reservoirs. The irregular flaky clay minerals lead to the exponential decline of permeability, and dissolution is the main kind of diagenesis to improve reservoir quality. The dolomitic siltstone reservoirs in the middle of a single sand bar have the best reservoir quality because the overlying dolomicrite layers resist compaction, resulted in a certain amount of primary pores remained. Besides, the dolomitic siltstone reservoirs are far from the sand-mudstone interfaces, which leads to the low carbonate cement content. Furthermore, abundant dissolution pores in dolomitic siltstone reservoirs improve the reservoir quality. These research results are crucial to reservoir evaluation and development in similar mixed depositional tight reservoirs.

Clay minerals and elemental composition of sediments on different sedimentary units in the northern East China Sea shelf: provenance tracing and genetic mechanism analysis

Clay minerals and elemental composition of sediments on different sedimentary units in the northern East China Sea shelf: provenance tracing and genetic mechanism analysis

Multi-method characterization of the recent sediment from the Dibi subsidence lake in the tropical Adamawa region (central Cameroon): Implications for the palaeoenvironmental reconstruction

The evolution and functioning of various tropical ecosystems is poorly understood due to a lack of quantitative techniques to characterize the physicochemical composition of soils and sediment. Here, a detailed multi-method study of lithological changes is provided from a core taken from the silted-up Dibi subsidence lake (central Cameroon). To unravel the provenance of sediment, mineral constituents, and organic matter sources, an array of tools are applied including a spectrophotometer, a laser particle sizer, Rock-Eval pyrolysis, X-ray diffractometer (XRD), a portable X-ray fluorescence (XRF) spectrometry, and an inductively coupled plasma-atomic emission spectroscopy (ICP-AES) instruments. The studied core consists of light-colored deposits at the base (Unit 1) overlain by dark humic deposits (Unit 2). The sediment is very well graded (grading index Sd < 0.35Ф), indicative of bottom suspended to rolling transport. Unit 1 is characterized by relatively low values of total organic carbon (TOC: 2%–5%) whereas the dark Unit 2 has high contents of TOC (10%–33%). The core shows a high oxygen index (OI) value (average = 207 mg carbon dioxide (CO2)/g TOC) and a low hydrogen index (HI) value (average = 107 mg hydrocarbon (HC)/g TOC). This indicates highly altered organic matter (OM), likely from decomposed terrestrial plants. The chlorophyll-α fingerprint (peak around 675 nm) also reveals an autochtonous primary production of organic matter. The mineralogical assemblage of Unit 2 comprises kaolinite, quartz, feldspars, montmorillonite, ilmenite, siderite, gibbsite, rutile, and anatase whereas that of Unit 1 is similar but differs with the presence of illite and the absence of gibbsite. The high titanium dioxide (TiO2) and zirconium (Zr) contents confirm that the source rocks also are comprised of granites, and gneiss without volcanic rocks, such as basalts and trachytes. The source rocks have been intensively weathered using some parameters such as ln(Al2O3/Na2O), K2O/Rb, K/Al, and weathering indices, where Al2O3 denotes aluminum oxide, Na2O denotes sodium oxide, K2O denotes potassium oxide, Rb denotes rubidium, K denotes potassium, and Al denotes aluminum. The enrichment factors (EF) of redox-sensitive trace elements and their relation with TOC, the negative values of manganese/iron ratio (Mn∗) associated to three elemental ratios (cupper/zinc (Cu/Zn), thorium/uranium (Th/U), and vanadium/chromium (V/Cr)) attest to the predominance of sub-oxic to anoxic bottom waters in Dibi lake during sediment deposition. The data also show low primary productivity at the base of the core, followed by an increase towards the top, linked to the intensification of weathering and facilitated by humid climatic conditions, usually increase terrestrial input and palaeoproductivity. The petrological data show a generally warm and humid palaeoclimate. This climatic variation has contributed to the large spread of the savannah and disappearance of the forest. This study sheds light on the late Pleistocene to Holocene palaeoenvironment evolution of the Adamawa region which could be integrated into the context of the Pleistocene to Present regional evolution of the tropical palaeoenvironment.

The thickness variability of fluvial cross‐strata as a record of dune disequilibrium and palaeohydrology proxy: A test against channel deposits

ABSTRACTStrata produced by fluvial dunes can provide insight into the hydrological regime of ancient rivers. Recent experiments indicate that conditions of disequilibrium between bedforms and formative flows may be inferred from the coefficient of variation of preserved dune cross‐set thickness, suggesting that this quantity may act as a proxy for the flashiness of river floods relative to the time required for full bedform translation. To assess whether this idea is applicable to interpretations of the stratigraphic record, this study examines published data relating to more than 2600 cross‐sets from 53 sedimentary units of 19 river systems. The presented analyses must not be over‐interpreted, because the considered rivers span different environmental settings, the data sources are heterogeneous in terms of type and dimensionality, and some variables were established by applying empirical relationships. Yet, significant findings are revealed. Larger rivers exhibit discharge and bedform characteristics that are more conducive to disequilibrium; however, a modest increase in the coefficient of variation of cross‐set thickness, CV(Dst), as opposed to the expected decrease, is seen as a function of river size. Crucially, smaller CV(Dst) values are not systematically associated with conditions that should favour dune disequilibrium. Meanwhile, only ca 25% of the studied examples demonstrate cross‐set thickness statistics compatible with quantitative formulations of the autogenic control by variable dune topography – the notion of ‘variability‐dominated’ preservation. These findings indicate that the variability in cross‐set thickness may be a poor predictor of discharge variability, perhaps because of the multiplicity of factors controlling dune preservation, such as bedform hierarchy, transport stage and depth‐dependent variations in dune disequilibrium. To improve interpretations of cross‐stratified deposits, further research is needed: (i) to establish the value of process‐to‐product models for reverse product‐to‐process interpretations; and (ii) to define representative samples for preserved dune deposits accounting for temporal and spatial variability in preservation potential.