Depositional Record最新文献

Coral reefs are hard calcified structures, mainly found in warm tropical water. These ecosystems serve important roles as, for example, a source of food, shelter and nursery for different organisms, and in coastal protection. Reef-building organisms have evolved to inhabit a narrow ecological niche and thus are particularly susceptible to rapid changes in their environment, for example, under predicted climate-change scenarios. Anthropogenic climate change is widely accepted as the leading cause of rising ocean temperatures, sea water acidity and sedimentation rate, which all affect a coral's productivity, health and, to some extent, skeletal strength. High-energy weather events, such as storms and hurricanes, can erode reefs, thereby increasing the amount of suspended sediment and consequently the turbidity of the water. The removal of suspended sediment from the reef is vital for the health of reef producers, and a natural process that removes suspended sediment from reefs are sediment gravity flows. A key factor that controls the ability of sediment gravity flows to transport sediment is cohesion, as cohesion determines the run-out distance of a flow through changes in its rheological properties. This study examines the cohesive nature of sediment gravity flows laden with fine-grained CaCO₃. These gravity flows laden with mud-grade calcite are compared with flows carrying non-cohesive, silt-sized, silica flour, weakly cohesive kaolinite clay and strongly cohesive bentonite clay, by means of laboratory experiments. The results of these experiments show that the mud-grade calcite flows behave more akin to the silica-flour flows by reaching maximum mobility at considerably higher volumetric suspended sediment concentrations (47% for silica flour and 53% for CaCO₃) than the kaolinite and bentonite flows (22% for kaolinite and 16% for bentonite). Fine CaCO₃ gravity flows can therefore be regarded as physically non-cohesive, and their high mobility may constitute an effective mechanism for removing suspended sediment from coral reefs, especially at locations where a slope gradient is present, such as at the reef front and forereef. However, biological cohesion, caused by ‘sticky’ extracellular polymer substances produced by micro-organisms, can render mud-grade calcite cohesive and sediment gravity flows less mobile. The present study should therefore be seen as a first step towards a more comprehensive analysis of the efficiency of removal of suspended sediment from coral reefs.

Numerous sedimentary volcanoes, recently exposed on the Colorado River delta surface at Lake Powell near Hite, Utah, were generated by sediment slurries propelled by gas, mainly microbially generated methane (CH₄). Two sedimentary volcanoes were excavated, one in 2016 and the other in 2019, in order to characterise the internal structures. Comparison of the internal structures of these features with those of previously documented seismic-generated sedimentary volcanoes helps in differentiating the various modes of mobilised sediment generation. Sedimentary volcanoes are commonly employed as tools in palaeoseismic reconstruction, thus it is important to establish criteria to differentiate non-seismic-generated sedimentary volcanoes and accompanying sediment deformation from those features generated by earthquakes. Trenches through the volcanoes and immediate subsurface areas reveal a complex cone stratigraphy of centimetre-scale graded sand-silt laminations and clastic dikes that cross-cut the cone and sub-cone (delta) sediment. Some cone strata have ripple cross laminations, a scoured base and are disrupted by soft-sediment deformation. In the 2016 volcano, the lowest 0.5 m of the dikes exposed in the trench are filled with organic-rich mud, but these conduits are empty nearer to the surface as a result of sediment settling after eruption cessation. The 2019 sedimentary volcano differs from the other by: (1) more cross laminations in the cone, (2) collapse structures surrounding the crater, (3) a relatively simple plumbing system assisted by desiccation-generated fissures and (4) a massive sediment infill of the vent. Both complex internal cone stratigraphy and the two distinct cross-cutting dike-conduit systems, unequivocally generated by recurrent gas and water discharge, add to the database of features for non-seismic-generated sedimentary volcanoes. This array of sedimentary structures from a non-seismic-generated sedimentary volcano demonstrates that certain features, including numerous internal laminations composing the cone and complex generations of dike systems are not unique to seismic-generated sand volcanoes.

Basin hydrology and subcrop are key controls on carbonate sedimentation in continental basins. Hydrologically sensitive carbonates can record groundwater fluctuations within an aquifer in deep time. Late Jurassic extension, footwall uplift, erosion and karstification of marine Jurassic carbonates in the western Cameros Basin (Spain) saw deposition of ?Upper Kimmeridgian-Tithonian syntectonic alluvial fan deposits (Señora de Brezales Formation). Biogenic laminar calcretes and phreatophytic rhizocretions record roots exploiting capillary fringe groundwater. Progressive infill of rift topography and footwall erosion lowered sedimentary gradients and clastic supply during deposition of the ?Tithonian–Berriasian Rupelo Formation. Distal alluvial marls (Las Viñas Member) contain charophytes, with 2 m thick carbonate lenses at the top reflecting intermittent rise of groundwater in ponds on the basin floor. Stacked palustrine limestones with rare charophytes and laminar calcretes (Ladera Member) record overstep of seasonal carbonate wetlands onto basin margins and footwall highs with intense pedogenetic modification during lengthy seasonal exposure. Overlying Berriasian charophyte-ostracod wackestones, displaying microkarst cavities and interbedded intraclastic conglomerates, with vivianite sauropod bones, footprints and polygonal desiccation cracks at the top (Mambrillas de Lara Member) record open lacustrine conditions with limited subaerial exposure and high water tables. Desiccation-cracked limestones and marls with correlatable evaporite horizons (Rio Cabrera Member) contain marginal marine foraminifera and dasycladaceae at the top. Lagoonal conditions reflected transgression to seaward and intermittent marine connection via the Basco-Cantabrian Basin. The distribution and thicknesses of hydrologically sensitive carbonates reflected onlap onto a faulted and karstified marine Jurassic carbonate pediment and the subtle influence on hydroperiod of fault (and potentially localised Triassic salt) controlled differential subsidence and transgressive groundwater rise. Hydrological facies evolution reflects progressive basin infilling and eustasy beyond. Transitions in this continental succession from clastic to carbonate facies and from closed to open hydrology record hydrological change over time rather than contemporaneous deposition under Walther's Law.

Syn-sedimentary compaction or consolidation is an important process in deltaic environments because it affects both the local morphodynamics and hydrodynamics as well as the delta-scale accommodation space. However, the impact of syn-depositional compaction on the sediment distribution and the interdependency between different delta areas related to the sediment budget are not fully understood. This paper simulates syn-depositional compaction using improved 1D grain-size compaction formulations, integrated into hydrodynamic and morphodynamic modelling software Delft3D. The updated code is used to model sedimentation in mud-rich deltas under various compaction rate scenarios, which represents the maximum compaction rate potential of sediment that experiences the highest overburden stress in the delta. The simulated deltas are analysed by first classifying their plan-view area development into depositional elements: distributary channel, underfilled channel, delta plain, mouth bar, delta front and pro delta depositional elements. Then, sedimentation by mass, accommodation space and depositional segment metrics are calculated using the interpreted depositional elements. The results for zero compaction rate scenarios (0 mm year⁻¹) show that limited space-varying and temporal-varying accommodation is available to deposit sediment in the delta plain depositional element. Therefore, the sedimentation mainly occurs in the mouth bar depositional element. For low-mid compaction rate scenarios (0.01–1 mm year⁻¹), the additional syn-depositional accommodation space in the delta plain depositional element increases sedimentation in this area, limiting sedimentation in the mouth bar depositional element. For high compaction rate scenarios (>1 mm year⁻¹), a further increase in the accommodation space in the delta plain depositional element leads to lateral sedimentation attributed to channel relocation, where the sedimentation mainly occurs in the mouth bar depositional element. This study shows that, although considered a gradual process, syn-sedimentary compaction does impact long-term delta evolution by influencing the distribution of sedimentation in the delta.

The stratigraphic, spatial and temporal variability of detrital zircon age populations in continental sedimentary successions is a critical tool in understanding palaeodrainage networks and how these systems distributed detritus within sedimentary basins. However, multiple factors, such as variations in sediment-transport processes, the scale of the depositional environment and the architecture of the sedimentary succession are often overlooked in detrital zircon studies. This article presents detrital zircon U–Pb geochronology from the fluvial-dominated Colton Formation in the western Uinta Basin (Utah, USA) to assess the system's provenance and evolution. Significant differences in zircon age populations between the Colton Formation and the overlying Green River Formation suggest a reorganisation of the source-to-sink system during the transition between the two lithostratigraphic units. Notably, detrital zircon age spectra are not homogeneous across the Colton Formation, therefore physical morphometric parameters were used to verify the possible influence of selective bias during sediment transport. These data reveal that a relatively finer-grained population of Precambrian, and to a less extent Mesozoic, zircon grains were affected by hydraulic sorting during transport, resulting in a greater relative abundance of older zircon grains in the distal reaches of the distributive fluvial system, whose basinward decrease in competence would have increased the relative proportion of finer zircon fractions in sandstones. Furthermore, there are different trends in the distributions of zircon age populations relative to their stratigraphic position, highlighting the complex architecture of the fluvial palaeo-fan. The spatial and stratigraphic variability of provenance signals in fluvial-fan successions must be carefully evaluated to improve the reliability of source-to-sink models and palaeodrainage reconstructions, as autogenically controlled noise can be generated during the dispersal of detrital zircon in fluvial sedimentary systems.

Gravelly cyclic steps formed by turbidity currents have recently been widely recognised in the geological record. However, the comparison between modern and ancient gravelly cyclic steps remains challenging. In this study, the facies variations of gravelly cyclic steps deposited from turbidity currents in an outcrop of Miocene fan delta front deposits in central Japan are compared with the geomorphic evolution of analogous cyclic steps on the active fan delta front in modern geological systems. These cyclic steps share common characteristics in setting, grain size and dimensions, allowing direct comparison between ancient and modern examples. Repeat bathymetric surveys of the modern Kurobe River fan delta have revealed various types of upslope migrating bedforms interpreted as cyclic steps. Most of these are short-lived due to erosion of thalwegs by powerful surge-type turbidity currents triggered by slope failures or burial of thalwegs by deposition, possibly from river-fed hyperpycnal flows. Such erosion and burial events occur annually on the fan delta front, resulting in compensational cycles. Sedimentary facies of the Miocene fan delta front deposits include conglomerate with a gently upslope dipping erosional base, backset-stratified sandstone and foreset-stratified sandstone, which are interpreted as deposits of hydraulic jumps in high-density turbidity currents in scours on the stoss sides of cyclic steps. Parallel-stratified conglomerate sandstone is an additional component. Although previous facies models of gravelly cyclic steps have focussed on deposits on stoss sides, a comparison of modern and ancient examples suggests that facies on the lee sides could be parallel-stratified conglomerate sandstone and undulating bedforms, reflecting supercritical flow conditions. The present study also suggests that hyperpycnal and surge-type high-density turbidity currents may deposit different types of facies and play different roles in the construction and destruction of cyclic steps. The present study has significant implications for facies models of gravelly cyclic steps.

A transgressive palustrine depositional model is described for the South-east Saline Everglades, Florida. The origin, development and termination of freshwater carbonate mud (marl) deposition along the very low gradient Late Pleistocene carbonate ramp are responses to changing rates of rising sea level during the Late Holocene. The onset of the Late Holocene is defined by a decrease in the rate of sea-level rise from between 2 and 3 to <1 mm year⁻¹. Freshwater marl deposition began with this decrease ca 3165 ± 187 year BP, in a shallow (<0.3 m deep), ephemeral wetland that developed landward of a fringing mangrove forest and is maintained by seasonal Everglades water delivery. Sedimentation kept pace with sea-level rise forming a 1.2 m thick wedge shaped, landward thinning deposit. The rate of global sea-level rise began to accelerate ca 1900, the Anthropocene Marine Transgression, and presently the regional rate is 9.4 mm year⁻¹. Saltwater encroachment rates >80 m year⁻¹ are driven by sea-level rise. Saltwater encroachment resulted in retreat and transformation of coastal communities and their biogenic facies, resulting in a decrease in freshwater wetlands and marl production. Inundation ponding, mangrove overstep and the beginning of submergence are the responses to the accelerating rate of sea-level rise, however, small scale topographic and tidal ingress differences create considerable variability between Biscayne Bay and Florida Bay coastal basins. The freshwater marl producing habitat will probably be lost within 55 years, and submergence within the next century at the present rate of sea-level rise. The unique South-east Saline Everglades depositional environment is compared to other Holocene palustrine depositional environments.

Western Anatolia, an important segment of the Alp-Himalayan Belt, hosts numerous Neogene lacustrine basins with potential oil shale reserves surpassing 1.6 billion tonnes. Among these basins, the Seyitömer Basin (Kütahya) stands out, containing oil shales that are intercalated with claystone, marl, limestone and coal layers. This study presents a comprehensive dataset of organic and inorganic chemistry to gain insight into the palaeoclimate and palaeoenvironmental factors that control the enrichment of organic matter. The studied samples exhibit high total organic carbon contents, averaging 12.85% (ranging from 2.22 to 36.21%), high hydrogen indices (486–812 mgHC/g rock) and low oxygen indices (33–70 mgCO₂/g total organic carbon), indicating their substantial hydrocarbon-source potential. These characteristics indicate predominantly ‘excellent’ to occasionally ‘very good’ source rock qualities and very high oil potential. Their pyrolysis, gas chromatography and gas chromatography–mass spectrometer parameters indicate an immature-early mature characteristic for Seyitömer oil shale samples. They comprise dominantly Type-I kerogen with minor Type-II kerogen and lacustrine algal organic matter. Their sedimentological characteristics, along with various geochemical values, such as total organic carbon versus S, B versus Ga and dibenzothiophene/phenanthrene, reveal a moderately deep fresh/brackish to saline lacustrine environment. The Ga/Rb, K/Al and Sr/Cu ratios suggest dominantly humid and warm climate conditions, occasionally interrupted by periods of less humidity. The prevalence of warm and humid climate conditions leads to intense chemical weathering processes, supported by high Chemical Index of Alteration and low Rb/Sr ratios in the associated oil shale samples. Intense chemical weathering and high runoff resulted in dissolved nutrient enrichment, promoting ecological dynamics favourable to increased productivity. Their low Pr/Ph and Mo/total organic carbon ratios, high Ni/Co ratio and, relatively low Mo_EF/U_EF ratio, along with well-developed lamination of the oil shales, indicate the presence of anoxic conditions in the bottom water. These anoxic conditions would have facilitated the preservation potential of organic matter in the samples. Thus, the palaeoclimate conditions integrated with sedimentary factors have an important role in the ecological dynamic and physical–chemical environmental conditions, ultimately contributing to the organic matter enrichment of the studied samples. This work provides a case study to better understand the sedimentary factors controlling organic matter enrichment in the lacustrine basins of the Alp-orogenic belt.

Lacustrine, riverine and spring carbonates represent archives of terrestrial climates and their geochemistry has been used to study palaeoenvironments. Clumped isotope thermometry is an emerging tool that has been applied to freshwater carbonates. Limited work has been done to evaluate comparative relationships between clumped isotopes and temperature in different types of modern freshwater carbonates. This study assembles an extensive calibration data set with 135 samples of modern freshwater carbonates from 96 sites and constrains the relationship between independent observations of water temperature and the clumped isotopic composition of carbonates (denoted by Δ₄₇), including new measurements, and recalculates published data in accordance with current community-defined standard values. For temperature reconstruction, the study reports a composite freshwater calibration and material-specific calibrations for biogenic carbonates (freshwater gastropods and bivalves), fine-grained carbonate (e.g. micrites), biologically mediated carbonates (microbialites and tufas) and travertines. Material-specific calibration trends show a convergence of slopes that are in agreement with recently published syntheses, but statistically significant differences in intercepts occur between some materials (e.g. some biogenics, fine-grained carbonates). These differences may arise due to unresolved seasonal biases, kinetic isotope effects and/or varying degrees of biological influence. The impact of different calibrations is shown through application to new data for glacial and deglacial age travertines from Austria and published data sets. While material-specific calibrations may yield more accurate results for biogenic and fine-grained carbonate samples, the use of material-specific and the composite freshwater calibrations generally produces values within 1.0–1.5°C of each other, and typically fall within calibration uncertainty given limitations of precision.

Diverse types of organic matter morphology were identified in Brazilian Pre-salt carbonates. Stromatolites and laminated facies contain organic layers, filaments and rounded features inside calcite structures, as shrubs and spherulites. Analyses with optical and fluorescent microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and ion mass spectrometry indicate the presence of organic compounds in thin sections. Fluorescent microscopy shows a high signal for organic portions in the thin section, mainly inside calcite structures and within the matrix. Scanning electron microscopy with energy-dispersive X-ray spectroscopy elemental mapping indicates the presence of carbon in the stromatolite facies, associated either with calcium and oxygen, indicating carbonate, or isolated from other elements, representing carbon content in the samples. The presence of organic matter along and inside calcite structures indicate a strong microbial influence in Brazilian Pre-Salt carbonates precipitation. The purpose of this research is to show that the presence of organic matter is connected to the process of carbonate precipitation and/or dissolution. The occurrence of these organic compounds in distinguishing facies raises the discussion of biotic versus abiotic genesis of the Pre-salt lacustrine reservoirs.