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<jats:p>Lacustrine basins and the sediments within them provide a critical component of regional tectonic development and climate history. Each sub-basin in the landscape records the interplay between active tectonism and shifting climate. Many of the basins in southern Nevada that contain deposits of the Muddy Creek Formation were closed fluvio-lacustrine systems during the latest Miocene and into the Pliocene. They were subsequently integrated into the regional Colorado River system. Lacustrine deposits of the Muddy Creek Formation are exposed along the trace of the Las Vegas Valley shear zone in the Nellis Dunes Recreation Area (NDRA), northeast of Las Vegas, NV. The Muddy Creek Formation in NDRA consists of approximately 130 m of mixed carbonates and clastics, and new tephrochronology suggests an early to late Pliocene age (about 4.7 to about 2.6 Ma) for the lowermost lacustrine deposits and an unknown, but younger age for the uppermost spring-fed lacustrine deposit. These sediments were deposited in an arid to semi-arid lake (Lake Nellis) and alluvial floodplain system based on the interpretation of lithologies and facies associations. The stratigraphic succession coarsens upward and reflects establishment of a lacustrine carbonate system overlain by a clastic succession of peripheral lake sediments of alluvial and floodplain origin. The peripheral lake deposits consist of spring-fed and fluvial wetland mudflats of brown claystone and siltstone. This brown claystone is capped by a succession of yellow and red sandstones deposited by fluvial and minor eolian processes. The second, and youngest freshwater limestone, likely disconformably, overlies the yellow and r ed sandstones, and is thought to be temporally and depositionally distinct from the underlying Muddy Creek deposits. The transition from the lower lacustrine carbonates to clastic fluvial channel and flood plain deposits indicates desiccation of Lake Nellis and possibly occurs soon after about 2.7 to about 2.6 Ma based on the ages of tuffs occurring within the uppermost limestone and marl beds. This is consistent with an interpreted increase in regional aridity after approximately 2.8 Ma (Smith et al. 1993). The second limestone deposit at the top of the section represents an even younger spring/lacustrine deposit of unknown age. Throughout the lower carbonate section, three tuffs were identified, and geochemically correlated, using a discriminant function analysis, to the tuff of Napa (≤ 4.70 ± 0.03 Ma), the Putah Tuff (about 3.3 Ma) and the lower tuffs of the Badlands ( about 2.7 – about 2.6 Ma). The timing of deposition of Lake Nellis sediments post-dates the integration of the three major lake syste ms in this region (Lake Grand Wash, Lake Hualapai, and Lake Las Vegas) into the Colorado River drainage (5.6 – 4.9 Ma), and also postdates the full integration of the river to sea level (4.8 - 4.63 Ma) (Howard et al. 2015; Crow et al. 2021). Lake Nellis represents an isolated lake basin that was one, and maybe the last, lacustrine system to be fully integrated into the Colorado River drainage in this region.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>Burrowing organisms alter sedimentary textures, influence cement distribution, and affect petrophysical characteristics of carbonate strata. Although many descriptions of carbonate successions reference bioturbation, quantitative data on spatial variability of trace fossils is rare, and fewer studies address trace-fossil influence on postdepositional modification of sedimentary deposits, which can affect petrophysical properties. To address these unknowns and determine the controls on ichnology in carbonate shoreface successions, this study evaluates the along- and across-strike distribution of sediment and bioturbation in recent, Holocene, and Pleistocene shoreface deposits on the leeward margin of Crooked–Acklins Platform (CAP), southern Bahamas. To the north, the extant margin shelf is characterized by poorly to moderately sorted, very fine–fine, skeletal–peloid–ooid sand with an average of 16% mud (&amp;lt; 62.5 µm) that is moderately to intensely bioturbated (ii3–6). Trace assemblages are diverse, and include horizontal tracks and trails, abundant horizontal deposit-feeding and locomotion traces, as well as dwelling and resting burrows attributable to the proximal Cruziana Ichnofacies. In marked contrast, shelf margin deposits to the south are well-sorted, medium ooid–peloid sand with &amp;lt; 1% mud, and display a range of bioturbation, from nonbioturbated to moderately intense bioturbation (ii1–4). Trace-fossil assemblages exhibit low ichnodiversity, dominated by vertical dwelling burrows with reinforced wall lining attributable to the Skolithos Ichnofacies. Holocene and Pleistocene strata show similar proximal-to-distal and along-strike variations in sediment attributes, ichnodiversity, and bioturbation. These trends reflect a progressive, north-to-south increase in energy reflecting the change in margin orientation relative to the direction of dominant wave energy, analogous to the recent system. This study provides data for an integrated sedimentologic–ichnologic conceptual model for processes and patterns of sediment accumulation on carbonate shorefaces, and are distinct from siliciclastic analogs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Crevasse-splay deposits play an important role in the reconstruction of the magnitude of past flood events and in understanding the behavior of river systems. Despite the extensive studies conducted on the geometry and facies of crevasse-splay deposits, their spatiotemporal developmental processes have remained insufficiently understood. In this study, scaled flume experiments were conducted to study the relationship between the developmental processes of crevasse splays and their characteristics. An experimental flume was set up in a tank to simulate the 2019 Chikuma River flooding event in central Japan. To model the overbank flow, an opening was created on the side of the flume’s wall through which the flow flooded onto a horizontal acrylic plate. The sediment used in the experiments consisted of particles with grain sizes of approximately 0.3 and 0.1 mm, which were determined to be equivalent to bedload gravel and suspended sand in a real-scale river using dimensional analysis. The results of the experiments revealed three important findings: 1) Crevasse-splay deposits initially developed an asymmetric shape extending downstream of the main river channel but gradually showed a symmetric geometry. The river mainstream initially influenced the direction of the inundation flow, but channel bifurcations after the deposition of the sediment piles later changed the geometry of splays into a more symmetric shape. 2) Crevasse-splay deposits developed in two distinct regions (proximal and distal splay), corresponding to sediment transport by bedload and suspended load, respectively. These two regions are commonly observed in the actual field scale. 3) The original overbank flow was a sheet flow without channels, which caused coarse-grained sediments to be spread over a wide area. Subsequently, the accumulation of coarse sands in the developed channel interiors resulted in the buildup of finer-grained sediments upstream of the proximal splay. Thus, the proximal splay deposits became slightly coarse downstream, whereas they rapidly became fine at the boundary with the distal splay. These findings indicate that the characteristics of crevasse-splay deposits vary with the landform’s development stage, thus providing a basis for interpreting their depositional facies.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>Playa basins contain saline lakes and the evaporitic mudflats around them. However, playa basins can be different if they are fed by marine incursions, dominated by perennial lakes of brackish or fresh water, or dominantly dry. A discrimination of playa types, which originated under such different conditions, can be difficult in the rock record. The present study contributes to our understanding of these settings by reconstructing the evaporitic facies evolution in the German Keuper Basin after the retreat of an epeiric sea. The Middle to Late Triassic Grabfeld Formation (ca. 237–233 Ma) consists of weathered gypsum and dolomitic marl at the surface. Non-weathered anhydrite and dolomitic marl successions were studied at the tunnel face and on drillcores for the Stuttgart 21 construction project around Stuttgart. From oldest to youngest, the following facies were recognized: 1) The Grundgipsschichten facies represents an environment of large, shallow, sulfate lagoonal lakes (saltern). Arenitic sulfate was deposited in very shallow waters, comprising many tepee-like structures, enterolithic folds, and numerous truncation surfaces. 2) The Bochingen-Horizont facies is characterized by greenish gray laminated mudstone and dolomite deposited in perennial saline lakes. Anhydrite was locally altered by brackish or fresh water. 3) The Dunkelrote Mergel facies contains the sediments of a dominantly dry playa basin, red mudstone and nodular anhydrite. Sheetfloods resulted in ephemeral lakes under a monsoonally controlled climate. Sedimentation was sparse with numerous truncation surfaces. Large, festoon-like structures on the tunnel face were interpreted as paleo-gilgai structures. This study concludes that an evaporative environment of a coast (coastal sabkha) can never undoubtedly be distinguished from a playa basin in the sedimentary record.</jats:p>

<jats:p>The modern Niger Delta has long been classified as a mixed tide-, wave- and fluvial-influenced delta. Still, no detailed studies have quantified the relative proportions of formative processes and facies. This work presents the first quantitative estimate of the relative influence of formative processes in Miocene deposits based on core data from the Greater Ughelli, Central and Coastal Swamp depositional belts of the Niger Delta Basin. Facies analysis of 288.2 m of core from 4 wells shows approximately 53% tidal facies, 33% fluvial facies and 14% wave-formed facies, indicating deposition in a prograding tide-dominated, fluvial- and wave-influenced delta. Cores from the Greater Ughelli and Central Swamp depobelts exhibit coarsening upwards, prograding deltaic facies successions overlain by fluvial mudstone. Tidal deposits in the Coastal Swamp depobelt show coarsening upwards prograding deltaic facies successions with well-developed tidal bundles indicating periodic deposition. The basal part of these facies successions also reveals repeated floods characterised by slump and load structures and dewatering features. Delta plain and delta front-prodeltaic facies associations are identified based on physical sedimentary and biological structures. The delta plain facies association consists of weakly bioturbated mudstone, fissile mudstone, and coarse-pebbly stratified sandstone facies with sparse trace fossils. The delta front-prodeltaic facies association contains muddy and sandy heteroliths, stratified, medium and coarse-grained, cross-bedded sandstone, and convoluted mudstone facies. The facies vary but characteristically contain trace fossil assemblages of the recently proposed Rosselia and Phycosiphon Ichnofacies, indicating delta front and prodeltaic settings, respectively. Variability in the facies is determined by the relative influence of hydrodynamic processes (tide, wave, and fluvial), variations in physicochemical stress, and the episodic character of deposition. In addition, based on the relative influence of each hydrodynamic processes, the facies differ through the successions, sometimes subtly.</jats:p>

<jats:p>In this study, we present a detailed investigation of C-O-S-Sr isotope systematics and elemental analysis of secondary sulfates and associated host rock carbonates of Cambrian to Devonian sedimentary successions along the eastern flank of the Michigan Basin, Ontario. This study evaluates the diagenetic evolution of pore fluids and their sources in fracture-fill and replacement sulfate minerals within low-permeability carbonate units in the Michigan Basin. Secondary sulfates, represented by gypsum and anhydrite, contain various petrographic types, represented by vug- and fracture-filling fibrous anhydrite in the Cambrian (δ18O vary between 16.8 to 17.6 permil VPDB and δ 34S 28.3 to 29.0 permil CDT, 87Sr/86Sr ratios vary from 0.70834 to 0.70991, respectively) and Ordovician fibrous anhydrite (δ18O 16.8 permil, δ 34S 28.2 permil, 87Sr/86Sr ratios 0.70829). These phases display mainly uniform REE patterns with Y/Ho and Zr/Hf ratios, flat La*, Gd*, and Y* and enriched LREEs. Idiotopic satin-spar δ18O values vary between 4.0 and 8.3 permil, δ 34S 23.4 and 31.4 δ with 87Sr/86Sr ratios 0.70816-0.70866), xenotopic porphyroblast gypsum δ18O value vary between 4.5 and 13.3 permil, δ34S 22.6 to 33.1 permil with 87Sr/86Sr ratios of 0.70850-0.70880, alabastrine gypsum δ18O values vary between 4.2 and 11.7 permil, δ34S 23.1 to 26.9 permil with 87Sr/86Sr ratios of 0.70816-0.70876) and felted anhydrite δ18O values of 11.1 permil, δ 34S 27.4 permil with 87Sr/86Sr ratio of 0.70849). These geochemical proxies suggest a comparable sulfate-rich source for both age groups under similar geochemical conditions. Gypsum in the Silurian Salina Group display a wide range of REE values with Y/Ho, and Zr/Hf ratios, Nd/YbN and Pr/YbN, flat to strong Ce/Ce*, and flat to strong Eu/Eu* anomaly, Gd/LaN and Tb/LaN, Sm/LaN). These sulfates formed at burial from fluids of variable isotopic, chemical composition and temperatures. The sources of these fluids range from brines migrating from a deeper part of the basin forming anhydrite in the Cambrian and Ordovician sequences which were also affected by dolomitization and later hydrothermal fluid influx, to rehydration of gypsum at shallower burial depths and affected by salt dissolution and incursion of meteoric water during and following the Alleghenian orogeny.</jats:p>

<jats:p>The type locality for the upper Oligocene Nuwok Member of the Sagavanirktok Formation (Carter Creek, North Slope, Alaska, USA) contains abundant occurrence of glendonite, a pseudomorph after the calcium carbonate mineral ikaite, which typically forms in the shallow subsurface of cold marine sediments. The region during the time of Nuwok Member deposition was located at a high latitude, similar to today, and the study site is characterized by sands and silty muds interpreted here to have been deposited in coastal and shelfal marine environments. Isotopic (Sr) and biostratigraphic (foraminifera) evidence presented here refine the depositional age of the outcrop to approximately 24 Ma. Glendonites occur in two basic forms: radial clusters, commonly centered around a single larger primary crystal ( approx. 10 cm; Type A) and larger single blades generally without accessory crystals (approx. 15–25 cm; Type B). Microscopic examination revealed a sequence of multiple types of replacive calcite that formed as a direct result of ikaite transformation: Type 1 rhombohedral crystals characterized by microporous and inclusion-rich cores and concentric zones, Type 2A, composed of clear calcite that overgrew and augmented Type 1 crystals, and inclusion-rich, microcrystalline Type 2B, which formed a matrix surrounding the rhombs and commonly dominates the outer rims of glendonite specimens. Type 3 calcite precipitated as fibrous, botryoidal epitaxial cement atop previous phases and is not ikaite-derived. These phases are distributed in similar ways in all examined specimens and are consistent with several previously described glendonite occurrences around the world, despite differing diagenetic and geologic histories. Stable isotope evidence (δ13C and δ18O) suggests sourcing of glendonite carbon from both organic and methanogenic sources. Glendonites of the Nuwok Member can therefore assist in the determination of a more comprehensive ikaite transformation model, improving our understanding of glendonite formation and the sedimentological and environmental context of their occurrence. Oligocene glendonites are uncommon globally; the well-preserved occurrence described here can allow future studies to better reconstruct Arctic environmental conditions and paleoclimates during this time.</jats:p>

<jats:p>The 2016 Mw7.8 Kaikōura Earthquake in Aotearoa New Zealand provides an opportunity to test widely applied turbidite sedimentation models because it triggered a co-seismic turbidity current. The resultant Kaikōura event bed (KEB), interpreted as a turbidite, is sampled for approx. 1300-km down-flow along the depositional system. Sediment core lithologies, computed tomography (CT), and particle-size data are used to test event-bed thickness, silt content, facies distribution and stacking patterns against the foundations of the turbidite conceptual model of Bouma (1962). KEB thickness is variable to approx. 100 km down-flow distance and attains a maximum thickness at approx. 700 km down-flow distance before thinning distally, similar to the predicted bell-shaped proximal to distal trend. Silt content is high throughout the KEB from canyon to fan. The KEB is dominated by laminated Td facies and Te facies that evolve down-system from laminated, then graded, to homogenous muds. CT and granulometry data ar e key to differentiating subtle density and textural variations within fine-grained deposits and reveal that KEB Td and Te facies in the KEB that are often not preserved or readily observed in older deposits. The KEB highlights a fine-grained sedimentary system that contrasts with more widely studied sandy turbidite basins. In particular, the KEB example reveals that Td and Te facies are ubiquitous in this fine-grained, silt-rich system. A varied conceptual model developed from the KEB may be applicable to many modern deep-sea turbidite systems and crucial for understanding present-day particulate transport to the deep sea and interpreting evidence from the stratigraphic record.</jats:p>

<jats:p>Submarine canyons are important deep-sea environments and conduits for transferring and accumulating sediment and organic matter and pollutants. Recent advances in observing, sampling, and analysing modern canyon sediment transport systems illustrate near-seafloor dynamics and highlight the potential roles of submarine canyons in transporting and storing organic carbon, nutrients, and contaminants in the deep sea, with implications for deep-sea ecosystems and global carbon budgets. Kaikōura Canyon, offshore northeastern Te Waipounamu South Island, Aotearoa New Zealand, is a benthic biomass hotspot that experienced an earthquake-triggered, canyon-flushing event in 2016. On return to the canyon in October 2020, benthic landers, with sediment traps at 2 m above the seafloor, were deployed along the canyon axis in approx. 900–1500 m water depths for a period of three weeks. These instrumented platforms provide a detailed view of near-seafloor sediment and organic carbon transport between canyon-flushing e vents, showing that the canyon environment hosts dynamic physical processes and short-term sediment fluxes and transport. Variations in sediment and organic carbon flux down-canyon and over time include small-scale sediment transport events, some of which are interpreted as turbidity currents, occurring on much shorter timescales than earthquake recurrence. We compare Kaikōura Canyon results with other longshore-fed, shelf-incised global submarine canyons and deep-ocean sites, revealing differences and likely multiple controlling factors for near-seafloor sediment flux. This Kaikōura Canyon high-resolution, benthic lander timeseries dataset highlights the complexity of submarine canyons and their role in organic carbon flux to the deep ocean, even under high present-day sea-level conditions. Evolving insights underscore the need for more observational data and samples to further quantify submarine canyon sediment and organic carbon transport and contribute to global evaluations of deep-sea canyon distribu tary systems.</jats:p>