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<jats:title>Abstract</jats:title> <jats:p>Examination of grain coats of chlorite, illite, detrital clay, microquartz, and siderite in deeply buried sandstones from the Norwegian continental shelf by scanning electron microscopy shows that the quartz surfaces beneath the grain coats are covered by tiny quartz outgrowths bounded by planar crystal faces. These very small euhedral quartz outgrowths also occur in gaps in the coats where there is no physical barrier to impede their continued growth into adjacent macropores, but such outward growth and expansion into the intergranular pore space was observed only where the gaps in the coats are larger than around 5 μm. We suggest that the inability of euhedral quartz outgrowths smaller than a certain size to grow through grain coats and form large pore-filling quartz overgrowths is a consequence of the increased solubility of micron-sized crystals compared to larger crystals. Due to surface energy effects, the smallest crystals of a mineral are unable to grow at conditions that do not prevent growth of larger crystals of the same mineral. This is a general thermodynamic effect that becomes important for tiny crystals with a large surface-to-volume ratio and is expressed quantitatively by the Ostwald-Freundlich equation. The reason microscopic outgrowths can develop on the quartz grain surfaces in the first place is probably that the initial pre-euhedral growth stages are able to grow at slightly lower silica supersaturations than euhedral outgrowths. Continued growth at the low supersaturations prevalent in most sandstones may consequently depend upon the outgrowths reaching a euhedral shape after they are larger than a critical size. Outgrowths nucleated in gaps in the grain coats smaller than around 5 μm develop planar crystal faces before they have attained the critical size because there is not enough space for larger euhedral outgrowths to form in these smaller gaps. The outgrowths nucleated in the smallest openings are therefore unable to grow through the grain coats and reach the adjacent pore space despite free access to the adjacent macropores. Grain coats can therefore prevent quartz cementation without being continuous at the microscopic scale.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Knowledge of how carbonates are produced on shelves is needed for working out how these “carbonate factories” generate stratigraphy by providing particles for potential export or local deposition. Production rates can be derived straightforwardly in low-energy environments from one-dimensional analysis (age–depth variations) but rates are less easily derived for high-energy hydrodynamical environments where particles are transported away from their sites of production. This particularly affects knowledge of spatial variations in production rates, needed for working out controlling influences of light, hydrodynamics, and nutrient availability. We show here that, if a non-carbonate component of the sediment, such as terrigenous particles arising from coastal and subaerial erosion, is conserved and thus acts as a tracer, rates of carbonate production can in principle be derived from carbonate content data, if sediment transport fluxes can also be constrained. In the equation developed here, the spatial rate of change of carbonate content is caused by dilution of the terrigenous component by the newly produced carbonate and depends on the sediment transport flux. We investigate this idea using data from Santa Maria Island, Azores, an inactive volcanic island in a temperate environment. Geochemical, X-ray diffraction (XRD), and X-ray fluorescence (XRF) data of surface–sediment grab samples indicate nearly simple mixing trends between two components (volcanic rock and marine carbonate), as needed for our simple dilution-based equation to apply. High-resolution boomer seismic data reveal thicker (&amp;gt; 1 m) deposits in the mid- to outer shelf of the island, which we interpret as having been emplaced during the Holocene. These effectively provide time-averaged depositional fluxes and, assuming conservation of mass, can be used to constrain transport fluxes. The derived equation is used to predict the observed deposit thicknesses into the mid-shelf alongside coincident increasing carbonate percentages. The thicknesses are replicated only if carbonate production rates increase with depth and distance away from the coastline into the mid-shelf, quantifying the variation of production of such a nearshore environment for the first time. We speculate that mollusks dominating the production have a preference for sand that is less frequently or strongly agitated by waves, although nutrient availability from occasional upwelling may also regulate growth to create this trend.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>We here present the first comprehensive provenance study of the Zambezi deep-sea fan, based on integrated petrographic, heavy-mineral, elemental-geochemistry, isotope-geochemistry, and detrital-zircon-geochronology analyses of middle Pleistocene to Holocene turbidites. The Zambezi Valley and Fan represent the submarine part of an ∼ 5000-km-long sediment-routing system, extending from the heart of the South African Plateau to the abyssal depths of the Indian Ocean. Sediment is derived not only from the African side, but also from Madagascar Island mostly via the Tsiribihina Valley. Being shed by two dissected rifted margins, detritus supplied from opposite sides of the Mozambique Channel shares similar feldspar-rich feldspatho-quartzose composition, although with significant differences in heavy-mineral and geochemical signatures. The εNd values of Madagascar sand are markedly more negative and TNd model ages notably older. Zircon grains yield mostly Irumide (late Stenian) U-Pb ages in African-derived sand and mostly Pan-African (Ediacaran–Cryogenian) U-Pb ages in Madagascar-derived sand, which also yields a few grains as old as Paleoarchean and many discordant ages reflecting Pan-African reworking of Archean cratonic rocks. Lower Valley and Lower Fan deposits have intermediate fingerprints, indicating that sediment supply from Madagascar is not much less than from Africa despite a much smaller catchment area, which can be explained by deposition of a conspicuous part of Africa-derived sediment in the Intermediate Basin confined between the Zambezi Shelf, the Beira High, and the Îles Éparses.</jats:p> <jats:p>By assuming that compositional differences between Quaternary submarine deposits and modern Zambezi River sands primarily resulted from sediment impoundment by large dams, we could evaluate the anthropogenic impact on natural sediment fluxes. Quaternary turbidites are somewhat higher in quartz and poorer in heavy minerals with higher relative amounts of durable ZTR species, and yield more Ediacaran, Neoarchean, and Carboniferous detrital-zircon ages than modern river sands. The Orosirian peak characterizing the Intermediate Basin sample points to prominent supply from the middle and upper parts of the Zambezi catchment in the middle Pleistocene. Rough calculations suggest that pre-dam Zambezi sediments were generated ≤ 10% in the upper catchment, ∼ 60% in the middle catchment, and only ≥ 30% in the lower catchment that provides the totality of sediment reaching the Indian Ocean today.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>Zircons extracted from 567 granitic cobbles, in middle to late Pleistocene tills of the Lake Michigan Lobe in Illinois, provide a remarkably consistent Archean age of ∼ 2.7 Ga, with 87% dating between 2.6 and 2.8 Ga. This finding suggests a persistent glacial flow path of the southern Laurentide ice sheet from the Superior Province into the Lake Michigan basin during Marine Isotope Stage 6 (Illinois Episode) and Marine Isotope Stage 2 (Wisconsin Episode). Based on published crystalline bedrock ages in the Canadian Shield, these cobbles are interpreted to have been transported as much as ∼ 2000 km southwestward from the Quebec–Labrador ice dome, east of Hudson Bay, to the ice-sheet terminus in central to southern Illinois, USA. Some of the glacial flow likely skirted eastern Hudson Bay (source of Omar erratics) and southern James Bay, and traversed outcrops of Huronian jasper conglomerate and diamictite along the north shore of Lake Huron. Transport across the Paleozoic strata may have been enhanced, in part, by an ice stream that advanced across relatively soft and water-saturated sediments that underlie the Lake Michigan basin. The Lake Michigan basin, although present earlier in some form, was likely significantly eroded and overdeepened by accelerated glacial flow and erosion during MIS-6, further constraining the southern Laurentide Ice Sheet (LIS) flow path and influencing its subsequent flow during the last glaciation. As the Lake Michigan Lobe thinned and radiated out from the Lake Michigan basin, topographic effects led to separation of sublobes during the LIS advance to its southernmost extent.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>Tepee structures, associated with cracks and intraformational breccias, are found in the basal part of the Thin Rhythmites Bed of the Irati Formation. The rhythmite alternates dark gray mm-thick laminae, formed by dolomicrite with crenulated microlamination rich in organic clay, and intermediate gray laminae, formed by dolarenite with peloids. Some of the rhythmic pairs are separated from each other by thin horizons (&amp;lt; 0.5 mm) with a concentration of quartz pseudomorphs of gypsum and/or pores resulting from bioturbation or dissolution. The close association of the peloids with microrosettes of early authigenic sodium sulfate, a typical salt of nonmarine brines, is suggestive of its formation under cyanobacterial action, favored by hypersaline conditions in inland lakes. This is consistent with the closing of the connection between the Paraná Basin and the Panthalassic Ocean, as has been suggested for the final stages of Irati sedimentation. The tepees analyzed are related to diapiric features of massive light gray dolomicrite, which is distinguished under the microscope as being poorer in organic matter and for presenting coalesced peloids (clots) rich in sodium sulfate. The hydroplastic rheology, overpressure, and density gradient required for the upward injection of light gray dolomicrite are attributed to supersaturation in water and the presence of eodiagenetic low-density hydrated sulfates (e.g., mirabilite and thenardite). Thus, the processes that form the tepees studied here differ from those described in previous models of lacustrine and lagoon tepees, especially regarding the fundamental role of the expansion and mobility of the sulfated dolomite sediment, controlled by the lake's hydrology and by the elevation of groundwater, without necessarily involving subaerial exposure processes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Turbidity currents transport vast amounts of sediment through submarine channels onto deep-marine basin-floor fans. There is a lack of quantitative tools for the reconstruction of the sediment budget of these systems. The aim of this paper is to construct a simple and user-friendly model that can estimate turbidity-current structure and sediment budget based on observable submarine-channel dimensions and general characteristics of the system of interest. The requirements for the model were defined in the spirit of the source-to-sink perspective of sediment volume modeling: a simple, quantitative model that reflects natural variability and can be applied to ancient systems with sparse data availability. The model uses the input conditions to parameterize analytical formulations for the velocity and concentration profiles of turbidity currents. Channel cross section and temporal punctuation of turbidity-current activity in the channel are used to estimate sediment flux and sediment budget. The inherent uncertainties of geological sediment-budget estimates motivate a stochastic approach, which results in histograms of sediment-budget estimations, rather than discrete values. The model is validated against small-scale experimental turbidity currents and the 1929 Grand Banks turbidity current. The model performs within acceptable margins of error for sediment-flux predictions at these smallest and largest scales of turbidity currents possible on Earth. Finally, the model is applied to reconstruct the sediment budget related to Cretaceous slope-channel deposits (Tres Pasos Formation, Chile). The results give insight into the likely highly stratified concentration profile and the flow velocity of the Cretaceous turbidity currents that formed the deposits. They also yield estimates of the typical volume of sediment transported through the channels while they were active. These volumes are demonstrated to vary greatly depending on the geologic interpretation of the relation between observable deposit geometries and the dimensions of the flows that formed them. Finally, the shape of the probability density functions of predicted sediment budgets is shown to depend on the geological (un)certainty ranges. Correct geological interpretations of deep marine deposits are therefore indispensable for quantifications of sediment budgets in deep marine systems.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The postglacial sea-level rise after the Last Glacial Maximum provided ideal conditions to study the transgressive sedimentary response to sudden shelf flooding driven by different rates of sea-level rise. In this study, a high-resolution seismic stratigraphic interpretation and sedimentological analysis were conducted on data from the northern Gulf of Cadiz continental shelf (SW Iberian Peninsula), in order to: 1) understand the succession of sedimentary processes during each shelf flooding episode and 2) explore the significance of variable rates of sea-level rise, sediment fluxes, and climatic conditions on the development of postglacial deposits.</jats:p> <jats:p>Four backstepping seismic postglacial transgressive units (PTUs; 4 to 1 from oldest to youngest) that are linked to the retreating mouth of the Guadiana River were interpreted. Together, these seismic units display a wedge-shape geometry, are located over the inner to middle shelf, and overlie a regional unconformity formed during the Last Glacial Maximum. Each PTU can be divided into several sub-units with distinctive seismic facies that have a similar stratigraphic organization. Each PTU contains lower sub-units that are composed of low-angle tangential-oblique clinoforms. The clinoforms are locally topped by a channelized sub-unit. The distal and/or lateral parts of the clinoforms are occasionally buried by sheet-like semitransparent subunits. The uppermost sub-units are present over the proximal and central parts of each seismic unit and are also sheet-like. PTUs can also be subdivided and described sedimentologically. Fine-grained sands with intercalated silty layers dominate the lower part of each PTU (lower clinoform sub-units). The upper part of each PTU (upper sheet-like sub-units) is characterized by reworked facies, composed of highly fragmented bioclasts within a mixture of silt and coarse to medium sand. Finally, mud deposits occur as a sediment drape over the PTUs.</jats:p> <jats:p>The internal structure of each PTU reveals several phases of development under a general process of transgressive submergence in which both coastal and marine deposits were formed and eventually preserved. The initial phase involved the development of coarse-grained deltas in shallow water, which were locally eroded by a network of distributary channels. In a transitional phase, the infilling of distributary channels and the offshore export of fine-grained sediments is related to a change in sediment sources, possibly triggered by enhanced hydrodynamic processes. The final phase involved the reworking of fluvio-deltaic sediments by shoreface processes to generate a sediment sheet. Age correlation with a suite of postglacial sea-level curves indicates that the formation of the postglacial transgressive deposits is bracketed between 14 ka and 9 ka. The studied deposits are related to a period of reduced sea-level rise, culminating in the Younger Dryas event (two oldest PTUs), and to phases of enhanced sea-level rise, such as Meltwater Pulse (MWP) 1B (two youngest PTUs). In spite of high rates of sea-level rise over MWP-1B, each PTU exhibits progradation and preservation of much of the delta. The preservation of progradational deltaic units is likely caused by increased sediment supply during progradational pulses. We suggest that those pulses of enhanced sediment fluxes during MWP-1B were strongly driven by the overall climatic conditions in the southwest of the Iberian Peninsula, probably resulting from enhanced rainfall runoff during humid periods and scarce land vegetation cover.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This work focuses on an exceptionally complex natural laboratory, the Triassic Latemar isolated platform in the Dolomite Mountains of northern Italy. It explores spatial and temporal gradients in processes and products related to contact metamorphism, dolomitization, and the dedolomitization of marine limestones. Rock samples were studied using dual fluid-inclusion thermometry and clumped-isotope thermometry. Independent of the spatial position at Latemar, Δ47 clumped-isotope and fluid-inclusion data provide contrasting paleotemperature estimates. An apparent lack of systematic patterns in fluid-inclusion data (homogenization temperature, salinity, density) results from analyses of micrometer-sized growth zones within a single crystal. The composition of the individual fluid inclusions represents a “snapshot” of fluid mixing with variable endmember elemental ratios. The bulk crush-leach data and slopes in Caexcessversus Nadeficit diagrams indicate different water–rock interactions and fluid signatures with evaporation sequences and crystalline rocks. The presence of three fluid types (crystalline basement brine, halite-dissolution brine, seawater) in all carbonates suggests that all fluids coexisted during contact metamorphism and dolomitization of Latemar carbonates. Non-equilibrium processes overruled thermodynamic controls on the precipitation of diagenetic phases. Fluid mixing resulted in the precipitation of two complex carbonate successions. The Δ47 data represent bulk temperatures, averaging the mixing ratio of fluids with different temperatures and their respective volume. Fluid-inclusions record patterns of remarkable complexity and shed light on the complexity of a multi-fluid system. Data shown here provide answers to the controversial interpretation of dolomitizing fluid temperature in the Latemar and exemplify the strengths of multi-proxy paleotemperature studies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This study illustrates the clay mineralogy and sedimentary geochemistry of the Red River and its major tributaries and distributaries in northern Vietnam and shows how these methods can be used to unravel grain size, provenance, hydraulic-sorting, and chemical weathering effects. All sand samples are SiO2-rich and consequently depleted in most chemical elements (but Sn and Pb) relative to the upper continental crust (UCC). The order of element mobility indicated by αAlE values, which estimate the degree of depletion in mobile element E relative to the UCC standard, is Ca ≥ Na &amp;gt; Sr &amp;gt; Mg &amp;gt; Ba ≥ K ≥ Rb. In mud fractions, SiO2 decreases, and other elements consequently increase. The grain size-dependent intrasample chemical variability of fluvial sediments reflects the grain size distribution of detrital minerals, which is strictly controlled in turn by the settling-equivalence principle. The 87Sr/86Sr ratio in Red River sands varies widely between 0.716 and 0.748, and εNd ranges from −8.5 to −13.8. The negative εNd values and high 87Sr/86Sr ratios point at a significant contribution from Precambrian crystalline basement, directly or through recycling of Triassic siliciclastic strata. Clay-mineral assemblages, dominated by illite and smectite with subordinate kaolinite and minor chlorite, suggest largely physical erosion in the upper catchment and stronger weathering in the monsoon-drenched lower catchment. Extremely intense weathering is demonstrated by a Quaternary soil sample from the Red River valley in northernmost Vietnam, which is a pure quartzose sand yielding a tourmaline-dominated heavy-mineral suite and a kaolinite-dominated clay-mineral assemblage. In the humid landscapes of northern Vietnam, no detrital mineral, excepting quartz, muscovite, tourmaline, prismatic sillimanite, anatase, and zircon, can resist even shallow early pedogenesis.</jats:p>

<jats:title>ABSTRACT</jats:title> <jats:p>What processes control grain size and bed thickness in submarine canyon deposits? Erosive, shelf-cutting canyons contrast with accretionary basin-floor submarine fan accretionary channels because the former tightly constrain turbidity flows in deep channels. This study addresses such a deep-water depositional system in the Indus Submarine Canyon using a series of cores collected along the canyon. Grain-size analysis was conducted for turbidite and hemipelagic sediment deposited in the Holocene Indus Submarine Canyon mostly by diffuse, fine-grained turbidity currents and hemipelagic hypopycnal plumes. We investigate the links between sedimentary grain size, bedding thickness, facies, and canyon morphology. Well-sorted silt in layers mostly &amp;lt; 2 cm thick dominates the canyon. Core sites in the canyon located downstream of knickpoints have coarser, less well sorted sediments because of current acceleration in these areas and then the slowing of flows downslope. Sediments fine with increasing height above the canyon thalweg, implying deposition from a turbulent plume head. The great depth of the canyon, caused by the exceptionally wide shelf and steep slope, prevents channel overspill which controls sedimentation and channel form in submarine fans. Thalweg sediment fines down-canyon into the mid canyon, where sediment bypassing is inferred. The thickest turbidites are found in the sinuous lower canyon where the gradient shallows from ∼ 0.7° to 0.3°. However, canyon gradient has little impact on mean grain size, but does correlate with bed thickness. The active canyon channel, located in a channel belt gradually becomes less steep, more meandering, and narrower farther downstream. Sinuosity is an influence on turbidite bedding thickness but does not control grain size, in contrast to the situation in submarine-fan channel–levee complexes. Compared to the well-known, more proximal Monterey Canyon of California the grain sizes are much finer, although both systems show evidence of &amp;gt; 200 m plume heads.</jats:p>