Basin Floor Research Articles

Spatiotemporal patterns of land surface temperature and their response to land cover change: A case study in Sichuan Basin

Land surface temperature (LST) is a critical geo-parameter in terrestrial environmental interaction processes, directly related to land cover change (LCC) which modifies surface energy balance. In this study, LST data from 2003 to 2019 were reconstructed in the Sichuan Basin with average R2 of 0.85 (daytime) and 0.91 (nighttime), effectively filling in the missing pixels and reducing the noise components. Emerging hot spot analysis (EHSA) and land cover transfer matrix were utilized to analyze the multi-patterns of LST spatiotemporal evolution and responses to LCC. Results indicate that LST hot spots are concentrated in low-altitude basin floor and are dominated by sporadic hot spots. Cold spots are mainly in marginal high-elevation mountains, but the dominant pattern varies with time scale. The largest proportions of hot and cold spots are found in summer (>46 %) and autumn (>29 %), respectively. Moreover, the significant upward and downward trends of LST cold and hot spots are most prominent in western plain and marginal mountains, respectively, and have the largest coverage in summer and autumn, respectively. In total LCC area, cropland-to-forest (CF), cropland-to-impervious (CI), and forest-to-cropland (FC) account for 93.55 %. Among them, CI significantly promotes the aggregation and upward trend of daytime LST hot spots. CF and FC have the strongest effect of aggregating LST cold spots and cooling LST in daytime, with CF being more effective. The information can serve as a reference for regional planning and climate change mitigation measures.

Seismic geomorphology of the basin floor area in the Northern North Sea: evolution of the Frigg submarine channels and their influence on sediment distribution

Seismic geomorphology of the basin floor area in the Northern North Sea: evolution of the Frigg submarine channels and their influence on sediment distribution

The interplay between siliciclastic and carbonate depositional systems: Maastrichtian to Danian basin‐floor sediments of the mid‐Norwegian Møre Basin

AbstractSource‐to‐sink sedimentary systems associated with volcanic rifted margins serve as important archives for basin development by recording lithospheric changes affecting the depositional systems. Distinguishing between sediment transport processes and their sediment source(s) can guide the interpretation of a basin's history, and thereby inform regional paleogeographic reconstructions. In this contribution, we integrate and utilize wireline geophysical logs, detailed petrographic observations from side‐wall cores, and seismic analysis to describe and decipher a Maastrichtian to Danian‐aged basin‐floor depositional system in the deep outer Møre Basin, mid‐Norwegian margin. Well 6302/6‐1 (Tulipan) is a spatially isolated borehole drilled in 2001 that penetrates Maastrichtian and younger strata. A succession of hitherto undescribed carbonates and sandstones in the outer Møre Basin was discovered. It is investigated for sediment transport, provenance, and depositional processes on the basin floor surrounded by structural highs and ridges. The strata from the lower parts form a basin‐floor apron consisting of redeposited carbonate sourced from a westerly sub‐aerial high. The apron transitions vertically from mixed siliciclastic and carbonate into a purely siliciclastic fan with intercalated sandstone and mudstone, providing a rare high‐resolution record of how depositional environments experience a complete shift in dominant processes. The development coincides with similar latest Cretaceous‐earliest Palaeocene sequences recorded south of this region (e.g., well 219/20‐1) and may have been influenced by regional uplift associated with the onset of magmatism in the Northeast Atlantic. This study improves our understanding of a late, pre‐breakup source‐to‐sink sedimentary system developed near the breakup axis of an infant ocean, and documents what is possibly the northernmost chalk deposit in the Chalk Group.

Rare earth element and yttrium (REY) geochemistry of 3.46–2.45 Ga greenalite-bearing banded iron formations: New insights into iron deposition and ancient ocean chemistry

Finely laminated cherts enclosing nanoparticles of greenalite and apatite are ubiquitous in Archean-Paleoproterozoic (3.46–2.45 Ga) ferruginous cherts, jaspilites and Banded Iron Formations (BIFs) and the greenalite and apatite are considered to be primary deposits. The cherts and BIFs are chemical sedimentary rocks interpreted to have been precipitated in marine settings prior to the first permanent rise in atmospheric oxygen at the Great Oxidation Event (GOE) ca. 2.45–2.32 M.y. ago. As chemical sediments, they are potential archives of the solutions from which they precipitated, incorporating signals from hydrothermal fluids and ambient seawater. Previous studies of rare earth elements and Y (REY) in pre-GOE BIFs have mostly found an “Archean seawater signature” with positive Eu anomalies, attributed to the influence of high-temperature hydrothermal processes, and positive anomalies for La, Gd and Y, ascribed to seawater. REY abundances determined by in situ LA-ICP-MS are presented for well-preserved, laminated greenalite-bearing cherts from ten formations of pre-GOE ferruginous cherts and BIFs from Western Australia. The samples come from a wide range of depositional environments, e.g., submarine proximal volcanic environments, basin floor, slope and deep marine shelf, and are between 3.46 Ga to 2.45 Ga in age. Five groups with different REY patterns are identified, namely (i) mafic-volcanic-influenced vent-proximal chert from the Marble Bar Chert Member of the Duffer Formation of the Warrawoona Group; (ii) felsic volcanic- and sediment-associated chert from the Kangaroo Caves Formation of the Sulphur Springs Group and the Wilgie Mia Formation of the Murchison Supergroup, (iii) ferruginous cherts in shelf sediments from the Bee Gorge Member of the Wittenoom Formation of the Hamersley Group, (iv) BIFs from the Nammuldi Member of the Marra Mamba Iron Formation and Joffre Member of the Brockman Iron Formation, Hamersley Group, and (v) BIFs from the Dales Gorge Member of the Brockman Iron Formation. Of these, only the Dales Gorge Member BIF has a typical Archean seawater signature while the others have REY patterns likely reflecting differing source fluids and environments of deposition but not necessarily global ocean chemistry. Analyses of chert containing sub-micron-sized particles of greenalite and apatite indicate that the likely hosts of the REEs are apatite, siderite and possibly greenalite. The REY patterns of the greenalite-bearing cherts may differ from those of bulk samples of the same formations, perhaps reflecting a diagenetic overprint in the bulk samples, whereas the greenalite-bearing cherts likely preserve their depositional compositions, locked in by early silicification.

Modern Sedimentation Patterns in Lake Issyk Kul (Kyrgyzstan), Derived From Surface Sediment and Inlet Stream Samples

AbstractThis study provides a descriptive characterization of the modern sedimentary processes in Lake Issyk Kul, Kyrgyzstan, important for the selection of a suitable coring or deep‐drilling site, interpretation of future core data and applicability of proxies. The quasi‐equidistant sampling grid of 66 sediment surface samples covers the entirety of the lake basin and is complemented by 10 samples from the major inflows. The methodological approach includes geochemical, granulometric, lipid biomarker, diatom, and statistical analyses. The quantitative and qualitative changes in sediment composition yield information on its generic origin and prevailing transport and depositional environments. The composition of the surface sediments in Issyk Kul is highly heterogenous. Nearshore deposition is mainly controlled by wave action and by fluvial sediment supply with highest quantities of detrital input coming from the high‐energetic, eastern tributaries. Sediments in the deep central basin are mainly produced in situ and dominated by authigenic calcite. Biogenic accumulation is overall low, except for the western extremity of the lake, where the nearshore, shallow‐water, and low‐energetic environment favors aquatic productivity and subsequent preservation of organic material and diatoms. Redeposition of sediments is a dominant process along the slopes across the southern and western basin floor, where run‐out distances of mass movement deposits are up to 5 km. Directional sediment transport by lake currents appears to be less important, except for the transport of very fine‐grained organic matter. Biomarker‐inferred temperature reconstructions suggest lake surface temperatures of ∼15°C in the western littoral zone and in Tyup Bay and a decrease to ∼13°C basinward.

Assessing mountain block water storage changes in river basins using water balance and GRACE: A case study on Lake Urmia Basin of Iran

Study regionLake Urmia Basin (LUB), northwestern Iran, encloses the largest salt lake in Iran, where severe drawdown of the lake water level is causing salt storms that threaten the health of the basin's inhabitants. Study focusDifferent in-situ and RS-based datasets are used to estimate the water storage change (WSC) in LUB and partition it into the basin floor WSC and mountain block WSC components. Water balance components for LUB were estimated for the 2001–2011 period, using RS-based datasets for precipitation, actual evapotranspiration, soil moisture and snow storage. Ground-based data were used for validation of RS data as well as water balance closure purpose. GRACE terrestrial water storage data were also used to validate the water balance method results. New hydrological insights for the regionGRACE results confirmed an average WSC of − 921 million cubic meters per year (MCM/yr) (−17.6 mm over the basin area). WSC time series in the basin floor (average: −913 MCM/yr, or −53 mm over the basin floor area) was estimated by summing the related water storage components, and then subtracted from the basin WSC to estimate the mountain block WSC time series (average: −8 MCM/yr, or −0.2 mm over the mountain block area). To evaluate its authenticity, the estimated mountain block WSC time series was then compared to mountain block rivers’ base flow and springs' discharge, showing a considerable correlation between the time series. Considering the faster water resources depletion in the basin floor (where anthropological factors are significant) than in the mountain block (where anthropological factors are rare), one can conclude that anthropological factors may have the primary role in deteriorating water resources conditions in the basin.

Potentiality of Charcoal as a Dendrochronological and Paleoclimatic Archive: Case Study of Archaeological Charcoal from Southeastern Altai, Russia

Archaeological charcoal from ancient nomad iron-smelting furnaces collected in the highland southeastern Russian Altai has great potential as a material for tree ring analysis. Dendrochronological dating was applied to 355 viable samples (>80% of the 448 collected ones), prepared using a new protocol. Individual tree ring series of 155 (~43%) samples were used to construct nine floating chronologies from 76 to 290 rings long. The archaeological and radiocarbon data on charcoal that fueled the hearths of the Kosh-Agach type bracket the floating tree ring chronologies between the second and tenth centuries AD. The results demonstrate that long tree ring “steppe” chronologies can be obtained for intermontane basins in the arid zone of Southern Siberia, using the analysis of charcoal samples. A strong climate signal imprinted in the annual growth of trees allowed for crossdating samples with relatively few rings. The revealed common climate signal for larches from different locations indicates similar paleoclimate conditions of their growth despite the strong modern southeastward aridization trend in the region, which was not so pronounced ca. 1.5 ka ago. The further matching of these chronologies to the calendar timeline will provide reference for the precise comparison of climatic conditions in the floors of intermontane basins and in the flanking mountains.

Flow transformations, mud partitioning and the variable stratigraphic architecture of basin-floor fan fringes

Highly efficient sediment gravity flows can bypass mid fan channels and lobes and deposit significant volumes of sand, mud and particulate organic matter in outer fan and basin plain settings. The Serpukhovian to Bashkirian fill to the Shannon Basin, western Ireland, includes deep-water fan deposits (Ross Sandstone Fm) that gradationally overlie basin floor shales (Clare Shale Fm). As part of a broader progradational succession, the upward transition from muddy basin floor to sandy fan preserves the stacked deposits of settings present prior to and outboard of mid-fan channels and lobes. Three fully cored boreholes and associated wireline data constrain the facies tracts in an 18 km long panel orientated oblique to original depositional dip. Two distal successions dominated by hybrid event beds (HEBs) are recognised, separated by a prominent condensed section. The lower Cosheen system includes m-thick, tabular HEBs with prominent linked debrites that pass down dip into much thinner sandstones overlain by sand-speckled mudstone caps that thicken distally before thinning. The latter are interpreted as secondary mudflows released following reconstitution of more thoroughly mixed sections of the up-dip linked debrites. Significant bypass and accumulation of mud by this mechanism helped heal local topography and maintain a relatively flat sea floor promoting an overall tabular geometry for the deposits of larger volume hybrid flows reaching the distal sector of the basin. The overlying distal Ross system fringe is characterised by very fine to fine-grained sandstones and is lateral to compensationally-stacked lobes further to the west. It has a progradational (at least initially) stacking pattern, facies transitions developed over shorter length scales, and includes outsized event beds but these are thinner than those in the Cosheen system. Common banding and evidence for turbulence suppression by dispersed clay rather than entrained mud clasts indicate these were transitional flows. In this case, event beds are inferred to taper distally, with significant mud emplaced by plug flow retained as caps to sandy event beds rather than bypassing down-dip. Different flow transformation mechanisms thus impacted how mud was partitioned across the fringe of the two systems and this influenced bed geometries, larger scale bed stacking patterns and stratigraphy. Whereas the flow efficiency concept stresses the ability of flows to carry sand in a basinward direction, it is also imperative to consider the variable efficiency of mud transport given the operation of clay-induced flow transformations. These can either promote bypass or trigger premature fallout of mud with implications for how systems fill accommodation, bed -scale facies transitions and the burial and preservation of particulate organic carbon fractionated along with the clay in deep-water system fringes.

Static Reservoir Simulations and Seismic Attributes Application to Image the Miocene Deep-Water Reservoirs in Southeast Asia

Globally, deep-water reservoir systems are comprised of a variety of traps. Lateral and downdip trapping features include sand pinch-outs, truncation against salt or shale diapirs, and monoclinal dip or faulting with any combination of trapping designs; the potential for massive hydrocarbon accumulations exists, representing significant exploration prospects across the planet. However, deep-water turbidites and submarine fans are two different types of traps, which are developed along the upslope and the basin floor fans. Among these two traps, the basin floor fans are the most prolific traps as they are not influenced by sea-level rise, which distorts the seismic signals, and hence provides ambiguous seismic signatures to predict them as hydrocarbon-bearing zones for future explorations. Therefore, the deep-water channel-levee sand systems and basin floor fans sandstone define economically viable stratigraphic plays. The subsurface variability is significant, and hence, characterizing the thick (porous) channelized-basin floor fans reservoir is a challenge for the exploitation of hydrocarbons. This study aims to develop seismic-based attributes and wedge modeling tools to accurately resolve and characterize the porous and gas-bearing reservoirs using high-resolution seismic-based profiles, in SW Pakistan. The reflection strength slices better delineate the geomorphology of sand-filled channelized-basin floor fans as compared to the instant frequency magnitudes. This stratigraphic prospect has an area of 1180 km2. The sweetness magnitudes predict the thickness of channelized-basin floor fans as 33 m, faults, and porous lithofacies that complete a vital petroleum system. The wedge modeling also acts as a direct hydrocarbon indicator (DHI) and, hence, should be incorporated into conventional stratigraphic exploration schemes for de-risking stratigraphic prospects. The wedge model resolves a 26-m thick hydrocarbon-bearing channelized-basin floor fans lens with a lateral distribution of ~64 km. Therefore, this wedge model provides ~75% correlation of the thickness of the LSL as measured by sweetness magnitudes. The thickness of shale that serves as the top seal is 930 m, the lateral mud-filled canyons are 1190 m, and the thick bottom seal is ~10 m, which provides evidence for the presence of a vibrant petroleum play. Hence, their reveals bright opportunities to exploit the economically vibrant stratigraphic scheme inside the OIB and other similar global depositional systems.

Predictable time preservation on passive continental margins revealed from forward stratigraphic models

AbstractAlthough the majority of the world's sedimentary basins are located along passive continental margins, the link between their stratigraphy and time architecture has not been fully investigated in three dimensions. Here, using a 3D numerical forward stratigraphic model, we report a previously unidentified trend: an increase in temporal completeness from the shelf to the upper slope and a reduction towards the basin floor. Sedimentation rates from our results are consistent with those measured from a global dataset; our results are also consistent with a chronostratigraphically well‐constrained subsurface example: the Eocene of the Santos Basin, offshore Brazil. Because our results reproduce both globally and locally observed time‐preservation trends, we suggest the use of such models to inform time architecture in the context of surface and subsurface accumulations. Applying these concepts will not only provide a spatiotemporal framework for passive‐margin settings but will provide a more complete understanding of the inherently incomplete geological record.

Extrinsic controls on turbidity fan lobes spatial distribution and potential reservoir presence prediction in half-graben lacustrine basin during early syn-rift: Insights from stratigraphic forward modelling

Turbidite strata are common along faulted margins of half-graben lacustrine basins, but complex lobe evolution may cause significant variability and uncertainty in the spatial distribution of turbidite sand bodies. This study integrates core samples, seismic and well log data from the Dongying Depression lacustrine basin in East China, and uses these data as inputs to a reduced-complexity stratigraphic forward model of turbidite fan lobe evolution. Data-unconstrained sensitivity analysis is used to investigate sensitivity of fan-lobe spatial distribution to fault-related subsidence rate, basin-margin slope, sediment input volume, and sediment input volume oscillation period. A data-constrained multiple-scenario approach then varied parameters within defined uncertainty ranges to generate a series of best-fit models to predict optimal reservoir presence locations. Results indicate that syn-rift segmentation of the Shengbei fault leads to spatial and temporal variation of fault-related subsidence in the hanging wall basin. External controls exert systematic impact on the spatial distribution of both smaller-scale flow beds and larger-scale fans on basin floor. Higher rates of fault-related subsidence and smaller sediment input volume produce more laterally confined fan lobe distribution. Higher basin-margin slope gradient produces more laterally clustered turbidites, but does not change fan lobe location, indicating break of slope is a more significant control on fan location. Multiple scenario reservoir presence probability maps suggest that bypass-dominated middle and inner fan areas, and smaller lengths of retrogradation-dominated feeder channels are most promising reservoir locations.

Deep‐water sand transfer by hyperpycnal flows, the Eocene of Spitsbergen, Arctic Norway

AbstractFlood‐generated hyperpycnal flows are dense, sediment‐laden, turbulent flows that can form long‐lived, bottom‐hugging turbidity currents, which undoubtedly transport large volumes of fine‐grained sediments into the ocean. However, their ability in transferring sand into deep‐water basins is debated. This study presents sedimentological evidence of sandy hyperpycnal flow deposits (hyperpycnites) in a series of basin floor lobe complexes associated with a progradational shelf margin in the Eocene of Spitsbergen, Arctic Norway. Four coexisting types of sediment gravity flow deposits are recognized: (i) sandy hyperpycnites deposited by quasi‐steady hyperpycnal flows; (ii) turbidites deposited by waning, surge‐type turbidity currents; (iii) hybrid event beds deposited by transitional flows; and (iv) mass transport deposits emplaced during rare slope failures. The abundance of thick‐bedded massive sandstones, frequent bed amalgamation, the distribution of hyperpycnites across the lobes and the abundance and systematic occurrence of plant‐rich hybrid event beds and associated climbing ripple cross‐laminated beds in the lobe fringes, suggest that hyperpycnal flow was the most important mechanism driving lobe progradation. Shelf‐edge positioned fluvial channels linked to the basin floor lobe complexes via deeply incised, sandstone‐filled slope channels, suggest that rivers fed directly onto the slopes where their dense, sand‐laden discharges readily generated quasi‐steady hyperpycnal flows that regularly reached the basin floor. The composite architecture and complex waxing–waning flow facies configuration of the hyperpycnites is consistent with sustained and concomitant suspension and traction deposition under fluctuating subcritical to supercritical conditions. Similar sandstone beds occur on the clinoform slopes, indicating that the hyperpycnal flows operated likewise on the slope. Plant‐rich hybrid event beds indicate transformation of initially turbulent flows by relative enrichment of clay and plant material via progressive sand deposition to such an extent that it suppressed turbulence. The multi‐faceted character of the hyperpycnites reported here, challenges traditional beliefs that hyperpycnites assumingly preserve the waxing–waning signal of single‐peaked floods.

Seismic characteristics and AVO response for non-uniform Miocene reservoirs in offshore eastern Mediterranean region, Egypt

The Eastern Mediterranean region, extending from the Offshore Nile Delta Cone of Egypt to the Levant Basin, is a confirmed hydrocarbon-rich territory with several giant gas discoveries. Numerous gas fields have been discovered in the Miocene reservoirs within the Nile Delta Cone, and the Levant Basin. The Miocene sedimentary sequences in this region are extremely heterogeneous, consisting mainly of turbiditic slope deposits, channels, and basin floor fans that were capped by evaporites formed during the Messinian Salinity Crisis. As a result, the seismic characteristics and interpreted properties of this heterogeneous section are ambiguous. The study area is located in the Offshore North Sinai Basin, where a thick Early Miocene section was deposited midway between the Nile Delta province, which includes the El-Fayrouz discovery, and the Levant Basin, which includes Tamar, Tanin, and several other discoveries. This study uses quantitative seismic interpretations methods, such as amplitude variations with offset and fluid replacement modeling, to assess the seismic acoustic impedance trend with depth. Also, determine the seismic amplitude response for the brine and gas sands reservoir of the Early and Late Miocene section to link the unexplored study area within the North Sinai Offshore Basin with the explored Nile Delta and Levant Basins. In addition to evaluate direct hydrocarbon indicator (DHI) of the dimming seismic amplitude that is compatible with the structure’s last closed contour of the Syrian Arc anticline of the Early Miocene reservoirs (EMT-1 prospect). Different vintages of 2D and 3D seismic data, six wells, and various published data were used in this study. The quantitative interpretation shows the pitfalls of the acoustic impedance trend and seismic response dependency on depth for gas and brine sand, which led to the drilling of the EMT-1 dry well. Also, the fluid replacement, P-wave velocity (Vp), and density (ρ) modeling confirmed that the seismic dimming amplitude was due to a seismic processing artifact, which was corrected by readjusting the overburden Messinian salt processing velocity model. This research concludes that the seismic quantitative interpretations are successfully used to assess the acoustic impedance versus depth and understand DHI pitfalls, as well as the processing workflow that could enhance the seismic image.

Transform margin source–sink clastic deposystems

Abstract Shelf to basin floor clastic-sediment-routing models for individual structural parts of a transform margin are presented. Using 3D and 2D seismic, gravity and well data from the Guyana, Coromandal, Romanche, Saint Paul and Zenith–Wallaby Perth margins as examples, and drawing from a wide range of analogues, four discrete tectonic segments are recognized as characteristic of all transform margins: (1) the transform margin sensu stricto ; (2) the local pull-apart segment on the transform margin; (3) the margin segment developed from the narrow horsetail splaying off from the transform; and (4) the margin segment developed from the extensional end of the horsetail structure, although there are other transitional variants specific to each margin. The routing of clastic sediments varies markedly across these segments. The shelfal staging area varies in width between the segments, increasing in width between segments 1 and 4, with wider shelves (10–25 km) characterized by significant sediment sorting through longshore drift, and narrower segments (0–10 km) often fed directly from focused fluvio-deltaic systems. The overall deep-water slope gradient decreases from segments (1) to (4), with sediment runout distance from shelf to basin floor increasing. The seafloor topography along the margin is highly variable, with significant sand sequestration on slopes with intra-slope ramps and terraces found in segments (2)–(4), with rapid downslope transitions from tributary slope gullies to slope channel complexes and then ponded intra-slope frontal splay complexes on the intra-slope terraces. Mass-transport deposits (MTDs) are ubiquitous and found as either regional slope MTDs or local collapses of slope channel complex margins. Stratigraphic and/or combination traps are associated with the ramp–terrace transitions. Local sectors show pinned long-lived intra-slope channel complex and canyon development, with prominent long-lived intra-slope stacking of intra-slope sandbodies. The outboard basin-floor- or trough-confined deep-water frontal splays (lobes), and their head area erosion by slope-originated MTDs, are directly controlled by the deposystems of the inboard slope systems. The lateral and vertical evolution of deep-water slope architecture is directly controlled by the inherited seafloor topography, set up by the underpinning crustal fabric across the four segments.

The response of high density turbidity currents and their deposits to an abrupt channel termination at a slope break: Implications for channel–lobe transition zones

ABSTRACTThe transition between the slope and basin floor is typically marked by a slope break, in some cases causing channels to terminate and turbidity currents to undergo a loss of confinement. It is thus essential to understand how these slope breaks and losses of confinement influence the hydrodynamic evolution of turbidity currents and impact their depositional variability within natural scale channel mouth settings. Flume experiments, utilizing Shields scaling, are conducted to study how channel slope angle (3°, 6° and 9°) and initial suspended sediment concentrations (12 to 18% by volume) impact the hydrodynamics and deposit geometries of high density turbidity currents, subject to a simultaneous break of slope and loss of confinement. Measured velocity and concentration profiles indicate that turbidity currents are supercritical, with mean velocities between 0.80 m s−1 and 1.04 m s−1 and depth‐averaged basal concentrations between 9.2% and 23.9%, yielding bed shear velocities between 0.050 m s−1 and 0.064 m s−1. Upon encountering the slope break and loss of confinement, turbidity currents exhibit increases to their densimetric Froude numbers and shear velocities. This is due primarily to two factors: firstly, turbidity currents continue to accelerate during an initial period of velocity lag as their residual momentum gradually dissipates; and, secondly, expansion via flow relaxation collapses their structure towards the bed. The corresponding depositional geometries of these processes reveal that turbidity currents produce elongate channel–lobe transition zones that disconnect channel and basin deposits. The length to width ratios of channel–lobe transition zones decrease as the initial sediment concentrations of turbidity currents increase, while a reduction in the channel slope break angle reduces their length to width ratios. Corresponding, lobe elements are observed to increase in length, width and thickness with increasing initial sediment concentrations, while a reduction in channel slope break angle reduces their dimensions due to enhanced slope deposition.

Sequence stratigraphic architecture, evolution, and geological controls of an Eocene isolated carbonate platform, NE Sirte Basin, Libya

The sequence stratigraphic architecture, evolution, and controlling mechanisms of a lower and middle Eocene isolated carbonate platform in the Sirte Basin in north-central Libya were interpreted from two- and three-dimensional (2D and 3D) seismic and well data. The platform contains six stratigraphic surfaces that divide the platform sedimentary successions into two stratigraphic sequences, namely Sequence 5 and Sequence 6, and five systems tracts. The five systems tracts vary in thickness and differ in depositional systems. The lowstand systems tract (LST) of Sequence 5 forms at the base of the focus interval and is composed of a basin floor fan system with hummocky to undulated seismic facies. The highstand systems tracts (HST) of Sequence 5 has the greatest thickness and comprises a well-defined slope system showing a funnel-shaped trend and suggesting progradational stacking pattern. The LST of Sequence 6 contains a middle ramp system formed during the lowest sea-level. The two transgressive systems tracts (TST) are the thinnest, several meters thick, and separating the LST from the HST. Log curves show an overall funnel-shaped motif through all three depositional systems, indicating a progradational stacking pattern. The main factor controlling the platform growth and demise is sea-level fluctuations. Additional factors, such as, subsidence, antecedent topography, and prevailing currents have also contributed to the evolution of the platform. Sea-level changes coupled with subsidence create accommodation for the platform growth and terminate deposition by drowning. The pre-existing topography creates a topographic relief and influences the growth pattern of the platform. Prevailing local currents influence the direction of platform progradation. This study provides insights on the evolution of isolated carbonate platform in a rift setting, which can help predict the lithofacies and depositional systems of economic significance.

Systematic vertical organization of matrix-rich and associated matrix-poor sandstones in ancient deep-marine slope and basin-floor deposits

AbstractDeepmarine two-part strata consisting of a sand-rich basal part overlain sharply by a mud-rich upper part have been termed linked debrites, hybrid event beds, transitional flow deposits, and bipartite facies. In continental slope and proximal basin floor strata of the Neoproterozoic Windermere Supergroup (western North America) and distal basin-floor strata of the Ordovician Cloridorme Formation (eastern North America), bipartite facies form the middle of a depositional continuum hundreds of meters long consisting upflow of thick-bedded, matrix-poor sandstone (<20% detrital mud matrix) to thin-bedded, sandy mud-stone (50%–90% mud matrix). This consistent lithofacies change is interpreted to reflect particle settling in a rapidly but systematically evolving, negligibly sheared sand-mud suspension developed along the margins (Windermere) and downflow terminus (Cloridorme) of a high-energy, mud-enriched avulsion jet.In both study areas, beds of similar lithofacies type succeed one another vertically and transform to the next facies in the depositional continuum at about the same along-strike position, forming stratal units two to nine beds thick whose grain-size distribution gradually decreases upward. This spatial and temporal regularity is interpreted to be caused by multiple surges of a single, progressively waning turbidity current, with sufficient lag between successive surges for the deposition of a traction-structured sandstone overlain by mudstone cap. Furthermore, the systematic back-stepping or side-stepping recognized at the stratal unit scale is interpreted to have been driven by a combination of knickpoint migration and local topographic steering of the flows, which continued until the supply of mud from local seafloor erosion became exhausted, the main channel avulsed elsewhere, or a new stratal element developed.

Stratigraphic expression of the Paleocene-Eocene Thermal Maximum climate event during long-lived transient uplift—An example from a shallow to deep-marine clastic system in the Norwegian Sea

Seismic geomorphology and stratigraphic analysis can reveal how source-to-sink systems dynamically respond to climatic and tectonic forcing. This study uses seismic reflection data from the Norwegian Sea to investigate the stratigraphic response to a short-lived (0.2 Myr) period of climate change during the Paleocene-Eocene Thermal Maximum (PETM), superimposed on a long-lived (∼8 Myr) period of hinterland uplift. The data show that long-term uplift resulted in ∼300 m of relative sea-level fall, forced regression and formation of incised valleys during the latest Paleocene-earliest Eocene. The short-lived PETM climate perturbation at ∼56 Ma changed the transport dynamics of the system, allowing sediment to be bypassed to wide channel complexes on the basin floor, feeding a large mud-rich basin-floor fan more than 50 km into the basin. Our analysis also suggest that sediment supply was up to four times higher during the PETM compared to earlier and later periods. Maximum regression at ∼55.5 Ma resulted in the formation of a subaerial unconformity. The style of subaerial incision was dictated by shelf accommodation and proximity to the area of direct sediment input. Out-of-grade shelves and slopes sourced by littoral drift were prone to incision, but direct-fed and graded shelves and slopes were not. Despite maximum regression, sediments were not transported significantly beyond the toe-of-slope aprons, suggesting that rapid climate change was more efficient in bypassing sediment to the deep-water than low stands of sea level. As long-term accommodation increased after the PETM, deltas were still able to reach shelf edge, but periods of maximum regression were not associated with deep incisions along the outer shelf and only smaller canyons and gullies formed. The shelf-slope wedge was finally transgressed at ∼51 Ma. The age of deep valley incisions overlaps with the time of subaerial erosion in the East Shetland and Faroe-Shetland basins, suggesting a common mechanism for North Atlantic uplift around 55–56 Ma. Other seismic stratigraphic surfaces do not seem to be regionally time-equivalent, highlighting the importance of local controls on internal architecture of shelf-slope wedges. This study demonstrates the high-resolution stratigraphic response to long- and short-term external forcing together with intrinsic processes and can help identify similar relationships in other areas.

Structural influences on groundwater circulation in the Makgadikgadi salt pans of Botswana? Implications for martian playa environments

Across the surface of Mars, evidence of past lacustrine and evaporitic environments has been found within basins and craters, where often layered sedimentary deposits and hydrated minerals are observed. However, the intensity, duration, and precise phases of aqueous processes during their deposition remain unresolved mostly for our inability to model subsurface structures. Although several geological processes and locations on Earth have been previously proposed as examples to describe these deposits on Mars, we lack a strong visualization of what water activity might have looked like during evaporitic stages within basins and craters. Here we propose to investigate the shallow subsurface of the Makgadikgadi salt pans of Botswana as a potential analog for understanding groundwater upwelling on Mars. The pans are found within the Makgadikgadi Basin, a depression located at the southwestern end of a northeast-southwest set of graben linked with the East African Rift. The Makgadikgadi Pans are evaporitic environment rich in hydrated minerals and groundwater activity. The purpose of this work is to identify buried faults and areas of relative water saturation within the lacustrine sediment of the Makgadikgadi Basin by means of electrical resistivity surveys. This work represents the first electrical resistivity survey of the basin floor which provides a precursory investigation of the relationship between groundwater, faults, basement depth, and the lacustrine sediments. We present four electrical survey lines from different locations in the pans which reveal distinct sedimentary units. Several faults are inferred from the vertical displacement of these units and accompanying low resistivity where displacement is observed. These results provide a framework for visualizing the sedimentary sequences of infilled basins and craters on Mars, which can broaden the ongoing discussion of hydrogeological processes that were active in the planet’s past. We propose Meridiani Planum, as well as Oyama and Becquerel crater of Arabia Terra as locations to establish this framework. Since such processes are still ongoing in the Makgadikgadi Basin, imaging the subsurface of the pans helps explain the formation of layered and salty deposits on the surface of Mars, how they may have interacted with flowing water, and whether they might have hosted life.

Heat flow and thermal regime in the Guaymas Basin, Gulf of California: Estimates of conductive and advective heat transport

AbstractHeat flow is estimated at eight sites drilled int the Guaymas Basin, Gulf of California, during the International Ocean Discovery Program Expedition 385. The expedition sought to understand the thermal regime of the basin and heat transfer between off‐axis sills intruding the organic‐rich sediments of the Guaymas Basin, and the basin floor. The distinct sedimentation rates, active tectonics, and magmatism make the basin interesting for scientific discoveries. Results show that sedimentation corrected heat flow values range 119–221 mW/m2 in the basin and 257–1003 mW/m2 at the site of a young sill intrusion, denominated Ringvent. Thermal analysis shows that heat in the Guaymas Basin is being dissipated by conduction for plate ages >0.2 Ma, whereas younger plate ages are in a state of transient cooling by both conduction and advection. Drilling sites show that Ringvent is an active sill being cooled down slowly by circulating fluids with discharge velocities of 10–200 mm/yr. Possible recharge sites are located ca. 1 km away from the sill's border. Modelling of the heat output at Ringvent indicates a sill thickness of ca. 240 m. A simple order‐of‐magnitude model predicts that relatively small amounts of magma are needed to account for the elevated heat flow in non‐volcanic, sediment‐filled rifts like the central and northern Gulf of California in which heating of the upper crust is achieved via advection by sill emplacement and hydrothermal circulation. Multiple timescales of cooling control the crustal, chemical and biological evolution of the Guaymas Basin. Here, we recognize at least four timescales: the time interval between intrusions (ca. 103 yr), the thermal relaxation time of sills (ca. 104 yr), the characteristic cooling time of the sediments (ca. 105 yr), and the cooling of the entire crust at geologic timescales.