Ponded Basins Research Articles

Paleoenvironmental Significance of Claystone in the Middle Ordovician Miboshan Formation of Ordos Basin, China: Evidence from Trace Elements

The Miboshan Formation in the Middle Ordovician plays a crucial role in the sedimentary evolution of the western margin of the Ordos Basin as it represents the transition from a carbonate platform to a deep-water slope-basin environment. This study focuses on the paleoenvironment of claystone in the Middle Ordovician Miboshan Formation, located in the Ningxia Hui Autonomous Region of the Ordos Basin. The study aims to analyze the influence of sea level and salinity on rare earth elements, investigate terrigenous input and redox conditions through trace element analysis, and exemplify the coupling relationship between depositional and tectonic environments. The Miboshan Formation profile consists of thick- to thin-bedded limestones, mainly composed of lenticular calcirudite with erosion surfaces and horizontal laminae. Grayish black claystone have deformation structures and graptolite fossils. Based on the total number of rare earth elements and the trace element indexes, the seawater properties, redox degree, and terrigenous input are located in two data sets in different parts of the profile (i.e., sample 6-1 to 6-5: Concentrated in lower part, and samples 6-6 to 6-8: Concentrated in upper part), implying that they were deposited at different subaqueous uplifts. Negative Ce anomalies, La/Ce, V/Cr, and Fe3+/Fe2+ ratios indicate an anoxic condition with stratified redox structure, whereas characteristic LaN/NdN, Y/Ho, and Sr/Ba suggest deep-water affected by fresh water. The ∑REEs and Th/U ratios indicated that the study area was mainly deposited from terrigenous materials in the stable tectonic area. According to the ages of deposition, lithologic analyses, and chemical parameters, the Miboshan Formation is related to the deep water environment in a ponded basin influenced by subaqueous uplift resulting from plate subduction in an active continental margin. This study provides valuable insights into paleoenvironment and paleotectonic environments of the Miboshan Formation in the Middle Ordovician.

Seismic geomorphology of a Late Cretaceous submarine channel system in the Kribi/Campo sub-basin, offshore Cameroon

In this study, a 3D seismic reflection dataset and well-log data were integrated to investigate the geometry and internal configuration of a submarine channel system within the Late Cretaceous interval of the deep-water Kribi-Campo sub-basin, offshore Cameroon. This interval is characterized by a well-developed submarine channel system consisting of an early and a late-stage channel. Morphologically, the submarine channel system has a northeast-southwest trend and is U-shaped in cross-section with a length of 56 km within the study area. The early-stage channel has a relatively straight morphology and varies in width and depth from 3 to 5 km and 89–197 m, respectively. However, the late stage of the channel is characterized by a narrower (1–3 km) and shallower (41–103 m) incision, with sinuous morphology carved into the early channel infill. The changing interaction of differential local tectonic, relative sea level, source sediment supply and change in slope gradient are the major control on the geometry and internal characteristics of the submarine channel system. At local scale, basin tectonics is associated with the development of a structural high, controlling submarine channel morphology and depositional patterns in these filled ponded basins. The filling of the channel system coincided with the long-term Maastrichtian relative sea level rise, punctuated by higher order falls in relative sea level. Sand appears to have been fed to the channel system by the palaeo-Sanaga and palaeo-Nyong Rivers, with sand rich aprons developed were these rivers crossed into the study area. The early-stage of the submarine channel is dominated by coarse-grained sediments in the southwest and fine-grained sediments in the northeast, while the late-stage channel is mainly filled with fine-grained sediments. The presence of coarse-grained sediments occurring within the submarine channel axis downstream represents a potential for hydrocarbon reservoirs. The 3D seismic geomorphological analysis of this ancient submarine channel system along the western African margin, as presented in this study, has broad implications in the understanding of the distribution of deep-water sediments with potential for hydrocarbon exploration in the region.

Strike-Slip Transpressional Uplift Offshore San Onofre, California Inhibits Sediment Delivery to the Deep Sea

The Inner California Borderlands is a complex margin where sediment delivery to the basin floor is largely routed through canyon-channel-gully systems. Using nested geophysical surveys, piston and gravity cores from the Eastern Gulf of Santa Catalina, this study compares two canyon systems and investigates how tectonics, shelf width, gradient, and autogenic processes influence turbidite emplacement timing and grain size. One end-member canyon is the Dana Point Canyon, which is ~2 km from the San Juan Creek drainage and has a concave-up channel profile. The other endmember system consists of the San Onofre North and South (SON and SOS) canyons that are detached from San Mateo Creek by a wide 10 km shelf and they traverse a tectonically-deformed slope with multiple ponded basins. Radiocarbon ages sampled from 8 cores reveal that turbidite deposition at Dana Point persists during the sea-level lowstand of Marine Isotope Stage (MIS) 2 through the subsequent transgression and highstand. On the contrary, turbidite emplacement adjacent to the SON and SOS canyons occurs mostly during MIS 2 and ceases around 8 ka. The main regional control on turbidite timing is the wide shelf adjacent to the SON and SOS canyons that is formed by a broad uplifted anticline. This anticline separates the SON and SOS canyons from a riverine source during the sea-level transgression. Much of the tectonic deformation offshore of San Onofre was created by transpression along the right-lateral Newport Inglewood-Rose Canyon Fault Zone. Second-order controls on local turbidite emplacement include small synclines and anticlines that form ponded basins and accommodate deformation on the San Mateo Fault Zone. These basins engender deposition and intervening steep slopes promote sediment bypass. Complex bathymetry offshore San Onofre also affects channel gradient by either accelerating or decelerating flow. Turbidity flow dynamics modified by gradient changes offshore of San Onofre have the ability to modulate channel architecture and grain size. The implications of this work are that tectonically-deformed morphology complicates the timing of turbidite emplacement throughout a sea level cycle and the interpretation of turbidites as paleoseismic records in such regions.

Reservoir deltas and their role in pollutant distribution in valley-type dam reservoirs: Les Království Dam, Elbe River, Czech Republic

Interpretation of catchment pollution history from sediment cores is a common approach for dam reservoirs, but relatively little is known about the spatial distribution of pollutants in the lithologically diverse depositional subsystems. We studied the depositional system of a hundred-year-old valley-type reservoir of the Les Království Dam built in 1919 on the upper reaches of the Elbe River, Czechia. Based on the analysis of pre-dam river valley morphology using historical topography maps with 1 m vertical resolution, 30 ground-penetrating radar sections on the lake and 137Cs dating of four cores, we described a deltaic sediment body with maximum thickness of ~11 m, accumulation rates ranging from 3.6 to 9.7 cm/yr, and an annual loss in reservoir capacity of 0.8%. The sediment body has a distinct delta shape in the longitudinal section, with a delta platform dissected by a channel (topsets) and delta slope (foresets) and a ponded basin (bottomsets) located near the dam. The upstream sections of the channels are prone to erosion and sediment redistribution into downstream parts of the reservoir, as indicated by ground-penetrating radar sections and distribution of 137Cs in younger sediment strata.We retrieved four cores 1.0 to 1.6 m long from different parts of the delta and analysed the sediment grain size using laser granulometry, geochemical composition (X-ray fluorescence, ICP-MS lithogeochemistry, total organic carbon (TOC)) and concentrations of polycyclic aromatic hydrocarbons (PAH). The grain size variation between the delta platform (sandy silts and silty sands) and prodelta (clayey silts) sediments strongly controls the concentrations of lithogenic elements (Al, Fe, K and Ti) but it has a relatively little effect on distribution of toxic metals (Zn, Cu, Pb) and TOC concentrations. The toxic metals show strong affinity to TOC and PAH show a distinct sawtooth vertical distribution suggesting that they were deposited from depositional events during hyperpycnal flows induced by river floods. This study shows that a hyperpycnal delta may serve as a good predicable model for toxic metal- and organic pollutant distribution in dam reservoirs. The role of hyperpycnal flows should not be overlooked in contamination studies of dam reservoirs.

Seismic stratigraphy and depositional architecture of Neogene intraslope basins, offshore western Niger Delta

Abstract Located on a divergent margin dominated by gravity tectonics above overpressured marine shales, the Niger Delta slope has been described as having a stepped profile characterized by ‘filled ponded basins’ that are prone to erosion and sediment bypass. Previous studies based on 3D seismic data have described the depositional architecture of the western Niger Delta's upper slope, but calibration of the seismic facies is lacking and the timing of major changes in sedimentary record remains elusive. In this study, seismic sequence-stratigraphy, 3D geomorphological analyses of high-resolution 3D seismic data, and bio/chronostratigraphic analyses from four boreholes, enabled the identification and characterization of the depositional architecture in Neogene ‘filled ponded basins’. Seven major seismic units were dated as Chattian, Burdigalian, Serravallian, Tortonian, Middle Pliocene and Middle Pleistocene to the present day. Major changes in the sedimentary record occurred in the Plio-Pleistocene, with the onset of erosive channel levee systems (CLSs) and mass-transport deposits (MTDs) generally capped by a hemipelagic drape. Amalgamated CLSs characterize the Tortonian-Late Miocene while erosive MTDs and CLSs characterize the Plio-Pleistocene units. Thick, laterally extensive MTDs are associated with regional slope instability, while active mobile shale triggered local spatially confined MTDs. Submarine channels evolved from moderate to highly sinuous. The degree of channel confinement generally decreases downstream where they are characterized by abandoned meander loops and avulsion resulting from levee breaching. Channel fills and levees/overbank deposits topped by hemipelagic drapes provide effective reservoir/seal (traps) for hydrocarbons. The alternation of channel deposits and hemipelagic layers indicate that eustasy controlled depositional patterns at a regional scale, while the spatio-temporal switches in submarine channel courses show that shale tectonics locally controlled deposition in intraslope basins.

Volume and recurrence of submarine‐fan‐building turbidity currents

AbstractSubmarine fans are archives of Earth‐surface processes and change, recording information about the turbidity currents that construct and sculpt them. The volume and recurrence of turbidity currents are of great interest for geohazard assessment, source‐to‐sink modelling, and hydrocarbon reservoir characterization. Yet, such dynamics are poorly constrained. This study integrates data from four Quaternary submarine fans to reconstruct the volume and recurrence of the formative turbidity currents. Calculated event volumes vary over four orders of magnitude (105 to 109 m3), whereas recurrence intervals vary less, from 50 to 650 years. The calculated turbidity‐current‐event volume magnitudes appear to be related to slope position and basin confinement. Intraslope‐fan deposits have small event volumes (ca 106 m3) while ponded‐fan deposits have very large event volumes (108 to 109 m3). Deposits in non‐ponded, base‐of‐slope environments have intermediate values (107 to 108 m3). Sediment bypass in intraslope settings and flow trapping in ponded basins likely account for these differences. There seems to be no clear relationship between event recurrence and basin confinement. Weak scaling exists between event volume and source‐area characteristics, but sediment storage in fluvial and/or intraslope transfer zones likely complicates these relationships. The methodology and results presented here are also applied to reconstruct the time of deposition of ancient submarine‐fan deposits of the Tanqua Karoo basin, South Africa. The volume and recurrence of submarine‐fan‐building turbidity currents form intermediate values between values measured in submarine canyons and channels (<105 m3 and <101 years) and on abyssal plains (>108 m3 and >103 years), indicating that small, frequent flows originating in submarine canyons often die out prior to reaching the fan, while rare and very large flows mostly bypass the fan and deposit sediment on the abyssal plain. This partitioning of flow volume and recurrence along the submarine sediment‐routing system provides valuable insights for better constraining geohazards, hydrocarbon resources and the completeness of the stratigraphic record.

Highly Seasonal and Perennial Fluvial Facies: Implications For Climatic Control On the Douglas Creek and Parachute Creek Members, Green River Formation, Southeastern Uinta Basin, Utah, U.S.A.

Abstract: The early to middle Eocene Green River Formation consists of continental strata deposited in Laramide ponded basins in Utah, Colorado, and Wyoming. This study (1) documents fluvial and lacustrine strata from the Douglas Creek and Parachute Creek members of the middle Green River Formation, southeastern Uinta Basin, Utah, and (2) uses new interpretations of the link between climate and fluvial sedimentary expression to interpret the terrestrial evolution of early Eocene climate. The stratigraphy was analyzed via outcrops along a 10 km transect in Main Canyon on the Tavaputs Plateau, and is divided into three distinct, stratigraphically separated depositional settings: (1) the lowermost Interval 1 is dominated by amalgamated sandstone channels that contain 70–100% upper-flow-regime sedimentary structures. The channels are interpreted to represent fluvial deposits controlled by a highly seasonal climate, where most deposition was limited to seasonal flooding events. (2) Interval 2 is dominated by alternating siliciclastic and carbonate lacustrine deposits, interpreted as local pulsed fluvial siliciclastic input into shallow Lake Uinta, and periods of fluvial quiescence represented by littoral carbonate deposition. (3) The uppermost Interval 3 is dominated by erosionally-based, trough cross bedded sandstone channels interbedded with littoral lacustrine and deltaic deposits. The Interval 3 sandstone channels are interpreted as perennial fluvial deposits with relatively little variation in annual discharge, akin to modern humid-temperate fluvial systems. The stratigraphic transition from seasonally controlled (Interval 1) to perennial (Interval 3) fluvial deposits is interpreted to represent a fundamental shift in Eocene climate, from the peak hyperthermal regime of the Early Eocene Climatic Optimum (EECO) to a more stable post-EECO climate.

Hybrid Event Beds Generated By Local Substrate Delamination On A Confined-Basin Floor

Abstract The outer parts of deep-water fans, and the basin plains into which they pass, are often described as areas where erosion is negligible and turbidite systems have net aggradation. Nevertheless, sedimentological and stratigraphic analysis of outer-fan-lobe and confined-basin-plain deposits in Cretaceous–Paleocene Gottero Sandstone (NW Italy) has revealed extensive but cryptic bedding-parallel substrate-delamination features at the base of many sheet-like event beds. These comprise a variety of shallow but wide scour structures showing evidence of lateral expansion by sand injection. The scours commonly occur at the base of beds made up of a basal clean sandstone overlain by argillaceous sandstone containing abundant mudstone clasts and locally large substrate rafts (up to 20 meters long). These strata are interpreted as a type of hybrid event bed. Field observations suggest that mud-clast entrainment occurred by delamination at the base of dense sandy flows. The large rafts, in some cases only partly detached, were incorporated in the flows locally and then carried for short distances (hundreds of meters to a few kilometers) before partly disaggregating and undergoing deformation due to internal shearing. The development of such features may be common in flat and/or confined basin settings where high-volume flows interact with a cohesive and well layered substrate (e.g., muddy outer fans or confined or ponded basins with thick mudstone caps). Delamination is therefore suggested as an alternative mechanism leading to the formation of hybrid event beds following local substrate entrainment on the basin floor as opposed to on more remote slopes and at channel–lobe transition zones.

Slip rate estimation along the western segment of the Main Marmara Fault over the last 405-490 ka by correlating mass transport deposits

[1] High-resolution 3-D seismic data acquired in the Sea of Marmara on the Western High, along the northwestern branch of the North Anatolian Fault (also known as the Main Marmara Fault), shed new light on the evolution of the deformation over the last 500–600 ka. Sedimentary sequences in ponded basins are correlated with glacioeustatic cycles and transitions between marine and low sea/lake environments in the Sea of Marmara. In the 3 × 11 km2 of the 3-D seismic survey, deformation over the last 405–490 ka is localized along the main fault branch and north of it, where N130°–N140° trending normal faults and N40°–N50° folding accommodated strike-slip deformation associated with active argillokinesis. There is some evidence that deformation was more distributed further back in the past, at least over the depth range (<600 m below seafloor) of our survey. A N110° basin and buried ridge system were eventually cut by the presently active fault. The southern part of the basin was then uplifted, while the northern part was folded but continued to subside along the fault. A mass transport deposits complex dated between 405–490 ka shows a lateral displacement of 7.7 ± 0.3 km, corresponding to an estimated slip rate of 15.1–19.7 mm/a. We conclude that this strand of the Main Marmara Fault on the Western High has taken up most of the strike slip motion between the Anatolian and Eurasian plates over the last 405 ka at least.

The effect of diagenesis and fluid migration on rare earth element distribution in pore fluids of the northern Cascadia accretionary margin

Analytical challenges in obtaining high quality measurements of rare earth elements (REEs) from small pore fluid volumes have limited the application of REEs as deep fluid geochemical tracers. Using a recently developed analytical technique, we analyzed REEs from pore fluids collected from Sites U1325 and U1329, drilled on the northern Cascadia margin during the Integrated Ocean Drilling Program (IODP) Expedition 311, to investigate the REE behavior during diagenesis and their utility as tracers of deep fluid migration. These sites were selected because they represent contrasting settings on an accretionary margin: a ponded basin at the toe of the margin, and the landward Tofino Basin near the shelf's edge. REE concentrations of pore fluid in the methanogenic zone at Sites U1325 and U1329 correlate positively with concentrations of dissolved organic carbon (DOC) and alkalinity. Fractionations across the REE series are driven by preferential complexation of the heavy REEs. Simultaneous enrichment of diagenetic indicators (DOC and alkalinity) and of REEs (in particular the heavy elements Ho to Lu), suggests that the heavy REEs are released during particulate organic carbon (POC) degradation and are subsequently chelated by DOC. REE concentrations are greater at Site U1325, a site where shorter residence times of POC in sulfate-bearing redox zones may enhance REE burial efficiency within sulfidic and methanogenic sediment zones where REE release ensues. Cross-plots of La concentrations versus Cl, Li and Sr delineate a distinct field for the deep fluids (z > 75 mbsf) at Site U1329, and indicate the presence of a fluid not observed at the other sites drilled on the Cascadia margin. Changes in REE patterns, the presence of a positive Eu anomaly, and other available geochemical data for this site suggest a complex hydrology and possible interaction with the igneous Crescent Terrane, located east of the drilled transect.

Interaction of Gravity Flows With a Rugged Mid-Ocean-Ridge Seafloor: An Outcrop Example from Macquarie Island

Rugged bathymetry along slow-spreading mid-ocean ridges has the potential to impinge a strong control on gravity flows derived from oceanic fault scarps. Sedimentary lithofacies from the Macquarie Island ophiolite supports this hypothesis by displaying systematic variations that correspond with volcanic substrate differences and proximity to rift-related faults. Pillow-basalt terranes are associated with tightly confined bedrock corridors that funnel gravity flows into one direction. Vertical lithofacies variations formed from high-density to low-density turbidity currents record successive fill stages of the corridor axis. During initial stages tight confinement in the axis suppressed flow dilution and fluid turbulence. With continued corridor-axis filling, more dilute gravity flows predominated and formed lateral gradations from axial coarse-grained turbidites into thinly interbedded overbank lithofacies along corridor margins. These gravity-flow lithofacies converge into very thin muddy condensed intervals along inter-corridor highs where significant bottom-current reworking occurred. Conversely, partly confined tabular-basalt-floored basins promoted lateral expansion and dilution of gravity flows throughout the duration of basin filling. Variable paleocurrent-indicator directions record multiple reflections of single gravity-flow events off basin-bounding fault barriers. Coarsening-upward trends in these partly confined basins from thinly interbedded pelagic chert and ripple-bedded sandstones up into stacked turbidites preserves the ponding of sediment-starved submarine fans. In general, these ponded basins preserve the fine-grained distal ends of a gravity-flow continuum from coarse-grained fault-proximal en masse failures and cohesionless debris flows into medial high-density turbidity flows and distal dilute turbidity flows.

Facies architecture of the Grès de Peïra Cava, SE France: landward stacking patterns in ponded turbiditic basins

Basins in which turbidity currents are completely or partially trapped are common in many tectonically active, deep-water settings. Field study of an Eocene–Oligocene turbiditic system in the Peïra Cava area, a sub-basin of the Alpine foreland in southeastern France, allows spatial characterization of a ponded basin fill on the basis of a correlation framework derived from measured outcrop sections and photomosaics. The basin-fill architecture comprises a sand-rich, proximal scour-and-fill facies and a downstream transition to mud-rich, basin-plain turbidite sheet facies. The proximal facies is interpreted to have formed directly downstream of a slope break, where currents were highly erosional during some periods and highly depositional during other periods, as a result of the interacting effects of turbulence enhancement and rapid deceleration. Both the proximal facies and the downstream transition to distal basin-plain facies occur in progressively landward positions at higher stratigraphic levels. The landward shift in depositional facies is likely to have resulted from the basin-floor aggradation and a landward migration of the slope break. This ‘back-stepping’ process may be expected to occur in many ponded turbiditic basins and to produce a similar type of sedimentary architecture.

Tectonic and paleogeographic implications of late Laramide geologic history in the northeastern corner of Wyoming's Hanna Basin

The Hanna Basin of south-central Wyoming has been considered anomalous among other Laramide depocenters of the Rocky Mountain region because of its combination of small size and great thickness of synorogenic strata. Most prior interpretations of the Hanna Basin have assumed a history of subsidence and sedimentary infilling discrete from surrounding basins. In contrast, we summarize new geological and paleontological information from the northeastern corner of the modern Hanna Basin suggesting that, prior to late Paleocene time, the Hanna Basin and nearby Carbon, Pass Creek, Laramie, and Shirley Basins were unified and depositionally continuous with the much larger Green River Basin to the west. Only late in the local expression of the Laramide orogeny (late Paleocene and early Eocene) did this “greater Green River Basin” become subdivided through completion of development of intrabasinal, basement-involved thrust faulting and associated anticlines. We view the present Hanna Basin as only a small, structurally defined remnant of an enormous, ponded basin that extended eastward during most of Paleocene time from the Wyoming–Idaho–Utah thrust belt to the newly uplifted Laramie Mountains. That basin was bounded on the south by the Uinta Mountains and combined Sierra Madre–Medicine Bow Mountains and on the north by the Gros Ventre Range, Wind River Mountains, and Sweetwater arch. When the original configuration of the unified greater Green River Basin is taken into account and combined with palinspastic removal of late Laramide faulting that defines its various margins, this basin at least rivaled dimensions of the Powder River Basin of Wyoming and Montana; the greater Green River Basin greatly exceeded the volume of sedimentary accumulation within the Powder River Basin. Rates of Paleogene basinal erosion associated with structural subdivision of eastern components of the greater Green River Basin were prodigious. Within context of a measured section, we describe and interpret the lithologic nature, depositional settings, source areas, previous geographic extent, and deformational history of the Hanna Formation as seen today in the eastern Hanna Basin. Temporal control is linked to summaries of included mammalian fossils, freshwater molluscs, leaf macrofloras, and palynomorphic assemblages. Unexpectedly early occurrences of certain palynomorphic assemblages suggest that paleoecological controls on distributions of pollen-forming plants during Paleocene time were particularly important. Deformation of strata in the eastern Hanna Basin chiefly reflects a complex interaction between a major, south-directed, low-angle, basement-involved thrust system and the thick and generally incompetent, mudstonerich Hanna Formation. We argue that out-of-the-basin faults, the result of spatial crowding in the basin, are kinematically linked to the basement-involved thrust system through a triangle-zone geometry. This trishear-style of deformation involved north-directed, out-of-the-basin, decollement-type thrusts and a synchronous south-directed, basement-involved, blind-thrust system. Map relationships along the northern margin of the basin indicate that many of the out-of-the-basin faults emplaced younger rocks onto older rocks, seemingly an anomalous structural relationship for contractional deformation. One explanation of these relationships involves synchrony of the: (1) cutting down section of north-directed, out-of-the-basin fault planes; with (2) upturning of basinal strata related to south-directed, basement-involved faulting along the northern margin of the Hanna Basin. Finally, the inherited Precambrian structural grain of the Archean Wyoming province was instrumental in controlling the orientation of many of the Laramide-age, basement-involved structural features. Tectonic heredity, rather than changing stress orientations, probably accounts for the variation in orientations of structural features associated with the northern and eastern margins of the Hanna Basin.

Quaternary neotectonics of the South Aegean arc

The sedimentary and tectonic Quaternary evolution of the South Aegean arc has been interpreted from 8000 line-km of sparker seismic reflection profiles. The older parts of basins formed by E–W-trending faults and accumulated hemipelagic sediment. Younger active faulting trends NNW in the western part of the arc and ENE in the eastern arc. The ENE-trending faults record sinistral strike-slip motion broadly parallel to the convergence direction of the Aegean–Anatolian and African plates. The north–south faults in the western arc are similar to those on land in the south Peloponnese. Chronology is estimated from sedimentation rates in cores and from stacked progradational units on basin margins controlled by eustatic changes in sea level. The younger fault pattern developed at 0.6–0.8 Ma in the western and central arc, but progressively younger in the southeastern part of the arc. The older basin fill with E–W faults is of early Quaternary and Pliocene age. An older regional unconformity corresponds to an early Pleistocene unconformity in the Cretan basin. Particularly in the area east of Santorini, faulting has resulted in startling changes in palaeogeography, such that some areas were late Pliocene basins, positive features during the Pleistocene and then subsided 600 m in the last 0.2 Ma. Such rapid basin inversion resulted in uplift of stratified hemipelagic muds, which were deformed by creep or failure, so that debris flow deposits accumulated in valleys and ponded basins. These fundamental tectonic changes in the past two million years indicate that much of the deformation resulting from the interaction of the Eurasian, African and Anatolian–Aegean plates is taken up at the southern margin of the Aegean microplate, probably because subduction of the African plate has slowed as a result of collision of continental crust. Regional fault patterns are a consequence of spatially varying effects of subduction roll-back.

Controls on reservoir distribution, architecture and stratigraphic trapping in slope settings

Submarine sand reservoir distribution and architecture across slope and base-of-slope systems vary as a function of accommodation, sediment flux rates, substrate mobility and sand-mud content. Slopes evolve through time depending on rates of substrata mobility and sediment flux. Above-grade slopes with ponded accommodation are associated with highly mobile substrata and episodic or relatively low sediment flux. Stepped slopes are associated with less mobile substrata and relatively high rates of sediment flux. Graded slopes are associated with less mobile substrata. Sheet sand deposition on above-grade slopes results from ponded basin ‘fill-and-spill’ processes. Pinchout of ponded sands into slope drapes deposited around ponded basins form lateral seals for the onlap traps common in this setting. Sheet sands are also found in basin floor positions and at the toes of graded (unconfined) slopes associated with stable substrates. The break in slope onto the basin floor provides a key setting for the deposition of both sheet and channel sands. Pinchout of sands or onlap onto the slope form the updip stratigraphic components forming stratigraphic traps with the potential for large hydrocarbon accumulations.

Calibration and visualization of depositional process models for above-grade slopes: a case study from the Gulf of Mexico

Mobile substrates with relatively large amounts of ponded-basin and healed-slope accommodation space across the mid-slope characterize above-grade slopes. There are many above-grade slopes around the world but the Gulf of Mexico (GOM) is arguably the best calibrated one. Because of the unique geologic processes attributed to the GOM, however, such as high rates of intraslope basin subsidence (locally >10 km/Ma) and meltwater spikes, the transfer of depositional process concepts to other deep-water provinces may not seem intuitively obvious. Ponded-basin ‘fill-and-spill’ processes dominate early phases of deposition on above-grade slopes and precede progradation of unconfined slopes. A stepped-equilibrium profile across a series of ponded basin forms a base for late unconfined slope progradation. Deposition in the unconfined slope occurs in both slope and healed-slope accommodation space. These spaces are filled as progradational delta fronts build beyond critical angles, and later collapsed. Sediments tend to be sand lean because the slope angles are too high to allow turbidite fan deposition. Sands are generally associated with channels with some localized sheet sands. This paper describes the use of a proprietary stratigraphic forward modeling application (STRATAGEM) to visualize and distill a GOM-based depositional process model potentially transferable to other slope and base-of-slope systems. Forward models show that the introduction of meltwater spikes do not radically change the depositional architecture of the slope but they do force gravity flow deposition to continue into eustatic sea level rises. These models also show that rapid salt withdrawal beneath intraslopes basins controls the distribution of accommodation space across the slope and thus its stratigraphic architecture.

A Model for Evolution of Laramide Axial Basins in the Southern Rocky Mountains, U.S.A.

The structural, stratigraphic, and sedimentologic development of Laramide axial basins of the southern Rocky Mountains is inconsistent with previous models relating them to transpressional tectonics. Axial basins are better explained as broad synclinal troughs in the hanging walls of large pop-up structures, in contrast to perimeter and ponded basins formed in the footwalls of these same structures. Laramide faults in the southern Rocky Mountains can be divided into the E-dipping Park Range thrust system and the W-dipping Sangre de Cristo thrust system. The W-dipping Front Range fault is the backthrust of the Park Range system, and the E-dipping Nacimiento fault is the back-thrust of the Sangre de Cristo system. The broad synclinal troughs formed between these two pairs of oppositely verging thrust systems were the locations for sediment deposition in axial basins, as exemplified by the Galisteo-El Rito basin of northern New Mexico. The Eocene Galisteo and El Rito formations were deposited on a broad syncline of Phanerozoic strata with crystalline basement along the basin margins. Most sediment was derived from the northeast, north, and northwest, except near the NE-trending Tijeras-Canoncito transfer zone along the southeast margin of the basin. Uplift of the Sangre de Cristo Range occurred first, followed by backthrusting to uplift the Sierra Nacimiento. This model explains Laramide uplifts and basins as the direct response to rapid NE-SW convergence between the North American and Farallon plates, without multiple reorientation of Laramide stress fields, and without major strike-slip along the eastern side of the Colorado Plateau.

Deep-sea tsunami deposits in the eastern Mediterranean: New evidence and depositional models

The tsunami wave induced by the collapse of the Santorini caldera after the Bronze age (Minoan) eruption (3500 BP) produced turbidites and large volume mega-turbidites in the abyssal plains of the Ionian Sea as well as on the floor of small basins of the Mediterranean and Calabrian Ridges, characterized by the so-called ‘Cobblestone Topography’. Since the first discovery in 1978, a Holocene mud layer which has been termed ‘homogenite’ and which typically shows a graded interval at its base, has been identified and correlated in over 50 deep-sea cores recovered in the eastern Mediterranean. Four types of ‘homogenite’ can be distinguished, each related to a particular depositional setting: 1. (a) ‘Closed Cobblestone’: these are from a few decimetres to several metres thick pelagic turbidites of local provenance, exclusively found at the bottom of small-sized ponded basins of the Mediterranean and Calabrian ridges. A debris flow may be present at the base of the turbidite where the vertical relief of the basins is over 200 m. 2. (b) ‘Abyssal Plain’: a 10 to 20-m thick megaturbidite recorded in the Ionian and Sirte abyssal plains. The source area is the African continental margin, possibly the continental shelf; it can be easily identified as a transparent acoustic layer that shows recent deformation across the deformation front of the Mediterranean Ridge accretionary prism. The volume of the Minoan ‘homogenite’ in the Ionian Abyssal Plain has been calculated at a minimum of 11 km 3. 3. (c) ‘Open Cobblestone’: this type is exclusively found on the outer slope of the Mediterranean Ridge, near the deformation front. Unlike types (a) and (b), the base of the turbidite here is erosional instead of depositional. This ‘homogenite’ has been deposited in small basins, and occasionally on topographic highs of the Mediterranean Ridge by the up-slope flow of turbidity currents of African provenance that formed the abyssal plain deposit (type b). 4. (d) A fourth depositional model has been identified: homogenites present in deep anoxic basins of the Mediterranean Ridge. This setting is substantially similar to type (a), but the vertical relief of the basin is much higher (up to 800 m) and the deposition occurs in high-density anoxic brines which modify the settling rate and hence the resulting sedimentological characters.

The inception and early evolution of the North Alpine Foreland Basin, Switzerland

AbstractThe stratigraphy of the Eocene‐Miocene peripheral foreland basin in Switzerland consists of basal deposits of Nummulitic Limestones and Globigerina Marls representing a phase of deepening, followed by two shallowing‐up megacycles culminating in fully continental sedimentation.The onset of sedimentation was diachronous and took place on an unconformity surface with increasing stratigraphic gap to the north and west. In the Ultrahelvetic units, which were derived from the south and have a provenance between the Helvetic shelf and the Penninic ocean, the stratigraphic gap is minimal. This restricts the initiation of erosion of the southern European margin due to emersion to post‐Maastrichtian and pre‐late Palaeocene. This coincides with the final closing of the Valais trough and may therefore be interpreted as the point at which continental flexure s. s. started. In the autochthon, the subcrop map of the unconformity surface shows that the regional pattern of subcropping units is oblique to both neo‐Alpine tectonic structures and Helvetic (Mesozoic) passive margin structures. There are local zones of disruption to the broad regional pattern suggesting that the basal unconformity was corrugated. Both the paliaspastic restoration of the autochthon relative to the thrust front during the Palaeocene, and the regional pattern of erosion indicate that the basal unconformity may be due to erosion of a flexural forebulge.Following deposition of the shallow water Nummulitic Limestones and the deeper water Globigerina Marls, clastic sediments were shed from the orogenic wedge in the south. These turbidites, the Taveyannaz Sandstones, filled both ponded basins at the contemporaneous thrust front and the frontal trench or foredeep. Evidently, early thrusts drove at a shallow level into the embryonic basin as ‘front‐runners’, whereas most shortening and uplift continued to take place within the main part of the orogenic wedge further to the south. Eventually, the frontal palaeohighs, together with the turbidite basins, were buried by the northward emplacement of surface mud‐slides, and sediment depocentres were translated northwards onto the foreland.The most likely cause of the underfilled ‘Flysch’ stage is the rapid advance of a submarine thrust wedge over the flexed European plate which resulted in (i) low sediment fluxes and (ii) high subsidence rates associated with the rapid migration of the load and depocentre. Later, as the rate of advance slowed and the wedge became subaerially exposed, the basin rapidly filled with coarse‐grained detritus representing the ‘Molasse’ stage.

Quaternary deposits on the South Barbados accretionary prism

A study of recent Quaternary deposits of the South Barbados prism has been carried out over a limited area close to the Venezuela margin. 3.5 kHz lines, submarine photographs and many piston and gravity cores have been collected throughout this area during the cruise of the Caracolante II. The detailed morphology of this area comprises a jumble of microbasins and mud diapiric highs: In the basins, the predominant deposits are sandy and muddy turbidites. On the tops of the highs, the diapiric mud is a mixture of Late Miocene, Pliocene and Quaternary sediments. These muds are clearly identified by their high content of smectite and sometimes by the presence of muddy gravels with a diagenetic calcareous cement. On the seafloor, the muds are often covered by an indurated crust on which deep-sea communities are frequently observed. The three major factors controlling sedimentation on the prism are tectonics, sea-level variations and sediment sources. Tectonics play the major role, being responsible for the mud diapiric processes, the fluid circulation throughout the deposits and the triggering of gravity flows on the steep slopes of the diapiric highs. As a consequence, significant inputs of diapir mud supply the deposits of the adjacent basins, and local calcareous crusts, linked to the upward fluid migration, occur on the seafloor at the tops of the diapirs. Sea-level variations and continental sediment sources partly control the character of the deposits in the ponded basins. During the Holocene, the sediment flux was low (1.7–3.7 g cm −2 ∗ 10 −3 yrs) and the deposits were composed of fine-grained particles comprising equally biogenic calcareous and continental material. The continental material is provided by the Orinoco and the Amazon rivers. During the last glacial period, the flux was much higher (8.5–19 g cm −2 ∗ 10 −3 yrs) as a consequence of a huge increase in coarse-grained terrigenous material introduced by the Orinoco river.