Thick Sediment Accumulations Research Articles

Oil and Gas Content of the South Caspian Basin

Abstract —We have compiled maps of areal isotope composition changes and constructed graphs of gas HC distribution depending on the stratigraphic age of the host rocks and graphs of isotope composition changes depending on the depth of sampling to study the hydrocarbon potential of the deep-seated oil and gas pools of the South Caspian Basin. The genesis of gas was studied using the techniques elaborated by M. Schoell and A. James. Two stages of hydrocarbon formation have been established by study of various kinds of gas manifestation. The first stage (Miocene–Eocene) began in the deposits underlying the Productive Series and continued up to the deposits of the latter. This stage was characterized by a frequent change in the directions of both downward and upward movements of gases. The second stage of hydrocarbon formation (Anthropogene–Pliocene) began in the deposits of the Productive Series and was characterized by a change in the regional geodynamic setting. Avalanche sedimentation and the predominance of downward movements over upward ones favored the accumulation of thick sediments at the time when the Productive Series formed. The sedimentation and tectonic processes (downwarping) in the deep-water zone of the basin led to harsh thermobaric conditions in the sedimentary strata. A detailed analysis of the results of gas survey in the deep-water zone of the South Caspian Basin has shown gas generation with a predominance of two components, methane and ethane. Study of the trends of temporal and areal hydrocarbon migration and of the areas of oil and gas generation makes it possible to reveal structures with evidence for large and giant hydrocarbon reserves. We have established that gas hydrocarbons in the bottom and upper-section sediments of the southern Caspian Sea are intimately related to the sources of hydrocarbons, their migration, and other processes running in the deep-seated sediments and in the upper section.

Tectonic and high-latitude climate controls on Quaternary sedimentary processes on the northern coast of Bohai Bay

Separating the relative roles of tectonics and climate change in geological evolution is complicated. The northern coast of Bohai Bay (NCBB), with a thick accumulation of Quaternary lacustrine sediments, is a subsiding area and is well suited to studying tectonic versus climatic controls on sedimentary processes. We used magnetostratigraphy and sedimentological analyses of borehole core JL01 from the NCBB to provide new insights into the effects of tectonic processes and climate changes in this region. The results show the following: (1) A shallow lacustrine delta, a deep-water lacustrine sedimentary system and a subaqueous fan-delta sedimentary system developed during 2.1–1.4 Ma, 1.4–0.78 Ma, and from 0.78 Ma to the present, respectively, corresponding to the rift-initiation, rift-climax, and late-rift tectonic stages of the evolution of an extensional basin, respectively. These stages constitute a low-order tectono-sedimentary cycle. (2) Tectonic and orbital-scale climate changes can be distinguished, particularly the 2.5 Ma climatic transition and a significant shift from 41- to 100-kyr cyclicity across the Mid-Pleistocene climatic transition. These changes indicate that the sedimentary processes of the NCBB were influenced by high-latitude climate forcing since the Late Pliocene. Our results demonstrate that detailed sedimentary facies analyses can provide valuable information about the effects of tectonics and climate changes on basin sedimentary evolution. This approach can be applied to other regional basins worldwide.

Accumulation of thick fluvial sediments in the Shinano River incised-valley fills: implications for sequence stratigraphy and alluvial architecture

ABSTRACTThe relationship between fluvial systems and base-level changes, controlled mainly by sea-level fluctuations and tectonic activity, on time scales of 103–104 years, is important for evaluating and improving nonmarine sequence stratigraphy and numerical and physical alluvial architecture models. However, there are not enough quantitative data available from field studies, especially for periods of rapid base-level rise. The Echigo Plain, Japan, is a fluvial–coastal lowland where the tidal range is very small and where a very deep valley was incised by the Shinano River during the latest Pleistocene. The depth of the incised valley near the shoreline, 160 m below mean sea level, is greater than the amount of sea-level fall during the Last Glacial Maximum (LGM) because of tectonic subsidence. We studied an approximately 100-m-long borehole sediment core obtained from the landward part of the plain, where thick fluvial deposits have accumulated since the LGM. Sediment facies, diatom assemblages, sulfur content, carbon to sulfur ratios, and radiocarbon age dates indicate that most of the core sediments were deposited in a fluvial environment during the past 12 kyr. Sediment accumulation rates were 10–15 m/kyr between 12 and 8 cal kyr BP, and relatively low (less than 5 m/kyr) subsequently, mainly because of glacio-eustatic sea-level rise. The timing of the reduction in the accumulation rate is one possible indicator of the position of the maximum-flooding surface in a sequence composed only of fluvial sediments. The presence of many thin layers of very fine to fine-grained sand (20–80 cm thick), interpreted as crevasse-splay deposits, that formed between 11 and 8 cal kyr BP, when the base level was rising rapidly, implies that crevasse-splay deposits are characteristic of aggrading fluvial sediments and the transgressive systems tract in nonmarine sequence stratigraphy. Tectonic subsidence at approximately 2 m/kyr has contributed markedly to the larger accumulation rate of fluvial sediments of the highstand systems tract on the Echigo Plain, compared with rates in other fluvial–coastal lowlands, since 5–6 cal kyr BP, when the eustatic sea-level rise had mostly ceased.

Gravity complexes as a focus of seafloor fluid seepage: the Rio Grande Cone, SE Brazil

Seafloor methane emissions can affect Earth’s climate and ocean chemistry. Vast quantities of methane formed by microbial decomposition of organic matter are locked within gas hydrate and free gas on continental slopes, particularly in large areas with high sediment accumulations such as deep-sea fans. The release of methane in slope environments has frequently been associated with dissociation of gas hydrates near the edge of the gas hydrate stability zone on the upper slope, with discharges in greater water depths less understood. Here we show, using data from the Rio Grande Cone (western South Atlantic), that the intrinsic, gravity-induced downslope collapse of thick slope sediment accumulations creates structures that serve as pathways for gas migration, unlocking methane and causing seafloor emissions via giant gas flares in the water column. The observed emissions in the study region (up to 310 Mg year−1) are three times greater than estimates for the entire US North Atlantic margin and reveal the importance of collapsing sediment accumulations for ocean carbon cycling. Similar outgassing systems on the Amazon and Niger fans suggest that gravity tectonics on passive margins is a common yet overlooked mechanism driving massive seafloor methane emissions in sediment-laden continental slopes.

The Importance of Dead Seagrass (Posidonia oceanica) Matte as a Biogeochemical Sink

We assessed the potential of dead seagrass Posidonia oceanica matte to act as a biogeochemical sink and provide a coherent archive of environmental change in a degraded area of the Mediterranean Sea (Augusta Bay, Italy). Change in sediment properties (dry bulk density, grain size), concentration of elements (Corg, Cinorg, N, Hg) and stable isotope ratios (δ13C, δ 15N) with sediment depth were measured in dead P. oceanica matte and unvegetated (bare) sediments in the polluted area, and an adjacent P. oceanica meadow. Principal Component Analysis (PCA) revealed a clear clustering by habitat, which explained 72% of variability in our samples and was driven mainly by the accumulation of N and Hg in finer sediments of the dead matte. Assessment of the temporal trends of Corg, N and Hg concentrations in the dead matte revealed changes in the accumulation of these elements over the last 120 years, with an increase following the onset of industrial activities 65 y BP (i.e., yr. 1950) that was sustained even after seagrass loss around 35 y BP. Despite a decrease in Hg concentrations in the early 1980s following the onset of pollution abatement, overall Hg levels were 2-fold higher in the local post-industrial period, with a Hg enrichment factor of 3.5 in the dead matte. Mean stocks of Corg, N and Hg in 25 cm thick sediment deposits (4.08 ± 2.10 kg Corg m-2, 0.14 ± 0.04 kg N m-2, 0.19 ± 0.04 g Hg m-2) and accumulation in the last 120 yr (35.3 ± 19.6 g Corg m-2 y-1, 1.2 ± 0.4 g N m-2 y-1, 0.0017 ± 0.0004 g Hg m-2 y-1) were higher in the dead matte than bare sediment or adjacent P. oceanica meadow. Our results indicate that dead P. oceanica matte maintained its potential as a biogeochemical sink and, like its living counterpart, dead matte can serve as an effective archive to allow for reconstructing environmental change in coastal areas of the Mediterranean where severe perturbations have led to P. oceanica loss. Appropriate management for contaminated areas should be prioritized to prevent release of pollutants and carbon from dead mattes.

Scoresbysund Composite Tectono-Sedimentary Element, East Greenland Rifted Margin, Denmark Strait

Abstract The little explored central East Greenland margin contains thick sedimentary accumulations confined within the Scoresbysund Basin. The geological evolution of the area distinguishes it from other parts of East Greenland. Even so, resemblances with the prospective basins onshore and offshore further north probably exist, and the margin may hold real petroleum potential. The Scoresbysund Composite Tectono-Sedimentary Element (CTSE) delineates the oldest part of the Scoresbysund Basin. It formed through multiple phases of rifting, volcanism, uplift and thermal subsidence between Devonian and Miocene times. The development of the CTSE concluded with the latest Oligocene or early Miocene continental break-up of the Jan Mayen microcontinent and East Greenland. The Scoresbysund CTSE contains approximately 4 km of Eocene–lower Miocene fan-delta deposits that accumulated during downfaulting along the East Greenland Escarpment and which further seawards intercalate with basalts. The fan-delta deposits rest on Paleocene basalts that most probably cover Paleozoic–Mesozoic strata. Equivalent to onshore, the deeply buried section probably includes source rock and reservoir intervals of Carboniferous, Permian and Mesozoic age. Together with the major fault structures existing in the western part of the area, this may form the basis for a working petroleum system.

Geological and geomorphological influences on a recent debris flow event in the Ice-scoured Mountain Quaternary domain, western Scotland

Debris flows in settings that have experienced net glacial erosion within the UK's Ice-scoured Quaternary domain are the result of a complex interaction of a range of geological and geomorphological factors. On the 11th of August 2016 a rainfall-triggered debris flow deposited 100 t of sediment onto local road and rail infrastructure blocking transport between town of Fort William and port of Mallaig in north-west Scotland. The debris flow occurred in an ice-scoured setting, where current 1:50,000-scale geological maps suggest that little or no sediment is expected on the valley slopes. In this study, we show how weathering and mass-wasting processes have interacted with bedrock structures to fill localised depressions with sediment on the upper parts of the slope. The intense rainfall event of August 2016 caused the destabilisation of this localised sediment, with eventual failure along bedrock joint surfaces resulting in two debris flows. This study demonstrates the combination of processes that can result in thick accumulations of sediment on slopes that are otherwise generally lacking in superficial sediment cover. These sediment accumulations have the potential to pose a significant landslide hazard in areas that might previously have been thought of as lower susceptibility. The research illustrates a need to improve understanding and representation of sediment thickness and distribution on hill slopes – particularly those that show an absence of superficial deposits at the scale of currently available geological maps.

The Long Timeline of the Ice

Ice ages constitute a significant part of Earth’s climate history with the first signs of widespread ice sheets occurring at about 2.4 billion years ago. In 2004, a nearly 450 metres thick accumulation of seafloor sediments on the submarine Lomonosov Ridge in central Arctic Ocean was drilled by the international Arctic Coring Expedition (ACEX). This geological archive has provided insights into the long-term history of the Arctic Ocean back to 56 million years. The first signs of extensive sea ice along the Arctic coasts appear 47.5 million years ago (Ma), while evidence for the type of pack ice we have today that survives more than one season occurs first 15–13 Ma. The Earth’s climate changed mode at about 2.6 Ma. Cold periods, characterized by large ice sheets covering the Northern Hemisphere, were intervened by warmer periods with climates more similar of today. These glacial-interglacial cycles were largely controlled by changes in solar insolation resulting from cyclical variations in Earth’s orbit around the Sun. In this article, I tell the personal story of how we mapped the Lomonosov Ridge and found evidence supporting a controversial hypothesis of the existence of kilometre-thick floating ice shelves in the Arctic Ocean during past glaciations.

Integration of remote-sensing data for mapping lithological and structural features in the Esh El-Mallaha area, west Gulf of Suez, Egypt

Esh El-Mallaha west of the Gulf of Suez is a potential area for hydrocarbon resources. In this article, Landsat-8 Operational Land Imager (OLI), Shuttle Radar Topography Mission (SRTM), and Advanced Land Observing Satellite (ALOS) Phased Array Type L‐band Synthetic Aperture Radar (PALSAR) data were utilized to identify the geological and structural features of this area which represents a part of the North Eastern Desert (NED), Egypt. The use of band ratios (BR) and principal component analysis (PCA) allowed characterizing the different varieties of rock units. These approaches allowed discriminating the various rock units e.g., metavolcanics, granitoids including the two phases of the older granites and younger granites along with the third phase which represented by elongated ridges cut the rocks and clearly allowed tracing the contacts of different lithological units of the Neoproterozoic basement and Phanerozoic sedimentary rocks. Applying the fused Landsat-8 OLI and ALOS/PALSAR data improved the structural elements that difficult to reveal by optical images. Combination of Landsat-8 OLI, ALOS/PALSAR, and SRTM data effectively display the structural and lithological contacts. The lineament extraction and interpretation indicated that the area is clearly shaped by the NW-SE graben and controlled by the Gulf of Suez tectonic trend. Such structures allowed the accumulation of thick sediments in the faulted basin that represents the promise area for oil, gas, and water resources. Lineament analysis revealed that the major tectonic trends controlling the area are NW-SE and NE-SW directions with less effect of N-S and E-W trends. The NW-SE sinistral and NE-SW dextral lateral movements are recognized. Overall results revealed that the integration of optical and radar remotely sensed data is an effective tool in deciphering geological and structural features in the arid regions.

Exploration And Exploitation Of Non-Living Natural Resources On The Continental Shelf Beyond 200 Nautical Miles: A Status Review

Activities by coastal States in relation to the exploration and exploitation of non-living natural resources (namely hydrocarbons and deep-sea minerals) on the continental shelf beyond 200 nautical miles (M) from their territorial sea baselines are reviewed. Geological conditions dictate such that hydrocarbons are likely to occur where there are thick accumulations of sediments (at least 2-3 km is needed for organic matter to generate significant amounts of hydrocarbons), whereas deep-sea minerals are found on or beneath the seabed of the deep oceans, which are generally “starved” of sediment. Thus, in general, sites for hydrocarbon exploration and for deep-sea mineral exploration are unlikely to overlap. On a ‘normal’ geological shelf with an average width of say ~60-100 km, hydrocarbon exploration is carried out generally within the 200 M limit of the Exclusive Economic Zone (EEZ) of the coastal State. Within the last decade, however, necessitated by depleting resources in the shallow waters of the shelf and slope, exploration has gradually moved from the geological shelf (water depth typically < 200 m) further out into deeper waters, and in some cases, beyond the 200 M limit. Thus far, only in a few places is oil and gas exploration being carried out on the continental shelf beyond 200 M. Examples include Australia, New Zealand, Norway, Argentina and Canada. Such activities mainly involve geological and geophysical investigations and assessment of the hydrocarbon potential, while some have resulted in commercial production. Besides the conventional hydrocarbons (oil and gas), continental margin sediments may also host significant accumulations of gas hydrates, which are regarded as a potentially important energy resource of the future. Along non-polar continental margins, gas hydrates are generally found beneath the continental slope and the continental rise, i.e. beyond the continental shelf proper, in water depths typically greater than 500 m but still mainly within 200 M of the territorial sea baselines. Where the continental margin is exceptionally wide, however, gas hydrates may occur in areas beyond the 200 M limit, on the extended continental shelf.

Predicting fluid pressure in sedimentary basins from seismic tomography

SUMMARY Gravitational compaction of thick (2–10 km) sediment accumulations in sedimentary basins is controlled by the interplay of mechanical and chemical processes that operate over many orders of magnitude in spatial scale. The compaction of sediments into rock typically involves a density increase of ≈500 to 1000 kg m−3, occurring over a depth-scale of several kilometres. The volume decrease in the compacting sediments releases vast volumes of water, which plays an important part in the global hydrological cycle and also in tectonic and geochemical processes; including the formation of hydrocarbon and mineral deposits. This study utilizes recently developed tomographic seismic images from the Porcupine Basin, which lies in the deep-water North Atlantic Ocean. A generic method for predicting fluid pressure variations that are driven by gravitational compaction is developed over the scale of the entire sedimentary basin. The methodology is grounded upon both observational evidence and empirically based theories, relying on geophysical measurements and relationships between sediment porosities and densities. The method is based upon physical concepts that are widely used in the petroleum industry and applied extensively in models of overpressure development in sedimentary basins. Geological and geophysical data from exploration wells are used to test the predictions of the method at two locations within the basin and are found to be in good agreement with the theory.

Testing Contrasting Models of the Formation of the Upper Yellow River Using Heavy‐Mineral Data From the Yinchuan Basin Drill Cores

AbstractThe upper Yellow River drains the central and northeastern Tibetan Plateau. Understanding the origin of this river is essential for unraveling the interplay between fluvial incision, basement uplift, and climate change. However, the formation age of the upper Yellow River is highly debated, with estimates ranging from Eocene to late Pleistocene. In order to clarify the history of the upper Yellow River, we present a heavy‐mineral dataset from drill core in the Yinchuan Basin, a depositional sink at the end of the upper Yellow River course. Our results reveal that the drainage area of the upper Yellow River (i.e., northeastern Tibetan Plateau) has been serving as a major sediment source region for the Yinchuan Basin since at least 3.3 Ma. A late Pleistocene formation of the upper Yellow River, and erosion of neighboring deserts or bounding mountains as an explanation for thick sediment accumulations in this area, is thus ruled out.

Late Cretaceous topographic doming caused by initial upwelling of Deccan magmas: Stratigraphic and sedimentological evidence

AbstractThis study focused on uppermost Cretaceous sedimentary rocks deposited in the Himalayan region and around the core of peninsular India just before the eruption of the Deccan Traps. Detailed stratigraphic and sedimentological analysis of Late Cretaceous successions in the Himalayan Range together with literature data from the Kirthar fold-and-thrust belt and central to southeastern India document a marked shallowing-upward depositional trend that took place in the Campanian–Maastrichtian before the Deccan magmatic outburst around the Cretaceous-Tertiary boundary. Topographic uplift of the Indian peninsula began in Campanian time and is held responsible for thick sediment accumulation associated with shorter periods of nondeposition in peripheral areas (Himalayan Range, Kirthar fold belt, and Krishna-Godavari Basin) than in the central part of the Deccan Province. Surface uplift preceding Deccan volcanism took place at warm-humid equatorial latitudes, which may have led to an acceleration of silicate weathering, lowered atmospheric pCO2, and climate cooling starting in the Campanian–Maastrichtian. The radial centrifugal fluvial drainage in India that is still observed today was established at that time.

Decompensative Gravity Anomalies Reveal the Structure of the Upper Crust of Antarctica

As Antarctica is almost entirely covered by thick ice shields impeding in situ measurements, information about upper crustal structures and sedimentary basins is still sparse and the analysis of the gravity anomalies offers new insights. Isostatic gravity anomalies are often used to investigate upper crust structures. However, compensating masses significantly reduce the gravity effect of unknown sedimentary and upper crustal structures. To separate these effects, we apply so-called decompensative corrections to the isostatic anomalies for the Antarctic continent, which reach values of up to ± 70 mGal. The obtained decompensative anomalies well correspond to the known sedimentary basins, such as in the areas of the Filchner-Ronne Ice Shelf and Lambert Graben, and also suggest the existence of other large sedimentary deposits both in West and East Antarctica, which are not or only sparsely mapped by existing seismic surveys, e.g. in coastal Dronning Maud Land and Enderby Land. A dipole-like structure exists at the Transantarctic Mountains and the Wilkes Subglacial Basin, suggesting the presence of isostatic disturbances linked to the dynamic uplift of the Transantarctic Mountains and thick sedimentary accumulations in the east. Extended positive anomalies in East Antarctica are likely related to the old and dense cratonic crust as well as to isostatic disturbances caused by the transition from local to regional compensation around the Lambert Graben.

A Recent Volcanic Eruption Discovered on the Central Mariana Back-Arc Spreading Center

Submarine volcanic eruptions are difficult to detect because they are hidden from view at the bottom of the ocean and far from land-based sensors. However, most of Earth’s volcanic activity is in the oceans along tectonic plate boundaries, and modern tools of oceanography now allow us to find and study recent eruptions in the deep sea. The first known historical eruption on the Mariana back-arc spreading center was discovered in December 2015 during exploration of the southern back-arc for new hydrothermal vent sites. A water-column survey along the axis of the back-arc showed hydrothermal plumes over the site characterized by low particle concentrations and relatively high reduced chemical anomalies. A dive with the autonomous underwater vehicle Sentry collected high-resolution (1 m) multibeam sonar bathymetry over the site, followed by a near-bottom photographic survey of a smaller area. The photo survey revealed the presence of a pristine, dark, glassy lava flow on the seafloor with no sediment cover. Venting of milky hydrothermal fluid indicated that the lava flow was still warm and therefore very young. A comparison of multibeam sonar bathymetry collected by R/V Falkor in December 2015, to the most recent previous survey of the area by R/V Melville in February 2013, revealed large depth changes in the same area, effectively bracketing the timing of the eruption within a window of less than 3 years. The bathymetric comparison shows the eruption produced a string of lava flows with maximum thicknesses of 40–138 m along a distance of 7.3 km (from latitude 15∘22.3′ to 15∘26.3′N) between depths of 4050–4450 m bsl (meters below sea level), making this the deepest known historical submarine volcanic eruption on Earth. The cross-axis width of the lava flows is 200–800 m. The Sentry bathymetry shows that the new lava flows are constructed of steep-sided hummocky pillow mounds and are surrounded by older flows with similar morphology. In April and December 2016, two dives were made on the new lava flows by remotely operated vehicles Deep Discoverer and SuBastian. The pillow lavas have many small glassy buds on the steep flanks of the mounds, locally thick accumulations of hydrothermal sediment near the tops of mounds, and small cones of radiating pillows at their summits. The 2015–2016 observations show a rapidly declining hydrothermal system on the lava flows, suggesting that the eruption had occurred only months before its discovery in December 2015. The morphology of the pillow lavas is similar to other historical eruption sites, so the greater depth and ambient pressure of this site had no apparent effect on the processes of lava extrusion and emplacement. This study reveals that some segments of the Mariana back-arc have active magmatic systems despite the relatively low spreading rate, and that other eruptions are possible in the near future.

Late Cretaceous–Cenozoic basin evolution and topographic growth of the Hoh Xil Basin, central Tibetan Plateau

The Hoh Xil Basin in the central Tibetan Plateau was the locus of thick accumulation of terrestrial sediments from the Late Cretaceous to Neogene, providing an archive of regional tectonic activity both before and after initiation of the early Paleogene India-Asia collision. This work focuses on the stratigraphy and provenance of the poorly studied western part of the Hoh Xil Basin. Lithostratigraphy, carbonate oxygen isotopic composition, and deformation features suggest that the braided river and alluvial-fan that dominated the Kangtuo Formation in the southern West Hoh Xil subbasin can be correlated with the Late Cretaceous-early Eocene Fenghuoshan Group deposits of the East Hoh Xil subbasin, whereas deltaic, shallow lacustrine, and evaporite strata of the Suonahu Formation in the central-northern West Hoh Xil subbasin can be correlated to the middle Eocene-early Oligocene-Yaxicuo Formation of the East Hoh Xil subbasin. These observations suggest that the eastern and western parts of Hoh Xil Basin evolved as a unified basin during Late Cretaceous-Oligocene time. Detrital zircon U-Pb ages indicate that the Kangtuo Formation and Feng-huoshan Group mainly received detritus from the Qiangtang terrane to the south, whereas the age probability distributions of the Suonahu Formation and Yaxicuo Formation sandstones are more similar to zircon ages reported for the northern Qiangtang terrane and within the Hoh Xil terrane. We favor a tectonic model with Late Cretaceous-early Eocene contractional deformation and topographic growth of the south-central Qiangtang terrane that caused flexural subsidence of the south-central Hoh Xil region within a retroarc foreland basin, relative to the Tanggula thrusts in central Qiangtang. Following the onset of India-Asia collision, the locus of contractional deformation moved northward, marked by activity of the Fenghuoshan and Hoh Xil thrust systems within the Hoh Xil region, and resulting in transformation of the Hoh Xil foreland basin to a hinter-land basin. We suggest that both middle Eocene to late Oligocene upper-crustal shortening and associated thickening of the lower crust and mantle lithosphere as well as late Oligocene to Miocene loss of dense mantle lithosphere contributed to the topographic growth of the Hoh Xil Basin.

Origin, evolution and sedimentary processes associated with a late Miocene submarine landslide, southeast Spain

A submarine landslide, the Alhama de Almería Slide, influenced late Tortonian and early Messinian (late Miocene) sedimentary processes in the vicinity of Alhama de Almería in southeast Spain. Its 220-m-high headscarp and deposits are now subaerially exposed. The landslide occurred at the northern slope of the antecedent relief of the present-day Sierra de Gádor mountain range. This is a large antiform trending east–west to east-northeast–west-southwest, which has been uplifting since the late Miocene due to convergence of the African and Eurasian plates. During the Tortonian, this relief was an island separated from the Iberian Peninsula mainland by the Alpujarra corridor, a small and narrow intermontane basin of the Betic Cordillera in the western Mediterranean Sea. The materials involved in the slope failure were Triassic dolostones and phyllites from the metamorphic Alpujárride Complex and Tortonian marine conglomerates, sandstones, and marls that formed an initial sedimentary cover on the basement rocks. Coherent large masses of metamorphic rocks and Miocene deposits at the base of the headscarp distally change to chaotic deposits of blocks of different lithologies embedded in upper Tortonian marine marls, and high-strength cohesive debrites. During downslope sliding, coherent carbonate blocks brecciated due to their greater strength. Phyllites disintegrated, forming a cohesive matrix that engulfed and/or sustained the carbonate blocks. Resedimented, channelized breccias were formed by continuing clast collision, bed fragmentation, and disaggregation of the failed mass. The conditions leading to rock/sediment failure were favoured by steep slopes and weak planes at the contact between the basement carbonates and phyllites. Displacement of collapsed rocks created a canyon-like depression at the southeast edge of the landslide. This depression funnelled sediment gravity flows that were generated upslope, promoting local thick accumulations of sediments during the latest Tortonian-earliest Messinian. The insights from this exposed outcrop have implications for understanding the mechanisms and products of mass-transport deposits on the modern seafloor and the recognition of past failures from subsurface records.

Estimation of seismic hazard in Odisha by remote sensing and GIS techniques

This paper determines the risk of earthquake hazard due to amplification of seismic waves in coastal Odisha. Seismic hazards has been estimated by analysis of geomorphological features and thickness of unconsolidated soil cover. Areas with quaternary to recent deposits have great potential to amplify intensity of seismic waves and consequently the ground motion. Morphometric analysis of the DEM data has been conducted to identify areas with high potential of accumulation of unconsolidated sediment, and other parameters that influence deposit of loose, unconsolidated soil in the region. Weighted overlay method has been used to create soil amplification susceptibility map for the coastal Odisha. The Mahanadi basin shows dominant structural control on seismic activity. Lineament patterns are mostly directed in the WNW–ESE, NE–SW and NNW–SSE directions and may induce elongation of isoseismic patterns. The analysis also shows that the western, northern and middle parts of the study region have low to moderate susceptibility whereas the coastal Odisha have high susceptibility for seismic amplification due to thick unconsolidated sediment accumulation.

Hydrochemical characterization of the main aquifers in Khartoum, the capital city of Sudan

The present study assesses groundwater resources of the densely populated area of the Khartoum State, Sudan by integrating conventional hydrochemistry and statistical analysis. Groundwater is exploited from two aquifers: Gezira and Nubian. The Gezira aquifer, which occupies the upper part, is separated by impermeable unit from the lower Nubian aquifer. Both aquifers are part of thick sedimentary accumulations formed under fluviolacustrine environment during Tertiary and Cretaceous, respectively. The groundwater flows in the two aquifers from the White and Blue Niles (both rivers bound the area from west and east, respectively) into the center of the study area suggesting recharge from the rivers. This river-induced recharge is demonstrated by the hydrochemical evolution of the groundwater along the flow direction. Groundwater evolves in the Nubian aquifer from Ca2+–Mg2+–HCO3 − type in the vicinity of the Niles to Na+–K+–Cl−–SO4 2− type in the central part of the area indicating precipitation of carbonates and dissolution of clay minerals and evaporites reported in the well logs. A third type of groundwater Na+–K+–HCO3 − is formed in the mid zones between the Niles and the central part showing the ionic exchange and minerals dissolution/precipitation with the flow direction. In the Gezira aquifer, the water only changes from Ca2+–Mg2+–HCO3 − type to Na+–K+–HCO3 − type indicating a lesser degree of mineral dissolution. The factor analysis reveals three factors controlling the chemistry of groundwater in the study area: mineral dissolution and weathering, carbonate system, and anthropogenic effect. Factor 1 (mineral dissolution and weathering) includes high values of TDS, EC, Na+, K+, CI−, HCO3 −, and SO4 2− in respective order; Factor 2 (carbonate system) includes Ca2+, Mg2+, CO3 2−, and pH; Factor 3 (anthropogenic effect) includes NO3 − and F−. It has been demonstrated that the integration of conventional hydrochemical analysis with factor analysis represents a powerful mean to understand the factors controlling groundwater chemistry.

Crustal and lithospheric structure of Northeast China from S-wave receiver functions

Lithospheric thickness is closely associated with lithospheric response to tectonic forces or thermal processes. Analysis of S-wave receiver functions (SRFs) from a dense seismic array has revealed lithospheric thickness variations along a 1200 km long profile that spans all major geological terranes of Northeast China. The SRF images identify the shallowest Moho and lithosphere–asthenosphere boundary (LAB) depths beneath the rifted Songliao Basin, thus spatially correlating well with the thick sediment accumulation. These features can be explained by a pure shear regime operating in the lower crust and upper mantle, suggesting the predominance of roughly symmetric lithosphere stretching from continental rifting. In contrast, thicker lithosphere in western and eastern terranes of NE China indicates the lithosphere in these regions was not strongly affected by the extensional processes during the Late Mesozoic. Flat LAB structure beneath the Erguna and Xing'an terranes along with the overlying relatively deeper Moho beneath the Great Xing'an Range, suggests the North–South Gravity Lineament may not be a trans-lithospheric structure.