Fan Complex Research Articles

The evolution of the Tugela canyon and submarine fan: A complex interaction between margin erosion and bottom current sweeping, southwest Indian Ocean, South Africa

The transfer of sediment from the upper continental slope to rise is poorly documented along the southeast African passive margin. New swath bathymetric and sub-bottom data collected in the Natal Valley, southwest Indian Ocean, provide insight into the evolution of the Tugela canyon and fan system. Several distinct downslope changes in canyon morphology are noted. The canyon increases in relief and widens with depth. Basement outcrop is restricted to the head of the canyon becoming less prominent with depth. Step-like terracing of the canyon walls and floor becomes prominent in the mid-slope portions of the canyon and is related to a marked increase in the cross sectional asymmetry of the canyon profile. The contemporary Tugela canyon rests within a depression of the last phase of infilling. The canyon is the product of downslope erosion, and incision, caused by several phases of hinterland uplift in the mid Oligocene, mid Miocene and late Pliocene. Each phase was followed by pelagic infilling of the palaeo-canyon form. Downslope, the uplift phases are preserved in the cut-terraces and axial incisions within the main canyon thalweg. The contemporary canyon is a moribund feature, sediment starvation of the shelf area by current sweeping of the Agulhas current has decreased the material available for canyon incision and fan development. Additional current sweeping by the North Atlantic Deep Water current has stunted the development of the associated fan complex.

Wheeler-transformed 2D seismic data yield fan chronostratigraphy of offshore Tanzania

Recent discoveries offshore Tanzania and Mozambique highlight East Africa as an emerging world-class pet-roleum province. Oil and gas estimates for this province total 12.5 BBO and 250 TCFG (Brownfield et al., 2012) as yet undiscovered. Play-opening reservoir systems have been verified in Paleocene, Eocene, and at least two Oligocene deep-water submarine fan and intraslope channel complexes (Law, 2011). In deep-water Tanzania, there have been seven gas discoveries (of eight attempts) since 2010, with recent announcements putting total gas reserves in Tanzania at 24–26 TCFG. In neighboring Mozambique, 19 wells were completed by Anadarko and ENI in the Ruvuma Basin from 2009 to June 2012, only two of which were not announced as commercial discoveries. With the additional drilling, the increase of reported reserves now approaches or exceeds 100 TCFG. Evidence continues to mount that suggests the Late Cretaceous section contains deposits from similar depositional settings (Tanzania Petroleum Development Corporation, 2003). There are also indications that the petroleum system may contain oil as well as the established gas.

Debris-flow simulations on Cheekye River, British Columbia

Cheekye River fan is the best-studied fan complex in Canada. The desire to develop portions of the fan with urban housing triggered a series of studies to estimate debris-flow risk to future residents. A recent study (Jakob and Friele 2010) provided debris-flow frequency-volume and frequency-discharge data, spanning 20-year to 10,000-year return periods that form the basis for modeling of debris flows on Cheekye River. The numerical computer model FLO-2D was chosen as a modelling tool to predict likely flow paths and to estimate debris-flow intensities for a spectrum of debris-flow return periods. The model is calibrated with the so-called Garbage Dump debris flow that occurred some 900 years ago. Field evidence suggests that the Garbage Dump debris flow has a viscous flow phase that deposited a steep-sided debris plug high in organics in centre fan, which then deflected a low-viscosity afterflow that travelled to Squamish River with slowly diminishing flow depths. The realization of a two-phase flow led to a modelling approach in which the debris-flow hydrograph was split into a high viscosity and low viscosity phase that were modelled in chronologic sequence as two separate and independent modelling runs. A perfect simulation of the Garbage Dump debris flow with modelling is not possible because the exact topography at the time of the event is, to some degree, speculative. However, runout distance, debris deposition and deposit thickness are well known and serve as a good basis for calibration. Predictive analyses using the calibrated model parameters suggest that, under existing conditions, debris flows exceeding a 50-year return period are likely to avulse onto the southern fan sector, thereby damaging existing development and infrastructure. Debris flows of several thousand years return period would inundate large portions of the fan, sever Highway 99, CN Rail, and the Squamish Valley road and would impact existing housing development on the fan. These observations suggest a need for debris-flow mitigation for existing and future development alike.

Paleogeographic and tectonic evolution of the Pranhita-Godavari Valley, Central India: a Stratigraphic perspective

The Pranhita-Godavari Valley of central India preserves records of repeated opening and closing of Proterozoic and Gondwana rifts along the zone of NW-SE trending Neoarchean suture between the Dharwar and Bastar cratonic nuclei. The Proterozoic succession in the Valley comprises several major unconformity-bound sequences, each with a distinctive set of litho-assemblage, deposited under diverse tectonic environments with highly variable modes and tempos of sedimentation. Analysis of sedimentary attributes of unconformity-bound sequences indicates that Purana sedimentation in the Valley started with the deposition of stable platformal assemblage of carbonate-quartzarenite in an extensional sag basin. The basin opened at c. 1700 Ma. The stability of the craton was disrupted when the first major cratonic rift nucleated at c. 1620 Ma, and shortly evolved into an oceanic basin along the northeastern margin of the Valley with consanguineous deposition of a thick wedge of conglomerates, tidal sandstones and shales in the Mulug shelf, and a succession of graywacke, carbonate, siltstone-mudstone-black shale and tuff turbidites of the Somanpalli flysch in two parallel adjoining belts. The Somanpalli flysch is bounded by two shallow marine successions, analogous to several geosynclinal deposits preserved in orogenic belts, and was deposited in a deep oceanic basin along a rifted continental margin. Paleocurrent analysis reveals that siliciclastics in the flysch succession were derived primarily from a continental provenance to the southwest of the Mulug shelf, and were transported to the flysch basin across the margin. Coarse sands were deposited in large submarine fan complexes of graywackes and mixed carbonate-siliciclastics at several points. The voluminous carbonate turbidites in the flysch were also derived from the adjoining Mulug shelf. High quartz content of graywackes, their close association with tidally deposited arenites, and ocean-ward transport of sediments from cratonic hinterlands collectively attest to the deposition of the flysch in a trailing margin basin. Opening of the oceanic basin and deposition of the flysch were accompanied by extensive granulite facies metamorphism at deep crustal level indicating a genetic linkage between them, and the litho-tectonic elements were deformed into an orogenic belt during re-assembly of Dharwar and Bastar blocks. The orogenic belt girdled the northeastern margin of the PG Valley, wrapped around its southeastern corner making a syntaxial bend, and continued into the Ongole-NKSB orogenic belt which also had its peak metamorphism at c. 1600 Ma. The age of the orogeny is not well constrained, but was followed by a Neoproterozoic episode of extension, and formation of cratonic rift basin with the deposition of several thousand meters of quartz-rich sandstones of the Sullavai, Albaka and Usur sequences.

A sedimentation model of the maikop deposits of the Tuapse Basin in the Black Sea according to the results of 2-D and 3-D seismic surveys and field works in the Western Caucasus and Crimea

This work is based on the results of 2-D and 3-D surveys in the Tuapse Basin and field works in the Crimea-Caucasus region. Seven zones were outlined in the model of sedimentation starting from the eroded mountain structure of the Greater Caucasus down to deep water sediments of the Tuapse Basin. The slope and deep-water sediments of channels and fan complexes are characterized. Volume models of the sedimentation system in the Black Sea are shown for the first time.

Evidence for multiple ice centres during the late Palaeozoic ice age in Oman: outcrop sedimentology and provenance of the Late Carboniferous–Early Permian Al Khlata Formation

Abstract This paper proposes a model for glaciation in Oman during the late Palaeozoic ice age (LPIA) based on sedimentological and provenance analyses of the Late Carboniferous–Early Permian Al Khlata Formation, exposed in the Huqf, Oman. The results demonstrate a complex pattern of glaciation across Oman, not fully recognized in previous models. Striated glacial pavements provide evidence for two phases of ice advance: a phase of ice sheet advance towards the NE, and a second and probably younger phase where an ice centre localized on the Huqf High flowed towards the SW. The stratigraphy is constrained by previous palynological studies and is subdivided into three units, from oldest to youngest: ‘early’ AKP5, ‘late’ AKP5 and AKP5/P1. ‘Early’ AKP5 palaeogeography is characterized by ice-contact glacial lacustrine and deltaic sedimentary environments along the western margin of the Huqf High. Meltwater discharge flowed into the lake from ice margins located to the east, upon the Huqf High, recorded by progradational delta and fan complexes. ‘Late’ AKP5 palaeogeography is characterized by pro-glacial fluvial-deltaic outwash braidplains that record high-magnitude meltwater discharge from an ice margin located to the SW of the study area. The youngest undifferentiated AKP5/P1 palaeogeography is characterized by re-establishment of ice-contact glaciolacustrine conditions.

The sedimentation model of the Tuapse Trough (Black Sea)

Based on the new 2D and 3D seismic data from the Tuapse Trough (Black Sea), the principle peculiarities of sedimentation have been studied in detail. A sedimentation model of the focused Maikop and Karagan-Chokrak intervals of the geological section has been suggested. A system of fan complexes referred to Maikop age has been found.

New seismo-stratigraphic data of the Volturno Basin (northern Campania, Tyrrhenian margin, southern Italy): implications for tectono-stratigraphy of the Campania and Latium sedimentary basins

A geological section of the Volturno Basin (northern Campania, continental margin, Italy) has been constructed based on new multichannel seismic data, to show the stratigraphic relationships between the filling in the Quaternary basin and the Meso-Cenozoic acoustic basement. The new seismic sections presented here outline the underlying structures of the basin and their relationships to the filling in the Quaternary basin. Deep exploration wells in Campania and Latium on the Tyrrhenian margin have gathered litho-stratigraphic and commercial multi-channel seismic data that can be used for better integration of the geological data for the area under study. The trending of the seismic units is controlled by the Massico Structural High, which forms the boundary of the Volturno Basin towards the north-west. This produces a geometry that is characteristic of a fan complex, with NE-SW trending. This qualitative calibration of the seismic sequences that fill the sedimentary basin was carried out through the litho-stratigraphic data of the «Castelvolturno 2» well, which highlights the pyroclastic layers and conglomeratic strata of the lagoon and delta environments as they evolve upwards towards marine sediments. Seismo-stratigraphic analysis shows the complex depositional geometries of the filling in the Volturno Basin, which overlie the Meso-Cenozoic carbonatic basement and the related flysch deposits. Coupled with regional geological evidence, the data interpretation here suggests that the Volturno Basin represents a half-graben structure that is characterized by down-thrown blocks along normal faults.

Facies and cyclicity within the Oligocene-Early Miocene Panjgur Formation, Khojak–Panjgur Submarine Fan Complex, south-west Makran, Pakistan

The Makran Accretionary Belt covers vast areas of the south-western Makran, Pakistan and extends westwards into coastal Iran. In Pakistan this belt is dominated by an overall regressive succession comprising the Siahan/Hoshab shale (a valley-forming claystone/siltstone-dominant facies) and the ridge-forming, sandstone-dominant facies of the Panjgur Formation, a very thick cyclic succession of Oligocene-Early Miocene turbidites. These formations form part of the “Khojak–Panjgur Submarine Fan Complex”. The Panjgur Formation comprises nine distinct facies, which are organized into seven facies associations distinguished by their constituent facies, vertical organizations and lateral geometries. Facies associations include: (1) mid-fan channels, (2) overbank/levee, (3) crevasse-splays, (4) inter-channel, (5) outer-fan-lobes, (6) fan-fringe, and (7) trench floor/basin-plain. The formation displays a hierarchy of 1st, 2nd and 3rd order sedimentary cycles. The 1st order cycles range in thickness from 60 m to 450 m and conceptually correspond to “sequences” or “depositional sequences” formed mainly in response to sea-level fluctuations. Their boundaries are characterized by gradual or abrupt replacement of claystone/siltstone facies of the basin-plain by thin- to thick-bedded mid- to outer-fan turbidites, representing a basinward shift of the facies. The 1st order cycles generally start with thick- to very thick-bedded sandstones of channelized mid-fan facies, passing upwards into a middle part consisting of thin- to thick-bedded sandstone and claystone facies of the outer-fan-lobes and capped by claystone/siltstone-dominant facies of the basin-plain association. These three parts of the 1st order cycles correspond to the lowstand systems tracts (LST), transgressive systems tracts (TST) and highstand systems tract (HST) of the full depositional sequence. The 2nd order cycles, which are generally thinning-up and thickening-up cycles, range in thickness from 4 to 65 m, and occur both as isolated and composite packages, are characterized by mid-fan channelized and outer-fan-lobe associations, respectively. We interpret the 2nd order cycles as parasequences, which formed in response to marine flooding events of relatively short duration. The 3rd order cycles are very small-scale (1–4 m thick), mostly thickening-up cycles, which generally represent compensation cycles of the outer-fan-lobes. Sedimentary logs from the measured sections display significant differences in the character of facies, facies associations and cyclicity style but exhibit sufficient similarities to demonstrate that all these sequences formed parts of the same very large submarine fan complex. The succession has been strongly deformed, as attested by the prevalence of asymmetrical/overturned folding, thrusting and imbrication, resulting in great thickening due to tectonic duplication, as well as disruption of the cycles.

Evidence for episodic alluvial fan formation in far western Terra Tyrrhena, Mars

A Late Noachian-aged alluvial fan complex within Harris Crater in far western Terra Tyrrhena, Mars, is comprised of two well-defined source regions and associated discrete depositional lobes. Three fan units were recognized based on common morphological characteristics, thermal properties and spectral signatures. Although the entire fan complex has been subjected to extensive erosional degradation, the preserved morphologies record episodic fan formation and indicate the type of flow processes that occurred; the bulk of the fan surface has morphology consistent with fluvial emplacement while one fan unit exhibits a rugged surface texture with boulders consistent with a debris flow. This transition from fluvial to late-stage debris flow(s) suggests a decline in available water and/or change in sediment supply. The thermal inertia values obtained for all three fan surface units (mean values ranged from 318 to 344 J m −2 K −1 s −1/2) are typical for coarse-grained and/or well-indurated materials on Mars, but subtle variations point to important distinctions. Variations in aeolian bedform coverage as well as the density of ridges (inferred inverted channels) and boulders contribute to these subtle fan thermophysical differences and likely reflect changes in the fan depositional mechanisms and variations in post-depositional modification histories. The majority of the alluvial fan surface has a spectral signature that is broadly similar to TES “Surface Type 2” (ST2), with some important exceptions at long wavelengths. However, a unique spectral component was identified in one of the fan units (unit 3), that likely reflects lithological differences from other fan materials. This spectral attribute of unit 3 matched locations within the western catchment providing confirmation of provenance and supporting the contention that sediment supply changed over time as the fan developed. Finally, we applied simple modeling to a well preserved subsection of the fan complex to quantify the developmental history. Using the computed eastern fan volume (32 km 3), significant water, likely from precipitation, was involved in fan construction (>50 km 3) and an extensive period of fan formation occurred over millennia or longer.

Fabric anisotropy induced by primary depositional variations in the silt: clay ratio in two fine-grained slope fan complexes: Texas Gulf Coast and northern North Sea

High-resolution X-ray texture goniometry (HRXTG) has been used to quantify the alignment (anisotropy) of phyllosilicate minerals in a series of diagenetically altered mudstone samples from the deep subsurface of the Texas Gulf Coast and the northern North Sea. The sampled formations have undergone a simple burial history with no overprint of tectonic deformation that may have influenced the phyllosilicate orientation. Observations have been made in two constrained temperature windows 148–150 °C (North Sea data) and 169–210 °C (Texas Gulf Coast) wherein less than 20% smectite remains in the mixed layer phase illite–smectite. Quantitative X-ray powder diffraction (XRPD) shows quartz (which is dominantly detrital) and phyllosilicate content having an inverse relationship. Quantified illite–smectite fabric intensity (phyllosilicate alignments) ranges from low alignment values of 2.42 m.r.d. (multiples of a random distribution) to high alignment values 6.75 m.r.d. and chlorite + kaolinite ranges from 1.80 to 6.46 m.r.d. We propose that the broad range of phyllosilicate fabric intensity observed reflects the range of quartz/phyllosilicate ratios that are the imprint of depositional setting, bedform truncation, and initial grain size. Detrital quartz acts to disrupt fabric intensity by being non-platy, producing areas sheltered from effective stress (‘pressure shadows’), and acting as a matrix support. There is no evidence that bioturbation is a significant control on phyllosilicate alignment in these quartz/phyllosilicate mixtures. These findings have important implications for the role of grain-scale alignment on seismic anisotropy in mudstone systems. Fabric intensity in post-diagenetic samples can be predicted from (1) quartz content and (2) total clay content where:(1)y=−7.4x+64.8x is fabric intensity (in m.r.d.) and y is total (wt.%) quartz(2)a=4.2b+33.7and a is total (wt.%) clay content and b is fabric intensity (in m.r.d.).

Volume balance of a submarine landslide in the Espírito Santo Basin, offshore Brazil: Quantifying seafloor erosion, sediment accumulation and depletion

Degrees of seafloor erosion, sediment accumulation and depletion are quantified using a 3D seismic volume of a small submarine landslide offshore Brazil. In the study area, the upper boundaries of large remnant blocks — kept in situ during the main instability event — and the interpreted non-failed margins of the landslide comprise a reliable estimate for the position of the seafloor at the time the submarine landslide was generated. Remnant blocks of strata show little internal deformation, particularly at their base, and were kept upright during a principal instability event triggered in response to regional halokinesis and associated overburden faulting. They are laterally bounded by a mixed succession of mass-wasted chaotic strata, rafted blocks and post-slide sub-horizontal units. Despite the thin accumulation of failed strata now visible, the interpreted data indicate that submarine landslides of small areal dimensions can erode substantial volumes of seafloor sediment. Consequently, the more than 300 m of eroded seafloor strata offshore Brazil is of a similar scale to the largest failures recorded on continental margins (e.g. Storegga Slide; Amazon Fan complex; Cape Fear slide). The scale relationships presented in this paper indicate that the magnitude of seafloor erosion experienced during instability events may not be recorded by distal mass-wasted strata, which can be demonstrably thinner than the original volume of failed sediment. Thus, we conclude that the relative expression of accumulated slide strata is not directly related to the original volume of failed material. In addition, small-scale landslides can be responsible for the erosion of thick seafloor deposits, a factor that can potentially cause significant losses of seal capacity in overburden successions due to the sudden release of confining pressures in a vertical direction.

Sublacustrine depositional fans in southwest Melas Chasma

Two depositional fan complexes have been identified on the floor of southwest Melas Chasma. The western fan complex is located near the center of an enclosed basin in southwest Melas Chasma and is composed of multiple lobes with dendritic finger‐like terminations. These fans are very flat and have a morphology unlike any other fan that has been previously identified on Mars. On the basis of the morphologic similarity of the western fan complex to the Mississippi submarine fan complex, we suggest that it may be a deep subaqueous fan depositional system. There are numerous channels on the surface of the western fan complex, and measurements of channel length, width, and sinuosity are consistent with channels observed on terrestrial submarine fans. The eastern Melas depositional fans are less well preserved and may be of deltaic or sublacustrine origin. Recognition of the fans supports earlier suggestions for the presence of a former lake in Melas Chasma and indicates that a significant body of water was present and stable at the surface of Mars for at least 102 to 104 years.

Anatomy of a subaqueous ice‐contact fan and delta complex, Middle Pleistocene, North‐west Germany

AbstractThis paper presents a detailed analysis of the high‐resolution facies architecture of the Middle Pleistocene Porta subaqueous ice‐contact fan and delta complex, deposited on the northern margin of glacial Lake Weser (North‐west Germany). A total of 10 sand and gravel pits and more than 100 wells were examined to document the complex facies architecture. The field study was supplemented with a ground‐penetrating radar survey and a shear‐wave seismic survey. All collected sedimentological and geophysical data were integrated into a high‐resolution three‐dimensional geological model for reconstructing the spatial distribution of facies associations. The Porta subaqueous fan and delta complex consist of three fan bodies deposited on a flat lake‐bottom surface at the margin of a retreating ice lobe. The northernmost fan complex is up to 55 m thick, 6·2 km wide and 6·5 km long. The incipient fan deposition is characterized by high‐energy flows of a plane‐wall jet. Very coarse‐grained, highly scoured jet‐efflux deposits with an elongate plan shape indicate a high Froude number, probably >5. These jet‐efflux sediments are deposited in front of a large ∼3·2 km long, up to 1·2 km wide, and up to 25 m deep flute‐like scour, indicating the most proximal erosion and bypass area of the jet that widens and deepens with distance downstream to the region of maximum turbulence (approximately five times the conduit diameter). Evidence for subsequent flow splitting is given by the presence of two marginal gravel fan lobes, deposited in front of 1·3 to 2·5 km long flute‐like scours, that are 0·8 to 1 km wide and 7 to 20 m deep. In response to continued aggradation, small jets developed at the periphery of these bar‐like deposits and filled in the low areas adjacent to the original superelevated regions, locally raising the depositional surface and characterized by large‐scale trough cross‐stratified sand and pebbly sand. The incision of an up to 1·2 km wide and up to 35 m deep channel into the evolving fan is attributed to a catastrophic drainage event, probably related to a lake outburst and lake‐level fall in the range of 40 to 60 m. At the mouth of this channel, highly scoured jet‐efflux deposits formed under hydraulic‐jump conditions during flow expansion. Subsequently, Gilbert‐type deltas formed on the truncated fan margin, recording a second lake‐level drop in the range of 30 to 40 m. These catastrophic lake‐level falls were probably caused by rapid ice‐lobe retreat controlled by the convex‐up bottom topography of the ice valley.

Palaeoseismology of the North Anatolian Fault near the Marmara Sea: implications for fault segmentation and seismic hazard

Abstract We conducted palaeoseismic studies along the North Anatolian fault both east and west of the Marmara Sea to evaluate its recent surface rupture history in relation to the well-documented historical record of earthquakes in the region, and to assess the hazard of this major fault to the city of Istanbul, one of the largest cities in the Middle East. Across the 1912 rupture of the Ganos strand of the North Anatolian fault west of the Marmara Sea, we excavated 26 trenches to resolve slip and constrain the earthquake history on a channel–fan complex that crosses the fault at a high angle. A distinctive, well-sorted fine sand channel that served as a marker unit was exposed in 21 trenches totaling over 300 m in length. Isopach mapping shows that the sand is channelized north of the fault, and flowed as an overflow fan complex across a broad fault scarp to the south. Realignment of the feeder channel thalweg to the fan apex required about 9±1 m of reconstruction. Study of the rupture history in several exposures demonstrates that this displacement occurred as two large events. Analysis of radiocarbon dates places the age of the sand channel as post ad 1655, so we attribute the two surface ruptures to the large regional earthquakes of 1766 and 1912. If each was similar in size, then about 4–5 m of slip can be attributed to each event, consistent with that reported for 1912 farther east. We also found evidence for two additional surface ruptures after about ad 900, which probably correspond to the large regional earthquakes of 1063 and 1344 (or 1354). These observations suggest fairly periodic occurrence of large earthquakes (RI= c . 283±113 years) for the past millennium, and a rate of c . 16 mm/a if all events experienced similar slip. We excavated six trenches at two sites along the 1999 Izmit rupture to study the past earthquake history along that segment of the North Anatolian fault. One site, located in the township of Köseköy east of Izmit, revealed evidence for three surface ruptures (including 1999) during the past 400 years. The other trench was sited in an Ottoman canal that was excavated (but never completed) in 1591. There is evidence for three large surface rupturing events in the upper 2 m of alluvial fill within the canal at that site, located only a few kilometres from the Köseköy site. One of the past events is almost certainly the large earthquake of 1719, for which historical descriptions of damage are nearly identical to that of 1999. Other earthquakes that could plausibly be attributed to the other recognized rupture of the Izmit segment are the 1754, 1878 or 1894 events, all of which produced damage in the region and for which the source faults are poorly known. Our palaeoseismic observations suggest that the Izmit segment of the North Anatolia fault ruptures every one and a half centuries or so, consistent with the historical record for the region, although the time between ruptures may be as short as 35 years if 1754 broke the Izmit segment. Release of about 4 m of seismic slip both west and east of the Marmara Sea this past century (1912, 1999) support the contention that Istanbul is at high risk from a pending large earthquake. In that historical records suggest that the last large central Marmara Sea event occurred in 1766, there may be a similar 4 m of accumulated strain across the Marmara basin segment of the North Anatolian fault.

Ice-marginal sedimentation associated with the Late Devensian Welsh Ice Cap and the Irish Sea Ice Stream: Tonfanau, West Wales

This paper provides the first comprehensive description and interpretation of Late Devensian glacigenic deposits exposed in a 2 km-long cliff section at Tonfanau, Mid-West Wales. The section offers crucial insight concerning glacier dynamics and sedimentation on the eastern margin of the Irish Sea Basin. Six lithofacies are identified: diamicton, sandy gravel, well-rounded gravel, well-sorted sand, muddy sand, and laminites. Two diamicton horizons are present: an upper brown clast-rich sandy diamicton, and a lower grey clast-poor muddy diamicton, the latter being only sporadically exposed by wave action. Sand and gravel occur in close association, as well as minor mud and gravel successions. The sedimentary succession at Tonfanau records the dynamics and deposition of both Welsh and Irish Sea Ice. The lowermost part of the exposed section records Welsh ice extending into Cardigan Bay, depositing a diamicton originating from the adjacent hinterland to the West. As the Irish Sea Ice Stream flowed south, it impinged upon the present coastline at Tonfanau, depositing sediment with a northern provenance on top of predominantly Welsh material, as indicated by clasts from the Irish Sea Basin, Anglesey and the Llŷn Peninsula. The depositional environment for the Irish Sea materials is interpreted as one where a fluctuating ice margin generated a grounding-line fan complex in an ice-contact lake that merged laterally with lake sediments derived from suspension and turbidity currents. Succeeding facies indicate over-riding by Irish Sea Ice. Finally, the upper few metres of the succession was subjected to cryoturbation under a periglacial climate.

Automated alluvial fan discrimination, Quaternary fault identification, and the distribution of tectonically reactivated crust in the Gobi Altai region, southern Mongolia

In this study, we demonstrate the utility of SRTM topographic data as a tool for mapping alluvial fans and documenting the distribution of tectonically reactivated crust in the Gobi Altai region of southern Mongolia. The topographic data clearly reveal three diagnostic indicators of crustal reactivation: visible fault scarps, sharply defined faulted mountain fronts, and alluvial fan complexes adjacent to steep mountain fronts. These three variables are combined to produce a new surface tectonic activity map of the region. By selecting terrain with slope thresholds between 1 and 8° and then applying a topographic roughness filter, alluvial fan complexes are automatically discriminated and mapped throughout the region for the first time. This allows clear identification of Quaternary uplifted regions (and associated thrust faults) and the distribution of clastic basins which have experienced a two‐stage history: Mesozoic rifting and Late Cenozoic alluvial sedimentation. By analysing mountain front sinuosity and alluvial fan topographic roughness, the tectonic activity of individual mountain fronts is quantitatively compared and ranked. Most ranges are upthrust fault blocks with outward directed thrusts and bajadas bounding their N‐NE and S‐SW fronts. The spatial distribution of youthful mountain ranges, flanking fan complexes, and Quaternary thrust and strike‐slip faults is consistent with ongoing sinistral transpressional crustal reactivation throughout the region.

Geomorphological evidence for a changing tectonic regime, Pasinler Basin, Turkey

The Pasinler Basin, in the ‘East Anatolian Contractional Province’, features a suite of geomorphological zones, visible in the field, air photographs and Landsat and Shuttle Radar Topography Mission (SRTM) digital elevation model imagery. These zones reflect past and current tectonically influenced processes. Relicts of the Erzurum–Kars Plateau representing Mio-Pliocene volcanism, associated with transtensional tectonics, have been modified by two stages of drainage development: an earlier, shallow valley network, which was modified following uplift and tilting to form the present system characterized by deep narrow valleys that supply alluvial fan complexes. These fans discharge onto the present, aggradation-dominated basin floor. Initial normal faulting induced massive slope failures on the basin's northern margin. This extensional phase within the basin was reversed by the Late Pleistocene, with thrust faults modifying and producing landforms, and affecting sediment sequences, along both its northern and southern margins. The shift from a transtensional regime, and the associated volcanism, to normal faulting in the Pliocene to Early Pleistocene, and then to the present regime of compression-induced thrusting appears to correspond to a regional tectonic shift resulting from the collision of the Eurasian and Arabian plates and the subsequent westwards movement of the Anatolian microplate.

Large and giant hydrocarbon accumulations in the transitional continent-ocean zone

The petroleum resource potential is considered for the Atlantic, West Pacific, and East Pacific types of deepwater continental margins. The most considerable energy resources are concentrated at the Atlantic-type passive margins in the zone transitional to the ocean. The less studied continental slope of backarc seas of the generally active margins of the West Pacific type is currently not so rich in discoveries as the Atlantic-type margin, but is not devoid of certain expectations. In some of their parameters, the margins bounded by continental slopes may be regarded as analogs of classical passive margins. At the margins of the East Pacific type, the petroleum potential is solely confined to transform segments. In the shelf-continental-slope basins of the rift and pull-apart nature, petroleum fields occur largely in the upper fan complex, and to a lesser extent in the lower graben (rift) complex. In light of world experience, the shelf-continental-slope basins of the Arctic and Pacific margins of Russia are evaluated as highly promising.

Newly recognized eastern extension of the Nile deep-sea fan

A previously unreported easternmost segment of the Nile River deep-sea fan complex has been identified in the deep Levant Basin, offshore Israel, based mainly on a recently released, high-quality three-dimensional seismic data set. This segment is characterized by densely spaced seabed and subseabed turbidite channel complexes, generally fed from the region of the historically active northeastern Damietta and Pelusian branches of the Nile. This pattern suggests a previously unnoticeable symmetry in the modern channel distribution between the eastern and western branches of the deep-sea fan. The base of the Nile9s eastern deep-sea fan is determined by a NW-trending system of pre-Nile turbidite slope channels at the top of the Messinian evaporites. The overlying Pliocene–Holocene fan complex is further divided into two distinct stratigraphic units; a lower, stratified, sand-rich unit deposited in a basin-floor setting, and an upper heterogeneous, mud-rich unit consisting of downslope, mass transport, and hemipelagic sediments, with encased slope channel complexes richer in sand. Due to gravity gliding and spreading above the underlying thick, mobile Messinian salt, both stratigraphic units as well as the upper part of the Messinian salt layer are faulted and folded.