Turbidite Systems Research Articles

Evolution of a turbidite system in a narrow basin setting: the Ropianka Fm (Campanian–Paleocene) in the Skole Nappe of the Polish Carpathians

Evolution of a turbidite system in a narrow basin setting: the Ropianka Fm (Campanian–Paleocene) in the Skole Nappe of the Polish Carpathians

A workflow for turbidite reservoir characterization—a case study of the Macedon member, Northern Carnarvon Basin, NW Australia

Deep-water turbidite systems on passive continental margins are of interest for oil and gas exploration. However, their complexity poses challenges for reservoir characterization. In this study, we proposed a reservoir characterization workflow for the Macedon member turbidite, employing a combination of 90° phase adjustment, geobody extraction, and genetic inversion, based on the abundant well logging and seismic data from the Enfield field, Northern Carnarvon Basin. Our workflow involved seismic sedimentology to determine the morphology of sand bodies and inversion to determine the net reservoir range, resulting in 3D geological attribute modeling. We applied a 90° phase adjustment correlated seismic events and well logging responses. By stratal slice interpretation and geological body extraction, it was revealed the turbidite reservoir distribution. Finally, we achieved net reservoir characterization of the Macedon member through genetic inversion porosity and geostatistical methods. The results showed that the Macedon turbidite reservoir can be divided into the top and base reservoirs. The top reservoir is sheet-like, and the base reservoir is channelized. The average porosity of the former was 24%, while the average porosity of the later is 20%. The top reservoir has better reservoir quality. Furthermore, we discussed sea level changes affect turbidite distribution and reservoir quality. During the Falling Stage Systems Tract (FSST), the long transportation distance led to relatively less sediment supply and a low sand/mud ratio, resulting in confined, channelized, poor quality turbidite reservoir. In contrast, during the Lowstand Systems Tract (LST), unconfined, amalgamated, good quality turbidite sheet reservoirs were formed. The improved workflow based on seismic sedimentology presented in this article proves effective in characterizing complex reservoirs and contributes to the simplified and efficient management of reservoirs.

Deep-sea Ordovician lingulide brachiopods and their associated burrows suggest an early colonization of proximal turbidite systems

Trace fossils from Ordovician deep-marine environments are typically produced by a shallow endobenthos adapted to live under conditions of food scarcity by means of specialized grazing, farming, and trapping strategies, preserved in low-energy intermediate to distal zones of turbidite systems. High-energy proximal zones have been considered essentially barren in the early Paleozoic. We report here the first trace and body fossils of lingulide brachiopods in deep-marine environments from an Upper Ordovician turbidite channel-overbank complex in Asturias, Spain. Body and trace fossils are directly associated, supporting the interpretation of a lingulide tracemaker. Ellipsoidal cross-section, cone-in-cone spreite, and spade morphologies suggest the specimens belong to Lingulichnus verticalis. The oblique orientation in both trace and body fossils is the result of tectonic deformation. The organisms were suspension feeders showing escape, dwelling, and equilibrium behaviours controlled by sedimentation rates associated with turbidite deposition. These trace fossils and their in situ producers represent the oldest evidence of widespread endobenthos colonization in high-energy, proximal areas of turbidite systems, expanding the bathymetric range of Lingulichnus and the variety of behaviours and feeding styles in early Paleozoic deep-marine environments.

Coarse-grained submarine channels: from confined to unconfined flows in the Colombian Caribbean (late Eocene)

Submarine channel mouth settings are hardly preserved in the stratigraphic record. Although they are still poorly known with respect to other segments of turbidite systems, conceptual models are being refined in the light of new discoveries in modern and ancient examples. Still, some questions such as the transition between expansion zones and the traditional Channel-Lobe Transition Zone (CLTZ) remains open in ancient systems. Upper Eocene deposits of the Colombian Caribbean (San Jacinto Fold Belt) are interpreted here as a fan-delta-fed, submarine, coarse-grained channel-lobe system. It displays a well-preserved channel inception stage in the shelf break represented by sigmoidal to lens-shaped gravels, and planar cross-stratified pebbly sandstones (foreset and backset) interpreted as cyclic steps in an expansion zone. In a later stage, a classical channel-levee complex was developed, represented by channel fill elements showing sharp- and erosional-based, fining-upward sequences that are meters thick, having basal massive matrix-supported pebble conglomerates (hard—extrabasinal—clasts, rip-up clasts, coastal bioclasts), vertically evolving to liquefied massive to planar-laminated coarse-grained sandstones with phytodetrital carbonaceous laminae. They are interpreted as concentrated flow deposits (high-density turbidites) coming from continental areas or from coastal systems (i.e., delta reworking). Undifferentiated channel belt thin-bedded turbidites associated with levees and terraces deposits are related to these confined systems. The channel-lobe transition zone is characterized by debrites from cohesionless debris flow in a channel-mouth bar setting, representing bypass processes that developed distally into low-angle, planar cross- and sigmoidally-stratified (upstream antidune) pebble-size to coarse-grained sandstones that fill low-angle scours (cut-and-fill structures) in an antidune field setting with supercritical conditions. When the currents lose channel confinement, the setting is characterized by changes from Froude supercritical to subcritical flow conditions in an inner lobe to lobe off-axis environment. Large seasonal fluctuations in precipitation favor high sediment concentrations, promoting the formation of volumetrically significant fan deltas and coarse-grained submarine channels with high erosive capacity; therefore, their record helps refine interpretations of depositional processes, providing criteria for recognizing areas of the turbiditic systems that are hardly preserved. The particular aggradational conditions for the preservation and stratigraphic characterization of the rare exhumed submarine channel mouth systems make it possible to decipher sediment dispersal patterns and thus connect the models proposed here, from supercritical systems to the traditional models of turbiditic systems.

Sedimentary architecture of submarine channel-lobe systems under different seafloor topography: Insights from the Rovuma Basin offshore East Africa

Seafloor topography plays an important role in the evolution of submarine lobes. However, it is still not so clear how the shape of slope affects the three-dimensional (3-D) architecture of submarine lobes. In this study, we analyze the effect of topography factors on different hierarchical lobe architectures that formed during Pliocene to Quaternary in the Rovuma Basin offshore East Africa. We characterize the shape, size and growth pattern of different hierarchical lobe architectures using 3-D seismic data. We find that the relief of the topographic slope determines the location of preferential deposition of lobe complexes and single lobes. When the topography is irregular and presents topographic lows, lobe complexes first infill these depressions. Single lobes are deposited preferentially at positions with higher longitudinal (i.e. across-slope) slope gradients. As the longitudinal slope becomes higher, the aspect ratio of the single lobes increases. Lateral (i.e. along-slope) topography does not seem to have a strong influence on the shape of single lobe, but it seems to affect the overlap of single lobes. When the lateral slope gradient is relatively high, the single lobes tend to have a larger overlap surface. Furthermore, as the average of lateral slope and longitudinal slope gets greater, the width/thickness ratio of the single lobe is smaller, i.e. sediments tend to accumulate vertically. The results demonstrate that the shape of slopes more comprehensively influences the 3-D architecture of lobes in natural deep-sea systems than previously other lobe deposits and analogue experiments, which helps us better understand the development and evolution of the distal parts of turbidite systems.

Confined turbidite system of the upper Paleozoic Itararé Group, Paraná Basin, Brazil: Beyond the topographic control paradigm

Recent studies in the eastern margin of the Paraná Basin, about the initial deposition of the Taciba Formation (Itararé Group) revealed a preserved, partially exhumed glacial trough as indicated by the morphology of its basal nonconformity. In this work, we reinforce the importance of the glacially-carved topography controlling the subsequent sedimentation by emphasizing turbidity currents and their deposits. This glacial trough is large enough to confine part of the following deglacial sediments, including a sand-rich turbidite system that represent phases of more consistent sand supply, a result from high sedimentation rates associated either with direct influx of meltwater-derived jets and/or with a rapid delta progradation at the trough head, causing over-steepening, unsteadiness, and eventual failure of the delta-front deposits. This turbidite system consists of three sand-rich stages (Ts1 to Ts3) intercalated with three fine-grained intervals (F1 to F3). Ts stages form bedsets with an overall lenticular geometry, thinning-out toward the trough flanks where the individual sandstone beds pinch-out close to the metamorphic Precambrian bedrock. They are ascribed to sinuous, laterally extensive channelized bodies representing different phases of channel activity through time. In general, each stage consists of an initial deposition derived from long-lived turbidity currents triggered by flood-driven hyperpycnal flows followed by short-lived, surge-type turbidity currents. F1, F2 and F3 deposits consist of fine-grained intervals that separate Ts1, Ts2 and Ts3 stages by an abrupt change in grain size and bed thickness. They comprise thin, sand-to-mud couplets showing granule-to-boulder sized basement-affinity dropstones, and several minor slumps, which are interpreted as overbank/levee sedimentation taking place during the successive passage of turbidity currents. A paleogeographic reconstruction of the glacial landscape reveal some similarities with modern fjords of British Columbia, Canada, that can be used to geometries and facies distribution prediction as an analog to assist seismic and well-log data.

Recycling effects in detrital zircon U[sbnd]Pb signatures in a foreland basin: Identifying the multicyclic sediment sources of the Eocene-Miocene Jaca basin (southern Pyrenees, Spain)

This work deals with the provenance evolution of the mid Eocene to early Miocene clastic deposits of the Jaca basin (southern Pyrenees), which record a main drainage network reorganization during the progressive tectonic uplift of the Pyrenean orogen. We present new detrital zircon UPb data which show a Variscan-dominated detrital zircon signature for the Lutetian Hecho Group turbidites, while the overlying late Eocene to early Miocene alluvial fan sediments record a Cadomian-dominated detrital zircon signature, allowing to document a major change in the source area. Moreover, a tectono-stratigraphic cyclicity can be identified in each of the turbidite systems that conform the upper Hecho Group, featuring an enrichment of the Variscan detrital zircon signal at the base of the system, which can be interpreted as the result of an efficient sediment transfer from distant Axial Zone sources during relative sea-level lowstands, while a dilution of this signal occurs during highstands, at the top of each system, due to the reduced erosion capability of the fluvial network. Integration of detrital zircon UPb data with sandstone petrography allows for improved resolution of the source-area shifts, for discrimination between first-cycle and multi-cycle zircons, and to identify that the detrital zircon signal of the alluvial fans does not fully represent the source area configuration. This study illustrates the importance of combining petrography with detrital zircon UPb data to improve provenance reconstructions and to identify the role of sediment recycling during progressive foreland evolution.

Feasibility of 4D Gravity Monitoring in Deep-Water Turbidites Reservoirs

We present a seafloor 4D gravity feasibility analysis for monitoring deep-water hydrocarbon reservoirs. To perform the study, we have simulated the gravity effect due to different density and pore pressure distributions derived from a realistic model of a turbiditic oil field in Campos Basin, offshore Brazil. These reservoirs are analogs of several other passive-margin turbiditic systems located around the world. We considered four reservoir scenarios including and not including seafloor subsidence. Our results indicate that the gravity responses are higher than the feasible value of 3 μGal 12 years following the base survey. The area of maximum gravity anomaly corresponds to where we suppose hydrocarbon extraction occurs. A maximum seafloor subsidence of 0.6 cm was estimated, resulting in no detectable gravity effects. Our results endorse the 4D seafloor gravity acquisition as a beneficial tool for monitoring deep-water passive-margin turbiditic reservoirs.

Turbidite system controlled by fault interaction and linkage on a slope belt of rift basin: Zhanhua depression, Bohai Bay Basin, China

Although the relationship between faulting and sedimentation has been extensively studied and discussed over the past decades using a variety of examples and surface and subsurface data. However, limited information is available regarding the evolutions within the interaction zones in sedimentary processes, depositional architecture and sand bodies dispersal, which are crucial for hydrocarbon exploration, specifically in deep-water sedimentary system. To investigate the effects of fault interaction and linkage on the sedimentary processes and architecture of deep-water turbidite systems and explore the impact of fault linkage patterns on the dispersal of sand bodies, 3D seismic data, cores and logging data were collected from the southern slope zone of the Zhanhua Depression, Bohai Bay Basin. The Kenxi area exhibits two typical fault-reworked geomorphologies (i.e. slope geomorphology with weak reworking and fault-trough geomorphology with strong reworking), which control the development of fan depositional architecture dominated by turbidity current and fault-confined channel depositional architecture dominated by mixed traction current and turbidity current, respectively. These turbidite systems indicate that they are connected to flood occurrence based on systematic lithofacies analysis. Nevertheless, two distinct sediment grain sizes and drainages have been formed and may be related to fault confinement and slope gradients. Additionally, we propose conceptual fault linkage models that regulate drainage and the dispersion of sand bodies, highlighting the effects of fault evolution stages and separation distance on local geomorphology. First, the region with relatively unconfined geomorphology, dominated by non-separated faults in the soft linkage stage, is where lobe deposits are more likely to have formed. The relay ramps, shaped by separated faults in the soft linkage stage, control the direction of the transportation of sediments in the proximal area. Second, the distribution of fault-confined channels is laterally confined by long extended fault-trough geomorphology formed following hard linkage by non-separated faults. The local footwall hump (i.e. local topographic high) formed in an overlapped zone by separated faults provides frontal confinement for sand bodies in the hard linkage stage. This study reveals that in addition to onshore river systems, the architecture and distribution of deep-water turbidite systems are significantly influenced by fault interaction and linkage patterns. Meanwhile, it provides a new model for facilitating the prediction of the reservoir distribution of turbidite systems in the slope zone of rift basins.

Submarine channel stacking patterns controlled by the autogenic 3D kinematics of meander bends

Abstract Channel kinematics play a pivotal but underappreciated role in determining submarine meandering channel stacking patterns. A stratigraphic forward model is here applied to turbidite systems to generate synthetic stratigraphic architectures and to compare channel trajectories recorded on cross-sections with the kinematics of meander bends. Various channel stacking patterns, which may be classified into four types, are obtained from a single set of constant parameters. This variety of stacking patterns observed from one 2D section to another is thus autogenic. It is the consequence of the 3D migration of meander bends. It reflects the number of consecutive bends that have intercepted the cross-section, which depends on the channel downstream migration rate. These 3D effects alone are sufficient to explain variations in the apparent migration rate and the reversal of migration direction. As a result, sigmoidal geometries can be preserved in aggrading systems without a significant change in channel geometry or varying aggradation and migration rates. Finally, despite these 3D effects, stratigraphic mobility numbers still provide good constraints on bend kinematics. These results should apply to meandering rivers and other meandering systems.

Ichnological characterization of deep-sea muddy deposits: Macrobenthic communities revealing palaeoenvironmental conditions within turbidite systems

Traditionally, studies on turbiditic systems were mostly focused on sedimentological features, but later some other features as bioturbation have been included. Ichnological analysis is probed as a powerful tool for deep-sea sediments studies, revealing accurate information about palaeoenvironmental conditions during deposition. For the first time, a detailed ichnological and sedimentological integrative analysis focused on Miocene muddy turbiditic deposits from the westernmost Mediterranean at the Tabernas Basin (SE Spain) is here presented. The representative Rambla de Tabernas section has been selected to identify dominant palaeoenvironmental conditions before the deposition of the well-known Gordo megabed. The ichnological content reveals a trace fossil association comprising 26 ichnospecies, belonging to 14 ichnogenera ascribed to the Nereites ichnofacies in an overall stable and well oxygenated environment dominated by low-energy conditions. The distribution, and abundance of trace fossils, integrated with sedimentological information, allow to characterize variation in depositional conditions within the turbiditic system. Before deposition of the Gordo megabed, the turbiditic system in the lower part of the studied area had generalized low energy conditions. These conditions are probably linked to distal depositional areas, characterized by the record of the Paleodictyon ichnosubfacies in interbedded sandstones-mudstones, with a common occurrence of Tab/Tabc Bouma intervals. In contrast, higher energy conditions and deposition prevailed in proximal settings (e.g., channels and proximal lobes) in the upper part. They arecharacterized by the Ophiomorpha rudis ichnosubfacies in interbedded sandstones-mudstones with dominant Tab Bouma intervals. Additionally, the low ichnodiversity in comparison with similar deposits from other worldwide areas, is probably caused by the influence of local environmental conditions in the studied basin.

Intensified lacustrine turbidite deposition as a response to the Carnian Pluvial Episode: Insights from the Triassic Ordos Basin in North China Plate

The Carnian Pluvial Episode (CPE) is a period during which the rainfall was extremely intense and greatly influenced the deposition in different sedimentary environments globally. However, the relationship between the CPE and turbidite deposition remains poorly known. Here we investigate a giant lacustrine turbidite system of the Triassic Ordos Basin in North China Plate, to determine how the CPE influenced turbidite deposition, by integrating geochronology, organic carbon isotope, major and trace elements, clay minerals and turbidite sedimentology. Results show that the lacustrine turbidite deposition in the Ordos Basin was strongly associated with the CPE. Although there is a temporal lag, the intensified turbidite deposition is considered as a response to the three humid periods during the CPE. Compared with marine environments, continental depositional settings tend to be more sensitive to the humid climate changes, and can record more detailed and long-term carbon fluctuations. This study highlights the potential for turbidite deposition affected by extremely humid events, and provides new insights into the prediction of deep-water turbidite systems. Furthermore, it enriches the theory of the CPE in terrestrial environments.

Early stages of trench-slope basin development: Insights from mass-transport deposits and their interactions with turbidite systems (southern Hikurangi margin, New Zealand)

Geological complexity, progressive tectonic overprint and prevailing submarine location of subduction margins generally hinder investigating the early stages of development of their oldest trench-slope basins, witnesses of subduction initiation and early history. Along the eastern North Island of New Zealand, the inner portion of the Hikurangi subduction wedge is emerged, thereby offering a unique opportunity to examine, at outcrop-scale, the tectonostratigraphic evolution of a trench-slope basin (Castlepoint trench-slope basin) that was linked to the onset of subduction. We present new occurrences of lowermost Miocene gravity-driven systems, suggesting a more intricate depositional framework to the ones previously inferred during this key period. Results show that the early stages of development of a trench-slope basin coeval with the birth of a subduction margin may deviate from traditional models either comprising (1) sustainable sediment sources connected to the basin very early in the history of the margin and (2) a sedimentation-deformation feedback mechanism promoting the long-term development of an aggradational turbidite system downslope. Analysis of the mass-transport deposits (MTDs) also revealed that the outboard migration of deformation was discontinuous and uneven along the margin during the earliest Miocene. Two major tectonic events, separated by a period of reduced tectonic activity, were recorded at the inboard border of the Castlepoint trench-slope basin, each resulting in seaward motion, oversteepening and frontal denudation of a thrust sheet. Each thrust sheet provided contrasting failed material and morphometric characteristics to the associated deposits, thereby allowing us to discriminate the nature of the nappe and related controls responsible for shedding each MTD as well as refine the timing of nappe emplacement along this part of the margin. Overall, this study draws new insights on the early structural evolution and stratigraphic infill during the birth of subduction zones, insights which may, in turn, help improve understandings of active margin settings.

The Tachrift Project: sedimentary architecture of turbidite channel- levée deposits (Tachrift Turbidite System, Taza-Guercif Basin, Tortonian, NE Morocco)

Turbidite channel-levée complexes have been the focus of extensive research from a number of modern and ancient deep-water turbidite systems over more than fifty years. Although high-resolution 3D seismic studies have recently yielded unprecedented imaging of these deposits, the internal facies complexity of a channel-levée complex remains elusive. To fill this gap, extensive well-exposed outcrops are particularly important, as they provide information on fine-scale facies heterogeneity.This contribution reports on the ongoing ‘Tachrift’ Project, which aims to explore 9 superimposed channel-levée complexes belonging to the Tachrift turbidite system (late Tortonian- early Messinian) of the Taza–Guercif Basin (NE Morocco). Arid climate and deep incision by ephemeral streams make for world-class, extensive, unexplored outcrops spread over an area of ~ 16 km2. Preliminary results provide valuable insights into facies and geometry of channel-fills and correlative levées over a ~150 m-thick and ~4 km wide transect largely oblique to palaeoflow, which may contribute to improving existing models of turbidite channel belt sedimentary heterogeneity and stratigraphic evolution, applied to understand the composition of subsurface analogues.

Ediacaran turbidites as geoheritage: Potential of the Itajaí Basin, Southern Brazil

Discovery and inventory of geoheritage remain urgent tasks for Brazil. Investigations in the state of Santa Catarina have allowed to realize the uniqueness of exposures of the Ediacaran turbidites of the Itajaí Basin. Their outcrops along the federal highway BR-470 in the valley of the Itajaí-Açu River have been examined to establish four geoheritage sites (geosites), namely Apiúna, Bergamota, Colibri, and Ibirama. Each of them has been studied in regard to the geological context and geoheritage properties. Geological descriptions and the related genetic interpretations of each geosite are provided. It appears that they represent different parts and different aspects of the regional Ediacaran turbidite system. The key localities are true geosites, which can be neither be combined into a single lengthy geosite nor considered as fully separate objects due to their evident similarity. For such kinds of geoheritage, a new idea of geosite series is proposed. The studied geosite series is dominated by sedimentary and paleogeographical geoheritage types, and it can be ranked nationally (the global rank is not excluded). The geosites are linear and point (punctual) sites, and most of them are artificial. A potential danger to them is linked to road maintenance, but there may also be damages from rockfalls, vegetation expansion, and irresponsibility of occasional visitors (rock graffiti and waste storage). A conservation plan should be developed to address these issues. This geosite series demonstrates significant potential for geological research and education linked to the Ediacaran world and turbidite sedimentation. Additionally, it can be exploited efficiently for training university students and company employees in dealing with turbidite hydrocarbon reservoirs. Further geoheritage exploration in the Itajaí Basin and the entire Santa Catarina State is recommended.

Late Paleocene to Middle Eocene Calcareous Nannofossil Assemblages from Península Mitre, Southeastern Austral Basin, Argentina

On the Fueguian Atlantic coast and in the southern Andean fold and thrust belt, the Paleogene is partially represented by numerous turbiditic systems. Between Río Bueno and Cabo Leticia on Península Mitre, the Paleocene-Eocene is represented by the Río Claro Group (Cabo Leticia, La Barca, Punta Noguera and Cerro Ruperto formations) and the Río Bueno Formation; which together constitute a ~1050 m thickness succession. Here, calcareous nannofossil assemblages recovered from 96 samples were analyzed to determine their relative ages. The Cabo Leticia Formation was barren in nannofossils. The upper LB2 Member of La Barca Formation, contained Rhomboaster cuspis and Fasciculithus richardii, frequent in the Paleocene/Eocene boundary (Subzones NP9a/NP9b). Nannofossils recovered from Punta Noguera Formation indicate an early Eocene age (biozones NP9b-NP10), with Fascilulithus tympaniformis, Rhomboaster cuspis and abundant Toweius spp. The Cerro Ruperto Formation provided one productive sample, with specimens of Reticulofenestra spp. and Toweius spp., which indicates an early Eocene age for the formation (biozones NP12-NP13). The Río Bueno Formation yield calcareous nannofossil assemblages characterized by Chiasmolithus eograndis, Chiasmolithus expansus, Toweius spp. and Reticulofenestra spp. which indicates a late early Eocene to middle Eocene age (biozones NP14-NP16). Although the calcareous nannofossil record is discontinuous due to sedimentary facies of the Río Claro Group, our data allow a better age constraint for the investigated formations and to correlate these units with others outcropping and subsurface units in the Austral Basin.

Peak Cenozoic warmth enabled deep-sea sand deposition

The early Eocene (~ 56–48 million years ago) was marked by peak Cenozoic warmth and sea levels, high CO2, and largely ice-free conditions. This time has been described as a period of increased continental erosion and silicate weathering. However, these conclusions are based largely on geochemical investigation of marine mudstones and carbonates or study of intermontane Laramide basin settings. Here, we evaluate the marine coarse siliciclastic response to early Paleogene hothouse climatic and oceanographic conditions. We compile an inventory of documented sand-rich (turbidite) deep-marine depositional systems, recording 59 instances of early Eocene turbidite systems along nearly all continental margins despite globally-elevated sea levels. Sand-rich systems were widespread on active margins (42 instances), but also on passive margins (17 instances). Along passive margins, 13 of 17 early Eocene systems are associated with known Eocene-age fluvial systems, consistent with a fluvial clastic response to Paleogene warming. We suggest that deep-marine sedimentary basins preserve clastic records of early Eocene climatic extremes. We also suggest that in addition to control by eustasy and tectonism, climate-driven increases in sediment supply (e.g., drainage integration, global rainfall, denudation) may significantly contribute to the global distribution and volume of coarse-grained deep-marine deposition despite high sea level.

Transitional flow deposits on submarine lobe flank (Veřovice and Lhoty Fms, Albian – Cenomanian, Polish Outer Carpathians)

The Zagórnik-Rzyki studied section includes the upper part of the Veřovice Fm and the lower part of the Lhoty Fm (Aptian–Albian), which are small fragments of the much thicker sedimentary succession of the Silesian Nappe (Polish Outer Carpathians). Logged section gives a good insight into the relatively proximal but muddy submarine fan environment with at least partially confined nature and widely distributed facies of heterolithic deposits and banded sandstone. Three distinguished facies associations represent a gradual lateral shift toward the depositional lobe flank in a relatively proximal setting, away from the main sediment distribution pathways. The studied heterolithic deposits show various internal sedimentary structures (muddy ripples, draped ripples, low-amplitude bed-waves, low-angle laminated bedforms, small lenticular bedforms and plane-parallel laminated mudstone) considered as a record of the dynamic of sedimentary processes on a submarine depositional lobe flank environment. Despite the predominance of finning upward grain size trends (wanning flow deposits), sedimentary structures in the heterolithic deposits may stack in a varied order, also forming coarsening upward trend (waxing flow deposits), bi-gradational trend (waxing to wanning flow deposits), and complex trends (deposits with multiple waxing to wanning flow pulses) indicating record of hyperpycnal flows. Lack of hybrid event beds despite the occurrence of transitional flow deposits is evidence that even in mud-dominated to mixed sand-mud submarine turbidite systems, the flow transformation from fully turbulent to cohesive laminar behaviour is incomplete in relatively proximal depositional environment. Instead, a variety of facies banded sandstone and heterolithic deposits may represent a significant fragment of the sedimentary record in the proximal depositional lobe flank setting.

Architectural complexities and morphological variations of the indus fan and its elements: Understanding of the turbidite system through seismic characterization

The investigations of the processes occurring in submarine fans improve the understanding of intricacies of deepwater turbidity system and their associated developed architectural elements. The seismic patterns and depositional geometries of the channel levee complexes of the Indus fan have been studied using 2D/3D seismic and well data. The Indus fan is the second largest submarine fan in the world, with a horizontal extent of some 1500 km and a thickness of approx. 9 km. The development source of the Indus fan is divided into two units primarily based on their stratigraphic architecture and depositional characteristics. Firstly, the Eocene-Oligocene to Miocene lower unit that is built of channel lobes, and regionally developed large mass-transport deposits including megaturbidites. The other unit is Miocene and the Quaternary upper part that constitute major channel levee complexes with minor intercalations of locally developed mass transport deposits. The former progressively increase in thickness and width upwards the Eocene-Oligocene to Quaternary. This gave rise to symmetrical and asymmetrical growth patterns as a result of multiple phases of erosion and deposition. Such an architecture is present at an extensive scale primarily in the Plio-Pleistocene channels where the vertical to lateral growth ratio is higher than the channels. A single episode of thick MTDs is recognized by seismic reflection geometries suggesting sea level fluctuations that occurred between the Eocene-Oligocene and the Miocene, and from the Pliocene and the Quaternary channels. Regional confinements drastically affected the development of the Indus fan from the Eocene-Oligocene to Miocene, diminishing from the Pliocene-Quaternary. Sediment zonation occurred owing to the presence of structural confinements that controlled the growth of channel levee complexes and in general the entire Indus fan. Our results based on seismic reflection data of channel levee complexes suggest that increasing but alternating sediment supply from Eocene till Plio-Pleistocene, assisted the active channels and levee growth. Continuous increase in turbidity current size and energy along with sedimentation rates modified (i.e., increased the channel aspect ratio) the channel architecture of the Indus Fan.

Provenance shift during Early‐Middle Triassic and its response to the palaeogeographic and tectonic evolution of the southwestern South China Block

To constrain the relationship between the plate boundary dynamics and the basin sedimentation in the southwestern South China Block (SCB), we undertook detrital zircon U–Pb–Hf isotope compositions of the Lower‐Middle Triassic turbidite system in the Youjiang Basin and biotite 40Ar/39Ar thermochronology of the adjacent Lingshan granite. The detrital zircons from Lower Triassic clastic rocks are dominated by age peaks at ~450 Ma and ~1,000 Ma and minor peaks at ~250–260 Ma with negative εHf(t) values (−6.4 to −10.1). In contrast, the Middle Triassic group contains more volcanic fragments and displays a different age peak at ~240–287 Ma with εHf(t) between −11.9 and 13.2 in addition to the former two peaks. These results suggest a potential provenance associated with juvenile and volcanic components in the adjacent region during the Middle Triassic. A summary of the Triassic tectonothermal history suggests that the eastern Youjiang Basin and Yunkai Terrane were uplifted throughout the Triassic, while the northeastern Indochina Block on the west of the SCB was uplifted mainly during the Middle Triassic. Combined with the palaeocurrent reconstruction, we infer that the turbidite system was filled primarily from east to west during the Early Triassic, mainly controlled by the Palaeo‐Pacific plate subduction. Subsequently, the Middle Triassic turbidite system involved juvenile and volcanic components from the eastern SCB and northeastern Indochina Block in addition to the Early Triassic provenance, as a result of dual impact from the Palaeo‐Pacific plate subduction and Indochina Block collision.