Variations In Sediment Supply Research Articles

Anatomy of a platform margin during a carbonate factory collapse: implications for the sedimentary record and sequence stratigraphic interpretation of poisoning events

Sequence stratigraphic interpretations are limited in their prediction of sedimentary architecture and changes in sea-level when used in systems characterized by marked fluctuations in sediment supply, particularly in carbonate-dominated environments. Pronounced variations in sediment supply occurred during the Pliensbachian–Toarcian transition, when significant perturbations of the carbon cycle and intense environmental disturbances led to a global shutdown of carbonate production. We studied the impact of this event on sedimentation and stratal stacking patterns in the Moroccan central High Atlas. We reconstructed the lateral variations in facies and sedimentary geometries along a carbonate platform margin and slope in the field by tracking six key discontinuity surfaces covering the Pliensbachian–Toarcian transition from the platform margin to the toe-of-slope. This work highlights the difficulties in sequence stratigraphic interpretations in cases of neritic carbonate factory collapse without assessments of shoreline movement because the stacking patterns in open marine environments do not necessary reflect the regional variation in base level in disturbed carbonate systems. This study also emphasizes the uncertainties associated with focusing solely on lower offshore strata to assess the history and causes of palaeoenvironmental perturbations because decreases in the rate of carbonate production dampen neritic carbonate shedding and therefore favour the creation of a hiatus in deep water settings.

Reconstruction of the gross depositional environment evolution in the northern Malay Basin, Malaysia-Thailand joint development area (MTJDA)

This paper provides new insight on the complex interactions between regional tectonic evolution, differential subsidence across the basin, and variation in sediment supply based on a reconstruction of the gross depositional environment in the northern part of Malay Basin. In addition, the variation in sedimentary facies, established from an integrated analysis based on seismic interpretation, well-log analysis, and core evaluation, are used to establish the gross depositional environment for key surfaces within the Oligocene to Miocene succession.The basin fill comprises Oligocene syn-rift and Miocene post-rift successions. The syn-rift successions are Syn-Rift Unconformity (SRU)-Base of Syn-Rift (BSR), and Base Chattian Unconformity (BCU)-Syn-Rift Unconformity (SRU) sequences. Whereas, the post-rift successions represent by Intra-Aquitanian MFS (IAM)-Base Chattian Unconformity (BCU), Intra-Burdigalian MFS (IBM)-Intra-Aquitanian MFS (IAM), Miocene Transgressive-Regressive (MTR)-Intra-Burdigalian MFS (IBM), Intra-Serravalian MFS (ISM)-Miocene Transgressive-Regressive (MTR), and Intra-Tortonian (ITM)-Intra-Serravalian MFS (ISM) sequences.The Oligocene-early Miocene syn-rift succession in the study area is characterized by aggradational stacking patterns, with an indication of retrogradation in individual sand packages for SRU-BSR, and BCU-SRU intervals, whereas an overall aggradational stacking pattern can be observed within the IAM-BCU sequence. The depositional environment of the syn-rift succession is mainly deltaic, fluvial, alluvial fan, shallow and deep lacustrine at the basin center.The early-middle Miocene post-rift succession is characterized by mostly aggradational and fining upwards stacking within the IBM-IAM sequence. This gradually changed to a retrogradational pattern in the MTR-ISM sequence. Depositional environments for this succession consist of an alternation between fluvio-marine and sub-tidal to marine sedimentation. Depositional environments for the overlying late Miocene Intra-Tortonian to Intra-Serravalian (ITM-ISM) was estuarine or tidally-influenced environments comprising fluvial channel, tidal or distributary channel, tidal sand flat, and tidal flat deposition. This interval mainly consists of coarsening upward units that gradually changed to a stacked higher-order fining upwards package. The deeper stratigraphic units are generally more continental (non-marine) in character, but fluvio-tidally influenced marine environments became more dominant in the shallower sequences.

The late Pleistocene-Holocene changing morphology of the Volturno delta and coast (northern Campania, Italy): Geological architecture and human influence

The present geomorphology of the Volturno River delta system and related strandplain is largely a product of complex, long-lived relationships between geological evolution and human impacts.In order to assess the main drivers of the changed landscape in the last centuries, a multidisciplinary study was carried out by combining geological and historical data. The study was based on geological and geophysical data, including about 1800 stratigraphic well logs to reconstruct the stratigraphic architecture of the delta plain and ca. 180 km of very high resolution single channel reflection profiles to image the stratigraphic pattern of the continental shelf and the offshore delta. Cartographic sources from the last 150 years were acquired, georeferenced and managed into a GIS environment, to support geomorphological interpretation. Land use maps were reconstructed for the 1957, 1990 and 2012. The Late Pleistocene and Holocene reconstruction of the Volturno coastal plain evolution evidenced the control of climatic changes (and consequently sediment supply and global eustatic variations) on the depositional history. The present landscape appears largely inherited by the past MIS5 and LGM landscapes.A progressive increment of anthropic forcing took place in the last 2000 years but the strongest modifications of the landscape occurred since the end of the XVII century, when, during the Spanish vice-kingdom, it was subjected to major land reclamation. More than 500 km of canals were built in the coastal area and resulted in the development of agriculture and farming on reclaimed land, promoting urbanization and increasing landscape fragmentation. A peak of major alterations of the deltaic environment, and retreat of the coastline was attained between the 1960s and the 1990s. Severe urbanization along the coastline, coupled with intensification of agricultural and tourism activities, resulted in a significant loss of natural ecosystems including humid coastal areas, lacustrine/marshy back-dune areas and mostly the beach-dune system. The negative sedimentary balance resulting from the reclamation works on the river courses, along with the interventions along the Volturno river basin, resulted in an accelerated and severe coastal erosion. The latter, coupled with subsidence rates and sea level rise, increase the vulnerability of the coast to flooding and storm surge and aquifer salinization.

A Relative Paleointensity (RPI)-Calibrated Age Model for the Corinth Syn-rift Sequence at IODP Hole M0079A (Gulf of Corinth, Greece)

The Corinth basin (Greece) is a young continental rift that recorded cyclic basin paleoenvironment variations (i.e., marine to lacustrine) caused by glacio-eustatic sea level fluctuations during its initial connection to the global oceans. The Corinth syn-rift sequence offers therefore a unique opportunity to determine the timing and modality of connection of young rifts to the global oceans, and investigate how sediment supply change during this extremely dynamic stage of their evolution. Here we use magnetostratigraphic and relative paleointensity (RPI) constraints from 885 discrete samples from International Ocean Discovery Program (IODP) Hole M0079A to generate an unprecedented high-resolution (∼15kyr) age model for the youngest part of the Corinth’s offshore syn-rift sequence. Our RPI-calibrated age model spans the last ∼850 kyr and reveals that initial connection of the Corinth basin to the Mediterranean Sea occurred at ∼530 ky, more recently than previously thought and after a short-lived marine incursion at ∼740 kyr. Accumulation rates calculated from our age model indicate two significant changes in sediment supply at 530 (from 74 to 156 cm/kyr on average) and 70 ka (from 156 to 258 cm/kyr on average), interpreted as due to increased local fault activity in the southern margin of the Corinth basin. Sedimentation rates also display a short-term variation indicating a lower sediment supply (98 cm/kyr on average) during interglacial periods and a higher input (156 cm/kyr on average) during glacial periods. We conclude that long-term variations of sediment supply in young rifts connecting to the global oceans are predominantly controlled by local tectonics (i.e., new depocenters formation), while short-term variations may be driven by global climate (i.e., increased erosion aided by fewer vegetation during glacial periods). Grain size of the Corinth syn-rift sequence shows a weak correlation with glacial cycles too (i.e., coarser sediments during interglacials), but we suggest this to be controlled by the hydrodynamics of the basin (i.e., stronger bottom currents when the basin was connected to the Mediterranean Sea during interglacial periods).

Fluvial and coastal landform changes in the Aceh River delta (northern Sumatra) during the century leading to the 2004 Indian Ocean tsunami

AbstractRiver deltas are strongly affected by demographic growth and by the intensification of land use. The migration of deltaic coastlines is often rapid, threatening urban settlements, coastal farming, and coastal biotopes. Some deltas benefit from centuries of monitoring, such that the evolution of their coastline is well documented. For most deltas, however, such long records do not exist. The study of their geomorphological evolution can benefit from overlapping maps drafted over time, combined with aerial photographs and satellite images, to track the evolution of fluvial and coastal landforms. Both fluvial and coastal landforms are sensitive to variations in water and sediment supply, such that covariations in the evolution of these landforms, or the lack thereof, provide clues on the contribution of water and sediment supply to delta evolution. We document the evolution of river channels and coastlines in the delta of the Aceh River in northwest Sumatra, by overlying maps, ortho‐rectified aerial photographs, and satellite images covering the past 130 years. We assess the accuracy of the overlays, and then use multivariate statistics to analyze the co‐evolution of fluvial and coastal landforms. We propose that a progressive decrease in sediment supply spurred river channel lengthening and narrowing, landward migration of the shoreline, and narrowing of beach ridges. The 2004 Indian Ocean tsunami generated an instantaneous retreat of the coastline that amounts to ∼53% of the coastal retreat from 1884 to 2019 ce. Post‐tsunami evolution is marked by an irreversible acceleration of previous trends. Beach ridges located up‐drift of rivers and tidal channel mouths are more sensitive to long‐term landward retreat and tsunamigenic erosion.

Seismic stratigraphy, sedimentary facies analysis and reservoir characteristics of the Middle Jurassic syn-rift sediments in Salam Oil Field, north Western Desert, Egypt

The Middle Jurassic syn-rift sediments (Khatatba Formation) of the Western Desert, Egypt hosting potential reservoir intervals are prospective targets for hydrocarbon exploration and development campaigns. However, their depositional evolution and factors controlling distribution of the best reservoir faces are not very well-constrained. This work integrates seismic, well logs and conventional core dataset in order to define the syn-rift sedimentary patterns and their impact on distribution and quality of the reservoir facies. Khatatba Formation comprises two discrete units; the lower unit constitutes lower progradational and upper retrogradational sedimentary packages that are interpreted in terms of discrete rift phases. Nine sedimentary facies associations (FA) were recognized and their stacking patterns are governed by the rift evolution and the interplay between variation in fault offsets and sediment supply. Distal sand bar sandstones, marine shales and organic-rich shales were accumulated during periods of high subsidence. Successive alternation between shallow and deep facies at the base of the lower unit reveals repeated short periods of progradation and retrogradation with an overall progradational trend reflecting an elevated rate of sediment supply.Episodic fault-controlled retrogradation and progradation continued during the deposition of the Khatatba upper unit where the progradational deltaic facies changes upward into retrogradational marine sediments and aggradational-progradational aeolian and shoreface sandstones. Five hydraulic flow units (HFUs) were identified and their distribution is mostly controlled by the rift evolution. The lowest reservoir quality HFU4 and HFU5 are often associated with the retrograding distal facies accumulated during highest rates of subsidence. These zones do not contribute to more than 10% of the reservoir flow capacity. On the other hand, the progradational deltaic facies accounts for approximately 85% of the reservoir flow capacity in both lower and upper Khatatba units.

Linking sediment supply variations and tectonic evolution in deep time, source-to-sink systems—The Triassic Greater Barents Sea Basin

Abstract Triassic strata in the Greater Barents Sea Basin are important records of geodynamic activity in the surrounding catchments and sediment transport in the Arctic basins. This study is the first attempt to investigate the evolution of these source areas through time. Our analysis of sediment budgets from subsurface data in the Greater Barents Sea Basin and application of the BQART approach to estimate catchment properties shows that (1) during the Lower Triassic, sediment supply was at its peak in the basin and comparable to that of the biggest modern-day river systems, which are supplied by tectonically active orogens; (2) the Middle Triassic sediment load was significantly lower but still comparable to that of the top 10 largest modern rivers; (3) during the Upper Triassic, sediment load increased again in the Carnian; and (4) there is a large mismatch (70%) between the modeled and estimated sediment load of the Carnian. These results are consistent with the Triassic Greater Barents Sea Basin succession being deposited under the influence of the largest volcanic event ever at the Permian-Triassic boundary (Siberian Traps) and concurrent with the climatic changes of the Carnian Pluvial Event and the final stages of the Northern Ural orogeny. They also provide a better understanding of geodynamic impacts on sedimentary systems and improve our knowledge of continental-scale sediment transport. Finally, the study demonstrates bypass of sediment from the Ural Mountains and West Siberia into the adjacent Arctic Sverdrup, Chukotka, and Alaska Basins in Late Carnian and Late Norian time.

High-resolution sequence stratigraphy and evolution of the Jeju Strait shelf, Korea, since the Last Glacial Maximum

Sequence analysis of high-resolution seismic profiles and sediment data from the Jeju Strait reveals that the shelf deposits form a depositional sequence consisting of a set of lowstand, transgressive, and highstand systems tracts deposited since the LGM. Six seismic units, each with different seismic facies and geometry, constitute three systems tracts. During the LGM, most of the continental shelf was exposed, resulting in sub-aerial erosion associated with paleo-channel incision, forming incised-channel fill (unit 1). The paleo-river may have supplied abundant terrigenous sediments to the study area around the paleo-river mouth. As the shelf flooded, these sediments were trapped within the paleo-estuary and formed estuarine deposits (unit 2). As transgression continued, the near-surface sediments were reworked and redistributed by shelf erosion, resulting in a thin transgressive sand sheet (unit 3) covering a large area of the shelf. Based on age dates and sea-level curves, a transgressive sand ridge (unit 4) formed during the stillstand or very slow rise period (13.7–11.5 ka BP). The Heuksan mud belt (HMB; unit 5), which is one of the prominent mud deposits located in the western part of the study area, can be divided into two subunits (5a and 5b). The lower part of the HMB (unit 5a) corresponds to shelf mud deposited during transgression. In contrast, the upper part of HMB (unit 5b) consists of recent shelf mud that was deposited during the highstand (after ∼7 cal kyr BP). The Seomjin subaqueous delta (unit 6), which consists exclusively of homogenous mud, was deposited after the sea-level highstand. Unit 6 indicates a transition from proximal to distal facies around the Seomjin River mouth. A single depositional sequence on the Jeju Strait shelf was mainly controlled by the complex interplay between bottom morphology, a varying sediment supply, and high-amplitude (∼130 m) sea-level changes, along with hydrodynamic conditions.

Simulated Dynamics of Mixed Versus Uniform Grain Size Sediment Pulses in a Gravel‐Bedded River

AbstractMountain rivers often receive sediment in the form of episodic, discrete pulses from a variety of natural and anthropogenic processes. Once emplaced in the river, the movement of this sediment depends on flow, grain size distribution, and channel and network geometry. Here, we simulate downstream bed elevation changes that result from discrete inputs of sediment (∼10,000 m3), differing in volume and grain size distribution, under medium and high flow conditions. We specifically focus on comparing bed responses between mixed and uniform grain size sediment pulses. This work builds on a Lagrangian, bed‐material sediment transport model and applies it to a 27 km reach of the mainstem Nisqually River, Washington, USA. We compare observed bed elevation change and accumulation rates in a downstream lake to simulation results. Then we investigate the magnitude, timing, and persistence of downstream changes due to the introduction of synthetic sediment pulses by comparing the results against a baseline condition (without pulse). Our findings suggest that bed response is primarily influenced by the sediment‐pulse grain size and distribution. Intermediate mixed‐size pulses (∼50% of the median bed gravel size) are likely to have the largest downstream impact because finer sizes translate quickly and coarser sizes (median bed gravel size and larger) disperse slowly. Furthermore, a mixed‐size pulse, with a smaller median grain size than the bed, increases bed mobility more than a uniform‐size pulse. This work has important implications for river management, as it allows us to better understand fluvial geomorphic responses to variations in sediment supply.

Influence of Early Low‐Temperature and Later High‐Temperature Diagenesis on Magnetic Mineral Assemblages in Marine Sediments From the Nankai Trough

AbstractDiagenesis can have a major impact on sedimentary mineralogy. Primary magnetic mineral assemblages can be modified significantly by dissolution or by formation of new magnetic minerals during early or late diagenesis. At International Ocean Discovery Program Site C0023, which was drilled in the protothrust zone of the Nankai Trough during Expedition 370, offshore of Shikoku Island, Japan, non‐steady state conditions have produced a complex sequence of magnetic overprints. Detailed rock magnetic measurements, which characterize magnetic mineral assemblages in terms of abundance, grain size, and composition, were conducted to assess magnetic mineral alteration and diagenetic overprinting. Four magnetic zones (MZs) are identified down‐core from ∼200 to 1,100 m below sea floor based on rock magnetic variations. MZ 1 is a high magnetic intensity zone that contains ferrimagnetic greigite, which formed at shallow depths and is preserved because of rapid sedimentation. MZs 2 and 4 are low magnetic intensity zones with fewer magnetic minerals, mainly coarse‐grained (titano‐)magnetite and hematite. This magnetic mineral assemblage is a remnant of a more complex assemblage that was altered diagenetically a few million years after deposition when the site entered the Nankai Trough. MZ 3 is a high magnetic intensity zone between MZs 2 and 4. It contains authigenic single‐domain magnetic particles that probably formed from fluids that circulated through faults in the accretionary prism. Varying sediment supply and organic matter input through time, burial temperature, and tectonic fluid circulation are the primary drivers of magnetic mineral assemblage variations.

Planform change of the Río Chubut (~42°S, ~70°W, Argentina) in response to climate drivers in the southern Andes

The Río Chubut (southern Argentina) displays complex geomorphological and sedimentological responses to long-term variations in hydrology and sediment supply. A 75 km study reach located 65 km downstream of the former ice margin and proglacial lake (Lago Epuyen) at the foothills of the Andes shows that the river has previously undergone large-scale planform changes from a braided to a meandering regime. The new luminescence chronology presented here constrains the timing of changes in fluvial characteristics in the Chubut valley, including the waning and abandonment of a braid plain dated at four locations, the minimum age for the shift to the modern meandering regime, and the timespan of activity for an alluvial fan. Sedimentology, geomorphology and geochronology findings show that the Río Chubut maintained a braided planform during the last deglaciation until the water supply to the headwaters in the Andes decreased because the mid-latitude storm tracks and westerlies in the Southern Hemisphere weakened and shifted southwards causing drier conditions across Patagonia. This encouraged a time-transgressive shift in the Río Chubut between 12.3 ± 1.0 ka and 9.4 ± 0.8 ka from a braided planform to the meandering system active today. These findings highlight that modern braided rivers (e.g., the Rakaia River, New Zealand) that are experiencing a reduction in discharge could be vulnerable to similar large-scale planform changes with the potential to impact upon unique habitats and ecosystems.

Variations in carbonate-evaporite shoreline and ramp facies trends: Middle Miocene Fatha Formation, Kurdistan Region, NE Iraq

A sedimentological investigation of Miocene deposits at the periphery of the Zagros foreland basin, Kurdistan Region, NE Iraq, reveals a cyclical arrangement of carbonate-evaporite ramp facies. The study aims to provide rare insight into the lateral variability of microfacies and environments of such systems' inner ramp and shoreline. Between 10 and 40 depositional cycles are preserved, separated by a flooding surface, and recording an overall basinward progradation. In each cycle, a shallowing-upward trend from a lower-energy calcareous mudstone and mudstone-wackestone carbonate microfacies at the base to a higher-energy packstone-grainstone-rudstone or low-energy algal mat/stromatolitic carbonate microfacies above is evident. Evaporite deposits of supratidal sabkha origin cap each carbonate deposit. Red clastic sediments that advanced south-westward into the basin from the adjacent Zagros hinterland overlie each evaporite deposit. A flooding surface and return to calcareous mudstones mark the start of the next cycle. Outcrop and thin-section analysis of the carbonate deposits of each cycle reveals a shoaling-up to inner-ramp facies with varied environmental settings that developed under a range of hydrodynamic conditions. Microfacies analysis indicates that these environments included normal marine salinity open lagoons, hypersaline lagoons, restricted and shallow lagoons, sand shoals, intertidal and supratidal flats, supratidal ponds, and a coastal alluvial plain that included channelised deposits and palaeosols. The cyclical facies trend changes toward the top of the succession in that the relative rate of siliciclastic supply markedly increased, whereas the rate of carbonate and evaporite production decreased. Progradation and shoreline migration through time caused lateral and vertical facies changes and thickness variations over the succession. Repeated relative sea-level changes, associated changes in climate, and variations in sediment supply from the hinterlands during the collision of the Arabian and Iranian plates, combined with a variable rate of accommodation generation, are inferred to have controlled the preserved cyclicity.

Magnetostratigraphy and stable isotope stratigraphy of the middle-Eocene succession of the Ainsa basin (Spain): New age constraints and implications for sediment delivery to the deep waters

Stratigraphic cycles preserved in sedimentary successions are controlled by the interaction of tectonics, climate, sediment supply and sea-level variations. Understanding the influence of these drivers on sedimentary systems dynamics is crucial to understand and extract information from sedimentary archives. In the deep marine deposits of the Ainsa foreland basin (lower to middle Eocene, southern central Pyrenees, Spain), the origin of well-preserved cyclicity between channelized sandy submarine fans and hemipelagic deposits remains subject to debate because of the absence of chronostratigraphic constraints on high resolution geochemical proxies. Here, we contrast a combination of newly acquired and legacy geochemical datasets (carbon and oxygen stable isotopes, organic matter content, major and trace elements and the mineralogical composition of bulk hemipelagic sediments) tuned by a new age model to global “target” curves to discuss the possible drivers of the stratigraphic cycles found in the deep marine sediment gravity flow deposits of the Hecho Group. Our new age model is based on magnetostratigraphic and biostratigraphic datasets acquired on a composite section going from the Banaston system to the distal deposits of the Sobrarbe deltaic complex. Four major polarity zones are identified in the studied succession covering the time span from C21n (lower members of the Banaston system) to C19r (Sobrarbe deltaic complex). Our age model is corroborated by the identification of the nannoplankton zone NP16 in the Guaso system (C20n).Comparison between global carbon isotope curve and local isotope dataset shows some differences, suggesting the preservation of a local isotope signal modulated by eustatism, changes in the environment of deposition and/or restriction in water circulation in the Ainsa basin. Yet, comparison of the stratigraphic record with global sea-level curves highlights that sands are mainly delivered to the basin during lowstands, pointing to the important role of eustasy even in an active foreland tectonic context. The exception to the rule is the Banaston member II, whose deposition during a sea-level highstand seems to be controlled by the growth of tectonic structures.

Evolution from syn‐rift carbonates to early post‐rift deep‐marine intraslope lobes: The role of rift basin physiography on sedimentation patterns

ABSTRACTThe stratigraphic architecture of Early Jurassic strata exposed along a >10 km long transect in the Chachil Graben, an exhumed marine rift depocentre in the Neuquén Basin (Argentina), provides insights into the sedimentological and stratigraphic expression of the syn‐rift to post‐rift transition. A change from syn‐rift intrabasinal carbonate to post‐rift extrabasinal siliciclastic sedimentation is recorded, as well as variations in sediment supply and dispersal patterns across rift‐related topography. The late syn‐rift was marked by a transgression and development of a shallow‐marine carbonate system, including carbonate platform deposits perched on fault‐block highs and periplatform deposits accumulated in fault‐block lows, which overlies continental volcano‐sedimentary syn‐rift deposits. Differential subsidence and basin deepening induced retrogradation of the carbonate system, which was progressively drowned and overlain by organic‐rich calcareous mudstone that draped across rift structures at the onset of the early post‐rift. The first extrabasinal siliciclastic influx led to progradation of an early post‐rift intraslope lobe complex into the graben, which is associated with kilometre‐scale clastic injectites. The depositional architecture, facies distribution and pinch‐out style of intraslope lobes record the effects of an inherited compaction hinge, which acted as an oblique counterslope to sediment gravity flows. The occurrence of combined‐flow bedforms, widespread erosion, and limited facies segregation across lobes bearing different hybrid event bed types, is in sharp contrast to sedimentological characteristics of existing intraslope lobe models. Documentation of the syn‐rift to post‐rift transition stratigraphy permitted identification of changes in thickness and facies resulting from the passive infill of inherited topography with early post‐rift differential compaction. This architecture contrasts markedly with those developed during syn‐rift normal faulting. Furthermore, the influence of local inherited topography on the development of early post‐rift lobes is key to improve subsurface prediction of sandstone distribution and quality during assessment of hydrocarbon reservoirs and carbon storage sites.

Facies analysis and sequence-stratigraphic control on reservoir architecture: Example from mixed carbonate/siliciclastic sediments of Raha Formation, Gulf of Suez, Egypt

Mixed carbonate-siliciclastic systems are complex, and their development can sometimes be difficult to understand, given the various responses to each sub-environment to specific forcing, such as variation in sediment supply, climatic conditions, or available accommodation. This work integrates a detailed facies, associated with a depositional environment reconstruction, all of which is placed in a sequence stratigraphy framework in order identify the different controls on the reservoir architecture of the Upper Cretaceous (Cenomanian) Raha Formation, Gulf of Suez. The study utilized outcrop data from Gabal Ekma and Gabal Nezzazat, as well as subsurface data from five wells drilled through the October oil field.Our findings revealed that the Raha Formation succession is subdivided into eleven facies associations (FA) deposited as one depositional sequence. The Abu Had Member of the Raha formation consists of mixed siliciclastic/carbonate packages, arranged in a retrogradational stacking pattern, which were deposited during a period of pulsative shoreline regression. As a result of the transgression, the siliciclastic input in the system increased, potentially due to increased precipitation and weathering in the hinterland of the study area. The upper part of the Raha Formation belongs to the Mellaha Sand Member, which is mostly composed of bioturbated quartz arenite with bioturbation, and is the main reservoir in the October Field. It was deposited during a period of shoreline progradation as testified by its progradational stacking pattern.The reservoirs of the Raha Formation can be divided into five distinctive types (G, C, Q, P, and M), based on the factors controlling the permeability (Diagenetic criteria and compositional framework). The outcrops-subsurface correlations indicated that these reservoirs in the Mellaha Sand Member are laterally extensive, and thicken from 25 m in the SE to 91 m northwestwards. It is predicted that these reservoir intervals thicken toward the unexplored areas northern of October Field. Pore-filling cement and detrital matrix decreased the permeability and the reservoir quality to minimum while, the grain coating prevented the collapse of the reservoir quality. Pore-filling cement and detrital matrix decreased the permeability values, consequently lowering the reservoir quality to minimum, whereas the grain coating prevented the collapse of the reservoir quality, retaining the highest permeability values in the overall pore system. The aforementioned study provides significant insight into the understanding of depositional facies and sequence-stratigraphic control on reservoir architecture. Additionally, it provides insights for further exploration activities in these mixed carbonate/siliciclastic intervals along the Gulf of Suez and adjacent basin, and the improved understanding of these reservoirs units could also be applied to future Carbon Capture and Storage projects.

Influence of sediment supply rate on sequence stratigraphic architecture change: A case study from the Kaiping Sag, northern South China Sea

The sequence stratigraphic architecture change is mainly controlled by three factors: basement subsidence or uplift, sea level change and sediment supply. However, the internal mechanism of the influence of the sediment supply on the sequence stratigraphic architecture change is not clear. In this paper, the Middle-Upper Miocene sequences in Kaiping Sag, northern South China Sea are taken as an example to discuss this issue. First, we divide and correlate the sequence through the comprehensive analysis of drilling and seismic data, and restore the seven seismic sequences in the study interval to their original form of sedimentary stage through the original form structural section restoration technique. Then, based on the original form structural section, the vertical changes of sequence stratigraphic architecture are recognized and the basement subsidence rate and sediment supply rate are estimated. Furthermore, through the correlation analysis between the sediment supply rate and the sequence stratigraphic architecture change, how the sediment supply rate affects the sequence stratigraphic architecture changes is recognized. The results show that the stratigraphic frameworks of the seven sequences are all LST-TST-HST-FRST combination, but the scale of systems tracts of each sequence varies greatly, which is quite different from the sequence stratigraphic architecture of the adjacent Baiyun Sag. The second-order cycle sea level change, basement subsidence, regional tectonic uplift and special paleogeographic environment (Kaiping Sag is located in the lateral edge of the trough zone) in the study area jointly lead to the variation of sediment supply rate in time and space, and this variable sediment supply rate is the main driving force for the change of sequence stratigraphic architecture in Kaiping Sag.

Porosity and permeability prediction through forward stratigraphic simulations using GPM™ and Petrel™: application in shallow marine depositional settings

Abstract. The forward stratigraphic simulation approach is applied to predict porosity and permeability distribution. Synthetic well logs from the forward stratigraphic model served as secondary data to control porosity and permeability representation in the reservoir model. Building a reservoir model that fits data at different locations comes with high levels of uncertainty. Therefore, it is critical to generate an appropriate stratigraphic framework to guide lithofacies and associated porosity–permeability simulation. The workflow adopted for this task consists of three parts: first, there is simulation of 20 scenarios of sediment transportation and deposition using the geological process modelling (GPM™) software developed by Schlumberger. Secondly, there is an estimation of the extent and proportion of lithofacies units in the stratigraphic model using the property calculator tool in Petrel™. Finally, porosity and permeability values are assigned to corresponding lithofacies units in the forward stratigraphic model to produce a forward stratigraphic-based porosity and permeability model. Results show a forward stratigraphic-based lithofacies model, which depends on sediment diffusion rate, sea-level variation, sediment movement, wave processes, and tectonic events. This observation is consistent with the natural occurrence, where variations in sea level, sediment supply, and accommodation control stratigraphic sequences and therefore facies distribution in a geological basin. Validation wells VP1 and VP2 showed a notable match after a comparing the original and forward stratigraphic-based porosity models. However, a significant discrepancy is recorded in the permeability estimates. These results suggest that the forward stratigraphic modelling approach can be a practical addition to geostatistical-based workflows for realistic prediction of porosity and permeability.

Modern isotopic signatures of Plata River sediments and changes in sediment supply to the western subtropical South Atlantic during the last 30 kyr

Sediments transported in rivers reflect the geology of the catchment area and its radiogenic isotopic composition. These isotopic signatures are not significantly altered by weathering, transport or deposition and hence can document variations in sediment supply. Here we present strontium (Sr), neodymium (Nd) and lead (Pb) isotope values from suspended and riverbed sediments of the Plata River drainage basin, the second largest on the South American continent, and from two marine sediment cores collected off the mouth of the Plata River in the western subtropical South Atlantic. Our modern riverine data suggest that the basin has three main sediment source areas, namely the upper Paraná River, the Uruguay River and the Andean draining rivers. Sediments from the Andean draining rivers (Salado and Bermejo Rivers) have the most radiogenic Pb (i.e. >18.5 for 206Pb/204Pb) and Sr (average of 0.726 ± 0.031; 2SD) isotopic signatures, and least radiogenic εNd values (average of −10.5 ± 3.1; 2SD). The upper Paraná and Uruguay Rivers have less radiogenic Pb (i.e. <18.5 for 206Pb/204Pb) and Sr (average of 0.715 ± 0.003; 2SD) isotopic signatures. While the upper Paraná River has average εNd values of −7.8 ± 1.1 (2SD), the Uruguay River has average εNd values of −5.9 ± 0.2 (2SD). The modern isotopic signature at the mouth of the Plata River is largely dominated by the Andean draining rivers. To reconstruct changes in sediment supply to the western subtropical South Atlantic, we used this new riverine dataset together with literature values from the Argentine continental margin to interpret the data from two marine sediment cores. The downcore records cover the last ∼30 kyr and show two short-lived excursions (i.e. Heinrich Stadial 1 and the Younger Dryas) and two long-term trends (i.e. late Pleistocene (i.e. ∼29 to 11 cal ka BP for Sr and ∼29 to 25 cal ka BP for Nd), and early and mid-Holocene). We suggest that the short-lived excursions result from increased precipitation in the headlands of the Andean draining rivers during Heinrich Stadial 1 and the Younger Dryas. The late Pleistocene long-term change showed an increase in the contribution of material from the Plata River drainage basin in relation to material from the Argentine continental margin most probably due to low sea-level. The early and mid-Holocene long-term trend showed the opposite change in sediment input and was related to decreased precipitation over most of the Plata River drainage basin.

A rules-based shoreface translation and sediment budgeting tool for estimating coastal change: ShoreTrans

Predicting change to shorelines globally presents an increasing challenge as sea level rise (SLR) accelerates. Many shoreline prediction models use the simplistic ‘Bruun rule’ for dealing with SLR profile translation, in-part due to alternative approaches being too complex and time-consuming to implement. To address this, we introduce ShoreTrans: a simple, rules-based, user-input driven, shoreface translation and sediment budgeting model, that applies the surveyed 2D-profile (not a parameterization), for estimating change to realistic coastlines, resulting from SLR and variations in sediment supply, while accounting for armouring, hard-rock cliffs and outcropping rocks. The tool can be applied to sand, gravel, rock and engineered coasts at a temporal scale of 10–100 years, accounting for shoreline trends as well as variability. The method accounts for: (1) dune encroachment/accretion; (2) barrier rollback; (3) non-erodible layers; (4) seawalls; (5) lower shoreface transport; (6) alongshore rotation; and (7) other sources and sinks. Uncertainty is accounted for using a probabilistic distribution for inputs and Monte Carlo simulations. We provide a first-pass assessment of two macrotidal UK embayments: Perranporth (sandy, dissipative, cross-shore dominant transport) and Start Bay (gravel, reflective, bi-directional alongshore dominant), then use idealised profiles to investigate the relative importance of forcing controls on shoreline recession and beach width. For the dissipative sandy site, the primary modes of coastal change are predicted to be short-term storm erosion and SLR translation while long-term trends may be important but are highly uncertain. For the reflective gravel site, the primary mode is multi-decadal longshore sediment flux, while short-term alongshore rotation and SLR translation are secondary. Relative to the ShoreTrans approach, the Bruun rule under-predicts shoreline recession in front of cliffs, seawalls and for low barriers that rollback, and over-predicts where large erodible dunes are present. ShoreTrans directly addresses change in beach width, with beaches in front of seawalls and cliffs predicted to shrink, such that narrow beaches (<50 m width) may disappear under 1-m SLR. As a standalone tool, ShoreTrans is transferable to many coast types and will provide coastal practitioners with a simple first-pass estimate of how the 2D appearance of a complex profile may change under SLR. A future benefit will be to combine this approach with existing hybrid modelling techniques to augment SLR translation predictions.

Stratigraphy, age, and provenance of the Eocene Chumstick basin, Washington Cascades; implications for paleogeography, regional tectonics, and development of strike-slip basins

Strike-slip faults form in a wide variety of tectonic settings and are a first-order control on the geometry and sediment accumulation patterns in adjacent sedimentary basins. Although the structural and depositional architecture of strike-slip basins is well documented, few studies of strike-slip basins have integrated depositional age, lithofacies, and provenance control within this context. The Chumstick basin formed in central Washington during a regional phase of dextral, strike-slip faulting and episodic magmatism associated with Paleogene ridge-trench interaction along the North America margin. The basin is bounded and subdivided by major strike-slip faults that were active during deposition of the intra-basinal, non-marine Chumstick Formation. We build on the existing stratigraphy and present new, detailed lithofacies mapping, conglomerate clast counts (N = 16; n = 1429), and sandstone detrital zircon analyses (N = 16; n = 1360) from the Chumstick Formation to document changes in sediment provenance, routing, and deposition. These data allow us to reconstruct regional Eocene paleo-drainage systems of Washington and Oregon and suggest that drainage within the Chumstick basin fed a regional river system that flowed to a forearc or marginal basin on the newly accreted Siletzia terrane. More generally, excellent age control from five interbedded tuffs and high sediment accumulation rates allow us to track the evolving sedimentary system over the Formation’s ca. 4−5 m.y. depositional history. This is the first time lithofacies and provenance variations can be constrained at high temporal resolution (0.5−1.5 m.y. scale) for an ancient strike-slip basin and permits a detailed reconstruction of sediment routing pathways and depositional environments. As a result, we can assess how varying sediment supply and accommodation space affects the depositional architecture during strike-slip basin evolution.