Delta Progradation Research Articles

Pleistocene forced regressive deposits on the Korea Strait shelf influenced by tectonic and ocean currents

We examined the architecture of Pleistocene sequences of the Korea Strait (KS) margin controlled by ocean currents and compressional tectonic regimes, using a dense grid of high-resolution single-channel seismic profiles and sediment cores. Along with uplifted strata featuring an erosional and/or non-depositional flat seabed in the northern shelf of the study area, three Middle–Upper Pleistocene sequences are characterized by forced regressive deposits recorded at 100-ka intervals covering one postglacial sequence across the shelf. The three forced regressions together comprise an offlapping stacking pattern, where the degree of erosion of the upper surface of the older sequence is greater than that of the younger sequence. The tectonic tilt involved in landward uplift and seaward subsidence across the shelf basin causes differential erosional rates among the forced regression deposits. The Upper Pleistocene forced regression deposits are preserved as a set of 20-ka clinoform wedges with aggradational to progradational stacking patterns, leading to a falling stage systems tract (FSST) during the stepwise fall in sea level, followed by a shelf edge-perched lowstand systems tract (LST) wedge during the Last Glacial Maximum (LGM). The northeast-facing Tsushima Current (TC) passing through the KS played an important role in allowing the fine sediments originating from the Nakdong River to form the FSST clinoform wedges and the LST oblique prograding delta lobe along the shelf break.

Assessing the Hydrocarbon Prospectivity in the Nigeria Offshore West Delta Using Seismic Volume and Well Log Data

Evaluation of Z-Field prospect located in the western Niger Delta at a shallow water depth of about 100m was carried out using 3-D seismic and well data. The aim of this study is to evaluate the hydrocarbon potential of the target bed (R01A reservoir) using checkshot, seismic and well log data. Results of the structural interpretation revealed extensional tectonics characterized by rollover structures which are bounded by regional and counter-regional listric (growth) normal faults. These structural features are associated with normal deltaic progradation and are conspicuous throughout the whole delta province. A key finding of this study is that subsurface structures in the study area lack closure to accumulate hydrocarbon. This is attributed to the small throw of faults relative to sand thickness, causing a significant sand to sand juxtaposition across faults. Consequently, the R01A reservoir is interpreted as wet sand. A lack of amplitude coherence with structure provided additional validation of the interpreted wet sand scenario and above all, increased our confidence on the result. Keywords: prospect evaluation, seismic and well log data, Niger Delta, structural interpretation, faults, horizons DOI : 10.7176/JEES/9-10-06 Publication date :October 31 st 2019

Historical earthquakes in the Lower Segura basin (SE Spain): geological and archaeological evidence from pre-roman to modern times

This paper deals with the analysis of ancient and historical earthquakes in the Lower Segura Depression (SE Spain) at the northern end of the Eastern Betic Cordillera Shear Zone (EBSZ), which is defined within the area by the Lower Segura blind-thrust fault. The work summarizes and updates the existing information on the building and environmental damage dispersed throughout several historical documents, as well as the new historical and archaeological research on the area. The analyses performed consider the evolving paleogeography of the old estuarine zone defined by Ibero-Roman "Sinus ilicitanus" and the ancient prograding delta of the Segura River over the marshes. Topographic data from old descriptions of the zone together with the analysis of the geometry of the medieval irrigation system in the growing delta from pre-Roman to modern (18th century) times, allow the paleogeographic evolution of the zone, until the eventual artificial infilling of the old embayment, to be outlined. Several strong earth- quakes (Intensity ≥ VIII EMS-98) occurred in the area during different historical times. Building damage for the different events was variable depending on the number of settlements (and increasing population) within the ancient embayment. Maximum Intensity X during the most recent earthquake (AD 1829 Torrevieja) mainly occurred over old lands reclaimed in the 18 th century. In addition, dominant earthquake secondary effects (EEEs) were caused by liquefaction processes. This study analyzes the dimensions and distribution of these EEEs for the two main earthquakes in the zone during the years AD 1048 and AD 1829 using the ESI-07 intensity scale. The results draw important inferences on the role of ancient paleo-geography in seismic hazard data from past earthquakes.

Valley-Confinement and River-Tidal Controls on Channel Morphology Along the Fluvial to Marine Transition Zone of the Ðồng Nai River System, Vietnam

Along the fluvial to marine transition zone (FMTZ) of river deltas, the river-tidal dynamics exert a primary control on channel width, sinuosity, and bed elevation; however, other local factors, such as valley confinements, bifurcations, and confluences, can modify the channel morphology. Here, we report a case study of the major channel of the Dong Nai River System (DNRS) that shows complex morphological trends linked to multiple factors. This study is based on the analysis of satellite images and bathymetric maps of the studied channel, together with a digital elevation model of the area and additional climate and hydrology data. Our study shows that channel width, sinuosity, and bed elevation show mutual relationships and complex upstream to downstream trends linked to the river-tidal dynamics and valley confinements, together with more local effects due to bifurcations and confluences. The tidal dynamics is mainly responsible for the seaward-widening and seaward-shallowing trends and the abrupt decrease in channel sinuosity observed in the downstream tract of the channel, whereas the relatively constant channel width and sinuosity in the upstream tract suggest a control of the river dynamics. The studied channel also shows three areas of valley widening or exit, which are characterized by high channel sinuosity, the presence of minor and major bifurcations, and additional changes in channel width and bed elevation, and they are considered important nodes in this system. Valley-related nodes also show different active and inactive features, implying that the degree of activity and importance of these nodes likely varied through time, migrating from upstream to downstream due to the deltaic progradation.

Episodes of tidally-forced swale erosion on the inner shelf interspersed with millennial fluviodeltaic progradational interludes: Insights from northern Bohai Bay, China

Erosional swales are common features on the seafloor with vigorous bottom flow(s). On continental shelves with energetical tidal currents and limited river discharge, the initiation and evolution of tidally-induced erosional depressions and bedforms have been extensively discussed, but little is known about the evolution of such features when interspersed with active deltaic progradation over millennial timescales. A recent boomer seismic investigation revealed a swale erosional complex within and proximal to the subaqueous delta in northern Bohai Bay (NBHB), China, providing us with an opportunity to investigate such features. Here, using the same seismic dataset, we analyze the morphology, reflective characteristics and evolution of the erosional and depositional structures. The erosional swale complex consists of two episodes of tidally-induced incised channels within a northern progradational system (NPS; located in the northernmost Bohai Bay and prograde to the southeast), followed by an episode of extensive trough-and-bump formation (negative-and-positive relief) within the middle and northern NBHB, which are also erosional features. These features are all highly lineated, oriented WNW-ESE; we attribute their formation to the similarly-oriented tidal flows in this region. The multi-episode evolution of the swale erosional complex is predominately associated with progradation of the NPS, whose lobes cap the pre-existing erosional features and provide substrate for new erosion. The trough-and-bump complex was subject to long-term erosion, and may represent an evolution from the previous linear, tidally-forced marine incisions. The complex was subsequently buried in part by the step-wise progradation of a southern progradational system (SPS; developed within the southern 2/3 Bohai Bay and prograde to the north/northeast). In addition, we also observed clusters of longitudinal bedforms with convex internal reflectors superimposed on the erosional remnant (bumps) coeval with the erosion-dominated environment. They are observable on both sandy and muddy substrates.

Late Cretaceous–Cenozoic sequence stratigraphic and paleogeographic controls on petroleum system elements of the Nicaraguan platform, western Caribbean Sea

Late Cretaceous–to–present-day mixed carbonate–clastic deposition along the Nicaraguan platform, western Caribbean Sea, has evolved from a tectonically controlled, rifted upper Eocene shallow–to–deep-marine carbonate–siliciclastic shelf to an upper Miocene–to–present-day tectonically stable shallow-marine carbonate platform and passive margin. By integrating subsurface data of 287 two-dimensional seismic lines and 27 wells, we interpret the Cenozoic stratigraphic sequence as 3 cycles of transgression and regression beginning with an upper Eocene rhodolitic–algal carbonate shelf that interfingered with marginal siliciclastic sediments derived from exposed areas of Central America bordering the margin to the west. During the middle Eocene, a carbonate platform was established with both rimmed reefs and isolated patch reefs. A late Eocene forced regression produced widespread erosion and subaerial exposure across much of the platform and was recorded by a regional unconformity. The Oligocene–upper Miocene sedimentary record includes a southeastward prograding delta of the proto-Coco river, which drained the emergent area of what is now northern Nicaragua. The late Miocene–to–present-day period marks a period of strong subsidence with the development of small pinnacle reefs. We describe favorable petroleum system elements of the Nicaraguan platform that include (1) Eocene fossiliferous limestone source rocks documented as thermally mature in vintage exploration wells and seen as active gas chimneys emanating from inferred carbonate reservoirs; (2) upper–to–middle Eocene reservoirs in patch and pinnacle reefs, middle Eocene calcareous slumps, and Oligocene fluvial-deltaic facies documented in wells; and (3) regional seal intervals that consist of both regional unconformities and Eocene–Oligocene intraformational shale.

Three‐fold nature of coastal progradation during the Holocene eustatic highstand, Po Plain, Italy – close correspondence of stratal character with distribution patterns

AbstractAlthough general trends in transgressive to highstand sedimentary evolution of river‐mouth coastlines are well‐known, the details of the turnaround from retrogradational (typically estuarine) to aggradational–progradational (typically coastal/deltaic) stacking patterns are not fully resolved. This paper examines the middle to late Holocene eustatic highstand succession of the Po Delta: its stratigraphic architecture records a complex pattern of delta outbuilding and coastal progradation that followed eustatic stabilization, since around 7·7 cal kyr bp. Sedimentological, palaeoecological (benthic foraminifera, ostracods and molluscs) and compositional criteria were used to characterize depositional conditions and sediment‐dispersal pathways within a radiocarbon‐dated chronological framework. A three‐stage progradation history was reconstructed. First, as soon as eustasy stabilized (7·7 to 7·0 cal kyr bp), rapid bay‐head delta progradation (ca5 m year−1), fed mostly by the Po River, took place in a mixed, freshwater and brackish estuarine environment. Second, a dominantly aggradational parasequence set of beach‐barrier deposits in the lower highstand systems tract (7·0 to 2·0 cal kyr bp) records the development of a shallow, wave‐dominated coastal system fed alongshore, with elongated, modestly crescent beaches (ca2·5 m year−1). Third, in the last 2000 years, the development of faster accreting and more rapidly prograding (up toca15 m year−1) Po delta lobes occurred into 30 m deep waters (upper highstand systems tract). This study documents the close correspondence of sediment character with stratal distribution patterns within the highstand systems tract. Remarkable changes in sediment characteristics, palaeoenvironments and direction of sediment transport occur across a surface named the ‘A–P surface’. This surface demarcates a major shift from dominantly aggradational (lower highstand systems tract) to fully progradational (upper highstand systems tract) parasequence stacking. In the Po system, this surface also reflects evolution from a wave‐dominated to river‐dominated deltaic system. Identifying the A–P surface through detailed palaeoecological and compositional data can help guide interpretation of highstand systems tracts in the rock record, especially where facies assemblages and their characteristic geometries are difficult to discern from physical sedimentary structures alone.

High frequency (4th order) sequence stratigraphy of Early Miocene deltaic shorelines, offshore Texas and Louisiana

Abstract Well logs and 3D seismic reflection data are integrated to image Lower Miocene depocenters of the upper Texas and westernmost Louisiana coastal and offshore areas. Although previously interpreted at a large scale (3rd order cycles), the detailed stratigraphy and depositional history of the early Miocene succession has not been fully developed. The upper lower Miocene interval from Robulus L (MFS10) to Amphistegina B (MFS9) has been further subdivided into five 4th order cycles (each 200–300 m thick) to provide finer scale stratigraphic detail and interpretation of depositional environments. Results of the finer scale correlations are presented in a series of sandstone percent maps. Overall, the maps display a strike-elongate (sub-parallel to the present day coastline) orientation for the sandstone bodies which thin to the southeast (basinward). Net sandstone thickness is relatively low in older cycles and increases in younger cycles suggesting an overall progradation of the deltaic system into the mapped area through time. Continued marine regression and southward movement of the shoreline are also confirmed by seismic amplitude maps. After a major transgression associated with Robulus L deltaic progradation occurred under rising sea level conditions. Deltaic sediments prograded southward and sandstone brought to the upper Texas coast was distributed laterally by longshore currents to form strandplain coast lines. Maximum regression occurred during the interval MFS9_2 to MFS9_3 when a deltaic depocenter formed offshore Texas in east High Island area. However, sandstone thickness progressively decreased laterally to the east (offshore Louisiana) where more shale was present and marine processes reworked deltaic derived sandstones into shore parallel bars. There was a clear retreat of the shoreline during the youngest cycle marking the beginning of transgression associated with Amphistegina B. Detailed stratigraphic interpretation (at a 4th order scale) shows more variability in the dominant shoreline processes during early Miocene than previously thought. Recognition of sedimentary systems variability at a 4th order scale is critical for improved hydrocarbon exploration and in understanding potential future CO2 storage in the area.

Coalesced Delta-front Sheet-like Sandstone Bodies from Highly Avulsive Distributary Channels: The Low-accommodation Mesa Rica Sandstone (Dakota Group, New Mexico, U.S.A.)

AbstractLow-accommodation deltaic systems are often challenging to interpret due to their condensed, low-gradient nature, which often results in extensive, sheet-like sandstone bodies. As a result, detailed studies of such systems are scarce, and their internal depositional architecture is still poorly understood. We analyze one such system, the Cenomanian deltaic Mesa Rica Sandstone (Dakota Group), which was deposited in the Western Interior Seaway, in east-central New Mexico, USA. A > 20-km-long escarpment, subparallel to the main delta progradation direction, allows a detailed analysis of facies distribution, depositional architecture, and the spatial extent of stratigraphic surfaces. Results reveal an arrangement of laterally variable shallowing-upward facies successions with three depositional cycles preserved. The first cycle is characterized by deltaic sheet-like sandstone bodies that are consistently overlain by sand-filled amalgamated distributary-channel deposits. The two successive cycles record a progressive reduction of sediment supply into the basin. Vertical and lateral relationships between facies associations and architectural geometries allow the recognition of regional key stratal surfaces, incised-valley fills, and the presence of lagoonal deposits at a sub-regional scale.The Mesa Rica deltaic system represents a river-dominated delta with multiple distributary channels. The sheet-like delta-front sandstone bodies are interpreted as the result of the combined effect of high sandy-sediment supply and low accommodation. The latter acted as an accelerator for autogenic depositional mechanisms such as mouth-bar deposition and abandonment, and for the highly avulsive character of distributary channels. After deposition, minor wave reworking facilitated lateral sand redistribution and favored bioturbation. This study demonstrates that sheet-like delta-front sandstone geometries from low-accommodation systems can be formed without the dominance of wave redistribution processes. This cautions against interpretations of amalgamated shoreline systems based solely on apparent sandstone geometries, without taking into account the preservation potential and postdepositional modification of primary deltaic characteristics.

Stratigraphy and depositional architecture of lobe complexes across a range of confinements: Examples from the Late Paleozoic Paganzo Basin, Argentina

Abstract The well-exposed, Late Paleozoic glacially-influenced Paganzo Basin offers a unique opportunity to compare and contrast the stratigraphy and depositional architecture of turbidite sheet/lobe complexes with distinct degrees of basin-scale confinements. These include sandstones deposited in narrow paleofjord (Quebrada Las Lajas), moderately narrow paleovalley (Quebrada Grande) and broad depression (Cerro Bola) that are part of the same synchronous transgressive-regressive succession recorded in the basin. This work emphasizes the importance of scales of observation and the importance in make the distinction between the degree of confinement experienced by individual flows and the degree to which the system as a whole is limited by the basin size and geometry. In Quebrada Las Lajas, sheet-like sandstones form lobe complexes largely reflecting the basin physiography. The succession was subdivided into two turbidite stages (Ts1 and 2), separated by a finer-grained interval (F1) that together represents lobe complexes and interlobe systems. Individual sandstone beds are laterally and longitudinally continuous and onlap the paleofjord walls, suggesting vertically-stacked beds. In Quebrada Grande paleovalley, the succession was subdivided into three stages (Ts1 to Ts3), representing lobe complexes, also separated by finer-grained packages (F1 and 2) ascribed to interlobe phases. Individual sandstone beds are truncated, thinning and pinching out, making them hard to correlate between logged sections. This depositional pattern may suggest that lateral stacking dominates during the construction of lobe complexes. At Cerro Bola, the succession was subdivided into five stratigraphic units (Ts1 to Ts5). These units also onlap the basin margin. Individual sandstone beds of Ts1 and Ts2 are similar to those recorded in Quebrada Grande area, also suggesting compensational stacking dominated systems. However, individual sandstone beds within Ts4 are thicker relative to the other units and more continuous longitudinally, reaching the basin margin thus pointing to larger volume flows ascribed to a vertically-stacked pattern. On the other hand, Ts3 and Ts5 correspond to the thinner sandstone beds in the succession and, as these intervals are as thick as the others, they may be attributed to lobe off-axis to fringe settings. In all three areas, the lobe complex geometry is determined by the basin-scale confinement and, at this scale, all of them are represented by more or less tabular, large sandstone bodies showing more similarities than differences. Each of these three successions record an upward increase in the sand-to-mud ratio, which may denote flow ponding or progradation of up-dip deltas that fed these systems.

Interplay of sediment supply and lake-level changes on the margin of an intrabasinal basement high in the Late Miocene Lake Pannon (Mecsek Mts., Hungary)

Lake Pannon, covering the Pannonian Basin (Hungary) during the Late Miocene, had a complex lake bottom with deeper sub-basins and intrabasinal basement highs, sometimes emerging above the lake level as islands and peninsulas. Above structural highs, the basin fill sequence usually commenced with deposition of transgressional, locally sourced coarse-grained deltas. These deposits are overlain by distally-sourced deltaic bodies associated with the prograding delta system that gradually filled up the entire basin. The transition between these two distinct delta systems was studied in a large outcrop on the edge of a former basement high (Mecsek Mts., southern Hungary). The transgressional phase is represented by the deposition of a mass flow dominated fan delta body, fed by local material from a granitic catchment area. An overlying fossil-rich, clayey unit records an episode for which sediment delivery into the basin was curtailed, possibly due to submergence of the granite body. The deposition of these two units took place between 8 and 6.8 Ma. The onset of sedimentation associated with the arrival of the distally sourced regressive delta system (around 6.8 Ma) is represented by deposition of shoreface sediments. This unit is characterized by distinctive bioturbation and storm related, sand filled scour-fills. Resedimented local material that forms mm thick, coarse laminas in the scour fills is indicative of denudation due to tectonic events and implies coupled storm-flood sedimentation. The deposition of the two distinct delta bodies and the interplay between tectonic events and lake-level changes occurred during a relatively short, ca. 1.5 Ma long time interval.

Can the growth of deltaic shorelines be unstable?

Abstract. We study a sedimentary delta prograding over a fixed adversely sloping bathymetry, asking whether a perturbation to the advancing shoreline will grow (unstable) or decay (stable) through time. To start, we use a geometric model to identify the condition for acceleration of the shoreline advance (auto-acceleration). We then model the growth of a delta on to a fixed adverse bathymetry, solving for the speed of the shoreline as a function of the water depth, foreset repose angle, fluvial top set slope, and shoreline curvature. Through a linearization of this model, we arrive at a stability criterion for a delta shoreline, indicating that auto-acceleration is a necessary condition for unstable growth. This is the first time such a shoreline instability has been identified and analyzed. We use the derived stability criterion to identify a characteristic lateral length scale for the shoreline morphology resulting from an unstable growth. On considering experimental and field conditions, we observe that this length scale is typically larger than other geomorphic features in the system, e.g., channel spacings and dimensions, suggesting that the signal of the shoreline growth instability in the landscape might be “shredded” by other surface building processes, e.g., channel avulsions and alongshore transport.

Fluvial incision and coarse gravel redistribution across the modern Dead Sea shelf as a result of base‐level fall

AbstractGlobal eustatic lowstands can expose vast areas of continental shelves, and occasionally the shelf edge and the continental slope. The degree of fluvial connectivity to receding shores influences the redistribution of sediments across these emerging landscapes. Shelf and slope emergence in the Dead Sea since the middle of the 20th century, offers a rare opportunity to examine evolution of stream connectivity in response to continuous base‐level decline. We characterize the connectivity evolution of two streams, using high‐resolution time series of aerial imagery and elevation models, field mapping, and grain‐size analyses. Our rich spatiotemporal dataset of evolving channel geomorphology, sediment transport conditions, and sediment redistribution, allows calculating potential coarse sediment mobility in response to base level decline. Following shelf emergence, alluvial fans first prograded onto the low‐gradient shelf under unfavourable conditions for transporting coarse sediment to the regressing shoreline. Then, with shelf and slope emergence, the two adjacent streams evolved differently. The smaller, more arid watershed still maintains its highstand delta progradation on the shelf and is practically disconnected from the receding lake. The larger catchment, heading in wetter environments and having a narrower shelf, has incised the shelf and renewed and gradually intensified the sediment transport from the highstand to the lowstand delta. Sediment mobilization to lowstand shorelines is controlled by the evolution of the channel profile and by the average speed of gravel transport (10s‐100s m yr‐1). These findings from the Dead Sea are relevant to fluvial processes operating on continental shelves during glacial maxima. Streams would have commonly stored high proportions of their coarse sediment on the continental shelves rather than efficiently connecting with the lowstand level. Additionally, differences in sediment routing patterns should exist among nearby streams, primarily due to continental margin geometry and watershed hydrology. © 2019 John Wiley & Sons, Ltd.

Mineralogical and isotopic evidence for the sediment provenance of the western South Yellow Sea since MIS 3 and implications for paleoenvironmental evolution

Changing sediment provenance and related paleoenvironmental evolution since marine isotope stages (MIS) 3 have been investigated based on accelerator mass spectrometry (AMS) 14C and optically stimulated luminescence (OSL) dating of core CSDP-01, recovered from the western South Yellow Sea (SYS). Based on our results, sea level fluctuations and monsoonal climate variations are identified as the principal factors driving these changes. Sea level fluctuations determined the accommodation space in the shelf area, while the monsoonal climate controlled the sediment supply capacity from river to sea. Mineral and SrNd isotopic records reveal the major contribution of the paleo-Changjiang River (Yangtze River) to the study core area during the early-mid MIS 3, which likely defined the northern limit of the paleo-Changjiang delta at that time. High sediment supply and limited accommodation space led to the development of sediment-fed systems on the SYS shelf, resulting in a high preservation potential for thick-stacking and overlapping deltaic sediments. Along with deltaic progradation, core sediment provenance gradually transformed from the paleo-Changjiang River to the paleo-Huanghe River (Yellow River) near the late MIS 3, implying that the paleo-Huanghe River likely emptied into the SYS and built a large delta during the MIS 3 interval. A strong summer monsoon during the early MIS 1 interval was favorable for the Changjiang to deliver abundant sediments to the study core area. A weak summer monsoon during the mid-late MIS 1 when the coastline had retreated to nearly its present-day position decreased the Changjiang and Huanghe supply to the study area. Low sediment supply and sufficient accommodation space gave rise to the development of sediment-starved systems during this period. ɛNd values fluctuated between the Changjiang and Huanghe sources at that time, suggesting that sea bed erosion materials are the main sediment contribution to the study area. In general, sedimentary evolution in the western SYS since MIS 3 is a good example of river-sea interaction in the marginal seas of Southeast Asia, in which sea level and monsoonal climate changes should play an important role.

Morphodynamics of River Deltas in Response to Different Basin Water Depths: An Experimental Examination of the Grade Index Model

AbstractBasin water depth (h) governs the long‐term morphodynamics of river deltas, which are embodied in the grade index (Gindex). The Gindex, a volume‐in‐unit‐time ratio of subaerial sediment allocation to the entire supplied sediment, can be given as a function of the dimensionless basin water depth (h*). Tank experiments reported herein reveal that delta progradation and deltaplain aggradation are suppressed and distributary channel migration and avulsion take place less frequently when the Gindex value is lower (i.e., when the basin water is deeper; h* ≫ 1). If the Gindex~0 (i.e., extremely deep basin water; h*~+∞), the delta can neither prograde nor aggrade, and the distributary channels tend to stabilize. The grade index model helps explain the contrasting morphodynamics of the Liwu Delta (east Taiwan) and Yellow River Delta, as natural examples of deepwater and shallow‐water deltas, respectively.

Self‐Similar Morphodynamics of Gilbert and Hyperpycnal Deltas Over Segmented Two‐Slope Bedrock Channels

AbstractDelta progradation over segmented two‐slope bedrocks is prevalent in nature, where the bedrock slope upstream or downstream of the slope‐break knickpoint is steepened by continued tectonic uplift or subsidence. Understanding the morphodynamics of the most common types of delta in different slope settings is important for interpreting the observed delta progradation into reservoir and predicting delta evolutions under future tectonic/climate scenarios or anthropogenic interventions. Here, we present an experimental and analytical study demonstrating the morphological responses of Gilbert‐type and hyperpycnal deltas to variations of bedrock slopes. Steepening the upstream slope accelerates shoreline migration; steepening the downstream slope decelerates shoreline migration. In either case, the subaqueous volume is enhanced yet the subaerial volume is reduced. Both types of delta exhibit self‐similar morphologies when evolving over segmented bedrocks. Hyperpycnal deltas, through enhanced sediment fluxes driven by dense underflows, develop larger subaqueous volumes. We further demonstrate the underlying self‐similarities in sediment flux and bed growth rate that come into play for attaining the self‐similar morphologies. The combined effect of flowrate (Q) and sediment supply rate (I) may be characterized by a dimensionless Q/I ratio. Increasing Q/I advances the entire delta. For Gilbert deltas, shoreline migration accelerates with Q/I. For hyperpycnal deltas, shoreline migration exhibits a “first‐accelerate‐then‐decelerate” trend with Q/I in a limited range of slope combinations close to the single‐slope setting, indicating that the effect of Q/I emerges only when the two‐slope effect is weak or absent. Away from this near‐single‐slope range, the two‐slope effect becomes dominant, thus suppressing the effect of Q/I.

Factors Controlling Storage, Sources, and Diagenetic State of Organic Carbon in a Prograding Subaerial Delta: Wax Lake Delta, Louisiana

AbstractWax Lake Delta, southern Louisiana, is a coastal delta that formed following the dredging of a river channel in 1941 and is a field model for investigating the geomorphology, ecology, carbon dynamics, and carbon storage capacity in young prograding deltas. However, it is unknown how the transition from subaqueous to subaerial sediments affects the sources and quality of the sequestered carbon. We investigated these variations within the sediments of Wax Lake Delta using amino acid, lignin, and stable carbon isotope compositions of the organic matter (OM). A principal component analysis of these proxies highlighted variability in organic carbon (OC) composition with changes in elevation. The transition from subaqueous to subaerial sediments at 0‐cm mean lower low water is an important component of the OM composition. In addition to the changes observed for OM source and quality, the OC loadings (OC/SA; mg C/m2) also increase as the delta aggrades and accumulates sediments with loadings typical of delta topsets and mobile mud banks (OC/SA < 0.4) to riverine sediments (0.5 < OC/SA < 1) and eventually to highly productive regions (OC/SA > 1). Linking this multiproxy approach with environmental variables such as elevation provides a path for incorporating OM dynamics into geomorphic models.

Sedimentology of a prograding delta complex: The Jurassic succession of the Wagad Uplift in the Kachchh Basin, western India

Sedimentology of a prograding delta complex: The Jurassic succession of the Wagad Uplift in the Kachchh Basin, western India

Tracing clinothem geometry and sediment pathways in the prograding Holocene Po Delta system through integrated core stratigraphy

AbstractThough clinothem geometry represents a key control on fluid flow in reservoir modelling, tracing clinothem boundaries accurately is commonly limited by the lack of sufficiently precise outcrop or subsurface data. This study shows that in basin systems with strongly heterogeneous compositional signatures, the combination of bulk‐sediment geochemistry and benthic foraminiferal distribution can help identify clinothem architecture and generate realistic models of 3D deltaic upbuilding and evolution. Middle‐late Holocene deposits in the Po Delta area form an aggradational to progradational parasequence set that reveals the complex interaction of W–E Po Delta progradation, S‐directed longshore currents (from Alpine rivers) and Apennines rivers supply. Unique catchment lithologies (ophiolite rocks and dolostones) were used to delineate basin‐wide geochemical markers of sediment provenance (Cr and Mg) and to assess distinctive detrital signatures. The geochemical characterization of cored intervals across different components of the sediment routing system enabled a direct linkage between clinothem growth, transport pathways and provenance mixing to be established. On the other hand, abrupt microfaunal variations at clinothem boundaries were observed to reflect the palaeoenvironmental response to sharp changes in sediment flux and fluvial influence. This study documents the ability of an integrated geochemical and palaeoecological approach to delineate three distinct sources (Po, Alps and Apennines) that contributed to coastal progradation and to outline the otherwise lithologically cryptic geometries of clinothems that using conventional sedimentological methods it would be virtually impossible to restore.

Giant sublacustrine landslide in the Cretaceous Songliao Basin, NE China

AbstractMass failure deposits in lacustrine settings are some of the most understudied facies associations in the ancient or modern rock record. We integrated seismic data and well logs to investigate the external morphology, internal architecture and deformation and reservoir distribution of the sublacustrine landslides in the Cretaceous Nengjiang Formation of the Songliao Basin (SLB). A large‐scale sublacustrine landslide, named the Qi‐Jia sublacustrine landslide (QJSL), has been identified in the Nengjiang Formation of the SLB. The QJSL is currently the largest known sublacustrine landslide in the world. This landslide covers an area that exceeds 300 km2, with an estimated volume of 30 km3. Seismic imaging and mapping reveal that the QJSL can be recognized by several distinguishing seismic characteristics: discontinuous and internal chaotic seismic facies, compressional structures in the downslope region, irregular top and basal surfaces and erosional grooves in basal shear surfaces. The QJSL is 20–200 m thick, and is composed of a succession of fine‐grained deposits. Sandy layers are present but sparse and thinner than 16 m, and form reservoirs of the petroleum discoveries in this area. Our analyses show that the mechanism that triggered the collapse of the QJSL is attributed to rapid deposition and deltaic progradation. This study demonstrates that sand‐rich sublacustrine landslides formed at delta front slope can serve as conventional reservoirs in the lake centre, and provide a new target for subaqueous hydrocarbon exploration and development.