Progradational Sequence Research Articles

Sedimentation record of a complete glacial-interglacial cycle: Down-slope deposits, contourites and plumites of the North Sea trough mouth fan

Trough mouth fans (TMFs) are major submarine depocentres that form in front of ice streams advancing onto the continental shelf, and they provide extensive records of past glaciations and ice-sheet dynamics. However, early research about TMFs was conducted using primarily 2D seismic data, which limits the insights on the deposit's geometries and internal structures and more recent studies using 3D data have focused on the general depositional history of TMFs. Here, we assess the spatial and temporal changes of the glacio-marine landforms and deposits throughout the last glacial-interglacial cycle (Marine Isotope Stage (MIS) 6 to 1, ∼130 ka to present) recorded in a >550 m thick progradational sequence. We use 3D reflection seismic data with significant vertical resolution (up to 2 m) imaging over 14000 km2 from the uppermost North Sea Fan (NSF) to document the seismic stratigraphy and sedimentary processes, by combining horizon picking and geomorphological analyses. The studied interval comprises five mappable units, four on the slope and one on the shelf, spanning from the modern seabed down to the top of the Tampen Slide (∼130 ka). Five different channel types (here included slide scars), as well as contourite and plumite packages are described based on their seismic facies, morphology, geometry, and stratigraphical position. We propose that contour currents are responsible for sediment delivery after the Tampen Slide deposition during the interglacial period before the onset of the Last Glacial Maximum, when high meltwater influx from the shelf produced turbidites. Sedimentation became debris-flow-dominated towards the end of the period of shelf-edge glaciation. The deglacial interval is characterized by the deposition of plumites on the slope. On the shelf, subglacial tills are deposited during both glacial and deglacial periods. We calculate an average sedimentation rate of <1 m/kyr during the interglacial (MIS 5-3), and around 50–65 m/kyr during the glacial and deglacial periods (MIS2-early MIS1). Thus, we document a change of two orders of magnitude in sedimentation rate during a glacial cycle on the slope of a glaciated margin.

Depositional cyclicity of lower Cambrian strata in the NW Himalayas: Regional sequence stratigraphy of the Indian passive margin

Lower Cambrian (538-512 Ma) strata have been deposited in the northern Hazara, Kashmir, Salt Range and Zanskar-Spiti basins, which were undergoing subsidence during this period. However, the southern part of the Hazara Basin remained uplifted (Muzaffarabad-Hazara paleo-high, MHP) and acted as a sediment source. Unlike the previous work, the present paper provides an integrated sequence stratigraphic framework of the Lower Cambrian in this region, based on outcrop data, petrography, and well, seismic and gravity data, thereby enabling a correlation among the basins. In the NW Himalayas (Pakistan), the Lower Cambrian strata outcrop in the Salt Range, northern Hazara and Kashmir basins were penetrated during drilling in the Salt Basin (Potwar, Punjab Platform and Bikaner-Naguar basins). Lower Cambrian stratal terminations and subaerial/composite unconformities formed towards the Sargodha paleo-high and the MHP. The Jehlum and Abbottabad groups are well preserved in outcrops of clastic and carbonate sequences. The top of the Khewra/Sangargali sandstone marks an erosional surface and separates two sequences – a progradational and a retrogradational/progradational sequence. The progradational sequence began with sandstone deposition (Khewra and Tanaki Boulder Bed/Sangar Gali formation), just after Khewrite volcanism (538 Ma), with fining upward cycles during a falling stage system tract. Sea level dropped further, as marked by an intraformational subaerial unconformity, and the fluvio-deltaic facies of a lowstand system tract was deposited; this was again capped by a subaerial unconformity. Once subsidence began, a transgressive systems tract developed in a marginal marine setting. Further transgression occurred and a widespread tidalflat was established. These subtidal facies marked the maximum flooding surface in Jutana and Abbottabad formations and a highstand system tract was developed. During the late stages of the highstand system tract the clastic Baghanwala and Hazira formations were deposited and subaerial unconformities were formed at the top and bottom of these formations. The Kashmir Basin remained uplifted during the late stages of the highstand systems tract and no deposition occurred until the Danian. The maximum flooding surfaces of the subtidal facies are correlatable on both shoulders of the MHP. The deposition ceased in the Middle Cambrian with the intrusion of the Mansehra type granites.

Stratigraphic framework and late Holocene history of a lacustrine beach-ridge complex: Paleoclimate archives within migrating strand promontories

This paper focuses on the physiography, stratigraphy, and age composition of a migrating strandplain promontory on Lake Michigan, discussing implied changes in alongshore sediment-transport dynamics within context of regional climate data. The Zion Beach-ridge Plain, a mainland-attached system believed to have migrated by >10 km over the past 4.5 kyrs, is partitioned into distinct physiographic zones. Its structural compartmentalization into distinct ridge sets, recognized in LiDAR-based topographic datasets and subsurface reflection geophysical records, reflects a punctuated morphodynamic development that has implications for understanding groundwater-flow patterns, wetland ecology, and coastal morphodynamic evolution. The most recent physiographic boundary within the strand dates to a high-amplitude lake-level rise event (>3 m in magnitude) that coincided with a regional shift in dominant storm-wind direction. The abrupt juxtaposition of young, high-relief dune-ridge terrain against old, low-relief wetland meadow attests to increased rates of littoral sand transport under conditions of heightened wave and current energies. Ongoing work to refine the geochronology of this and similar events is underway and stands to enhance our understanding of late Holocene coastal evolution. Strandplains are studied globally as important coastal paleoclimate archives, yet in the Great Lakes region the emphasis has been on embayed systems. While sheltered environments (e.g., bedrock-confined strandplains) foster high preservation potentials, optimal for paleohydrographic reconstructions from progradational sequences, the complex depositional architectures of strandplain promontories may provide information on open-water processes not contained within the former.

Impact of sedimentation and diagenesis on deeply buried sandy conglomerate reservoirs quality in nearshore sublacustrine fan: A case study of lower Member of the Eocene Shahejie Formation in Dongying Sag, Bohai Bay Basin (East China)

The sandy conglomerates of the lower member of Shahejie (Es4x) in the north of Dongying Sag, Bohai Bay Basin, were investigated to understand the formation mechanism of the good reservoir and controlling factors in deeply buried strata. This research is based on seismic, logging, and core data and comprehensively utilizes methods such as core description, petrographic analysis, cathodoluminescence image analysis, SEM-EDS analysis, and mercury intrusion. The sandy conglomerates are predominantly lithic arkose and litharenite. The reservoirs in the Es4x have experienced three diagenetic processes, compaction, dissolution, and cementation. Compaction remains the major factor affecting the reservoir quality, mainly in the progradation sequence, and cementation has a destructive effect on reservoirs, principally in the retrogradation sequence. The quantification of the compaction by the compaction index revealed that mechanical compaction is higher in the progradation sequence (0.68) than in the retrogradation sequences (0.59). Compaction is suppressed by carbonate cementation, but the extensive cementation significantly degrades the reservoir quality, especially in the retrogradation sequence. Dissolution of different rock fragments, feldspar, and the whole dissolution, in general, enhance the reservoir's quality in both intervals but more in the progradation sequence. Three types of reservoirs representing type I, type II, and Type III mercury intrusion capillary pressure curves were encountered in the Es4x. The braided channels in the progradation and retrogradation sets encompass the greatest reservoir quality and are characterized by type I and II reservoirs with good petrophysical properties. The preeminent reservoirs appear in the braided channels of the progradation set. The development of high-quality reservoirs is governed by the depositional subfacies, compaction, and dissolution in the Es4x. This study will contribute to comprehending the origin of the genesis mechanism of high-quality in deep sublacustrine sandy conglomerate and will help the exploration and pre-drill for favorable reservoirs in similar basins around the world.

Frontal expansion of an accretionary wedge under highly oblique plate convergence: Southern Indo-Burman Ranges, Myanmar

The formation of accretionary wedges with oversteepened slopes and uplifted axial zones has been demonstrated to be potentially associated with highly oblique plate convergence by numerical and analog studies. The direct role of this mechanism, or other factor(s) in producing the described structural and morphological features in nature, however, has yet to be confirmed. We used seismic reflection sections, detrital zircon U-Pb ages, and detrital apatite fission-track thermochronological data to examine the effects of highly oblique convergence and sediment reworking on accretionary wedge growth in the Indo-Burma Subduction Zone. A detailed subsurface structural analysis of a two-dimensional seismic survey from the outer wedge of the southern Indo-Burman Ranges, Myanmar, yielded three primary characteristics. These are (1) a narrow, steep deformation front (average width 15.6 km) and a vast, low-relief shelf terrace (average width 49 km); (2) a comparatively long-lived growth thrust fault (FT1) with a convex-up geometry at the rear of the deformation front that controlled the vertical stack of the progradational sequences in the shelf terrace; and (3) a group of NE-striking transtensional faults that cut through entire outer-wedge successions and displays as a series of negative flower-like structures. These characteristic features are roughly consistent with the results of laboratory analog modeling of highly oblique plate convergence but significantly differ from those of natural accretionary wedges that formed under highly oblique convergence conditions, such as those in the Sumatra, Hikurangi, Chile, and Cascadia. We further analyzed the sediment provenance of the southern Indo-Burman Ranges and discovered that the outer-wedge rocks are a product of sediment reworking of the hinterland wedge that began to be uplifted and exhumed in the early Miocene (22−12 Ma) due to transpressional motion between the Indian plate and West Burma Terrane. Our analyses indicate that active sedimentation behind the major growth thrust fault (FT1) provided additional basal shear stress that strengthened the coupling of the interface between the wedge base and décollement and promoted the vertical expansion of the outer wedge of the southern Indo-Burman Ranges from the Neogene to the present day. In contrast, the outer wedge of the central Indo-Burman Ranges has experienced stronger forward accretion since the late Miocene, which could be explained by a smaller degree of obliquity and weaker sediment reworking. Our findings demonstrate that both highly oblique plate convergence and sediment reworking were the primary driving forces that triggered vertical development of accretionary wedges. The results of this research have significant implications for understanding the structures and kinematic evolution of wedge systems at other convergent plate margins, in which seamount passage or subduction erosion is often interpreted as the cause of the steeply tapered wedges.

Deep water sedimentary processes in the Enderby Basin (East Antarctic margin) during the Cenozoic

AbstractThe thick sequence of mid‐late Cenozoic sediments preserved within the Enderby Basin of the East Antarctica margin contains key information regarding glacial history and palaeo‐oceanographic conditions during the last 34 My. The interplay between glacial processes and ocean circulation can be reconstructed from seismic stratigraphic studies. Here, interpretation of seismic sequences and geomorphology from an extensive 2D seismic dataset (∼75,000 km) are correlated with lithological data of the ODP site 1165 drilled on the continental rise, and used to assess the age and origin of the sediment, and the possible influence of oceanic currents on its distribution. Mapping of seismic units and facies reveals that, in addition to glacial sediments derived from the Antarctic mainland, the upper Cenozoic succession includes drift units with prograding sequences building out from the Mac. Robertson Land margin, west of the Prydz Bay. Three contourite drifts grew on the western side of submarine channels and large sediment wave fields suggest a mixed system of turbidity currents influenced by west‐flowing bottom currents. The drifts are composed of four seismic units representing stages of onset (Lower Oligocene), main growth (Early‐Middle Miocene), maintenance (Middle‐Late Miocene) and burial (Pliocene). The internal geometry and reflection patterns of the drifts imply an intensified current activity from the Early to Middle Miocene. The results plausibly reflect that the formation of proto Antarctic Bottom Water (AABW) started around the Eocene–Oligocene boundary and intensified episodically from the early to middle Miocene.

Sedimentological and diagenetic impacts on sublacustrine fan sandy conglomerates reservoir quality: An example of the Paleogene Shahejie Formation (Es4s Member) in the Dongying Depression, Bohai Bay Basin (East China)

A section of the northern Yanjia nearshore subaqueous fan sandy conglomerate was investigated to understand high-quality reservoirs' distribution and controlling factors in the retrogradation and progradation sequences. These conglomerates have been demonstrated to have strong heterogeneity, tightly cemented, and feature low porosity and permeability. To provide an inclusive understanding of the formation mechanisms and factors governing the distribution of the high-quality reservoirs, we utilized integrated methods including seismic, cores description, wireline, petrography, scanning electron microscopy, cathodoluminescence, and mercury intrusion capillarity. The results showed that the retrogradation rock types are dominated by arkose and lithic arkose and the progradation by lithic arkose and feldspathic litharenite. The dominant diagenesis events are compaction, carbonate cementation, and dissolution. The mechanical compaction effect is similar in the progradation and retrogradation sequence. The average compaction index of 0.70 and 0.68 for the transgressive system tract and highstand system tract, respectively, revealed that compaction is the dominant mechanism in reducing reservoir quality in the nearshore subaqueous fan.The carbonate cementation is more extensive in the highstand system tract than the transgressive system tract. The braided channel sandy conglomerate from transgressive system tract and highstand system tract have the best reservoir quality and features type I and II mercury intrusion capillarity cures with large pore throat and good physical properties. However, the braided channel reservoir quality from the highstand system tract developed during the progradation phase is relatively better than the braided channel of the transgressive system tract in the retrogradation phase. These microfacies are characterized by a substantial dissolution of rock fragments and feldspar. The main channel and the interchannel deposited during the transgressive and highstand system tract, respectively, represented by type III mercury intrusion capillarity curves with small pore throats, are non-reservoirs. The formation mechanism of the high-quality reservoirs in the highstand system tract is guided by sedimentary facies, compaction resistant ability, dissolution of rock fragment, and feldspar. The genetic mechanism of the high quality in the transgressive system tract is governed by the sedimentary facies, compaction resistant ability, carbonate and feldspar dissolution. This study revealed that the progradation sequence retained the favorable high-quality in the nearshore subaqueous fan. This study proved that, for adequate assessment of reservoirs in the Yanjia area and similar reservoirs elsewhere, reservoir characterization must link sequence stratigraphy, sedimentary facies, and diagenesis to comprehend the high-quality reservoir distribution to help the predrill evaluation of reservoirs.

Metamorphism of the Buchan type-area, NE Scotland and its relation to the adjacent Barrovian domain

The metamorphism of the Buchan block in northeast Scotland, and its relation to the Barrovian domain to its west, have been reassessed from consideration of mineral assemblages, microstructures, phase equilibrium modelling and monazite U–Pb geochronology. Zones of increasing metamorphic grade surround a central low-grade domain (biotite zone) and define a northward-opening, U-shaped metamorphic map pattern. The eastern and southern parts of the Buchan domain show the classic Buchan-type prograde sequence of cordierite – andalusite – sillimanite – migmatite/gneiss, representing a metamorphic field gradient of gently increasing pressure between (2.5–3.0 kbar, c. 550°C) and (3.5–4.0 kbar, c. 750°C). A slightly lower pressure metamorphic field gradient (by less than c. 0.5 kbar) is interpreted for the northeastern Buchan domain. The west Buchan domain shows a prograde sequence of staurolite+andalusite – sillimanite – gneiss/migmatite, representing a metamorphic field gradient of higher pressure by c. 1 kbar or less than the classic sequence over a similar temperature range. Unique to the northwestern Buchan domain is a staurolite+cordierite+andalusite domain in which staurolite-bearing schists have been overprinted by cordierite + andalusite assemblages. Monazite U–Pb geochronology of schists and gneisses from the Buchan block, including the Cowhythe and Ellon gneisses, yields ages in the range 470 ± 5 Ma, supporting geological evidence that the gneisses are metamorphosed Dalradian strata rather than older basement gneisses. The metamorphic ages are similar to the ages of mafic igneous intrusions in the Buchan block, even though many of the exposed intrusions post-date the regional metamorphic zones. The Buchan metamorphic zones are truncated to the west by the Portsoy–Duchray Hill Lineament, a ductile shear zone that juxtaposes the Buchan rocks against higher pressure, lower temperature (kyanite-bearing) Barrovian schists to the west ( c . 5.5–7.0 kbar, c. 580–650 °C). A 2–15 km wide corridor of andalusite pseudomorphed by kyanite occurs between the Portsoy–Duchray Hill Lineament and the Keith shear zone to its west. Monazite geochronology of the Barrovian rocks west of Portsoy shows little evidence of the c. 470 Ma signature of the Buchan block, instead yielding a dominant cluster of ages at c. 450 Ma and a more poorly defined grouping at c. 500 Ma. Supplementary materials: Analytical procedures; Thermodynamic modelling; Tables S1 to S13 (mineral assemblages, whole rock compositions, mineral compositions, isotopic analyses); Figures S1 to S5 (supplementary mineral assemblage map, graphs of mineral composition vs. grade, supplementary thermodynamically calculated phase diagrams, back-scattered electron (BSE) images of monazite grains, concordia diagrams for monazite U–Pb results) are available at https://doi.org/10.6084/m9.figshare.c.5536745

Evidence for a Highly Dynamic West Antarctic Ice Sheet During the Pliocene

AbstractMajor ice loss in the Amundsen Sea sector of the West Antarctic Ice Sheet (WAIS) is hypothesized to have triggered ice sheet collapses during past warm periods such as those in the Pliocene. International Ocean Discovery Program (IODP) Expedition 379 recovered continuous late Miocene to Holocene sediments from a sediment drift on the continental rise, allowing assessment of sedimentation processes in response to climate cycles and trends since the late Miocene. Via seismic correlation to the shelf, we interpret massive prograding sequences that extended the outer shelf by 80 km during the Pliocene through frequent advances of grounded ice. Buried grounding zone wedges indicate prolonged periods of ice‐sheet retreat, or even collapse, during an extended mid‐Pliocene warm period from ∼4.2–3.2 Ma inferred from Expedition 379 records. These results indicate that the WAIS was highly dynamic during the Pliocene and major retreat events may have occurred along the Amundsen Sea margin.

Sequence stratigraphy of the Cryogenian Nantuo Formation in South China: Constraints on Marinoan glaciation dynamics

• Diverse sedimentary environments capture the evolution of Marinoan glaciation . • These Marinoan deposits record two complete, symmetrical sedimentary cycles. • Patterns of cyclic environmental changes are consistent with global-scale controls. • Marinoan glaciation gradually transited into the Ediacaran greenhouse. Cryogenian low-latitude glaciations mark the ‘Snowball Earth’ events and were thought to be dynamic on the basis of sedimentary features, especially glacial cycles. Although the glaciation dynamics and associated environmental changes can be investigated through the sedimentary records, there are sparse sedimentary studies. Studies from the Marinoan deposits in South China provide the basis for establishing a sequence stratigraphic framework that includes two complete glacial cycles across a basin-to-platform transect. Both cycles are characterized by symmetrical facies patterns, with a lower ice-advance succession and an upper ice-retreat succession. Each ice-advance succession consists primarily of a massive diamictite lithofacies association, and is dominated by proximal glaciomarine deposits. The gravel abundance and size of the deposits increase upward gradually, suggesting a progradational sequence. Each ice-retreat succession is composed of both a massive diamictite lithofacies association and a fine-grained lithofacies association, representing a mix of distal glaciomarine, proximal glaciomarine, and non-glacial marine deposits. The gravel abundance and size of these varied deposits decrease upward gradually, interpreted to reflect a retrogradational sequence. This sequence stratigraphic framework, interpreted to reflect gradual alternation from ice advance to ice retreat, indicates dynamic co-evolution of the sedimentary environments, paleoclimate, and sea level during the Marinoan glaciation. The glaciation dynamics, as they are reflected globally, highlight a gradual transition from the Marinoan glaciation to the Ediacaran greenhouse, and indicate a time lag between the onset of the deglaciation and the formation of the cap carbonates.

Evaluation of Hydrocarbon Reserve in AD Field, Offshore Niger Delta

This study was carried out to quantify uncertainty in the reserve estimate of hydrocarbon in the reservoirs of AD Field, offshore, Niger Delta. Three Dimensional (3D) seismic data and log suites of seven wells (AD1 to AD7), gamma ray, resistivity, neutron and bulk density logs, well deviation and checkshot data in AD Field acquired from companies in the area. Twelve faults (Fault1 to Fault12) were identified from seismic structural interpretation while Six hydrocarbon-bearing sand intervals (Sand A - F) were delineated from the petrophysical analysis. The sand intervals thin-out basin wards, suggesting a prograding sequence. The porosity of the sand intervals ranges between 0.19 and 0.32, implying good to excellent porosity. The water saturation values ranged from 0.19 to 0.39, indicates a prospective accumulation of hydrocarbon. Sand A reservoir had the largest accumulation of hydrocarbon in-place with hydrocarbon pore volume of 2343 106 Reserve Barrel (RB), Stock Tank Oil-Initially-In-Place (STOIIP) of 175 MMbbl and gas initially-in-place of 0.30 TCF. The coefficient of variation in the reserve estimates of the reservoirs ranged from 0.09 to 0.15 indicating very low uncertainty of substantial hydrocarbon reserve that could be exploited.

Metamorphic and structural evolution of the Flin Flon – Athapapuskow Lake area, west-central Manitoba

The Flin Flon – Athapapuskow Lake area, situated in the Flin Flon Greenstone Belt, Manitoba, consists of ocean-floor and island-arc assemblages, deformed and metamorphosed during the Trans-Hudson Orogeny (∼1.86–1.69 Ga). A new map of metamorphic mineral assemblages and isograds has been compiled that reveals a largely coherent regional metamorphic sequence increasing in metamorphic grade from prehnite–pumpellyite to amphibolite facies. Regional metamorphism postdates most of the deformation within the area, with the exception of the reactivation of major block-bounding faults. The regional prograde sequence has been subdivided into 10 metamorphic zones, separated by 9 isograds, that describe the transition from prehnite–pumpellyite to greenschist to amphibolite facies. The formation of contact metamorphic aureoles, pre-dating regional metamorphism, record conditions up to amphibolite facies. Equilibrium phase diagrams for the island-arc (low-Mg) and ocean-floor (high-Mg) assemblages were calculated and allow for the evaluation of the modelling techniques and determination of pressure–temperature conditions. Discrepancies between the modelling predictions and natural observations occur due to (1) limitations in the thermodynamic models for some of the complex minerals (e.g., amphibole); and (2) metastable persistence of some minerals to higher grade due to sluggish reaction kinetics. Notwithstanding these discrepancies, the modelling suggests that metamorphosed mafic rocks in the Flin Flon – Athapapuskow Lake area reached about 430–480 °C and 3.0–4.5 kbar. Peak metamorphic conditions within contact aureoles that preceded regional metamorphism did not exceed 500 °C (at a pressure between 2.7 and 4.4 kbar). The metamorphic field gradient records a transition from 250–300 °C/1.5–2.3 kbar to 430–480 °C/3–4.5 kbar (100–150 °C/kbar), defining a geothermal gradient of approximately 25–31 °C/km.

Constraining stratal architecture and pressure barriers in the subsalt Karachaganak Carboniferous carbonate platforms using forward stratigraphic modelling

Predicting reservoir quality and pressure barriers is a challenging task in carbonate systems. In this paper, we present new model results from the Lower Carboniferous Serpukhovian carbonates in the Karachaganak Field (Northern Kazakhstan), which is characterized by complex facies architectures and reservoir compartmentalization. The Serpukhovian sequence at Karachaganak is poorly imaged by seismic due to the presence of thick Permian salt canopies. The carbonate sequence comprises two carbonate build-ups: a larger Main build-up (MBU) in the eastern portion of the field, and a smaller isolated Western build-up (WBU). We used diffusion-based DionisosFlow forward stratigraphic modeling (FSM) coupled with a CougarFlow sensitivity analysis workflow to (1) review sub-salt seismic horizon picks based on process-modeling constraints, (2) understand the regional controls on the stratigraphic stacking patterns, (3) understand the distribution of reservoir facies, including potential lateral pressure barriers, and (4) constrain the impact and uncertainties of our choice of boundary conditions in the model. Results point out the need for revisions of existing reservoir-scale static models as FSM simulations indicate that the current seismic reflector pick for the base of the Serpukhovian Stage below the WBU is incompatible with the seismic geometries and facies distribution for this system. To reconcile modelling results with existing seismic geometries, the base of the Serpukhovian stage is expected to be about 180 m higher in the stratigraphy. This suggested revision is also supported by the drilling of a recent well that penetrated the top of the Permian 200 m higher in the stratigraphy on the WBU than anticipated. Modeling results also show that fast regional subsidence rates were the primary control for the Early Serpukhovian aggradational stacking pattern, but that slowing subsidence rate during the Late Serpukhovian due to the Uralian orogeny resulted in a switch to progradational sequence patterns. The forward stratigraphic model additionally demonstrates the major role of wind direction and short-term eustatic changes on the presence and distribution of reefs and breccia reservoir facies. Models show that the clinoforms’ angle of repose varies between the leeward and windward sides of the build-up, which leads to the deposition of mud draping on the leeward side that acted as fluid barriers. The presence and distribution of the reservoir and mud facies in the model can explain the observed reservoir compartmentalization at Karachaganak. Finally, our forward stratigraphic modeling workflow coupled with uncertainty analysis provides new quantitative constraints to understand the impact of diffusion coefficients and sediment production rates on the vertical and lateral reservoir heterogeneities and associated lateral pressure-barriers.

Late Holocene Red Sea Coastal Evolution: Evidence from Shallow Subsurface Sedimentary Facies, North Al-Wajh, Saudi Arabia

The stratigraphy of the late Holocene shallow subsurface coastal sediments, North Al-Wajh, Saudi Arabia was investigated to reconstruct the environmental evolution of the area in relation to sea-level changes. Five shallow cores (1.1 to 2.2 m long) were collected from the intertidal flat bordering the Dumaygh Lagoon, and the mouths of wadis Antar and Haramil. The cores exhibit siliciclastic-dominated sediments, in some parts containing reworked calcareous shell fragments of bivalves, gastropods and coral remains. The sediments were analyzed for grain size, loss on ignition (LOI), CaCO3 content, and bulk mineralogy. Mineralogically, the sediments were dominated by siliciclastic minerals (quartz, plagioclase, feldspars, and hornblende) followed by low Mg-calcite (LMC), high Mg-calcite (HMC) and aragonite. In addition, traces of mica, amphiboles, clay minerals, and dolomite were recognized. There is a slight lateral variation in the relative abundance of aragonite and high Mg calcite (HMC), particularly at the base of cores. The results provide a simple scenario for the late Holocene Northern Red Sea coastal evolution. Two vertically stacked sedimentary facies were recognized from the cores; grey mud-dominated lagoonal/bayfill at the base and yellowish-brown sand-dominated intertidal flat at the top. The vertical facies stacking suggests a forestepping pattern or progradational sequence possibly attributed to the late Holocene relative sea-level fall.

Controls of pre‐existing structures on clinoform architecture and the associated progradational system elements

AbstractThere remains a limited understanding of the controls of pre‐existing structures on the architecture of deep‐water progradational sequences. In the Northern Taranaki Basin (NTB), New Zealand, Pliocene post‐extensional sedimentary sequences overlie Miocene back‐arc volcaniclastic units. We utilize seismic reflection datasets to investigate the relationships between the buried back‐arc mound‐shaped structures, and the spatio‐temporal changes in clinoform architecture and the associated progradational system elements within the overlying continental slope margin sequences. Our results reveal the following: (a) buried mound‐shaped structures in the northern domain of the study area, overlain by younging progression of shelf‐to‐basin prograding clinoforms; (b) folding of the deeper clinoforms that systematically decrease in magnitude with shallowing depth from the top of the seamounts; (c) overall, the N‐S‐trending continental slope margin evolves from a highly curvilinear/angular trend in the deeper clinoforms (Units 1 and 2) into a rectilinear geometry within the shallower post‐extensional intervals (Unit 3 and shallower); (d) Units 1 and 2 characterized by dominance of stacked offlap breaks and over‐steepened (7–10°) clinoform foreset slopes in the northern domain, and dominance of gently dipping foreset slopes (&lt;6°) in the south; (e) Unit 3 shows very low (&lt;5°) and intermediate (5–7°) foreset slopes across the entire survey; (f) in the northern domain, differential loading by prograding sequences about the buried seamounts and horst–graben structures induced a differential compaction of the deeper units, which influenced a temporal pinning of the prograding slope margin in pre‐Unit 2 times and (g) wide, closely spaced channel incision into over‐steepened slopes dominate the deeper prograding sequence in the northern domain, whereas narrower, straighter channels dominate the south. We show that the buried pre‐existing structures constitute rigid buttresses that modulated the syn‐depositional topography and post‐depositional architecture of the prograding sequences in the NTB. Our findings present a distinction in the controls on progradational sedimentation patterns between magmatic and non‐magmatic continental margins.

Chronology of Quaternary shoreline progradational sequences related to eustatic sea-level changes: Sedimentation and subsidence in Saronikos Gulf, Greece

The stacking pattern of shoreline progradational sequences in subsiding basins have been used as a chronologic tool in the Mediterranean region. Most previous studies have used a few key seismic lines seaward of deltas, where the record is complicated by deltaic distributary switching. Southeastern Saronikos Gulf, in the western Aegean Sea at the northwestern end of the South Aegean Arc, lacks large river input of sediment. The ENE-WSW and NW-SE trending neotectonic Aegina and Methana basins lie between the tectonically active Gulf of Corinth and the relatively stable Cyclades plateau. New high-resolution seismic profiles from southeastern Saronikos Gulf have been interpreted according to the principles of seismic and sequence stratigraphy. Alpine basement and marine Pliocene sediments have been recognized in the surrounding basin margins and more than 300 m and 150 m of unconsolidated sediments have been mapped in Aegina and Methana basin respectively. Progradational clinoforms that toplap against transgressive surfaces, have been traced along strike, leading to the establishment of a robust chronostratigraphic framework further controlled by sedimentation rates as extracted from cores. Southeastern Saronikos Gulf poses an outstanding example of development of progradational wedges formed within a microtidal, wave dominated regime of low sedimentation rates, between 2.8 cm/ka and 3.2 cm/ka, within the framework of low subsiding basins with rates between 0.03 and 0.31 m/ka. In this environment, more than 180 well preserved shoreline progradational units, with attributes similar to the ones reported from the Aegean and Eastern Mediterranean seas, have been mapped and correlated to sea level lowstands back to 866 ka. Deeper Mid-Pleistocene progradational units are also recognized, tentatively back to 1.4 Ma. Subsidence rate shows a dramatic decrease in the last 1 Ma and significant numbers of faults became inactive during the last 130 ka. In Early-Middle Quaternary, Methana basin was an isolated lake and extended terrestrial areas were shaped in the Poros-Agios Georgios plateau during sea level lowstands. Aegina basin was continuously connected to the Aegean through the Agios Georgios fault valley. This study demonstrates the robustness of chronology based on stacked shoreline progradational sequences and its applicability to determining rates of tectonic subsidence.

Investigation of reservoir characteristics, depositional setting and T\u2013R sequences of the Lockhart Limestone of Meyal Oil Field, Pakistan: a petrophysical approach

The present study is focused on formation evaluation of the Lockhart Limestone in two wells (Meyal-05P and Meyal-10P) located in Northern Deformed Potwar Zone of the Potwar sub-basin, Pakistan. The geological formations ranging from Triassic to Pliocene have been drilled in these wells. The formation evaluation of the Lockhart Limestone mainly involves reservoir potential evaluation, interpretation of depositional environment and transgressive–regressive sequences using petrophysical logs. In either wells, the reservoir characterization is steered by various petrophysical parameters including calculation of volume of shale, porosity, permeability and hydrocarbon saturation. The thickness of the Lockhart Limestone is 50 m and 77 m in the Meyal-05P and Meyal-10P wells, respectively. In Meyal-05P and Meyal-10P wells, the average petrophysical parameters values and ranges are given as follows: volume of shale 48% and 20%; density porosity 1–5.6% and 1–31.7%; neutron porosity 1–23% and 1–42.9%; sonic porosity 1–29% and 1–39%; effective porosity < 1–> 5% and 1–21%; and hydrocarbon saturation 92.21–99.8% and 97–99.6%. The petrophysical parameters indicate that the Lockhart Limestone of Meyal-10P well is quantitatively better reservoir than that of the Meyal-05P. In Lockhart Limestone of either wells, the permeability is < 0.1 mD. The bulk volume water deciphered the presence of vuggy and intercrystalline porosity in the Lockhart Limestone. Similarly, the lithological interpretation using logs shows mainly limestone with minor shales. Different electrofacies are interpreted from the log trends of gamma ray log such as aggrading, prograding and retrograding depositional sequences deposited in tidal channel fill, shallow water, shore line and offshore buildup and regressive-to-transgressive shore face depositional setting.

Holocene Sedimentary Record and Coastal Evolution in the Makran Subduction Zone (Iran)

The western Makran coast displays evidence of surface uplift since at least the Late Pleistocene, but it remains uncertain whether this displacement is accommodated by creep on the subduction interface, or in a series of large earthquakes. Here, we address this problem by looking at the short-term (Holocene) history of continental vertical displacements recorded in the geomorphology and sedimentary succession of the Makran beaches. In the region of Chabahar (Southern Iran), we study two bay-beaches through the description, measurement and dating of 13 sedimentary sections with a combination of radiocarbon and Optically Stimulated Luminescence (OSL) dating. Our results show that lagoonal settings dominate the early Holocene of both studied beach sections. A flooding surface associated with the Holocene maximum transgression is followed by a prograding sequence of tidal and beach deposits. Coastal progradation is evidenced in Pozm Bay, where we observe a rapid buildup of the beach ridge succession (3.5 m/years lateral propagation over the last 1950 years). Dating of Beris Beach revealed high rates of uplift, comparable to the rates obtained from the nearby Late Pleistocene marine terraces. A 3150-year-old flooding surface within the sedimentary succession of Chabahar Bay was possibly caused by rapid subsidence during an earthquake. If true, this might indicate that the Western Makran does produce large earthquakes, similar to those that have occurred further east in the Pakistani Makran.

Use of seismic-based new rose diagram to determine the major sediment-supply direction of progradational systems

A conventional method for identifying sediment-supply directions is to characterize the seismic progradational reflection configuration, which is based mainly on qualitative observation of numerous seismic profiles. We have developed a more quantitative and practical way to determine the major sediment-supply direction (MSSD) using a new type of rose diagram based on seismic progradational sequence angles. In accordance with similar principles of the rose diagram used in structural geology, we have developed an analytical method and a workflow for a new rose diagram of seismic-based progradational sequence angles to determine MSSD. The Bozhong sag, a subbasin of the Bohai Bay Basin with two typical progradational sequences (I and II), provides a suitable example to analyze MSSD and test the new method. Our result indicates that the MSSD of the two progradational sequences (I and II) corresponds to azimuths of 10°–20° and 340°–350°, respectively, intuitively indicating two sequences derived from different provenance-transport systems. The new rose diagram of seismic progradational angles offers a powerful and quantitative method for seismic-based sedimentary provenance and paleocurrent analysis.

Storm response of a mixed sand gravel beach ridge plain under falling relative sea levels: A stratigraphic investigation using ground penetrating radar

AbstractBeach ridge stratigraphy can provide an important record of both sustained coastal progradation and responses to events such as extreme storms, as well as evidence of earthquake induced sediment pulses. This study is a stratigraphic investigation of the late Holocene mixed sand gravel (MSG) beach ridge plain on the Canterbury coast, New Zealand. The subsurface was imaged along a 370 m shore‐normal transect using 100 and 200 MHz ground penetrating radar (GPR) antennae, and cored to sample sediment textures. Results show that, seaward of a back‐barrier lagoon, the Pegasus Bay beach ridge plain prograded almost uniformly, under conditions of relatively stable sea level. Nearshore sediment supply appears to have created a sustained sediment surplus, perhaps as a result of post‐seismic sediment pulses, resulting in a flat, morphologically featureless beach ridge plain. Evidence of a high magnitude storm provides an exception, with an estimated event return period in excess of 100 years. Evidence from the GPR sequence combined with modern process observations from MSG beaches indicates that a palaeo‐storm initially created a washover fan into the back‐barrier lagoon, with a large amount of sediment simultaneously moved off the beach face into the nearshore. This erosion event resulted in a topographic depression still evident today. In the subsequent recovery period, sediment was reworked by swash onto the beach as a sequence of berm deposit laminations, creating an elevated beach ridge that also has a modern‐day topographic signature. As sediment supply returned to normal, and under conditions of falling sea level, a beach ridge progradation sequence accumulated seaward of the storm feature out to the modern‐day beach as a large flat, uniform progradation plain. This study highlights the importance of extreme storm events and earthquake pulses on MSG coastlines in triggering high volume beach ridge formation during the subsequent recovery period. © 2019 John Wiley &amp; Sons, Ltd.