Regressive Systems Tract Research Articles

The sequence stratigraphy and depositional characteristics of fan‐delta complexes in the Upper Bayingebi Member (Lower Cretaceous) in Chagan Sag, Inner Mongolia, China

The Chagan Sag is a small Early Cretaceous intracontinental passive rift subbasin in the Yingen‐Ejinaqi Basin Group generated on the Tianshan‐Xingmeng Orogenic Belt. The Lower Cretaceous strata contain the Bayingebi, Suhongtu, and Yingen formations deposited during the syn‐rift phase. The Wuliji Structural Zone bounded by a high‐dip syn‐sedimentary fault is an intensively studied area with an extent of ~300 km2 having abundant available subsurface dataset and great hydrocarbon potential. According to well‐ and seismic‐based sequence stratigraphic study, the Upper Bayingebi Member generally corresponds to a complete third‐order transgressive–regressive sequence in the Wuliji Structural Zone. The transgressive system tract gradually thins towards the north, but the regressive system tract covers the entire study area in this third‐order sequence. Further investigations reveal that tectonic subsidence and climate change are two predominant allogenic factors for controlling stratigraphic development in the Wuliji Structural Zone.During the deposition of the Upper Bayingebi Member, transverse gravity flow dominated fan‐delta complexes sourced from the Maodun Subuplift are well developed in the Wuliji Structural Zone. The retrogradational conical fan deltas are mainly located in the southern sector during the transgressive system tract stage, but the progradational Gilbert‐type fan deltas are widely developed during the regressive system tract stage. The sedimentary evolution and stratigraphic architecture are directly linked with preexisting topography, accommodation, and sediment supply. In addition, climate change and vegetation types are thought to be critical controls for fluid properties originated from feeder drainage systems and depositional processes of the construction of fan‐delta complexes in the distinct system tracts.

Sequence stratigraphy and depositional architecture of the Pearl River Delta system, northern South China Sea: An interactive response to sea level, tectonics and paleoceanography

Using a combined dataset including 3D seismic volumes, 2D profiles and 127 industrial wells, this study systematically investigated sequence stratigraphy and depositional architecture of the Pearl River Delta system (PRDS) during the Middle Miocene. In total, six stratigraphic sequences (SQ1 to SQ6) were recognized for the Hanjiang Formation, each of which could be further subdivided into a transgressive systems tract (TST) and a regressive systems tract (RST) according to a T-R sequence stratigraphic model. Seismic geomorphologic approaches were then conducted to interpret and map the key depositional elements, including fluvial channel systems, river mouth bars, longshore bars, shelf sand ridges and shelf sand sheets. After a detailed construction of the paleogeography for each of the twelves systems tracts, it was found that the types, geometries and depositional regimes of PRDS significantly altered at ca. 13.8 Ma. Before ca. 13.8 Ma, the PRDS were dominated by well-developed fluvial systems and an overall lobate shape, indicating a fluvial-dominated process. However, after 13.8 Ma, the whole PRDS began to form enormous shoreline-parallel depositional elements such as longshore bars, shelf sand ridges and shelf sand sheets, indicating dominant shore-parallel regimes. Besides, the whole deltaic system displayed obvious southwest deflection in map view after 13.8 Ma.Detailed analysis showed that this sudden change in the evolution of the PRDS could be ascribed to an interactive response to several factors. At ca. 13.8 Ma, the sea level began to rapidly rise and caused the fluvial energy to decrease, which was likely to lead to the diversion of the fluvial systems. Besides, the gradual uplift of the Dongsha Rise resulted in the raised shelf topography in the east region, thus confining the fluvial channels to flow southwestward. What's more, a few key paleoceanographic events, including the reglaciation of the Antarctic ice-sheet and the shoaling of the Pacific-Indian Ocean Seaway, might have contributed to the intensification of the southwesterly flowing paleocurrent along the northern South China Sea, thus triggering the delta asymmetry and deflecton of the PRDS after 13.8 Ma.

Seismic-stratigraphic architecture of the Oligocene-Pliocene Camaná Formation, southern Peruvian forearc (Province of Arequipa)

The Camaná-Mollendo Basin is an active-margin depression ~NW-SE elongated, which is located in the forearc of southern Perú and extends from the Coastal Cordillera to the Perú-Chile Trench. This basin consists of a grabens and half-graben complex, filled with deltaic and fluvial sedimentary rocks of the Oligocene-Pliocene Camaná Formation (~500 m thick). An integration of compiled onshore stratigraphic logs, reinterpreted 2D seismic offshore information, sediment provenance data, and previous zircon U-Pb geochronology on volcanic reworked ash supports a refined tectono-chronostratigraphic framework for the whole Camaná-Mollendo Basin fill. To complete this integration we needed firstly to elaborate a geological reinterpretation of seismic offshore data and highlight their most prominent features (i.e., erosive surfaces). This step allowed establishing a first correlation between onshore and offshore deposits of Camaná Formation by means of their sequence boundaries, giving as result a consistent division for Camaná Formation: (i) “CamA Unit” (coarse-grained deltas) and (ii) “CamB Unit” (fluvial deposits). CamA Unit is further subdivided into three subunits based on minor erosive surfaces (i.e., A1: Oligocene, A2: Early Miocene, and A3: Middle Miocene). CamA reflects prograding geometry (subunits A1 and A2) as well as onlapping geometry (subunit A3). CamB Unit (Late Miocene to Pliocene) consists of high-energy hyperpycnal flows composed of fluvial conglomerates in onshore, which very possibly changes to progradational deltaic in offshore. Each one of these units and subunits extends offshore and preserves similarities in depositional geometry and sequence boundaries with Camaná Formation onshore. Subunits A1 and A2 observed in offshore are grouped in this paper as “A1+A2” (Oligocene to Middle Miocene) because they show similar progradational geometry and it is difficult to differentiate them from each other. A regressive systems tract (RST) represents these subunits. These deposits reach up to ~2.5 km thick, and they are intensely affected by normal faulting associated to pinch-out depositional geometry. Strata of subunit A3 (Middle Miocene) reflect a transgressive systems tract (TST), and blanket the entire basin with fine-grained sediments. These deposits are up to ~1 km thick, being less affected by synsedimentary tectonic and show minor effects of synsedimentary tectonics. Finally, deposition of CamB Unit (Late Miocene to Pliocene) occurred during a new regressive systems tract (TST), which turned to progradational geometry similar to deltaic deposits in offshore, and according to seismic lines they are much less affected by synsedimentary faulting. Stratigraphic boundaries between “A1+A2” and A3, and between A3 and CamB observed in onshore outcrops are used here as tools to differentiate, correlate and predict the main depositional geometries in offshore. High-frequency seismic reflectors represent such boundaries and support divisions and subdivisions within Camaná Formation. These boundaries are also used to define depocentres of Camaná Formation along the entire Camaná-Mollendo Basin, where the thickests are located in the proximity of the large river mouths (e.g., Planchada, Camaná, and Punta de Bombón). Strata of subunits “A1+A2” are considered as potential reservoir for hydrocarbon due to their high rate of sediment accumulation. Deposits of A3 are transgressive and they are considered as potential potential seal rock. Structurally, Camaná-Mollendo Basin is composed of graben and half-graben components ~NW-SE-oriented, typical of a trantensional tectonic regime.

Regional T-R sequence stratigraphy and lithostratigraphy of the Bearpaw Formation (Upper Campanian), west-central and southwestern Alberta plains

Abstract In west-central and southwestern Alberta, the lower and upper tongues of the marine mudstone-dominated Bearpaw Formation have a complex lateral relationship with marginal marine and non-marine strata of the Horseshoe Canyon and Blood Reserve formations. Wireline log, core and outcrop data permit the establishment of a regional transgressive-regressive (T-R) sequence stratigraphic framework for the upper Campanian Bearpaw strata. This provides a context within which lithostratigraphic boundaries of the Bearpaw tongues with laterally equivalent and overlying strata can be more rigorously mapped. Maximum flooding (MFS) and transgressive (TS) surfaces were defined on the basis of stratal stacking patterns and inferred lapout relationships wherever possible. Lower Bearpaw tongue and laterally equivalent strata are assigned to four regionally mappable T-R sequences. In the study area the top of the underlying Belly River Group is placed at the MFS in the lowermost of these sequences. In the overlying lower Bearpaw sequences, the TS is generally considered to coincide with the MFS within the limits of wireline log resolution, and the succession consists mainly of stacked regressive systems tracts which usually show a near-parallel internal stratal geometry. Upper Bearpaw tongue and laterally equivalent strata are assigned to three regionally mappable T-R sequences. The basal upper Bearpaw sequence has a well-developed transgressive systems tract consisting of backstepping, individually regressive parasequences, and southeast-prograding clinoform geometry is clear in each of the upper Bearpaw tongue regressive systems tracts. The lithostratigraphic upper boundaries of the lower and upper Bearpaw tongues are time-transgressive facies contacts that step up-section to the southeast (paleoseaward) through the respective regressive systems tracts. The base of the upper Bearpaw tongue steps up-section from the basal TS of the lowermost sequence in the southeast, through the overlying transgressive systems tract, to coincide with the maximum flooding surface to the northwest (paleolandward).

Evolutionary history and controlling factors of the shelf breaks in the Pearl River Mouth Basin, northern South China Sea

The migration history of shelf breaks in the stratigraphy of a basin contains significant information about sediment-budget partitioning into the deep water area, which is thus important in predicting the distribution and quality of deepwater reservoirs. Previous studies primarily focused on the sedimentary-dominated shelf breaks (e.g., progradational-type), which are controlled by sediment supply and relative sea-level changes. The location and migration pattern of structure-controlled shelf breaks are comparatively less well documented.The evolutionary history of shelf breaks in the Pearl River Mouth Basin from 30 Ma to present is examined here. Shelf breaks are picked from 280 2-D depositional dip-oriented seismic profiles in the forced regressive systems tracts of 20 3rd-order sequences (SQ 1-20) in four super sequences (SSQ 1-4). Planview distribution maps indicate these shelf breaks can be divided into two groups of different character. Shelf breaks in SSQ 1 (30–23.8 Ma) have migrated progressively and considerably basinward (∼50 km) along with the progradation of shelf-margin deltas, which were propelled by a very strong sediment supply even under the background of relative sea-level rise. They are consequently classified as sedimentary-dominated types. In contrast, shelf breaks in SSQ 2-4 have stayed fairly close (∼20 km) to the boundary between the Panyu Low Uplift and the Baiyun Sag, which is identified as a tectonic hinge zone across which subsidence rate increased abruptly basinward. Shelf breaks were close to the hinge zone even in SQ 11 and 12, in which the depositional shoreline breaks were located ∼80 km further landward. They are classified as structure-controlled types. Our study indicates that through the evolutionary history of the Pearl River Mouth Basin, the locations and migration pattern of the shelf breaks were mainly sediment-supply controlled during 30–23.8 Ma but changed to structure-controlled (i.e., tectonic hinge zone) during 23.8 Ma-Present.

Complex coastal change in response to autogenic basin infilling: An example from a sub‐tropical Holocene strandplain

AbstractThick bay‐fill sequences that often culminate in strandplain development serve as important sedimentary archives of land–ocean interaction, although distinguishing between internal and external forcings is an ongoing challenge. This study employs sediment cores, ground‐penetrating radar surveys, radiocarbon dates, palaeogeographic reconstructions and hydrodynamic modelling to explore the role of autogenic processes – notably a reduction in wave energy in response to coastal embayment infilling – in coastal evolution and shoreline morphodynamics. Following a regional 2 to 4 m highstand at ca 5·8 ka, the 75 km2 Tijucas Strandplain in southern Brazil built from fluvial sediments deposited into a semi‐enclosed bay. Holocene regressive deposits are underlain by fluvial sands and a Pleistocene transgressive–regressive sequence, and backed by a highstand barrier‐island. The strandplain is immediately underlain by 5 to 16 m of seaward‐thickening, fluvially derived, Holocene‐age, basin‐fill mud. Several trends are observed from the landward (oldest) to the seaward (youngest) sections of the strandplain: (i) the upper shoreface and foreshore become finer and thinner and shift from sand‐dominated to mud‐dominated; (ii) beachface slopes decrease from >11° to ca 7°; and (iii) progradation rates increase from 0·4 to 1·8 m yr−1. Hydrodynamic modelling demonstrates a correlation between progressive shoaling of Tijucas Bay driven by sea‐level fall and sediment infilling and a decrease in onshore wave‐energy transport from 18 to 4 kW m−1. The combination of allogenic (sediment supply, falling relative sea‐level and geology) and autogenic (decrease in wave energy due to bay shoaling) processes drove the development of a regressive system with characteristics that are rare, if not unique, in the Holocene and rock records. These findings demonstrate the complexities in architecture styles of highstand and regressive systems tracts. Furthermore, this article highlights the diverse internal and external processes and feedbacks responsible for the development of these intricate marginal marine sedimentary systems.

CHARACTERISTICS OF ORGANIC MATTER OF OIL SHALE IN THE SEQUENCE STRATIGRAPHIC FRAMEWORK AT THE NORTHERN FOOT OF BOGDA MOUNTAIN, CHINA

Analysis of the abundance and type of organic matter of oil shale in the sequence stratigraphic framework of the Middle Permian Lucaogou Formation at the northern foot of Bogda Mountain, NW China, was carried out. The Lucaogou Formation consists of two well-completed 3rd order oil shale sequences, sequence 1 and sequence 2. With respect to organic matter abundance, in each sequence, the TOC of oil shale in the lowstand systems tract (LST) and the regressive systems tract (RST) is of medium abundance. The TOC of oil shale in the transgressive systems tract (TST) is of higher abundance, and in the highstand systems tract (HST), of highest. In regard to type, the organic matter of oil shale in the LST of either sequence is mainly of type II2 or type II1. In TST and HST, it is predominantly of type II1 and type I, respectively, and in RST, of type II1 or II2. The proportion of lake algae in the organic matter of oil shale is the highest in HST, while the share of terrestrial plants is the highest in LST and RST. Being originated from lake algae and terrestrial plants, the organic matter of oil shale in TST is of mixed type.

Depositional environment and hydrocarbon potential of the Middle Triassic strata of the Sverdrup Basin, Canada

This study summarizes the results of petrographic and geochemical analysis of Middle Triassic strata from the Sverdrup Basin in the Canadian Arctic. In this work, we investigate the distribution and depositional conditions of dispersed organic matter (OM) as a preliminary step towards understanding the potential of this stratigraphic interval as an unconventional reservoir. Closely-spaced samples from three Middle Triassic cores (southern margin, basin centre, northern margin) are analyzed using Rock-Eval analysis, inductively coupled plasma-mass spectrometry (ICP-MS), and organic petrology. Total organic carbon (TOC) ranges between 0 and 4.8wt.%, with the most organic-rich interval having a median TOC value of 3.2wt.%. Kerogen type varies from Type II to Type III throughout the sampled intervals. Samples from near the top of the regressive systems tract of the Anisian 3rd order sequence (basin centre) and near the middle of the Ladinian 3rd order sequence (southern margin) contain predominantly reworked, highly oxidized macerals and abundant coarser clastic material. Results support oxic to suboxic depositional conditions for these intervals. By contrast, samples from near the base of regressive systems tracts of both sequences (basin centre and northern margin) have the highest amounts of TOC (i.e., median=3.2wt.% and 1.4wt.%), containing retained migrabitumen and abundant labile primary kerogen, respectively. The base of the Ladinian regressive systems tract near the basin axis was deposited under anoxic conditions and can be considered a prospective shale oil interval. Small-scale cyclic clastic influx episodes along the northern margin of the basin show changes from oxic to suboxic bottom waters. These cycles may be considered evidence for northerly-derived sediment from Crockerland during the Middle Triassic. The results and interpretations of this study can be applied to analogous fine-grained successions in other basins to better understand their unconventional reservoir potential.

DEPOSITIONAL ENVIRONMENT AND LITHOSTRATIGRAPHY OF THE PALEOPROTEROZOIC MOOIDRAAI FORMATION, KALAHARI MANGANESE FIELD, SOUTH AFRICA

Research Article| December 01, 2014 DEPOSITIONAL ENVIRONMENT AND LITHOSTRATIGRAPHY OF THE PALEOPROTEROZOIC MOOIDRAAI FORMATION, KALAHARI MANGANESE FIELD, SOUTH AFRICA M. KUNZMANN; M. KUNZMANN Department of Mineralogy, Technical University Bergakademie Freiberg, Brennhausgasse 14, 09596 Freiberg, Germany, Current address: Department of Earth and Planetary Sciences/GEOTOP, McGill University, 3450 University Street, Montréal, QC H3K 0E8, Canada Corresponding author, e-mail: marcus.kunzmann@mail.mcgill.ca Search for other works by this author on: GSW Google Scholar J. GUTZMER; J. GUTZMER Helmholtz Institute Freiberg for Resource Technology, Halsbruecker Str. 34, 09599 Freiberg, Germany and Paleoproterozoic Mineralization Research Group, Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa, email: j.gutzmer@hzdr.de Search for other works by this author on: GSW Google Scholar N.J. BEUKES; N.J. BEUKES Paleoproterozoic Mineralization Research Group, Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa, e-mail: nbeukes@uj.ac.za Search for other works by this author on: GSW Google Scholar G.P. HALVERSON G.P. HALVERSON Department of Earth & Planetary Sciences/GEOTOP, 3450 University Street, McGill University, Montréal, QC H3A 0E8, Canada, e-mail: galen.halverson@mcgill.ca Search for other works by this author on: GSW Google Scholar South African Journal of Geology (2014) 117 (2): 173–192. https://doi.org/10.2113/gssajg.117.2.173 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation M. KUNZMANN, J. GUTZMER, N.J. BEUKES, G.P. HALVERSON; DEPOSITIONAL ENVIRONMENT AND LITHOSTRATIGRAPHY OF THE PALEOPROTEROZOIC MOOIDRAAI FORMATION, KALAHARI MANGANESE FIELD, SOUTH AFRICA. South African Journal of Geology 2014;; 117 (2): 173–192. doi: https://doi.org/10.2113/gssajg.117.2.173 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract The Paleoproterozoic Mooidraai Formation is an up to 220 m thick succession of marine carbonate rocks that caps the Fe- and Mn-bearing Hotazel Formation in the Kalahari Manganese Field, South Africa. Although it occupies an important stratigraphic position within the upper Transvaal Supergroup, which records major perturbations of the early Paleoproterozoic biosphere, a detailed sedimentological study on the Mooidraai Formation has never been conducted. Here we present a detailed facies analysis that distinguishes eight carbonate and two iron formation lithofacies types. The lower Mooidraai Formation is dominated by carbonate rhythmites and slope breccias deposited on a foreslope, occasionally interbedded with oxide or carbonate facies iron formation. The upper part of the formation reflects various shelf and peritidal environments arranged in shallowing-upward parasequences. Clastic-textured massive dolarenites deposited in shelf and lagoonal environments typically form the base of parasequences and are overlain by subtidal thrombolites, lagoonal to intertidal microbialaminites, and upper intertidal to supratidal smoothly laminated stromatolites. Supratidal intraclast breccias cap shallowing-upward parasequences. Strong base level rise in the lower Mooidraai Formation reflects a transgressive systems tract tied to rapid early subsidence. Together with considerable lateral thickness variation in the following regressive systems tract, this suggests deposition in a basin with significant seafloor relief. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The Oligocene succession in the eastern North Sea: basin development and depositional systems

AbstractThe Oligocene sedimentary succession in the eastern North Sea is revised and re-interpreted by applying new state-of-the-art reflection seismic data integrated with new bio- and Sr-stratigraphy data from three key wells in the study area. The Oligocene succession in the eastern North Sea is divided into four transgressive–regressive (T-R) sequences, characterized by non-accretional and/or aggradational transgressive systems tracts and prograding regressive systems tracts. Detailed studies of three wells, including biostratigraphy and Sr analysis, constrain the age relationships between the T-R sequences. Internal clinoform geometry indicates that the sediments were sourced from the present southern Norwegian mainland to the north of the depositional area. The direction of progradation shifted from being SE-directed in the earliest Rupelian (early Oligocene) to S- and SW-directed during Chattian time (late Oligocene). Rapid basin subsidence is indicated by the development of non-accretionary transgressive systems tracts, with subsequent progradation into water depths of hundreds of metres. The creation of accommodation space was out of phase relative to eustatic sea-level changes, and mainly controlled by regional-scale differential vertical movements where uplift and exposure of landmasses of the hinterland (southern Norway) occurred concurrently with basin subsidence. Halokinesis had an intra-basinal influence on the main sediment transport direction, but probably did not contribute much in creation of accommodation space.

Depositional facies and stratal cyclicity of dolomites in the Lower Qiulitag Group (Upper Cambrian) in northwestern Tarim Basin, NW China

The Upper Cambrian Lower Qiulitag Group in the Tarim Basin, NW China, is overwhelmingly composed of cyclic dolomites. Based on extensive field investigations and facies analysis from four outcrop sections in the Bachu-Keping area, northwestern Tarim Basin, four main types of facies are recognized: open-marine subtidal, restricted shallow subtidal, intertidal, and supratidal facies, and these are further subdivided into ten lithofacies. In general, these facies are vertically arranged into shallowing-upward, metre-scale cycles. These cycles are commonly composed of a thin basal horizon reflecting abrupt deepening, and a thicker upper succession showing gradual shallowing upwards. Based on the vertical facies arrangements and changes across boundary surfaces, two types of cycle: peritidal and shallow subtidal cycle, are further identified. The peritidal cycles, predominating over the lower-middle Lower Qiulitag Group, commence with shallow subtidal to lower intertidal facies and are capped by inter-supratidal facies. In contrast, the shallow subtidal cycles, dominating the upper Lower Qiulitag Group, are capped by shallow-subtidal facies. Based on vertical lithofacies variations, cycle stacking patterns, and accommodation variations revealed by Fischer plots, six larger-scale third-order depositional sequences (Sq1–Sq6) are recognized. These sequences generally consist of a lower transgressive and an upper regressive systems tract. The transgressive tracts are dominated by thicker-than-average cycles, indicating an overall accommodation increase, whereas the regressive tracts are characterized by thinner-than-average peritidal cycles, indicating an overall accommodation decrease. The sequence boundaries are characterized by transitional zones of stacked thinner-than-average cycles, rather than by a single surface. These sequences can further be grouped into lower-order sequence sets: the lower and upper sequence sets. The lower sequence set, including Sq1–Sq3, is characterized by peritidal facies-dominated sequences and a progressive decrease in accommodation space, indicating a longer-term fall in sea level. In contrast, the upper sequence set (Sq4–Sq6) is characterized by subtidal facies-dominated sequences and a progressive increase in accommodation space, indicating a longer-term rise in sea level.

Cenomanian to Santonian radiolarian biostratigraphy, carbon isotope stratigraphy and paleoenvironments of the Sverdrup Basin, Ellef Ringnes Island, Nunavut, Canada

An upper Albian to Santonian sedimentary record on Ellef Ringnes Island, Canadian Arctic Archipelago, records variable paleoenvironmental conditions within the Cretaceous Polar Sea and Sverdrup Basin. The upper Albian to lower Cenomanian uppermost Christopher and Hassel formations represent a regressive system tract from offshore to shoreface/terrestrial paleoenvironments. The upper Cenomanian to Santonian shales of the Kanguk Formation signify a distal offshore basin setting controlled by increased subsidence and high global sea levels. Siliceous pelagic faunas and floras dominate the basin and herein, three informal radiolarian partial range zones are proposed for the Polar Sea. Alternating diversity and abundance patterns are interpreted as a response to sea-level controlled productivity systems. Transgressive phases correspond to low diversity shallow dwelling radiolarian taxa with an expanded oxygen minimum zone (OMZ); regressive phases are coupled with radiolarian radiations of deeper dwelling species and a depressed OMZ. The upper Cenomanian to Turonian was marked by increased preservation of marine-type organic matter and organic carbon isotope excursions indicate the presence of the Oceanic Anoxic Event 2 (OAE 2) at the base of the Kanguk Formation. Rock Eval data suggest that an increasing terrestrial influence prevailed during the Coniacian to Campanian time covering the OAE 3. Benthic environments are dominated by anoxic conditions, as suggested by the near lack of benthic foraminifera and extensive intervals of fine platy shale lacking bioturbation. Only the upper Coniacian records a return to dysoxic benthic conditions. Radiolarian faunal comparisons to more southern localities suggest migration routes from the east through a narrow North Atlantic pathway and from the Pacific through the Alaskan–Asian Pathway.

Organic matter accumulation, redox, and diagenetic history of the Marcellus Formation, southwestern Pennsylvania, Appalachian basin

Variations in the concentration of redox sensitive elements combined with pyrite framboid size data documented from a Marcellus Formation (Middle Devonian) core recovered from southwestern Pennsylvania elucidate the redox, organic matter accumulation, and diagenetic history of these deposits in this region of the basin. Uranium and Mo enrichment and Fe/Al display sharp increases coincident with diminishing Th/U upward through the initial 3rd order trangressive systems tract (lower Union Springs Member). These data as well as abundant small (<6 μm) pyrite framboids record establishment of strongly reducing benthic conditions, perhaps related to the expansion of an oxygen minimum zone induced by increased surface productivity. Strongly anoxic, even euxinic, conditions were interrupted by episodes of dysoxia, perhaps seasonal or longer term. Overlying regressive systems tract (RST) deposits record modestly improved redox conditions, likely a reflection of a receding oxygen minimum zone as base level dropped. A subsequent 3rd order base level rise and renewed expansion of the oxygen minimum zone triggered by increased surface productivity resulted in the accumulation of the organic-rich lower Oatka Creek Member. Still, the mix of abundant small and subordinate large (>10 μm) framboids preserves the record of oxygen deficient to sulfidic bottom conditions frequently interrupted by episodes of (dys)oxia. Improving redox conditions through the overlying RST were accompanied by a two-fold increase in Al and consequent dilution of the organic matter flux and authigenic trace metal uptake at the sediment–water interface. The upper half of the Oatka Creek comprises a depositional sequence not obvious from core inspection or gamma-ray signature but revealed by Mo enrichment and Al concentration profiles. Diagenetic modification of the Marcellus includes several horizons of authigenic calcium carbonate concretions and marked Ba enrichment. Both features reflect the effects of non-steady state microbial diagenesis within a methane-rich sedimentary column.

Sedimentary facies and stratigraphic architecture in coarse-grained deltas: Anatomy of the Cenozoic Camaná Formation, southern Peru (16°25′S to 17°15′S)

In the external forearc of southern Peru (Arequipa region), the sedimentary facies and the stratigraphic architecture of the Cenozoic Camaná Formation are presented in the context of tectono-eustatic controls. The Camaná Formation is defined as ∼500 m thick coarse-grained deltaic complex that accumulated in a fault-bounded elongated depression extending from the Coastal Cordillera in the east to the offshore Mollendo Basin in the west and likely up to the Peruvian Trench. Based on the analysis of facies associations, we propose a refined stratigraphic scheme of the Camaná Basin fill. The Camaná Formation was formerly divided into the Camaná “A” and Camaná “B” units (CamA and CamB, respectively). We reinterpret the stratigraphic position and the timing of the CamA to CamB boundary, and define three sub-units for CamA, i.e. sub-units A1, A2, and A3. Each depositional unit shows individual stacking patterns, which are linked with particular shoreline trajectories through time.Strata of A1 form the basal succession of the Camaná Formation and consist of distributary channels and mouth bars, unconformably overlain by beds of A2. A2 consists of delta front deposits arranged in voluminous clinothems that reflect a progradational downstepping complex. A3 consists of delta front sandstones to prodelta siltstones arranged in retrogradational onlapping geometry. A pebbly intercalation in proximal onlapping A3 deposits is interpreted to reflect pulses of uplift in the hinterland. The overlying CamB unit is characterized by a thick alternation of fluvio-deltaic conglomerates and sand bars. The ages of the individual units of the Camaná Formation are not yet well defined. Based on the available information and stratigraphic correlations we tentatively assign A1 to the Late Oligocene, A2 to the Early Miocene, A3 to the late Early Miocene to early Middle Miocene, and CamB to the Late Miocene to? early Pliocene.The sub-units A1 and A2 represent a regressive systems tract, where the shoreline was forced to migrate seaward. This scenario differs from the Early Miocene eustatic sea-level rise suggesting that significant tectonic uplift along the Coastal Cordillera controlled the high sediment influx during A2 deposition. The sub-unit A3 represents a transgressive systems tract, triggering landward migration of the shoreline. This scenario is well in line with the global sea-level chart suggesting that A3 has been deposited during a phase of eustatic sea-level rise with minor tectonic activity. The fluvial deposits of CamB reflect an increased sediment flux due to uplift of the hinterland. The observed stratigraphic patterns support predominant tectonic control on sedimentation in the Camaná Basin and the established stratigraphic framework provides an essential baseline for future correlations of the Cenozoic sedimentation in the forearc area of the Central Andes.

Seismic stratigraphy of the Messinian Nile Delta coastal plain: Recognition of the fluvial Regressive Systems Tract and its potential for hydrocarbon exploration

The Upper Miocene strata of the Nile Delta (Egypt) record the dramatic events of the Messinian opening and closing of the Mediterranean Sea. Furthermore, the complexity of the associated stratigraphic relations within the Lower Messinian Qawasim and the Upper Messinian Abu Madi formations contribute to present challenges in their effective gas exploration and production. Through recognition and delineation of the Regressive Systems Tract on the Messinian Nile coastal plain, a new understanding of fluvial responses to changes in sea level as observed in the sedimentary record and to its optimal hydrocarbon reservoir exploration may be obtained.Seismic stratigraphic analysis of 1800km of 2D seismic with eighteen boreholes of these two formations reveals the dynamic interplay between fluvial downcutting and fill as a response to global and Mediterranean sea level oscillations. The observation of fluvial channel terraces on the delta plain during downstepping relative sea level falls reveal correlatable RST (Regressive Systems Tract) terraces incised by LST channels and then subsequent flooding by TST delta incised back stepping channel fills culminating in HST (High Systems Tract) deposition. While the Qawasim fluvial downcutting and fill are in response to global sea level changes, the Abu Madi responses are antithetic to global sea level changes.Specifically, the RST channels of the Qawasim Formation are represented by fluvial terraces of lateral accretion units in response to downward stepping base levels owing to a slowly falling global sea level base and shale channel fill during a global sea level rise. The RST channels of the Abu Madi Formation are represented by incised valley fluvial channels which eroded most of Qawasim Formation deposits especially in the northward of Nile Delta in response to rapidly falling local sea level as the Mediterranean Sea was cut off from the global ocean then are capped by a rapid transgression when the Mediterranean suddenly reopened. The RST and LST in both the Qawasim and Abu Madi fluvial channels exhibit potentially good reservoir continuity, sand quality, and charging potential. Productive boreholes confirm the hydrocarbon potential of the RST and LST in the Qawasim and the LST in the Abu Madi.Proper understanding and interpretation of the coastal fluvial RST stages on sand deposition as a response to sea level changes are a key issue in assessing Messinian reservoir quality of the Nile Delta and for coastal fluvial deposits elsewhere in the world.

Tectonic and climate control of oil shale deposition in the Upper Cretaceous Qingshankou Formation (Songliao Basin, NE China)

Oil shales were deposited in the Songliao Basin (NE China) during the Upper Cretaceous period, representing excellent hydrocarbon source rocks. High organic matter (OM) contents, a predominance of type-I kerogen, and a low maturity of OM in the oil shales are indicated by bulk geochemical parameters and biomarker data. A major contribution of aquatic organisms and minor inputs from terrigenous land plants to OM input are indicated by n-alkane distribution patterns, composition of steroids, and organic macerals. Strongly reducing bottom water conditions during the deposition of the oil shale sequences are indicated by low pristane/phytane ratios, high C14-aryl-isoprenoid contents, homohopane distribution patterns, and high V/Ni ratios. Enhanced salinity stratification with mesosaline and alkaline bottom waters during deposition of the oil shales are indicated by high gammacerane index values, low MTTC ratios, high β-carotene contents, low TOC/S ratios, and high Sr/Ba ratios. The stratified water column with anoxic conditions in the bottom water enhanced preservation of OM. Moderate input of detrital minerals during the deposition of the oil shale sequences is reflected by titanium concentrations. In this study, environmental conditions in the paleo-lake leading to OM accumulation in the sediments are related to sequence stratigraphy governed by climate and tectonics. The first Member of the Qingshankou Formation (K2qn1) in the Songliao Basin, containing the oil shale sequence, encompasses a third-order sequence that can be divided into three system tracts (transgressive system tract—TST, highstand system tract—HST, and regressive system tract—RST). Enrichment of OM changed from low values during TST-I to high-moderate values during TST-II/III and HST-I/II. Low OM enrichment occurs during RST-I and RST-II. Therefore, the highest enrichment of OM in the sediments is related to stages of mid-late TST and early HST.

Significance of Terrace Deposits in Fluvial Sequence Stratigraphy

The terrace deposits in a river valley are key records to the research of fluvial sequence stratigraphy. Terrace deposits and the basal sequence boundary comprise the half-cycle of base level fall, and the fluvial infillings belong to the half-cycle of base level rise. Thus, terrace deposits and the basal sequence boundary are part of the regressive systems tract, and should be separated from the transgressive or lowstand systems tracts in previously published littoral fluvial sequence stratigraphic models. In addition, in the upstream portions of the fluvial system where sea level cannot reach, the fluvial sequence is influenced by tectonism and/or climate. The terrace deposits can provide specific information about the main controlling factor (e.g., tectonism or climate) and its varying pattern during the half-cycle of base level fall. Because the two half-cycles of base level fall and rise are at the same stratigraphic levels and belong to the same base level cycle, it is possible to research the controlling factor and its varying pattern during the rising half-cycle, which will be significant to an inland fluvial sequence stratigraphic model. Finally, the authors assert that seeking isochronous parasequence correlation based on 4-division models (4 different systems tracts), along with the blend of sedimentology and geomorphology and diversification of models based on different controlling factors will collectively produce more robust-interpretations of fluvial sequence stratigraphy in the future.

Architectural characterization of a delta-front reservoir analogue combining Ground Penetrating Radar and Electrical Resistivity Tomography: Roda Sandstone (Lower Eocene, Graus-Tremp basin, Spain)

Three-dimensional reconstruction of reservoir analogues can be improved combining data from different geophysical methods. Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT) data are valuable tools, since they provide subsurface information from internal architecture and facies distribution of sedimentary rock bodies, enabling the upgrading of depositional models and heterogeneity reconstruction. The Lower Eocene Roda Sandstone is a well-known deltaic complex widely studied as a reservoir analogue that displays a series of sandstone wedges with a general NE to SW progradational trend. To provide a better understanding of internal heterogeneity of a 10m-thick progradational delta-front sandstone unit, 3D GPR data were acquired. In addition, common midpoints (CMP) to measure the sandstone subsoil velocity, test profiles with different frequency antennas (25, 50 and 100MHz) and topographic data for subsequent correction in the geophysical data were also obtained. Three ERT profiles were also acquired to further constrain GPR analysis. These geophysical results illustrate the geometry of reservoir analogue heterogeneities both depositional and diagenetic in nature, improving and complementing previous outcrop-derived data. GPR interpretation using radar stratigraphy principles and attributes analysis provided: 1) tridimensional geometry of major stratigraphic surfaces that define four units in the GPR Prism, 2) image the internal architecture of the units and their statistical study of azimuth and dips, useful for a quick determination of paleocurrent directions. These results were used to define the depositional architecture of the progradational sandbody that shows an arrangement in very-high-frequency sequences characterized by clockwise paleocurrent variations and decrease of the sedimentary flow, similar to those observed at a greater scale in the same system. This high-frequency sequential arrangement has been attributed to the autocyclic dynamics of a supply-dominated delta-front where fluvial and tidal currents are in competition. The resistivity models enhanced the viewing of reservoir quality associated with cement distribution caused by depositional and early diagenetic processes related to the development of transgressive and regressive systems tracts in high-frequency sequences.

Organic matter accumulation in the oil shale- and coal-bearing Huadian Basin (Eocene; NE China)

The Huadian Basin, located in northeastern China, is a fault-controlled basin filled by Eocene non-marine sediments assigned to the Huadian Formation. The formation is subdivided from bottom to top into three members: Pyrite Member, Oil Shale Member, and Carbonaceous Shale Member. Using bulk geochemical data from borehole Hd3 and core descriptions from a high number of wells, the factors controlling organic matter accumulation have been evaluated.The organic matter content of the Pyrite Member is relatively low (average TOC: 0.9wt.%). Mudstones deposited in shallow lacustrine environments contain between 1 and 2wt.% TOC (max. 6wt.%) and a kerogen Type II (HI 400–600mg HC/g TOC). An arid climate prevented the accumulation of thick coal.The overlying Oil Shale Member contains 13 oil shale layers, which are mined underground. The Oil Shale Member has been interpreted as a 3rd order sequence. Significant differences exist between oil shales deposited in different systems tracts: 2-m-thick coaly oil shale of low-quality (oil yield 3.5wt.%) developed in the lowstand systems tract. Oil shale, up to 7m thick, of moderate quality (oil yield 4.1–8.0wt.%) was deposited during the transgressive systems tract (TST). Thinner (<3m) high quality oil shale (oil yield 6.4–19.8wt.%) is found in the highstand systems tract (HST) and at the base of the regressive systems tract. The lateral extent of the oil shale layers reaches a maximum in the upper TST and the lower HST. The high number of oil shale layers deposited in an overall deep lacustrine environment notifies frequent changes in base level, controlled by tectonic movements, short-term climatic cycles, or cycles in organic matter production.The Carbonaceous Shale Member representing the balanced-fill to overfilled stage of basin evolution hosts economic coal seams, which are occasionally accompanied by shallow lacustrine shales with abundant hydrogen-rich organic matter. Otherwise non-coal layers are typically low in organic matter (average TOC: 0.9wt.%).In contrast to the Huadian Basin, a very thick coal seam overlain by a single oil shale layer more than 100m thick developed in the Eocene Fushun Basin. This indicates major differences in the evolution of basins with similar tectonic setting and age.

Incised valleys and tidal seaways: the example of the Miocene Uzès-Castillon basin, SE France

Abstract The sedimentology and stratigraphy of the Miocene deposits of the Uzès-Castillon basin are revisited. This basin, located in SE France at the junction between the perialpine foreland basin and the W Mediterranean margin, sits in a syncline that formed during the latest Cretaceous Pyrenean tectonic phase. It records the succession of shallow-water mixed siliciclastic to dominantly bioclastic carbonates that alternate with shelf marls. The clastic carbonates were accumulated as a stack of subtidal dunes and bars that were formed by tidal currents channelized in a seaway following the syncline axis. The marls indicate deposition in more protected and locally deeper waters, as interfluves of the sea-way were drowned. Borehole data suggest that the marls are encased over tens of meters in the underlying bioclastic deposits, thus pointing to incised-valley fills. Contrarily to what is observed in the main Rhodanian basin, the molassic deposits are not restricted to transgressive systems tracts but may also correspond to forced regressive systems tracts. Four depositional sequences are identified, ranging from the Lower Burdigalian to the Langhian. They constitute a transgressive-regressive sequence set which might express the uplift of the area starting in the Late Burdigalian. This is consistent with the incision of the Middle Miocene deposits into the Lower Miocene ones as observed in other places of the main Rhodanian basin.