Basin Subsidence Rates Research Articles

Petrographic characteristics and palaeoenvironment of the Permian coal resources of the Barapukuria and Dighipara Basins, Bangladesh

Abstract Twenty-seven coal samples from the Barapukuria and Dighipara Coal Basins of Bangladesh were analysed for their maceral content, petrographic characteristics and vitrinite reflectance. The most predominant maceral was the inertinite group (mean 40%), followed by vitrinite (mean 31%) and liptinite (mean 22%), with considerable amounts of mineral matter (mean 7%). Semifusinite, fusinite and inertodetrinite were the most common macerals of the inertinite group. Collotelinite, collodetrinite and vitrodetrinite were the most frequently found macerals of the vitrinite group, while sporinite and cutinite were the most common in the liptinite group. Clay minerals occurred in higher concentrations than other minerals. The measured vitrinite reflectance values (%Ro) ranged from 0.71 to 0.80, indicating a high volatile bituminous B ranking. Facies modelling using maceral composition and maceral indices suggested an environment of forest swamps with alternating oxic–anoxic depositional conditions. Microlithotype-dependent depositional modelling indicated evolution in limno-telmatic zones under fluvio-lacustrine control, accompanied by the development of upper to lower deltaic plain conditions. A terrestrial origin with dry forest to piedmont plain conditions was suggested by the Gelification Index (GI) and Tissue Preservation Index (TPI). The lateral variation of the measured TPI values indicated an increase in the rate of basin subsidence. A cross-plot of the Ground Water Index (GWI) vs. the Vegetation Index (VI) suggested mires under ombotrophic to mesotrophic hydrogeological conditions containing herbaceous plants.

River-gulf system—the major location of marine source rock formation

Petroleum was generated from sedimentary rocks. The world’s oldest oil source rock so far was found in Proterozoic rocks. Since then, 73% to 81% of the earth’s surface has been covered with sedimentary rocks. However, only quite a limited area is rich in oil and gas. It is found that source rocks have controlled oil and gas distribution, and they are mainly formed in two systems: (1) river-lake systems and (2) river-gulf systems. Phytoplankton is an important source of kerogen, the blooming of which is strongly dependent on nutrients. Rivers are the major nutrient provider for basins. Rivers around lakes and an undercompensation (where the sedimentation rate is less than the rate of basin subsidence) environment provide favorable conditions for phytoplankton blooming in lakes. Gulfs are usually located at the estuary of big rivers, characterized by restricted current circulation and exchange with the open sea, which benefit maintaining the nutrient density, phytoplankton levels and organic matter preservation. The river-gulf system is the most favorable place for marine source rock development. Most of the world famous marine petroleum-rich provinces are developed from river-gulf systems in geological history, such as the Persian Gulf Basin, Siberian Basin, Caspian Basin, North Sea, Sirte Basin, Nigerian Basin, Kwanza Basin, Gulf of Mexico, Maracaibo Basin and the Eastern Venezuelan Basin.

Stratigraphic Architecture of An Experimental Basin With Interacting Drainages

Abstract The stratigraphic architecture of intracontinental rift basins is defined by a dynamic relationship between depositional processes associated with the basin floor and flanking tributary streams. The resulting depositional belts are sensitive to a variety of factors, including basin geometry, subsidence rate, and sediment discharge. The Experimental EarthScape run in 2006 (XES06) examined the development of fluvial morphology and alluvial architecture as a function of subsidence and sediment flux in an experimental basin based on the form of a simple half graben. Sediments from tributary drainages were introduced into the axial stream through toe cutting and realignment of transverse drainage courses to parallel the prevailing axial-flow direction. Transverse sediment contributions to the axial stream were almost equally apportioned over a wide range of sediment discharges tested in the experiments. Sediment tracers showed a larger contribution of footwall-derived sediment into the axial belt, probably due to more frequent and aggressive toe cutting by axial streams. Changes in the axial–transverse deposit boundary to external forcing (by subsidence and sediment discharge), and relatively rapid intrastage stabilization of the depositional belts, resembles the large-scale self-organization observed in moving boundaries that define the morphology of fluviodeltaic systems. Basin sedimentation was matched to subsidence in order to maintain a constant base level, which made the location and width of the axial belt sensitive to the relative sediment fluxes from the transverse systems, rather than the axis of maximum subsidence. The asymmetrical subsidence pattern and the transverse-fan morphology influenced the preservation of sedimentary sequences. Stage-bounding stratigraphic lacunae were well preserved in the hanging-wall succession, providing a reliable record of basin development.

Multiple controls on rift basin sedimentation in volcanic settings: Insights from the anatomy of a small Early Cretaceous basin in the Yanshan belt, northern North China

This paper deals with a small continental rift basin in a volcanic setting and tries to decipher potential controls on its synrift sedimentation. The Luanping basin, which is a well-exposed Early Cretaceous rift basin in the Yanshan belt on the northern periphery of the North China block, was chosen as a case study. We show that extensive and vigorous volcanism took place just prior to the onset of basin formation and continued into a synrift period. Basin fills consist predominantly of lacustrine, fan-delta, braid-delta, and volcaniclastic deposits. Lacustrine facies are composed mostly of deep-lake deposits that appear to have been established soon after basin initiation. Fan-delta systems developed along two high-angle border faults, the master northern Hongqi fault and the secondary western Xiaobaiqi fault. Fan-delta fronts were built up primarily by gravelly and sandy debrites and turbidites. Braid-delta deposits are restricted to the eastern corner of the basin and are characterized by an aggregation of braid-plain conglomeratic deposits. Underwater extrusions of magma and pyroclastic flows are inferred from the presence of volcanic breccias, ignimbrites, andesitic pillows, and peperites, which are enclosed by host lacustrine deposits. Deep-lake and fan-delta systems persisted throughout the synrift period, indicating a rapid subsidence rate, with both adequate sediment and water supply. The high-angle border faults are thought to have played a critical role in creating large accommodation space, and simultaneous displacements of the Hongqi and Xiaobaiqi faults led to the localization of a major depocenter in the western part of the basin. One-dimensional backstripping analysis of three stratigraphic sections shows that the Luanping basin experienced marked synrift tectonic subsidence up to 2 km at a subsidence rate close to 0.2 mm yr −1 . We propose that the high rate of basin subsidence might have been caused mainly by left-lateral transtensional faulting and was enhanced by the superposition of basement downsag induced by underlying magma withdrawal. A predominance of volcanic particles in both debrites and sandstones suggests that source areas were erodible volcanic edifices. A humid paleoclimate is inferred, which not only provided enough water supply, but also promoted weathering of volcanic rocks in source areas, thus maintaining both the deep-lake environment and sediment influx. We conclude that relatively small and isolated rift basins in volcanic settings can experience both rapid subsidence and receive thick lacustrine deposits if they are under the combined control of favorable structure, climate, and magmatism. The model proposed here is believed to be applicable to other rift basins in similar volcano-tectonic settings.

Controls on marine–erg margin cycle variability: aeolian–marine interaction in the mid‐Cretaceous Iberian Desert System, Spain

AbstractThe interaction between aeolian dunes of the Iberian erg and Tethys waters during the mid‐Cretaceous led to a variety of sedimentary facies associations such as subtidal deposits, aeolian dunes, playa lakes, coastal lakes with tidal creeks, and marshes and lagoonal embayments with tide‐influenced delta deposits. Facies associations are organized in several stacked cycles. Every cycle is defined by a sand‐drift surface separating playa lake deposits below from aeolian dune deposits above, followed by a transgressive surface separating aeolian deposits below from shallow marine deposits above. The latter are covered by playa lake deposits and finally topped by the next sand‐drift surface. Similar marine–erg margin cycles have been explained previously in terms of high‐order relative sea‐level variations (normally controlled by glacioeustasy). The studied erg margin developed during the mid‐Cretaceous which is considered to be the archetypal example of a polar ice‐free greenhouse period. This manuscript presents an alternative explanation for the cycles as caused by climate‐induced variations in the aeolian sediment supply. In this scenario, orbitally induced latitudinal shifts of the boundary between climate belts led to alternating periods of increased and decreased precipitation in the highland catchments of the back‐erg system (Variscan Iberian Massif). When climate belts shifted to lower latitudes, back‐erg highlands were under the influence of the Northern Warm Humid Belt. While arid conditions prevailed in the lowland central‐erg, increased precipitation in the highlands and the consequent recharge of ground water led to a rise of the phreatic level in the erg system; that diminished wind erosion and windblown sediment input to the fore‐erg, so that the desert margin contracted. With ongoing basin subsidence this favoured the transgression. The increased desert‐ground water flux favoured permanent coastal lakes in the fore‐erg margin and the local development of vegetation. In places where such lakes (lagoons) were connected to the sea, tidal channels were active, as seen nowadays along the desert coast of Qatar (Persian Gulf). When climate belts moved to higher latitudes, the catchment areas in the back‐erg Iberian Massif were under the influence of the Northern Hot Arid belt and a decrease of precipitation led to a drop of the phreatic level, allowing deflation of dunes and exposed wadi channel floors, and the formation of desert pavements and deflation lags in the back‐erg area; this favoured the import of large volumes of windblown sand and dust, forcing progradation of the erg and consequently a retreat of the coastline. The sand fraction accumulated in climbing aeolian dunes and dust was trapped in extensive playa lake systems. Another long‐term allocyclic control is formed by active extensional tectonics that enhanced the creation of accommodation space, especially in the first cycle. A high ground water table sustained by subsurface water supply from the Variscan Iberian Massif generated coastal fresh/brackish lakes in which tide‐influenced meandering channels and salt marshes developed. Erg margin cycles thin upward in response to a decrease of the rate of basin subsidence, suggesting that transgressions led to deep erosion of the underlying aeolian dune sands.

Geochemistry of Permo-Triassic mudstone of the Satpura Gondwana basin, central India: Clues for provenance

Major and trace element data of the Permo-Triassic mudstones from the intracratonic Satpura Gondwana basin, central India have been used to investigate provenance. The Satpura succession (~ 5 km thick) unconformably overlies the Precambrian basement. Sediment dispersal pattern suggests that the Precambrian rocks straddling the southern margin of the Satpura basin were the most probable source for the sediments. The lowermost unit of the Satpura succession comprises glacio-marine and glacio-fluvial deposits. The rest of the succession largely represents a variety of fluvial depositional systems with some records of fluvio-deltaic and fluvio-lacustrine sedimentation under a climatic spectrum of temperate, humid to warm, semi-arid. The present study is confined to the lower six formations namely Talchir, Barakar, Motur, Bijori, Pachmarhi and Denwa, arranged in that order from bottom to top. The oldest rocks of this sequence, the Talchir Formation, are enriched in mobile elements such as Na, Ca and Mg, depleted in alumina and have high ICV (0.93–1.29) and lower CIA values (61.82–74.89) compared to those of the younger mudstones. K 2O/Al 2O 3 ratios of the Talchir mudstones (0.24–0.28) are higher than the younger mudstones in this sequence. These results suggest that the Talchir mudstones were weathered less intensely and are thus more immature than the younger mudstones. This is consistent with the prevailing cold climate and relatively higher rate of basin subsidence. In contrast, the majority of the mudstones from the younger formations are depleted in mobile elements, have relatively low ICV (0.18–0.87) and K 2O/Al 2O 3 values (0.07–0.26), higher CIA values (76.99–92.86), and appear compositionally more mature reflecting moderate to high intensity source rock weathering. Among them, the Barakar mudstones likely have been more intensely weathered than mudstones from any of the other formations. The trace element compositions and ratios are consistent with most mudstones being derived from a felsic source with some mudstones being derived from a more mafic source. For example, La/Sc (0.805 and 0.114), La/Th (6.245, 5.072, 7.418, 6.245, and 5.072) and Eu/Eu* (1.431, 0.868, and 0.805) of some mudstones indicate mafic source. Bivariate plot of Th/Sc and Zr/Sc indicates considerable enrichment of zircon that suggests recycling from meta-sedimentary rocks. Prominent negative Eu anomaly, high LREE/HREE, and flat HREE pattern reflect sediment derivation from predominantly felsic rocks of the old upper continental crust. SiO 2/Al 2O 3 versus K 2O/Na 2O plot for the mudstones suggests that they formed in a passive margin. Also, total REE content of most of the mudstones is conformable with passive margin tectonic setting and craton interior type of provenance. Plotting in La–Th–Sc, Th–Sc–Zr/10 and La/Sc versus Ti/Zr diagrams largely indicates continental margin settings for majority of the mudstones but fails to differentiate between active and passive continental margins.

The contribution of peat compaction to total basin subsidence: implications for the provision of accommodation space in organic-rich deltas

ABSTRACT Provision of accommodation space for aggradation in Holocene deltaic basins is usually ascribed to eustatic sea‐level rise and/or land subsidence due to isostasy, tectonics or sediment compaction. Whereas many Holocene deltas contain peat, the relative contribution of peat compaction to total subsidence has not yet been quantified from field data covering an entire delta. Subsidence due to peat compaction potentially influences temporal and spatial sedimentation patterns, and therefore alluvial architecture. Quantification of the amount and rate of peat compaction was done based on (1) estimates of the initial dry bulk density of peat, derived from a relation between dry bulk density and organic‐matter content of uncompacted peat samples and (2) radiocarbon‐dated basal peat used to reconstruct initial levels of peat formation of currently subsided peat samples. In the Rhine‐Meuse delta, peat compaction has contributed considerably to total basin subsidence. Depending on the thickness of the compressible sequence, weight of the overburden and organic‐matter content of peat, subsidence of up to approximately 3 m in a 10‐m thick Holocene sequence has been calculated. Calculated local subsidence rates of peat levels are up to 0.6 mm year−1, averaged over millennia, which are twice the estimated Holocene‐averaged basin subsidence rates of 0.1–0.3 mm year−1 in the study area. Higher rates of subsidence due to compaction, on the order of a few mm year−1, occur over decades to centuries, following a substantial increase in effective stress caused by sediment loading. Without such an increase in effective stress, peat layers may accumulate for thousands of years with little compaction. Thus, the contribution of peat compaction to total delta subsidence is variable in time. Locally, up to 40% of total Holocene accommodation space has been provided by peat compaction. Implications of the large amount of accommodation space created by peat compaction in deltaic basins are: (1) increased sediment trap efficiency in deltas, which decelerates delta progradation and enhances the formation of relatively thick clastic sequences and (2) enhanced local formation of thick natural levees by renewing existing accommodation space.

Mudstone compaction curves in basin modelling: a study of Mesozoic and Cenozoic Sediments in the northern North Sea

ABSTRACTBasin modelling studies are carried out in order to understand the basin evolution and palaeotemperature history of sedimentary basins. The results of basin modelling are sensitive to changes in the physical properties of the rocks in the sedimentary sequences. The rate of basin subsidence depends, to a large extent, on the density of the sedimentary column, which is largely dependent on the porosity and therefore on the rate of compaction. This study has tested the sensitivity of varying porosity/depth curves and related thermal conductivities for the Cenozoic succession along a cross‐section in the northern North Sea basin, offshore Norway. End‐member porosity/depth curves, assuming clay with smectite and kaolinite properties, are compared with a standard compaction curve for shale normally applied to the North Sea. Using these alternate relationships, basin geometries of the Cenozoic succession may vary up to 15% from those predicted using the standard compaction curve. Isostatic subsidence along the cross‐section varies 2.3–4.6% between the two end‐member cases. This leads to a 3–8% difference in tectonic subsidence, with maximum values in the basin centre. Owing to this, the estimated stretching factors vary up to 7.8%, which further gives rise to a maximum difference in heat flow of more than 8.5% in the basin centre. The modelled temperatures for an Upper Jurassic source rock show a deviation of more than 20 °C at present dependent on the thermal conductivity properties in the post‐rift succession. This will influence the modelled hydrocarbon generation history of the basin, which is an essential output from basin modelling analysis. Results from the northern North Sea have shown that varying compaction trends in sediments with varying thermal properties are important parameters to constrain when analysing sedimentary basins.

Seismic stratigraphy of the western South Korea Plateau, East Sea: implications for tectonic history and sequence development during back-arc evolution

The western South Korea Plateau in the East Sea (Sea of Japan) is occupied by rifted continental fragments formed in association with the early phase of back-arc opening. The present study focuses on the seismic stratigraphy of the sedimentary succession and the underlying acoustic basement in this region, based on closely spaced multichannel seismic reflection profiles. The sedimentary succession occurs mainly within a series of subparallel basement troughs (grabens or half grabens) bounded by faulted continental blocks (horsts) or volcanic ridges, and commonly floored by extrusive volcanic rocks showing hyperbolic reflectors. These features are strongly suggestive of continental rifting accompanied by normal faulting, volcanic activity and high rates of basin subsidence. The sedimentary succession can be subdivided into four seismic units. Unit 1 is characterized by short and irregular high-amplitude reflectors and interpreted as a syn-rift deposit consisting of a non-marine volcanics/sediment complex in topographic lows. Units 2 and 3 formed in an open marine environment during the Middle Miocene to Early Pliocene, characterized by an onlap-fill and later draping marine sedimentary succession dominantly composed of hemipelagic sediments and turbidites with frequent intercalation of mass-flow deposits. Along the western margin of the plateau, these units were deformed under a compressional regime in the Early Pliocene, associated with the back-arc closing phase. Unit 4 (deposited since the Early Pliocene) comprises hemipelagic sediments and turbidites with evidence of sporadic slides/slumps.

Bacterial methane in the Atzbach-Schwanenstadt gas field (upper Austrian Molasse Basin), Part II: Retracing gas generation and filling history by mass balancing of organic carbon conversion applying hydrogeochemical modelling

In the Austrian Molasse Basin bacterial methane gas accumulations occur in Upper Oligocene to early Miocene deepwater clastic sediments. Gas is produced from the Upper Puchkirchen Formation (Aquitanian) in the Atzbach-Schwanenstadt gas field. The diagenetic pathway of the reservoir cements was controlled by the conversion of metabolizable organic carbon incorporated in the fine-grained sediments. These pathways have been retraced by hydrogeochemical modelling the redox-conversion of metabolizable organic carbon. This approach unravels the relative timing of the coupled processes gas generation and precipitation/dissolution of cements. The labile organic material was decomposed by fermentation and subsequent CO 2 reduction. CO 2 released via these reactions was nearly completely fixed as carbonate cement. Methane generated during early diagenesis (10 s to max., 100 m sediment depth) was dissolved in pore water until saturation. After exsolution as a free gas phase, methane could have been fixed as hydrate within pore space due to the prevailing paleoceanographic conditions (sediment/water interface ∼1000 mbsl; ∼4 °C). The temperature increase in consequence of the rapid basin subsidence and high sedimentation rates led to the decomposition of the hydrates and to charging of the reservoir by methane still during the Aquitanian. A further consequence of hydrate decomposition was dilution of pore water salinity. According to the results, the presented approach offers (a) a tool to retrace the bacterial methane potential by analysis of diagenetic cement as a quantitative indicator, and (b) to predict the interaction between porosity development and reservoir charging by methane. Additionally, (c) gas field water salinity and hydrochemistry may be applied in similar architectural elements of deepwater channels as tracers for fossil gas hydrate formation as low chloride concentrations are result of sediment compaction and dilution by pure H 2O due to gas hydrate dissociation.

Bacterial methane in the Atzbach-Schwanenstadt gas field (Upper Austrian Molasse Basin), Part I: Geology

Bacterial methane gas accumulations occur in Upper Oligocene to Early Miocene clastic deepwater sediments in the Austrian Molasse Basin. Methane gas is produced from the Upper Puchkirchen Fm. (Aquitanian) in the Atzbach-Schwanenstadt gas field which is one of the largest gas fields in this basin. The bacterial gas is composed of >97 vol% methane ( δ 13C ∼ −62‰, δD ∼ −200‰). Connate pore water below the gas–water contact is characterized by low salinity (cCl −: ca. 0.25 mol/kgw or 8900 mg/kgw). The top of the main reservoir zone A4 is approximately 1600 m subsurface. Thickness of reservoir intervals in the A4 sands (the main reservoir) is variable and ranges from 8 to 30 m with decreasing thickness to the north. The porosity of the sand ranges from 13% to 20%, permeability from 6 mD to 70 mD. The reservoir temperature is 63 °C. Reservoir rocks of this field wedge out to the north and represent dam break-through (splay) sediment. This reservoir architecture enabled early gas accumulation in a stratigraphic trap. The source rocks and reservoir rocks are intimately connected. Claystone layers intercalate and seal the reservoir sediments. These fine-grained sediments with potential source rock characteristics contain immature organic matter of kerogen types II–III. The TOC contents of these fine-grained sediments vary from 0.34 to 0.94 wt.%. The cement inventory of the source and reservoir rocks is characteristic for diagenetic pathways of organic-rich sediments. Pyrite is preserved in the sediments as the first precipitation product due to rapidly developing anoxic pore water conditions. A following dolomite precipitation/dissolution phase was replaced by precipitation of calcite, ankerite and siderite. A last cement phase is chlorite. The about 700 m thick Upper Puchkirchen Fm. was deposited during a time interval of about 2.6 Ma (Aquitanian) in a deep-sea fan environment (water depth ≥1000 m, bottom water temperature of about 4 °C). Free gas phases may have been trapped as gas hydrate. Due to basin subsidence and high sedimentation rates, hydrates have been decomposed below the base of the gas hydrate stability zone (∼200–40 mbsf) still during the Aquitanian and, thus, still during or shortly after deposition of the Upper Puchkirchen Fm.

Depositional facies, architecture and environments of the Sihwa Formation (Lower Cretaceous), mid-west Korea with special reference to dinosaur eggs

This paper presents detailed facies and architectural analyses and palaeoenvironmental reconstruction of the Sihwa Formation (Lower Cretaceous), mid-west Korea, which comprises an about 3-km-thick non-marine succession containing abundant dinosaur eggshells. Based on constituent facies, bedset geometry, stacking pattern, and bounding surface characteristics, the entire succession can be classified into three architectural elements. Element I occurs along the basin margin and shows a monotonous stacking of tabular or crudely stratified conglomeratic units. It represents alluvial-fan deposits of debris-flow-dominated fan and sheetflood-dominated fan. Element II is characterized by multi-storey, sheet or upward-widening, conglomeratic channel-fills whose maximum thickness exceeds 1.5 m. Each channel-fill unit is encased within red–brown silty sandstones of Element III with sharp erosional bases but diffuse gradational upper boundaries. It consists generally of (1) cut-and-fill deposit (trough cross-stratified or openwork conglomerate) in the lower part and (2) composite low-relief bar deposit (lenticular conglomerate and stratified gravelly sandstone) in the upper part. Shallowness of each cut-and-fill unit, absence of fining-upward lateral accretion package and the predominance of simple-bar deposit collectively suggest deposition from ephemeral braided streams. Element III typically shows a fining-upward stacking of (1) single- or multi-storey small-scale (<1.5 m thick) channel fills with limited lateral extent of less than 15 m, (2) poorly sorted, graded and diffusely bounded silty conglomerates or gravelly siltstones with discontinuous gravel sheets and pockets and (3) homogeneous or graded, red–brown fine-grained deposits with calcretes and burrows in ascending order. Element III is interpreted as channel-margin to floodplain, including crevasse channel fill, crevasse splay and floodplain fines. The entire sequence of the Sihwa Formation can be divided into the alluvial-fan and terminal-fan successions. The alluvial-fan succession displays a progradational stacking pattern and indicates a low rate of basin subsidence in the initial phase of rifting. The upper terminal-fan succession consists of proximal braided stream and distal floodplain deposits in the western and central parts of the basin and is characterized by an axial dispersal pattern and an aggradational stacking. It suggests rapid subsidence of the basin floor during the main phase of rifting. The asymmetrical cross-basin distribution of each architectural element reflects a half-graben structure of the basin with steep-gradient fault-bounded eastern margin (footwall block) and gently sloped, flexural western margin (hangingwall block). The predominance of ephemeral braided-stream deposits along with red–brown fine-grained floodplain deposits with common calcretes indicates arid to semi-arid palaeoclimates. Approximately 140 dinosaur eggs (Faveoloolithidae and Dendroolithidae) were identified mainly from the (gravelly) siltstones and small-scale channel fills of Element III deposits and partly from the cut-and-fill conglomerates of Element II deposits. The eggs commonly retain their original oval shape but are invariably breached and stuffed with the substrate of gravels and silt. They are either isolated or clustered, forming a circular concentration in plan view. The abundant yield of eggs, more than 20 eggs in 5 separate nests from a single depositional unit, suggests a dense population of the parental dinosaurs. The repetitive occurrence in many stratigraphic horizons reflects site preference as a nesting habitat of the near-channel or abandoned channel areas.

Regressive and transgressive cycles in a rift-basin: Depositional model and sedimentary partitioning of the Middle Jurassic Hugin Formation, Southern Viking Graben, North Sea

The Jurassic Hugin Formation consists of shallow-marine sandstones that belong to a significant hydrocarbon reservoir in the Sleipner area in the Norwegian North Sea. The formation encompasses coarsening-upward units of mouth bar and shoreface facies, interpreted to record delta outbuilding during regression; and fining-upward units with tidal channel, dune, and tidal flat facies interpreted as part of an estuary environment during transgression. The correlations reveal that the studied part of the Hugin Formation consists of 8 sequences, each with a transgressive and a regressive unit, representing the transgressive systems tract and the highstand systems tract respectively. The sequences are stacked retrogradationally landward as a result of rapid tectonic subsidence and rifting of the Viking Graben. Rifting led to the development of an elongate graben where tidal currents were amplified, wave-action damped and longshore drift (as sediments supply) reduced or absent. Lowstand and forced regressive systems tracts are not identified, and their absence is interpreted to reflect suppression of relative sea level falls in a rapidly subsiding basin where the basin subsidence rate outpaced any potential fall in eustatic sea level. Through facies interpretation and sequence-stratigraphic correlations between wells, these regressive and transgressive units are shown to exhibit characteristic thickness trends in the form of sigmoidal-shaped wedges, stacked in an offset manner in a landward to basinward orientation. These thickness trends illustrate sediment partitioning within the sequences and are explained by the relationship between accommodation versus sediment supply in terms of mass-balance. During regression, the focus of sedimentation was pushed basinward, and during transgression it was pushed landward as sediments were trapped there. The mapping of these sequence-stratigraphic units serves as input to reservoir models and to help increase recovery and identify new exploration targets.

Tectonic and climatic controls of alluvial-fan size and source-catchment relief

The geometries of alluvial fans and their upland catchments subject to known rates of basin subsidence V and upland precipitation P , respectively, are compared with predictions from a quantitative analysis of an idealized landscape. We find that the dimensionless ratio V / P explains systematic trends in relative fan size and source catchment relief previously reported from environmentally wide-ranging regions worldwide, and contributes to the interpretation of recently reported observations of fan-like phenomena on Mars.

Organic petrology of Paleocene Marcelina Formation coals, Paso Diablo mine, western Venezuela: Tectonic controls on coal type

Abstract About 7 Mt of high volatile bituminous coal are produced annually from the four coal zones of the Upper Paleocene Marcelina Formation at the Paso Diablo open-pit mine of western Venezuela. As part of an ongoing coal quality study, we have characterized twenty-two coal channel samples from the mine using organic petrology techniques. Samples also were analyzed for proximate–ultimate parameters, forms of sulfur, free swelling index, ash fusion temperatures, and calorific value. Six of the samples represent incremental benches across the 12–13 m thick No. 4 bed, the stratigraphically lowest mined coal, which is also mined at the 10 km distant Mina Norte open-pit. Organic content of the No. 4 bed indicates an upward increase of woody vegetation and/or greater preservation of organic material throughout the life of the original mire(s). An upward increase in telovitrinite and corresponding decrease in detrovitrinite and inertinite illustrate this trend. In contrast, stratigraphically higher coal groups generally exhibit a ‘dulling upward’ trend. The generally high inertinite content, and low ash yield and sulfur content, suggest that the Paso Diablo coals were deposited in rain-fed raised mires, protected from clastic input and subjected to frequent oxidation and/or moisture stress. However, the two thinnest coal beds (both 0.7 m thick) are each characterized by lower inertinite and higher telovitrinite content relative to the rest of Paso Diablo coal beds, indicative of less well-established raised mire environments prior to drowning. Foreland basin Paleocene coals of western Venezuela, including the Paso Diablo deposit and time-correlative coal deposits of the Tachira and Merida Andes, are characterized by high inertinite and consistently lower ash and sulfur relative to Eocene and younger coals of the area. We interpret these age-delimited coal quality characteristics to be due to water availability as a function of the tectonic control of subsidence rate. It is postulated that slower subsidence rates dominated during the Paleocene while greater foreland basin subsidence rates during the Eocene–Miocene resulted from the loading of nappe thrust sheets as part of the main construction phases of the Andean orogen. South-southeastward advance and emplacement of the Lara nappes during the oblique transpressive collision of the Caribbean and South American tectonic plates in the Paleocene was further removed from the sites of peat deposition, resulting in slower subsidence rates. Slower subsidence in the Paleocene may have favored the growth of raised mires, generating higher inertinite concentrations through more frequent moisture stress. Consistently low ash yield and sulfur content would be due to the protection from clastic input in raised mires, in addition to the leaching of mineral matter by rainfall and the development of acidic conditions preventing fixation of sulfur. In contrast, peat mires of Eocene–Miocene age encountered rapid subsidence due to the proximity of nappe emplacement, resulting in lower inertinite content, higher and more variable sulfur content, and higher ash yield.

Intraslope Basin, Seismic Facies and Sedimentary Processes in the Kaoping Slope, Offshore Southwestern Taiwan

Occurrence of intraslope basins and distinct seismic faices assemblages of the basin fills in the Kaoping Slope, offshore SW Taiwan, reflect interactions between regional convergent tectonics, local mud diapirism and sedimentary processes of fill-and-spill during slope development. Located west of the Kaoping Submarine Canyon, three major intraslope basins separated by diapiric mud ridges mainly trending NNE-SSW are determined. They are elongated depressions with a length ranging from 10 to 40 km and a width of about 12 km, similar to intraslope basins east of the Kaoping Canyon. Basin fills are characterized by a distinct upward change in seismic facies beginning with a basal convergent-baselapping facies, succeeded by chaotic facies and overlain by parallel and draping facies. The basal convergent-baselapping facies is the most common and the parallel and draping facies is restricted to slope areas shallower than 1000 m in water depth. Sediments from the prograding shelf and upper slope are transported and deposited mainly in the confined basal accommodation space of intraslope basins, forming convergent-baselapping seismic facies in the early stage of the basin fill history. Rates of deposition being slower than rates of basin subsidence due to local mud diapirism kept the early intraslope basins partially filled by sediment, representing a confined style of deposition. In the late stage of basin development sediments have been transported to a lower slope distal to the sediment sources, progressively filling and spilling intraslope basins in a generally southwestward direction.

Plate tectonics and basin subsidence history

Research Article| January 01, 2009 Plate tectonics and basin subsidence history Xiangyang Xie; Xiangyang Xie † 1Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA *Present address: Institute for Geophysics, University of Texas at Austin, 10100 Burnet Road Building 196, Austin, Texas 78758, USA. †E-mail: xiangyang@utig.ig.utexas.edu Search for other works by this author on: GSW Google Scholar Paul L. Heller Paul L. Heller 1Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2009) 121 (1-2): 55–64. https://doi.org/10.1130/B26398.1 Article history received: 31 Dec 2007 rev-recd: 15 Jun 2008 accepted: 18 Jun 2008 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Xiangyang Xie, Paul L. Heller; Plate tectonics and basin subsidence history. GSA Bulletin 2009;; 121 (1-2): 55–64. doi: https://doi.org/10.1130/B26398.1 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 SocietyGSA Bulletin Search Advanced Search Abstract Tectonic setting exerts first-order control on basin formation as reflected in basin subsidence history. While our approach ignores the effects of flexural loading and eustatic sea-level change, consistency of backstripped subsidence histories (i.e., with local loading effects of sediment removed) suggests consistent tectonic driving mechanisms in each tectonic setting, with the possible exception of forearc basins.Based on published subsidence curves and open-file stratigraphic data, we show the subsidence characteristics of passive margins, strike-slip basins, intracontinental basins, foreland basins, and forearc basins. Passive margin subsidence is characterized by two stages, rapid initial, synrift subsidence and slow post-rift thermal subsidence, with increasing subsidence rates toward the adjacent ocean basin. Subsidence of intracontinental basins is similar in magnitude to that seen in passive margin settings, but the former is generally slower, longer lived, and lacks initial subsidence. Long-lived subsidence for many intracontinental basins is consistent with cooling following thermal perturbation of thick lithosphere found beneath old parts of continents. Basins associated with strike-slip faults are usually short lived with very rapid subsidence. Changes in local stress regimes as strike-slip faults evolve, and migrate over time, coupled with three-dimensional heat loss in these small basins likely explain this subsidence pattern. Foreland basin subsidence rates reflect the flexural response to episodic thrust loading. Resultant subsidence curves are punctuated by convex-up (accelerating) segments. Forearc basins have the least consistent subsidence patterns. Subsidence histories of these basins are complex and may reflect multiple driving mechanisms of subsidence in forearc settings.Second-order deviations in subsidence suggest reactivation or superimposed tectonic events in many basin settings. The effects of eustatic sea-level change may also explain some deviations in curves. For many of these settings, subsidence histories are sufficiently distinctive to be used to help determine tectonic setting of ancient basin deposits. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

40Ar/ 39Ar dating of volcanism and subsequent very low-grade metamorphism in a subsiding basin: example of the Cretaceous lava series from central Chile

40Ar/ 39Ar geochronological method is applied to date both emplacement and subsequent very low-grade metamorphism of a thick lava series, the Veta Negra Formation from the Cordón de Chacana area, in the Coastal Range of central Chile. On the same lava series, and even on the same rock sample, it was possible to measure apparently valid ages of both the emplacement of lava flows (by dating transparent plagioclase) and the very low-grade metamorphic event (by dating sericite and/or adularia). Sericite was dated on step heated single grains of strongly altered plagioclases, the radiogenic argon from remaining fresh plagioclase appearing as negligible on most part of the age spectrum. The concordance between one plateau age of 118.7±0.6 Ma displayed by fresh plagioclase and a previously measured plateau age on plagioclase from one lava flow from a region due west from Santiago [Bustamante Hill, Aguirre, L., Féraud, G., Morata, D., Vergara, M., Robinson, D., 1999. Time interval between volcanism and burial metamorphism and rate of basin subsidence in a Cretaceous Andean extensional setting. Tectonophysics 313, 433–447] may indicate that the volcanic activity of the Veta Negra Formation was synchronous along the 80-km long latitudinal segment studied. Ages of 96.8±0.2 and 97.0±1.6 Ma displayed by adularia and sericite (respectively) are slightly older than ages of 93–94 Ma given by adularia from the Bustamante Hill. These data allow to define a period of about 22 Ma between volcanism and metamorphism. Because of the contemporaneity of some metamorphic minerals and Cretaceous plutons of the region, the very low-grade metamorphic event may be the result of the additional effect of burial and a regional thermal event. Nevertheless, a significant effect of burial (relatively to the contribution of high thermal gradient event(s)) seems revealed by an apparent age gradient on very low-grade minerals with the stratigraphic depth.

04/02645 A short report of the investigations made on thefacies of German coal deposits: Dehmer, J. International Journal of Coal Geology, 2004, 58, (1–2), 41–51

This paper reviews current research in Canada relating to the sedimentology of coal-bearing sequences and the petrographic character of contained seams from selected intermontane and foreland basin settings.The intermontane Cumberland and Stellarton basins of Nova Scotia contain Westphalian coal-bearing strata of different character. Coal seams that formed in fluvial-dominated depositional environments of the Springhill Coalfield, Cumberland Basin, commonly brighten upward and laterally display distinct areal zones: a piedmont zone formed by interfingering of mire and distal fan sheetflow deposits; an inner mire zone largely devoid of partings and a riverine zone with large-scale seam splits about multistorey sandstone bodies. Maceral-based groundwater influence and vegetation indices, combined with miospore analyses, indicate that the peat precursors of the No. 3 seam of the inner mire zone accumulated from a groundwater-influenced (rheotrophic to mesotrophic) forest mire (swamp, fen). Both the gelification of lignin-derived maceral precursors and the domination of mire vegetation by lycopsid trees reflect this groundwater influence.Coal that formed from the frequently flooded paleomires of the Stellarton Basin is generally dull, microbanded and mineral-rich. The location of mires within the basin was largely determined by basin subsidence rates. When subsidence rates were high, mires developed around the margin of a central basin lake. Coal seams that formed from these mires (e.g. McLeod seam) thicken toward basin margins and grade into sapropelic shale near the basin centre. Petrographic analyses of the McLeod seam suggest development from limnic to wet forest swamp conditions and a return to a limnic environment at the top of the seam. Thick coal (e.g. Foord seam) developed near the basin centre during periods of lower subsidence rates and grades into red beds and paleosols toward the basin margin. The Foord seam of the basin centre is characterized by low mineral matter contents and a high proportion of degraded vitrinite macerals in the central parts of the seam, interpreted to reflect prolonged peat accumulation with very limited clastic input. The top and the base of the seam, in contrast, were subjected to significant clastic input, as indicated by microbanding associated with significant amounts of detrital minerals and macerals.Coal seams of the Lower Cretaceous Gates Formation in the Western Canada Basin formed in depositional settings ranging from coastal swamps (strandplains) to the upper delta plain. Strandplain coal is characterized by great lateral continuity and substantial thickness, whereas coal of the upper delta plain is thin and discontinous. The strandplain coal is characterized by variable lithotype sequences (oscillatory, brightening-up, dulling-up). Maceral-based facies parameters indicate a wide range of mire facies for these lithotype successions: open moor, forest moor, herbaceous and/or shrubby marshes and slightly raised mires. Results from megafossil and phyteral analyses suggest that the coastal plain mires were dominated by taxodiaceous conifers, whereas ferns, angiosperms and herbaceous lycopods are thought to have occupied the more marshy and/or marginal (stream/lake side) environments.

A multistorey sandstone complex in the Himalayan Foreland Basin, NW Himalaya, India

Ten parallel stratigraphic sections (1500–1800 m thick) spread over an area of >400 km 2 in Dehra Dun sub-basin (DSB) of the Himalayan Foreland Belt (HFB) were studied to understand the anatomy of one of the largest (900–1200 m thick) fluviatile Multistorey Sandstone Complexes (MSC) of the world using fluvial geometry, compositional data and magnetic fabrics over a magnetostratigraphically controlled master section. The multistorey sandstone complex, between 10–5 Ma representing the Middle Siwalik sub-Group, comprises of grey, medium- to fine-grained lithic arenites to lithic greywacke and records tectonic and/or climatic episodes. Three main facies associations are recognised: sandstone–mudstone, sandstone, and conglomerate-sandstone that represent fluvial fan deposit. Palaeocurrent data show radial palaeoflow pattern with major palaeodrainage towards the southern quadrant. The magnetic fabric studies suggest three major tectonic pulses. The first pulse at ∼8.7 Ma resulted in the development of major depocenter for the MSC, the second pulse at ∼7.65 Ma enhanced the sedimentation and progradation, while the third pulse at ∼6.5 Ma records overlapping earlier fluvial fan by another coarse grained piedmont alluvial fan. Thrust movement in the northern fold belt, basement lineaments and rate of basin subsidence controlled the lateral and vertical facies distribution and palaeodrainage. The sedimentation pattern of the multistorey complex is characterised by mainly sheet flood deposits of laterally avulsing unconfined braided rivers and resembles to the modern megafan sedimentation in the Ganga Basin to the south.