Basin Subsidence Rates Research Articles

Evidence for subsidence rate variation in the Newark Basin and its influence on the deposition of fluvial sediments of the Stockton Formation

AbstractThe Stockton Formation of the Newark Basin represents an exciting time in Earth history during the early stages of rifting of the North Atlantic, with rapid subsidence and sediment deposition. Much of the previous work on this formation has been done using drill cores, with development limiting surface exposure. While this allows us to build a full stratigraphic sequence of deposition, it has the potential to miss smaller‐scale variability and sedimentary structures. It is also difficult to understand the three‐dimensional geometries, architecture and relationships between the depositional elements from drill core alone. An outcrop in North Bergen, NJ that was recently exposed during construction provided an opportunity to study the primary and secondary sedimentary structures of a previously hidden part of the Stockton Formation. These sediments and structures were investigated in the field and laboratory, with geochemical data assisting in the interpretation of their origin and history. Despite its small size, this outcrop provides strong evidence for varying rates of basin subsidence, with rocks deposited during more rapid subsidence also showing secondary structures associated with major earthquakes. Rapid subsidence during fluvial deposition resulted in the preservation of more fine‐grained, lower‐porosity sediments. Recently the Newark Basin has been identified as having characteristics that are favourable for CO2 storage, however, a detailed understanding of sedimentary lithologies is essential to assessing that potential. If these periods of rapid subsidence have similar lithological consequences basin‐wide, this could potentially impact the capacity for carbon sequestration, by reducing porosity and permeability in many areas, and potentially creating barriers to flow.

Consequences of Continental Core Complexes on Rifting Patterns: Insights From Multichannel Seismic Data From the Northern Margin of the South China Sea

AbstractCore complex type structures are common in continental margins. Recent studies have proposed exhumation of deeper crustal and mantle levels during extension of the continental margin along the Northern South China Sea (NSCS) in a core complex mode. Here, we present high‐resolution seismic profiles across different sections of the NSCS that allow us to observe two types of core complex systems. The Kaiping Rift and eastern Baiyun Rift are characterized by a sub‐horizontal Moho and exhumation of ductile deeper crust beneath an extremely thinned brittle upper crust. The central Baiyun Rift in contrast is marked by homogeneous thinning of the entire crust that is floored by mantle unroofing with a concave‐down Moho geometry. While the former type, referred to as crustal core complexes, coincides with relatively intense syn‐rift magmatism, the latter, referred to as mantle core complexes, is marked by limited magmatism. Consistently, basin subsidence rates are lower over crustal core complexes than mantle core complexes. Compared to mantle core complexes at the magma‐poor Iberian margin, the widely distributed crustal core complexes in the NSCS indicate higher geotherms and more intense magmatism during extension of the continental lithosphere. We propose that the continental core complexes observed at the NSCS represent a typical outcome of extension of a gravitationally unstable lithosphere.

The sedimentary facies and tectono-stratigraphic successions of the Carboniferous–Lower Permian deposits in western South Qiangtang Block: Implication for a rifting process on the Gondwana margin

The South Qiangtang Block (SQB) was widely acknowledged as a part of the Cimmerian Continent, which rifted away from Gondwanan margin during the Early Permian. However, the sedimentary response to this rifting event has thus far not been unequivocally confirmed, which makes this event ambiguous. In this contribution, three stratigraphic successions are recognised, which are characterised by distinct facies and record different stages in the tectonic evolution of the basin and associated changes in the rates of basin subsidence and sediment accommodation. Succession 1 comprises glacio-marine deposits which are dominated by dark shales and diamictites (Cameng and Zhanjin formations) originated mainly from both gravity flow and downslope resedimentation. Succession 2 is predominated by shallow-water sandstones of delta setting (lower Qudi Formation). Succession 3 is composed of deposits of tidal flat and platform (upper Qudi and Tunlonggongba formations). The sedimentary facies changes fit well with marine rift-basin successions: (1) Succession 1 clearly records ‘sediment underfilled’ stage characterised by rapid tectonic subsidence, low sediment supply, and marks an early to climax stage of syn-rift; (2) deltaic sandstones facies of Succession 2 records ‘sediment filled and overfilled’ when sediment supply consumes up the accommodation, and marks a late stage of syn-rift during the tectonic quiescence period; (3) tidal-rhythmites of Succession 3 is likely a record of short-term autogenic cycles, indicating a possible post-rift stage. Therefore, these successions within the western SQB during the Early Permian was best explained by the tectonic subsidence resulted from the rifting of the SQB from the Gondwanan margin.

Last Interglacial sea-level data points from Northwest Europe

Abstract. Abundant numbers of sites and studies exist in NW Europe that document the geographically and geomorphologically diverse coastal record from the Last Interglacial (Eemian, Ipswichian, Marine Isotope Stage 5e). This paper summarises a database of 146 known Last Interglacial sea-level data points from in and around the North Sea (35 entries in the Netherlands, 10 Belgium, 23 in Germany, 17 in Denmark, 9 in Britain) and the English Channel (24 entries for the British and 25 for the French side, 3 on the Channel Isles) believed to be a representative and fairly complete inventory and assessment from ∼80 published sites. The geographic distribution (∼1500 km SW–NE) across the near field of the Scandinavian and British ice sheets and the attention paid to relative and numeric age control are assets of the NW European database. The research history of Last Interglacial coastal environments and sea level for this area is long, methodically diverse and spread through regional literature in several languages. Our review and database compilation effort drew from the original regional literature and paid particular attention to distinguishing between sea-level index points (SLIPs) and marine and terrestrial limiting points. We also incorporated an updated quantification of background rates of basin subsidence for the central and eastern North Sea region, utilising revised mapping of the base Quaternary, to correct for significant basin subsidence in this depocentre. As a result of subsidence, lagoonal and estuarine Last Interglacial shorelines of the Netherlands and the German Bight are preserved below the surface. In contrast, Last Interglacial shorelines along the English Channel are encountered above modern sea level. This paper describes the dominant sea-level indicators from the region compliant with the WALIS database structure and referenced to original data sources (https://doi.org/10.5281/zenodo.6478094, Cohen et al., 2021). The sea-level proxies are mostly obtained from locations with good lithostratigraphic, morphostratigraphic and biostratigraphical constraints. Most continental European sites have chronostratigraphic age control, notably through regional pollen association zones with duration estimates. In all regions, many SLIPs and limiting points have further independent age control from luminescence, uranium series, amino acid racemisation and electron spin resonance dating techniques. Main foreseen usage of this database for the near-field region of the European ice sheets is in glacial isostatic adjustment modelling and fingerprinting Last Interglacial ice sheet melt.

Depositional environment of polymictic conglomerate of the Gadag greenstone Belt, Western Dharwar Craton, south India: An insight for Neoarchean marginal sedimentation

Clast morphometry and sedimentary facies analysis of polymictic conglomerate of the Hiriyur Formation in the Gadag greenstone Belt, Western Dharwar Craton, India, was conducted to constrain the palaeohydraulic condition, depositional environment, and type of sedimentary basin. The conglomerate grades from clast‐supported to matrix‐supported with siltstone‐sandstone intercalations. Eight lithofacies along with five major lithofacies associations are recognized in the Majjur and Attikatti Domains of the Gadag greenstone Belt. The lithofacies architecture suggests sedimentation commenced with rapid deposition of slope‐derived debris in a proximal high‐energy alluvial fan setting followed by a braided river environment. Clast morphometry and palaeohydraulic data indicate a low palaeoslope (0.000024 m/m), and stream discharge value (1.913 m3/s) calculated from the channel fill conglomerates. Greywacke overlying the conglomerate has been interpreted as turbidites from a continental slope. The accompanying 40‐m‐thick banded iron formation and carbonate rocks also support a marine context. The lack of transitional deposits between river and deep marine settings suggests that the greywacke turbidites sequence is separated from the conglomerate deposits by substantial unconformities. This change in depositional setting could be due to a change in basin subsidence rate, tectonic rejuvenation, or major sea‐level changes.

Eolian stratigraphic record of environmental change through geological time

Abstract The terrestrial sedimentary record provides a valuable archive of how ancient depositional systems responded to and recorded changes in Earth's atmosphere, biosphere, and geosphere. However, the record of these environmental changes in eolian sedimentary successions is poorly constrained and largely unquantified. Our study presents the first global-scale, quantitative investigation of the architecture of eolian systems through geological time via analysis of 55 case studies of eolian successions. Eolian deposits accumulating (1) under greenhouse conditions, (2) in the presence of vascular plants and grasses, and (3) in rapidly subsiding basins associated with the rifting of supercontinents are represented by significantly thicker eolian dune-set, sand-sheet, and interdune architectural elements. Pre-vegetation eolian systems are also associated with more frequent interactions with non-eolian environments. The interplay of these forcings has resulted in dune-set thicknesses that tend to be smallest and largest in Proterozoic and Mesozoic successions, respectively. In the Proterozoic, the absence of sediment-binding plant roots rendered eolian deposits susceptible to post-depositional wind deflation and reworking by fluvial systems, whereby highly mobile channels reworked contiguous eolian deposits. During the Mesozoic, humid greenhouse conditions (associated with relatively elevated water tables) and high rates of basin subsidence (associated with the breakup of Pangea) favored the rapid transfer of eolian sediment beneath the erosional baseline. The common presence of vegetation promoted accumulation of stabilizing eolian systems. These factors acted to limit post-depositional reworking. Eolian sedimentary deposits record a fingerprint of major environmental changes in Earth history: climate, continental configuration, tectonics, and land-plant evolution.

The role of subsidence and accommodation generation in controlling the nature of the aeolian stratigraphic record

Despite a well-documented record of preserved aeolian successions from sedimentary basins characterized by widely variable subsidence rates, the relationship between aeolian architecture and subsidence-driven accommodation generation remains poorly constrained and largely unquantified. Basin subsidence as a control on aeolian sedimentary architecture is examined through analysis of 55 ancient case-studies categorized into settings of ‘slow’ (>1–≤10 m Myr −1 ), ‘moderate’ (>10–≤100 m Myr −1 ) and ‘rapid’ (>100 m Myr −1 ) time-averaged subsidence rates. In rapidly subsiding basins, aeolian successions are thicker and associated with (1) thicker and more laterally extensive dune-sets with increased foreset preservation, (2) greater proportions of wet-type interdunes and surface stabilization features and (3) more extensive interdune migration surfaces, bounding sets that climb more steeply. In slowly subsiding basins, aeolian successions are thinner, and associated with a greater proportion of (1) aeolian sandsheets and (2) supersurfaces indicative of deflation and bypass. Rapid subsidence promotes (1) steeper bedform climb, resulting in increased preservation of the original dune foreset deposits and (2) relatively elevated water tables, leading to sequestration of deposits beneath the erosional baseline and encouraging development of stabilizing agents; both factors promote long-term preservation. Slow subsidence results in (1) lower angles of climb, associated with increased truncation of the original dune forms, and (2) greater post-depositional reworking, where sediment is exposed above the erosional baseline for extended time-periods. Quantitative analysis of sedimentary stratal architecture in relation to rates of basin subsidence helps constrain the mechanisms by which sedimentary successions are accumulated and preserved into the long-term stratigraphic record. Supplementary material: Results of statistical analyses presented here are available at https://doi.org/10.6084/m9.figshare.c.5515695.v1

Sequence-stratigraphic dynamics: Variations of genetic stratigraphic units driven by basin subsidence

Rapid basin subsidence can cause the stacking of all strata deposited within a third-order eustatic cycle in a backstepping pattern. However, such extreme changes in stratal stacking patterns remain unexplored due to the lack of case studies. In this study, we first introduce the concept of sequence-stratigraphic dynamics based on previous achievements, and investigate the normal variations of genetic stratigraphic units of a third-order cycle driven by basin subsidence using mathematical simulations and a case study. We have established a dynamic equation and a system for the evaluation of the variations in genetic stratigraphic units based on which 6 potential driving mechanisms and 36 genetic unit variations, including 2 extreme variants of normal and reverse, were identified. The results confirm that third-order cyclic sea level change (Rsea-level), generalized basin subsidence (Rbase), and the sediment supply (Rsediment) drive the changes in the stratigraphic architecture. However, the variations of genetic stratigraphic unit are driven by the residual basin subsidence rate (Rbase - Rsediment). The stratal stacking pattern depends on the ratio of sediment supply rate to the residual accommodation rate (Rsea-level + Rbase - Rsediment). Sequence-stratigraphic dynamics are applicable to all basins, and may lend themselves as a theoretical basis for wider stratigraphic correlations.

Oligocene-Miocene sequence stratigraphy in the northern margin of the South China Sea: An example from Taiwan

Oligocene-Miocene sediments in the Taiwan region were accumulated in the NE passive-continental margin of the South China Sea. We utilized around ~200 boreholes and reflection seismic data to study the Oligo-Miocene sequence stratigraphic framework in the Taiwan region. Major sequence boundaries are used to map out various sediment isopach maps, enabling us to decipher dominant tectonic events during the course of passive-margin evolution. The Oligocene-Miocene succession is divided into 16 sequences on the basis of well-log correlation. These 16 sequences can be grouped into four (A, B, C, D) sequence sets. Isopach maps of sequence sets B and C (~21–12.5 Ma) show that they blanket the west Taiwan basins with relatively uniform thickness deposited during uniform and slow basement subsidence. Sequence sets A (~30–21 Ma) and D (~12.5–6.5 Ma), however, thickened into fault-bounded troughs, recording two extensional events that were especially active in the outer margin (i.e., the Tainan Basin). There is a general correlation between the Taiwan Miocene sequences and the glacioeustasy during the interval ~21–6.5 Ma. Therefore, eustasy is the dominant control on the Taiwan Miocene stratigraphic development. The deposition of the sequence set A during ~30–21 Ma and possibly the sequence set D in the outer margin during the late Miocene, however, appears to have been strongly modulated by extensional tectonics and local sedimentary factors (e.g., rates of basin subsidence, sediment supply and basin physiography, etc.).

Numerical Modelling to Evaluate Sedimentation Effects on Heat Flow and Subsidence during Continental Rifting

Sedimentation impacts thermal and subsidence evolution in continental rifting. Estimating the blanketing effect of sediments is crucial to reconstructing the heat flow during rifting. The sedimentary load affects the basin subsidence rate. Numerical investigation of these effects requires active and complex simulations of the thermal structure, lithospheric stretching, and sedimentation. In this paper, we introduce a numerical model to quantify these effects, which was developed using the COMSOL Multiphysics® simulation software. Our numerical setting for the analytical and numerical solutions of thermal structure and subsidence is based on previous continental rifting studies. In our model, we accumulate a column of 5 m thick sediment layers with varied stretching factors and sedimentation rates, spanning the syn-rift to early post-rift phases over a period of 12 myr. Our results provide intuitive models to understand these sedimentation effects. The models show that an increase in sedimentation thickness significantly decreases surface heat flow, leading to lower geothermal temperature, and amplifies the subsidence magnitude. The findings also demonstrate that increases in the stretching factor and sedimentation rate enhance the blanketing effect and subsidence rate. Based on these results, we discuss key outcomes for geological applications and the possible limitations of our approach.

Geochemical conditions of oil and gas potential of the South Caspian basin on the basis of pyrolytic studies of mud volcanoes

This paper provides the results of geochemical studies with products of mud volcanoes conducted for a purpose of evaluating the generative potential of the South-Caspian basin. The kerogen types have been identified for different stratigraphic intervals and stages of the organic matter (OM) thermal maturity have been determined. A correlation has been established between the generative potential and the basin deposition and subsidence rate.

Detrital cosmogenic 21Ne records decoupling of source-to-sink signals by sediment storage and recycling in Miocene to present rivers of the Great Plains, Nebraska, USA

The preservation of conglomerates far from mountainous sources is commonly interpreted in terms of tectonic or climatic forcing. To relate a depositional signal to changing conditions in source areas, the process and duration of sediment routing from source to sink need to be determined. For the first time, we quantified sediment transport histories using cosmogenic 21Ne in quartzite pebbles from modern river gravels and Neogene conglomerates from the modern and ancient North Platte River of the Great Plains of Nebraska, United States. We demonstrate that at ∼400 km distance from the Front Ranges of the Rocky Mountains, the majority of pebbles were stored in older channel deposits for up to several millions of years before being recycled; this was enabled by very slow to zero basin subsidence rates. This implies that upstream tectonic or climatic controls on surface processes were decoupled from the downstream depositional record—a result supported by the similarities in cosmogenic 21Ne values among Miocene, Pliocene, and modern river channel pebbles despite known changes in tectonic and climatic forcing.

PETROLEUM SYSTEMS IN THE AUSTRIAN SECTOR OF THE NORTH ALPINE FORELAND BASIN: AN OVERVIEW

Two separate petroleum systems have been identified in the Austrian sector of the North Alpine Foreland Basin: a lower Oligocene – Cenomanian/Eocene oil and thermogenic gas system; and an Oligocene‐Miocene microbial gas system. Recent studies by both academic and industry‐based research groups have resulted in an improved understanding of these petroleum systems, which are reviewed in this paper.Lower Oligocene organic‐rich intervals (up to 12 %TOC; HI: 400–600 mgHC/gTOC), capable of generating slightly more than 1 t of hydrocarbons/m2, are the source rocks for the thermogenic petroleum system in the Austrian sector of the North Alpine Foreland Basin. The present‐day distribution of this source rock is controlled by submarine mass movements which removed a large part of the organic‐rich interval from its depositional location during the late early Oligocene. The transported material was redeposited in locations to the south which are at the present day buried beneath Alpine thrust sheets. In addition, source rock units were incorporated into Molasse imbricates during Alpine deformation. Hydrocarbon generation began during the Miocene, and the oil kitchen was located to the south of the Alpine thrust front. Hence, lateral migration over distances of up to 50 km was required to charge the mainly Eocene and Cenomanian non‐ and shallow‐marine sandstone reservoir units. Hydrocarbons are in general trapped in structures related to east‐west trending normal faults, and differences in source rock facies resulted in the development of separate western and eastern oil families. Surprisingly, with the exception of some fields in the eastern part of the study area, associated gas contains varying (and sometimes very high) percentages of primary and secondary microbial methane. The composition of oil in some fields is influenced by both biodegradation and water washing. Post‐Miocene uplift in the Austrian sector of the basin had further effects on biodegradation and the consequent formation of secondary microbial gas, and also resulted in re‐migration.The upper Oligocene to lower Miocene succession (Puchkirchen Group, Hall Formation) provides both source and reservoir rocks for the microbial petroleum system in the Austrian sector of the North Alpine Foreland Basin. TOC contents (<1.0 %) and HI values (<140 mgHC/gTOC) of pelitic source rocks are typically low. Microbial gas was generated shortly after deposition during early diagenesis and was subsequently fixed in gas hydrates. Basin subsidence and high sedimentation rates resulted in decomposition of the hydrates below their stability zone, and reservoirs were filled during the early Miocene. Subsequent mixing of microbial gas with thermogenic gas and condensates is widespread. However, biodegradation has prevented precise determination of the fraction of thermogenic hydrocarbons present in gas samples. Reservoir sandstones were deposited within a deep‐marine channel belt along the axis of the North Alpine Foreland Basin, and reservoir quality depends on the precise position within this belt. In the study area, gas is trapped in compaction anticlines or at channel margin pinch‐outs and additional traps are formed by imbrication structures.

Tectonic controls on the stratigraphic development of the rifted Taipei Basin: A late quaternary marine-influenced inland half graben

We establish the three-dimensional stratigraphic architecture of the Taipei Basin and its spatiotemporal palaeoenvironmental development during the past 50 kyr by analysing 36 borehole cores and 177 age dates. We calculate the rates of basin subsidence from the borehole data at depths where radiocarbon age dates are available. Our results indicate that, during the eustatic sea level falling period (35–20 ka), low rates of sediment supply and/or rapid basin subsidence controlled sedimentation, leading to a change in the depositional environment from gravelly braided rivers, through sandy braided rivers, to meandering rivers with falling eustatic sea level. During the early stage of eustatic sea level rise (∼20–10.2 ka), balanced rates of sediment supply, eustasy and basin subsidence maintained the meandering river environment. Rapid sea level rise led to the initial appearance of estuarine facies at ∼10.2 ka and widened the distribution of the estuarine environment after 8.5 ka; however, the coeval phases of rapid basin subsidence ∼10.6–10.2 ka and 9–8.5 ka promoted the first appearance and widening of the estuary, respectively. After 7 ka, when the eustatic sea level and rate of basin subsidence remained relatively stable, sufficient sediment supply gradually infilled the estuary. The established stratigraphy improves our understanding of the factors controlling stratigraphic development in marine-influenced inland half grabens, specifically in the Taipei Basin with high rates of sediment supply. Accommodation space in the Taipei Basin was governed by eustatic fluctuations with modulations by basin subsidence and sediment supply since the last glacial period.

Subsidence control on river morphology and grain size in the Ganga Plain

The Ganga Plain represents a large proportion of the current foreland basin to the Himalaya. The Himalayan-sourced waters irrigate the Plain via major river networks that support approximately 10 percent of the global population. However, some of these rivers are also the source of devastating floods. The tendency for some of these rivers to flood is directly linked to their large scale morphology. In general, the rivers that drain the east Ganga Plain have channels that are perched at a higher elevation relative to their floodplain, leading to more frequent channel avulsion and flooding. In contrast, those further west have channels that are incised into the floodplain and are historically less prone to flooding. Understanding the controls on these contrasting river forms is fundamental to determining the sensitivity of these systems to projected climate change and the growing water resource demands across the Plain. Here, we present a new basin scale approach to quantifying floodplain and channel topography that identifies areas where channels are super-elevated or entrenched relative to their adjacent floodplain. We explore the probable controls on these observations through an analysis of basin subsidence rates, sediment grain size data and sediment supply from the main river systems that traverse the Plain (Yamuna, Ganga, Karnali, Gandak and Kosi rivers). Subsidence rates are approximated by combining basement profiles derived from seismic data with known convergence velocities; results suggest a more slowly subsiding basin in the west than the east. Grain size fining rates are also used as a proxy for relative subsidence rates along the strike of the basin; the results also indicate higher fining rates (and hence subsidence rates for given sediment supply) in the east. By integrating these observations, we propose that higher subsidence rates are responsible for a deeper basin in the east with perched, low gradient river systems that are relatively insensitive to climatically driven changes in base-level. In contrast, the lower subsidence rates in the west are associated with a higher elevation basin topography, and entrenched river systems recording climatically induced lowering of river base-levels during the Holocene.

Paleobathymetry of the Late Jurassic-Neocomian basin in northern West Siberia and the impact of natural processes

Paleobathymetrical reconstructions were performed for the Volgian-Neocomian basin in northern West Siberia. The proposed technique takes into account a number of factors, such as the rates of basin subsidence and sedimentation, sediment lithification and types of lithology, sea level changes, and isostasy. The role of each factor controlling the depth of the paleobasin is considered. The study reveals several stages of formation of the Neocomian clinoform complex of West Siberia, with different regimes of basin subsidence, sedimentation, and isostatic compensation.

Origins of Bimodal Stratigraphy In Fluvial Deposits: An Example From the Morrison Formation (Upper Jurassic), Western U.S.A.

Abstract Changes in stacking density of fluvial channel-belt sand bodies are one of the most obvious aspects of alluvial architecture. The proximity of sand bodies to each other has been used as a field criterion to suggest major changes in external factors, such as basin subsidence rates, relative changes in base level, and changes in climate. In places rapid changes in stacking density are found in vertical succession between very high to very low net sandstone. In the absence of an intervening unconformity such changes are not the result of two unrelated, but juxtaposed, fluvial regimes but represent a more transitional change of formative conditions or preservation style. To study whether a rapid change in stacking density was controlled by external factors rather than autogenic behavior, we sought to document other possible changes in deposition that took place in concert with changes in stacking pattern. The Morrison Formation, Upper Jurassic of eastern Utah and western Colorado, U.S.A., contains a rapid transition from the Salt Wash Member, with an average 63% net sand, to the overlying Brushy Basin Member, dominated by muddy floodplain deposits (10% net sand). We measured nine sedimentary characteristics related to fluvial system properties in both members along a down-paleoflow-oriented transect. The only significant change found between the two members is the composition and abundance of floodplain clay minerals. The transition in stacking density is coincident with a rapid increase in smectitic clay, interpreted to result from increased volcanic ash influx, at the expense of illitic clay. The ash was preferentially accumulated in the floodplain, either as airfall or carried in the wash load of rivers. Geometric calculations suggest that in order to generate the observed change in stacking pattern by the addition of volcanic ash alone, more than half of the flood-plain deposition would have to be composed of ash. An increase in ash supply would increase floodplain sedimentation rate and reduce the frequency of avulsion. Together these effects could reduce the stacking density by the requisite 50%. Dependence of stacking density on floodplain sedimentation rate highlights the danger in assuming changes in stacking density observed in alluvial sequences are mainly controlled by other external factors such as sea-level fluctuation, subsidence rate, or overall aggradation rates.

Tectono-stratigraphy of Lower Cretaceous Tanan sub-basin, Tamtsag Basin, Mongolia: Sequence architecture, depositional systems and controls on sediment infill

Tanan sub-basin is an active-fault bounded basin. The spatial distribution and temporal evolution of depositional systems were significantly influenced by tectonics. Fault movement and stages of basin development controlled the subsidence rates and the potential for erosion and the rate of sediment supply. Distinct stages of rift evolution during the early Cretaceous can be recognized, namely the early syn-rift, rift climax and late syn-rift stages. Three types of lacustrine sequence, consisting of distinctive depositional systems, are distinguished: (1) the early syn-rift sequences (SQ1 + SQ2), which are composed mainly of fan delta and shallow lacustrine depositional systems; (2) the rift climax sequences (SQ3) which developed in response to rapid and differential tectonic subsidence rates, and consist of fan delta, deep lacustrine and sublacustrine fan depositional systems; and (3) the late syn-rift sequences (SQ4) which are comprised of braided-delta and shallow lacustrine depositional systems. Each of the three lacustrine sequence architectures stands for a particular stage of basin fill and reflects variable rates of basin subsidence. Within each sequence, depositional systems and their stacking patterns are interpreted to have been a function of the interaction between tectonics and sediment supply. Differential subsidence across the basin, related to rotation of fault blocks, resulted in the formation of distinct paleomorphologies in different structural settings. These settings were fault-scarp zones controlling the development of fan-deltas, fault-terrace zones controlling the development of fan-delta and sublacustrine fans, half-graben dip-slope zones controlling the development of braided river and braided deltas, and intra-basinal fault-break zones controlling the development of sublacustrine fans. During the late syn-rift stage, active tectonism, displacement on the boundary faults had ceased. At this stage the depositional systems and their stacking patterns were dominantly related to the sediment supply rates, and not to tectonic activity.

Sedimentological constraints on the evolution of the Cordilleran arc: New insights from the Sonsela Member, Upper Triassic Chinle Formation, Petrified Forest National Park (Arizona, USA)

The Sonsela Member of the Upper Triassic Chinle Formation in Petrified Forest National Park, Arizona, forms a distinctive part of an extensive fluviolacustrine complex that blanketed the Colorado Plateau region and surrounding areas. Upper Triassic sediments were deposited within a continental backarc setting, synchronous with the development of the Cordilleran magmatic arc. Although the Chinle Formation was derived from a broad variety of source terranes, petrographic and geochemical data clearly fingerprint the Cordilleran arc as a region important to provenance. The Sonsela Member exhibits a stratigraphically abrupt change in depositional style and sedimentary architecture that likely reflects the dynamics of the evolving backarc fluvial system and syndepositional arc magmatism. The stratigraphic boundary between the two disparate depositional styles is marked by a laterally persistent red silcrete horizon that is also associated with a biostratigraphically significant faunal turnover. The lower Sonsela Member—a coarse-grained assemblage dominated by persistent sheet sandstone and conglomerate bodies—reflects a coarse-grained progradation of sediment that suggests low rates of dynamic subsidence and high rates of sediment input. The upper Sonsela Member—characterized by an overall finer-grained assemblage and ribbon sand bodies with an increased proportion of encasing mudstone—reflects an increasing rate of basin subsidence that likely persisted throughout the deposition of the overlying Petrified Forest Member. These packages reflect a sharp change from lower- to higher-sinuosity river systems that closely coincides with the increased rate of subsidence across the regional stratigraphic marker. Previous studies have suggested the importance of the silcrete horizon as a key biostratigraphic marker associated with a significant faunal turnover. This study supports the hypothesis that this horizon may represent a regional unconformity as opposed to local channeling, perhaps the product of an abrupt change in basin geometry followed by an increase in basin subsidence. Because the Sonsela Member is the stratigraphically lowest unit of the Chinle Formation dominated by volcanic clastic detritus on the Colorado Plateau, architectural analysis of the Sonsela Member serves as the most reliable indicator of short-term fluctuations in arc dynamics of the poorly preserved and disjointed Mesozoic portion of the Cordilleran magmatic arc.

Sediment dispersal and accumulation in tectonic accommodation across the Gaoping Slope, offshore Southwestern Taiwan

Distribution and architecture of slope basins across a continental slope vary as a consequence of accommodation forming, sediment dispersal rates, canyon cutting, sediment filling and different sediment transporting mechanisms. The area offshore Southwestern Taiwan is generally recognized as having active tectonics and high sediment deposition rates. In the Gaoping Slope, slope basins are formed by the developments of folds, faults and diapiric intrusions. Portions of the sediments discharged from the Taiwan mountain belt have been trapped in these basins in the Gaoping Shelf and Gaoping Slope. The rest of the sediments were transported to deep sea areas through submarine canyons. This complex system of folds, faults, diapirs, slope basins, submarine canyons, and sediment deposits has also readjusted the morphology of the Gaoping Slope. This study examines the linkage between accommodation spaces of tectonic and sedimentary processes in the Gaoping Slope through seismic facies analysis. Four seismic facies which include convergent-symmetrical facies, convergent-baselapping facies, chaotic facies, and parallel and drape facies, and different deposition patterns have been recognized in the Gaoping Slope basins. The thick mud layers which are regarded as the source of diapiric intrusions are first observed beneath the basin. Strata records show that the accommodation spaces in various slope basins have increased or decreased during different stages of basin evolution. Because of the competition between regional tectonism (accommodation space variations) and sediment routing distance from provenance to depository (sediment input variations), most under-filled basins lie in the lower slope domain in the Gaoping Slope, but also in the upper slope domain east of the Gaoping Submarine Canyon. This observation suggests that in the inner Gaoping Slope west of the Gaoping Submarine Canyon, sediment deposition rate is higher than the basin subsidence rate, the topography of the upper slope domain there is “healed”, and most sediments are overfilled in the slope basins now. Besides the sequential steps of sedimentary disposal in the filling-and-spilling model, we have also observed evidences which indicate that mass movements and submarine canyons in the area have significantly changed the sediment dispersal patterns in the slope basins of the Gaoping Slope. We suggest that although filling-and-spilling is a key sedimentary process in the Gaoping Slope, tectonic activities, mass wasting events and canyon feeding processes have diversified sediment transporting mechanisms from the inner to outer slopes in the area offshore Southwest Taiwan.