Tectonic Subsidence Analysis Research Articles

Tectonic subsidence and uplift within Canterbury Basin, South Island, New Zealand

ABSTRACT The Canterbury Basin is a portion of the mostly submerged continent of Zealandia that formed along the eastern portion of the Gondwanan front. Based on tectonic subsidence analyses of IODP Expedition 317 boreholes and Clipper-1 well data, we argue for a rapid subsidence event (∼84 Ma to ∼76 Ma) which we interpret as transit away from a region of mantle upwelling. Breakup was followed by thermal subsidence between 76 Ma and 20 or 10 Ma. Sea-level estimates based on our data are consistent with eustatic estimates in the literature between 76 and 30 Ma. From about 7 Ma to 3.8 Ma, there is evidence that over a kilometre of uplift could have occurred within the basin. This uplift event is consistent with earlier suggestions of lower mantle delamination based on local volcanism and the thickness of the lithosphere. Isostatic calculations are consistent with the hypothesis that delamination of some dense mantle lithosphere could account for the uplift seen in our tectonic subsidence analyses.

Tectonic Subsidence Modeling of Diachronous Transition From Backarc to Retroarc Basin Development and Uplift During Cordilleran Orogenesis, Patagonian‐Fuegian Andes

AbstractBackstripped tectonic basin subsidence histories are critical for interpreting phases of lithospheric deformation and paleoenvironmental change from the stratigraphic record. This study presents new subsidence modeling of the Rocas Verdes Backarc Basin (RVB) and Magallanes‐Austral retroarc foreland basin (MAB) of southernmost South America to evaluate along‐strike changes in tectonic subsidence related to the Late Jurassic through Miocene history of the Southern Andes. We compiled composite stratigraphic sections for seven basin localities that span 47°–54°S from published sedimentological records of paleoenvironment, paleobathymetry, and geochronology. Modeling results resolve regional trends in basin tectonic subsidence, uplift, and sedimentation rate that influenced the depositional environment during five broad phases of RVB‐MAB development: (a) Late Jurassic tectonic subsidence and basin deepening associated with rift‐related backarc extension that postdated regional diachronous rift‐related magmatism. (b) Southward younging of Early to Late Cretaceous pronounced acceleration in tectonic subsidence interpreted as the initiation of flexural loading and development of the MAB foreland basin system. (c) Late Cretaceous (ca. 85–70 Ma) tectonic uplift within the central foredeep ∼49° to 52°S, coeval with a shift from slope to shelf deposition at these latitudes. (d) A protracted period of low‐magnitude basin uplift and relative tectonic quiescence during the Paleogene, with the exception of southernmost localities; and (e) Synchronous latest Oligocene‐early Miocene tectonic subsidence linked to basin deepening and transgression across the northern and central basin sectors. Backstripped tectonic subsidence analysis corroborates existing interpretations for orogenic development in the RVB‐MAB and sheds new light on complex polyphase basin histories where extension precedes convergence.

The Characteristics and Geological Significances of Tectonic Regime Changes in Chepaizi Uplift, Junggar Basin, Western China

Tectonic regime change refers to the process in which the two periods of tectonic movement changes and produce corresponding tectonic regime change surfaces (unconformity surfaces) and other geological responses in the process of basin development and evolution. The change of tectonic movement is the root cause of tectonic regime change. Tectonic regime changes produce different geological responses, which can be used as the signs to identify tectonic regime changes. In order to study the characteristics of tectonic regime changes of Chepaizi Uplift in Junggar Basin and the control on oil and gas migration and accumulation, four stages of tectonic regime changes were identified by using the techniques of the rock acoustic emission (AE) technology, tectonic subsidence analysis, and tectonic stratigraphic sequence analysis, which occurred at the end of Early Permian, the end of Late Triassic, the end of Jurassic, and the end of Paleogene, respectively. The main stratigraphic product of tectonic regime change is the unconformity structure. The unconformity structure has obvious stratification, including the bottom conglomerate layer, the weathered clay layer, and the semiweathered rock layer, and plays an important role in controlling oil and gas migration and accumulation. The weathered clay layer and the hydrolysis layer have a sealing and shielding effect on oil and gas; the leaching layer can become the effective reservoir; at the same time, the leaching layer can provide a channel for the lateral transportation of oil and gas.

Tectonic subsidence analysis of the Ancestral Rocky Mountains from the interior to the southern margin

Southwestern Laurentia experienced intraplate deformation during the Pennsylvanian and early Permian, an orogenic event termed the Ancestral Rocky Mountains (ARM). Deformation consisted of uplifted Precambrian-cored basement blocks separated from adjacent basins by high-angle faults. The tectonic drivers of this orogen are debated, which is likely in part due to significant changes to the chronostratigraphy of the geologic time scale since many of the models have been proposed. To better understand the orogen, we assess spatial subsidence patterns with 1-D backstripped tectonic subsidence curves from eight ARM basins across the orogen using the 2020 Geologic Time Scale for temporal calibration. These patterns indicate the following: 1) basins largely initiated in the late Morrowan—early Atokan (Bashkirian); 2) most subsidence curves suggest flexure from a fixed-load foreland basin that steadily increased until the Missourian (Kasimovian) where most basins reached peak subsidence; 3) diminished subsidence occurred in most basins in the Late Pennsylvanian and shut off across most of the orogen by the end of the Wolfcampian (Asselian—early Artinskian); and 4) basin subsidence renewed in the southern basins during the Leonardian (late Artinskian—Kungurian). The synchronous start to basin subsidence is coeval to the initiation of highly oblique convergence between the Laurentia and Panthalassan plates along the southwestern margin. Influences from the Ouachita-Marathon margin are best reflected by Late Mississippian subsidence of the Anadarko Basin and transpressional deformation in the Orogrande Basin during the Late Pennsylvanian. The decrease in early Permian subsidence is coeval to the cessation of movement on most ARM faults and burial of Precambrian-cored highlands indicating that classical ARM tectonics is mostly a Pennsylvanian event. The increase in subsidence observed during the Leonardian (late Artinskian—Kungurian) in the southern basins may reflect renewed oblique convergence along the southwestern margin.

Reconstruction of the Cenozoic tectono-thermal history of the Dongpu Depression, Bohai Bay Basin, China: Constraints from apatite fission track and vitrinite reflectance data

The Dongpu Depression is an important oil-producing area in the Bohai Bay Basin, China. The exploration focus in this area has recently shifted to intervals with greater depths (>3500 m) because of decreasing hydrocarbon production at depths shallower than 3500 m. Deep petroleum resource evaluation is becoming important and the tectono-thermal history is a major part of this evaluation. In this study, Cenozoic tectono-thermal histories of the Dongpu Depression are reconstructed by coupling an inversion method of vitrinite reflectance and apatite fission track data from 13 wells. Moreover, the maturation history of the deep source rocks was modeled based on these histories. The results clearly show that the Dongpu Depression experienced two heat flow maxima during the deposition of the middle parts of the Eocene Shahejie 3 member and the Oligocene Dongying Formation, which exhibit maximum heat flow values of 70.5–77.5 mW/m2 and 64.8–70.0 mW/m2, respectively. These two periods of high heat flow are linked to the rifting events of the Dongpu Depression, corresponding to the intense rifting substage (45-38 Ma) and the later rifting substage (38-27 Ma). Tectonic subsidence analysis revealed that the Dongpu Depression experienced initial syn-rift subsidence during the Paleocene, followed by subsequent thermal subsidence since the Neogene. The maturation history indicates that these source rocks experienced only one hydrocarbon generation phase in the mid-northern sags, and experienced a hydrocarbon generation peak during the Oligocene Dongying Formation deposition.

The formation of the Sichuan Basin, South China, during the Late Ediacaran to Early Cambrian

AbstractThe Upper Ediacaran to Lower Cambrian of the Sichuan Basin in South China has long been considered to be dominated by shallow‐water deposition. Hydrocarbon exploration, however, has revealed that a NW‐SE trending intraplatform trough formed in the basin during the same period. Although different models have been proposed, the formation and evolution of the trough are still not fully understood. In this study, we investigate both the origin of the intraplatform trough and the formation of the Sichuan Basin by integrating seismic interpretation, well correlation and tectonic subsidence analysis. The seismic and well data clearly show three stages of development of the trough. The first stage, in the early Late Ediacaran, is characterized by considerable thinning of the lower two members of the Upper Ediacaran from the platform margins to the trough. In the second stage, in the late Late Ediacaran, the platform margins backstepped and the extent of the trough expanded significantly to a width of ca. ~400 km. The third stage, in the early Early Cambrian, was dominated by gradual filling of the trough and onlapping of the platform margins. Backstripped tectonic subsidence curves show one, or two closely spaced episodes of linear subsidence starting at ~550 Ma and then decreasing exponentially until ~450 Ma. The shape of the subsidence curves is consistent with formation of the Sichuan Basin by low, and slow amounts of lithospheric stretching of thickened cratonic lithosphere. The tectonic subsidence increases from the centre to the NW of the basin. Interestingly the margins of the trough do not correlate with contoured values of increased tectonic subsidence and we infer that the trough was a palaeogeographic embayment in a large carbonate platform that developed in a broad, ramp‐like area of slow and low subsidence tilting down to the proto‐Tethyan ocean located to the NW of the basin.

Cretaceous Evolution of the Central Asian Proto‐Paratethys Sea: Tectonic, Eustatic, and Climatic Controls

AbstractThe timing and mechanisms of the Cretaceous sea incursions into Central Asia are still poorly constrained. We provide a new chronostratigraphic framework based on biostratigraphy and magnetostratigraphy together with detailed paleoenvironmental analyses of Cretaceous records of the proto‐Paratethys Sea fluctuations in the Tajik and Tarim basins. The Early Cretaceous marine incursion in the western Tajik Basin was followed by major marine incursions during the Cenomanian (ca. 100 Ma) and Santonian (ca. 86 Ma) that reached far into the eastern Tajik and Tarim basins. These marine incursions were separated by a Turonian‐Coniacian (ca. 92–86 Ma) regression. Basin‐wide tectonic subsidence analyses imply that the Early Cretaceous sea incursion into the Tajik Basin was related to increased Pamir tectonism. We find that thrusting along the northern edge of the Pamir at ca. 130–90 Ma resulted in increased subsidence in a retro‐arc basin setting. This tectonic event and coeval eustatic highstand resulted in the maximum observed geographic extent of the sea during the Cenomanian (ca. 100 Ma). The following Turonian‐Coniacian (ca. 92–86 Ma) major regression, driven by eustasy, coincides with a sharp slowdown in tectonic subsidence during the late orogenic unloading period with limited thrusting. The Santonian (ca. 86 Ma) major sea incursion was likely controlled by eustasy as evidenced by the coeval fluctuations in the west Siberian Basin. An early Maastrichtian cooling (ca. 71–70 Ma), potentially connected to global Late Cretaceous trends, is inferred from the replacement of mollusk‐rich limestones by bryozoan‐ and echinoderm‐rich limestones.

Chronostratigraphic Revision of the Cloverly Formation (Lower Cretaceous, Western Interior, USA)

The Cloverly Formation is an important geologic unit for understanding the development of North American terrestrial landscapes and ecosystems, but the age of this unit is poorly constrained. We report U–Pb radiometric dates determined by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and chemical abrasion thermal ionization mass spectrometry (CA-TIMS) from euhedral zircons derived from fluvial sandstone and bentonitic claystone. We reanalyzed published biostratigraphic, paleomagnetic, and radiometric datasets, which have generally disregarded younger (late Albian–Cenomanian) ages for the formation. New data reported in this study suggest that deposition of the Cloverly Formation spanned the Valanginian–Cenomanian stages (ca. 140 Ma–98 Ma), a longer time interval than the commonly cited Aptian–Albian depositional timeframe. The lowest member of the Cloverly Formation, the Pryor Conglomerate, was deposited ca. 140–130 Ma in response to the onset of the Sevier Orogeny shedding sediment from the west. The overlying Little Sheep Mudstone Member was deposited ca. 124–109 Ma in a time of low sediment supply. In the mid–late Albian to early Cenomanian (ca. 109–98 Ma), sediment sourced from the east was deposited as the Himes Member and Greybull Sandstone. Following this, the Sykes Mountain Formation began nearshore deposition as the Western Interior Seaway transgressed from the north. Our revised chronostratigraphic framework for the Cloverly Formation is congruent with tectonic subsidence analysis showing a rapid increase in accommodation space in the mid-Albian. We hypothesize that more intensive sampling may yield multiple fossil assemblages within the formation, paralleling its correlates to the south. Furthermore, we hypothesize that some poorly represented taxa will be synonymized with taxa from those same units now that their temporal equivalence has been demonstrated.

Detrital zircon microtextures and U‐PB geochronology of Upper Jurassic to Paleocene strata in the distal North American Cordillera foreland basin

AbstractDetrital zircon surface microtextures, geochronologic U‐Pb data, and tectonic subsidence analysis from Upper Jurassic to Paleocene strata in the Black Hills of South Dakota reveal provenance variations in the distal portion of the Cordillera foreland basin in response to tectonic events along the outboard margin of western North America. During Late Jurassic to Early Cretaceous time, nonmarine strata record initially low rates of tectonic subsidence that facilitated widespread recycling of older foreland basin strata in eolian and fluvial systems that dispersed sediment to the northeast, with minimal sediment derived from the thrust belt. By middle Cretaceous time, marine inundation reflects increased subsidence rates coincident with a change to eastern sediment sources. Lowstand Albian fluvial systems in the Black Hills may have been linked to fluvial systems upstream in the midcontinent and downstream in the Bighorn Basin in Wyoming. During latest Cretaceous time, tectonic uplift in the study area reflects dynamic processes related to Laramide low‐angle subduction that, relative to other basins to the west, was more influential due to the greater distance from the thrust load. Provenance data from Maastrichtian and lower Paleocene strata indicate a change back to western sources that included the Idaho‐Montana batholith and exhumed Belt Supergroup. This study provides a significant contribution to the growing database that is refining the tectonics and continental‐scale sediment dispersal patterns in North America during Late Jurassic‐early Paleocene time. In addition, it demonstrates the merit of using detrital zircon grain shape and surface microtextures to aid in provenance interpretations.

Subsidence Analysis and Burial History of the Late Carboniferous to Early Jurassic Soutpansberg Basin, Limpopo Province, South Africa

AbstractThe subsidence history of the Soutpansberg Basin was reconstructed by a tectonic subsidence analysis coupled with backstripping calculations based on data of newly interpreted sequence boundaries. Furthermore, burial and time plots were constructed in order to understand the burial and thermal history of the basin. Input data were based on facies, lithostratigraphic models and tectonic interpretations. The studied succession is up to 1000 m and is underlain by the Achaean Limpopo Mobile Belt. The subsidence within the basin supports the primary graben system which must have been centred within the present basins, and later became a region of faulting. The subsidence and burial history curves suggests two phases of rapid subsidence during the Early‐Late Permian (300–230 Ma) and Middle Triassic (215–230 Ma). The areas of greater extension subsided more rapidly during these intervals. Two slow subsidence phases are observed during the Late Triassic (215–198 Ma) and Early Jurassic (198–100 Ma). These intervals represent the post‐rift thermal subsidence and are interpreted as slow flexural subsidence. Based on these observations on the subsidence curves, it is possible to infer that the first stage of positive inflexion (300 Ma) is therefore recognised as the first stage of the Soutpansberg Basin formation.

Basin deconstruction–construction: Seeking thermal–tectonic consistency through the integration of geochemical thermal indicators and seismic fault mechanical stratigraphy ​– Example from Faras Field, North Western Desert, Egypt

To construct a model of a sedimentary basin's thermal tectonic history is first to deconstruct it: taking apart its geological elements, searching for its initial conditions, and then to reassemble the elements in the temporal order that the basin is assumed to have evolved. Two inherent difficulties implicit to the analysis are that most organic thermal indicators are cumulative, irreversible and a function of both temperature and time and the non-uniqueness of crustal strain histories which complicates tectonic interpretations. If the initial conditions (e.g. starting maturity of the reactants and initial crustal temperature) can be specified and the boundary conditions incrementally designated from changes in the lithospheric heat engine owing to stratigraphic structural constraints, then the number of pathways for the temporal evolution of a basin is greatly reduced. For this investigation, model input uncertainties are reduced through seeking a solution that iteratively integrates the geologically constrained tectonic subsidence, geochemically constrained thermal indicators, and geophysically constrained fault mechanical stratigraphy.The Faras oilfield in the Abu Gharadig Basin, North Western Desert, Egypt, provides an investigative example of such a basin's deconstructive procedure. Multiple episodes of crustal extension and shortening are apparent in the tectonic subsidence analyses which are constrained from the fault mechanical stratigraphy interpreted from reflection seismic profiles. The model was iterated with different thermal boundary conditions until outputs best fit the geochemical observations. In so doing, the thermal iterations demonstrate that general relationship that basin heat flow increases decrease vertical model maturity gradients, increases in surface temperatures shift vertical maturity gradients linearly to higher values, increases in sediment conductivities lower vertical maturities with depth, and the addition of “ghost” layers (those layers removed) prior to the erosional event increase maturities beneath, and conversely. These integrated constraints upon the basin evolution model indicate that the principal source rocks, Khatatba and the lowest part of the Alam El Bueib formations, entered the oil window at approximately 95 Ma and the gas window at approximately 25 Ma. The upper part of the Alam El Bueib Formation is within the oil window at the present day.Establishing initial and boundary value conditions for a basin's thermal evolution when geovalidated by the integration of seismic fault mechanical stratigraphy, tectonic subsidence analysis, and organic geochemical maturity indicators provides a powerful tool for optimizing petroleum exploration in both mature and frontier basins.

Delineating the Exmouth mantle plume (NW Australia) from denudation and magmatic addition estimates

Volcanic margins are a class of large igneous provinces (LIPs) characterized by rifting-derived basaltic magmatism. This is commonly attributed to extension-related lithospheric thinning, generating decompression melting. Another mechanism influencing magmatism on volcanic margins is mantle plume–induced lithospheric thinning. Unfortunately, it is difficult to differentiate between these mechanisms because they seem to take place almost contemporaneously. Whereas rifted volcanic margins produce linear denudation and magmatic addition patterns, mantle plumes or active upwellings would generate more subcircular domal patterns. Here, I use magmatic addition and denudation patterns to discriminate between these scenarios in a data set from the volcanic margin offshore NW Australia. Seismic and well data results suggest the presence of a domal component that is used to delineate the Late Jurassic Exmouth mantle plume. This upwelling was centered on a highly extended and subsided continental fragment bounded by the present-day subsea Sonne and Sonja Ridges and includes the Cuvier margin and Cape Range fracture zone. The region is characterized by ∼2.6 km of denudation and ∼500 m of tectonic uplift, with erosion products acting as source material for the Early Cretaceous Lower Barrow delta. Denudation analysis indicates that only ∼40% of the seismically detected magmatic underplate is melt related, with the effective underplate ∼4 km thick near the locus of uplift and decreasing in the outer regions. Tectonic subsidence analysis, seismic stratigraphy, and plate reconstruction suggest that the plume-induced domal uplift preceded magmatism and breakup. Plume activity was followed by a westward-propagating hotspot track, possibly terminating in Greater India (present Tibet).

Geothermal regime and source rock thermal evolution in the Chagan sag, Inner Mongolia, northern China

The Chagan sag has the greatest oil and gas exploration potential among other sags in the Yingen Ejinaqi Basin, Inner Mongolia. The average geothermal gradient in the Chagan sag is 33.6 °C/km, whereas the heat flow ranges from 65.9 mW/m2 to approximately 85.5 mW/m2, with an average value of 74.5 mW/m2. Thermal history reveals that the Chagan sag experienced the following 4 stages of thermal evolutions: (1) a rapidly increasing geothermal gradient stage from the Early Cretaceous Bayingebi Formation depositional period to the Early Cretaceous Suhongtu Formation depositional period; (2) a geothermal gradient peak stage during the Early Cretaceous Yingen Formation depositional period; (3) a high geothermal gradient continuation stage during the Late Cretaceous Wulansuhai Formation depositional period; and (4) a thermal subsidence stage during the Cenozoic. Tectonic subsidence analysis reveals that the area experienced an initial synrift subsidence during the Early Cretaceous followed by a subsequent long-term thermal subsidence since Late Cretaceous. Thermal and tectonic subsidence histories of this area are of great significance to petroleum exploration and hydrocarbon resource assessment because they bear directly on issues of source rock maturation. The maturation histories of the 3 sets of source rocks in the sag were modeled on the basis of the present geothermal field, thermal history and tectonic subsidence history. The results reveal that the hydrocarbon generation of the Chagan sag was controlled by the Early Cretaceous geothermal fields, and the source rock maturity reached the maximum at the end of the Yingen Formation depositional period. Moreover, the maturation evolution degree shows a difference for the 3 sets of source rocks. The source rocks of the Bayingebi 1 and 2 Formations reached the middle mature and dry-gas stage. In contrast, the source rocks of the Suhongtu 1 Formation only reached the early mature and middle mature stage. This work may provide new insights for the understanding of the oil and gas exploration potential of the Chagan sag.

Geothermal regime and hydrocarbon kitchen evolution in the Jianghan Basin

The present geothermal gradient and terrestrial heat flow was calculated of 18 wells in the Jianghan Basin. Thermal gradient distribution of the Jianghan Basin was obtained based on data of systematical steady-state temperature and oil-test temperature. The basin-wide average thermal gradient in depth interval of 0–4000 m is 33.59°C/km. We report nine measured terrestrial heat flow values based on the data of detailed thermal conductivity and systematical steady-state temperature. These values vary from 41.9 to 60.9 mW/m2 with a mean of 52.3 ± 6.3 mW/m2. However, thermal history analyses based on vitrinite reflectance (VR) and apatite fission track (AFT) data indicate that thermal gradient in the northern and southern Qianbei Fault reached its peak of ∼36 and ∼39°C/km respectively in the Middle Jurassic and the Oligocene, and it descended during the early Miocene to the present-time value. Furthermore, tectonic subsidence analysis reveals that the tectonic subsidence of the Jianghan Basin in the Cretaceous to early Miocene was characterized by synrift initial subsidence followed by the subsequent thermal subsidence. The thermal history and tectonic subsidence history of Jianghan Basin are of great significance to petroleum exploration and hydrocarbon source assessment, because they bear directly on issues of petroleum source rock maturation. Based on the thermal history and tectonic subsidence history, with the combination of geochemical and thermal parameters, the maturation and the hydrocarbon generation intensity evolution history of the P2 d source rocks are modeled. The results show that the P2 d source rocks are in a higher degree of maturation at present, and the Yuan’an and Herong sags are the two most important kitchens in the Late Jurassic, Xiaoban Sag is another most important kitchen during the Late Cretaceous to late Paleogene, and the Zhijiang and Mianyang sags are other two important hydrocarbon kitchens in the Late Cretaceous. The Mianyang Sag and Yichang Ramp are the favorable exploration targets in the future. This study may provide new insight for the understanding of the oil and gas exploration potential for the Jianghan Basin.

Geothermal regime and hydrocarbon kitchen evolution of the offshore Bohai Bay Basin, North China

The offshore Bohai Bay Basin, located in the central Bohai Bay Basin, north China, one of the most petroliferous basins in China. In this article, based on formation-testing temperature, drill-stem tests, and bottom-hole temperature data, 80 thermal gradient values at the depth interval of 0 to approximately 3000 m (~9843 ft) in the offshore Bohai Bay Basin were obtained. The basinwide average thermal gradient is 31.8 4.6C/km. Based on the above thermal gradient data and the corresponding average weighted thermal conductivity data, 80 measured terrestrial heat flow values were obtained. These values range from 33.5 to 84.0 mW/m2, with an average value of 60.8 8.7 mW/m2. The heat flow and thermal gradient distribution in this region generally show higher values in the uplifts and lower ones in the sags. A thermal history, derived from vitrinite reflectance and apatite fission-track) data, indicates that Paleogene cooling occurred after a period of much higher paleogeothermal gradient (3854C/km). Tectonic subsidence analysis reveals that the area experienced initial synrift subsidence during the Paleogene followed by subsequent thermal subsidence since the Neogene. Thermal and tectonic subsidence histories of this area are of great significance to petroleum exploration and hydrocarbon resource assessment because they bear directly on issues of petroleum source rock maturation. The maturation and hydrocarbon expulsion histories of the Paleogene Shahejie 3 Formation (E2s3), which is the most important source rock in the offshore Bohai Bay Basin, are modeled. Results show that the Shahejie 3 Formation is in a high mature stage at the present day, and the Bozhong and Qikou sags are the most important kitchens. The Huanghekou sag became the third most important hydrocarbon kitchen in the early Neogene. Based on this hydrocarbon kitchen evolution, oil and gas mainly accumulated after 12 Ma. The evolution of kitchen areas may provide new insights for the understanding of the oil and gas exploration potential of the offshore Bohai Bay Basin.

Cretaceous–Neogene tectonic evolution of the northern margin of the Black Sea from seismic reflection data and tectonic subsidence analysis

Abstract Three fundamental stages of the Cretaceous–Neogene tectonic evolution of the Odessa Shelf and Azov Sea (northern margins of western and eastern Black Sea basins, respectively) have been documented from the analysis of reinterpreted regional seismic profiling and one-dimensional (1-D) subsidence analysis of 49 wells, for which the stratigraphic interpretation was recently revised. (1) An initial active rifting stage began within the Early Cretaceous (not later than Aptian–Albian times) and continued until the end of the Santonian in the Late Cretaceous ( c . 128–83 Ma). A system of half-grabens with mainly south-dipping normal faults developed on the Odessa Shelf at this time. The most profound faulting, accompanied by volcanic activity, occurred in the NE–SW orientated Karkinit-Gubkin rift basin at the boundary between the Eastern European and Scythian platforms. The footwalls of half-grabens were exposed above sea level and subject to erosion at this time. Active extensional processes affected the western part of Azov Sea and, while the onset and cessation of these cannot be tightly constrained, they are compatible with the well constrained results from the Odessa Shelf. (2) The second tectonic stage is one of passive post-rift thermal subsidence that lasted from the Campanian (Late Cretaceous) until the end of the Middle Eocene (83–38.6 Ma). (3) The third stage of basin evolution is one of inversion tectonics in a compressional setting. Discrete inversion events occurred at the end of the Middle Eocene, during the Late Eocene, during the Early Miocene and at Middle Miocene times ( c . 38.6 Ma, c . 35.4 Ma, c . 16.3 Ma, c . 10.4 Ma, respectively) and typical inversion structures developed on the Odessa Shelf, some parts of which were uplifted and significantly eroded (down to the Lower Cretaceous succession). The southern part of the Azov Sea, opening into the northernmost eastern Black Sea basin, subsided rapidly during this time; thereafter, until the Quaternary, rapid subsidence was limited to its southeastern part, which was incorporated into the Indolo-Kuban foreland basin of the Greater Caucasus orogen.

Rifting process of the Xihu Depression, East China Sea Basin

Having a maximum depositional depth up to 15 km, the NE-trending Xihu Depression is evolved from a deep Paleogene continental margin rifting along the present-day East China Sea continental shelf. In this paper we use deep seismic reflection, well logging, and gravity data to synthesize early rifting process of the depression. To study the regional tectonic subsidence history we developed a computer program that performs backstripping and simultaneous inversion for stretching factor, initial lithospheric thickness and incipient age of thermal subsidence. Tectonic subsidence analyses of 40 industrial wells reveal nonuniform stretching — preferential crustal extension along the depocenter but preferential mantle extension at the western flank. Uniform extension may have occurred only somewhere between the central inversion zone and the western margin. In the early rifting stage, subdued initial subsidence or initial uplift is observed on several wells near the western margin, due possibly to flexural isostatic balance. The initial mechanical lithospheric thicknesses from subsidence inversion seem to vary from about 55 km to almost 130 km, suggesting significant longitudinal segmentation as well as transverse variation in the prerifting lithosphere. It is likely that the southern part of the Xihu Depression was developed initially on a region of relatively thin lithosphere, a statement conformable to geological evidences. NW–SE trending deep seismic profiling clearly reveals the deep basement structure of the depression, as well as the synrift and postrift sedimentary packages separated by a breakup unconformity. Crustal layer thicknesses are independently estimated from gravity modeling/inversion, tectonic subsidence analyses, and deep seismic profiling, respectively. These methods all arrive at very small present-day thicknesses of the crustal layer beneath the depocenter of the Xihu Depression.

PALEOCENE-MIDDLE MIOCENE FLEXURAL-MARGIN MIGRATION OF THE NONMARINE LLANOS FORELAND BASIN OF COLOMBIA

A foreland basin is a dynamic system whose depositional systems migrate in response to changes in tectonic uplift patterns, sedimentary filling processes and isostatic rebound of the lithosphere. The Paleocene-middle Miocene foreland system of the Llanos foothills and Llanos basin of Colombia includes regional unconformities, abrupt changes in lithology/stacking patterns and flooding surfaces bounding reservoir and seal units. Here we integrate a systematic biostratigraphic study, stratal architecture and tectonic subsidence analyses, regional seismic profiles, and provenance data to define the diachronism of such surfaces and to document the direction of migration of foreland depozones. In a flexurally-deformed basin, sandstone composition, rates of accommodation and sediment supply vary across and along the basin. We show how a coeval depositional profile in the Llanos foothills-Llanos foreland basin consists of litharenites interbedded with mudstones (seal rock, supplied from the orogenic front to the west) that correlate cratonward with organic-rich mudstones and coal (source rock), and to amalgamated fluvial-estuarine quartzarenites (reservoir rock, supplied from the craton to the east) adjacent to a subaerial forebulge (unconformity). This system migrated northward and eastward during the Paleocene, westward during the early-middle Eocene, and eastward during the Oligocene. In the lower-middle Miocene succession of the Llanos basin, identification of flooding events indicates a westward encroaching of a shallow-water lacustrine system that covered an eastward-directed fluvial-deltaic system. A similar process has been documented in other basins in Venezuela and Bolivia, indicating the regional extent of such flooding event may be related to the onset of Andean-scale mountain-building processes.

The Cenozoic Tectono‐Thermal Evolution of Jiyang Depression, Bohai Bay Basin, East China

AbstractThe thermal history of the sedimentary basins is an important parameter for the study of tectonic evolution, hydrocarbon accumulation and resource assessment. The thermal gradient evolution histories of 70 wells during the Cenozoic time in the Jiyang Depression were modeled by using the vitrinite reflectance and apatite fission track data in this paper. Based on these modeling results, the characteristics of thermal evolution of the Dongying, Zhanhua, Huimin and Chezhen sags in the Jiyang depression were analyzed. The thermal gradients of the depression decreased during the Cenozoic time. However, it decreased quickly in the Eogene, but only changed a little during the Neogene time. The thermal gradient was 54.0~50.0°C/km during the deposition of the Kongdian Group, 50.0~40.0°C/km during the period of Shahejie group, 40.0~38.5°C/km of Dongying group and 38.5~35.5°C/km during the Neogene. It changed little after that time and decreased down to 35°C/km at the present‐day. The four sags had different thermal evolution history, especially after the Dongying tectonic movement at the end of Eogene. The thermal gradient of the Dongying sag is the highest, then the Zhanhua sag is next, the Huimin sag is relative lower and the Chezhen sag lowest. The Chezhen sag underwent the lowest thermal history during the whole period of Cenozoic time. The differential thermal gradients resulted in the different threshold depth of hydrocarbon generation in the four sags. The modeling results of thermal history fits well with the evolution stages of rift‐subsidence basin to down‐warped basin by the tectonic subsidence analyses of the Jiyang depression.

Transformation of accommodation space of the Cretaceous Qingshankou Formation, the Songliao Basin, NE China

ABSTRACTAnalysis of accommodation space variation during deposition of the Cretaceous Qingshankou Formation in the Songliao Basin, NE China, indicates that accommodation space changed both through time and across the basin as a seesaw movement. The mid‐upper Qingshankou Formation is divided into three units. In each unit, changes of accommodation space differ in the southern and northern part of the basin. Increasing accommodation in the southern part is accompanied by a decrease in the northern part, and vice versa. Between the northern and southern basin, there was a neutral belt that is like a fulcrum, called the transformation belt here, where the accommodation did not change to any significant degree. We call this response ‘accommodation transformation’, whose characteristics are defined by tectonic subsidence analysis, palaeontological and sedimentary analyses. The accommodation increasing belt, decreasing belt, transformation belt and accommodation transformation boundary together constitute the accommodation transformation system. The recognition of accommodation transformation in the Songliao Basin provides a new insight into sequence stratigraphy and might be widely applicable.