Southern Basin Margin Research Articles

Deep thermal state on the southern margin of the Zhangzhou Basin based on the electrical conductivity model

Exploring the internal spatial and thermal structure of the Zhangzhou Basin is of great scientific significance in understanding the properties of the deep heat sources and the heating mechanism of hot springs in this region. This study estimates the temperature distribution within the upper mantle of the Basin's southern margin using the Arrhenius equation and Hashin-Shtrikman bounds based on a two-dimensional crust-mantle electrical resistivity model. We also employ a layered simulation technique to calculate the crustal temperature distribution using a one-dimensional steady-state heat conduction equation, constrained by the upper mantle's top and ground surface temperatures. This approach displays the characteristics of the longitudinal variations and horizontal inhomogeneities in crust-mantle temperature. Additionally, we estimate the heat flow values within the study area. Our findings reveal that: (i) the upper mantle (at depths of 30 - 50 km) exhibits a temperature range of 700 - 1100 °C, with the presence of local Moho and upper mantle uplifts; (ii) the crustal temperature spans from 21 - 900 °C, with a diminishing influence of the upper mantle uplift area on crustal temperature at shallower depths; (iii) the surface heat flow values derived from our simulations range between 87 and 100 mW/m2, averaging at 93.23 mW/m2; (iv) the exploration of dry heat rock in this region is likely to reach a depth of at least 6 km. These results suggest that the genesis of hot springs in the study area is not solely influenced by the heat energy extracted from large-area granitic surrounding rocks during a long transport process, but is also considerably affected by local deep thermal anomalous bodies and deep-large faults.

Composition and distribution of sedimentary organic matter in nearshore Berriasian strata (‘German Wealden’) of the eastern Lower Saxony Basin, NW Germany

Abstract In the Lower Saxony Basin of Northern Germany, the Earliest Cretaceous (Berriasian, ‘German Wealden’) is represented by organic-rich shales assigned to the Isterberg Formation, which have been deposited under brackish-lacustrine conditions in a partially restricted basin. Towards the southern basin margin, these shales interfinger with nearshore sandstones sourced from the Deister-Hils delta. In order to better understand the environmental conditions and depositional dynamics of the Isterberg Fm, the sedimentary organic matter has been studied with a combined approach including bulk rock organic geochemistry and palynofacies analysis. The lower part (W 1 to W 3) is interpreted to reflect very shallow-water conditions and episodic emergence, indicated by multiple occurrences of palaeosol horizons, rhizoliths and intercalated coal beds formed within a mud-dominated and protected domain of the delta plain. The overlying sand-rich interval represents a nearshore deltaic setting. A distinct change is observed in the upper part (W 4), indicating more distal conditions characterized by clay-dominated sedimentation, abundant lumachelle interbeds and a predominance of aquatic-derived organic matter. The newly acquired data fill a gap in the record between the proximal and distal strata of the Berriasian Lower Saxony Basin and provide new insights into the accumulation and preservation of organic matter within this exceptional depositional setting.

Multiple compression directions and basinal response in a rhomb-shaped terrestrial basin: The Cuevas de Cañart syncline (Iberian Chain, eastern Spain)

Rhomb-shaped basins have been commonly attributed to strike-slip tectonics, linked to fault bends and jogs (pull-apart basins). The case-study presented in this work (Las Cuevas de Cañart basin, Iberian Chain) is a 2 km × 5 km continental basin that shows a particular combination of geometric and sedimentary features. It shows a syncline geometry with steeply-dipping limbs, thickness of syn-tectonic sedimentary continental filling of about 1000 m, high amplitude/wavelength ratio, and different fold trends, some of them oblique to the main trend of the Iberian Chain. All these features make it an interesting case of a mixed-type basin, sharing both compressional and strike-slip features. The Cuevas de Cañart basin shows a Mesozoic, pre-compressional sequence linked to the extensional processes dominating in the marginal zones of the Maestrazgo basin, with a series up to 1500 m thick of limestones, sandstones and shales. These units overlie a detachment level (Upper Triassic Keuper facies) and show thickness variations controlled by NW-SE and NE-SW striking normal faults. During the Cenozoic compression, both fault systems were re-activated, and newly formed E-W folds (perpendicular to one of the dominant shortening directions) also appeared in the southern basin margin. The detailed structural study of this basin evidences the role of different types of structures (basement faults, thrusts formed under different compression directions) and the relevance of the detachment level in the evolution of compressional basins and thin-skinned fold-and-thrust belts.

A Multi-proxy Provenance Study of Late Carboniferous to Middle Jurassic Sandstones in the Eastern Sverdrup Basin and Its Bearing on Arctic Palaeogeographic Reconstructions

A multi-proxy provenance study of Late Carboniferous to Middle Jurassic sandstones from the eastern Sverdrup Basin was undertaken employing optical petrography and heavy mineral analysis, chemical analysis of apatite, garnet and rutile grains, as well as detrital zircon U–Pb geochronology and Hf isotope analysis. Late Carboniferous to Middle Jurassic strata on the southern basin margin are inferred as being predominantly reworked from Silurian to Devonian strata within the adjacent Franklinian Basin succession. Higher-grade metamorphic detritus appeared during Middle to Late Triassic times and indicates exhumation and erosion of lower (Neoproterozoic to Cambrian) levels within the Franklinian Basin succession and/or a direct detrital input from the Canadian-Greenland Shield. The provenance of northern-derived sediments is more enigmatic owing to the subsequent opening of the Arctic Ocean. Northern-derived Middle Permian to Early Triassic sediments were likely derived from proximal areas of the Chukotkan part of the Arctic Alaska-Chukotka microplate. Late Triassic northern-derived sediments have different detrital zircon U–Pb age spectra from Middle Permian to Early Triassic ones and were likely derived from the Uralian orogenic belt and/or the Arctic Uralides. The loss of this sand input during latest Triassic times is interpreted to reflect drainage reorganisation farther upstream on the Barents Shelf. Middle Jurassic sands in the northern and axial parts of the basin were largely reworked from local northern-derived Late Triassic strata. This may have been facilitated by rift flank uplift of the northern basin margin in response to rifting in the adjacent proto-Amerasia Basin.

Origin of synchronous extension and inversion in a rift basin: The Phitsanulok Basin, central Thailand

Abstract The Phitsanulok Basin is a Cenozoic rift basin in central Thailand. The basin opened in the Oligocene to Early Miocene with the development of N-S and NNW-SSE trending normal faults. In the Middle Miocene the northern part of the basin continued to experience extension, while the southern part was affected by compressive inversion. Extension resumed in the Late Miocene to Pliocene, followed by post-rift subsidence in the Quaternary. The Middle Miocene anomalous deformation is attributed to activities of the NE-SW Uttaradit Fault and NW-SE Mae Ping Fault, respectively at the northern and southern basin margins. Both faults had limited activities during the Oligocene to Early Miocene rifting, where E-W extension was probably accompanied by vertical maximum principal stress. In the Middle Miocene, the maximum principal stress rotated to a N-S direction and produced sinistral motion on the Uttaradit Fault and dextral motion on the Mae Ping Fault. The strike-slip motions contributed to a counter-clockwise rotation of the continental block west of the Phitsanulok Basin, creating the synchronous extension and contraction. The kinematic model introduces the possibility of local inversion in a rift basin being originated from short-term switch between the maximum and intermediate principal stress axes and reactivation of long-lived strike-slip faults, as opposed to major change in regional stress related to plate movements. The model implies that the segment of the Mae Ping Fault south of the Phitsanulok Basin was inactive during the Oligocene to Early Miocene and was reactivated as a dextral fault in the Middle Miocene.

Evolution of the South-Iberian paleomargin: From hyperextension to continental subduction

Three crustal-scale sequentially restored cross-sections along the Central External Betic Cordillera enable us to pinpoint the role of extreme crustal thinning, tectonic inheritance and salt tectonics during the evolution of the South-Iberian paleomargin from Mesozoic rifting to Cenozoic continental subduction. This interpretation puts forward the existence of a former highly extended Mesozoic rift system, namely the Subbetic Basin. The basin comprises three main domains that coincide with the classical zoning of the External Betics: (i) The Intermediate units in the northern basin margin represent primary thick minibasins separated by salt walls; (ii) the External Subbetic units attest an inflated salt body in a central trough; and (iii) the Median and Internal Subbetic units in the southern basin margin are analogous to a group of primary minibasins with intercalations of submarine volcanic rocks overlying hyperextended crust. Shortening led to the extrusion of a salt canopy and the development of secondary minibasins. Furthermore, the tectonic inversion of the Subbetic Basin created two major thrusts sheets detached at the Upper Triassic evaporites, accommodating a shortening of ≈100–145 km at early Eocene-middle Miocene time. Compression reshaped the hyperextended domain into a subduction trench, and the former transfer faults into tear faults. Ongoing shortening led to the subduction of the South-Iberian paleomargin beneath the Alborán Domain lithosphere. Our results provide a new perspective on the inversion of segmented rift basins partly floored by mantle rocks and call for a major reconsideration on the tectonic architecture and evolution of the Betic-Rif Cordillera.

Controls on Early Cretaceous desert sediment provenance in south‐west Gondwana, Botucatu Formation (Brazil and Uruguay)

AbstractThe Lower Cretaceous Botucatu Formation records the development of widespread dry–aeolian desert sedimentation throughout the Paraná Basin in south‐west Gondwana. To reconstruct the provenance of the aeolian sediment, petrography, granulometric analysis, U‐Pb detrital zircon ages have been determined from along the southern basin margin in Rio Grande do Sul state (southern Brazil) and Uruguay (Tacuarembó region). The dataset reveals a mean composition Qt89F8L3, comprising very fine to medium‐grained quartozose and feldspatho‐quartzose framework. Heavy mineral analysis reveals an overall dominance of zircon, tourmaline and rutile grains (mean ZTR0.84) with sporadic garnet, epidote and pyrolusite occurrences. The detrital zircon U‐Pb ages are dominated by Cambrian to Neoproterozoic (515 to 650 Ma), Tonian to Stenian (900 to 1250 Ma) and Orosirian to Rhyacian (1.8 to 2.2 Ga) material. The detrital zircon dataset demonstrates a significant lateral variation in sediment provenance: Cambrian to Neoproterozoic detrital zircons dominate in the east, while Tonian to Stenian and Orosirian to Rhyacian ages predominate in the west of the study area. Sandstones are quartz‐rich with dominantly durable zircon, tourmaline and rutile heavy mineral suite, with subtle but statistically significant along‐strike differences in heavy mineral populations and detrital mineralogy which are thought to record local sediment input points into the aeolian system. The similar age spectra of Botucatu desert with proximal Paraná Basin units, the predominance of quartzose, and zircon, tourmaline and rutile components, suggests that recycling is the mechanism responsible for the erg feeding.

Distinct petrographic responses to basin reorganization across the Triassic–Jurassic boundary in the southwestern Barents Sea

AbstractA general shift towards higher mineralogical and textural maturity changes the reservoir character across the Triassic–Jurassic transition in the southwestern Barents Sea basin (SWBSB), largely affecting the hydrocarbon prospectivity in the region. Petrographic and geochronological provenance data presented in this paper suggest that the shift from mineralogically immature to mature sandstones initiated during the deposition of the Norian–Rhaetian Fruholmen Formation, and varies with basin location. Strong contrasts between the Fruholmen Formation and underlying formations are associated with proximity to the rejuvenated Caledonian and Fennoscandian hinterlands and are mainly restricted to the southern basin margins. In the basin interior, subtle petrographic variations between the Fruholmen Formation and older Triassic sandstones reflect a distal position relative to the southern hinterland. The long‐lived misconception of a regional compositional contrast in the Arctic at the turn of the Norian can be attributed to higher sampling frequency associated with hydrocarbon exploration activity along the southern basin margins, and masking by increased annual precipitation and subsequent reworking during the Jurassic. Geothermal signatures and rearrangement of ferric clay material across the Carnian–Norian transition support a recycled origin for the Fruholmen Formation in the basin interior. As the closest tectonically active region at the time, the Novaya Zemlya fold‐and‐thrust belt represents the best provenance candidate for polycyclic components in Norian–Rhaetian strata. In addition to recycling in the hinterland during the Late Triassic, local erosion of exposed intrabasinal highs and platforms at the Triassic–Jurassic transition represents a second process where thermodynamically unstable mineral components originally sourced from the Uralides may be removed. Textural and mineralogical modification may also have occurred in marginal‐marine depositional environments during periods with elevated sea level. Mature sediment supply from the rejuvenated hinterland in the south, multiple cycles of reworking and gradual accumulation of polycyclic grains have likely led to the extreme compositional maturity registered in the Tubåen, Nordmela and Stø formations in the SWBSB. It is likely that increased annual precipitation since the latest Carnian had an amplifying effect on sandstone maturation across the Triassic–Jurassic boundary, but we consider the effect to be inferior compared to provenance shifts and reworking. Findings from this study are important for understanding compositional and textural maturity enhancement processes in siliciclastic sedimentary basins.

Impact of a pre‐existing transverse drainage system on active rift stratigraphy: An example from the Corinth Rift, Greece

AbstractModels to explain alluvial system development in rift settings commonly depict fans that are sourced directly from catchments formed in newly uplifted footwalls, which leads to the development of steep‐sided talus‐cone fans in the actively subsiding basin depocentre. The impact of basin evolution on antecedent drainage networks orientated close to perpendicular to a rift axis, and flowing over the developing hangingwall dip slope, remains relatively poorly understood. The aim of this study is to better understand the responses to rift margin uplift and subsequent intrabasinal fault development in determining sedimentation patterns in alluvial deposits of a major antecedent drainage system. Field‐acquired data from a coarse‐grained alluvial syn‐rift succession in the western Gulf of Corinth, Greece (sedimentological logging and mapping) has allowed analysis of the spatial distribution of facies associations, stratigraphic architectural elements and patterns of palaeoflow. During the earliest rifting phase, newly uplifted footwalls redirected a previously established fluvial system with predominantly southward drainage. Footwall uplift on the southern basin margin at an initially relatively slow rate led to the development of an overfilled basin, within which an alluvial fan prograded to the south‐west, south and south‐east over a hangingwall dip slope. Deposition of the alluvial system sourced from the north coincided with the establishment of small‐scale alluvial fans sourced from the newly uplifted footwall in the south. Deposits of non‐cohesive debris flows close to the proposed hangingwall fan apex pass gradationally downstream into predominantly bedload conglomerate deposits indicative of sedimentation via hyperconcentrated flows laden with sand‐ and silt‐grade sediment. Subsequent normal faulting in the hangingwall resulted in the establishment of further barriers to stream drainage, blocking flow routes to the south. This culminated in the termination of sediment supply to the basin depocentre from the north, and the onset of underfilled basin conditions as signified by an associated lacustrine transgression. The evolution of the fluvial system described in this study records transitions between three possible end‐member types of interaction between active rifting and antecedent drainage systems: (a) erosion through an uplifted footwall, (b) drainage diversion away from an uplifted footwall and (c) deposition over the hangingwall dip slope. The orientation of antecedent drainage pathways at a high angle to the trend of a developing rift axis, replete with intrabasinal faulting, exerts a primary control on the timing and location of development of overfilled and underfilled basin states in evolving depocentres.

Tectonostratigraphic framework and depositional history of the deepwater Ulleung Basin, East Sea/Sea of Japan

AbstractThe Ulleung Basin, East Sea/Japan Sea, is a Neogene back‐arc basin and occupies a tectonically crucial zone under the influence of relative motions between Eurasian, Pacific and Philippine Sea plates. However, the link between tectonics and sedimentation remains poorly understood in the back‐arc Ulleung Basin, as it does in many other back‐arc basins as well, because of a paucity of seismic data and controversy over the tectonic history of the basin. This paper presents an integrated tectonostratigraphic and sedimentary evolution in the deepwater Ulleung Basin using 2D multichannel seismic reflection data. The sedimentary succession within the deepwater Ulleung Basin is divided into four second‐order seismic megasequences (MS1 to MS4). Detailed seismic stratigraphy interpretation of the four megasequences suggests the depositional history of the deepwater Ulleung Basin occurred in four stages, controlled by tectonic movement, volcanism, and sea‐level fluctuations. In Stage 1 (late Oligocene through early Miocene), syn‐rift sediment supplied to the basin was restricted to the southern base‐of‐slope, whereas the northern distal part of the basin was dominated by volcanic sills and lava flows derived from initial rifting‐related volcanism. In Stage 2 (late early Miocene through middle Miocene), volcanic extrusion occurred through post‐rift, chain volcanism in the earliest time, followed by hemipelagic and turbidite sedimentation in a quiescent open marine setting. In Stage 3 (late middle Miocene through late Miocene), compressional activity was predominant throughout the Ulleung Basin, resulting in regional uplift and sub‐aerial erosion/denudation of the southern shelf of the basin, which provided enormous volumes of sediment into the basin through mass transport processes. In Stage 4 (early Pliocene through present), although the degree of tectonic stress decreased significantly, mass movement was still generated by sea‐level fluctuations as well as compressional tectonic movement, resulting in stacked mass transport deposits along the southern basin margin. We propose a new depositional history model for the deepwater Ulleung Basin and provide a window into understanding how tectonic, volcanic and eustatic interactions control sedimentation in back‐arc basins.

Characteristics of helium accumulation in the Guanzhong Basin, China

ABSTRACT Guanzhong Basin is located in the transitional zone between the Qinling orogenic belt and the Ordos plateau. Analyses of drill and geothermal wells depict that the Guanzhong Basin has abundant gas, and its major source rocks are the U-rich granites. In this study, the granitoid intrusive samples were collected from the Huashan, Baoji, Muhuguan rocks in Guanzhong Basin. A micro laser Raman spectrum examination was used to measure the composition of inclusion in the granite quartz fissures. The results depict that the inclusions include both gas-liquid and H2O-NaCl-CO2 inclusions and that their composition primarily includes H2O and CO2, with small amounts of CH4, H2 and H2S. These inclusions can be classified into nearly-primary, early secondary, and late secondary inclusions, which have homogenization temperatures of greater than 430 °C, 330–370 °C and 170–230 °C, respectively, based on the inclusion measurements. Additionally, the apatite fission-track investigations of six samples, which were collected from the granites at Huashan, Baoji rocks and the southern margin of Muhuguan along with the Cretaceous Sigou Formation sandstones that are located in the northwestern margin of the Guanzhong Basin reveal that the northern Guanzhong Basin began to receive deposits as early as 84–69 Ma. This period was accompanied by the rapid uplift of the Qinling orogenic belt, which was followed by an uplift of the southern basin margin and the Qinling orogenic belt from 44–28 Ma. The authors obtained an age histogram and a probability density distribution of three sample points. The results show that the age spectra of the zircons in the Cretaceous Sigou Formation sandstones can be divided into four tectonic events. Combined with the ages of apatite fission tracks and zircon, the Guanzhong Basin has experienced five tectonic stages as follows: 28–84 Ma, 170–260 Ma, 280–510 Ma, 610–1200 Ma, and 1210–2870 Ma. Using the thermal chronology constraints, inclusion composition analyses, which include the homogenization temperature measurements, and regional burial history, this paper conclude that the early secondary inclusions are primarily composed of CO2 and N2, whereas the late secondary inclusions are composed of CH4. Furthermore, this paper identify two periods of reservoir accumulation, out of which the later period is assumed to be the main accumulation period. Therefore, the period of the formation of the late secondary inclusion in the Guanzhong Basin and the Miocene era is observed to overlap with the main helium reservoir accumulation period. © 2019 China Geology Editorial Office.

Seismotectonics of the Tajik Basin and Surrounding Mountain Ranges

AbstractSeismologic and geologic fault‐slip data characterize the active deformation of the intramontane Tajik basin and its margins, the Tian Shan, Pamir, and Hindu Kush at the northwestern tip of the India‐Asia collision zone. Within this complexly deforming region, the Tajik basin lithosphere forms the backstop for the north‐dipping Indian‐slab subduction beneath the Hindu Kush but itself delaminates and retreats west and northward beneath the Pamir. Herein, we link crustal deformation to these lithosphere‐scale processes, using data from recently deployed seismic networks and geologic observations. Transpressive strike‐slip deformation dominates the bounding fault zones along the basin's northern and eastern margins. Seismicity is most intense in the Garm region/Peter I. range of the northeastern basin, where these bounding faults converge and gain a dominant thrust component. Within the basin, seismically and geologically derived P axes align with the ~W‐trending GPS velocity vectors. Seismicity is concentrated in and at the base of a southward deepening, ∼9–15‐km‐thick wedge. Seismic deformation at the basin's southern margin occurs beneath the Afghan platform, where deep crustal earthquakes likely trace the western end of the Hindu Kush subduction zone. Roughly NNE‐striking sinistral strike‐slip events outline the Hindu Kush‐Pamir transfer system, a zone of distributed shear in the crust overlying the transition of the two oppositely dipping slabs at subcrustal depths. Our observations suggest that crustal deformation in the Pamir and Hindu Kush links with lithosphere‐scale processes, whereas deformation in the basin is controlled by the westward gravitational collapse of the Pamir and the resultant basin inversion.

Structure of the basement surface and sediments in the Kochkor basin (Tien Shan): geological and geophysical evidence

The basement surface and sediments of the Kochkor basin have been studied by structural geological and geophysical methods. The work included high-resolution mapping of the southern basin margin, with a focus on Cenozoic basin stratigraphy, structural unconformities, basement/sediment contacts, and latest deformation (folds, fractures, and faults). Magnetotelluric (MT) soundings provided insights into basin and basement structure, especially important in the poorly exposed eastern flank of the basin margin. The sections across the southern margin of the basin based on geological and geophysical data reveal deformation in both the basement and the sediments. Deformation in sediments shows up as folding, conformal peneplain surfaces, large faults, low-angle detachment faults, and related thrust-fold belts. Thrusting in sediments is inferred to result from cataclastic flow and mass redistribution in disintegrated basement granites. With this mechanism, the total amount of thrusting in the central part of the basin can exceed the convergence of the basin sides.

Salt tectonics in front of the Outer Carpathian thrust wedge in the Wieliczka area (S Poland) and its exposure in the underground salt mine

Salt deposits in the Wieliczka area (Wieliczka Salt Deposit – WSD) in southern Poland comprise salt-rich strata belonging to an evaporite succession that originated in the Carpathian Foredeep basin in the Middle Miocene Badenian (Serravallian) times, ca 13.81–13.45 Ma. Although they have been mined since the 13th century and decades of investigations provided abundant data on their origin and structure, some aspects of their geological evolution are still not fully understood. This study presents current concepts on the lithostratigraphy and tectonics of the WSD. The salt-bearing facies developed near to the southern basin margin, delineated by the Carpathian orogenic front. Such a location triggered the redeposition of sediments and gravity-driven deformation followed by tectonic deformation related to the forelandward advancement of the Carpathian thrusts. As a result, the WSD consists of folds and slices composed of two main salt members: (1) the stratified salt member, with intercalating salt, sulphates and siliciclastics, and (2) the boulder salt member, built of clays with large, isolated blocks of salt. The stratified member contains abundant meso-scale tectonic structures recording the soft-sediment deformation and deformation related to the northward tectonic push exerted by the advancing Carpathian thrust wedge. The boulder member originated due to the syntectonic erosion of evaporites along the basin margins and their redeposition during progressive northward migration of the Carpathian front. Recent interpretations of seismic data imply that the WSD constitutes the core of a triangle zone developed at the contact of the Carpathian orogenic wedge with the backthrust-displaced foredeep sedimentary fill. Meso-scale examples of sedimentary and tectonic structures in the salt-bearing succession exposed in the underground Wieliczka Salt Mine are described and their formation modes discussed.

Geology of the Falcón Basin (NW Venezuela)

ABSTRACTThis paper presents a geological map and cross-section of the Falcón Basin based both on published and unpublished work and on new data collected in the northern and southern basin margins. The geological map covers an area of 4600 km2 at 1:100,000 scale. The cross-section is oriented NNW-SSE, traversing perpendicular to the main structures. In general, the structure of the study area results from the inversion of a graben (Oligocene-early Miocene back-arc basin), that started in the middle Miocene due to the convergence between the Caribbean and South American plates. The map, the cross-section and the observations made in the field have been used to generate a tectonostratigraphic reconstruction of the Falcón Basin. The Oligocene-early Miocene sedimentary succession mapped and described is relevant to the hydrocarbon exploration in the Caribbean and in the Gulf of Venezuela, where new hydrocarbon resources have recently been discovered (i.e. Perla gas field).

Provenance and depositional conditions of fluvial conglomerates and sandstones and their controlling processes in a rift setting, mid-Permian lower and upper Quanzijie low order cycles, Bogda Mountains, NW China

This study investigates how provenance lithology, transport distance, and depositional and paleoclimatic conditions had affected the composition and texture of fluvial conglomerates and sandstones in the Middle Permian lower and upper Quanzijie low-order cycles, Bogda Mountains, greater Turpan-Junggar intracontinental rift basin, NW China. Composition and texture of gravels in conglomerates and sandstones define two conglomerate and two sandstone petrofacies, respectively, in Tarlong-Taodonggou area in southern Bogda and Dalongkou area 70km to the north in northern Bogda. Conglomerate Petrofacies I occurs in Tarlong-Taodonggou and is dominated by basaltic gravels, whereas Conglomerate Petrofacies II occurs mainly in Dalongkou and is dominated by sedimentary gravels. Sandstone Petrofacies I occurs in Tarlong-Taodonggou and contains dominantly basaltic lithics, few sedimentary lithics, and minimal quartz. It is compositionally immature and texturally immature to submature. The compositional maturity increases upsection. Conglomerate Petrofacies I and sandstone Petrofacies I both indicate the young Tian Shan arc to the south as the main sediment source and rift shoulders as a local source. Sandstone Petrofacies II occurs in Dalongkou and contains dominantly sedimentary lithics and abundant and well-developed pedogenic clay coats. The petrofacies in Dalongkou indicate older rift sedimentary rocks exposed at rift shoulders as the main sediment source and distant suture zones as a minor source. In summary, the composition and texture of Quanzijie conglomerates and sandstones are mainly controlled by provenance lithology and, secondarily, depositional and paleoclimatic conditions and transport distance. The results substantiate the rift origin of the Turpan-Junggar basin in Middle Permian, which had many half-grabens and grabens and was bordered by a volcanic arc at the southern basin margin.

Geological controls on the present temperature field of the western Sverdrup Basin, Canadian Arctic Archipelago

AbstractAnalysis of current temperature data in the Canadian Arctic Archipelago results in the recognition of two major thermal regimes. High temperature regions are observed where salt diapirs and salt cored anticlines are present. Low temperature fields are observed along the western and southern basin margins and around Cornwall‐Amund Ringnes islands, where regional Mesozoic aquifers are exposed to surface, connected to basin boundary faults, or regional unconformities. Meteoric and Holocene sub‐glacial water recharge are inferred to be responsible for the low geothermal regime and low formation water salinity. Neither exhumation associated with the Eocene “Eurekan” orogeny nor volcanic intrusion associated with opening of Amerasia Basin in late Jurassic‐early Cretaceous have been interpreted to be a significant influence on the present day temperature field, although thermal indicators show evidence of elevated thermal alteration of organic matter pointing to earlier, but now dissipated, thermal anomalies.

Minibasins and salt canopy in foreland fold-and-thrust belts: The central Sivas Basin, Turkey

The Sivas Basin in the Central Anatolian Plateau (Turkey), which formed in the context of a foreland fold-and-thrust belt (FTB), exhibits a typical wall and basin (WAB) province characterized by symmetric minibasins separated by continuous steep-flanked walls and diapirs. Extensive fieldwork including regional and detailed local mapping of the contacts and margins of minibasins, and interpretation of a set of 2-D regional seismic lines, provide evidence for the development of a shallow evaporite level separating two generations of minibasins within the WAB province. Here beds of symmetric exposed minibasins along diapir flank are younger than minibasins observed over autochthonous evaporites. Laterally away from the WAB province, increase in wavelength of the tectonic structures suggests a deepening of the decollement level. We interpret that a shallower evaporite level developed in the form of an evaporite canopy, triggered by significant lateral shortening. The Upper Eocene-Lower Oligocene autochthonous Tuzhisar evaporite level was remobilized by the northward migrating sedimentary load and the tilting of the southern basin margin during propagation of the foreland fold-and-thrust belt. Asymmetric and symmetric primary minibasins were overrun by an allochthonous sheet forming a canopy. A second generation of salt withdrawal minibasins subsided into the allochthonous salt sheet. The polygonal pattern of the WAB province influences the growing fold-and-thrust belt system during the late stage of the secondary minibasins development. The Sivas FTB basin is the result of the interaction between fold-and-thrust belt propagation, evaporite remobilization, and interaction between evaporite flow and sedimentation in the minibasins.

Evidence for the reactivation of a pre-existing zone of weakness and its contributions to the evolution of the Küçük Menderes Graben: a study on the Ephesus Fault, Western Anatolia, Turkey

Detailed geological mapping at the western end of the Küçük Menderes Graben (KMG) in western Turkey reveals two main sedimentary packages separated by a regional unconformity: (1) Miocene units and (2) KMG basin-fill deposits of Quaternary age. The older basin-fill is represented by colluvial/alluvial fan facies association, which was controlled by a NW–SE-trending and SW-facing dip-slip normal fault (the Ortaburun Fault) and the conformably overlying fluvial and lacustrine deposits. The younger basin-fill, besides being characterised by lateral colluvial fan and axial river sediments deposited under the control of the Ephesus Fault, a southern basin-margin fault character, is also responsible for the evolution of the modern KMG. The analysis of structural, stratigraphic and sedimentological data indicates that three different deformation phases dominated during the Miocene to Recent time in the region: (i) during Early–Middle Miocene Phase 1 deformation (D1), the NW–SE-trending Ephesus Fault moved as a left-lateral strike-slip fault and occurred within the NE–SW-trending dextral shear zone of the İzmir-Balıkesir Transfer Zone (İBTZ) time; (ii) Middle Miocene Phase 2 deformation (D2) was associated with Ortaburun Fault, the northern basin-margin fault of the ancient basin. During this phase, the sinistral Ephesus Fault was reactivated as a dip-slip normal fault; and (iii) Phase 3 deformation (D3) was related with the formation of the KMG during the Quaternary and the Ephesus Fault forms the southern margin of the modern KMG. Structural evidence and computed palaeostress results show that the main extension direction during phase 1 and phase 3 has changed from north-west to north-east direction. This further suggests an approximately 60° rotation around the vertical axes and is attributed to the fact the region lies within the strike-slip dominated İBTZ.

Control of sedimentation by active tectonics, glaciation and contourite-depositing currents in Endurance Basin, South Georgia

Endurance Basin is an elongate broadly WNW–ESE trending basin located on the northern margin of the Scotia Sea, adjacent to the southern margin of the South Georgia micro-continent. Bathymetric and TOPAS sub-bottom profile data acquired in 2010 by the British research ship RRS James Clark Ross map this basin and its sedimentology for the first time. Endurance Basin contains a number of sub-basins and a substantial glaciogenic fan. The northern margin of Endurance Basin is formed by a series of steep slopes and intervening troughs. These are interpreted as a left-stepping en echelon array of oblique, strike–slip faults whilst the sub-basins are separated by compressional dip–slip faults. It appears that South Georgia is moving NW with respect to the basin. We interpret five seismic facies from TOPAS data, which are associated with distinct sedimentologies. The most striking units in the basin fill are: substantial contourite drifts located in the NW of the basin and on its southern margin; and two distinct mass transport deposits that pond in the centre of the basin. Combined with the known regional oceanographic setting, the contourites provide evidence of broadly eastward flowing bottom currents, entering the basin from at least two locations. Although landslide scars are present on the steep northern basin margin, the imaged mass transport deposits are interpreted to have been sourced from the glaciogenic fan, located in the SE of the basin, and from a contourite unit located on the basin's southern margin. Sediments from these events are transported at least 40km. The contourite drift sequence is at least 100m thick in the west of the basin and may contain a palaeoenvironmental archive of Antarctic Circumpolar Current (ACC) flow and the climate of South Georgia extending to the Pliocene. Such an archive would allow the reconstruction of ACC flow through the Pleistocene glaciations and provide a means of linking ocean circulation and climate records in the sub-Antarctic Polar Front region.