‘Block and basin’ style rift basins: sedimentological insights from the Mississippian Fell Sandstone Formation

The block and basin tectono-stratigraphic framework for the northern Pennine (rift) Basin, within which buoyant granite intrusions core intra-basin fault-bound blocks, has long held traction. However, many of the elements of this framework are rooted in primitive tectonic models and, perhaps unsurprisingly, corresponding depositional models often reflect this. Using sedimentological and sedimentary provenance approaches, the syn-rift (Mississippian) fluvio-deltaic Fell Sandstone Formation and age-equivalent strata within the northern Pennine Basin are examined. Highlighted divergences from classically depicted models relate to occurrences of pre-Carboniferous basement domes or monoclines, which are unbound by major vertically displacing (>100 m) fault systems. Such structures in the northern Pennine Basin are all granite-cored and their origins are associated with their buoyancy and flexural isostatic processes. One such basement dome, the Cheviot Block, confined and deflected the Fell Sandstone fluvio-deltaic system from the west, causing locally elevated net sand content and variations in dominant palaeodrainage direction. Central parts of the Alston Block, which forms a regional monocline along an E-W axis, were comparatively uplifted because of flexural isostatic responses to granite intrusions. The findings presented are not just at variance with classically depicted depositional models for the region, but also with more general depictions of dominantly normal fault-driven rift basin systems.Supplementary material: [table of data locations with derivation, trace element data, and major element (oxide) data] is available at https://doi.org/10.6084/m9.figshare.c.5733257

Late Permian ultrapotassic rhyolites in SE Thailand: Evidence for a Paleotethyan continental rift basin

Volcanic rocks in the Chanthaburi zone are rarely reported and important for investigating the tectonic evolution of Paleotethyan Ocean in SE Thailand. Four rhyolitic samples from the Ko Chang Island yield zircon ages of 254–258 Ma, confirming the presence of Late Permian volcanic rocks in SE Thailand. These rocks consist of Group 1 rhyolites and Group 2 rhyolitic ignimbrites and have high K2O contents of 4.92–7.10 wt.% and A/CNK values of 1.10–1.69. They are enriched in LREEs, Rb, Th, U, Zr and Y, and show negative anomalies of Ba, Sr, Nb, Ta and Ti with obvious Eu anomalies. Their whole-rock εNd (t) values range from −1.7 to −3.1. Zircon in-situ εHf (t) and δ18O values range from 0.0 to +5.6 and 8.2‰ to 9.6‰, respectively. They belong to peraluminous, ultrapotassic A-type rhyolites, and were derived from partial melting of a mixed source of Mesoproterozoic metasedimentary rocks with a component of juvenile mafic crust. These ultrapotassic rhyolites formed in a continental rift setting in response to the rollback of subducted Paleotethyan oceanic slab beneath the Indochina Block. Combining previous geological observations, we propose that there are some sporadically distributed continental rift basins along the Eastern Paleotethyan domain during the Permian.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5635390

Controlling Factors Analyses of Sediment Dispersal From Source-to-Sink Systems of Lacustrine Rift Basin: A Case Study From Paleogene Shahejie-Dongying Formations of Nanpu Sag, Eastern China

Tectonic activity not only shapes the basic stratigraphic framework of rift basins, but also profoundly affects the sediment dispersal in rift basins. In this study, analyses of heavy mineral assemblages in different periods demonstrate that there are three obvious tectono-sedimentary evolutionary stages (Es3–Es2, Es1–Ed2, and Ed1, respectively) in the Paleogene provenance area of Nanpu Sag, and the volume of sand bodies increases from the bottom of the Paleogene Shahejie (Es) Formation to the top of the Dongying (Ed) Formation in Nanpu Sag. Besides, this study comprehensively utilize the analyses of seismic interpretation, palynology, heavy mineral, and borehole core samples to investigate the controlling factors of sediment dispersal in the rift basin. The assemblages of heavy minerals in different periods reflect the rock composition and catchment area of different provenance areas, and their vertical differences reflect the evolution process of the provenance area and reflect the uplift-denudation process of the provenance area. The results reveal that the synergy of the evolution of tectonic activity and the adjustment of topographical evolution are the main controlling factors of sediment dispersal in Nanpu Sag, while climate change is not the main controlling factor. We conclude that an increased sediment supply rate in the long term reflects the control of tectonic activity on basin topography, rather than climate fluctuations. The differences in morphological modification result in differential sediment dispersal, which is principally related to the differential extrusion of the fault system. The catchment area and provenance distance adjustment is evidenced by the vertical changes of heavy mineral characteristics of single-well and interaction and linkage of boundary faults, and the adjustment of topography evolution. A consideration is that the interaction and linkage of boundary faults and complex subsidence history are multi-directional, and differential evolution of provenance area is universal in lacustrine rift basins, all of this highlights the adjustment of sediment pathways generated by this characteristic of rift basins and emphasizes the importance of controlling factors analyses in understanding differential sediment dispersal that presents in the rift basins. Besides, four sets of sediment dispersal patterns were delineated based on different developmental regions in the rift basin, which are fault segmental point and multi-stage fault terrace, single-stage fault terrace and axial fault valley, axial fault terrace, and paleo-terrace and axial fault valley, respectively. This study has a certain guiding significance for the prediction of the spatial distribution of sand bodies in the rift basin and the exploration of potential oil and gas targets in the rift basin.

Contribution of gravity gliding in salt-bearing rift basins – a new experimental setup for simulating salt tectonics under the influence of sub-salt extension and tilting

Basin-scale salt flow and the evolution of salt structures in rift basins is mainly driven by sub- and supra-salt faulting and sedimentary loading. Crustal extension is often accompanied and followed by thermal subsidence leading to tilting of the graben flanks, which might induce an additional basinward-directed driver for salt tectonics. We designed a new experimental analogue apparatus capable of integrating the processes of sub-salt graben extension and tilting of the flanks, such that the overlapping effects on the deformation of a viscous substratum and the brittle overburden can be simulated. The presented experimental study was performed to demonstrate the main functionality of the experimental procedure and setup, demonstrating the main differences in structural evolution between conditions of pure extension, pure tilting, and extension combined with tilting. Digital image correlation of top-view stereoscopic images was applied to reveal the 3D displacement and strain patterns. The results of these experiments suggest that in salt basins affected by sub-salt extension and flank inclination, the salt flow and downward movement of overburden affects the entire flanks of the basin. Supra-salt extension occurring close to the graben centre is overprinted by the downward movement; i.e. the amount of extension is reduced or extensional faults zones are shortened. At the basin margins, thin-skinned extensional faults developed as a result of gravity gliding. A comparison with natural examples reveals that such fault zones can also be observed at the margins of many salt-bearing rift basins indicating that gravity gliding played a role in these basins.

Red Sea Holocene carbonates: Windward platform margin and lagoon near Al-Wajh, northern Saudi Arabia

ABSTRACT Analysis of Holocene sedimentary seascape is focused on the Red Sea windward Al-Wajh platform margin, its central lagoon, and nearby isolated platforms based on data that include mapped ecological facies (habitats), water depths, grain sizes, and allochem types and abundances determined from thin sections. On this basis, a depositional model applicable to Red Sea Plio-Pleistocene and other ancient icehouse carbonate platforms is presented. The model highlights favorable reservoirs in analogous ancient systems to include coral crests and columnar framework habitats with primary porosity developed in boundstone lithologies and windward platform margins to contain considerable open pore space, including cavernous openings, of which not all should be anticipated to be occluded with marine cements and sediments. Meteoric diagenesis is expected to be minor as limited freshwater is available due to extreme aridity, but may play a role during glaciation. Most habitats have potential for secondary (enhanced) porosity resulting from dissolution of aragonite skeletons, particularly mollusk shells and calcareous coral (Scleractinia) endoskeletons. Central-lagoon habitats are expected to have the least favorable reservoir potential of environments considered because they are dominated by peloids. Central-lagoon sediment differs from other published localities, having higher peloid abundances, greater peloid distribution, and little or no association with Halimeda and quartz grains. Under the likely scenario that platform-interior sediments are completely bioturbated and comprise peloid-rich, grain-dominated fabrics, with many smaller peloids (most of them likely fecal pellets) at or near 4 μm in size (i.e., mud fraction), it is possible that grain size will control pore size once the considered deposits are lithified. If so, platform-interior sediments will lithify as mudstones, wackestones, or very fine-grained grainstones, an outcome which might otherwise be unexpected given the abundance of coarse peloid grains. The Al-Wajh platform is compared with 15 Holocene analogs and found to be unique with respect to rift-margin type, restricted-marine circulation, in having a lagoon with high peloid content, and lack of karst. In further comparison with ancient reservoir analogs, two greenhouse and four icehouse, it compares favorably to icehouse platforms deposited in rift basins with respect to mineralogy of deposition, meter-scale cycle thicknesses, and general peloid content and distribution. It provides a snapshot as to how an icehouse platform might have nucleated and attached along an active rift margin; it is a broadly applicable carbonate analog for the Red Sea Plio-Pleistocene and similar icehouse, rift basins.

Spatiotemporal evolution of the Jehol Biota: Responses to the North China craton destruction in the Early Cretaceous

The Early Cretaceous Jehol Biota is a terrestrial lagerstätte that contains exceptionally well-preserved fossils indicating the origin and early evolution of Mesozoic life, such as birds, dinosaurs, pterosaurs, mammals, insects, and flowering plants. New geochronologic studies have further constrained the ages of the fossil-bearing beds, and recent investigations on Early Cretaceous tectonic settings have provided much new information for understanding the spatiotemporal distribution of the biota and dispersal pattern of its members. Notably, the occurrence of the Jehol Biota coincides with the initial and peak stages of the North China craton destruction in the Early Cretaceous, and thus the biotic evolution is related to the North China craton destruction. However, it remains largely unknown how the tectonic activities impacted the development of the Jehol Biota in northeast China and other contemporaneous biotas in neighboring areas in East and Central Asia. It is proposed that the Early Cretaceous rift basins migrated eastward in the northern margin of the North China craton and the Great Xing’an Range, and the migration is regarded to have resulted from eastward retreat of the subducting paleo-Pacific plate. The diachronous development of the rift basins led to the lateral variations of stratigraphic sequences and depositional environments, which in turn influenced the spatiotemporal evolution of the Jehol Biota. This study represents an effort to explore the linkage between terrestrial biota evolution and regional tectonics and how plate tectonics constrained the evolution of a terrestrial biota through various surface geological processes.

STRUCTURAL SETTING AND HYDROCARBON POTENTIAL OF KHARITE-NUQRA-KOMOMBO RIFT BASINS, SOUTH EGYPT: A PROSPECTIVE APPROACH

— The sedimentary basins of Kharite, Nuqra, and Komombo are outlined with the potential geophysical data where the southern N-S Egyptian Nile course separates Nuqra and Kharit as the East Nile basins. Two commercial discoveries of Al Barka and West El Barka oil fields have been declared in the West Nile basin of Komombo. This work presents our insights on the structural setting and hydrocarbon system of these basins through our integrating results in form of interpreted seismic profiles and structural mapping on the different horizons, 1D basin modeling, geochemistry, and geologic maps based on high-resolution satellite images. Structurally, these rift basins are developed as NWtrending asymmetric fault-bounded half-grabens (oblique to the Red Sea trend) through the reactivation of a major Precambrian Pan African tectonic zone by the Neocomian extensional tectonics. The high potential source rock with up to 7wt. % TOC of kerogen II are proved in the Komombo basin. The seismic and drilling results show Neocomian-Barremian maximum subsidence and the possible occurrence of similar Neocomian source rocks in the eastern Nile basins. Additionally, the convenient clastic reservoir rocks occurred in the entire stratigraphic succession and seal capacity in the upper interval of Senonian-Paleocene. Good opportunities for hydrocarbon structural trapping take place in form of rotated fault blocks by the Early Cretaceous extensional rift and mildly inverted structures by a long span of Late Cretaceous to post-Early Eocene Syrian Arc compression in South Egypt. These elements were verified by Al Baraka discovery and present a promising play concept for hydrocarbon potential in the Kharit and Nuqra basins. The geochemical data indicate different basins exhumation and maturation levels, as the 0.5% calculated vitrinite reflectance "Ro" values occur at the depths of 1200ft and 2100ft in Nuqra and Komombo basins, respectively