Basin Strata Research Articles

Probably proximal pebbles? An outcrop-constrained quantitative analysis of clast transport distances in the Lower Triassic Sherwood Sandstone Group, UK

Lower Triassic Sherwood Sandstone Group fluvial strata in England record northward flow of the Budleighensis river system through fault-bounded syn-rift grabens from the Wessex Basin to the Irish Sea Basin. Pebbles in the Sherwood Sandstones are typically argued to originate mostly from the Armorican Massif, Northern France. Northwards transport should mean pebbles decrease in concentration northwards, yet it is also argued that pebble-rich strata in several basins across central and northern England suggest multiple sediment source areas contributed pebbles along the river system. To further test and constrain this multiple source hypothesis pebble concentration data were used to constrain a simple source-to-sink exponential decay model predicting pebble concentration versus distance from source. The model was inverted on number and location of clast input sources to calculate best-fit matches. Results indicate three distinct pebble sources best fit these data, with major tributaries originating in the Welsh Massif and the London-Brabant Massif, supporting a multiple sediment source interpretation for the Early Triassic river system. Multiple sediment input points increase prediction uncertainty for Triassic strata. Unanticipated heterogeneity has implications for practical subsurface prediction, for example related to proposed carbon and nuclear waste storage.

Characteristics of the structure and hydrocarbon prospectivity of the deeply buried strata in the eastern Precaspian basin

The article examines the geological structure and oil and gas prospects of the pre-salt complex in the eastern Precaspian Basin (PB). Based on the synthesis and comprehensive analysis of geological exploration (GE) results and the analysis of geological-geochemical criteria for hydrocarbon potential, the oil and gas geological zoning has been updated, and effective directions for GE have been identified. The justification of a new hydrocarbon resources base within the eastern PB margin can be ensured by further investigating of the deeply buried Devonian-Middle Carboniferous horizons in the known petroleum plays, as well as within the less explored Sakmar-Kokpektinsky segment of the Ural fold-and-thrust belt. Within the productive KT-I and KT-II formations, there is an unrealized hydrocarbon potential at depths of 5-6 km. Using the example of the Bozoba West area, the oil and gas prospects of the Visean-Bashkirian and Lower Permian strata are examined, highlighting the significance of faults as elements of the hydrocarbon system. The applied set of 3D seismic survey data and deep drilling allowed for the interpretation of deep seismic sections, up to depths of 7.0-7.5 km. The Middle-Upper Devonian strata are considered prospective but have not been extensively explored by deep drilling. To establish a new hydrocarbon resource base within the eastern Precaspian Basin margin, it is recommended to conduct advanced regional seismic surveys and parametric exploration drilling.

Influence of seawater loading on the thermal history of underlying strata in an oceanic basin—an example from the eastern Gulf of Papua

The eastern Gulf of Papua, at the easternmost end of the Papuan Basin, has been subjected to extended seawater loading during the Cenozoic, allowing an investigation into the influence of seawater loading on the thermal development of the underlying rock layers in the oceanic basin. Utilising paleontological, lithologic and paleobathymetric data, along with present-day temperature fields, this study reconstructed the burial history, thermal history and maturity of the eastern Papuan Basin using PetroMod2012.2 1D software. Burial history curves for the virtual wells were employed to trace the evolutionary stages in different regions, revealing a positive relationship between predicted vitrinite reflectance (R o) and modelled thermal history. R o values displayed a gradual decrease from northeast to southwest, with higher R o values observed in areas unaffected by seawater loading. The presence of seawater loading had a notable impact on thermal history, particularly influencing the upper boundary condition and the sediment–water interface temperature of the temperature field. This research enhances our understanding of the Meso-Cenozoic thermal history of the eastern Papuan Basin and reveals the factors influencing stratigraphic thermal evolution.

Reconciling the onshore/offshore stratigraphy of the Canning Basin and implications for petroleum prospectivity

The Canning Basin is a prospective hydrocarbon frontier basin and is unusual for having limited offshore seismic and well data in comparison with its onshore extent. In this study, seismic mapping was conducted to better resolve the continuity of 13 key stratigraphic units from onshore to offshore to delineate prospective offshore hydrocarbon-bearing units, and better understand the distribution of mafic igneous units that can compartmentalise migration pathways and influence heat flow. The offshore Canning Basin strata are poorly constrained in six wells with limited seismic coverage; hence data availability was bolstered by integrating data from the onshore portion of the basin and adjacent basins into a single 3D seismic stratigraphic model. This model integrates over 10 000 km of historical 2D seismic data and 23 exploration wells to allow mapping of key stratal surfaces. Mapped seismic horizons were used to construct isochores and regional cross-sections. Seven of the 13 units were mapped offshore for the first time, revealing that the onshore and offshore stratigraphy are similar, albeit with some minor differences, and mafic igneous units are more interconnected than previously documented whereby they may constitute a mafic magmatic province. These basin-scale maps provide a framework for future research and resource exploration in the Canning Basin. To better understand the basin’s geological evolution, tectonic history and petroleum prospectivity, additional well data are needed in the offshore Canning Basin where Ordovician strata have yet to be sampled.

Thermochronological Evidence for Eocene Deformation in the Southern Patagonian Andes: Linking Orogenesis Along the Patagonian Orocline

AbstractThermochronologic results from zircon fission track and (U‐Th)/He data collected across the Patagonian batholith, basement and thrust belt of the southern Patagonian Andes between 51°S and 53°S resolves new spatiotemporal patterns of Paleogene rock cooling that allows us to reconstruct deformational and erosional events along‐ and across‐strike. Our study applies a novel modeling strategy, the Path Family Approach, to filter geologically plausible thermal solutions from inverse modeling results for rocks in this study according to a sample's structural and tectonic context. Our results identify minimal cooling and interpreted exhumation of batholith rocks throughout the Paleogene. However, in the western domain we identify synchronous cooling of Jurassic volcaniclastic rocks in the thrust belt both along‐ and across‐strike between 50 and 35 Ma, which we interpret as a period of out‐of‐sequence deformation that coincides with the start of a distinct period of orogenesis in the Fuegian Andes (54°S). This finding may suggest that the southern Patagonian Andes and Fuegian Andes evolved as a connected orogenic system along the bend of the Patagonian orocline. In the central domain, modeled cooling of thermally reset Cretaceous basinal strata from 60 to 50 Ma corresponds to a well‐recognized erosional unconformity in the adjacent Cenozoic foreland depocenter, indicating that contemporaneous exhumation occurred beyond the margins of the basin. Although not diagnostic, exhumation within the orogenic belt, beyond the Cenozoic foreland basin, provides a new regional context to interpret the cause of this regional erosion event. Collectively these results inform the Paleogene tectonic evolution of the orogen.

Research on main controlling factors of tight sandstone gas accumulation in coal-bearing strata in the southern North China Basin: Comparison with the Ordos Basin

Tight sandstone gas (TSG) reservoirs develop extensively in the upper Paleozoic coal bearing strata in both the southern North China Basin and the Ordos Basin. The former has not achieved important advances in TSG exploration, while the latter has built the largest TSG production facility in China. By comparing the TSG accumulation conditions in the Tongxu area of the southern North China Basin and the Fuxian area of the Ordos Basin, the main controlling factors of TSG accumulation in the southern North China Basin were analyzed in this article. The results indicate that the organic matter type of the upper Paleozoic source rocks are mainly type III kerogen, vitrinite reflectance values (Ro) are greater than 3.1%, source rocks are over mature, and the reservoir strata are characterized by low porosity and extra low permeability; therefore reservoir forming conditions are similar to those of the Ordos Basin. During the Late Jurassic-Early Cretaceous period, after a large-scale generation of hydrocarbons from source rocks in the two basins, the tectonic movements in the Yanshan period controlled the differential accumulation of TSG. The Ordos Basin has been uplifted as a whole by tectonic processes since the Triassic, which allowed a continuous deposition of Triassic strata, thus providing good sealing conditions for the upper Paleozoic TSG reservoirs. The southern North China Basin has experienced multi-stage compressive and extensive tectonic actions, so the original unified Paleozoic basin was divided into several residual blocks. However, the residual thickness of Triassic strata in slopes and sags is higher. The source rocks, reservoir strata, caprocks, and overlying strata continuously deposited in time, and the time allocation of reservoir forming elements is favorable. Therefore, this is conducive to the preservation of TSG reservoirs in the upper Paleozoic. Such reservoirs are defined by high gas saturation and enriched sandstone gas.

Seismic diagenetic facies prediction of tight sandstone in the offshore sparse well area: An example from the Xihu Depression of the East China Sea Basin

The purpose of this study is to forecast the spatial distribution of diagenetic facies (DF) of tight sandstone in the offshore sparse wells area. Analytical test data, rock physics experiment data and prestack seismic data were used to study the spatial distribution of seismic diagenetic facies (SEISDF) of tight sandstone of the second (H4b) submember of the fourth (H4) member of the Huagang (E3h) Formation in the N gas-field, Xihu Depression, East China Sea Basin. Based on diagenesis and diagenetic minerals, core-based DF of the H4b sandstone were divided into chlorite-coated facies (CHF), calcite-cemented facies (CAF), dissolution facies (DIF), tightly compacted facies (TIF), and quartz-cemented facies (QUF). Various seismic elastic parameters were obtained by prestack elastic parameter inversion method, and sensitive seismic elastic parameters were selected according to the seismic identification principle of DF. In order to predict the spatial distribution of DF, four DF and sensitive seismic elastic parameters were integrated to establish a SEISDF prediction model based on supervised learning, and obtain a diagenetic facies comprehensive index (DFCI) that can distinguish four DF. Then, the 90° phase conversion technique of seismic lithology was used to realize the consistency of the DFCI between isochronous stratigraphic interfaces with core-based DF. The stratal slicing technique of seismic geomorphology was used to make stratal slices of the DFCI between isochronous stratigraphic interfaces. Representative stratal slices were singled out, and the spatial distribution of the SEISDF was interpreted. This study shows that the H4b1 sublayer primarily develops the TIF, while the H4b2 and H4b3 sublayers chiefly develop the QUF, CHF, and DIF. Compared with the H4b2 and H4b3 sublayers, the areas of the QUF and DIF in the H4b4, H4b5, and H4b6 sublayers slightly increase. The QUF are mainly distributed in the subaqueous distributary channel and a small number of sheet sand and channel bar depositional facies in the form of continuous sheets. The CHF are primarily developed in lenticular shape in the channel bar and a small amount of sheet sand and subaqueous distributary channel depositional facies. The most favorable DIF are chiefly developed in the subaqueous distributary channel, channel bar, and sheet sand depositional facies near the fault, which are distributed in strips. This study proposes a very valuable method for the SEISDF prediction of tight sandstone, which can provide a reference for the study of DF of similar strata in other sedimentary basins.

Overview of Lower Cretaceous Achimov Formation: Physical Properties and Their Distribution Pattern in West Siberian Basin, Russia

The Achimov Formation is one of the most important oil- and gas-bearing strata in the West Siberian basin in Russia. The total estimated reserves of this stratum exceed one billion tons. The formation was first explored in 1981, but it remains largely underdeveloped due to its deep burial depth and poor physical properties. Therefore, further research on the genetic mechanisms and distribution characteristics of the reservoirs in the formation can contribute to its further exploitation. The Achimov Formation is dominated by of fine- to medium-grained sandstones interbedded with shale. Based on analysis of well logging data, hand specimens, and previous research, this study analyzed the properties of three members (Ach1, Ach2, and Ach3) of the Achimov Formation and summarized their distribution patterns. Research on reservoir rocks from different oil and gas fields reveals varying physical properties across the formation with permeability and porosity increasing from the northern to central areas and decreasing from the central to the southern areas. Burial depth is one of the major controlling factors for reservoir properties in the formation. Reservoirs in both the northern and southern parts of the formation are buried deeper than those in the central areas, resulting in a disparity in reservoir quality.

Determining sediment provenance history in a Gondwanan erg: Botucatu formation, Northern Paraná Basin, Brazil

The Lower Cretaceous Botucatu Formation comprises a dry-aeolian system developed in western Gondwana and preserved within the Paraná Basin of central South America. Multiproxy provenance analysis (detrital zircon UPb dating, heavy mineral, petrographic and granulometric analysis) was undertaken along two 500 km transects of the northern Paraná Basin (NW and NE transects). To assess the provenance variation within the aeolian stratigraphy, samples were taken from the base and top of the Botucatu Formation and from sandstones interbedded with volcanics in the overlying Serra Geral Formation. Granulometric analysis shows a mean fine- to very fine-grained sand. The bulk petrography yields an average composition of Q91F6L2, and heavy mineral analysis gives a mean of 86% of zircon-tourmaline-rutile, demonstrating the overall polycyclic nature of the sediment. The discrete occurrence of garnet, apatite and epidote indicates local sediment input points, providing indirect evidence for point-sourced fluvial input into an overall dry aeolian system. Detrital zircon UPb LA-ICP-MS dating demonstrates a dominant Cambrian to Late Neoproterozoic (520–750 Ma) population with subsidiary Tonian-Stenian (0.9–1.2 Ga) and Orosirian-Rhyacian (1.9–2.3 Ga) contributions. The Botucatu Formation along the northern basin margin displays similar provenance to the southern part of the basin, pointing to a predominance of recycling processes within the basin. Statistical plots illustrate the detrital zircon age variability - recording an upward decrease in the age proportion of Permian and Tonian-Stenian populations and an increase in Cambrian-Late Neoproterozoic dates towards the top. Such variability can be related to the recycling of distinct Paraná Basin strata. The proportion of Cambrian-Late Neoproterozoic dates increases in the NE, indicating a possible input from the Ribeira Belt granitoids. Similar to major-scale dune-fields, Botucatu erg register variable sand sources there are possibly linked with coexisting depositional systems. In summary, the northern Botucatu erg is mostly fed by local sources reworked from underlying Paraná Basin units, with little direct input from basement sources and limited impact of regional wind-pattern variability.

Neotectonic Activity in the Low-Strain Broken Foreland (Santa Bárbara System) of the North-Western Argentinean Andes (26°S)

AbstractUplift in the broken Andean foreland of the Argentine Santa Bárbara System (SBS) is associated with the contractional reactivation of basement anisotropies, similar to those reported from the thick-skinned Cretaceous-Eocene Laramide province of North America. Fault scarps, deformed Quaternary deposits and landforms, disrupted drainage patterns, and medium-sized earthquakes within the SBS suggest that movement along these structures may be a recurring phenomenon, with yet to be defined repeat intervals and rupture lengths. In contrast to the Subandes thrust belt farther north, where eastward-migrating deformation has generated a well-defined thrust front, the SBS records spatiotemporally disparate deformation along structures that are only known to the first order. We present herein the results of geomorphic desktop analyses, structural field observations, and 2D electrical resistivity tomography and seismic-refraction tomography surveys and an interpretation of seismic reflection profiles across suspected fault scarps in the sedimentary basins adjacent to the Candelaria Range (CR) basement uplift, in the south-central part of the SBS. Our analysis in the CR piedmont areas reveals consistency between the results of near-surface electrical resistivity and seismic-refraction tomography surveys, the locations of prominent fault scarps, and structural geometries at greater depth imaged by seismic reflection data. We suggest that this deformation is driven by deep-seated blind thrusting beneath the CR and associated regional warping, while shortening involving Mesozoic and Cenozoic sedimentary strata in the adjacent basins was accommodated by layer-parallel folding and flexural-slip faults that cut through Quaternary landforms and deposits at the surface.

Detrital zircon geochronology and Hf isotope geochemistry of Mesozoic sedimentary basins in south-central Alaska: Insights into regional sediment transport, basin development, and tectonics along the NW Cordilleran margin

AbstractThe Jurassic–Cretaceous Nutzotin, Wrangell Mountains, and Wellesly basins provide an archive of subduction and collisional processes along the southern Alaska convergent margin. This study presents U-Pb ages from each of the three basins, and Hf isotope compositions of detrital zircons from the Nutzotin and Wellesly basins. U-Pb detrital zircon ages from the Upper Jurassic–Lower Cretaceous Nutzotin Mountains sequence in the Nutzotin basin have unimodal populations between 155 and 133 Ma and primarily juvenile Hf isotope compositions. Detrital zircon ages from the Wrangell Mountains basin document unimodal peak ages between 159 and 152 Ma in Upper Jurassic–Lower Cretaceous strata and multimodal peak ages between 196 and 76 Ma for Upper Cretaceous strata. Detrital zircon ages from the Wellesly basin display multimodal peak ages between 216 and 124 Ma and juvenile to evolved Hf compositions. Detrital zircon data from the Wellesly basin are inconsistent with a previous interpretation that suggested the Wellesly and Nutzotin basins are proximal-to-distal equivalents. Our results suggest that Wellesly basin strata are more akin to the Kahiltna basin, which requires that these basins may have been offset ∼380 km along the Denali fault. Our findings from the Wrangell Mountains and Nutzotin basins are consistent with previous stratigraphic interpretations that suggest the two basins formed as a connected retroarc basin system. Integration of our data with previously published data documents a strong provenance and temporal link between depocenters along the southern Alaska convergent margin. Results of our study also have implications for the ongoing discussion concerning the polarity of subduction along the Mesozoic margin of western North America.

Loess in eastern equatorial Pangea archives a dusty atmosphere and possible upland glaciation

Abstract Carboniferous–Permian strata in basins within the Central Pangean Mountains in France archive regional paleoequatorial climate during a unique interval in geological history (Pangea assembly, ice-age collapse, megamonsoon inception). The voluminous (∼1.5 km) succession of exclusively fine-grained red beds that comprises the Permian Salagou Formation (Lodève Basin, France) has long been interpreted to record either lacustrine or fluvial deposition, primarily based on a local emphasis of subaqueous features in the upper ∼25% of the section. In contrast, data presented here indicate that the lower-middle Salagou Formation is dominated by up to 15-m-thick beds of internally massive red mudstone with abundant pedogenic features (microscale) and no evidence of channeling. Up-section, limited occurrences of ripple and hummocky cross-stratification, and mudcracks record the intermittent influence of shallow water, but with no channeling nor units with grain sizes exceeding coarse silt. These data suggest that the most parsimonious interpretation for the Salagou Formation involves eolian transport of the sediment and ultimate deposition as loess in shallow, ephemeral lacustrine environments. Provenance analyses of the Salagou Formation indicate coarse-grained protoliths and, together with geochemical proxies (chemical index of alteration [CIA] and τNa) that correspond respectively to a low degree of chemical weathering and a mean annual temperature of ∼4 °C, suggest that silt generation in this case is most consistent with cold-weathering (glacial and associated periglacial) processes in the Variscan highlands. Together with previous studies that detailed voluminous Permian loess in western equatorial Pangea, this work shows a globally unique distribution of dust at low latitudes that can be linked either directly to glaciated alpine terranes or to reworked and deflated deposits of other types (e.g., fluvial outwash) where fine-grained material was originally generated from glacial grinding in alpine systems. These results further support a revised model for early Permian climate, in which extratropical ice sheets coexisted with a semiarid tropics that may have hosted significant ice at moderate elevation.

Stratigraphic architecture of Solander Basin records Southern Ocean currents and subduction initiation beneath southwest New Zealand

AbstractSolander Basin is characterized by subduction initiation at the Pacific‐Australia plate boundary, where high biological productivity is found at the northern edge of the Antarctic Circumpolar Current. Sedimentary architecture results from tectonic influences on accommodation space, sediment supply and ocean currents (via physiography); and climate influence on ocean currents and biological productivity. We present the first seismic‐stratigraphic analysis of Solander Basin based on high‐fold seismic‐reflection data (voyage MGL1803, SISIE). Solander Trough physiography formed by Eocene rifting, but basinal strata are mostly younger than ca. 17 Ma, when we infer Puysegur Ridge formed and sheltered Solander Basin from bottom currents, and mountain growth onshore increased sediment supply. Initial inversion on the Tauru Fault started at ca. 15 Ma, but reverse faulting from 12 to ca. 8 Ma on both the Tauru and Parara Faults was likely associated with reorganization and formation of the subduction thrust. The new seabed topography forced sediment pathways to become channelized at low points or antecedent gorges. Since 5 Ma, southern Puysegur Ridge and Fiordland mountains spread out towards the east and Solander Anticline grew in response to ongoing subduction and growth of a slab. Solander Basin had high sedimentation rates because (1) it is sheltered from bottom currents by Puysegur Ridge; and (2) it has a mountainous land area that supplies sediment to its northern end. Sedimentary architecture is asymmetric due to the Subtropical Front, which moves pelagic and hemi‐pelagic sediment, including dilute parts of gravity flows, eastward and accretes contourites to the shelf south of Stewart Island. Levees, scours, drifts and ridges of folded sediment characterize western Solander Basin, whereas hemi‐pelagic drape and secondary gravity flows are found east of the meandering axial Solander Channel. The high‐resolution record of climate and tectonics that Solander Basin contains may yield excellent sites for future scientific ocean drilling.

Provenance changes across the mid-Cretaceous unconformity in basins of northeastern China: Evidence for an integrated paleolake system and tectonic transformation

Abstract Detrital zircon U-Pb dating and whole-rock Nd isotopic analyses were carried out on selected stratigraphic horizons across a major unconformity between synrift and postrift stages in the Songliao Basin and Dasanjiang basin group of NE China to constrain the crustal evolution of the source area providing detritus into these basins. The strata underlying the mid-Cretaceous unconformity in the Songliao Basin show regionally distinct detrital zircon age populations and Nd isotopic compositions, which generally are characterized by Phanerozoic age peaks and relatively depleted Nd isotopic compositions, indicating derivation from nearby highlands. In contrast, the overlying strata are dominated by Proterozoic zircon ages and enriched Nd isotopic compositions, which imply that the provenance source region shifted to the northern part of the North China craton. A coeval provenance change also affected the sedimentary architecture in the eastern Dasanjiang basin group, marking the migration of erosion centers from west to east. The contribution from Lesser Xing’an–Zhangguangcai ranges was pronounced during deposition of synrift strata but became negligible afterward in the Songliao and Dasanjiang areas, which is consistent with both basin complexes temporarily forming an extensive lake system during the early Late Cretaceous. This paleolake was likely responsible for transgressive events recorded in the Late Cretaceous strata of basins in NE China. Combining observations from seismic reflection profiles and the stratigraphic record of neighboring intracontinental sedimentary basins as well as widespread contemporaneous exhumation and denudation events, we suggest that the provenance variation in basin strata was controlled by large-scale tectonic transitions in East Asia. The switch from extension to contraction during the mid-Cretaceous is attributed to the docking of the Okhotomorsk block along the East Asian continental margin. The resulting lithospheric buckling might have been responsible for reshaping the basin-and-range configuration in NE Asia.

New hermit crabs (Crustacea, Anomura, Paguroidea) from the Lower Oligocene of the Ligure Piemontese Basin, northwest Italy

Extinct hermit crabs from Italy have been recorded by several authors, mainly on the basis of both complete or fragmentary chelipeds. Here we add three new paguroids, Dardanus cherpionensis n. sp.,Paguristes collinsi n. sp. and Paguristes laurae n. sp., from Lower Oligocene (Rupelian) strata in the Ligure-Piemontese Basin of northwest Italy. Paguristes laurae n. sp. is preserved in situ within the internal mould of a indeterminate xenophorid gastropod.

Quantitative reconstruction of formation paleo-pressure in sedimentary basins and case studies

Paleo-pressure reconstruction in sedimentary basins is one of the most important aspects of hydrocarbon accumulation research. In view of the advantages and disadvantages of the current methods for paleo-pressure research, a new method to reconstruct the paleo-pressure is presented in this paper. According to the geological background, quantitative analyses of the factors that might control overpressure were first conducted to clarify the contributions of each mechanism during different geological periods. Pressure evolution was reconstructed by fluid-compaction modelling with constraints imposed by the paleo-pressures obtained from fluid inclusions or differential stress methods. Determining the mechanisms responsible for overpressures during geological history is the basic prerequisite for paleo-pressure research. Thus, quantitative studies were conducted of the contributions of disequilibrium compaction, gas charging, oil cracking, temperature reduction, and tectonic uplift and subsidence to overpressures. Three case studies of paleo-pressure reconstruction were performed for the Sinian strata in the Sichuan Basin, Ordovician strata in the north uplift in the Tarim Basin and the Permian strata in the Sulige Gas Field in the Ordos Basin, where these three study sites are normally pressured, weakly over-pressured and abnormally low pressured at present, respectively. The new method developed in this paper is very important for the practical reconstruction of the paleo-pressure in marine strata and ancient strata in deep basins.

Tectono‐sedimentary evolution of transverse extensional faults in a foreland basin: Response to changes in tectonic plate processes

AbstractLate Paleocene to Middle Eocene strata in the easternmost part of the Southern Pyrenees, up to 4 km thick, provide information on tectono‐sedimentary evolution of faults transversal to the Pyrenean chain. To know how changes in tectonic plate processes control the structural evolution of transverse faults and the synchronous thickness and lithological distribution of sedimentary strata in a foreland basin, field observations, interpretation of 2D seismic lines tied to lithostratigraphic data of exploration wells and gravity modelling constrains were carried out. This resulted in the following two tectono‐sedimentary phases in a foreland basin: first phase, dominated by transverse extensional faulting, synchronous with deposition of marine carbonates (ca. 57 to 51 Ma); and second phase, characterized by transverse contractional faulting, coeval to accumulation of marine and transitional siliciclastics (51 to 44 Ma). During the first phase, Iberia and Adria were moving to the east and west respectively. Therefore, lithospheric flexure in the easternmost part of the Iberian plate was developed due to that Sardinia was over‐thrusting Iberia. Consequently, activation of E‐dipping normal faults was generated giving rise to thick‐deep and thin‐shallow carbonate platform deposits across the hanging walls and footwalls of the transverse structures. During the second phase, a shearing interaction between Iberia and Sardinia prevailed re‐activating the transverse faults as contractional structures generating thin‐shelf and thick‐submarine fan deposits across the hanging walls and footwalls of the transverse structures. In the transition between the first and second phases, evaporitic conditions dominated in the basin suggesting a tectonic control on basin marine restriction. The results of our study demonstrate how thickness and lithology distribution, controlled by transverse faulting in a compressional regimen, are influenced by phases related to processes affecting motions and interactions between tectonic plates and continental blocks.

Along-strike variations in sediment provenance within the Nanaimo basin reveal mechanisms of forearc basin sediment influx events

Abstract The along-strike variability in sediment provenance within the Nanaimo basin is important for understanding the tectonic evolution of North America’s Late Cretaceous Pacific margin, providing context for paleogeographic reconstructions. Here, we provide 35 point-counted sandstone samples and 22 new detrital zircon samples from the Nanaimo basin. These new detrital zircon samples compose a portion of a basin-wide data set (N = 49, n = 10,942) that is leveraged to discern spatio-temporal changes in sediment provenance. Provenance data demonstrates that the majority of Nanaimo basin strata were sourced from regions within and east of the Coast Mountains Batholith, while only the southernmost Nanaimo basin, exposed in the San Juan Islands, was supplied sediment from the North Cascade thrust system. Additionally, near-identical age modes and synchronous changes in detrital zircon facies are used to hypothesize a correlation between the Nanaimo Group and the protolith of the Swakane Gneiss. These observations, along with previously identified events in the Cordillera, are used to define two basin-wide events that affected the Nanaimo basin: the first at 84 Ma and the second at 72 Ma. The first event is correlated to the onset of Kula-Farallon spreading, which affected basin subsidence, introduced Proterozoic detrital zircon to the central and southern Nanaimo basin, and uplifted the North Cascade thrust system. The second basin-wide event, which is speculated to have been driven by increased rates of subduction and obliquity, resulted in localized high-flux events in the arc, increased exhumation of the Cascade Crystalline Core, underplating of the Swakane Gneiss, and coarse-grained sedimentation across the basin. The data presented here provides added context for the evolution of the basin and provides insight into the protracted geodynamics of forearc basins undergoing oblique subduction.

Paleoweathering, hydrothermal activity and organic matter enrichment during the formation of earliest Cambrian black strata in the northwest Tarim Basin, China

The earliest Cambrian black strata are widely deposited in many continents, and attracted increasing attention from scholars worldwide. Based on detailed investigations of strata from the Shiairike section in the Aksu area, northwest Tarim Basin, China, the effects of paleoweathering and hydrothermal activity on the organic matter enrichment of this black series was revealed. Combined organic and inorganic geochemistry evidence indicated that relatively strong weathering carried abundant nutrient elements and terrigenous detritus into the sea, which promoted a period of paleoproductivity and enhanced the sinking of dissolved organic matter. Moreover, the hydrothermal activity triggered the enrichment of abundant reducing gases (e.g. H2S) and minerals, whereby gases created euxinic benthic conditions that were favorable for the preservation of sedimentary organic matter, while minerals simultaneously diluted primary productivity. As a result, the low section of the black strata was characterized by dominant siliceous rocks with enrichments of P, Ba, Zn and Cu; whereas the upper section contained abundant organic matters that had the potential to generate and expel a remarkable volume of hydrocarbons. These results provide a theoretical basis for the international exploration of paleo-hydrothermal minerals within the early Cambrian black strata as well as that of the deep Cambrian oil and gas, particularly in the Tarim Basin, northwest China.

A new homolid crab, Cherpihomola italica gen. nov., sp. nov. (Decapoda, Brachyura), from the Rupelian of the LigurePiemontese Basin (Alessandria, northern Italy)

A new genus and species of homolid from lower Oligocene (Rupelian) strata in the Ligure-Piemontese Basin (northern Italy) is introduced. Cherpihomola italica gen. nov., sp. nov. represents the first record of homolids from Oligocene deposits across Europe and extends the palaeogeographical distribution of extinct homolids.