Basin Margin Research Articles

A New Geological Map of the Marginal Basins of Eastern Papua New Guinea: Implications for Crustal Accretion and Mineral Endowment at Arc–Continent Collisions

Abstract Accretion of island arc terranes is a fundamental process of crustal growth and the formation of new continents. Convergent margin tectonics, both compressional and extensional, in accretionary orogens also control the origin and distribution of their contained mineral resources, including many of the world’s important Cu and Au deposits. However, the details of crustal growth and accretion are often lost because of deformation and selective preservation during subduction. The Melanesian Borderland, which includes the offshore regions of eastern Papua New Guinea and the Solomon Islands, contains several active and relict arc and backarc systems that have formed in response to more than 50 Ma of subduction and complex plate tectonic adjustments. The composite terrane is a region of some of the fastest growing crust on Earth and also spectacular mineral endowment, including three of the top ten porphyry Cu and epithermal Au deposits in the world. However, more than 80% of the belt is submerged, and so little is known about its geological evolution and makeup. Here, we present the first detailed geological map of the region in one map sheet, including the marginal deep ocean basins. The map identifies and groups the key lithostratigraphic formations and correlates associated tectonic events across the belt. The final compilation is presented at 1:1,000,000 scale, which is sufficient to allow quantitative analysis of crustal growth and accretion during ocean–continent collision throughout the region. The map shows the diversity of assemblages in accreting terranes that may eventually become part of a growing continent and highlights their complex formation and structural relationships. Because so much of that history has occurred offshore, the new map presents the first complete picture of the geology of the region in the critical period leading up to its eventual incorporation in the Australian continent.

Tectonostratigraphic models of an extensional back-arc basin: inferences for the evolution of the Pannonian Basin System

The subsidence history and sedimentary architecture of extensional basins are controlled by the interplay between tectonics, mantle dynamics and climatic variations. Observations from outcrop to regional seismic scales coupled with numerical modelling techniques, including basin-scale stratigraphic, crustal-scale tectonic and mantle-scale subduction models, contribute to the quantification of basin evolution. Here, we review and discuss both tectonic and stratigraphic applications of such models and compare them with observations from the Pannonian Basin system of Central Europe. We show that diachronous localization of back-arc extension, crustal thinning, asthenospheric upwelling and subsequent thermal relaxation are superimposed on an overall slow plate convergence. These processes result in contrasting subsidence and uplift patterns and a variable heat flow evolution in different parts of the basin system. The crustal stress-field of the sub-basins does not always reflect their contrasting vertical motions. Extensional deformation generally migrates from the basin margins towards the basin centre. Structural inversion is localized along hot and weak inherited zones from the Middle Miocene to Present. Tectonic subsidence focuses sedimentation along deep depocentres, sourced by exhumed footwalls and from the neighbouring orogens. The overall post-rift sediment progradation is influenced by inherited bathymetries from the preceding syn-rift stage and by enhanced differential vertical motions.

Hydrologically sensitive carbonates: Tectonic and groundwater controls on synrift sedimentation in the Late Jurassic–Early Cretaceous of the western Cameros Basin, Northern Spain

AbstractBasin hydrology and subcrop are key controls on carbonate sedimentation in continental basins. Hydrologically sensitive carbonates can record groundwater fluctuations within an aquifer in deep time. Late Jurassic extension, footwall uplift, erosion and karstification of marine Jurassic carbonates in the western Cameros Basin (Spain) saw deposition of ?Upper Kimmeridgian‐Tithonian syntectonic alluvial fan deposits (Señora de Brezales Formation). Biogenic laminar calcretes and phreatophytic rhizocretions record roots exploiting capillary fringe groundwater. Progressive infill of rift topography and footwall erosion lowered sedimentary gradients and clastic supply during deposition of the ?Tithonian–Berriasian Rupelo Formation. Distal alluvial marls (Las Viñas Member) contain charophytes, with 2 m thick carbonate lenses at the top reflecting intermittent rise of groundwater in ponds on the basin floor. Stacked palustrine limestones with rare charophytes and laminar calcretes (Ladera Member) record overstep of seasonal carbonate wetlands onto basin margins and footwall highs with intense pedogenetic modification during lengthy seasonal exposure. Overlying Berriasian charophyte‐ostracod wackestones, displaying microkarst cavities and interbedded intraclastic conglomerates, with vivianite sauropod bones, footprints and polygonal desiccation cracks at the top (Mambrillas de Lara Member) record open lacustrine conditions with limited subaerial exposure and high water tables. Desiccation‐cracked limestones and marls with correlatable evaporite horizons (Rio Cabrera Member) contain marginal marine foraminifera and dasycladaceae at the top. Lagoonal conditions reflected transgression to seaward and intermittent marine connection via the Basco‐Cantabrian Basin. The distribution and thicknesses of hydrologically sensitive carbonates reflected onlap onto a faulted and karstified marine Jurassic carbonate pediment and the subtle influence on hydroperiod of fault (and potentially localised Triassic salt) controlled differential subsidence and transgressive groundwater rise. Hydrological facies evolution reflects progressive basin infilling and eustasy beyond. Transitions in this continental succession from clastic to carbonate facies and from closed to open hydrology record hydrological change over time rather than contemporaneous deposition under Walther's Law.

Imaging Complex Structures of the Los Angeles Basin via Adjoint-State Travel-Time Tomography

ABSTRACT In this study, we present high-resolution seismic velocity models for the Los Angeles basin (LAB) and its adjacent area using adjoint-state travel-time tomography, fitting an extensive database of P- and S-wave travel times accumulated from 1980 to 2021. We select 151,193 first P-wave travel times and 149,997 first S-wave travel times from local earthquakes archived in the Southern California Earthquake Data Center to determine the velocity models, with earthquake locations updated at each iteration. With seismic stations spaced more than 3.5 km apart, our dataset has limited resolution in the uppermost 1–2 km. However, starting from three different initial models, our VP models, which are optimally imaged between 3 and 15 km, show similar velocity heterogeneity and provide a better fit to the observed first travel-time data compared to the Community Velocity Model-Harvard 15.1.0 and Community Velocity Model-Southern California Earthquake Center 4.26. Our models provide a detailed delineation of the subsurface structure beneath the LAB, revealing significant velocity variations across active faults, a 10-km-thick sequence of sedimentary rocks within the basin, and a distinct basin margin marked by transitions from low to high-velocities. In addition, these models highlight basement structures with elevated VP and VS located at depths of 9 to 12 km and beyond. Specifically, beneath the northeastern part of the basin, the models demonstrate improved accuracy and reliability in reflecting the linear relationship between VP and VS in mafic rocks. The accurate delineation of the basin’s structure provided by our models could also offer robust constraints for seismic response modeling and seismic hazard assessment in the region.

Geological and hydrological controls on the pressure regime of coalbed methane reservoir in the Yanchuannan field: Implications for deep coalbed methane exploitation in the eastern Ordos Basin, China

The pressure regimes of the No. 2 coalbed methane (CBM) reservoir in the Yanchuannan field located in the southeastern Ordos Basin are highly variable and divided into overpressured (pressure gradient >9.80 kPa/m), slightly underpressured (pressure gradient of 8–9.80 kPa/m), and moderately underpressured (pressure gradient of 5–8 kPa/m). The controlling factors for the variable pressure regimes were investigated through the analysis of geological and hydrological characteristics. The pressure regimes are controlled by different mechanisms in different hydrodynamic environments. In the closed hydrodynamic environment characterized by TDS > 10,000 mg/L and NaCl type of groundwater, the pressure regime is dominated by overpressured to slightly underpressured and is controlled by CBM migration. Overpressure was developed by thermogenic CBM generation during the coalification process and is maintained by thermogenic CBM migration from the extended northwestward and deeply buried CBM reservoir during tectonic uplift. The transition from overpressure to slight underpressure and then to moderate underpressure towards the southeast is the result of the progressively weakened migrated thermogenic CBM with increasing migration distance. In the open hydrodynamic environment characterized by TDS < 10,000 mg/L and NaHCO3 type of groundwater, the pressure regime is dominated by slightly to moderately underpressured and is governed by hydrodynamics. Groundwater is fed by meteoric recharge along the structurally upturned basin margin and creates the hydrodynamic framework during tectonic uplift. The transition from moderate to slight underpressure towards the southwest is associated with the minor decrease range in ground elevation from basin margin to basin interior and the gradually weakened runoff intensity of groundwater with increasing distance to meteoric recharge. The idealized models for the pressure regimes are established, which can provide guidance to deep CBM sweet spot identification in CBM fields in the eastern Ordos Basin and elsewhere.

Provenance and tectonic intricacies revealed by in situ Rb-Sr dating of detrital micas

The use of detrital minerals to reconstruct sedimentary provenance is subject to a range of biases, which may reduce the geological information they retain. With the advent of in situ Rb-Sr geochronology, rapid analyses of a representative (>100) number of grains can now be performed on radiogenic Sr-bearing minerals to provide more comprehensive knowledge of source-to-sink processes. Here, we test the in situ Rb-Sr technique on detrital white mica and biotite from basin margin and axis in a simple rift basin (Perth Basin, Australia) for which previously published detrital zircon U-Pb and Hf isotopic data exist. For the basin margin adjacent to Archean basement, which has unimodal detrital zircon ages at c. 2600 Ma, two mica samples reveal a dominant age peak at c. 500 Ma, reflecting thermal resetting in the craton proximal to the Gondwanan orogenic front, and a subordinate portion of Archean mica detritus that can be interpreted as having been distally sourced (>100 km away). Similarly, a basin axis sample yielded minor c. 1200 Ma apparent mica ages, representing distal sources from the Albany-Fraser-Wilkes Orogen, and c. 500 Ma grains are likely a resetting product. Whilst obscured in the detrital zircon record, mica samples allow quantification of the relative contributions of distal and proximal sources to the basin. Finally, detrital biotite that was (partially) altered to chlorite yielded partially to fully reset ages between c. 500 and 130 Ma, the latter linked to heating from the c. 137–130 Ma Bunbury Basalt. Ultimately, the use of in situ Rb-Sr geochronology from detrital micas reveal previously unrecognized provenance and tectonic information that is critical to understanding the true complexity of ancient geological histories, but which remains obscured in standard detrital zircon U-Pb geochronology.

Geochemical evolution of the Dead Sea brine during the last glacial cycle from chemical compositions of interstitial soluble salts

The chemical evolution of the brines that filled the Dead Sea Basin during the final phase of the last interglacial and throughout the last glacial period is constructed from the temporal variations in the Na/Cl, Mg/Cl, Br/Cl, and Br/Mg ratios of soluble salts that extracted from cores that were drilled at the modern Dead Sea floor and from sediments of the last glacial Lisan Fm. that are exposed at the high terraces above the modern Dead Sea (covering the ∼ 100–13 ka period).The main observations are: (1) Variations in the Na/Cl ratios reflect processes of halite precipitation/dissolution during arid/wet periods in the drainage basin, respectively, and exchanges between the upper and the lower brines; (2) Ions of Na + and Cl-were supplied to the brines by the dissolution of halite from the Mount Sedom salt diapir, and of halite deposits, which precipitated in the lake during the hyper-arid periods of the last interglacial; (3) The upper brine of Lake Lisan was sensitive to the hydroclimatic conditions in the lake’s drainage basin, since being directly exposed to the atmosphere, and to variations in flows of freshwater and groundwater brines, which had distinct influence on its chemical record. At the same time, the lower brine was isolated from the surroundings, by the overlying brine and received chemical inputs only by restrict mixing between the brines which buffered the intensity of regional hydro-climatic events.Temporal patterns in the Na/Cl ratios indicate that between ∼ 100–30 ka, the deep brine evolved through a moderate but steady “enrichment” by Na + and Cl-ions due to continuous dissolution of halite by the upper brine of the lake. Towards the end of this period, between ∼ 43–30 ka, the Amiaz plain, a marginal basin, comprised a semi-isolated water-body that witnessed frequent episodes of halite precipitation/dissolution with temporal patterns that resemble millennial temperature (δ18O) variations in the Greenland ice core.Between ∼ 30–18 ka (MIS 2), when Lake Lisan reached its highest stands and maximumspatialexpansion, the soluble salts from the deepest basin and from the high sections of the Lisan Fm. indicate on centennial dissolution cycles of the Mount Sedom salt diapir that took place in the upper brine and sank down to the lower brine. During the ∼ 18–14 ka decline of the lake to its low levels of the Holocene, the elemental ratios reveal several episodes of enhanced supply of freshwater to the shrinking lake, causing intensified halite dissolution and supply of Na + and Cl- ions to the deep basin, setting the grounds for massive halite precipitation, which initiated after a sharp level decline at ∼ 14 ka.The long-term (∼100–13 ka) temporal pattern in the elemental ratios of the lower brine resembles global CO2concentrations and sea surface temperature trends, while the short-term fluctuations in the upper brine are correlated with short warm/cold cycles in the Greenland ice core δ18O data, indicating a strong impact of the global climate.

Assessing the Geochemical Correlation Between Petroleum Source Rocks in the Brazilian Equatorial Margin Basins and Global Oceanic Anoxic Events

Assessing the Geochemical Correlation Between Petroleum Source Rocks in the Brazilian Equatorial Margin Basins and Global Oceanic Anoxic Events

Miocene to Quaternary evolution of the northern Danube Basin: a review of geodynamics, depositional systems and stratigraphy

This review aims to present an updated lithostratigraphic framework of the northern Danube Basin in Slovakia, consistent with recent shifts in geochronology and depositional system redefinitions based on sedimentology and seismic stratigraphy. Several transgressive–regressive sequences are distinguished: The Lower Badenian (Middle Miocene), represented by the Špačince Fm, mainly occurred in peripheral Blatné and Želiezovce sub-basins. The central part of the Danube Basin formed an elevation during this period, coinciding with the onset of intermediate volcanic activity. The Upper Badenian (Middle Miocene), encompassed within the Pozba Fm, saw the flooding of the central Danube Basin, signifying a change in transport direction. The inception of this cycle is well constrained by recently published multiple 40 Ar/ 39 Ar dating to c. 13.8 Ma. The Sarmatian deposition (Middle Miocene), characterized by the Vráble Fm, also occurred in newly significantly deepened Komjatice and Rišňovce sub-basins, coinciding with a gradual cessation of calc-alkaline volcanism, observed only at the basin's eastern edge. The Pannonian (Upper Miocene) deposition includes lacustrine Ivanka, deltaic Beladice and alluvial Volkovce formations, representing interconnected depositional systems prograding towards Lake Pannon. The subsequent evolution entails a post-rift stage (9.5–6 Ma), primarily marked by the alluvial Volkovce Fm deposition, and basin inversion, with alluvial deposition mostly confined to the basin centre and differentially eroded basin margins (from 6 Ma to the present).

Tectonic and non-tectonic basin margin depositional systems and water/gas escape structures developed during the Zanclean transgression; İskenderun-Arsuz sub-basin, S Türkiye

Tectonic and non-tectonic basin margin depositional systems and water/gas escape structures developed during the Zanclean transgression; İskenderun-Arsuz sub-basin, S Türkiye

Organic petrographic and geochemical insights into organic matter derived from land plants and marine algae in the Lark Formation, Danish North Sea

Climatic fluctuations from the Eocene to the Miocene highlight the importance of investigating the paleoenvironment of the latest Eocene to the Middle Miocene Lark Formation in the Danish North Sea. This study investigates immature sedimentary organic matter in the Lark Formation using 54 cuttings samples and one core sample collected from seven wells in the eastern North Sea Basin. Organic petrography and molecular geochemistry analyses were performed to determine the variations in the quantity and origin of allochthonous and autochthonous organic matter. Additionally, the study assesses the impact of climate fluctuations on marine productivity in the eastern North Sea Basin and land plant vegetation at the basin margins during the latest Eocene to the Middle Miocene.The organic matter in the Lark Formation originated from mixed sources, primarily land plants, with a secondary contribution from marine algae. This is indicated by the maceral composition and the types and abundance of aliphatic and aromatic hydrocarbon biomarker compounds. Moreover, the presence of diterpenoids (gymnosperm biomarkers) and non-hopanoid triterpenoids (angiosperm biomarkers) reveals that the allochthonous organic matter originated from conifers and angiosperms.Climatic impacts on land plants and marine algae during the latest Eocene to the Middle Miocene are revealed by several parameters: the Averaged Chain Length (ACL) of land plant waxes, the proportion of coniferous contribution (C/(C + A)), and the whole rock volume percentages of huminite, inertinite (H + I, vol%) and liptinite (L, vol%). The shifts to cooler and drier climates highlighted the cold adaptation of onshore conifers and resulted in the input of higher molecular weight waxy components into the sediments. However, under these conditions, reduced precipitation and runoff resulted in lower amounts of terrigenous organic matter supplied to the basin. Additionally, the drop in water temperature and the warm-affinity of local algae assemblage led to reduced marine productivity. Together, these factors contributed to an overall decrease in organic richness. In contrast, during shifts to warmer and more humid climates, the trend reversed. The contribution of conifers to the floral assemblage diminished, but higher amounts of terrigenous organic matter were transported to the basin due to increased precipitation and runoff. This was accompanied by warmer water temperatures, boosting the productivity of organic-walled microplankton in the marine environment and contributing to greater organic richness.

Legacy of aerosol radiative effect predominates daytime dust loading evolution

Dust radiative effect imposes pronounced perturbations on planetary boundary layer (PBL) development. In turn, the modified PBL characteristics and circulation fields regulate subsequent dust processes, which have not been explored sufficiently. In this study, parallel experiments are designed to isolate the instant, legacy and nonlinear impacts of aerosol radiative effect on daytime dust storm evolution over the Tarim Basin. During a typical dust storm event, legacy radiative effect is found to dominate dust loading dynamics and modulates mean dust burden by more than 16 % in the central basin and − 41 % in the marginal basin. Specifically, the dust column concentration increases in central regions but decreases in marginal regions. Dust aerosols cause opposite heating rate distributions and PBL structure between the central and marginal regions through altering radiative balance. Dust-induced cooling effect in the marginal regions leads to PBL suppression and attenuates entrainment mixing. Negative net heating also results in lowered potential temperature, elevated air pressure and thus increases their horizontal gradients. Accordingly, wind speeds are amplified through geostrophic and thermal wind effects, which further accelerate deposition rates, and eventually weaken dust suspension. In the central basin, dust plumes stimulate a warm mixing layer and unstable entrainment zone, which inhibit dry deposition removal and favor dust accumulation in the atmosphere. Our study highlights the importance of accounting PBL dynamics and geostrophic balance in quantifying the impacts of preceding radiative effect on subsequent dust evolution.

Hydrocarbon Generation Characteristics of Coal‐measure Source Rocks and their Contribution to Natural Gas: A Case Study of Middle and Lower Jurassic Targets from the Southern Junggar Basin Margin

AbstractIn order to study the hydrocarbon generation (HCGE) characteristics of coal‐bearing basins, the coal‐measure source rocks of the Middle Jurassic–Lower Jurassic (MLJ) of the piedmont thrust belt in the southern margin of the Junggar Basin in Northwest China are taken as research objects. More than 60 MLJ samples were collected from outcrops and wells. Total organic carbon (TOC), rock pyrolysis (Rock–Eval), organic petrological, vitrinite reflectance (%Ro), and hydrous pyrolysis were performed to analyze the relevant samples. The pyrolysis gases and liquid products were measured, and then the chemical composition, as well as carbon isotopes of the gases, were analyzed. The results indicate that the MLJ source rocks have the capacity for large‐scale gas generation. In addition, for coal‐measure source rocks, the heavier the carbon isotope of kerogen (δ13Ckerogen), the lower the liquid hydrocarbon and hydrocarbon gas yield, and the easier it is to produce non‐hydrocarbon gas. It is worth noting that when the δ13Ckerogen in organic matter (OM) is relatively heavier, the fractionation of its products may become weaker in the evolutionary process. The vital contribution of the MLJ source rock to natural gas resources in the study area was further confirmed by comparing it with the Jurassic source gas.

Paleogeographic reconstruction and sedimentary evolution of tidal-dominated estuarine depositional systems: Insights from the campanian M1 sandstone formation, Oriente Basin, Ecuador

The Oriente Basin is a back-arc basin located east of the Ecuadorian Andes in South America. Evidence suggests that during the Cretaceous period, the basin's margins received a terrigenous shallow marine sedimentation. Due to regional variations in accommodation and depositional controlling factors near a shoreline, the sedimentary environments in the fluvial-marine transitional zones exhibit considerable variability. In this study, we analyzed the sedimentological characteristics of the M1 Sandstone Formation unit (∼83 Ma-72 Ma), which comprises a set of ancient estuarine deposits preserved in the northern part of the basin. We quantified the impact of mixed hydrodynamic processes on the distribution of tidal-dominated estuarine facies and discussed the development conditions and evolutionary processes of an estuarine formation under the background of persistent transgression. Core, well log, and seismic data provide evidence for reconstructing the tidal-dominated estuarine environment. In the core section, we identified 14 lithofacies and 7 major facies association types. The frequent occurrence of sedimentary structures associated with tidal currents indicates that tidal processes extensively reworked the deposits. The spatial distribution trends of facies associations reveal the evolution of mixed hydrodynamic conditions dominated by tidal processes in the estuary and allow us to divide the M1 Sandstone Formation into four depositional periods: the initial development, rapid development, decline, and the post-infilling open coast tidal flat development periods. Furthermore, through a systematic analysis of hydrodynamic conditions and sediment distributions, we identified multiple depositional centers in the tidal-dominated estuary influenced by different hydrodynamic processes. These correspond to the upstream fluvial-dominated tidal point bar depositional region, the middle mixed-energy depositional interaction zone, and the downstream tidal-dominated tidal sand bar depositional region. In these regions, the substantial accumulation of sandy deposits, represented by tidal sand bars, reflects the high accommodation space characteristic of tidal-dominated estuaries. Our findings indicate that the slow subsidence of a broad and gently sloping coastal topography, stable material transport, and sea level change dominated by marine transgression ensured the necessary accommodation for the development of the estuary in the M1 Sandstone Formation. The sedimentological study of the M1 Sandstone Formation provides a case for understanding the sedimentary evolution in fluvial-marine transitional zones.

UPPER CRETACEOUS–LOWER EOCENE MUDSTONES OF THE OUTER CARPATHIANS (PETROCHEMICAL AND PALEOGEODYNAMIC ASPECTS)

The mineral types of the Upper Cretaceous–Lower Eocene greenish-gray mudstones of the Skyba and Boryslav-Pokuttya nappes of the Outer Carpathians were studied. According to sedimentological features, these mudstones belong to hemipelagites and contain information about the background sedimentation conditions of the deep-sea oceanic basin. The purpose of the work is to clarify the paleogeodynamic features of the basin based on the results of studying the material composition of the Upper Cretaceous–Lower Eocene background mudstones, which in particular are part of the variegated-colored horizons. Research methods were geological mapping, X-ray structural, sedimentological, lithostratigraphic, petrogeochemical, geodynamic analysis. On the classification module diagram (Na2O+K2O)/Al2O3–(FeO*+MnO+MgO)/SiO2, the figurative points of the contents of the Upper Cretaceous–Lower Eocene mudstones of the Stryi, Yamna, and Manyava suites fall into the fields corresponding to two mineral types: a mixture with a predominance of montmorillonite and three-component mixture of chlorite+montmorillonite+hydromica composition. According to the obtained data, a gradual change in the conditions of the sedimentary environment from the Late Cretaceous to the Eocene can be traced, with a successive increase in the normalized alkalinity modulus and a decrease in the phemic modulus. On the paleogeodynamic discriminant diagrams (FeO*+MgO)–TiO2 and F1–F2, figurative points of Upper Cretaceous–Lower Eocene mudstones form petrochemical distribution trends that cover the fields of geodynamic conditions from passive to active margins of the sedimentation basin. The Cretaceous–Paleogene pelagic mudstones of the Sicilian domain of the Alpine Belt have a similar distribution of petrochemical components. The mineral assemblages found in the mudstones of the Skyba and Boryslav-Pokuttya nappes are typical for deep-sea clay sediments of modern oceans. The presence of montmorillonite and chlorite in the background argillites indicates a high probability of a contribution to the background petrofund of the sedimentatary basin by a femic magmatic component of endogenous origin, realized as a manifestation of volcanic and hydrothermal activity, synchronous to sedimentogenesis. An exogenous source could be the magmatic material transferred or changed by the processes of halmyrolysis, which is not synchronous with sedimentation. The Late Cretaceous–Early Eocene geodynamic events of the Outer Carpathian sedimentary basin developed in front of the ALCAPA and Tisza-Dacia terranes of the Alpine Tethys. Convergence, which caused the formation of the accretionary prism in front of the terranes, could contribute to the riftogenic (?) opening, deepening of the Outer Carpathian Basin, where the penetration of synsedimentary endogenous material, mainly of the basic composition, took place. This material could be the rock-forming source of the basin substrate, on which the mineral assemblages of the background hemipelagic mudstones were formed.

Prototypical basin reconstruction and evolutionary models for the Precambrian of the Qinshui Basin, North China craton

The thick Precambrian strata in the Qinshui Basin (QB) have high potential for hydrocarbon exploration. Tectonic evolution restoration and prototype basin reconstruction are key to hydrocarbon exploration and evaluation for Precambrian strata. We studied the 2D/3D seismic data and Precambrian field outcrops of the QB to elucidate its geological attributes, major regional unconformities, tectonostratigraphic framework, tectonic evolution and prototype basin. The Precambrian strata of the QB are the sedimentary products of the continuous transgression from south to north and are more appropriately attributed to the Xiong'er Aulacogen in the Changchengian and Jixian periods. We identified six regional unconformities: the Archean or Palaeoproterozoic/Xiong'er Group, the Xiong'er Group/Chy, Chc/Chl, Chl/Jxl, the Jxl/Cambrian System, and the Ordovician/Carboniferous. Seven tectonostratigraphic units can be delineated: the Archean–Palaeoproterozoic, Xiong'er Group, Yunmengshan–Cuizhuang, Luoyukou, Jixian, Cambrian–Ordovician, and Carboniferous–Triassic tectonostratigraphic units. The tectonic evolution was divided into seven stages: the formation and evolution of the basement (∼1800 Ma), the synrift stage in the Xiong'er period (1800–1720 Ma), the postrift stage in the Yunmengshan–Luoyukou period (1720–1600 Ma), the passive continental margin basin stage in the Jixian period (1600–1400 Ma), the marine craton stage during the Cambrian–Ordovician (542–440 Ma), the marine–continental transitional–continental craton stage during the Carboniferous–Triassic (316–200 Ma), and the intense deformation stage (200–0 Ma). Three stages of prototype basin models of the Precambrian in the QB have been reconstructed: (1) In the synrift basin model, numerous normal faults have developed, and the section shows a symmetrical composite graben. The topography in the south is low, that in the north is high, and the northeast and northwest areas are palaeo-uplifted. A set of volcanic rocks with coarse-grained clasts was deposited. (2) In the postrift basin model, the fault activity weakened, and the depositional range became larger than that of the synrift stage, and a set of marine clastic–carbonate rocks was deposited showing a gradual coarsening–upwards trend. (3) In the passive continental margin basin model, the fault became almost inactive, the topography was low in the southeast and high in the northwest, and the depositional area was more widespread, resulting in a set of marine carbonates. These results contribute to a better understanding of the break-up process of the Columbia supercontinent and the Precambrian evolution of the North China Craton (NCC) and can be used to predict the distributions of source rocks and hydrocarbons.

Pervasive calcite veins and cleavage dilation in low-grade metamorphic rocks as a marker of lower Jurassic rift-basin margins: A signature of microbial colonization

We report herein for the first time the occurrence of low-grade metamorphic rocks dilated by the growth of calcite veins induced by microbial communities inhabiting the cleavage planes. This process took place at the rock/sea-water interface in a rocky shore environment when the Hercynian basement rocks of the European-Iberian continental margin in Calabria (Italy) experienced stepwise flooding by a shallow tropical sea in the Early Jurassic, a process which was accompanied by synsedimentary extension, resulting in the birth of the Longobucco Basin. The veins exhibit a multiphase filling history, as, in an early phase, microstromatolites lining the walls of cleavage planes document the initial development of microbial biofilms. Subsequently, the growth of bands of radiaxial fibrous calcite enlarged the cavities through force of crystallization, also producing fissures at a high angle with respect to cleavage, which were in turn enlarged by crystal growth. Carbonate clumped isotope analysis indicates crystallization of calcite from sea water, at temperatures (T47) ranging from c. 33 to c. 44 °C. The inferred palaeoenvironment is that of a rocky coastline, locally with tide pools, where the seawater lapped cliffs made of Palaeozoic metasandstone. Microbially induced mineralization was a very rapid process, as clasts of veined metamorphic rocks are found in only slightly younger Early Jurassic deposits, like the sub-reefal carbonate bodies that grew in the Pliensbachian attached to the Palaeozoic bedrock. The occurrence of low-grade metamorphic rocks bearing calcite veins can be mapped in the field for kilometers, following the high-angle unconformity that separates the shallow-water carbonates from the basement. This microbial overprint therefore is a marker of the margins of a rift basin, where the exposure of basement rock along steep submarine surfaces was the result of footwall unroofing.

The Miocene Acceleration of Strike-Slip Deformation in the Northern Tian Shan, Central Asia

Abstract The Tian Shan has been deformed during the Cenozoic as a far-field response to the India–Eurasia collision. This contribution reports new apatite fission-track (AFT) and apatite (U-Th)/He data from the northern Tian Shan, including areas along the southern margin of the Junggar Basin and adjacent to the western segment of the Bolokenu-Aqikekuduk Fault (BAF). Thermal history modeling of the presented data suggests that the Cenozoic exhumation along the basin margin started &amp;gt;20 Ma, and the oblique-slip BAF could have been active since at least ~10 Ma with a total exhumation magnitude of ~2 km during the late Cenozoic. Since then, the mean exhumation rate on southern wall of the BAF is comparable to the Quaternary uplift rate previously measured on the same segment of the fault. To examine the extent of the Miocene acceleration of the transpressional deformation pattern, an exhumation model since 50 Ma was established by inverse modeling &amp;gt;1000 published and new AFT and (U-Th)/He ages from the Tian Shan and the northeastern Tibetan Plateau. The model suggests that after the initial unroofing, a significant acceleration in exhumation occurred during 15–10 Ma, in regions including the interiors of northern and southwestern Tian Shan near major strike-slip structures. This change coincided with the northward propagation of the Pamir and the eastward expansion of the northeastern Tibetan Plateau along the west and south margins of the Tarim Basin, respectively.

Evolution of the Paleozoic (Silurian-Devonian?) Sredogriv metamorphics, NW Bulgaria

The Sredogriv metamorphics are located in NW Bulgaria and referred to the Balkan Terrane. They represent an alternation of different parametamorphites and, to a lesser extent, polymict metaclastic rocks, phyllites and calcareous schists. Various in size allochthonous bodies from metamorphosed magmatites have been tectonically included among them. Recent studies on the Sredogriv metamorphics indicate their formation in a marginal basin of probable Silurian–Devonian age affected by subsequent Carboniferous tectonic processes and greenschist metamorphism.

The Miocene Acceleration of Strike-Slip Deformation in the Northern Tian Shan, Central Asia

Abstract The Tian Shan has been deformed during the Cenozoic as a far-field response to the India–Eurasia collision. This contribution reports new apatite fission-track (AFT) and apatite (U-Th)/He data from the northern Tian Shan, including areas along the southern margin of the Junggar Basin and adjacent to the western segment of the Bolokenu-Aqikekuduk Fault (BAF). Thermal history modeling of the presented data suggests that the Cenozoic exhumation along the basin margin started &amp;gt;20 Ma, and the oblique-slip BAF could have been active since at least ~10 Ma with a total exhumation magnitude of ~2 km during the late Cenozoic. Since then, the mean exhumation rate on southern wall of the BAF is comparable to the Quaternary uplift rate previously measured on the same segment of the fault. To examine the extent of the Miocene acceleration of the transpressional deformation pattern, an exhumation model since 50 Ma was established by inverse modeling &amp;gt;1000 published and new AFT and (U-Th)/He ages from the Tian Shan and the northeastern Tibetan Plateau. The model suggests that after the initial unroofing, a significant acceleration in exhumation occurred during 15–10 Ma, in regions including the interiors of northern and southwestern Tian Shan near major strike-slip structures. This change coincided with the northward propagation of the Pamir and the eastward expansion of the northeastern Tibetan Plateau along the west and south margins of the Tarim Basin, respectively.