Carbonate Platform Research Articles

GEOLOGICAL FEATURES OF SYRIAN OIL FIELDS

Over the past 60 years, exploration in Syria has focused on the major late Paleozoic and Mesozoic sedimentary basins. Source and reservoir rocks were deposited during major regional extensional periods in the late Paleozoic and Mesozoic. Oil and gas fields are concentrated mainly in the eastern and northeastern regions of the country, including the Palmyra, Deir-ez-Zor and Homs areas. The main oil fields are concentrated in the north-eastern and eastern regions of the country, in the oil and gas regions of Rmeilan, Tishreen, Jibsin, Tim and Ward. Most of the gas fields are located in the Palmyra region. The reserves of recoverable oil in Syria are estimated at 350 mln m3, and the reserves of recoverable gas – at 250 bln m3. According to some estimates, the recoverable resources of shale oil on land are about 7 bln m3. On the territory of Syria, with a total area of 2190 km², there are huge gas reserves – 600–700 bln m3 and oil reserves – 50 mln m3. New objects can be explored in Paleozoic and Mesozoic petroleum systems. Stratigraphic traps may include Paleozoic siliciclastic successions, isolated Cretaceous carbonate buildups or Jurassic-Cretaceous carbonate platforms and karsts, and marine basin-floor siliciclastic fans.

The oldest fossil record in the Iberian Peninsula; lower Ediacaran acritarchs of the Tentudía Formation, Ossa-Morena Zone (OMZ), Southwest Iberian Massif.

AbstractA diverse assemblage of acritarchs, that represents the oldest fossil record of the Iberian Massif, is described from Ediacaran metasedimentary rocks of the Tentudía Formation included in the Ossa Morena Zone stratigraphy (Southwestern Iberia). The microfossils found include Assesserium pyramidalis, Cavaspina sp. A, Ceratosphaeridium sp. A, Dictyotidium sp. A, Multifronsphaeridium sp. A, Schizofusa zangwenlongii, Tanarium megaconicum Tanarium sp. A, and Tanarium ? sp. B, This assemblage is diagnostic of the mainly lower Ediacaran Doushantuo-Pertatataka acritarchs (c. 633—565 Ma.). The lithological diversity of the Tentudía Formation suggests that these Ediacaran sedimentary rocks were deposited in a diversity of environments (platform, slope and submarine fans, including mass transport deposits in a back-arc basin that extended into the southern part of the Central Iberian Zone. The mass transport deposits are represented in the Ossa-Morena Zone by the Salvaleón Olistostrome composed by turbidites including chert clast probably derived from the shelf. The migration of the mass transport deposits into the Central Iberian Zone (Orellana Formation) indicates the migration of the back-arc basin depocenter. Later inversion of the back-arc basin is marked by the deformation of the lower Ediacaran sedimentary rocks Serie Negra Group in the Ossa-Morena Zone and Domo Extremeño Group in the Central Iberian Zone. In the upper Ediacaran-Terreneuvian a carbonate platform (Ibor Group) was established in the southern part of the Central Iberian Zone unconformably overlying the previously deformed Domo Extremeño Group. The most proximal areas in the Ossa-Morena Zone are represented by the Malcocinado Formation which overlies the Serie Negra Group and the distal areas of the southern part of the Central Iberian Zone are represented by distal shelf and slope deposits of the Cijara Formation, which are overlain by mass transport deposits that include carbonate olistolites from the Ibor Group (such as the Fuentes and Membrillar olistostromes).

Geological Sites of the Anergui Region: Description and Place in the Alpine Geological History of the M'goun UNESCO Global Geopark (Morocco)

The M'goun UNESCO Global Geopark is located in the central part of the High Atlas Mountains in Morocco. Numerous studies have highlighted the richness of the geological heritage of this area. Despite these increased efforts in characterization, some areas, such as Anergui, remain underexplored. This mediation work aims to describe the most significant geological landscapes of this region and place them within the broader geological history framework of the UNESCO M'Goun Geopark, thereby enriching the list of geosites within this geopark and promoting geological awareness in the area. This study focused on describing 16 geosites selected based on scientific, educational and geotourism values. These geosites stand out for their geodiversity, showcasing both deep-seated and surface geological phenomena. They provide an excellent framework for understanding the alpine geological history of the M'Goun Geopark. Each site bears witness to one or several key stages of this history, highlighting the extension of the High Atlas basin, the development of carbonate platforms, Jurassic diapirism and magmatism, Late Cretaceous and Tertiary compression, Tertiary and Quaternary uplift, and erosion, resulting in a variety of geological features relating to deformation and alteration.

Facies Analysis and Depositional Environment of the Euphrates Formation in Selected Sections, Southwestern Iraq

The current study aims to investigate the microfacies, diagenetic processes, and depositional environments of the twenty-three rock samples from the Lower Miocene Euphrates Formation of two outcrops collected at Bahar-Najaf in Najaf governorate and Al-Shinafiya in Diwaniyah governorate, southern Iraq. Thin sections of these samples were prepared; hence, the nature of microfacies and related depositional environments was established. The formation contains abundant benthonic foraminifers and other fossils like miliolids, echinoderm, coral, gastropods, and pelecypods. Seven distinct microfacies were identified: lime mudstone, miliolid packstone, Pelletal Grainstone, Lime Wackestone, Peloidal Grainstone, Oolitic grainstone Microfacies, and fossiliferous packstone packed with bioclasts. Diagenetic processes evidenced in this study are dissolution, neomorphism, cementation, micritization, and dolomitization. The Euphrates Formation was deposited in a shallow marine setting with fluctuating energy levels, ranging from low-energy lagoons to moderate and high-energy shoals and fore-reef environments. Various microfacies indicate a complex depositional environment on a carbonate platform influenced by biota and sedimentary processes. These observations support the inference that the Euphrates Formation accumulated in shallow open marine, inner barrier, and shoal settings, providing a detailed interpretation of its para-depositional and diagenetic development.

Field geology under the sea with a remotely operated vehicle: Mona Rift, Puerto Rico

We implemented concepts of field geology at great ocean depths by constructing virtual outcrops from a string of overlapping video frames collected by remotely operated vehicles (ROVs). This lower-cost alternative to drilling boreholes allows stratigraphic extension into the offshore and regional interpretation of marine seismic profiles. The imagery was collected along a dive transect on the western wall of Mona Rift, a deep and narrow rift northwest of Puerto Rico, between water depths of 1560 m and 3927 m. The northern coast of Puerto Rico and its large offshore area are underlain by a mid-Eocene and younger forearc basin topped by a thick carbonate platform. There are no drill holes offshore, and tying seismic lines across the shoreline there is problematic. We describe our virtual outcrop and constrain its age and stratigraphy using seven rock samples collected by ROV and compare the outcrop’s stratigraphy to deep boreholes and outcrops on land. Our formation descriptions and ages agree, for the most part, with those on land, but we identified a 100-m-thick section that is represented on land by an unconformity. Our stratigraphic interpretation indicates lateral variations in formation thicknesses and establishes a cross-section for additional sampling of the Eocene–Pliocene geology. It also suggests that Mona Rift has formed since the mid-Pliocene. The presence or absence of ferromanganese (Fe-Mn) crust on rocks along the transect may be correlated with the smoothness of the rock surface.

Sequence stratigraphic analysis of the late Permian Changhsingian platform marginal reef, Western Hubei, South China

This study presents a comprehensive analysis of the late Permian platform marginal reefs in the Sichuan Basin, focusing on reefal lithofacies and sequence stratigraphic patterns. Field outcrop observations and rock sample analyses from the Jiantianba reef were conducted to establish an evolution model of sponge reef development and spatial distribution. Four stages of marginal carbonate platform were documented: open platform, gently sloping reef, steeply sloping reef, and reef bank system. Distinct lithofacies were identified in these stages, reflecting different depositional environments and growth rates. The gently sloping reef was composed of filled skeleton framestone, filled skeleton bafflestone, and micrite organism limestone, indicating limited reef-building capacity. In contrast, the lithofacies of steeply sloping reefs were composed of open skeleton framestone, open skeleton bafflestone, binding skeleton bafflestone, and benthic organism bindstone, indicating stronger reef-building ability. Based on depositional features and carbon isotopic trends, the reef strata were divided into two sequences. Sequence 1 corresponds to the formation of unit 1, and sequence 2 can be further divided into units 2 and 3. In unit 1, reefs developed in a relatively deeper-water setting. It was characterized by rich micrite limestone, forming a gentle margin. Unit 2 witnessed reef development in shallower waters. Early marine cementation and microbial clots were prevalent, contributing to form a steep margin. In the early stage of unit 3, reefs primarily developed in a tidal-controlled environment. Subsequently, reef strata experienced a transition to a wave-influenced environment, leading to the formation of a reef bank system. In general, sequence 1 mainly formed in a heterozoan-dominated factory, and reefs contributed to a relatively gently sloping platform margin. In contrast, sequence 2 formed in a photozoan-dominated factory, and reefs contributed to a relatively steeply sloping platform margin.

U–Pb geochronology of carbonate-hosted Pb–Zn ores reveals plate-tectonic evolution of eastern Asia during the early Paleozoic

The Mississippi Valley–type (MVT) deposits reached their maximum abundance during the final assembly of Pangea. The intense orogenic activity during this assembly in relatively low latitudes created abundant opportunities for the migration of sedimentary brines into the interior carbonate platforms landward of the orogenic belts, leading to the formation of MVT deposits. Thus, dating the MVT deposits can potentially aid in the reconstruction of the plate tectonic evolution during the assembly of Pangea. The Yangtze Craton hosts significant carbonate-hosted Zn–Pb deposits (> 60 Mt Pb + Zn metals), accounting for 30% of China’s Zn–Pb resources. However, determining the timing of zinc and lead mineralization in these reservoirs is challenging. This study employs LA-ICP-MS U–Pb geochronology on calcites to date Zn–Pb deposits hosted in Lower Cambrian limestone in the Huayuan orefield. Three generations of calcite formation were dated: the first recorded the pre-ore deposition of Lower Cambrian limestone at 517 ± 10 Ma, the second marked a hydrothermal event linked to stratiform sphalerite ore formation at 501.4 ± 8.4 Ma, and the third was associated with discordant breccia-hosted Zn–Pb mineralization at 397.5 ± 9.6 Ma. Our results indicate that Paleozoic carbonate-hosted Pb–Zn mineralization in the Yangtze Craton is linked to (1) the final assembly of Gondwana in the late Cambrian-early Ordovician (520–480 Ma); and (2) the intracontinental orogeny response to Jiangnan Uplift (420–400 Ma). This study highlights the temporal relationship between low temperature carbonate-hosted mineralization and orogenic events that are consistent with classic MVT models worldwide. It also contributes geochronological data for the reconstruction of plate-tectonic evolution during Pangea assembly. Furthermore, it demonstrates the potential of in situ U–Pb calcite geochronology to date ore deposits lacking syn-ore minerals suitable for traditional dating methods.

Stratigraphy and microfacies analysis of the Lower–Middle Jurassic platform carbonate succession in the Yeşilovacık (Mersin) area (Central Taurides, S Turkiye)

This study covers the detailed analyses of stratigraphy, microfacies and depositional environments of the Lower-Middle Jurassic carbonate succession in the southern part of Anatolide-Tauride Carbonate Platform in southern Türkiye (south of Central Taurides, around Yeşilovacık). The carbonate succession is composed of the Dibekli and Tokmar formations, and the Işıklıkızıtepe Member which forms the base of the Tokmar Formation. The Dibekli Formation (Upper Sinemurian-Lower Bajocian) is composed of limestones intercalated with intraformational conglomerates in the lower parts, with dolostones in the lower to middle parts and with oncoidal limestones in middle to upper parts. The Işıklıkızıtepe Member (Upper Bajocian) starts with basal conglomerates containing brown-red- iron nodules and consists of sandstone and sandy-clayey limestone alternations. These are overlain by thin limestone layers passing upward to thick-bedded dolostones of the Tokmar Formation (Upper Bajocian–Bathonian). The middle to upper parts of the formation are composed of sandy, oncoidal limestones rich in bivalve shells and end with dolostones-limestone alternations in the upper part. According to microfacies analyzes and litho-bio content; Late Sinemurian-Plesbachian is a period that low-to moderate-energy, restricted inner platform conditions dominated the depositional environments. The presence of comman intraformational conglomerates shows tectonic activity from time to time in this period. The Toarcian to the earliest Bajocian, low-energy intertidal and shallow lagoon conditions dominated the depositional environments, and in the Early Bajocian, the depositional environment changed to a high-energy sand shoal and above wave base environment. The basal conglomerate consisting of brown-red, iron-noduler and bauxite grains at the base of the earliest Late Bajocian indicates a short-term emersion and continued under low energy shallow lagoonal conditions during the Late Bajocian–Bathonian. Environmental changes during the Toarcian to Early Bajocian, and the earliest Late Bajocian short-term emersion, and the environmental changes during the Late Bajocian-Bathonian are interpreted to short-term sea level changes. Yeşilovacık Lower-Middle Jurassic carbonate sequences are correlated with those in peri-Mediterranean platforms. They show close similarities to the other Tauride carbonate sequences in terms of stratigraphy and facies. Paleontological and sedimentological analyses enable us to reconstruct a detailed dating and paleoenvironmental evolution for the Yeşilovacık carbonate deposits during the Lower-Middle Jurassic period.

Carbon isotopic record of a platform-to-basin transect through the Permian Reef Complex (Guadalupian) in the Delaware Basin of Texas and New Mexico

The Guadalupian Permian Reef Complex of the Delaware Basin is one of the most studied carbonate reef systems of the Paleozoic. Despite extensive work on the carbonate sedimentology, sequence stratigraphy, and diagenetic history of the Delaware Basin, a high-resolution carbonate carbon isotope record along a platform to basin transect for the Capitanian (264.3–259.5 Ma, the youngest age of the Guadalupian Epoch) does not yet exist. The carbon isotopic record of the Delaware Basin is important because 1) it allows us to test hypotheses about controls on the carbon isotope proxy, 2) it provides constraints on how well modern carbonate platforms like the Great Bahama Banks serve as analogues for ancient carbonate settings, and 3) these types of restricted basins likely played an important role in Permian carbon cycling and the Capitanian extinctions.In this study we present 493 new Capitanian carbonate carbon isotopic values paired with a detailed sedimentological and sequence stratigraphic framework from the platform, slope, toe of slope, and deep basin of the Delaware Basin. The bulk of the new δ13C values fall within the range of previously reported unaltered carbonates from the basin, suggesting that these results record primary environmental processes and were not significantly altered by diagenetic overprinting. With this dataset, we test hypotheses about sources of carbon isotopic variability in shallow carbonate platforms. Our results indicate that in the Delaware Basin there are no systematic and resolvable depth or lateral gradients in carbon isotopic values, that δ13C values do not vary as a function of grain type, and that there is no resolvable relationship between carbon isotopic composition and sea level change. However, we do document statistically significant differences in δ13C distributions among facies associations which we attribute to the isotopic evolution of an upwelling water mass due to direct precipitation of mud along the slope. Our results support the idea that increasing carbon isotopic values through the Capitanian were driven by increased organic carbon burial in restricted basins.

A new species and genus of Lower Jurassic rhynchonellide (Brachiopoda) from Livari (Rumija Mountain, Montenegro): taxonomic implications of the shell microstructure

ABSTRACT A new rhynchonellide brachiopod genus and species, Skadarirhynchia semicostata gen. et sp. nov., is described from the late Pliensbachian of Livari, Rumija Mountain, southeastern Montenegro. It occurs in shallow-water brachiopod-crinoid packstone beds (bioclastic limestones) of the periplatform facies of the Dinaric Carbonate Platform. Stratigraphy is constrained by means of 87Sr/86Sr dating indicating a late Pliensbachian age, and by the fact that the brachiopod beds lie immediately below the Toarcian marly limestones, which is consistent with the regional stratigraphical position. The new species has a circular to roundly pentagonal outline and semicostate shells with 10‒12 strong angular ribs. Internally, it shows reduced dental plates, narrow and thin hinge plates inclined dorsally with small crural bases, crescent-like and laterally convex, and hamiform crura. The shell microstructure of the new taxon is characterised by a homogeneous secondary layer (a single layer with no sublayers) built of rhombic fibres that are typically of coarse-fibrous type (eurinoid pattern) 35‒50 μm wide and 20‒30 μm thick. Other co-occurring rhynchonellide species such as Prionorhynchia fraasi and Cuneirhynchia dalmasi are also described. Shell microstructures for the genus Cuneirhynchia are presented.

Shallow subsurface fluid dynamics in the Malvinas Basin (SW Atlantic): A geoacoustic analysis

Using a database consisting of sub-bottom profiles, 2D and 3D seismic data, a series of seep structures and acoustic anomalies associated with a plumbing system in the subsurface of the southern part of the Malvinas Basin off the Argentine coast are presented. The seep morphologies consist of mounds, pockmarks, and a carbonate mound, derived from hydrocarbons migrating from the Early Cretaceous Springhill and Lower Inoceramus formations through extensional faults and overthrusts of the Malvinas Fold-Thrust Belt and accumulating in the gas hydrate stability zone. This configuration is widely observed in the anticlines of the Malvinas Fold-Thrust Belt, which are characterized by a vertical structure highlighting a Bottom Simulating Reflector (BSR) overlain by a blanked-out zone at the seabed, interpreted as a gas hydrate stability zone. The plumbing system is influenced by active transtensional tectonics, as shown by two sets of extensional faults concentrated over some anticlines. These faults lead to displacements that, in many cases, reach the seabed. One nuance of the influence of tectonic activity on fluid escape is most evident in the Malvinas anticline, where all the pockmarks and the carbonate mound are concentrated. In the western part of the Malvinas anticline, five pockmarks are observed in an area characterized by a shallow BSR. In contrast, in the eastern part of the Malvinas Basin, one pockmark and one carbonate mound are derived from a series of extensional faults. The presented data, as well as a comparison between the western and eastern parts of the Malvinas anticline, indicate that the anticlines are the main cause of seepage in this area, as they allow the accumulation of migrating fluids. Likewise, the seepage morphologies outside the anticlines are much less pronounced, as can be observed in the mounds that overlie the bottom vents.

Slag Inclusions in Iron Artifacts from Cemeteries at Kichigino I and Krasnaya Gorka, and the Metallurgy of the Early Iron Age Itkul Culture

Silicate slag inclusions in iron artifacts from the Trans-Urals and in iron slags from sites of the Itkul culture were analyzed to assess the geochemical characteristics of iron ore sources exploited during the Early Iron Age. Slag inclusions were found in 19 out of 25 samples from Kichigino I and Krasnaya Gorka. For comparison, we used 12 iron slag samples from Early Iron Age and medieval sites near Lake Irtysh and from Zotino mine. Via statistical analysis, four geochemical groups were separated, each including one or more Kichigino artifacts, which suggests a variety of iron ore sources used by the nomads. Slags and artifacts of the first group are associated with infiltration-sedimentary ironstone ores of the Middle Trans-Urals. Smithing slag from the Itkul site of Shatanov V suggests that these ores were already smelted in the Early Iron Age. The fact that group 1 includes only one artifact from Kichigino I demonstrates that the nomads of the Southern Trans-Urals obtained iron mainly from other sources. Group 2 is characterized by a higher content of Mn and sometimes Ba and S in inclusions. This may attest to the use of Fe-Mn ironstone associated with barite-polymetallic deposits of Central Kazakhstan. Group 3 shows an elevated content of CaO and MgO, indicating the use of ironstone from platform carbonate strata. In the fourth group, the content of K2O is high, and that of MnO, low.

Architectural development of a land-attached carbonate platform in the African–Arabian Desert Belt: the late Pleistocene to Holocene evolution of the Al Wajh Platform, NE Red Sea, Saudi Arabia

ABSTRACT Carbonate platform architectures are indicators of environmental changes, such as sea level, climatic variations, and tectonic influence, which all control platform evolution. While analog studies on modern carbonate platforms have predominantly focused on tropical settings, limited attention has been given to arid and semiarid environments, although many ancient carbonate sequences were developed under these settings. This study aims to bridge this gap by investigating the Al Wajh carbonate platform lagoon in the NE Red Sea, Saudi Arabia, using geophysical and remote-sensing data to unravel its architecture and development since the last interglacial highstand (MIS 5e). We collected and analyzed sub-bottom profiles extending over 675 km and airborne lidar multibeam bathymetry data covering an area of 1700 km2. Surface sediment samples and vibracores with a maximum penetration of three meters were integrated to strengthen our interpretation. Furthermore, a recently published Red Sea sea-level curve was used to establish an age model and supplemented by available climate data to reconstruct depositional models. The Al Wajh lagoon is a “bucket” structure hosting five distinct depositional units since the late Pleistocene: U0 (pre-MIS 5e and MIS 5e), U1, U2, U3, and U4 (MIS 1), which are composed of five hydroacoustic facies, ranging from mounded to wavy laminated facies. Based on combining climate data, sea-level curves, and platform topography with our geophysical data, we conclude that the lagoon hosts carbonate, siliciclastic (fluvial and eolian), and potentially evaporitic deposits of open-marine and playa-lake origin. Intriguingly, karst architecture (i.e., sinkholes, caves, and collapsed cavities) is absent despite intermittent pluvial episodes and exposure during the late Pleistocene. Data analysis indicates that the Al Wajh lagoon architecture and development since the late Pleistocene are controlled by a combination of antecedent topography, sea-level variation, climate fluctuation, siliciclastic influx, carbonate production, and reef growth and drowning. Finally, insights from this study enhance our understanding of the architecture and sedimentary infill of ancient land-attached carbonate platforms deposited in a mature rift basin under alternating arid and pluvial climate settings.

Ni-based compounds in multiwalled graphitic shell for electrocatalytic oxygen evolution reactions

Here, we report a general strategy for designing a metal/carbon system, via a facile and environmentally friendly one-step approach, from metal acetate as an active electrocatalyst in oxygen evolution reaction (OER) during water decomposition. As a demonstration, a nanostructured Ni/C composite induced from nickel acetate is revealed in great detail. The resulting material is composed of: metallic nickel (Ni), nickel(II) oxide (NiO), and nickel carbide (Ni3C) coated with a graphitic shell and deposited on a carbon platform. Our findings underscore the prominent role of nickel species, including Ni0, Ni2+, and Ni3+, in driving the catalytic activity. Notably, the catalyst exhibits an overpotential of 170 mV, a Tafel slope of 49 mV·dec−1, an electrocatalytic surface area (ECSA) of 964.7 cm2, and a turnover frequency (TOF) value of 52.8 s−1, surpassing RuO2. The Raman spectra also suggest a graphitic "self-healing" phenomenon post-OER, attributed to the reduction of oxygen-containing groups. Carbon in the system (i) facilitates electron transfer, (ii) allows homogeneous distribution of Ni nanoparticles avoiding their agglomeration, and (iii) promotes durability of the electrocatalyst by serving as a protective barrier, shielding the core metal compounds. What is more, density functional theory (DFT) calculations allowed to optimized geometry of the model cluster Ni8O8(OH)8 describing two different sites on the β-NiOOH surface (001) and two different intermediates, (i)L-OOH and (ii)L-OOH. This facilitated to propose the reaction mechanisms involving both hydroxide ions and water molecules as reducers. Therefore, the chemisorption of OH− and H2O molecules at the NiOOH active center accompanied by bond breakage and the formation of a lattice hydroperoxide as an important intermediate is presumed. What is more, the proposed fabrication method for electroactive metal/carbon composites was validated with an iron and iron/nickel mixture.

Early Aptian development and OAE 1a-linked demise of a carbonate platform in the Western Tethys: Lower Cretaceous of Sierra Mariola (South Iberian Paleomargin, SE Spain)

A carbonate platform succession of early Aptian age is described from the Sierra Mariola, which is located within the Prebetic Zone of the Betic External Zones (BEZ) of the Southern Iberian Palaeomargin, in SE Spain. The facies and stratigraphic architecture of the studied succession are described and analysed from multiple logged sections to characterize different depositional environments.The cyclic stacking of facies observed suggests a possible orbital forcing of climate transmitted to sedimentation. Superbundles are recognized describing two sequences of Regressive-Transgressive (R-T) evolution. Analysis of carbon-isotope data identifies both the interval before the hyperthermal event of the early Aptian Oceanic Anoxic Event (OAE 1a) and the onset of the latter event, with an abrupt change in sedimentation marking the demise of the carbonate platform. The field outcrop thus preserves a record of the transition from a greenhouse world to a hothouse event.

Dynamic simulation of differential accumulation history of deep marine oil and gas in superimposed basin: A case study of Lower Paleozoic petroleum system of Tahe Oilfield, Tarim Basin, NW China

According to the complex differential accumulation history of deep marine oil and gas in superposition basins, the Lower Paleozoic petroleum system in Tahe Oilfield of Tarim Basin is selected as a typical case, and the process of hydrocarbon generation and expulsion, migration and accumulation, adjustment and transformation of deep oil and gas is restored by means of reservoine-forming dynamics simulation. The thermal evolution history of the Lower Cambrian source rocks in Tahe Oilfield reflects the obvious differences in hydrocarbon generation and expulsion process and intensity in different tectonic zones, which is the main reason controlling the differences in deep oil and gas phases. The complex transport system composed of strike-slip fault and unconformity, etc. controlled early migration and accumulation and late adjustment of deep oil and gas, while the Middle Cambrian gypsum-salt rock in inner carbonate platform prevented vertical migration and accumulation of deep oil and gas, resulting in an obvious “fault-controlled” feature of deep oil and gas, in which the low potential area superimposed by the NE-strike-slip fault zone and deep oil and gas migration was conducive to accumulation, and it is mainly beaded along the strike-slip fault zone in the northeast direction. The dynamic simulation of reservoir formation reveals that the spatio-temporal configuration of “source-fault-fracture-gypsum-preservation” controls the differential accumulation of deep oil and gas in Tahe Oilfield. The Ordovician has experienced the accumulation history of multiple periods of charging, vertical migration and accumulation, and lateral adjustment and transformation, and deep oil and gas have always been in the dynamic equilibrium of migration, accumulation and escape. The statistics of residual oil and gas show that the deep stratum of Tahe Oilfield still has exploration and development potential in the Ordovician Yingshan Formation and Penglaiba Formation, and the Middle and Upper Cambrian ultra-deep stratum has a certain oil and gas resource prospect. This study provides a reference for the dynamic quantitative evaluation of deep oil and gas in the Tarim Basin, and also provides a reference for the study of reservoir formation and evolution in carbonate reservoir of paleo-craton basin.

The mid-Cretaceous bauxites of SE France: Geochemistry, U-Pb zircon dating and their implications for the paleogeography at the junction between Alpine Tethys and Pyrenean Rift

Karst bauxites mark episodic exhumation of carbonate platforms, thus providing key information for basin analysis and paleoclimate processes at the regional to continental scale. Most karst bauxite deposits of SE France lie between Jurassic platform carbonates in the footwall and Upper Cretaceous marine to continental sediments in the hanging wall. These deposits delineate a stratigraphic gap coeval with the Durance extensional tectonics, which led to the separation of the Vocontian and South Provence Basins, and shaped the junction between the Alpine Tethys and the Pyrenean Rift.Our new mineralogical and geochemical data show that SE France karst bauxites were affected by in-situ weathering and alteration in conjunction to sedimentary reworking. Statistical analysis of geochemical data indicates that bauxite deposits have a similar chemical footprint, likely pointing to a common and long-lasting bauxitization process. New U-Pb zircon data from the Provence deposits confirm that the source material for the SE France bauxites is to be primarily found in the Hercynian basement. The data suggest the presence of an additional exotic zircon source deriving either from Avalonia and/or Baltica. The comparison of the new U-Pb zircon data with those on coeval bauxites evidences a marked difference between the SE France and the Sardinian deposits. This difference indicates diversification in the detritus provenance of the two areas since the Lower Cretaceous, setting the bauxites of SE France and Sardinia in lateral continuity with the bauxites occurring on the two opposite margins of the Pyrenean Rift, and supporting the development of these deposits on the shoulders of the rift-related basin formed at the eastern termination of the Pyrenean Rift.

Widespread coastal upwelling along the marginal Yangtze Platform (South China) during the early Cambrian: Implications for hyper-enrichment of organic matter

Early Cambrian Earth history witnessed significant changes in marine environments and biological evolution contemporaneous with extensive accumulation of organic-rich shale. However, major factors controlling hyper-enrichment of organic matter (OM) of lower Cambrian shale deposits remain controversial. Black shale of the lower Cambrian Niutitang Formation (NTT) of the Marginal Yangtze Platform (South China) deposited during the Cambrian middle Age 2 are especially organic-rich, with total organic carbon (TOC) concentrations of as much as 13.0 wt%. Geochemical evidence suggests that cool, dry paleo-climatic conditions that prevailed on the Yangtze Platform during the Cambrian Fortunian-late Age 2, induced vigorous coastal upwelling. Paleo-productivity level assessments indicate that the magnitude of primary productivity contemporaneous with deposition of the NTT shale deposits exceeded that of modern upwelling systems (e.g., Peruvian Margin). The widespread occurrence of phosphate nodules within these deposits and decreased Co-EF × Mn-EF values of associated lower Cambrian black shale successions deposited along the margin of the Yangtze carbonate platform suggest extensive coastal upwelling. Widespread and strong coastal upwelling in tandem with elevated surface water primary productivity and anoxic (even euxinic) bottom water conditions are manifested by deposition of OM hyper-enriched black shale during Cambrian Fortunian to middle Age 2 time. However, weakened seasonal upwelling that appears to have prevailed during the late Cambrian Age 2 was accompanied by accumulation of NTT shale deposits of diminished TOC content. In summary, this study provides robust evidence of extensive coastal upwelling along the Marginal Yangtze Platform during early Cambrian time that favored accumulation of OM hyper-enriched shale. These results help to elucidate the distribution of high-quality lower Cambrian natural gas source rocks in South China.

Impact of Tethyan domain evolution on the formation of petroleum systems in the Sichuan super basin, SW China

Based on the “unidirectional break-up and convergence” geodynamic model, this study investigates the impact of the evolution of the Tethyan domain on the formation of petroleum systems in the Sichuan super basin and explores the enrichment pattern of natural gas. The results show that, firstly, the Sichuan Basin and its surrounding areas have experienced two unidirectional rifting-aggregation cycles triggered by the Proto-Tethys Ocean and the Paleo-Tethys Ocean during the Neoproterozoic to Triassic. During Jurassic–Cenozoic, the Sichuan Basin is incorporated in the circum-Tibetan plateau basin-mountain coupled tectonic domain system. The episodic tectonic movements within the plate control the sedimentary infill styles. Second, the evolution of the Tethyan domain, paleoclimatic environment and major geological events controlled the formation and distribution of high-quality source rocks within the basin. The rift valley and intracratonic rift, passive continental margin slope, and intracratonic sags are favorable areas for the development of source rocks. Third, the evolution of the Tethyan domain, supercontinent cycles, global sea level changes, and tectono-climatic events controlled the distribution of carbonate platform and reservoir-caprock combinations. The cratonic platform margins and sub-platform internal high terrains are key areas for finding carbonate high-energy facies belts. Syndepositional paleo-uplifts and surrounding slopes, regional unconformities, and later faults zone are areas where large-scale carbonate reservoirs are distributed. The regional evaporite or shale caprock are beneficial for the large-scale preservation of oil and gas in the basin. Fourth, the spatio-temporal matching relationship of reservoir forming factors influenced by the early tectonic-sedimentary evolution pattern and the degree of later tectonic modification is the key to oil and gas enrichment. Future oil and gas exploration should focus on potential gas systems during the Sinian rift period, Cambrian pre-salt gas systems in the eastern and southern Sichuan, as well as whole oil and gas systems of Permian and Triassic.

Basin inversion, drifting and hyper-extension in the Central Atlantic Ocean and Maghrebian Tethys as fluid driving mechanisms for the superimposed base metal mineralization events in the Jbel Bou Dahar carbonate-hosted Pb-Zn-Ba deposits (High Atlas, Morocco)

The Early Jurassic Jbel Bou Dahar reef-bearing carbonate platform in the eastern High Atlas, Morocco, contains numerous carbonate-hosted and fault-controlled Pb-Zn-Ba deposits, prospects, and showings. Combined field, petrographic and geochemical data, including REE + Y analyses, stable (C-O-S), radiogenic (SrPb) and noble gas (He, Ne, Ar) isotopic compositions, record two temporally distinct metallogenic events. Both events are related to post-rifting and inversion of the inherited Mesozoic Atlas paleorift. The ore deposits are thought to have been formed during large-scale episodes of transtensional basin evolution, which developed as a far-field effect of the drifting of the Central Atlantic Ocean and Maghrebian Tethys while the basin continued to invert in response to the ongoing convergence between the African and the Eurasian plates. The paragenetically earliest Zn-rich ore was generated in a transtensional setting coincident with the hyper-extension of Maghrebian Tethys and the initial stages of drifting and formation of the Central Atlantic passive margin. Crustal extension and high heat fluxes provided by the hot upwelling mantle would have triggered buoyancy-driven convection of deeply sourced fluids and maturation of organic matter dispersed within the host carbonates to produce hydrocarbons within an extensional basin setting. These relatively reduced Zn-rich ore-forming fluids acquired metals mainly through protracted interaction with the country rocks including the underlying Triassic siliciclastic series and the granitic basement rocks. Regional ENE- to E-W-trending major faults would have acted as conduits for upward fluid flow and traps for Zn-Pb-Ba mineralization. Conversely, the late Pb-rich mineralization stage II is broadly constrained to have occurred between ca. 70 Ma and 10 Ma and is thought to be related to the transition from orogenic shortening (late Eocene) to post-orogenic crustal extension and exhumation (early Miocene) following Alpine orogenic collapse. Mixing of down-ward percolating meteoric fluids and ascending rock-buffered hydrothermal brines that had previously equilibrated with the radiogenic basement rocks along with thermochemical sulfate reduction of transported sulfate and/or thermal cracking, would have been the main ore-forming processes that controlled ore deposition. Given these fluid characteristics and geodynamic settings, the Jbel Bou Dahar ore field is classified as a hybrid carbonate-hosted Pb-Zn-Ba district formed by the juxtaposition of two deposit types rather than one progressively evolving mineralizing system. From an exploration standpoint, new delineation here of the two metallogenic events provides valuable exploration tools for further targeting PbZn and barite resources in the Atlas system of North Africa and other areas where similar orogenic belts experienced post-rift subsidence and basin inversion.