Mesozoic Sandstones Research Articles

Chemical characteristics and assessment of groundwater quality in Halayieb area, southeastern part of the Eastern Desert, Egypt

Halayieb area is located at the southeastern corner on the border between Egypt and Sudan. The area has very important strategic aspects to Egypt. Groundwater is the only source of fresh water in the area. The hydrogeochemical characterizations of groundwater in the area were carried out, to assess the quality of groundwater for its suitability for drinking and irrigation purposes. Geologically the Precambrian rocks underlain the Mesozoic sandstone and Tertiary marine sediments. The groundwater of the area is recorded at the Miocene sedimentary succession and the fractured basement aquifers with a maximum water depth of 26.5 m from the ground surface. Groundwater quality is mostly saline caused by the sources of geogenic, anthropogenic, and marine origin of the water bearing formations. The resulting groundwater is characterized by Na+ > Ca2+ > Mg2+/Cl− > HCO3− > SO42−: Na+ > Ca2+ > K+/SO42− > Cl− > HCO3− facies, following the topographical and water flow-path conditions. The hydrochemical facies in this area fall in the field of NaCl type and the hydrogeochemical signatures indicated active hydrolysis and dissolution process of Ca-bearing minerals of the basement rocks and some sodium is lost, most probably through reverse ion exchange. Enrichment of Mn+ in some wells is regarded to the mining activity for manganese ores in the area. Groundwater quality is mostly not suitable for drinking purposes. For irrigation, the groundwater is mostly suitable in regard to the residual sodium carbonate and the magnesium hazard. According to the water quality assessment using United States salinity laboratory (USLL) diagram, most water samples located in category C3–S2, C3–S3, C3–S4, C4–S2 highlighting high to very high salinity hazard and medium to very high sodium content class. Most of the groundwater samples that are located away from the shoreline are suitable for livestock and poultry consumption. High salinity contents in the study area create severe problems for using water supplies and for future exploitation.

Hydrocarbon migration and accumulation history in deep reservoirs: a case study of Mesozoic sandstone gas reservoirs in the Kelasu-Yiqikelike structural belt of the Kuqa Depression, Tarim Basin

Numerous deep oil and gas reservoirs have recently been discovered in the Kelasu-Yiqikelike structural belt of the Kuqa Depression in the northern Tarim Basin, north-western China. The sources and accumulation processes of the oil and gas are determined in this study through a series of biomarker geochemical parameter analyses and fluid inclusion analyses, respectively. The geochemical parameters show that the oil of the Kela 2 gas field originated from the Triassic Huangshanjie (T3h) Formation lacustrine source rock and that the oil of the Jurassic reservoirs in the Dibei gas field was sourced from Jurassic coal measures, with some contribution from the T3h source rock. Furthermore, the gas in the Kela 2, Keshen and Dibei gas fields was derived from the Jurassic coal measures. Based on petrographic and fluid inclusion analyses, combined with a reconstruction of the reservoir burial history, timing estimates and charge models of the hydrocarbon accumulation have been obtained. Two stages of oil charging and one stage of gas charging were identified in the Kela 2 gas field. The two stages of oil charging occurred in the middle–late Miocene and in the early Pliocene. The gas charge occurred in the middle–late Pliocene. Additionally, one stage of gas charging occurred in the Keshen gas field in the late Pliocene to Quaternary. In contrast, two hydrocarbon charging stages were identified in the Dibei gas reservoirs, with the first occurring in the early Miocene and the second occurring in the Pliocene.

Regional Mapping of Groundwater Resources in Data-Scarce Regions: The Case of Laos

This study focuses on Laos, a landlocked nation located in South-East Asia with sub-tropical climate and highly seasonal rainfall distribution. Laos is one of the world’s least developed countries, and currently witnesses an unprecedented level of development that is highly reliant on its natural resources, including groundwater. There is currently very limited data and no nationwide assessment of shallow (<30 m) groundwater resources to support sustainable management. This study provides a first step towards addressing this issue by (i) identifying the major aquifer units of the country; (ii) integrating localized data and regional maps into an assessment of the groundwater potential; and (iii) producing quantitative maps of key hydrogeological indicators. Eight aquifer units have been described and evaluated: (i) Basement aquifers, (ii) Volcanic aquifers, (iii) Schists, (iv) Paleozoic sedimentary, (v) Karsts, (vi) Limestones, (vii) Mesozoic sedimentary and (viii) Alluvial sediments. The Mesozoic sandstones and the Alluvial aquifers are the most extensive and productive hydrogeological systems in the country. The Volcanic and Karstic aquifers, although poorly known, might also have important potential. This assessment, along with the maps of quantitative aquifer indicators, provide a significant improvement in both spatial resolution and accuracy compared to previously available information. It will likely support improved management plans and the identification of areas with higher potential for groundwater development.

Provenance analyses of early Mesozoic sediments in the Ningwu basin: Implications for the tectonic–palaeogeographic evolution of the northcentral North China Craton

ABSTRACTThis paper reports results from detrital zircon U–Pb geochronology, Hf isotopic geochemistry, sandstone modal analysis, and palaeocurrent analysis of the early Mesozoic strata within the Ningwu basin, China, with the aims of constraining the depositional ages and sedimentary provenances and shedding new light on the Mesozoic tectonic evolution of the northcentral North China Craton (NCC). The zircons from early Mesozoic sandstones are characterized by three major populations: Phanerozoic (late Palaeozoic and early Mesozoic), late Palaeoproterozoic (with a peak at approximately 1.8 Ga), and Neoarchaean (with a peak at approximately 2.5 Ga). Notably, three Phanerozoic zircons in the Early Triassic Liujiagou Formation were found to have positive εHf(t) values and characteristics typical of zircons from the Central Asian Orogenic Belt (CAOB). Therefore, the CAOB began to represent the provenance of sediment in the sedimentary basins in the northern NCC no later than the Early Triassic (261 Ma), implying that the final amalgamation of the NCC and CAOB occurred before the Early Triassic. The U–Pb geochronologic and Hf isotopic results show that the Lower Middle Triassic sediments were mainly sourced from the Yinshan–Yanshan Orogenic Belt (YYOB), and that a sudden change in provenances occurred, shifting from a mixed YYOB and CAOB source in the Middle Jurassic to a primarily YYOB source in the Late Jurassic. The results of the sandstone modal analysis suggest that the majority of the samples from the Lower Middle Jurassic rocks were derived from either Continental Block or Recycled Orogen sources, whereas all the samples from the Upper Jurassic rocks were derived from Mixed sources. The change in source might be ascribed to the southward subduction and closure of the Okhotsk Ocean and the resulting intense uplift of the YYOB during the Late Jurassic. This uplift likely represents the start of the Yanshan Orogeny.

Structural characteristics and petroleum exploration of Levant Basin in Eastern Mediterranean

Abstract By using geologic and seismic data, this study restored the proto-type basins and lithofacies paleogeography of the Levant basin in Eastern Mediterranean during main geological periods, carried out comparison analysis on the basin architecture characteristics, and based on careful examination of the characteristics of discovered gas reservoirs, established the reservoir forming pattern and discussed the favorable reservoir forming combinations and future exploration direction in this region. Three structural architectures can be identified in the basin, the early-stage faults, the mid-stage faults and the late-stage faults. The early-stage faults are mainly controlled by intercontinental depression, which were less influenced by later compression stress in the southern deep water area of the basin. Controlled by the lateral structural stress and the Syrian Arc Fold Belt, the mid-stage faults became less active from north to south and from east to west. Influenced by the collision and/or Dead Sea strike-slip Fault Zone, the late-stage faults were active but did not pierce the thick Upper Miocene evaporites. Combined with the discovered reservoirs and outcrops, the Mesozoic sandstones and carbonates in deep water area near Eratosthenes seamount of Israel offshore and the Cenozoic carbonates and Tamar sands of Lebanon offshore are the main petroleum exploration targets in the next step.

Characteristics and Productivity of the Sediments and Volcanic Rocks Aquifers in Sunuta Sub-Basin, Northeast Ethiopia

Sunuta sub-basin is found within the lower Awash basin, Northeast Ethiopia, having an area of 1490.5km2. The objective of the research was to characterize the different sediments and volcanic rocks aquifers and evaluate their respective productivity. To achieve these objectives, primary and secondary data were collected. Primary data such as geological, geological structures, and 82 water levels were collected during field investigation. 35 constant pumping test and 33 borehole log data were collected as secondary data from water offices in the area. With the exception of specific capacity, all other hydraulic properties were determined from recovery test data using Theis and Neuman analysis methods. Specific capacity was determined from constant discharge test data. The Mesozoic sandstone, Tertiary and Quaternary volcanic rocks and recent sediments are the main geological formations of the sub-basin. The aquifer types around the escarpments are unconfined whereas in the rift floor the aquifers are confined and semi-confined. In the rift floor the sediment thickness varies from 166-200m and also found interlayered with volcanic rock of rhyolite and basalt, forming multilayer confined and semi-confined aquifer. The general groundwater flow direction is from west to east. The different geological formations that are found constituting the area are categorized hydrogeologically into aquifer with intergranular weathered and fracture porosity and permeability, extensive aquifer with intergranular porosity and permeability and aquifer with fracture porosity and permeability. Analysis of pumping test data revealed that hydraulic conductivity ranges from 0.268 to 31.1 m/day and transmissivity ranges from 9.6 to 2420 m²/day with mean values of 9.55 m/day and 632.79 m²/day, respectively. Specific capacity ranges from 0.07 to 65.31 l/sec/m with mean values of 5.45 l/sec/m. On the basis of their corresponding transmissivity and specific capacity value, the different aquifers of the studied area were categorized into three aquifer potentiality groups: low, moderate and high potentiality aquifer. Any future development of groundwater should be focused on the moderate and high potentiality aquifers.

El petróleo de San Cristóbal. ¿Realidad o leyenda?

El presente trabajo tiene como objetivo hacer un resumen de las actividades exploratorias desarrolladas en la zona de San Cristóbal, provincia de Santa Fe (República Argentina) desde el año 1913 a la actualidad. Trata de valorar, dentro del análisis del Sistema Petrolero, las manifestaciones de hidrocarburos descriptas tanto en el pozo N° 8, perforado por el Ministerio de Agricultura en la búsqueda de agua para el ferrocarril del Estado, como en el perforado por Yacimientos Petrolíferos Fiscales (YPF) entre los años 1933 y 1935.Es importante destacar que con la perforación del pozo San Cristóbal-1 se inició formalmente la exploración de petróleo en el sector argentino de la cuenca Chacoparaná. Las manifestaciones de hidrocarburos descriptas en ambos pozos durante la perforación, desataron en su momento expectativas en la sociedad y fueron responsables de grandes títulos en la prensa provincial y nacional sobre lo que podría constituirse en un nuevo yacimiento de petróleo. Pero lamentablemente no fue así. Sin embargo, la lectura crítica realizada sobre legajos de pozos, informes técnicos y diarios de la época, como también la incorporación de nuevos datos de laboratorio, han posibilitado mejorar el análisis de los elementos y procesos del Sistema Petrolero. Estos avances permiten aseverar que niveles de areniscas de probable edad mesozoica del sondeo San Cristóbal-1, cercanos a la profundidad de 1.350 mbbp, han estado expuestos a procesos de migración de hidrocarburos líquidos.

Heavy-mineral analysis and provenance of Yellow River sediments around the China Loess Plateau

In its upper-middle reaches the Yellow River has high sand contents after traversing through large areas of desert and the China Loess Plateau. Understanding riverbed sediment composition in the channel is critical for the interpretation of the potential provenance, aeolian sand transport and the linkage between the Loess Plateau and the Yellow River. To address these issues, we collected 52 samples from the modern riverbed, proximal deserts, and major tributaries and used analyses of grain size, grain morphology, and heavy-mineral compositions, to establish the spatial distribution and characteristics of source regions and riverbed sediments. The heavy-mineral assemblages demonstrate significant variations for the different sections of the Yellow River. The riverbed samples from the upper reach are dominated by opaque minerals (limonite and magnetite), amphibole and epidote, with minor zircon, tourmaline and rutile. Riverbed sediments from the middle reach are garnet-rich, reflecting the widespread distribution of Mesozoic sandstones. This variability closely reflects the source regions. Our data show that seasonal tributaries (the “Ten Great Gullies”) carrying detritus from the Ordos Plateau may account for the localized high garnet concentrations in the Inner Mongolia section of the upper reach. Scanning electron microscope (SEM) imaging of quartz grains show that the river sediments are characterized by composite microtextures acquired in both fluvial and eolian environments of the Hedong, Ulan Buh and Kubuq Deserts. The mineralogical composition in the upper reach (Lanzhou–Yinchuan) is similar to that of sediments in the Loess Plateau and Northeast Tibet Plateau (Western Lanzhou). However, the composition differs markedly from that in the Inner Mongolia section of the upper and middle reaches. This variation indicates that in the upper reach the Northeast Tibet Plateau contributes significant volumes of sediment to the Yellow River and Loess Plateau, but compositions change across the Inner Mongolia section of the upper and middle reaches owing to local sediment supply from arid desert areas and seasonal tributaries.

Provenance of Triassic and Jurassic sandstones in the Banda Arc: Petrography, heavy minerals and zircon geochronology

Quartz-rich sandstones in the Banda Arc Islands are thought to be equivalent of Mesozoic sandstones on the Australian NW Shelf where they are important proven and potential reservoirs. Previous studies suggested that rivers draining Australia provided most of the sediment input and there have been suggestions of a northern provenance for some Timor sediments. We present results from a provenance study of Triassic and Jurassic sandstones of the Banda Arc between Timor and Tanimbar, which used several methodologies, including conventional light and heavy mineral point counting, textural classification and laser ablation (LA-ICP-MS) U–Pb dating of detrital zircons. Most sandstones are quartz-rich and detrital modes suggest a recycled origin and/or continental affinity, consistent with an Australian source. However, many of the sandstones are texturally immature and commonly contain volcanic quartz and volcanic lithic fragments. In the Tanimbar Islands and Babar, acid igneous material came from both the Australian continent and from the Bird's Head, whereas sandstones in Timor have a greater metamorphic component. Heavy mineral assemblages are dominated by rounded ultra-stable minerals, but mixed with angular grains, and indicate an ultimate origin from acid igneous and metamorphic sources. Detrital zircon ages range from Archean to Mesozoic, but variations in age populations point to differences in source areas along the Banda Arc both spatially and temporally. Significant zircon populations with ages of 240–280Ma, 1.5Ga and 1.8Ga are characteristic and are also common in many other areas of SE Asia. We interpret sediment to have been derived mainly from the Bird's Head, Western and Central Australia in the Triassic. In the Jurassic local sources close to Timor are suggested, combined with recycling of NW Shelf material.

Single-grain apatite geochemistry of Permian–Triassic granitoids and Mesozoic and Eocene sandstones from Chiapas, southeast Mexico: implications for sediment provenance

ABSTRACTThis article reports single-grain multi-elemental results (Sr, Y, Th, U, and rare earth elements) obtained in 966 apatites from 18 rocks (sandstones and granitoids) that were sampled from the Mesozoic (Todos Santos and San Ricardo Formations) and Eocene (the El Bosque Formation) successions as well as from the Permian–Triassic Chiapas Massif Complex (CMC), all of which are exposed within the Sierra de Chiapas (SCH), SE Mexico. The objectives of the present study are (1) to establish changes in provenance between the Mesozoic and Eocene sedimentary sequences using single-grain apatite geochemistry, and (2) to identify source areas for siliciclastic materials from the Todos Santos, San Ricardo, and the El Bosque Formations. The results of the present work strongly suggest that apatites from the Todos Santos and San Ricardo Formations were mainly derived from intermediate to felsic I-type granitoids as well as from arc-related volcanic rocks, indicating that the CMC basement was the most important source area for the Mesozoic sandstones in the SCH. An abrupt change in provenance from Mesozoic to Eocene units was identified based on single-grain apatite geochemistry. Detrital apatites of the Ypresian–Lutetian El Bosque Formation were derived from diverse source rocks such as mafic–ultramafic rocks, intermediate to felsic I-type plutons, strongly fractionated S-type granites and pegmatites, as well as from different metamorphic source lithologies (including high-pressure rocks) such as gneisses, migmatites, metapelites, and/or eclogites. It was proposed, therefore, that most Eocene sediments of the SCH were derived from the Guatemala Suture Complex, which involves all the rock types mentioned above. A minor portion of the El Bosque Formation sediments was derived from the CMC area and/or from recycled sandstones from the Mesozoic Todos Santos and San Ricardo Formations. Some advantages and disadvantages of provenance studies based on detrital apatite chemistry were also observed and briefly discussed.

Genetic constraints on world-class carbonate- and siliciclastic-hosted stratabound fluorite deposits in Burgundy (France) inferred from mineral paragenetic sequence and fluid inclusion studies

Stratabound fluorite deposits occur at the unconformity between the Variscan crystalline basement and the Mesozoic sandstone, conglomerate, limestone, and dolomite rocks of the Morvan Massif in central Burgundy. This study describes their petrographic characteristics in an attempt to determine the nature and temperature of mineralizing fluids in order to better understand the fluid migrations that led to massive stratabound fluorite deposition. The general paragenesis encompasses two major mineralizing events causing a succession of fluorite, barite, and quartz in all deposits. The two mineralizing events were preceded by two corrosion (dissolution or karstification) events affecting both the dolomite host rock at Pierre-Perthuis and Marigny-sur-Yonne and the limestone host rock at Courcelles-Frémoy with the creation of 1–10m cavities and microscopic vugs. At Antully, the blocky calcite initially cementing the sandstone was partially dissolved. Microthermometric data on aqueous two-phase inclusions attest to CaCl2-rich fluids giving rise to fluorite deposition in the Pierre-Perthuis, Courcelles-Frémoy, and Antully deposits. Homogenization temperatures range from 80 to 100°C at Pierre-Perthuis and Courcelles-Frémoy, with sporadically higher temperatures. The range of CaCl2 contents is 6.5–15wt.% at Pierre-Perthuis, 1.7–9.4wt.% at Courcelles-Frémoy, and 1.6–16.3wt.% at Antully. The thermal history of the northwestern Morvan, compiled from organic matter, clay minerals and apatite fission track data indicates that the temperatures in fluorite and barite are higher than the maximum temperature recorded in sediments. This implies deep ascendant hydrothermal brine circulation during the Early Cretaceous. The impermeable cap rock retained the ascendant hydrothermal brine and allowed the deposition of massive fluorite stratabound mineralizations.

Diagenetic barite and sphalerite in middle Mesozoic sandstones, Scotian Basin, as tracers for basin hydrology

Diagenetic barite and sphalerite in middle Mesozoic sandstones, Scotian Basin, as tracers for basin hydrology

Reconstruction of tectonic events on the northern Eurasia margin of the Arctic, from U-Pb detrital zircon provenance investigations of late Paleozoic to Mesozoic sandstones in southern Taimyr Peninsula

The Taimyr fold-and-thrust belt records late Paleozoic compression, presumably related to Uralian orogenesis, overprinted by Mesozoic dextral strike-slip faulting. U-Pb detrital zircon analyses of 38 sandstones from southern Taimyr were conducted using laser ablation–inductively coupled plasma–mass spectrometry to investigate late Paleozoic to Mesozoic sediment provenance and the tectonic evolution of Taimyr within a regional framework. The Pennsylvanian to Permian sandstones contain detrital zircon populations of 370–260 Ma, which are consistent with derivation from the late Paleozoic Uralian orogen in northern Taimyr and/or the polar Urals. Late Neoproterozoic through Silurian ages (688–420 Ma), most consistent with derivation from Timanian and Caledonian age sources, suggest an ultimate Baltica source. Southern Taimyr represents the proforeland basin of the bivergent Uralian orogen in the late Paleozoic. Triassic sedimentary rocks contain detrital zircon populations of Carboniferous–Permian (355–260 Ma), late Neoproterozoic to Early Devonian (650–410 Ma), and minor Neoproterozoic (1000–700 Ma) ages, which suggest a similar provenance as the Carboniferous to Permian strata. The addition of a Permian–Triassic (260–220 Ma) zircon population indicates derivation of detritus from Siberian Trap–related magmatism. Jurassic samples have a dominant age peak at 255 Ma and a distinct reduction in Carboniferous–Permian and late Neoproterozoic to Early Devonian input, suggesting that erosion and contributions from Uralian sources ceased while greater input from Siberian Trap–related rocks of Taimyr dominated. Comparison of these results to the published literature demonstrates that detritus from the Uralian orogen was deposited in Taimyr, Novaya Zemlya, and the New Siberian Islands in the Permian, but not in the Lisburne Hills or Wrangel Island. In the Triassic, Taimyr, Chukotka, Wrangel Island, the Kular Dome in the northern Verkhoyansk of Siberia, Lisburne Hills, Franz Josef Land, and Svalbard shared sources from Taimyr, the Siberian Traps, and the polar Urals, indicating that there were no geographic barriers among these locations prior to opening of the Amerasia Basin. Detritus from the Uralian orogen in Taimyr was shed northward into the retroforeland basin and was then transported farther 20–30 m.y. after Uralian orogenesis. The widespread distribution of material eroded from Taimyr and the polar Urals during the Triassic is likely due to the arrival of, and sublithospheric spreading associated with, the Siberian mantle plume head at ca. 250 Ma. The subsequent motion of the lithosphere relative to the plume-swell likely caused a northwestward migration of the uplifted regions. Taimyr and the polar Urals were probably affected. In the Jurassic, detrital zircon spectra from Taimyr, Chukotka, the Kular Dome, and Svalbard show great differences, suggesting that these locations no longer shared the same provenance from Taimyr and the Urals. The restricted distribution of detritus from Taimyr and the Urals indicates that erosion of the Uralian orogen was reduced. In the Late Jurassic, the depositional setting of southern Taimyr probably changed from a foreland to an intracratonic basin.

Detrital zircon U–Pb geochronology, Hf isotopes and geochemistry constraints on crustal growth and Mesozoic tectonics of southeastern China

In situ U–Pb geochronological, Hf isotopic and REE geochemical analyses of detrital zircons from Mesozoic sandstones in central Jiangxi and east Hunan of the South China Block (SCB) are used to provide not only information about crustal evolution process, but more importantly new constraints on sedimentary provenances as well as Mesozoic basin evolutions in central SCB. A total of 417 concordant zircon analyses define five U–Pb age populations at ca. 2.6–2.3Ga, ca. 2.0–1.7Ga, ca. 1.0–0.7Ga, ca. 500–400Ma and ca. 300–200Ma. Integrated analyses of zircon U–Pb ages and Hf isotopes of detrital zircons reveal five episodes of juvenile continental crust growth: ca. 2.5Ga, ca. 1.7Ga, ca. 850Ma, ca. 440Ma and ca. 230Ma, with all but the ca. 2.5Ga episode likely represent that of the SCB.None of the three samples from T3–J1 strata showed strong ca. 1850Ma and ca. 230Ma peaks suggesting that the T3–J1 sediments probably sourced from the Yangtze Block. In contrast, stronger peaks of ca. 1850Ma and ca. 250–230Ma in post-J1 strata relative to that of T3–J1 strata suggest a dominantly local Cathaysian provenance. In addition, the distinct low εHf(T) values for zircons of ca. 430Ma from T3–J1 strata in comparison with higher εHf(T) values for that from post-J1 strata also support aforementioned viewpoint. Such sharp changes between the pre-J1 and post-J1 strata coincide with the remarkable change in regional palaeogeography from a broad shallow marine basin in the Late Triassic–Early Jurassic time to a basin-and-range-style province in the Middle Jurassic. The characteristics and time evolution of detrital zircons from the studied area are consistent with the flat-slab subduction model which involves the development of a broad sag basin during the T3–J1 time, and a rapid regional uplift in the Cathaysia Block caused by the reinitiating of normal subduction along the coastal region at ca. 190Ma.

Analyzing geochemical characteristics and hydrocarbon generation history of the Middle and Upper Jurassic source rocks in the North Yellow Sea Basin

The North Yellow Sea Basin is still in the early stages of exploration. Oil has been recovered from Mesozoic sandstone intervals, but the characteristics of source rocks are not fully understood in this basin. In this study, the geochemical characteristics and the hydrocarbon generation history of the Jurassic source rocks in the North Yellow Sea Basin have been evaluated. The major findings of the study are as follows: (1) The Middle and Upper Jurassic dark gray and gray black mudstones are the main source rocks in the North Yellow Sea Basin. (2) The organic matter of the Middle Jurassic source rocks is derived from terrigenous higher plants and the type of organic matter is predominantly Type III kerogen. The content of organic carbon is moderate for this type of kerogen, and the hydrogen index (HI) is below 100 mg HC/g TOC mostly; therefore, the Middle Jurassic source rocks will produce gas mainly. The organic matter in the Upper Jurassic source rocks was derived from a mixture of terrigenous higher plants and aquatic lower organisms, and is characterized by the coexistence of Types I, II and III kerogen, there are some excellent local source rock intervals with high organic carbon and higher HI values, which constitute the main oil source rocks. (3) The Middle Jurassic source rocks have fair-poor hydrocarbon-generative potential and the Upper Jurassic source rocks have fair-good hydrocarbon-generative potential. (4) Hydrocarbon generation history models indicate that the Middle Jurassic source rocks reached late mature stages and the Upper Jurassic source rocks reached the oil window at the present-day. These two sets of source rocks all didn’t reach the peak of oil and gas generation in NYS2 well.

Mesozoic sandstones and the reconstruction of tectonic depositional environments in the Bureya sedimentary basin in the Far East

The early Jurassic-Early Cretaceous tectonic environments were reconstructed for the first time on the basis of the study of sandstones from the Soloni-Urgal interfluve (Bureya sedimentary basin, Far East). The mineralogical-petrographic and lithochemical studies revealed that the sandstones are mostly quartz-feldspathic and feldspathic graywackes of acid composition with less common litites, graywacke arkoses, and arkoses. It was shown that the Lower-Middle Jurassic sediments were formed in active continental margin and continental volcanic arc settings, while the Upper Jurassic-Lower Cretaceous sediments were accumulated in a passive continental margin setting. Orogenic events in the Toarcian-Aalenian, Late Bajocian, and Late Oxfordian-Kimmeridgian led to sedimentation gaps.

(U-Th)/He geochronology and chemical compositions of diagenetic cement, concretions, and fracture-filling oxide minerals in Mesozoic sandstones of the Colorado Plateau

Oxide minerals in diagenetic cements, concretions, and fracture fill reflect episodes of ancient groundwater flow that have the potential to record tectonic, geomorphic, and climatic changes through time. To better understand the ages, conditions of formation, and potential geologic significance of these diagenetic materials, we have measured (U-Th)/He ages and element concentrations in hematite, goethite, and Mn-oxide in Mesozoic sandstones from several locations in the Colorado Plateau. Most (U-Th)/He ages are Pliocene–Pleistocene, but some samples are as old as 25 Ma, the age of previously determined 40 Ar/ 39 Ar ages on Mn-oxide cement. In one region, texturally diverse Mn- and Fe-oxides yield relatively reproducible ages of ca. 2–3 Ma, and in another region, vitreous Fe-oxide fracture coatings yield ages of ca. 300 ka. Elsewhere, most cements and concretions show a wide range of ages among aliquots taken over millimeter length scales. Hematite-dominated samples show a broad positive correlation between age and U-Th concentrations, whereas most goethite-dominated samples show a negative correlation. Exterior portions of spherical goethite concretion rinds have higher U-Th concentrations and younger (U-Th)/He ages than interior portions. Taken together, the age-composition relationships of these samples suggest that wide ranges of ages in some samples largely reflect relatively recent (Pliocene–Pleistocene) U-Th addition, recrystallization, or later oxide growth that affected precursor cements that may have been oxides or other minerals. In some cases, these precursors may have formed as early as 25 Ma. In at least two areas, the (U-Th)/He dates (or in cases where samples show a wide range in ages, the minimum dates) are associated with major climate or local incision rate changes. We speculate that diagenetic oxides, and possibly other types of fine-grained secondary oxide minerals, remain open to U-Th uptake, recrystallization, or continued growth through contact with groundwater long after initial formation. This may provide opportunities to understand groundwater compositions and flow regimes as samples are exhumed through the shallow crust, or as surface conditions change through time in diagenetic systems in the critical zone of Earth’s crust and on Mars.

Fluvial landforms and their implication towards understanding the past climate and seismicity in the northern Katrol Hill Range, western India

The tectonically active Kachchh peninsula in western India lies in the southwest monsoon trajectory and hence provides a rare opportunity to decipher the temporal changes in climate–tectonics interaction in the evolution of the fluvial landforms. Reconstructions based on geomorphology, sedimentology, and geochemistry supported by optical chronology suggest that the fluvial aggradation in the region was initiated during the onset of the Indian Summer Monsoon (ISM) after the Last Glacial Maximum (LGM). The sedimentary characteristics and major elemental concentrations suggest that the sediments are dominated by fluvially reworked miliolites with subordinate contribution from the Mesozoic sandstones and shales and were deposited with the initiation of the ISM after the LGM. Temporal changes in facies architecture and major element concentrations suggest a progressive strengthening of the monsoon between 17 and 12 ka. This was succeeded by an overall strengthened ISM phase with fluctuations after 12 ka and <8 ka. Following this, a gradual decline in the ISM is inferred until around 3 ka. However, presence of the younger valley-fill sediments which are dated to ∼1 ka are ascribed to a short-lived phase of renewed strengthened ISM in the region before the onset of present day aridity.Based on the morphology of the fluvial landforms, two major events of enhanced uplift can be suggested. The geomorphic expression of the older uplift event dated to >17 ka is represented by the beveled Mesozoic bedrock surfaces which accommodated the post LGM valley-fill aggradation. The younger event of enhanced uplift which is assigned to <3 ka was responsible for the incision of the fill sediments and the Mesozoic bedrock, and the evolution of the present day fluvial landforms. The time averaged incision/uplift rate indicates that the Katrol Hill Range is uplifting at the rate of ∼4 mm per year, implying seismically active terrain.

Composition, provenance and source weathering of Mesozoic sandstones from Western-Central Mediterranean Alpine Chains

Forty-two Mesozoic sandstone samples from three different sedimentary successions of the Internal Domains along the Western-Central Mediterranean Alpine Chains (Betic Cordillera, Rif Chain and Calabria-Peloritani Arc) were chemically analyzed to characterize their composition and the degree of weathering in the source area(s). The Rif Chain sandstones have SiO2 contents higher than those of the Calabria-Peloritani Arc and Betic Cordillera sandstones, whereas Al2O3 contents are higher in the Calabria-Peloritani Arc sandstones rather than in the Rif Chain and Betic Cordillera sandstones. The indices of compositional variability (ICV) of the studied samples are generally less than 1, suggesting that the samples are compositionally mature and were likely dominated by recycling. Recycling processes are also shown by the Al–Zr–Ti diagram indicating zircon addition and, thus, recycling processes. The Chemical Index of Alteration (CIA) values are quite homogeneous for the Calabria-Peloritani Arc (mean=76) and Betic Cordillera sandstones (mean=55), whereas the Rif Chain sandstones are characterized by CIA values ranging from 54 to 76. The CIW and PIA values are high for all the studied sandstones indicating intense weathering at the source areas. The different values of weathering rates among the studied sandstones may be related to variations of paleoclimatic conditions during the Mesozoic, that further favored recycling processes. Thus, these differences among the studied samples, may be related to an increase in continental palaeoweathering conditions and sediment recycling effects from the Middle Triassic to the earliest Jurassic due to rising humidity. In addition, regional tectonic movements promoted structural changes that allowed sedimentary recycling and subsidence, which in turn caused diagenetic K-metasomatism. These processes could significantly affect the CIW and PIA weathering indices, which likely monitor a cumulative effect, including several cycles of weathering at the source. The source areas are mainly composed of intermediate-felsic rocks with minor, but not negligible, mafic supply, as suggested by provenance proxies.

Late Palaeozoic and early Mesozoic tectonic and palaeogeographic evolution of central China: evidence from U–Pb and Lu–Hf isotope systematics of detrital zircons from the western Qinling region

The western Qinling region of central China is situated centrally in the Kunlun, Qilian, Qinling, Longmenshan, and Songpan–Ganzi orogens. Late Palaeozoic and Early Mesozoic sediments deposited here may provide keys to understanding the tectonic evolution of the Palaeo-Tethys and collision of the North China and Yangtze Cratons. We conducted in situ U–Pb and Lu–Hf isotope analyses of 568 detrital zircons collected from Upper Palaeozoic to Mesozoic sandstones in the central Qinling block, Taohe depression, and Bailongjiang block in western Qinling to constrain the sources of these sandstones. Our results reveal that the Bailongjiang block has affinities with the Yangtze Craton, from which it may have been rifted. Therefore, the Palaeo-Tethyan Animaqen suture between the two cratons lies north of the Bailongjiang block. We identified the North China Craton as the main source for Triassic flysch in central China. It is possible that the Bailongjiang block could have blocked detritus shed from the North China Craton into the main depositional basins in the Songpan–Ganzi area. The dominance of 300–200 Ma detrital zircons of metamorphic origin in Lower Jurassic sandstones indicates that the Dabie–Qinling orogen was elevated during Early Jurassic time. In addition, our Lu–Hf isotopic results also reveal that Phanerozoic igneous rocks in central China were mostly products of crustal reworking with insignificant formation of juvenile crust.