Recycled Orogen Research Articles

Mineralogy, geochemistry and possible provenance of desert sand dunes from western Rub' al Khali area, southeastern Saudi Arabia

The Rub' al Khali desert dune sands are major constitutes of the southern part of the Arabian Peninsula. The investigated dunes in the present work are located in its western extreme where they display three major forms (seif, sigmoidal and barchan) with distinct variations in size and unique homogeneity of mineral composition. The Rub' al Khali sand dunes in its western part are placed in the craton interior and based on the contents of Quartz-FeldsparsLithic fragments, they are originating from a recycled orogen in which intrusive, sedimentary and partly metamorphosed sources have contributed to the composition of the sands. The presence of minerals like clay minerals and amphiboles in the bulk composition of the dune sands supports the influence of granitic, granodioritic and schistose sources. They are all fine sand, moderately well sorted, nearly symmetrical to fine skewed and mostly mesokurtic. The heavy mineral fractions are dominated by a variety of amphiboles (winchite-riebeckite-richterite-arfvedsonite) in addition to cordierite. The geochemistry of the Rub' al Khali dune sands show that the dune sands are associated with acid, felsic plutonic detritus linked to an active continental margin. Correlations between Fe2O3, SiO2, Al2O3, TiO2, MgO, and other oxides in the dune sands indicate the presence of ilmenite, magnetite and zircon in the samples. With respect to the provenance, there are two possibilities which are the Zagros Mountains in Iran and the Sahara Desert in North Africa. Orientation of linear dunes in the Rub' al Khali area is controlled by the dominant shamal (north) wind.

Tectonic linkage between the Korean Peninsula and mainland Asia in the Cambrian: Insights from U–Pb dating of detrital zircon

The establishment of robust Paleozoic tectonic links between parts of the Korean Peninsula and cratonic blocks within China remains uncertain, despite their important implications for the overall tectonic evolution of East Asia. Here we provide new SHRIMP U–Pb detrital zircon geochronological constraints on correlations between sedimentary rocks of the Taebaeksan Basin (Cambrian–Ordovician) of South Korea and possible source rocks in the North and South China cratons. The detrital grain compositions and whole-rock rare earth element (REE) compositions of sandstones from the Cambrian formations in western (Sambangsan) and eastern (Myeonsan) parts of the Taebaeksan Basin suggest that the sedimentary provenance of these two formations is either a recycled orogen or a magmatic arc. The magmatic (eastern part) versus metamorphic (western part) origins inferred for the youngest populations (ca. 0.5–0.6Ga) of detrital zircon grains from the Cambrian formations collectively indicate that rapid uplift and erosion of the source rocks for the formations took place soon after the associated magmatic and metamorphic events. Thus, we propose that the paleo-sedimentary environments in which these two formations were deposited may have been retroarc basins with the detrital zircons originating from magmatic arcs. The Early Cambrian formation in the eastern Taebaeksan Basin contains populations of detrital zircon grains that show prominent age peaks at ca. 2.0Ga and ca. 1.8Ga, and a distinct lack of Meso- to Neoproterozoic ages, whereas the Middle Cambrian formation in the western Taebaeksan Basin exhibits age peaks at ca. 1.0Ga and ca. 0.7Ga. These age spectra imply that the western Taebaeksan area at the margin of the North China Block may once have been near Gondwana, whereas the eastern Taebaeksan area may have been situated at the margin of the North China Block more distant from Gondwana.

Petrography, heavy mineral study and tectonic setting of Walash Naopurdan Series Sandstones, Qalander area, Northeastern Iraq

The Petrography and Heavy mineral study of Walash-Naopurdan Series Sandstone (Middle-Late Eocene) at Qalander area is carried out. Thin section study of twenty seven samples showed that these sandstones consist of quartz, feldspar, rock fragments (lithics), matrix, and cement. The rock fragments are of sedimentary, igneous, and metamorphic types as an indication of multiple source rocks originated from the complex thrust zone of northeastern Iraq. The Heavy mineral analysis also showed different types, dominated by opaques and transparent minerals as a further indication of multiple source rocks. The main constituents of the studied sandstones (quartz, feldspar, rock fragment and matrix) are used in their classification which showed that the sandstones are of lithic greywacke type.The provenance indicating triangular diagrams (QtFL and QmFLt) showed that the Walash-Naopurdan Series Sandstone is of recycled orogen sources shared between transitional, mixed, dissected and transitional arcs tectonic settings. These represent a complex convergent boundary with dissected transitional volcanic arc which was subjected to uplift and erosion.

Sedimentological Characterization of the Pre-Santonian Siliciclastic Deposits of Lower Benue Trough, Southeastern Nigeria

The study which involves forty-one (41) sandstone samples’ collected from the area delimited by longitudes 7°00'E and 8°30'E and latitudes 5°00'N and 6°30'N, entailed evaluating and characterizing these sediments. Detailed field studies to establish the lithostratigraphy was carried out and fresh samples were subjected to petrographic, granulometric and heavy mineral analyses. Field observations revealed that the sandstones of the Awi Formation are angular to subangular, feldspathic, and generally fines upward and Amaseri are calcareous, indurated and laterally extensive. Agbani Sandstone consists of thick vertical sequences of ferruginized and indurated sandstones. Granulometric study shows medium to coarse-grained (0.78-1.30?), poorly to moderately sorted (0.87-1.19?), coarse to strongly fine skewed (-0.17-0.57?) and very platykurtic to leptokurtic (0.66-1.31?). This indicates mostly high energy condition and this is characteristic of fluvial environments. Petrographic studies for Awi samples indicate that they are texturally immature to submature, subarkosic arenites from a continental block provenance, while Amaseri Sandstones are texturally submature sublitharenites from a recycled orogen provenance. Agbani Sandstones are texturally immature to mature subarkosic arenites, sublitharenites and quartz arenites. Heavy mineral studies revealed zircon, tourmaline, rutile and hornblende to be common to all formations, sillimanite, kyanite, garnet, and staurolite are mostly common to Awi and Amaseri Sandstones while Agbani Sandstone has a dominance apatite with spinel. This suite of minerals suggests an acid igneous rock to typical dynamothermal metamorphic rock sources. The ZTR indices (74.0-94.4%) indicate mineralogically mature sediments. The study established that the pre- Santonian siliciclastic sequences of the Lower Benue Trough are texturally immature to mature and compositionally submature to supermature products of a continental block and recycled orogenic provenance under humid climates and deposited in fluvial to tidally influenced fluvial environments with high to moderate energy conditions humid climates which are deposited under high to moderate energy conditions.

Petrography and Provenance of Sandstones from the Aghajari Formation, Folded Zagros Zone, Southwestern Iran

The Late Miocene- Pliocene Aghajari Formation is exposed throughout the Folded Zagros Zone and consists of fluvial sediments. Detailed petrographic studies of sandstone samples from the Aghajari formation contain abundant quartz and lithic grains with subordinate feldspars, accessory amounts of micas. The feldspar content mostly ranges from 0 to 5 %. The abundance of lithic grains shows a wide range of variation (5.9 to 69.8 %). Although the lithics are mainly sedimentary, but fragments of metamorphic rocks are observed. Micas, including both muscovite and biotite, are generally less than 5 % of the total detrital grains. On the basis of the framework composition (point counting), the sandstones are classified as lithic arenite and sublitharenite. The modal analysis data of 75 collected (medium size and well sorted) samples, imply a recycled orogen (quartzose and transitional recycled) tectonic provenance. Moreover, petrographic point count data indicate the sources of quartzs are low-grade and middle to high-grade metamorphic rocks. Also quartz-rich (sedimentary) and granitic/gneissic are parent rocks for the Aghajari Formation sandstones.

Geochemistry of Lower Jurassic Sandstones of Shemshak Formation, Kerman Basin, Central Iran: Provenance, Source Weathering and Tectonic Setting

Abstract Lower Jurassic sandstones of Shemshak Formation of Kerman basin, central Iran were analyzed for major and select trace elements to infer their provenance, palaeoweathering of source rocks and tectonic setting. Average modal framework components (Qt: F: L= 67.25: 2.41: 30.48) and chemical composition of the sandstones classify them as litharenites. The sandstones are quartz-rich (∼ 67% quartz; 75.34 wt.% SiO2) and derived from a recycled orogen composed of quartzose sedimentary rocks. Average CIA, PIA and CIW values (69%, 76% and 80%, respectively) indicate moderate to intense chemical weathering of the source material. The inferred index of weathering/alteration is the sum total of intensities of weathering witnessed by the lithocomponents during atleast two cycles of sedimentation involving (1) chemical weathering of the source rocks («ultimate» granodiorite source and «proximal» quartzose sedimentary source), (2) chemical weathering during fluvial transport of the detritus, (3) chemical weathering of the detritus in depocenters, and (4) chemical weathering during diagenesis. Sandstones exhibit moderate maturity and were deposited under humid climatic conditions. Plots of the chemical analyses data on tectonic setting discrimination diagrams indicate active continental margin setting, which is in agreement with the tectonic evolutionary history of the Central Iran during Jurassic period.

Depositional and diagenetic controls on reservoir attributes within a fluvial outcrop analog: Upper Triassic Sonsela member of the Chinle Formation, Petrified Forest National Park, Arizona

The Upper Triassic Sonsela member of the Chinle Formation in the Petrified Forest National Park was evaluated using sedimentologic, stratigraphic, paleopedologic, and petrographic criteria along a continuous 0.5-km (0.3-mi) outcrop. The study interval consists of interbedded sandstones and mudstones and is composed of a two-tiered hierarchy of cyclic alluvial deposits with bounding paleosols. The succession is composed of 15 fluvial aggradational cycles (FACs) that comprise two FAC sets (FAC-Sets). The FAC-Sets are composed of architectural elements suggestive of a mixed-load fluvial system that is alternately dominated by bed-load deposits and suspended-load deposits. A thinning and fining stacking pattern within FAC-Sets is accompanied by an upward increase in pedogenic modification, suggesting that cycles systematically stack in response to a longer period decrease in the rate of accommodation gain. Sandstones are classified as litharenites, feldspathic litharenites, and lithic subarkoses, and occur within recycled orogen, dissected arc, and transitional arc provenance fields. Sandstone compositional maturity increases upward through the FAC-Sets. Point counts of intergranular volume (as a proxy for primary porosity) within channel facies and subsequent transform to syndepositional permeability provide a two-dimensional depiction of the lateral variability in reservoir quality. Paleosols are weakly to moderately developed and have little stratigraphic variation. These characteristics suggest that climatic fluctuations are not responsible for evolving fluvial depositional style or associated reservoir quality. Trends in sandstone compositional maturity suggest that fluvial stacking patterns and depositional style are related to pulses of tectonism. Sandstones are volcanogenic rich and have undergone an almost complete diagenetic loss of porosity caused by the precipitation of authigenic clays. Paragenetic reconstruction suggests that porosity loss occurred contemporaneous with the silicification of fossil logs in channel deposits. Log compaction at the time of silicification averaged 9.1%, suggesting that log silicification and porosity loss occurred soon after deposition.

Modal and Sandstone Composition of the Representative Turbidite from the Majalengka Sub-Basin, West Java Indonesia

The Majalengka sub-basin is composed of an approximately 4 km thick turbidite-sequence subdivided into three formations as follows Cisaar, Cinambo and Cantayan Formations. The last formation is composed by two members, i.e. Halang and Bantarujeg Formations, which is distinguished by the volcanic content. All sedimentary rocks were deposited during the middle to late Miocene, where the magmatic and tectonic influences are particularly dominant. Petrography and geochemical analyses suggested that the sandstone composition was derived from multi-source sediment, which is incorporated in same strata sediment. This indicates that the tectonic event occurred actively. Most sediment-sources were derived largely from two main provinces (geological terrain) such as recycled orogen and the magmatic arc. The recycled orogen is represented by the development of thrust-fault belts, which the sediment was eroded from uplifting the paleohigh. On the other side, the magmatic arc corresponded to the Southern Mountains, as a product of the early subduction in Java during the Oligocene. According to geochemical data, this indicates that there is no evidence supporting from the sediment source derived directly from the continental terrain. The quartz content is interpreted as occurring from resedimentation processes of previous sediment. Meanwhile, lithic fragment are dominantly composed by andesitic grains, which indicates that the magmatic terrain as a sediment source relates to subduction processes.

Stratigraphy, sedimentary petrology and provenance of the Sobral and Cross Valley formations (Paleocene), Marambio (Seymour) Island, Antarctica.

The unconformity bounded Paleocene Sobral and Cross Valley formations represent part of the uppermost infill of the James Ross Basin of northeastern Antarctic Peninsula. Both units have been subdivided into allomembers since they also present internal unconformities. The Sobral Formation represents silicoclastic sedimentation on a marine shelf during at least two transgressive-regressive cycles. The Cross Valley Formation fills in a narrow valley with volcaniclastic deposits representing an incised valley system with estuarine and finally deltaic facies. Sandstones of the Sobral Formation are feldspathic litharenites and lithic arkoses while those of the Cross Valley Formation are feldspathic litharenites to litharenites (volcanic). The sandstone composition (petrofacies) of the Sobral and Cross Valley formation suggest provenance from a dissected volcanic arc that increased its activity during the Danian but decline again towards the late Thanetian. A detailed analysis of the sandstone compositional trends allowed to differentiate two petrofacies (S and CV) and two sub-petrofacies (S I, S II, CV I and CV II respectively). The sub-petrofacies suggest a control from the sedimentary environments upon the detrital modes and their interference with the true provenance signal. The increase in quartz and glaucony in some units may be related with the unconformities and reworking of the underlying sedimentary units as well as development of high energy environments. On the other hand, volcanic, plutonic and metamorphic rock fragments are related to the provenance area. The overlap of two main sources of sediments, one from the basin edge and other within the basin is then envisaged. The first one represents the unroofing of a volcanic arc located at the present day position of the Antarctic Peninsula. This source shed volcanic rock fragments and minor metamorphic rock fragments with variable amount of quartz and feldspars. This composition plots within the recycled orogen and dissected arc fields of the provenance diagrams representing periods of arc inactivity and deep erosion and plots within the volcanic arc fields after times of volcanic activity. On the other hand, sandstones with high proportion of quartz recorded at specific levels within the sequence suggest breakdown of less resistant components and reworking of the loose underlying sedimentary rocks favoured by low sedimentary rates and/or in high energy environments.

Geochemistry of sandstones from the Neoproterozoic Shijia Formation, northern Anhui Province, China: Implications for provenance, weathering and tectonic setting

The Neoproterozoic Shijia Formation sandstones in northern Anhui Province, China were analyzed for major oxides and trace elements to infer their provenance, intensity of paleo-weathering of the source rocks and their depositional tectonic setting. Discrimination diagrams based on geochemistry and some ratios of elements indicate that felsic rocks constitute their source rocks, probably a quartzose recycled orogen provenance. The values of Chemical Index of Alteration (CIA=53) are low, which was considered to be affected by K-metasomatism, whereas the high CIW (82, Chemical Index of Weathering) values indicate moderate to intensive weathering of the source material. Tectonic discrimination method based on geochemical data of sandstones, as well as the low ICV (0.94, Index of Compositional Variation) values reveal that they were deposited in a passive continental margin or intra-plate basin. Research progress (including geochronological and geochemical study, etc.) and the study therein, imply that the tectonic background of the southeast margin of North China Craton (NCC) before and after 0.85Ga were active and passive, respectively.

Petrology and geochemistry of Carboniferous siliciclastics from the Argentine Frontal Cordillera: A test of methods for interpreting provenance and tectonic setting

Petrological and geochemical characteristics of sandstones and shales from the Carboniferous Cerro Agua Negra Formation (Río Blanco basin, western Argentina) are discussed. The sandstones are mostly feldspathic litharenites with subordinate litharenites and lithic arkoses, and their modal compositions indicate two major sources. The first represents a recycled orogen and can be identified as the Protoprecordillera, a N–S trending mountainous area that separated the Paganzo and Río Blanco basins and that was a positive element at least up until the end of the Carboniferous. The second was further east, in the Sierras Pampeanas terrane. It consisted of a variety of metasedimentary and felsic plutonic crystalline rocks. The Protoprecordillera must have been crossed by transverse valleys that facilitated the transfer of Pampean terrigenous material towards the Río Blanco basin. A lack of volcanogenic sand suggests that the basin was open towards proto-Pacific in the west, rather than being separated from it by a magmatic arc as previously suggested. Bulk geochemical analysis of different lithological types (arenites, wackes and shales) demonstrates a strong relationship between texture and chemical composition of the rocks, even taking into account the immobile elements. The largest differences are between shales and arenites, while the wackes have intermediate compositions. The CIA (chemical index of alteration) indicates partial remobilisation of oxides from source rocks and enrichment of aluminium and potassium in the shales, which reflects their potassic clay mineral composition. Overall, siliciclastics of the Cerro Agua Negra Formation have a similar composition to the upper continental crust (with slight net enrichment of SiO2 in the arenites and of Al2O3 in the shales). Rare earth element profiles reflect terrigenous contributions, since they are enriched in light-REE, have a pronounced negative Eu anomaly and a relative depletion of the heavy-REE. The results show that discrimination plots commonly employed to infer provenance and tectonic setting from siliclastics are compromised where bulk chemical composition is strongly dependent on grain size and sorting.

Geochemistry and Provenance of Maastrichtian Clastic Rocks in the Dikmendede Formation of Orhaniye in Kazan‐Ankara‐Turkey Region

Abstract:An integrated petrographic and geochemical study of the sandstones of the Maastrichtianaged in the Orhaniye (Kazan‐Ankara‐Turkey) was carried out to obtain more information on their provenance, sedimentological history and tectonic setting. Depending on their matrix and mineralogical content, the Maastrichtian sandstones are identified as lithic arenite/wacke. The Dikmendede sandstones derived from types of provenances, the recycled orogen and recycled transitional. The chemical characteristics of the Dikmendede sandstones, i.e., fairly uniform compositions, high Th/U ratios (>3.0), negative Eu anomalies (Eu/Eu* 0.72–0.99) and Th/Sc ratios (mostly less than 1.0), favor the OUC (old upper continental crust) provenance for the Dikmendede sandstones. The SiO2/Al2O3, Th/Sc (mostly <1.0) and La/Sc (<4.0) ratios are; however, slightly lower than typical OUC, and these ratios may suggest a minor contribution of young arc‐derived material. The rare earth element (REE) pattern, and La/Sc versus Th/Co plot suggests that these sediments were mainly derived from felsic source rocks. The Dikmendede sandstones have high Cr (123–294 ppm) and Ni (52–212 ppm) concentrations, Cr/Ni ratio of 1.93, and a medium correlation coefficient between Cr and Ni and corresponding medium to high correlation of both (Cr and Ni, respectively) elements with Co. These relationships indicate a significant contribution of detritus from ophiolitic rocks. As rare earth element data are available for the Dikmendede sandstones, the Eu/Eu* is compared with LaN/YbN. Samples plot in the area of overlapping between continental collision, strike‐slip and continental arc basins. The predominantly felsic composition of the Dikmendede sandstones is supported by the REE plots, which show enriched light REE, negative Eu anomaly and flat or uniform heavy REE. The Dikmendede sandstones have compositions similar to those of the average upper continental crust and post‐Archean Australian shales. This feature indicates that the sediments were derived mainly from the upper continental crust. The Dikmendede sandstones have chemical index of alteration (CIA) values of 28–49, with an average of 40 indicating a low degree of chemical weathering in the source area. The compositional immaturity of the analyzed sandstone samples is typical of subduction‐related environments, and their SiO2/Al2O3 and K2O/Na2O ratios and Co, Sc, Th and Zr contents reflect their oceanic and continental‐arc settings. The Dikmendede sandstones were developed as flysch deposits derived from mixed provenance in a collision belt.

Provenance, tectonics and source weathering of modern fluvial sediments of the Brahmaputra–Jamuna River, Bangladesh: Inference from geochemistry

This present study describes the elemental geochemistry of fluvial sediments in the Kurigram (upstream) to Sirajganj–Tangail (downstream) section of the Brahmaputra–Jamuna River, Bangladesh, with the aim of evaluating their provenance, weathering and tectonic setting. Petrographically, the sediments are rich in quartz (68%), followed by feldspars (8.5%) and lithic grains (7%). The bulk sediment chemistry is influenced by grain size. Concentrations of TiO 2, Fe 2O 3, MgO, K 2O, P 2O 5, Rb, Nb, Cr, V, Y, and, Ce, Th and Ga slightly decrease with increasing SiO 2/Al 2O 3 and grain size, suggesting clay matrix control. In contrast, concentrations of CaO, Na 2O, Sr and Pb increase with increasing SiO 2/Al 2O 3 and grain size, suggesting residence of these substances in feldspar. Decrease in Zr as grain size increases is likely controlled both by clay matrix and heavy minerals. In addition, heavy minerals' sorting also influences Ce, Th, Y and Cr abundances in some samples. The sediments are predominantly quartzose in composition with abundant low-grade metamorphic and sedimentary lithics, low feldspars and trace volcanic detritus, indicating a quartzose recycled orogen province as a source of the sediments. Discriminant diagrams together with immobile element ratio plots show that, the Brahmaputra–Jamuna River sediments are mostly derived from rocks formed in an active continental margin. Moreover, the rare earth element ratios as well as chondrite-normalized REE patterns with flat HREE, LREE enrichment, and negative Eu anomalies indicate derivation of the sediments of Brahmaputra–Jamuna River from felsic rock sources of upper continental crust (UCC). The chemical indices of alteration suggest that Brahmaputra–Jamuna River sediments are chemically immature and experienced low chemical weathering effects. In the A–CN–K ternary diagram, most of the samples close to the plagioclase–K-feldspar join line and to the UCC plot, and in the field of various lithologies of Higher Himalayan Crystalline Series, suggesting that rocks in these series are likely source rocks. Therefore, the elemental geochemistry of the Brahmaputra–Jamuna River sediments is controlled mostly by mechanical breakdown of lithic fragments and subsequent preferential attrition of muscovite > albite > quartz.

Early Cretaceous Gangdese retroarc foreland basin evolution in the Selin Co basin, central Tibet: evidence from sedimentology and detrital zircon geochronology

Abstract The Selin Co basin in the northern Lhasa terrane includes more than 3000 m of upward coarsening Lower Cretaceous strata, and the sedimentary sequence from the flysch to the molasse indicates the evolution of a foreland basin. Petrographic analysis shows that sandstones are rich in volcanic and sedimentary lithics and most of them fall into recycled orogen and magmatic arc. Uranium–lead (U–Pb) ages were determined for 435 detrital zircons from the Lower Cretaceous strata in the Selin Co basin. Relative probability of detrital zircon ages shows the Eshaerbu Formation was rich in zircon grains with the age of 125–140 and 160–180 Ma, and the Duoni Formation was dominated by one main age cluster of 125–150 Ma. Analysis of the potential provenances suggests the Early Cretaceous zircon grains were primarily derived from the Gangdese magmatic arc to the south. The youngest zircon ages in the lowermost exposure of the Eshaerbru Formation are c . 130 Ma, providing a maximum depositional age of sediments in the Selin Co basin. Collectively, our studies, together with previously documented Cretaceous thrusting in the Lhasa terrane, suggest the Lower Cretaceous Selin Co basin was deposited in a retroarc foreland basin. From 145–90 Ma, a retroarc foreland basin was presumed to develop in the Lhasa terrane, migrating from the south to the north. Crustal thickening, likely associated with the evolution of the retroarc foreland basin, was speculated to start in the Early Cretaceous in the Lhasa terrane.

Modal analysis and geochemistry of two sandstones of the Bhander Group (Late Neoproterozoic) in parts of the Central Indian Vindhyan basin and their bearing on the provenance and tectonics

The Neoproterozoic Bhander Group in the Son Valley, central India conformably overlying the Rewa Group, is the uppermost subdivision of the Vindhyan Supergroup dominantly composed of arenites, carbonates and shales. In Maihar-Nagod area, a thick pile of unmetamorphosed clastic sedimentary rocks of Bhander Group is exposed, which provides a unique opportunity to study Neoproterozoic basin development through provenance and tectonic interpretations. The provenance discrimination and tectonic setting interpretations are based on modal analysis and whole rock geochemistry. The average framework composition of the detrital sediments composed of quartz and sedimentary lithic fragments are classified as quartz arenite to sublitharenite. The sandstone geochemically reflects high SiO2, moderate Al2O3 and low CaO and Na2O type arenite. The high concentration of HFSE such as Zr, Hf, and Th/Sc, Th/U ratios in these sandstones indicate a mixed provenance. The chondrite normalized REE pattern shows moderate to strong negative Eu anomaly which suggests that major part of the sediments were derived from the granitic source area. The sandstone tectonic discrimination diagrams and various geochemical plots suggest that the provenance of the lower and upper Bhander sandstone formations was continental interior to recycled orogen.

Petrography and provenance of subsurface Neogene sandstones of Bengal Basin, Bangladesh

This study deals with petrography and provenance of the Neogene reservoir sandstones encountered in the Kailas Tila, Titas, Bakhrabad and Shahbazpur Gas Fields of Bengal Basin. Framework grains are sand-sized to silt-sized particles of mainly detrital origin. The most common detrital grains are quartz, feldspars, and rock fragments. Mica occurred as minor and non-opaque heavy minerals found as minor accessories. Among the main detrital framework grains, quartz constitutes 51-60%, feldspar 3-15%, lithic fragments 8-22%. Sandstones encountered in the studied wells have been classified as sublithic arenite, feldspathic arenite and lithic arenite in order of abundance. Different triangular plots reveal that the Neogene sandstones of the studied wells exhibit a quartzolithic composition, low feldspar, very low volcanic grains and abundant sedimentary and low grade metamorphic lithic clasts indicating that the sands were derived from quartzose recycled orogen province, such as a fold thrust province or a collision suture zone. This study suggests that either the eastern Himalayas or Indo-Burman Ranges might act as the source of the sandstones of the studied wells of the Bengal Basin.

Detrital record of mountain building: Provenance of Jurassic foreland basin to the Dabie Mountains

[1] The Huangshi foreland basin developed on the southern margin of the Dabie Mountains as a result of tectonic loading during Triassic collisional suturing between the North China and South China cratons. Modal and detrital zircon data for Jurassic samples within the basin suggest a multicomponent source with input from both the South China Craton and Dabie Orogen. Samples are predominantly quartz arenites derived, on the basis of framework compositions, from a recycled orogen source. Detrital zircons range in age from Archean to Triassic with a dominant component in the late Paleoproterozoic between 1.9–1.7 Ga and subsidiary components at 2.6–2.2 Ga, 0.8–0.7 Ga, 0.5–0.4 Ga, and 0.33–0.2 Ga. Age data integrated with cathodoluminescence and trace element data for the zircons indicate that the Archean and Proterozoic detritus was derived from igneous and metamorphic sources that overlap with time-equivalent pulses of such activity within the South China Craton. Phanerozoic zircon ages overlap the times of the Ordovician, Carboniferous and Triassic high-pressure metamorphism in the Dabie Mountains. The provenance record, integrated with paleocurrent and regional relations, enables a paleogeographic reconstruction in which the Huangshi Basin was fed by a major axial flowing trunk river system carrying detritus from eastern and southern sources within the South China Craton and was also fed by short south flowing tributaries supplying some detritus from the evolving Dabie Orogen. The dominance of cratonic-derived detritus within the provenance record of the Huangshi Basin contrasts with that of the Hefei foreland basin that lies to the north of the Dabie Mountains, which is dominated by Neoproterozoic - Mesozoic detritus derived directly from the Dabie Mountains and lacks any significant older Paleoproterozoic or Archean components. Easterly extensions of the Dabie-Sulu collisional suture and of the resultant Huangshi Basin occur in Korea and Japan over an along strike length of some 2000 km.

Petrography and whole-rock geochemistry of the Tertiary Sylhet succession, northeastern Bengal Basin, Bangladesh: Provenance and source area weathering

Detrital modes and the geochemical compositions of sandstones and mudrocks from the Paleocene to Plio-Pleistocene Jaintia, Barail, Surma, Tipam and Dupitila Groups of the Sylhet basin in Bangladesh have been examined to identify their provenance and source area weathering conditions. Barail and Surma Group sandstones are quartz-rich, feldspar-poor, and are rich in sedimentary and metamorphic lithic fragments, indicating a recycled orogen source. Geochemically the succession is divisible into three parts. Paleocene–Late Eocene Jaintia Group mudrocks form separate trends, and have very high Chemical Index of Alteration (CIA) values, suggesting derivation from a stable cratonic source. The second part, the Late Eocene to Miocene Barail and Surma Groups, forms single trends on variation diagrams. Maximum CIA ratios decrease from the Barail to the Surma Group, suggesting rapid influx of detritus from a common felsic source undergoing active uplift, compatible with weathering and erosion proxies from the Bengal and Indus fans. Average bulk geochemical and REE characteristics of these two groups are identical, as are A–CN–K trends. These features and comparison with potential Himalayan sources support derivation of both the Barail and Surma Groups from that orogen, and hence supply of Himalayan detritus to the Sylhet basin as early as the Late Eocene, rather than from the Neogene. The third part, the non-marine Tipam (Late Miocene–Pliocene) and Dupitila (Pliocene–Pleistocene) Groups, forms slightly differing geochemical trends and has higher maximum CIA values. REE fractionation between sandstones and mudrocks is more marked, but REE patterns and parameters remain unchanged, suggesting that the overall source remained unchanged. Higher CIA and greater REE fractionation in the Tipam and Dupitila Groups may be a product of their fluvial deposition and more intense weathering on the floodplain during intensification of the South Asian monsoon from 4 Ma onwards.

Detrital composition of Lower-Middle Jurassic sandstones from Huangshi, Hubei: Implication for provenance types and geotectonics

The detrital modes of the sandstones from the south basin of Dabie (大别) orogenic belt during the Early-Middle Jurassic are complex due to multiple supplying. Detrital compositions of medium-coarse sandstones from the Lower-Middle Jurassic, Huangshi (黄石), show three main provenances: recycled ororgen, volcanic arc (arc orogen), and continental block on the bases of the Dickinson discriminating diagrams of modal composition and analysis of sandstone petrofacies. Combined with sparse published paleocurrent data, geotectonic setting of the study area, and the unpublished detrital zircon age data, the positions of the main provenances are inferred as follows: coastal orogenic belt (COB) in the East China provided detritus as the recycled orogen provenance; Dabie orogenic belt (DOB) to the north was the source of volcanic arc (arc orogen) materials; and the continental block clasts were likely from the uplift of the Yangtze basement (UYB) (Jiangnan (江南) uplift). Six sedimentary cycles are recognized in the studied section, one in Wuchang (武昌) Formation, and five in Huajiahu (花家湖) Formation. During the deposition, the three main provenances play different roles. The quantitative petrofacies analysis revealed distinct changes of the effect from each source, that is, 61.9% (Cycle I)→54.5% (Cycle III)→50% (Cycle IV)→57.9% (Cycle V)→14.3% (Cycle VI), 14.3% (Cycle I)→21.2%( Cycle III)→40% (Cycle IV)→36.8% (Cycle V)→14.3% (Cycle VI), and 23.8% (Cycle I)→24.2% (Cycle III)→10% (Cycle IV)→5.3% (Cycle V)→71.4% (Cycle VI) from COB, DOB, and UYB, respectively. The results show that (1) COB behaved in considerable activation during the Early Jurassic but weakened in the Middle Jurassic; (2) the vigorous tectonic uplift of DOB initiated in Middle Jurassic; and (3) UYB was in stabilization basically from the Early to Middle Jurassic.

Evidence of Miocene crustal shortening in the North Qilian Shan from Cenozoic stratigraphy of the western Hexi Corridor, Gansu Province, China

New sedimentologic, stratigraphie, and compositional data from the Paleogene-Neogene stratigraphie succession exposed in the northwest Hexi Corridor and within the North Qilian Shan, provide evidence to suggest that crustal shortening in the North Qilian Shan fold-thrust belt initiated during die Miocene. The section is composed of four lithostratigraphic units: Oligocene-Miocene fine- to coarse-grained Unit 1, Miocene conglomeratic Unit 2, and Pliocene-Pleistocene conglomeratic Units 3 and 4. Unit 3 lies in angular unconformity over both Units 1 and 2, and Unit 4 contains a progressive unconformity. The onset of conglomerate deposition at the base of Unit 2 suggests an increase in depositional energy, which we interpret as me result of proximal orogenesis in the North Qilian Shan fold and tiirust belt. Supporting evidence includes the appearance of strongly northeast-trending paleocurrents, indicat-ing paleoflow away from the Qilian Shan, clast lidiologies that match sources in the North Qilian Shan, and sandstone with detrital framework modes that indicate a recycled orogen source. In contrast, Unit 1 contains paleocurrent indicators that are variable but generally trend northward and sandstone and clast compositions which are more diagnostic of a continental block source. Detrital zircon age determinations from Unit 1 are also not consistent with a source in the North Qilian Shan; rather, they suggest a provenance in hinterland regions within the South Qilian Shan and North Qaidam terranes. In sum, these results are all consistent with initiation of proximal uplift of the North Qilian Shan during deposition of the gradational transition from Unit 1 to Unit 2, demonstrating shortening in the Qilian Shan before die late Miocene. This comprehensive study tightens our understanding of when far-field stress related to the India-Eurasia continent-continent collision reached the northeastern edge of the Tibetan Plateau.