Early Cretaceous Sediments Research Articles

Five series of benzohopanes in early Cretaceous sediments from the Chaoyang Basin, NE China

Five series of benzohopanes were identified in a set of immature to early-oil-window early Cretaceous sediments from the ZK1006 well, Chaoyang Basin, NE China. Series a (C31-C35), b (C33-C35), and c (C31-C35) benzohopanes form by different pathways, while the newly-found series d (C31-C34, maybe to C35?) and e (C31-C32, maybe to C35?) benzohopanes have similar formation mechanisms. Series a is usually the predominant benzohopane series, but occasionally samples are dominated by series c benzohopanes. Series b benzohopanes may be associated with terrigenous organic matter. Series a and b benzohopanes are possibly influenced by redox properties, while paleosalinity more likely controls the formation and enrichment of series c benzohopanes. Two novel parameters (a benzohopane index, and the C35/C34 benzohopane ratio) are proposed to be useful paleoenvironmental proxies in the study area. A high benzohopane index and C35/C34 benzohopane ratio may indicate an anoxic environment.

Structure and provenance of the Cretaceous Pingshanhu Basin in the Hexi Corridor: Implications for Mesozoic tectonics in the northern Tibetan Plateau

Abstract The construction of Earth’s largest highland, the Tibetan Plateau, is generally considered to have been generated by the Cenozoic India-Asia collision. However, the extent to which high topography existed prior to the Cenozoic remains unclear. The Hexi Corridor foreland basin of the northern Tibetan Plateau is an ideal region in which to investigate this history, given its widespread exposure of Early Cretaceous sedimentary sequences. In this study, we examined the Early Cretaceous strata in the northern Hexi Corridor to understand the relationships between pre-Cenozoic sedimentation and tectonic deformation and constrain the late Mesozoic tectonic setting of the adjacent Qilian Shan and Alxa blocks bordering the northern Tibetan Plateau. Results of sandstone petrology analyses, paleocurrent observations, and U-Pb geochronology suggest that the oldest Early Cretaceous sediments deposited in the northern Hexi Corridor were sourced from the southern Alxa block during the earliest Cretaceous. By the late Early Cretaceous, Hexi Corridor sediments were sourced from both the southern Alxa block to the north and the Qilian Shan to the south. Sandstone petrologic results indicate that the northern Hexi Corridor experienced a tectonic transition from contraction to extension during the Early Cretaceous. These findings suggest that the northern Tibetan Plateau region was partially uplifted to a high elevation during the late Mesozoic before the India-Asia collision.

Polar location of Teete dinosaur fauna (Eastern Siberia, Yakutia)

A few localities world wide are known to have remainsof dinosaurs andothervertebrate animalsthat livedin thepolarlatitude region during the Mesozoic era. The Teete locality in the Vilyui River Basin, Yakutia (Russia) is one of the few known dinosaur localities in the Northern Hemisphere. In 1988, 2002–2012 school children participated in asearch for Early Cretaceous dinosaurs and other vertebrates at the Teete locality, and teeth and bones were collected and briefly described.Additional vertebrate remains, including lizards, salamanders, choristoderes, and tritylodonts, were discovered in Early Cretaceous sediments in Yakutia, which expanded the number of known locations wherethese animals lived in polar regions. In 2017–2019 comprehensive paleontological studies were conducted in Teete,during which time fragmentary skeletal elements and teeth of various dinosaur groups, as wellas bone elements from other vertebrates, were collected using surface collection methods. This study also yielded new genera of Mesozoic mammaliforms,mammals,and salamanders.The presence of astem salamander, basalturtle, and other Jurassic relicts in the Early Cretaceous vertebrate fauna of Teete suggests that the area was a refugium for these animals during that time. Further study of the Teete locality is expected to lead to the description of new dinosaur and other vertebrate taxa, as wellas to theacquisitionof new data on the adaptation of these animals to circumpolar conditions.

Record of Early Cretaceous dinoflagellate cysts from well JM-A, Dhansiri Valley of Upper Assam Shelf, India

A palynological study on subsurface Early Cretaceous sediments (1550–1860 m) in well JM-A located in Dhansiri Valley, Upper Assam Shelf has been carried out for determination of age and depositional environment. The palynological investigations resulted into the identification of the characteristic and diversified occurrence of Early Cretaceous dinoflagellate cysts comprising Batioladinium micropodum, Achomosphaera? neptuni, Batiacasphaera asperata, Lagenorhytis sp. cf. L. delicatula, Mendicodinium caperatum and Canningia sp. along with associated dinoflagellate cysts. The significant assemblage of spore-pollen assemblage represented by Cicatricosisporites australiensis, Ceratosporites equalis, Gleicheniidites circinidites, Contignisporites cooksonii, Microcachryidites antarcticus, Podosporites tripakshii and Callialasporites trilobatus has also been recorded. The Early Cretaceous sediments are regarded as Bamangaon Formation in Dhansiri Valley. The occurrence of dinoflagellate cysts suggests marginal marine environment for Bamangaon Formation deposited during the Early Cretaceous period corresponding to the Rift Phase. The Formation overlies the Metamorphic Basement Complex, and it is unconformably overlain by the sediments of Tura Formation of Ypresian (Early Eocene) age, deposited under subtidal to inner shelf environment during the Passive Margin Tectonic Phase.

Fossils of the oldest diplodocoid dinosaur suggest India was a major centre for neosauropod radiation

The Early Jurassic and Cretaceous deposits of India are known for their diverse sauropod fauna, while little is known from the Middle and Late Jurassic. Here we report the first ever remains of a dicraeosaurid sauropod from India, Tharosaurus indicus gen. et sp. nov., from the Middle Jurassic (early–middle Bathonian) strata of Jaisalmer Basin, western India. Known from elements of the axial skeleton, the new taxon is phylogenetically among the earlier-diverging dicraeosaurids, and its stratigraphic age makes it the earliest known diplodocoid globally. Palaeobiogeographic considerations of Tharosaurus, seen in conjunction with the other Indian Jurassic sauropods, suggest that the new Indian taxon is a relic of a lineage that originated in India and underwent rapid dispersal across the rest of Pangaea. Here we emphasize the importance of Gondwanan India in tracing the origin and early evolutionary history of neosauropod dinosaurs.

The first record of Sexual dimorphism in Toxasterid Echinoid Heteraster from the Early Cretaceous deposits of the Kopet‐Dagh Basin, NE Iran

AbstractThe paper describes the spatangoid echinoids belonging to Heteraster, which could be found in the Barremian‐Aptian deposits (Tirgan and Sarcheshmeh formations)8 at the Bahman jan‐Bala stratigraphic section in northern flank of the Borouj syncline, situated in eastern Kopet‐Dagh Basin, Northeast of Iran. The aim is to introduce a species of toxasteridae family: Heteraster renngarteni as a sexually dimorphic species. Sexual dimorphism is a common features in echinoids and in this study, for the first time, sexual dimorphism was detected in the toxasteridae family.

Zirabia cylindrica comb. nov. provides evidence of Doyleales in the Jurassic.

In recent years, Doyleales have played an important role in the discussion and exploration of seed plant relationships and the origin of angiosperms. This order comprises a diversity of recently described genera with cupule-bearing compound ovulate cones recovered from Early Cretaceous deposits in North America and Asia. Their relatively late appearance in the fossil record, stratigraphically near the appearance of angiosperms in the Early Cretaceous, has been noteworthy. Here, we report a new genus of Doyleales, Zirabia gen. nov. from the Early Jurassic of Iran, that was originally described as the ginkgophyte Karkenia. We reinvestigated material previously assigned to Karkenia cylindrica from the Lower Jurassic of the Zirab locality, Alborz Mountains, northern Iran. The studied specimen features a main axis bearing helically to irregularly arranged bract-cupule complexes, each composed by a long laminar bract subtending and sheathing a cupule stalk that bears a single-seeded cupule with a dorsal protrusion. The morphological features of this taxon do not conform with those of Karkenia, and suggest affinities with Doyleales rather than Ginkgoales. Within Doyleales, this fossil has a unique combination of characters indicating that it is a new genus within the order; thus, a new combination is erected, Zirabia cylindrica. Our results indicate that Doyleales is significantly older than previously thought, with their stratigraphic range now extending from the Lower Jurassic to the Cretaceous. The Early Jurassic occurrence of Doyleales provides important data on the emergence of seed-enclosing structures seen in seed plants throughout the Mesozoic.

Early Cretaceous palynoflora from palaeotropics of NE Africa (correlation and significance): an example from the Shushan Basin, Egypt

We re-assessed and re-evaluated the diverse spores and pollen associations, presently recovered from clastics of the Shushan Basin. Eight (informal) Early Cretaceous (Valanginian to middle Cenomanian) spores/pollen zones are suggested, dated and correlated with regional/interregional records. Palynological dating offered bases for borehole stratigraphic resolution and basin correlation. It permitted revision of the homogeneous Early Cretaceous sediments of the borehole. Intrabasinal correlation, based on closely-spaced palynologically- productive samples, revealed the existence of an undetected sediment hiatus east of the basin, manifested by the wedging/missing of the Aptian Dahab clastics from west to east. The Shushan palynoflora exhibits great similarity with their counterparts in other provinces of the Northern Gondwana continent. But, however, A fern-dominated hygrophilous spores, along with Classopollis pollen, validated previous assumptions that humid conditions were responsible for the delayed appearance and scarcity of Dicheiropollis pollen in NE Africa (Egypt, Libya and Sudan), by the late Hauterivian. This humidity is thought to have triggered the production of Afropollis in the regional North African records, which reached an acme. Three main peaks of this pollen are inferred from the late Aptian, early Albian and early-middle Cenomanian intervals of the Shushan-1X well. Chronologically, these peaks can be of great stratigraphic value in NE Africa or other areas in Northern Gondwana that witnessed wet palaeoclimates during the Early Cretaceous.

Biometry and biostratigraphy of the Early Cretaceous belemnite genus Castellanibelus from the southeast of France

Early Cretaceous deposits (Berriasian–Albian) crop out over large areas in the Vocontian Basin (VB, southeast of France). The important exposures have provided rich marine fossil faunas, including many specimens of ammonites and belemnites over the last 200 years. From the early 19th century onward, the definition of Lower Cretaceous belemnite species from the VB was essentially based on descriptive, qualitative approaches. This resulted in a variety of morphologically very closely related species, sometimes difficult to differentiate between each other. Biometric data and their statistical analysis offer a mathematical and objective framework to clearly delineate and define morphological species, especially when consecutive belemnite assemblages are continuously available from different stratigraphic levels. The present study is based on the analysis of 1762 specimens of Castellanibelus collected by ammonite zones and subzones across the entire Valanginian interval of the VB. Biometric data of this genus have been statistically analyzed and used to define four species, including one new to science: Castellanibelus orbignyanus, Castellanibelus vaubellensis, Castellanibelus suborbignyanus, and Castellanibelus toucasi sp. nov.

Carbon isotope of the Early Cretaceous sediments from the West Pacific and the Sulu orogenic belt: Implying the global atmospheric pCO2 changes during the Early Aptian Oceanic Anoxic Event 1a

Multiple lines of evidence revealed that enormous CO2 was input into the ocean-atmosphere system during Oceanic Anoxic Event 1a (OAE 1a), which led to a series of environmental perturbations (e.g. temperature rising, enhanced weathering, promoted primary productivity and marine anoxia). Among them, increased carbon isotope fractionation (Δ13Ccarb-org) between the carbonate (δ13Ccarb) and organic carbon (δ13Corg) in the sediments is one of the most important indicators to the enhanced atmospheric pCO2. However, only a few research reported high-resolution paired carbon isotopes during OAE 1a, which were almost limited around the western Tethys. Here, we report new paired carbon isotopes of the Early Cretaceous sediments from the ODP site 866A in the western Pacific and the Lingshan Island section in the Sulu orogenic belt. The δ13Ccarb curves from both sections correlate well with OAE 1a, in which a positive δ13Ccarb excursion is identified between the C3–C6 segments. The Δ13Ccarb-org displays a ∼7–11‰ positive shift coinciding with the δ13Ccarb excursion, indicating a remarkable increase and a gradual decrease in CO2 in water and atmosphere, which further support significant atmospheric pCO2 changes during OAE 1a on a global scale. The sediments also show a few variations in carbon isotope records during OAE 1a between different locations, which may reflect different influences from local environments, and the deviations of stratigraphic correlation and diagenesis cannot be ruled out either.

Structural Restoration of Cretaceous Inversion Events in the Bjørnøyrenna Fault Complex, Western Barents Shelf

Inversion structures including folds, reverse faults are observed along the Bjørnøyrenna Fault Complex in the western Barents Sea, although the fault complex is extensional in origin and developed in mid-Jurassic to Early Cretaceous. Subsidence along the fault complex was interrupted in Early Cretaceous (Valanginian to early Barremian) because of syn-rift localized tectonic inversion, itself related to the uplift of the Loppa High. The Early Cretaceous inversion caused dextral transpression along the boundary faults adjacent to the Loppa High. The second phase of inversion is interpreted to be Late Cretaceous (mid-Cenomanian) in age, coeval to the deposition of the Kolmule Formation in the Bjørnøyrenna Fault Complex. The later phase of compression is of regional significance and related to NW‒SE directed far field stresses in Late Cretaceous which caused head-on inversion in the study area. The aim of present study is to identify and decipher eventual Cretaceous inversion structures in the Bjørnøyrenna Fault Complex by means of structural restoration. To these aims, 2D MOVETM, structural modeling and analysis software by Midland Valley Exploration Ltd (Glasgow, Scotland), is used and three key seismic lines crossing the central and northern segments of the Bjørnøyrenna Fault Complex are restored. Key profiles 1 and 2 reveal null point positions at the base of the Cretaceous (Hekkingen Formation). Null point positions show progressive compressional inversion of syn-rift Early Cretaceous deposits (Knurr Formation). Below and above null points the geometries of the restored faults show normal and reverse faulting respectively. The results of the restored key profiles 1 and 2 confirm reverse faulting at the Lower Cretaceous triggered by inversion of the study area. The restored sections also show positive inversion features associated with folding of the hanging wall of the base of the Upper Cretaceous (Kolmule Formation). The reconstruction of the amount of eroded material on the footwall block also suggests reverse faulting of the base of the Upper Cretaceous. In key profile 3 the footwall block is eroded up to the base of the Upper Cretaceous (Kolmule Formation) due to the uplift of the Loppa High. The corresponding restored section shows a compressional anticline associated with both Early and Late Cretaceous inversion events.

Early Cretaceous Slump Deposits in Laiyang Group (Lingshan Island, East China): New Constraints for Provenance Identification and Tectonic Evolution

The sedimentary strata in the Lingshan Island area are gaining attention because of their unique sedimentary and tectonic characteristics. However, the provenance and the depositional and tectonic setting in this area remain the focus of controversy. There is a significant slump deposit with lateral length up to 250 m in the Laohuzui section at the top of the Laiyang Group, which differs from the underlying turbidite deposits in morphology and composition. The sandstone in the Laohuzui section was continuously sampled and analyzed for major trace and rare earth elements. The results showed that the Laohuzui section is mixed with a continental margin provenance from the re-cyclic deposition in the arid region, which is different from the continental island arc provenance in the lower part of the Laiyang Group. Through the geochemical study of the igneous gravel contained in the olistolite and the comparison with the igneous rocks in the surrounding area, it is observed that the properties of the igneous gravel are most like those of the igneous rock deposit in the Zhucheng-Taolin area. In addition, the Lingshan Island and the Zhucheng-Taolin areas have similar sedimentary processes, suggesting that both received provenance from the Jiaonan uplift at the end of the Early Cretaceous. This study clarified the depositional processes of the later period of the Laiyang Group deposition in the Lingshan Island area.

Eustasy in the Aptian world: A vision from the eastern margin of the Iberian Plate

Eustatic controls on Early Cretaceous (Aptian) sedimentation in the western Tethys are discerned in outcrops of carbonate platforms that developed in the Maestrat rift basin located at the eastern margin of the Iberian Plate. The relative sea-level fluctuations with a dominant eustatic contribution investigated had estimated magnitudes of between 50 and 60 m in <0.9 My and ≥115 m in <3 My, and occurred respectively during the late early and early late Aptian. The major relative sea-level falls of mainly eustatic nature were recorded as forced regressive sedimentary wedges or as incised valleys carved into highstand carbonate platforms, whereas the subsequent sea-level rises back-filled the incised topographic lows created, or favoured the development of lowstand platforms. The finding of 50–115 m amplitude fluctuations of Aptian age is of relevance in that show magnitudes of relative sea-level fall in the order of that recorded during the last glacial maximum in the late Pleistocene ( c . 120 m). The current knowledge on Cretaceous climate history shows an Earth with non-uniform greenhouse conditions. However, geological evidence of temporary icehouse states with ice-cap magnitudes close to late Pleistocene scales during the Aptian is absent, or at least has not been reported so far. Thus, although falling within the glacio-eustatic domain, the driving processes of these widespread drops and subsequent rises in relative sea level remain a mystery. Finally, this paper is an example of how sequence stratigraphy can be applied to carbonate successions, and of how this methodology indeed permits to unravel ancient relative sea-level fluctuations which controlled carbonate production and accumulation. • Eustatically-driven changes in accommodation deciphered • The Aptian world recorded a strong eustatic signal • Development of incised valleys during the Aptian

Palaeoenvironments Of The Permian-Cretaceous Sediments Of The Bintuni Bay, Papua

This paper presents a part of the result of Lemigas in-house research entitled Paleogeography and Hydrocarbon Potentiality of the pre-Tertiary Sediment of the Bintuni Basin, Papua, which is financially supported by the Government through a project so called DIPA 2009. In addition, this paper specifically discusses a palaeoenvironment of the Late Permian-Cretaceous sediment of the Bintuni Bay based on biostratigraphy. Data used in this paper is mostly secondary data obtained from National Data Center and an oil company which is therefore, classified as a confidential information. Paleoenvironment appeared in a non-marine setting during Permian-Triassic to form Ainim Formation in which, shale of this formation acts as a primary sourcerock for the studied area. Early Jurassic is characterised by a non-deposition, whilst Middle Jurassic is indicated by the occurrence of non-marine environment to deposit fluvial sandstone of the Lower Kembelangan Formation which is considered to be a main reservoir. Subsequently, environment shifted to the marine setting where deep marine shale occurred to form caprock. Mean while, the Early Cretaceous sediment disappears from the studied area suggesting massive erosion. Finally, depositional environment took place in the marine setting during the Late Cretaceous resulting in the formation of deep marine shale of Jass Formation which may contribute as a caprock in the element of petroleum system

Paleomagnetism, magnetostratigraphy, provenance, and tectonic setting of the Lower Cretaceous of nuclear southern Mexico

We studied the sedimentology, provenance, and paleomagnetism of Lower Cretaceous strata in nuclear southern Mexico deposited in continental, marginal and marine settings in order to better understand their tectonic setting and paleographic correlations. The studied units have been assigned to the Zicapa, Atzompa, Caltepec, Xonamanca, and Jaltepetongo formations, which are interpreted as an eastward-deepening paleogeography (in present day coordinates) deposited between Valanginian and Aptian time in a system of extensional basins contemporaneous with arc magmatism. Provenance interpreted from sandstone petrology, conglomerate clast counts, and detrital zircon U–Pb geochronology indicates that these successions consist of polymictic conglomerate, quartz-lithic metamorphoclastic and feldspathic-quartz lithic volcaniclastic sandstone, and mudstone. These were sourced from the underlying Precambrian and Paleozoic basement rocks, as well as from proximal suites of mafic to acid Jurassic (∼182-145 Ma), and Cretaceous volcanic rocks (∼140-123 Ma). The remanent magnetization in the Atzompa and Caltepec formations is multivectorial, and the characteristic remanent magnetization resides in hematite. For the Atzompa the grand mean is Dec = 335.3° and Inc = 25.4° (k = 15.4, α95 = 12.7°; N = 10 accepted sites). For the Caltepec the grand mean is Dec = 354.3°, Inc = 27.9° (k = 29.15, α95 = 6.1°, N = 20 accepted sites). Magnetizations in both units predate folding and pass reversal tests. For the uppermost Zicapa the magnetization is nearly univectorial and resides in a soft magnetic phase; the grand mean is D = 275.2°, I = 36.0° (k = 34.4, α95 = 10.1°, N = 7 accepted sites). For the Caltepec and Atzompa formations, I/E corrected directions indicate a paleolatitude of ∼20° to 23°N which is indistinguishable from that expected assuming stability with respect to the North America craton (∼24°), implying only minor tectonic motions since Early Cretaceous deposition, and demonstrating that the present distribution of units studied resembles their paleographic relations. The magnetostratigraphy of these units can be correlated with some confidence to the M10-M0r sequence of the geomagnetic polarity time scale, suggesting that the formations record late Valanginian and early Aptian marine transgressions that might correlate with global eustatic curves. The temporal and paleogeographic distribution of magmatism in southern Mexico is consistent with the presence of a continental arc formed by eastward subduction under the North American plate continuously from Early Jurassic to Aptian time, and extension in a back-arc setting during the Hauterivian-Barremian driven by slab rollback. We assign the system of extensional basins to the “southlands rift”, a short-lived event that predates amalgamation of oceanic terranes in the west and Albian carbonate platform development.

Provenance of the early Cretaceous sediments in the southern Alxa Area: Implications for tectonic evolution of the south Central Asian Orogenic Belt

The Central Asian orogenic belt is an accretionary orogenic belt that lies between the Siberian block and the Tarim and North China blocks. Since the central south of the Central Asian Orogenic Belt has been covered by desert and the Meso-Cenozoic Bayingobi Basin, its spatial configuration, evolution, closure time, and the Paleo-Asian ocean location have not been well described. Through zircon UPb dating, in-situ Hf isotope and rock geochemistry of the Lower Cretaceous Bayingobi Formation sandstones, the provenance of the Bayingobi Formation, and the central south boundary of the Central Asian orogenic belt were determined, the tectonic evolution process was discussed, and the tectonic evolution models were established. The provenance of the Bayingobi Formation mainly originated from Permian to Early Triassic granodiorite, diorite and potassium feldspar granite that cover a large area of the Zongnaishan-Shalazhashan tectonic belt. In the early Permian, this tectonic belt was mainly a continental island arc but gradually transitioned to a continental active margin, accompanied by intense tectonic magmatic activity. With the boundary as the Quagan Qulu ophiolite belt, the north is the Central Asian Orogenic Belt that mainly exhibits juvenile crustal materials, while the south is the Alxa block, which has an affinity with the North China block, and mainly exhibits older crustal materials. From the late Carboniferous to the early Permian, the Paleo-Asian Ocean plate was compressed, subducted along the Enger Us suture, and magmatic distributed along the Nuru-Langshan tectonic belt; from the late early Permian to late Permian, the Paleo-Asian Ocean plate rolled back, changing the subduction zone stress state from compression to extension. During this period, there were large-scale developments of magmatic rocks in the Zongnaishan-Shalazhashan tectonic belt. From early Early Triassic to Middle Triassic period, the Siberian active margin collided with the Alxa block, the Paleo-Asian Ocean was closed, and the overlying Alxa plate experienced lithospheric extension and thinning, accompanied by asthenospheric upwelling, partial melting and the addition of new crustal material. The Meso-Cenozoic basin sediments along the original suture belt are characterized by an enrichment of large ion lithosphere elements, a loss of high field strength elements, LREE enrichment and loss of HREE.

X-ray diffraction studies of onshore mud volcanoes in parts of the Upper Benue Trough, northeastern Nigeria

The mineralogical studies of clay from the onshore mud volcanoes discovered in parts of the Upper Benue Trough of Nigeria provide a clue about the geological formation from which the extruded mud originates. The study area is a part of the Cretaceous Upper Benue Trough filled with Early Cretaceous continental deposits and Late Cretaceous marine deposits, having a history of magmatism dating from the Albian to the Pleistocene. The study approach involves integrated inorganic geochemical analysis of the samples to reveal their composition and origin. The results of XRD analysis of the fresh clays from the mud volcano revealed the presence of quartz, kaolinite, and other clay minerals (illite-smectite), feldspars, and in much lower quantities, other accessory minerals including muscovite, evaporites, calcite and dolomite, trona, barite, goethite. The saprolite samples are composed mainly of quartz, kaolinite, smectite-illite associations, and feldspars, traces of goethite, calcite, and evaporate minerals (sylvite, halite). The presence of calcite, dolomite, sylvite, and halite suggests the marine origin of the rocks, while trona mineral is a non-marine evaporate. The coexistence of these minerals in some of the analyzed samples suggests the deposition of sediments in a transitional environment of deposition. Traces of marine minerals are present in some of the samples but completely absent in others collected from another site. This suggests that the source rock formations from which the material originated are within the Upper Bima Sandstone interpreted as being deposited in a non-marine environment or the Yolde Formation, which is known as a transitional unit (transitional between the outcropping continental Upper Bima Sandstone and marine Pindiga Formation).

Response of provenance transition of Middle Jurassic–Early Cretaceous sediments to tectonic domain transformation in the North Yellow Sea Basin, Eastern North China Craton

In the Late Mesozoic, the Eastern North China Craton changed from being controlled by the Palaeo‐Asian tectonic domain to the marginal Pacific tectonic domain. The Eastern North China Craton transformed the E–W compression to NNE–SSW extensional tectonics under the influence of two tectonic domain transformations. However, the timing of the transformation of the tectonic domains remains controversial. The North Yellow Sea Basin is located in an important position in the Eastern North China Craton at the junction of the Pacific and Eurasian plates and is controlled by two tectonic domains. Therefore, the sediments in the basin are faithful records of the transformation of the two tectonic domains. Based on the latest and high‐precision detrital zircon U–Pb dating data, sandstone modal analysis, and elemental geochemical analysis in the North Yellow Sea Basin combined with regional tectonic, palaeontological, and palaeoclimatic evidence, this paper discusses the provenance from the Middle Jurassic to Early Cretaceous, which responds to the Late Mesozoic tectonic domain transformation in the Eastern North China Craton, and provides important evidence of provenance in the North Yellow Sea Basin to determine the time of tectonic domain transformation. These results suggest that the source rocks of sediments in the North Yellow Sea Basin have changed from ancient sediments (ancient craton/recycle orogenic belt) in the Middle Jurassic to Late Jurassic, to felsic igneous rocks in the Early Cretaceous. The peak of zircon U–Pb ages changed from 234, 1,842, and 2,429 Ma in the Late Jurassic to 217 and 1,871 Ma in the Early Cretaceous. The provenance changed from the Sulu Orogenic Belt and Precambrian basement of the Jiaodong Peninsula in the Late Jurassic, to the igneous rocks and Precambrian basement of the Liaodong Peninsula and Korean Peninsula in the Early Cretaceous. The provenance direction of the sediments changed from south‐west in the Late Jurassic to the north and south‐east in the Early Cretaceous. The tectonic setting of the basin changed from compression to extension. The changes in the peaks of zircon U–Pb age, characteristics of the source rocks, provenance direction, and basin tectonic setting in the Middle Jurassic to Early Cretaceous in the North Yellow Sea Basin are a response to the change from E–W compression to NNE–SSW extensional tectonics caused by the transformation of two tectonic domains. In the Early Cretaceous, the Eastern North China Craton completed the transformation of two tectonic domains that were influenced and controlled by the marginal Pacific tectonic domain.

Monocotyledon fossil leaf from the Early Cretaceous of India

Reports of the angiosperm macrofossils from the Early Cretaceous sediments of India are relatively poor, with only one report from the Krishna-Godavari Basin. The present study documents a monocotyledon leaf fossil from the Barremian-Aptian (Early Cretaceous) of Gangapur Formation, Pranhita-Godavari Basin, India. The present fossil leaf placed under a new genus Sahniophyllum and it is characterised by the ribbon shaped leaves, with parallel venation, arranged in rosette form suggests its probable affinity with Hydrocharitaceae. The taphocoenosis demonstrates its autochthonous preservation and aquatic habitat.

Geologically based integrated approach for zonation of a Late Jurassic–Early Cretaceous carbonate reservoir; a case from Persian Gulf

AbstractIn this study, our attempt is to integrate sedimentological and petrophysical data for reservoir evaluation in the sequence stratigraphic framework. Petrographic analysis of the Late Jurassic–Early Cretaceous Fahliyan Formation reservoirs of two oilfields in the northwest of the Persian Gulf led to recognition of twelve microfacies. They can be classified into four facies associations, including open marine, shoal, lagoon and tidal flat, which are deposited in a homoclinal ramp carbonate. Sequence stratigraphy of the studied successions led to the recognition of three third-order depositional sequences based on vertical changes in microfacies and gamma ray analysis. Except for the upper boundary of the third sequence, the other sequence boundaries are type I (SBT.1). Dissolution is the most important diagenetic feature that affected the lower depositional sequence which is caused by the development of subaerial exposure after the deposition of the Fahliyan Formation, whereas cementation is the main diagenetic feature affecting the second- and third depositional sequences, causing their lower reservoir quality. In order to identify the flow units, the flow zone index methods, porosity throat radius (R35) and modified Lorenz based on stratigraphy were applied. The key wells studied in this area have shown good correlation throughout the studied oilfields which may potentially be used for hydrocarbon exploration and field development in the Late Jurassic–Early Cretaceous deposits of the Persian Gulf. This study integrates geological and petrophysical data (rock typing) toward sequence stratigraphic framework.