Cretaceous Research Articles

Cretaceous stratigraphy in the Songliao Basin, NE China

The Songliao Basin is one of the largest non-marine oil- and gas-bearing basins that developed during the Cretaceous period, recording an almost complete Cretaceous stratigraphy. With oil and gas exploration, as well as the Continental Scientific Drilling Project of Cretaceous Songliao Basin (CCSD-SK) (2006–21), significant progress has been made on the stratigraphy of the Songliao Basin. The Songliao Basin is therefore important for understanding the non-marine Cretaceous system. Based on lithostratigraphy, sequence stratigraphy, biostratigraphy, geochronology, magnetostratigraphy and cyclostratigraphy, a comprehensive stratigraphical framework of the Songliao Basin has been established in this study. The Lower Cretaceous strata (Hauterivian–Albian) of the basin are dominated by volcanic–sedimentary deposits, while the lower-middle Upper Cretaceous (Cenomanian mid-Campanian) strata are dominated by lacustrine deposits. The upper Upper Cretaceous strata (late Campanian–Maastrichtian) are dominated by fluvial–lacustrine deposits. Fossils are very abundant in the Songliao Basin, and three biotas – the Jehol Biota sensu lato , the Songhuajiang Biota and the Mingshui Biota – are recognized in the Songliao Basin. Furthermore, several important geological events, such as lake anoxic events, seawater incursion events and the K/Pg boundary extinction events are all recorded in the Songliao Basin.

Phylogenetic and divergence analysis of Pentatomidae, with a comparison of the mitochondrial genomes of two related species (Hemiptera, Pentatomidae).

Pentatomidae, the most diverse family of Pentatomoidea, is found worldwide. Currently, the phylogenetic relationships among Pentatomidae tribes remain unstable, and subfamily divergence has not been estimated. Here, we sequenced and analyzed the complete mitochondrial genomes of two species of Lelia, and studied the phylogenetic relationships among Pentatominae tribes. We also selected three available fossil as the calibration points in the family, and preliminarily discussed the divergence time of Pentatomidae. Trees of Pentatomidae were reconstructed using the Bayesian inference method. Divergence times of Pentatominae were estimated based on the nucleotide sequences of protein-coding genes with a relaxed clock log-normal model in BEASTv.1.8.2. The results showed that the gene arrangements, nucleotide composition, and codon preferences were highly conserved in Lelia. Further, a phylogenetic analysis recovered Eysarcorini, Strachiini, Phyllocephalini, and Menidini as monophyletic with strong support, however, the monophyly of Antestiini, Nezarini, Carpocorini, Pentatomini and Cappaeini were rejected. Moreover, Pentatominae diverged from Pentatomidae soon after the origin of the Cretaceous Period, at approximately 110.38 Ma. This study enriches the mitochondrial genome database of Pentatomidae and provides a reference for further phylogenetic studies, and provides a more accurate estimate of divergence time.

Cicada nymph trace fossils from South American Maastrichtian paleosols

The Cretaceous was a pivotal Period in the evolution of major insect groups, including cicadas. Insect diversification led to an increased complexity in the paleosol ichnofabrics due to the emergence of chambers associated with reproductive and feeding behaviors. Therefore, any new record of trace fossils attributed to cicadas from the Cretaceous period represent a significant advancement in understanding the diversification of this group and the emergence of insect feeding chambers, throughout the geological record. This work describes the record of the ichnogenus Feoichnus attributed to feeding chambers of cicada nymphs (Hemiptera: Cicadidae) from Maastrichtian paleosols developed in floodplain deposits of The Marília Formation (Bauru Basin, Brazil). The described Feoichnus chambers are elongated, hemispherical, and upwardly concave, with a lining covering the inner surface of the wall. The inner surface exhibits thin, irregular ridges and grooves, likely associated with fine roots. Feoichnus occurs in association with Beaconites antarcticus and root traces found within the feeding chamber, it could be indicating the movement of the trace maker and the feeding chamber from one root to another. These characteristics indicate the xylem-feeding behavior of Feoichnus trace maker in accordance with extant cicada nymph ecology. The presence of Beaconites antarcticus associated with Feoichnus and rhizoliths probably represents the foraging behavior of cicada nymphs and the displacement of feeding chambers in well-drained, rooted soils. Therefore, the cicada nymph could be the trace maker of both traces representing feeding and locomotion behavior. This contribution expands the knowledge about plant–insect interactions and insect groups that compose the Cretaceous paleosols ichnofabrics from South America.

The First Report of Late Valanginian–Early Aptian (Early Cretaceous) Ammonites and Chemostratigraphy of Eastern Anatolian, Olur‐Erzurum, Türkiye

ABSTRACTThis study is based on stable isotope analysis of a rich ammonite assemblage from the Sogukcam Formation, which is widely exposed in Yesilbaglar (Olur‐Erzurum, NE Türkiye). The presence of ammonid, planktic, and benthic foraminifers in the marine sediments suggests that they are from the early Cretaceous period. The late Valanginian‐early Aptian‐rich ammonite assemblage includes the following genera and species: Acrioceras sp., Barremites difficilis, Barremites sp., Crioceratites duvalii, Crioceratites sp., Deshayesites aff. dechyi, Deshayesites sp.1, Deshayesites sp.2, Deshayesites sp.3, Deshayesites sp., Dufrenoyia cf. dufrenoyi, Dufrenoyia cf. furcata, Dufrenoyia sp., Hemihoplites sp., Heteroceras sp., Neocomites sp., Phyllopachyceras infundibulum, Protetragonites cf. quadrisulcatus, Protetragonites sp., Ptychoceras sp., Turkmeniceras cf. geokerense, and Turkmeniceras sp. This assemblage suggests that the Sogukcam Formation's deeper facies formed in the late Valanginian to early Aptian period. Fossils and δ18O data show normal paleosalinity levels. During the late Valanginian‐early Aptian period, δ18O values ranged from −3.67‰ to −2.24‰, with paleotemperatures ranging from 21.3°C to 27.9°C. δ13C positive values range from +0.65‰ to +2.86‰. δ13C isotope data show the oxygen minimum zone (OMZ) and changes in sea level and productivity. The presence of planktonic foraminifera and the ammonite assemblage indicates that the formation was deposited in warm subtropical waters ranging from the outer shelf to the open sea.

Comparative Mitogenomics Analysis Revealed Evolutionary Divergence among Purpureocillium Species and Gene Arrangement and Intron Dynamics of Ophiocordycipitaceae.

The species of Purpureocillium are cosmopolitan and multitrophic fungi that can infect a wide range of invertebrate hosts. This study reports the mitogenome of P. atypicola, a specialized spider pathogenic fungus. The 112,465 bp mitogenome encoded genes typically found in fungal mitogenomes, and a total of 52 introns inserted into seven genes. A comparison with three other Purpureocillium species revealed significant differences in length and intron number, primarily due to intron variation; however, there was no dynamic variation in the introns of the cox1 gene within the same species of the Purpureocillium genus. Different mitochondrial protein-coding genes showed variable degrees of genetic differentiation among these species, but they were all under purifying selection. Additionally, frequent intron loss or gain events were detected to have occurred during the evolution of the Ophiocordycipitaceae mitogenomes, yet the gene arrangement remains conserved. A phylogenetic analysis of the combined mitochondrial gene set gave identical and well-supported tree topologies. The estimated age of the crown of Ophiocordycipitaceae and Purpureocillium were around the Early Cretaceous period (127 Mya) and Late Cretaceous period (83 Mya), respectively. The results of this study advance our understanding of the genomics, evolution, and taxonomy of this important fungal group.

The evolution of ectomycorrhizal symbiosis and host-plant switches are the main drivers for diversification of Amanitaceae (Agaricales, Basidiomycota)

BackgroundEvolutionary radiation is widely recognized as a mode of species diversification, but the drivers of the rapid diversification of fungi remain largely unknown. Here, we used Amanitaceae, one of the most diverse families of macro-fungi, to investigate the mechanism underlying its diversification.ResultsThe ancestral state of the nutritional modes was assessed based on phylogenies obtained from fragments of 36 single-copy genes and stable isotope analyses of carbon and nitrogen. Moreover, a number of time-, trait-, and paleotemperature-dependent models were employed to investigate if the acquisition of ectomycorrhizal (ECM) symbiosis and climate changes promoted the diversification of Amanitaceae. The results indicate that the evolution of ECM symbiosis has a single evolutionary origin in Amanitaceae. The earliest increase in diversification coincided with the acquisition of the ECM symbiosis with angiosperms in the middle Cretaceous. The recent explosive diversification was primarily triggered by the host-plant switches from angiosperms to the mixed forests dominated by Fagaceae, Salicaceae, and Pinaceae or to Pinaceae.ConclusionsOur study provides a good example of integrating phylogeny, nutritional mode evolution, and ecological analyses for deciphering the mechanisms underlying fungal evolutionary diversification. This study also provides new insights into how the transition to ECM symbiosis has driven the diversification of fungi.

A new carcharodontosaurid specimen sheds light on the anatomy of South American giant predatory dinosaurs.

Carcharodontosaurids were gigantic terrestrial dinosaurs and top predators of dinosaur faunas in Gondwanan landmasses during the "Mid"-Cretaceous Period. Despite their wide geographical and stratigraphical distribution, essential parts of their anatomy are still poorly known. The present contribution aims to describe a new partial skeleton of the carcharodontosaurid Taurovenator violantei, which was previously known only by an isolated postorbital bone coming from Cenomanian-Turonian beds of northern Patagonia, Argentina. The neck of Taurovenator is composed of notably high anterior cervicals, bearing neural spines with expanded, flange-like dorsal tips which are successively imbricated. This condition has been reported previously in the carcharodontosaurid Acrocanthosaurus, but its occurrence in Taurovenator and other members of the clade suggests it may represent a synapomorphy of this theropod family. This unique neck morphology was probably related to strong modifications in musculature and restriction in the range of movements within the neck, but not with the head. The new specimen also affords valuable anatomical information on the forelimb of Patagonian carcharodontosaurids. As in other giganotosaurines, Taurovenator shows strongly reduced forelimbs, particularly the forearm, showing hand elements with elongated non-ungual phalanges, and well-marked articular surfaces and muscular insertions, suggesting highly movable digits. This new specimen of Taurovenator allows us to expand anatomical and morpho-functional discussions about the carcharodontosaurid clade.

Molecular phylogenetic and estimation of evolutionary divergence and biogeography of the family Schizoparmaceae and allied families (Diaporthales, Ascomycota)

The Diaporthales includes 32 families, many of which are important plant pathogens, endophytes and saprobes, e.g., members of the families Pseudoplagiostomataceae, Pyrisporaceae and Schizoparmaceae. Nucleotide sequences derived from five genetic loci including: ITS, LSU, TEF1-α, TUB2 and RPB2 were used for Bayesian evolutionary analysis to determine divergence times and evolutionary relationships within the Schizoparmaceae. Molecular clock analyses revealed that the ancestor of Schizoparmaceae split during the Upper Cretaceous period approximately 75.7 Mya (95 % highest posterior density of 60.3–91.3 Mya). Reconstructing ancestral state in phylogenies (RASP) with using the Bayesian Binary Markov chain Monte Carlo (BBM) Method to reconstruct the historical biogeography for the family Schizoparmaceae indicated its most likely origin in Africa. Based on taxonomic and phylogenetic analyses, the Pseudoplagiostomataceae and Pyrisporaceae relationships were clarified and a total of four species described herein. For Pseudoplagiostomataceae, three new species and one known species that include, Pseudoplagiostoma fafuense sp. nov., Ps. ilicis sp. nov., Ps. sanmingense sp. nov. and Ps. bambusae are described and a key of Pseudoplagiostomataceae is provided. With respect to Pyrisporaceae, we considered Pseudoplagiostoma castaneae to be a synonym of Pyrispora castaneae. In addition, a new species of Schizoparmaceae, Coniella fujianensis sp. nov. is described and illustrated.

Paleozoic-Mesozoic multistage tectonic evolution of the North Qilian Shan revealed by detrital zircon U-Pb and fission-track double dating

Knowledge of the tectonic history of the North Qilian Shan contributes to our understanding of the formation of the Tibetan Plateau. However, when the North Qilian Shan were formed has been controversial. We report new detrital zircon U-Pb (n = 899) and double dating fission track and U-Pb (n = 450) results from nine samples of Lower Cretaceous and Oligocene sandstone units, integrating with published geochronology and thermochronology data in order to reconstruct the evolution history of the North Qilian Shan. Nine samples from this unit show detrital zircon fission track age populations that center at: 636–603, 495, 406–331, 290–266, 247–224, 193–151, and 144–102 Ma. These fission track data are older than their corresponding depositional ages, suggesting that the fission track ages are unreset and record magmatic-related cooling or exhumation stages of the North Qilian Shan since the Late Neoproterozoic. Deconvolved fission track peak ages document major cooling events associated with the opening of the North Qilian Ocean at 636–603 Ma. Late Cambrian peak age (495 Ma) is attributed to the early phase of the subduction of the North Qilian Ocean. The Devonian period exhibited a cooling phase between 406 and 381 Ma, corresponding to the collision event between the Qaidam terrane, Central Qilian Shan, and Alxa Block. The peak age of 331 Ma signifies the cooling event associated with the subduction of the Paleo-Asian Ocean. The peak ages during the Early-Middle Permian period (290–266 Ma) provide evidence of significant exhumation events that occurred during the Late Paleozoic era. These events were linked to the subduction of the Paleo-Tethys Ocean to the south and the Paleo-Asian Ocean to the north. The Triassic peak ages (247–224 Ma) unveil exhumation signals in the North Qilian Shan region that were generated by the far-field effect of the collision between the Qiangtang and Kunlun terranes. During the Jurassic (193–151 Ma) and the Early Cretaceous periods (144–102 Ma), the exhumation of the North Qilian Shan region was a consequence of the subduction of the Neo-Tethys Ocean and the collision between the Lhasa and Qiangtang blocks, respectively. The peak ages of the Xinminpu Formation in the Early Cretaceous (123–121 Ma) are in close proximity to their depositional age (125–105 Ma), indicating that the North Qilian Shan underwent rapid exhumation during this period. The peak ages observed in the Oligocene Baiyanghe Formation (31–24 Ma) from 144 to 102 Ma, indicate that it has been influenced by the recycled sediments originating from the Cretaceous Xinminpu Formation. The North Qilian Shan gradually emerged during the late Paleozoic and Mesozoic eras, providing the foundation for its subsequent reactivation in the Cenozoic era. The multi-stage cooling or exhumation events of North Qilian Shan since Late Neoproterozoic reflect the complex formation process of the northeastern margin of Tibetan Plateau.

Age and provenance relationships between the basal Great Valley Group and its underlying basement: implications for initiation of the Great Valley forearc basin, California, U.S.A.

ABSTRACT The Great Valley forearc (GVf) basin, California, records deposition along the western margin of North America during active oceanic subduction from Jurassic through Paleogene time. Along the western GVf, its underlying basement, the Coast Range Ophiolite (CRO), is exposed as a narrow outcrop belt. CRO segments are overlain by the Great Valley Group (GVG), and locally, an ophiolitic breccia separates the CRO from basal GVG strata. New stratigraphic, petrographic, and geochronologic data (3865 detrital and 68 igneous zircon U-Pb ages) from the upper CRO, ophiolitic breccia, and basal GVG strata clarify temporal relationships among the three units, constrain maximum depositional ages (MDAs), and identify provenance signatures of the ophiolitic breccia and basal GVG strata. Gabbroic rocks from the upper CRO yield zircon U-Pb ages of 168.0 ± 1.3 Ma and 165.1 ± 1.2 Ma. Prominent detrital-zircon age populations of the ophiolitic breccia and GVG strata comprise Jurassic and Jurassic–Early Cretaceous ages, respectively, with pre-Mesozoic ages in both that are consistent with sources of North America affinity. Combined with petrographic modal analyses that show abundant volcanic grains (> 50%), we interpret the breccia to be mainly derived from the underlying CRO, with limited input from the hinterland of North America, and the basal GVG to be derived from Mesozoic igneous and volcanic rocks of the Sierra Nevada–Klamath magmatic arc and hinterland. Analysis of detrital-zircon grains from the lower and upper ophiolitic breccia yields MDAs of ∼ 166 Ma and ∼ 151 Ma, respectively. Along-strike variation in Jurassic and Cretaceous MDAs from basal GVG strata range from ∼ 148 to 141 Ma, which are interpreted to reflect diachronous deposition in segmented depocenters during early development of the forearc. The ophiolitic breccia was deposited in a forearc position proximal to North America < 4 Myr before the onset of GVG deposition. A new tectonic model for early development of the GVf highlights the role of forearc extension coeval with magmatic arc compression during the earliest stages of basin development.

VERTEBRATE PALEOBURROW AS A SEASONALITY INDICATOR IN EARLY CRETACEOUS TRÊS BARRAS FORMATION (BRAZIL)

Vertebrate burrows serve as windows into the past, revealing the activities of various organisms and providing clues about their paleoenvironmental conditions. This study focuses on a vertebrate paleoburrow from the Três Barras Formation, Minas Gerais state, southeastern Brazil, aiming to detail and reconstruct aspects of the paleoclimatic conditions that acted in this area during the early Cretaceous within a predominantly eolian paleoenvironment. Through detailed analysis of the sedimentary facies and morphological examination of the burrow, this study suggests that the structure was likely produced by lungfish or lizards. It is located within proximal crevasse splay deposits interbedded with fine floodplain sediments, indicating periods of flooding in a meandering fluvial setting that developed in the marginal areas of the eolian system of the Três Barras Formation. Comparison with other paleoburrows from neighboring basins further enhances our understanding of the paleoenvironmental conditions during the early Cretaceous Period. These findings reinforce evidence of seasonality and suggest a period of intense humidity during the deposition of the Três Barras Formation, which had previously been interpreted as exclusively aeolian.

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

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

Mitogenome-Based Phylogeny with Divergence Time Estimates Revealed the Presence of Cryptic Species within Heptageniidae (Insecta, Ephemeroptera).

Heptageniidae are known for their flat heads and bodies and are divided into three subfamilies. Despite the extensive diversity within this group and considerable efforts made to understand their evolutionary history, the internal classifications and origin time of Heptageniidae remains controversial. In this study, we newly sequenced 17 complete mitogenomes of Heptageniidae to reconstruct their phylogenetic positions within this family. Because of the ambiguous time of origin, our study also estimated the divergence time within Heptageniidae based on five fossil calibration points. The results of BI and ML trees all highly supported the monophyly of Heptageniidae and three subfamilies. The phylogenetic relationship of Rhithrogeninae + (Ecdyonurinae + Heptageniinae) was also recovered. The divergence time showed that Heptageniidae originated from 164.38 Mya (95% HPD, 150.23-181.53 Mya) in the mid-Jurassic, and Rhithrogeninae originated from 95.54 Mya (95% HPD, 73.86-120.19 Mya) in the mid-Cretaceous. Ecdyonurinae and Heptageniinae began to diverge at 90.08 Mya (95% HPD, 68.81-113.16 Mya) in the middle Cretaceous. After morphological identification, analysis of the mitogenome's composition, genetic distance calculation, phylogenetic analysis, and divergence time calculation, we suggest that two different populations of Epeorus montanus collected from Aksu, Xinjiang Uygur Autonomous Region (40°16' N, 80°26' E) and Xinyuan, Xinjiang Uygur Autonomous Region (43°20' N, 83°43' E) in China are cryptic species of E. montanus, but further detailed information on their morphological characteristics is needed to fully identify them.

A new bryozoan genus from the Sea of Okhotsk and the taxonomy and geological history of ‘stratocormidial’ cyclostome bryozoans

ABSTRACT A remarkable new genus and species of cyclostome bryozoans is described from the Sea of Okhotsk off the Kamchatka Peninsula, Russia. Kamchatkapora ozhgibesovi gen. et sp. n. has large, multilayered colonies, each layer constructed of numerous subcolonies joined at their outer edges. This colony-form was previously unknown in extant cyclostomes, although common in the geological past, especially during the Cretaceous period. The term ‘stratocormidial’ is here introduced for such colonies, and their taxonomy and geological history are reviewed. Six fossil stratocormidial cyclostome genera (Blumenbachium, Cellulipora, Centronea, Multifascigera, Reptomulticava and Semimulticavea) are illustrated and briefly characterised. http://www.zoobank.org/urn:lsid:zoobank.org:pub:D97F2AD0-7012-46E5-BEDF-E5956AA69AEA

Sampling poorly studied lineages improves resolution in mitogenome-based phylogenies of leafhoppers (Hemiptera: Cicadellidae)

Abstract Cicadellidae (leafhoppers) may be the most diverse and abundant insect herbivores in terrestrial ecosystems worldwide, with more than 23,000 described species in 20 extant subfamilies. Although prior studies have supported the monophyly of most recognized subfamilies, relationships among these groups remain inconsistently resolved and previous molecular phylogenies have failed to support the monophyly of a few subfamilies. To help address this deficiency, we combined 24 new complete mitogenomes representing 6 previously unsequenced subfamilies and 13 tribes with previously available data to create a dataset of 79 cicadellid taxa representing 16 subfamilies for phylogenetic analysis. The new analyses confirm that leafhopper mitochondrial genomes are highly conservative in overall structure, with only a few rare rearrangements of tRNAs. All phylogenetic analyses consistently supported the monophyly of previously recognized cicadellid tribes for which more than 1 representative was included and all of the included subfamilies were also consistently recovered as monophyletic with the exception of Aphrodinae and Eurymelinae. Bayesian inference and Maximum Likelihood analyses with site-homogeneous models are only slightly affected by nucleotide compositional heterogeneity and yield more stable phylogenetic relationships of family-group taxa than analyses with a heterogeneous-site mixture model using PhyloBayes. Molecular divergence time estimates indicate that the main lineages of Cicadellidae, most corresponding to recognized subfamilies, diverged during the Cretaceous period (93–121 Mya).

Integration of seismic and well log data for evaluating the upper cretaceous reservoirs of Horus oil field, Alamein Basin, Northern Western Desert, Egypt

Horus field stands out as one of the main oil-rich areas in Alamein Basin. Formation and evolution of Horus field were influenced by tectonic processes occurring from Jurassic to Cretaceous periods. The main objectives of this study are to characterize structural elements, identify hydrocarbon potential, and pinpoint promising zones within Early Cretaceous rocks for hydrocarbon accumulations in Horus reservoirs. By utilizing high-quality 2D seismic reflection sections enhanced with structural smoothing attribute, which help eliminate random noise while preserving structural details and horizon geometry, building a 3D structural model becomes facile. Analysis of well logging data provides a comprehensive understanding of Cretaceous reservoirs, simplified by 3D static reservoir modeling to depict their varying ranges and anisotropies. 3D structural model shows that the trap of Horus field is linked to a structural uplift in an ENE-WSW trend, bordered to north and south by sediment-filled lows. This anticlinal ridge within the model is segmented into blocks by a series of NW-SE normal faults. 3D static reservoir models reveal high-quality reservoirs in Upper Bahariya and Abu Roash (G) Dolomite, characterized by substantial thicknesses of net pay zones. 3D static modeling of Cretaceous reservoirs guides the oilfield development and optimizes production strategies in Horus area.

Geodynamic development of structures of the North Absheron uplift zone within the South Caspian megadepression and oil-gas-bearing

The article discusses the geodynamic development of the structures of the North Absheron uplift zone. The Pirallahi-Kelkor trough is a polyfocal sub-basin due to the fact that in its sedimentary section, at least the Jurassic, Lower Cretaceous, Lower Pliocene and Quaternary deposits, are characterized by favorable conditions for the accumulation and burial of organic matter. It follows from this that, in accordance with its paleogeotemperature regime, several main stages of hydrocarbon migration could have taken place here. For identifying the formation and further structural-tectonic development , the Absheron bank, the Arzu, Chilov, Palchig Pilpilasi, Chirag and Garabag uplifts have been studied. To solve this issue, paleoprofiles for the end of the Jurassic, Early Cretaceous, Miocene and Pliocene based on the seismic geological profile across the strike of the Pirallahi-Kelkor trough have been compiled. As a result of these studies we established that the uplifts are of syndepositional origin, formed simultaneously with the sedimentation process. The sedimentation and geotemperature regime of the subbasin play a significant role . İt was found that by the end of the Pliocene, the main oil formation zone (MOFZ) contained sediments from the second half of the Lower Cretaceous to the second half of the Lower Pliocene, and both Lower Cretaceous and Lower Pliocene deposits took part in the main stage of hydrocarbon migration. Finally, the MOFZ currently contains sediments from the tops of the Lower Cretaceous to the bottoms of the Upper Pliocene. As can be seen, the main stage of migration covered both Lower Cretaceous and Lower Pliocene deposits. İn addition, we concluded that the natural reservoirs of local uplifts that formed within the Absheron archipelago, regardless of the time of their formation, could be saturated with hydrocarbons depending on the level of their development, position in the structural-tec- tonic plan and reservoir characteristics of the strata. Due to the fact that the uplifts were formed no later than the Miocene, it was even considered that they began to appear by the end of the earlier Miocene, and that they could have captured hydrocarbons of the Lower and Later Cretaceous period.

Detrital zircon U–Pb geochronology of the trench-fill sandstone on the Cretaceous Shimanto accretionary complex in SW Japan: Implications for provenance and igneous activity in the eastern edge of East Asia

Cretaceous igneous rocks are widely distributed in the East Asian margin, and their formation is due to the large-scale migration of igneous activity areas from the continental interior to near the subduction margin. Detrital zircon U–Pb ages of trench-fill sandstones of the Shimanto accretionary complex in the Akaishi Mountains of southwest Japan can provide information on eroded igneous rocks, and their location at the eastern edge of East Asia makes them essential for better understanding the intensity and migration of the igneous activity. As a result of the dating, the Cretaceous zircons in the trench-fill sandstones were found to increase dramatically in the middle Cretaceous and to be abundant in the Late Cretaceous. In addition, these large amounts of Cretaceous zircons were found to be derived from igneous rocks such as the Abukuma Granites and Ryoke Granites distributed in the proto-Japan arc. These results indicate that migration of igneous activity from the continental side reached the eastern edge of East Asia in the middle Cretaceous and that large-scale igneous activity continued to occur in the eastern edge of East Asia until the Late Cretaceous. Thus, the detrital zircon age spectra in trench-fill sediments provide a clear picture of the degree of igneous activity in the source area and migration of the igneous activity on active continental margins.

30 million years of orbitally influenced sedimentation across the Jurassic—Cretaceous boundary and Early Cretaceous period

A continuous sedimentary succession spanning the Early Cretaceous through the Latest Jurassic was retrieved from the Lingshan Island Scientific Borehole 1 (LS-1), located on Eastern Asia southwest of Qingdao. Spectral analysis of different intervals in the data reveals a hierarchy of meter-to decameter-scale cyclicity. The ratios of the cycles in several stratigraphic units are ∼20:5:2:1, corresponding to those of Milankovitch cycle periods of 405 kyr (long orbital eccentricity), 100 kyr (short orbital eccentricity), 40 kyr (obliquity), and 20 kyr (precession), indicating astronomical control on sedimentation. From interpreted 405 kyr long orbital eccentricity cycles along the magnetic susceptibility, uranium, and gamma ray stratigraphic series, a floating astronomical time scale with a duration of ∼30 Myr is established. This ATS provides numerical ages for stratigraphic boundaries and geological events, and serves as the basis for correlation of strata and events between marine and terrestrial systems. The ATS is anchored to a rather imprecise U-Pb determined age of 125 Ma for the K1l (Laiyang Formation of Early Cretaceous)-K1q (Qingshan Formation of Early Cretaceous) boundary from the Lingshan Island outcrops. The anchored time scale places the location of the Jurassic/Cretaceous (J-K) boundary at 677-674 m (∼144.6 Ma). The Purbeckian marine regression at the J/K boundary impacts the Milankovitch signals around the J/K boundary. Distinct spectral peaks with periods of ∼11-Myr are observed in the power spectra of the proxy time series, indicating a possible tectonic imprint. This ∼11-Myr cycle may be attributed to the subduction of the paleo-Pacific plate under Eurasia during the Late Mesozoic, which is being recorded in the ∼30 Ma here investigated sedimentary record. The interplay between the ∼11-Myr tectonic cycle and the ∼2.4-Myr orbital eccentricity cycle appears to jointly control the variation in depositional rates and environments.

Palaeoenvironment and bio-events of the Cretaceous sediments of the Cauvery Basin, India

The Cauvery Basin is an important rift margin basin on the east coast of India. Its long research history began in the mid-nineteenth century with the pioneering work of H. F. Blanford. While much of the Cretaceous succession in the basin is fault-controlled, some of the recorded events represent global sea level changes, especially in the mid-Cretaceous. Macrofossils (ammonites, bivalves, etc.) and foraminifera are abundant throughout, and there is an important occurrence of fossil wood and ‘log-grounds’ in the Turonian–Coniacian. The basin is subdivided into a series of sub-basins (known as depressions in earlier literature), which, in places, have their own distinctive depositional history. The results of our collective fieldwork have provided a re-assessment of the lithostratigraphy, biostratigraphy and the tectono-stratigraphical history of the Ariyalur outcrop. Three sedimentary units have been identified: the syn-rift Gondwana Group (of early Cretaceous age), the syn-rift Uttatur Group (of Albian to Coniacian age) and the post-rift Ariyalur Group (of Santonian to Maastrichtian age). Both microfossil and macrofaunal information have been integrated in order to construct a biostratigraphical framework for the basin and develop a tectono-stratigraphical model. Structures exposed onshore, which have occasionally been interpreted as Albian reefs, are thought to be irregularly shaped limestone olistoliths and olistostromes produced by significant intra-Cretaceous faulting and slumping within the basin.