Jurassic Research Articles

Paleolatitudinal movements of the eastern Sakarya Zone from Jurassic to Eocene

The study area covers a region oriented north-south from the Black Sea coastline in the north to the Kelkit Basin in the south within the eastern Sakarya Zone in northern Türkiye. The objective of this study is to investigate the paleolatitudinal movements of the eastern Sakarya Zone during the Jurassic-Eocene time interval through paleomagnetism. Various volcanic and sedimentary units (e.g., the Şenköy, Berdiga, Mescitli, Çatak, Kızılkaya, and Çağlayan Formations) spanning the time interval from the Early Jurassic to Middle Eocene were identified. A total of 98 locations belonging to Early/Middle Jurassic to Eocene volcanic and sedimentary units were selected for paleomagnetic core sample collection. The samples were subjected to demagnetization through thermal and alternating field methods. Characteristic remanent magnetization directions (ChRM) were obtained. Isothermal remanent magnetization (IRM) and high temperature susceptibility (HTS) measurements were made to identify the minerals responsible for magnetization. To ascertain whether magnetization was acquired through rock formation or as a consequence of subsequent tectonic processes, conglomerate and fold tests were performed. The results showed that magnetization was acquired before folding, i.e., the rocks have primary magnetization. Polarity tests were also conducted using coeval normal and reverse polarity sites. The results indicate that the mean magnetization direction for the Early-Middle Jurassic is 18.1°/55.2° (D/I) and 3.3°/51.5° (D/I) for sedimentary and volcanic rocks, respectively, and 348.7°/46.7° (D/I) for Late Jurassic/Early Cretaceous sedimentary rocks. In the Late Cretaceous period, the mean magnetization direction is 8.0°/49.3° (D/I) and 9.1°/47.0° (D/I) for sedimentary and volcanic rocks, respectively. In the case of the Early/Middle Eocene, the mean magnetization direction is 348.6°/52.7° (D/I) and 5.9°/48.8° (D/I) for sedimentary and volcanic rocks, respectively. In this study, the E/I correction was applied to the Late Jurassic/Early Cretaceous sedimentary rocks, and paleolatitude data obtained from sedimentary rocks were also utilized. Our paleomagnetic results indicate that the eastern Sakarya Zone was situated at latitudes spanning from 27.9° to 35.7° during the Early Jurassic - Middle Eocene time interval. In consequence, the eastern Sakarya Zone constituted a portion of the southern margin of the Eurasian continent during the Late Jurassic and Middle Eocene periods.

IMPROVING THE RELIABILITY OF THE THREE-DIMENSIONAL GEOLOGICAL BASIS OF COMPLEX DEVELOPMENT TARGETS

This article proposes a new method for identifying different groups of reservoirs when constructing a three-dimensional geological and hydrodynamic model of the target. Productive formations of the Bajocian and Bathonian stages of the Jurassic system of the Kalamkas field were selected as the object of study. This field is tectonically associated with the northern part of the North Buzachinsky arch, located at the northwestern end of the Turan plate. It was noted that these productive deposits have a complex geological structure, due in lithological terms to uneven alternation of sand-siltstone and clay rocks. In addition, four different reservoir classes are identified within each tier, which are characterized by their own permeability-porosity correlation relationships. As a result, for reliable construction of the filtration field, it is necessary to determine the distribution zones of each of the identified reservoir classes within the reservoir. This is due to the fact that due to the different filtration field, the development of reserves from each group of reservoirs will occur unevenly both in area and in section. In this regard, the integrated Flow Zone Indicator (FZI) was evaluated using the results of laboratory core studies. In order to obtain a continuous FZI parameter for wells without core sampling and laboratory analysis, the results of laboratory studies were compared with the results of well geophysical studies (well logging). As a result, analytical dependence of FZI and log data was obtained. Based on this analytical dependence, new three-dimensional models were constructed and zones of distribution of different groups of reservoirs were identified. To verify the obtained results, the synthetic FZI curve calculated from the obtained analytical relationship was compared with the FZI estimate based on the results of laboratory core studies. It is concluded that the synthetic FZI curve is consistent with the FZI estimate based on the results of laboratory core studies and, therefore, the proposed approach can be used when performing work related to 3D modeling.

Evaporites and red beds of a syn-rift Atlantic series: evidence of continental depositional environment (Berrechid sub-basin, Morocco)

ABSTRACT The Berrechid sub-basin of Morocco consists of Late Triassic–Early Jurassic evaporites and red beds that are part of the syn-rift Atlantic series. Although some of the Berrechid sub-basin has been extensively studied, the depositional environment of the Upper Salt-Mudstone Formation has long been debated, with some early studies proposing a marine origin. This study documents the sedimentological, mineralogical, and geochemical characteristics of core materials from two boreholes and mine outcrops covering the entire series of the Upper Salt-Mudstone Formation. Our analysis of the lithology, mineralogy, sedimentary structures, sedimentary textures, and geochemical data suggests deposition in a continental setting. In addition, detailed observations of sedimentary structures and textures indicate additional features of periods of flooding, evapoconcentration, and desiccation. The continental setting in a dry climate is also supported by the occurrence of Classopollis pollen. This study provides new insights of the paleoenvironmental conditions in the Berrechid sub-basin, and significantly advances our understanding of the paleoenvironment and climate of Pangea during the Late Triassic–Early Jurassic period.

A new leaf inhabiting ascomycete from the Jurassic (ca 170 Mya) of Yorkshire, UK, and insights into the appearance and diversification of filamentous Ascomycota

Leaf-associated fungi, the fungi that depend on leaves to sporulate, have a rich Cenozoic record, however their earlier diversity is poorly characterized. Here we describe Harristroma eboracense gen. et sp. nov., a Middle Jurassic leaf-associated fungus colonizing the leaf cuticle of Nilssonia tenuicaulis (cycadophyte). To place our newly described species into a picture of the diversification of Mesozoic fungi, we reassess fossils with leaf-associated stromata in the context of fungal molecular phylogeny. Being melanized, with radiate stromata, and on leaves, H. eboracense and other fossils from the Jurassic and earlier periods are probably related to filamentous Ascomycota in the superclass Leotiomyceta. Characters needed for further resolution of leaf-associated fungal biology and classification, such as the presence of an ostiole for spore discharge and appressoria for entry into leaf tissue first appear in the Mesozoic fossil record. Among Early Cretaceous fossils, Spataporthe taylorii represents the oldest unambiguous evidence of perithecial Sordariomycetes while Protographum luttrellii and Bleximothyrium ostiolatum are the oldest Dothideomycetes thyriothecia. Environmental observations show that broad leaved gymnosperms (especially cycadophytes) growing in warm temperate wet forests might have been the first environment for the radiation of Leotiomyceta.

High-resolution isochronous stratigraphic framework through well-seismic integration in tight sandstone: a case study of Luodai gas field, Sichuan, China

Tight gas sandstone represents a significant unconventional resource extensively discovered across numerous sedimentary basins around the world. Tight sandstone reservoirs are characterized by low porosity, low permeability, variable source material, rapid spatial and temporal changes, poor reservoir properties, and strong heterogeneity. Traditional geophysical methods struggle to meet the demands of exploration and development of these types of reservoirs. This study applies a high-precision comparative approach using well-seismic integration to establish a relative isochronous stratigraphic framework. Based on this framework, extracting seismic properties can effectively predict tight sandstone reservoirs. This paper, focusing on the Penglaizhen Formation in the Luodai Gas Field of the Western Sichuan Jurassic system. This entire process accomplished in three steps: starting with regional marker layers as the initial framework; followed by the establishment of a relative isochronous framework through precise well-seismic integration; and finally stratigraphic slicing techniques to delineate isochronous stratigraphic framework with shorter time intervals. Thereby enhancing the reliability of subsurface stratigraphic information and data accuracy. The study posits that current technological means cannot create a truly isochronous stratigraphic framework; thus, “isochronous” is considered a relative concept in this context. The framework aims to ensure temporal consistency by minimizing discrepancies through mutual constraints between well and seismic data, serving to exploration and development requirements. Furthermore, analyses such as sensitive attribute extraction, impedance inversion, and assessment of hydrocarbon potential in tight sandstone reservoirs demonstrate strong correlation with drilling results. This validation underscores the framework’s efficacy in interpreting industrial gas production flows, thereby providing robust support for future oil and gas exploration.

Spatial and Temporal Variation of Precipitation Drives the Genome Size Variation in Scolopendra in Chinese Mainland.

Genome size is an adaptive trait, and its variations influence the organismal phenotype and fitness. In this study, we propose a hypothesis linking variations in genome size within Scolopendra to ecological factors. To test this hypothesis, we employed flow cytometry to estimate genome size in seven Scolopendra species from Chinese mainland. Subsequently, we reconstructed the phylogenetic relationship of these species using the cytochrome c oxidase subunit 1 gene and conducted phylogenetic comparative analysis to assess the relationships between genome size and niche breadth or 19 bioclimatic variables. Our findings indicate the following: (1) genome size in Scolopendra can be categorized into three groups, similar to the phylogenetic clades; (2) there is a negative correlation between genome size in Scolopendra species and the precipitation niche breadth of species; (3) the estimated divergence time of Scolopendra dates back 153 Mya, during the Jurassic period. We assume that consistent aridity geological periods may promote the evolution of Scolopendra species with a large genome size, whereas rapidly fluctuating humidity geological periods may have the opposite effect.

Piercing the Mystery: Predator Identification Using the Perforated Tests of the Sea Urchin Brissus unicolor (Leske, 1778)

ABSTRACTDrilling predation on echinoids (sea urchins) has been known to occur in marine ecosystems since the Jurassic Period; however, it has rarely been studied in existing species. Tests of the irregular sea urchin Brissus unicolor (Leske, 1778), which frequently occurs in shallow substrates of the Canary Islands, mostly show very evident perforations through their skeletons. The aim of this study was to describe the characteristics of these perforations in order to determine their possible origins as well as document their size, site selectivity, and frequency of occurrence among different sample sites. Of the 104 tests of B. unicolor that were collected from 15 locations off the island of Tenerife (Canary Islands, Spain), 94% showed a least one perforation. These boreholes exhibit a circular morphology, penetrating the sea urchin tests perpendicularly and entirely. Notably, they display a unique acid signature, diverging from those documented in the fossil record and other relevant studies. Our analysis showed size and site selectivity by the predator as the perforations were mainly located on the oral side of the test. The perforations are attributed to drilling predation. The characteristics of these boreholes on B. unicolor match published records of predation marks suggesting that they are produced by the predatory gastropod family Cassidae, with Semicassis undulata (Gmelin, 1791) considered to be the most probable predator.

COMPLICATED THERMAL HISTORY OF THE LITHOSPHERIC MANTLE OF THE ANABAR REGION: RECONSTRUCTIONS BASED ON XENOCRYSTS FROM KIMBERLITES

The thermal history and thickness of the lithospheric mantlebeneath the kimberlite fields of the Eastern Anabar shield and adjacent territories of the Siberian craton were reconstructed based on the composition of clinopyroxene xenocrysts from the concentrate of kimberlite heavy fraction and mantle xenoliths. Garnet and spinel peridotites are most abundant in the lithospheric mantle beneath the five studied fields of the Siberian craton. Almost in all fields, the Mg# index of clinopyroxene decreases through depth. In the oldest Chomurdakh kimberlite field, both TiO2 and FeO contents vary slightly. The titanium oxide values markedly vary from 0 to 0.6 wt. % in the Triassic fields. The high titanium oxide contents in minerals are indicative of deep­seated metasomatic transformations of lithospheric mantle blocks in the northern Yakutia kimberlite province. The geotherm was fitted to the PT data set in the Gtherm program with the model involved D. Hasterok and D. Champan. The thermal lithosphere beneath the studied fields retained the thermal thickness up to 260 km. In the period between 430 and 230 Ma, it underwent a significant metasomatic transformation resulting in the formation of high­Fe and high­Ti blocks. It appears, that the thermal thickness declined to 190–200 km only in the north of the Siberian craton during the Jurassic period. This assumption is verified by the values of lithosphere thickness beneath the northern Kuoika field.

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

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

Petrogenesis of REE-mineralized granitic plutons in central Thailand, Southeast Asian tin belt: New insights from geochemistry and zircon U–Pb geochronology

Granitic rocks including biotite granite and biotite-muscovite granite exposed in the Uthai Thani area, central Thailand are located on the main eastern and central granitic belts of Southeast Asia. The biotite granites are characterized by an equigranular texture, whereas biotite-muscovite granites exhibit a porphyritic texture with K-feldspar megacrysts. Geochemically, biotite granites show metaluminous to weakly peraluminous high-K calc-alkaline affinity, whereas biotite-muscovite granite exhibits strongly peraluminous and shoshonitic. The biotite granites and biotite-muscovite granites have trace element features consistent with formation in subduction and syn-collision settings, respectively. The pressure–temperature conditions of emplacement in biotite and biotite-muscovite granite types are 1.94–2.28 kbar/676 °C–713 °C and 1.39–2.00 kbar/669 °C–698 °C, respectively, indicating solidification in upper crustal paleo-depths. Positive εHf (t) values of zircon in the biotite granites indicate similarity to I-type granite of the Sukhothai Terrane, whereas negative εHf (t) values of zircon in the biotite-muscovite granites compare well with S-type granites form in the Inthanon zone. Zircon U–Pb geochronology indicates that biotite granites might have emplaced during the Late Triassic is related to Paleo-Tethys subduction beneath the Indochina terrane, whereas biotite-muscovite granites might have emplaced during the Late Triassic to Early Jurassic period, probably as a result of collision between the Sibumasu and the Indochina Terranes. In the Uthai Thani area, the high total REE contents and the presence of primary REE minerals in granitic rocks reflect mineralization potential with respect to light REE, together with the magmatism related to Fe-Cu and Sn mineralization along the main granite belts in Thailand.

Geochronology and Geochemical Characteristics of Granitoids in the Lesser Xing’an–Zhangguangcai Range: Petrogenesis and Implications for the Early Jurassic Tectonic Evolution of the Mudanjiang Ocean

This article focuses on zircon U-Pb isotope dating and a whole-rock elemental analysis of granodiorites, monzonitic granites, granodioritic porphyries, and alkali feldspar granites in the Yangmugang area of the Lesser Xing’an–Zhangguangcai Range. The zircon U-Pb isotope-dating results revealed that these granitic rocks formed during the late Early Jurassic period (182.9–177.2 Ma). Their geochemical characteristics and zircon saturation temperatures suggest that the granodiorites are moderately differentiated I-type granites and the monzonitic granite, granodioritic porphyries, and alkali feldspar granites are highly differentiated I-type granites. The degree of magma differentiation progressively increased from granodiorites to alkali feldspar granites. By combining the regional Nd and Hf isotope compositions, it was inferred that the magma source involved the melting of lower crustal material from the Mesoproterozoic to the Neoproterozoic eras. By integrating these findings with contemporaneous intrusive rock spatial variations, it was indicated that the late Early Jurassic granitoids in the Lesser Xing’an–Zhangguangcai Range formed within an extensional tectonic setting after the collision and closure of the Songnen–Zhangguangcai Range and Jiamusi blocks. Additionally, this study constrains the closure of the Mudanjiang Ocean to the late Early Jurassic period (177.2 Ma).

METHOD FOR ASSESSING THE IMPACT OF GEOLOGICAL HETEROGENEITY ON OIL SATURATION DISTRIBUTION

This article examines a method for assessing the impact of reservoir heterogeneity on the distribution of oil saturation in pay zones using the example of the Bajossian and Bathonian stages of the Jurassic system of the Kalamkas field. Within this field, the Jurassic oil and gas stratum under consideration lies on the eroded surface of various horizons of the Middle and Lower Triassic and is represented by uneven alternation of sand-siltstone and clay rocks, as a result of which these deposits have a complex geological structure, due in the lithological plan to uneven alternation of sand-siltstone and clay rocks. As a result, a rather complex distribution of oil (water) saturation may occur in the formation, which differs from the standard ideas about the geological structure of the object under study, i.e. the presence of such «unconventional» reservoir boundaries (oil-bearing contour) as capillary barriers of the first kind is possible. As a result of this approach, the following is obtained. For the conditions of occurrence of productive formations of the Bajossian stage of the field in question, in order to ensure that the dimensions of the capillary barrier in the reservoir do not exceed the height of 1 m at an average value of the porosity coefficient Kп = 27,6 % it is necessary to fulfill the inequality of Kпр ≥ 6,1∙10−3 μm2. For the conditions of occurrence of productive formations of the Bathonian stage, in order for the dimensions of the capillary barrier in the reservoir not to exceed the height of 1 m with an average value of the porosity coefficient Kп = 28,0 % it is necessary to Kпр ≥ 7,5∙10−3 μm2. Also, on the basis of this method, various ratios of Kпр permeability coefficients and porosity were obtained Kп at which the dimensions of the capillary barrier in the deposit will exceed the heights of 1.0, 1.5 and 2.0 m above the level of the accepted oil-water contact (OWC) for the conditions of occurrence of the Kalamkas field in question. It was noted that this approach makes it possible to assess uncertainties in the position of fluid contacts when justifying the boundaries of the oil potential contour and the distribution of oil reserves in formations with a wide range of reservoir properties.

Lu-Hf and U-Pb dating of the Zayanderud eclogites: Implications for Jurassic subduction initiation along the Neotethys margin in Iran

The time at which the Neotethys Ocean started to subduct along the southern margin of Eurasia within Iran has been debated in recent years. This margin, referred to as the Sanandaj-Sirjan Zone (SaSZ), features a series of Jurassic calc-alkaline igneous formations which were emplaced at c. 170 Ma. However, an alternative model suggests that subduction initiation occurred during the Cretaceous period. To address this age controversy, we utilized the Lu-Hf isochron method and employed SIMS U-Pb zircon and rutile geochronology to determine the metamorphic history of the earliest known Neotethyan eclogite outcrop along the upper Zayanderud River section of the SaSZ. Two eclogites separated by ∼25 km yielded Lu-Hf garnet dates of 175.1 ± 1.0 Ma and 172.5 ± 0.6 Ma. Rare <20 μm eclogitic zircon crystals in one of the eclogites are strongly zoned and yielded U-Pb dates for which a 177 ± 10 Ma rim age was deconvolved. The relatively low Dy/Yb of these zircon rims suggests that they crystallized prior to garnet formation, or retrograde in disequilibrium with garnet. Homogeneous U-Pb rutile ages averaging 162 ± 7 Ma are only marginally younger than the Lu-Hf garnet ages, consistent with the petrographic observation that rutile is predominantly found in the matrix or within garnet rims, and open-system behavior of radiogenic Pb during cooling. The newly obtained ages are close to previously published 40Ar/39Ar phengite dates and indicate a narrow time window during the Middle Jurassic for deep burial within a subduction channel, followed by eclogitization and rapid exhumation. These new constraints on the metamorphic history support subduction initiation along the SaSZ margin in the Jurassic period.

Overpressure of Deep Jurassic System in the Central Junggar Basin and Its Influence on Petroleum Accumulation

Overpressure of Deep Jurassic System in the Central Junggar Basin and Its Influence on Petroleum Accumulation

Early Jurassic A-type granite and monzodiorite from the Baoji batholith: Implication for tectonic transition from post-collision to post-orogenic extension in the Qinling Orogenic Belt, China

Introduction: The early Jurassic granitoids in the Qinling Orogenic Belt (QOB) play a crucial role in understanding the tectonic implications for the geological evolution of China. To elucidate the early Jurassic tectonic setting of QOB, we performed a comprehensive analysis of zircon U-Pb ages, whole-rock geochemistry, and in situ zircon Lu-Hf isotopes from early Jurassic monzodiorite and Kfeldspar granite within the Baoji batholith in western QOB.Geochronology Method and Results: The intrusions yielded zircon U-Pb ages of 186 ± 2 Ma and 188 ± 2 Ma, respectively.Geochemistry Results: The monzodiorites are characterized by relatively high MgO, Rb, Th, U, and LREE contents, as well as low P, Ti, and HREE contents. They also exhibit high Nb/Ta ratios (20.6–23.4). The zircon εHf(t) values for the monzodiorite sample range from −4.36 to 6.47, indicating significant contributions from a fertile continental lithospheric mantle with the involvement of crustal components. The K-feldspar granites are enriched in K2O+ Na2O, Rb, Zr, Hf, and Nb, and lower Ba, Sr, Ti, and P. They exhibit high Nb/Ta and Ga/Al ratios but low Y/Nb and Yb/Ta ratios. Their geochemical characteristics reveal an A-type granite affinity with elevated zircon saturation temperatures (848°C–900 °C). Additionally, the K-feldspar granite exhibits REE and trace element patterns similar to those observed in the monzodiorite. However, a wide range of zircon εHf(t) values (−4.72 to 3.98), differing from those of the monzodiorite, indicate that the parental magma of the K-feldspar granite experienced magma mixing between a monzodioritic magma and a crustal-derived felsic magma.Discussion: These findings suggest that both A-type K-feldspar granite and monzodiorite likely formed during post-orogenic processes. Additionally, the QOB commenced its postorogenic evolution as an extensional tectonic environment during the early Jurassic period.

Phylogeny and diversification analyses of extant planthopper families (Hemiptera: Fulgoromorpha) based on a mitochondrial dataset reveal ancient lineages originating during the Jurassic and originally feeding on gymnosperms

Abstract Phylogenetic analyses of planthoppers were conducted using a mitogenome dataset to examine the evolutionary relationships of current families based on both maximum likelihood (ML) and Bayesian inference methods. Delphacoidea, including Cixiidae and Delphacidae, and Fulgoroidea, including all other families, were consistently identified as monophyletic groups. However, Nogodinidae displayed a polyphyletic pattern, with various lineages emerging sister to several issidoid families. Variations were observed across different analyses in the positioning of (Dictyopharidae + Fulgoridae) and the relationships of Ricaniidae sister either to Issidae or to (Flatidae + Acanaloniidae). Several statistical tests indicate that the ML topology has the highest level of statistical confidence. The (Dictyopharidae + Fulgoridae) clade is best positioned as sister to (Derbidae + (Achilidae + (Tropiduchidae + other “higher” planthoppers families))) and the Ricaniidae as sister to (Flatidae + Acanaloniidae). With 13 fossil calibration points, origin times for Delphacoidea and Fulgoroidea were dated back to the Late Permian, approximately 257.46 million years ago. Delphacidae and Cixiidae split during the Late Triassic, while Fulgoroidea diversified earlier during the Middle Triassic. Divergence and diversification times are also provided for all other extant planthopper families. These results suggest that Delphacoidea and Fulgoroidea likely diverged from the older planthopper fossil families prior to the emergence of angiosperms and may have initially fed on gymnosperms and ancient ferns. The diversification of extant planthopper families occurred during the Jurassic and Cretaceous periods, influenced by evolving climatic conditions, the decline in gymnosperms, and the increasing diversity of angiosperm plants.

A Novel Method for Analyzing Sandbar Distribution in Shelf-Type Tidal Deltas Using Sediment Dynamic Simulation

Shallow marine shelf sedimentation is a hot and difficult topic in today’s reservoir sedimentology research, and it is widely present in the world. The shallow marine shelf sedimentation is not only affected by complex hydrodynamic effects such as tides and waves, but also controlled by bottom tectonic features, forming a complex and varied sedimentation pattern. During the Middle Jurassic period, the northern part of West Siberian Basin was characterized by a shallow marine shelf sedimentary environment. In the central reion of this basin, a typical tectonic uplift zone developed, forming a tectonic background of “one uplift zone between two depressions”. Simultaneously, the dominant influence of tides in the shallow marine shelf environment facilitated the formation of a typical shelf-type tidal delta sedimentation system in the Jurassic strata of the northern part of West Siberian Basin. This sedimentation constitutes a significant natural gas reservoir, and it is important to investigate the sedimentary evolution of shelf-type tidal deltas and to clarify the internal structure and distribution of sedimentary sand bodies and interlayers in shelf-type tidal deltas, which is the basis for the fine development of this type of reservoir. This paper takes the Jurassic strata in the Y region of northern part of West Siberian Basin as the research object, and conducts numerical simulation based on sedimentary dynamics for the shelf-type tidal delta sedimentation formed under the tectonic background of “one uplift zone between two depressions”. In addition, tidal amplitude and initial water level were selected for different hydrodynamic factors to study the main controlling factors of shelf-type tidal delta sedimentation. The simulation results show that tidal amplitude is positively correlated with three-dimensional configuration characteristic parameters of the sedimentary sand bodies, and the development of tidal bars becomes more and more limited as the initial water level increases. This paper systematically investigates the sedimentary evolution of shelf-type tidal delta under the tectonic background of “one uplift zone between two depressions” by the sedimentary dynamics method, which deepens the understanding of the shelf-type tidal delta sedimentation process and provides a new thinking for the development of this sedimentary reservoir type (School of Geosciences China University of Petroleum (East China)).

New record of Cretaceous Protocircoporoxylon wood from the Guyang Basin, northern China and its palaeoclimatic implications

Abundant and diversified Mesozoic fossil wood records have been reported in China. However, fossil woods have never been reported in the Guyang Basin, northern China. Here, a new calcified fossil wood specimen was discovered from the Lower Cretaceous Guyang Formation in the Guyang Basin. The present fossil are characterized by araucarian radial tracheid pitting and circopore cross-field pitting, typical of the genus Protocircoporoxylon. The specimen described here are mostly distinguishable from other fossil species of Protocircoporoxylon by the araucarian radial tracheid pitting and the number of pits per cross-field. Therefore, the present wood fossil is established as a new species, Protocircoporoxylon guyangensis Xu X.H. et Zhao Y.M. sp. nov. Up to now, the fossil detail records of Protocircoporoxylon have predominantly been found in the Triassic and Jurassic periods thus far. However, this discovery in Inner Mongolia, northern China indicates that the genus Protocircoporoxylon still into the Early Cretaceous period. The quantitative growth rings analysis of P. guyangensis sp. nov. indicates that it is an evergreen gymnosperm with a leaf retention time of 5–7 years. The fossil wood living in an environment with complacent water supply and weak seasonal fluctuations.

Large Fe-Mn oncoids from Early Jurassic Ammonitico Rosso Facies (eastern Sakarya Zone, NE Turkey): new insight into palaeogeographic conditions of Tethys Ocean

ABSTRACT Oncoids, significant sedimentary structures within the Jurassic strata of the Mediterranean Region, serve as valuable indicators of paleoenvironmental conditions during their formation. One of the important examples of oncoids has been discovered in the Pliensbachian (Early Jurassic) Ammonitico Rosso Facies (ARF) of the eastern Sakarya Zone (Eastern Pontides, NE Turkey). This study presents the first comprehensive sedimentological and petrographic (textural and compositional characteristics) examination, as well as geochemical analyses (trace and rare earth elements) of these Fe-Mn oncoids. The oncoids consist of nuclei coated with irregular laminae and exhibit a range of sizes, from 10 to over 45 mm, displaying various colours such as brown, reddish, and metallic-looking. They mostly have a discoidal shape, although some are spherical. The nuclei consist of bioclastic wackestones, containing remnants of ammonoid shells. Some oncoids, especially the discoidal forms, have multiple nuclei. The cortex of the oncoid predominantly consists of wrinkled bands displaying micritic laminae, with an abundance of filamentous bodies and the local presence of encrusting microfossils. In the cortex of the oncoids, iron predominates over manganese, and there are compositional variations within the cortex, especially enriched in Si, Fe, and Ca. They predominantly fall within the region associated with hydrothermal Fe and Mn sediments, as indicated by discrimination diagrams involving Ni, Co, Zn, and plots of Ce/Ce* vs Y/HoN and Nd contents, suggesting a hydrothermal origin. Furthermore, their rare earth elements (REE) chemistry displays distinct Y/Ho, Sm/Yb, Ce/Ce, and Nd values, indicating the presence of seawater mixing with hydrothermal fluids. However, they show relatively low Sm/Yb, Y/Ho, Eu/Sm, Nd/YbN, and La/Yb values, suggesting a limited contribution from hydrothermal sources to the surrounding seawater. Nevertheless, the cortex of the oncoids exhibits a complex and variable mineralogy that changes over short distances, implying the dynamic nature of the depositional environment, characterized by fluctuating hydrological regimes, varying oxygen levels, elemental supply, and the saturation of specific elements in seawater. The increased presence of specific trace elements, including Fe, and REE during this period, is likely linked to hydrothermal fluid input into marine environments, coinciding with intensified syn-sedimentary tectonic activity, where ongoing extensional tectonic movements occasionally influenced paleoenvironmental conditions. In these conditions, the formation of oncoids is influenced by various sedimentary factors, including the availability of metal sources, specific paleoenvironmental conditions, and the presence of microbial organisms, thereby enriching our understanding of palaeogeography during the Early Jurassic period. Additionally, the studied oncoids, with their comparable stratigraphic position and petrographic characteristics to those in both the eastern and western parts of the Tethyan basin, underscore their significance in palaeogeography and stratigraphy.

Jurassic system stratigraphy at the Kamianka village. Part 2. The Cherkas’ka formation

Jurassic system stratigraphy at the Kamianka village. Part 2. The Cherkas’ka formation