Early Neogene Research Articles

A systematic revision of herrings (Teleostei, Clupeidae, Clupeinae) from the Oligocene and early Miocene from the Eastern Paratethys and the Carpathian Basin

ABSTRACT Clupeids are one of the most diverse groups of marine fishes represented by numerous extant genera and species. The diversity of European clupeids was even greater in the past, especially during the Paleogene and early Neogene. Here we present the results of a thorough revision of numerous fish fossils assigned to the subfamily Clupeinae. They come from Oligocene and early Miocene deposits of the former Eastern Paratethys and the Carpathian Basin, and are represented by complete and fragmented skeletons. A new endemic genus—†Rupelia Baykina and Kovalchuk, gen. nov.—is established for small-sized herrings from the early Oligocene (Rupelian) of the Caucasus. It occurred only in the Eastern Paratethys and was represented by a single species—†R. rata (Daniltshenko, 1959). At that time, another herring inhabited the entire Paratethys. It completely fits into †Clupeonella (Maicopiella) sensu Menner, 1949a—a subgenus which is raised here to genus level. Based on our review, this herring was represented during the Oligocene by †Maicopiella longimana (Heckel, 1850) —a widespread species with numerous fossils found in deposits mostly of Rupelian and partly of Chattian age. †Rupelia rata went extinct at the beginning of the Miocene, while †Maicopiella longimana was replaced by †M. brevicauda (Menner, 1949a) in the Eastern Paratethys and by †Sardinella sardinites (Heckel, 1850) in the Carpathian Basin. A detailed morphological description of all mentioned taxa is presented. The results of our study shed more light on the diversity and distribution of herrings within the central and eastern parts of the Paratethys during the Oligocene and early Miocene.

Rethinking coral reef functional futures

Abstract Tropical coral reefs currently face an unprecedented restructuring since their extant form and function emerged ~24 million years ago in the early Neogene. They have entered the Anthropocene—an epoch where humans have become the dominant force of planetary change. Human impacts on and interactions with coral reefs are escalating across multiple trophic levels and scales, but we have a rudimentary understanding of what this means for their functional ecology. The overall goal of this special feature is to unpack what the Anthropocene means for the functional ecology of coral reefs, laying the foundations for new approaches and research directions in coral reef science. The collection describes the functional changes and novel dynamics that characterise Anthropocene reefs, from variations in their taxonomy and geology through to the resulting shifts in ecosystem services they provide to humanity. Common changes to coral reefs are occurring that are challenging their historical functional role. These include reductions in benthic calcifiers and declining carbonate production, and benthic assemblage shifts leading to a loss of structural complexity and flattening of reef seascapes. As reefs as we know them are lost from some locations, range extensions and the “tropicalisation” of temperate locations present novel ecosystem configurations that are challenging ecological paradigms and our historical approach to ecosystem management. Hindering our progress, however, is a “functionality crisis.” Coral reef functional ecology to date has lacked a clear and universal definition of the term “function,” and many assumed links between taxa and reef processes lack empirical evidence. Moving forward, we must establish causal links between functional traits, the species that possess them, and specific ecosystem processes if we are to successfully manage Anthropocene reefs. The functional space coral reefs occupy has arguably widened, presenting ethical challenges surrounding the increasingly interventionist management practices required to achieve particular functional endpoints. For us to steer coral reefs towards a desirable functional future will require a more mechanistic understanding between ecosystem attributes and the provision of services, acknowledging that such services are coproduced by the ecosystem and society. Ultimately, this era in coral reef ecology requires a new approach to coral reef science, one that addresses the complex socio‐ecological nature of coral reefs. These works outline a path ahead for defining and studying the functional ecology of coral reefs, drive debate as to what we want their functional future to look like and call for ecosystem function to be at the heart of managing coral reef futures during this period of rapid transition.

Relative contributions of tectonics and dynamic topography to the Mesozoic-Cenozoic subsidence of southern Patagonia

Sedimentary basins result from a complex interaction between mantle, crustal and surficial erosional-driven processes, which act at different time and spatial scales. While shortening and crustal loading drive flexural subsidence toward the foreland, stretching produces normal faulting and graben depocenters. In this contribution we analyze the Mesozoic-Cenozoic subsidence history of southern Patagonia, using backstripping from sixty eight oil well data and outcrops, distributed in the Santa Cruz and Chubut provinces, Argentina, in the Golfo San Jorge and Austral basins. These data are compared with three flexural analyses from six regional balanced cross sections along the southern Patagonian Cordillera, a stretching-thermal model (McKenzie) assuming lateral extension changes, five dynamic topography models localized in the core of the basins and a paleotopographic analysis derived from a paleolithospheric thickness approach (basalt geochemistry). The comparison between stratigraphic observations (backstripping in this case) and subsidence models provide us a residual subsidence value in southern Patagonia. These values are compared with dynamic topography and paleotopographic computations. No additional subcrustal forces are needed to explain the sedimentary accommodation during the Jurassic-early Cretaceous (extensional basin stage). However, from the late Cretaceous to the early Neogene, the foreland stages do require additional processes to account for the subsidence or uplift events. We reassert, like in our previous contributions, that subcrustal forces (lithospheric mantle thickness changes and asthenospheric flows) worked together with flexural accommodation to create a sedimentary basin, occasionally provoking drastic paleoenvironmental and landscape changes.

Mesozoic-Cenozoic evolution of the Eastern Kunlun Range, central Tibet, and implications for basin evolution during the Indo-Asian collision

Abstract The present-day Tibetan plateau, which is the largest highland on Earth, formed primarily due to the India-Asia collision since 50–60 Ma. The development of the plateau has been associated with the Cenozoic development of two large intra-plateau sedimentary basins in north-central Tibet: the Qaidam and Hoh Xil basins to the north and south of the Eastern Kunlun Range, respectively. We conducted an integrated study of these two basins and the Eastern Kunlun Range that separates them to understand the timing and mechanisms of their development in order to decipher the growth and uplift history of the plateau. Crustal shortening in the Fenghuoshan-Nangqian and Qilian Shan-Nan Shan thrust belts initiated no later than the early Eocene, which formed the northern and southern boundaries of the combined Hoh Xil and Qaidam basins in central Tibet. The distinct two-stage development of the Hoh Xil basin suggests emergence of a topographic barrier between the Hoh Xil basin in the south and Qaidam basin in the north in the early Neogene, which is supported by the existing and new apatite fission-track data from the Eastern Kunlun Range that suggest rapid cooling after ca. 20 Ma. Previous and newly collected geochronological, petrological, and thermochronological data are best interpreted in the context of the Paleogene Paleo-Qaidam hypothesis, which requires Hoh Xil and Qaidam basins to have been parts of a single integrated basin during the early stage of the Cenozoic Tibetan plateau development.

Phylogeny and species delimitation based on molecular approaches on the species of the Australoheros autrani group (Teleostei, Cichlidae), with biogeographic comments

Three distinct and independent molecular-based species delimitation analyses were performed among the species and populations included within theAustraloherosautranigroup, based on sequences of the mitochondrial gene Cytochrome b: a tree-based method proposed by Wiens and Penkrot (WP), a Character-based DNA Barcoding (CBB) and coalescent species delimitation method termed the Bayesian Implementation of the Poisson tree processes (bPTP). The congruence of WP and CBB delimited 11 independent lineages (species), while the bPTP delimited just nine lineages. We did not favour any of the methods, and we considered the possibility of two slightly variant scenarios. A time-calibrated phylogenetic analysis is proposed based on the predominant congruence of the results of these three species delimitation methods herein applied. The monophyly of theA.autranispecies group was highly supported with maximum node support value and diagnosed by 11 nucleotide substitutions. The sister clade of theA.autranispecies group is the clade comprisingA.sp. Timbé do Sul andA.minuano. The phylogenetic analysis supports three main clades within theA.autranispecies group, supported by maximum node support value, with the Southern Mata Atlântica clade as the most basal clade. Divergence time estimates indicate that the diversification of theAustraloherosoriginated during the early Neogene, but only in the late Neogene did the processes of diversification in the southeast and north regions occur. Diversification within theAustraloherosautranispecies group occurred synchronically for the three main clades during the beginning of the Quaternary. It is demonstrated that molecular characters are valuable tools for species recognition, particularly in speciose groups with inconspicuous or difficult to record morphological characters. The resulting phylogeny of theAustraloherosautranigroup is highly compatible with the geological and biogeographic scenarios proposed for the Neogene and Quarternary shaping of the extant river basins of eastern Brazil. Despite the origin of theA.autranigroup being dated to the late Miocene, species level diversification occurred in the Pleistocene and was probably driven by headwater capture events and sea-level fluctuations.

Age constraints on a Neogene tropical rainforest in China and its relation to the Middle Miocene Climatic Optimum

Tropical rainforests have strongly influenced Earth systems throughout their evolutionary history. Plant taxa found in the Fotan Group of Fujian Province indicate that an Asian tropical rainforest prevailed in southeastern China during the Miocene. Abundant insect-bearing ambers co-occur with diagnostic plant fossils in outcrop. Fotan Group fossils demonstrate that highly diverse tropical ecosystems existed during the early Neogene in southeastern China. This study reports a robust 40Ar/39Ar age of 14.7 ± 0.4 Ma for the Fotan fossils. This age constrains interpretations of 1) when tropical rainforest ecosystems developed in China, 2) whether the Fotan flora temporally overlapped with the Asian tropical forest in India, and 3) whether the Middle Miocene Climatic Optimum triggered expansion of tropical rainforests in Asia. A precise age for Fotan units provides important constraints on the biogeographic history of the field area and paleographic models linking Asian and Indian biota.

Simbakubwa kutokaafrika, gen. et sp. nov. (Hyainailourinae, Hyaenodonta, ‘Creodonta,’ Mammalia), a gigantic carnivore from the earliest Miocene of Kenya

ABSTRACTHyainailourine hyaenodonts are among the largest terrestrial carnivorous mammals known. The clade is widely dispersed, found in Eurasia, North America, and Afro-Arabia in the Paleogene and early Neogene. In this study, we describe dental and postcranial material from Simbakubwa kutokaafrika, gen. et sp. nov., the most complete hyainailourine known from sub-Saharan Africa. The material is from a relatively young adult from the early Miocene locality of Meswa Bridge, Kenya. Simbakubwa differs from Hyainailouros in exhibiting lingually oriented molar protocones, gracile metastyles, and buccolingually compressed, shearing canines. Like other large Miocene hyainailourines, Simbakubwa has deep carnassial notches on the molars and tall paracones fused to shorter metacones forming single piercing cusps. A Bayesian phylogenetic analysis recovers Simbakubwa as the sister taxon of a clade of large-bodied Miocene hyainailourines that includes Hyainailouros and Megistotherium. Bayesian ancestral state reconstruction supports an Afro-Arabian origin for Hyainailourinae with subsequent dispersal to Eurasia during the early Miocene. Regression analysis based on carnassial size is applied to Simbakubwa and closely related hyainailourines, recovering a body mass up to 1,500 kg for the new taxon. The evolution and extinction of Hyainailourinae offers important insights for interpreting ecological transitions from Paleogene to Neogene faunas in Afro-Arabia and Eurasia.

Late Cenozoic unification of East and West Antarctica

The kinematic evolution of the West Antarctic rift system has important consequences for regional and global geodynamics. However, due to the lack of Neogene seafloor spreading at the plate boundary and despite being poorly resolved, East-West Antarctic motion was assumed to have ended abruptly at 26 million years ago. Here we present marine magnetic data collected near the northern edge of the rift system showing that motion between East and West Antarctica lasted until the middle Neogene (~11 million years ago), long after the cessation of the known mid-Cenozoic pulse of motion. We calculate new rotation parameters for the early Neogene that provide the kinematic framework to understand the varied lithospheric settings of the Transantarctic Mountains and the tectono–volcanic activity within the rift. Incorporation of the Antarctic plate motion into the global plate circuit has major implications for the predicted Neogene motion of the Pacific Plate relative to the rest of the plates.

Early Miocene climate estimations in Patagonia: The case of Pico Quemado, Ñirihuau Formation (Lower-Middle Miocene)

The climate during the early Neogene in Patagonia is characterized by the increase of the average temperatures until the mid-Miocene Climatic Optimum. However, the terrestrial paleoclimate of southern South America during this period is unclear. Therefore, a physiognomic analysis on the Pico Quemado (Ñirihuau Formation, lower-middle Miocene) megaflora was realized. Three types of analyses were performed: 1) Leaf Margin Analysis (LMA); 2) Leaf Area Analysis (LAA); and 3) a CLAMP analysis (Climate Leaf Analysis Multivariate Program) with two different dataset. The LMA and CLAMP predicted an estimated a Mean Annual Temperature of 10.4 ± 2.1 °C, 8.5 ± 2.1 °C and 7.2 ± 1.4 respectively. The estimations of Mean Annual Precipitation were of 123.7 ± 21.2 cm. Through the CCA, other parameters were estimated, i. e. Cold Mean Month Temperature (−3.3 ± 3.8 °C, 1.6 ± 1.6 °C); Warm Mean Month Temperature (17.4 ± 3.3 °C; 14.1 ± 1.2 °C); Mean Growing Season Precipitation (121.9 ± 42.6 cm; 78.1 ± 42.6 cm); Precipitation of the Three Consecutive Wettest Months (116.2 ± 15.3 cm; 88.5 ± 15.3 cm); and Precipitation of the Three Consecutive Driest Months (40.2 ± 19.8 cm; 54.1 ± 19.8 cm). From these results, the Pico Quemado megaflora can be characterized as having a cool temperate climate, with moderate precipitations and the development of bi-seasonality. The obtained estimations are concordant with previous morphological studies in Pico Quemado, which had proposed the same climate conditions. However, these results are inconsistent compared to other studies of early Neogene Southern Hemisphere that suggest that the climate could be warmer. This difference might be due to the few studies of climatic estimations during the early Neogene in Patagonia, precluding detailed comparisons. In conclusion, Pico Quemado paleoflora exhibits unique climatic conditions, and also floral compositions, as suggested in previous works and here corroborated. The study realized constitutes the first climatic estimations for an Argentinean megaflora developed during the Neogene.

Evolutionary trends in leaf morphology and biogeography of Altingiaceae based on fossil evidence

The extant woody family Altingiaceae, consisting of only one genus Liquidambar L. with ca. 15 species, demonstrates a typical disjunctive distribution among East Asia, North America, and the Mediterranean. However, the fossil record throughout the Cenozoic indicates that Altingiaceae was once widespread in the Northern Hemisphere. After studying the abundant Altingiaceae fossil leaf collections, we revised the easily-confused fossil leaves and corrected the misidentifications. Consequently, we proposed an evolutionary history of Altingiaceae leaf morphology in consulting the modern leaf characteristics. It is revealed that the trilobated leaf morphology is the ancestral character state, whereas both the pentalobated and the undivided, pinnate-veined lineages evolved separately. The latter diverged from the trilobated ancestor in South China in Eocene. The lobed and undivided lineages represent the deciduous and evergreen, respectively. An extensive fossil database of Altingiaceae was built to reconstruct its biogeographical history. We reconfirmed that Altingiaceae developed into a temperate and a subtropical-tropical patterns and migrated across both the Bering and North Atlantic land bridges since Cretaceous, independently. It was widespread in the early Neogene of North America and Eurasia, and became extinct in the high latitude triggered by the global cooling and aridification. The modern disjunctive distribution was finally formed, with southeast Asia as its modern diversity center. This study provides new fossil evidence for understanding the morphology and biogeography of the family Altingiaceae.

GEOLOGICAL EVOLUTION - STRATIGRAPHY OF FLORINA, PTOLEMAIDA, KOZANI AND SARADAPORO GRABEN

The purpose of this research is to comprehend the geological and stratigraphical evolution of Fiorina, Ptolemaida, Kozani and Sarandaporo graben. This graben extends North of the Greek borders and is more than 150 Km long. The activity of big and profound faults ofNW-SE direction, in NW Macedonia, after the end of the Alpine orogenesis cycle and during the Early Miocene was related to the formations ' deposition. A large number of samples were collected from drill cores for the examination of palynology, paleoflora, fossils, and diatoms in order to determine the formations ' sequence and age. The basement and the borders of the depression, belong to the Pelagonian geotectonic zone. The deposition of the Early Neogene 's series is following. During the Late Pliocene the previous series, is developing into a lacustrine-marshland system, resulting to the deposition of Late Neogene's series formations. In the Quartenary the following formations are deposited: Proastion formation, Perdika formation, terrestrial, fluvial-terrestrial formation, recent formation. Four (4) phases of lignitogenesis have been specified, mainly in the Ptolemaida - Amynteo basin. In this graben they have been deposited the most important lignite deposits of Greece.

Himalayan Paleogene Foreland Basin, its collision induced early volcanic history and failed rift initiation

The Himalayan Foreland Basin was formed over a failed rift zone that produced early Paleogene volcanism, which was synchronous to Indo-Asia collision. The rift zone was located over acutely flexed leading edge of the Indian continental crust. The volcanism preceded upliftment of the proto-Himalaya. The Jammu Himalaya is one of the few areas exposing the basal part of the foreland basin comprising a persistent horizon of volcani-sedimentary rhyolitic chert breccia at the base of the Subathu Formation, which unconformably overlies the Precambrian Jammu Limestone. Contemporaneous felsic ash beds occur in the Subathu-Kalka area in the Simla Hills at the base of the Subathu Formation unconformably overlying the Precambrian Simla Group. In Arunachal Pradesh, in the eastern-most Himalaya, early-mid Eocene foraminifera fauna bearing Yinkiong Formation overlies the Abor Volcanics. The age of the latter is disputed: whether it is early Permian or Eocene in age, or it exposes a mixture of both components. Recent U-Pb SHRIMP zircon geochronological study indicates Abor Volcanics being part of the Kerguelen mantle plume trail traversing Southern Tibet, Sylhet, Rajmahal, Bunbury and Kerguelen Plateau. Trace element geochemistry of the Abor Volcanics, the exposed volcanic rocks around Yinkiong and those exposed between Pangin and Rotung indicate rift signature. In the frontal belt, early Eocene shallow marine sediments locally associated with mafic volcanics occur tectonically at the base of the early Neogene foreland sequence. The latter is locally thrust at MBT by the early Permian meta-sediments tectonically intermixed with marine Eocene rocks. Early Eocene sediments and rift related mafic volcanics from Arunachal Pradesh possibly occur at the tectonic base of the Tertiary foreland basin sequence from northeastern Himalaya. The early Paleogene mafic volcanics from the Arunachal Pradesh and coeval acid volcanics occurring at the base of the Paleogene sequence in Jammu-Simla Himalaya might represent cogenetic bimodal volcanism.The Subathu Formation with its coal and carbonaceous sediments is lithologically similar to the coal and mud-rock bearing late Paleocene Patala Formation or the Hangu Formation and early Eocene Ghazij Formation from the adjacent Indus Foreland Basin, Pakistan, which overlie the Mesozoic-Paleocene carbonate flat. Although, the lithofacies and sedimentary tectonic setting of the Patala, Hangu and the Ghazij formations are similar to that of the Subathu Formation, the former units typically lack the presence of syn-sedimentary ash beds or any other volcanic rocks that are characteristically present at the base of the Subathu Formation. Mainly late Paleocene coal bearing Patala and the Hangu formations in Salt Range and North Potwar area, Pakistan, although located close to the Jammu sector of the Himalayan Foreland Basin is free of any volcanic activity. Salt Range and Potwar areas are possibly not parts of the foreland fold-and-thrust belt of the Himalaya, as postulated by some workers. Geodynamically Salt Range and Potwar basins belong to northern parts of the Indus Foreland Basin, because the depositional basin from Potwar extending into the adjacent Kohat area during the Paleocene and the Eocene time probably formed a collision zone between the India-Pakistan plate and a micro-continent prior to the collision of the former with Asia. The micro-continent possibly buffered intensity of collision, thereby, there was no tectono-magmatic activity along this belt as distinct from that of direct collision between India and Asia continent.

Late Cretaceous–Cenozoic thermochronology in the southern Songliao Basin, NE China: New insights from apatite and zircon fission track analysis

The Late Cretaceous–Cenozoic thermochronology in the southern Songliao Basin was determined using apatite and zircon fission track analysis data. It is crucial to deciphering the evolution of the Songliao Basin and changes in the movement direction of the Pacific Plate. We present eight new apatite and eight corresponding zircon fission track data from borehole samples across the Baixingtu uplift. The apatite fission track (AFT) thermochronological modeling reveals that the basin underwent two distinct compression- and extension-related uplift stages of rapid cooling during the Late Cretaceous–Cenozoic: stage I during the Late Cretaceous–Early Paleogene (∼70–52 Ma), stage II in the Late Paleogene–Early Neogene (∼38–10 Ma). The AFT data vary from 76.0 ± 5.0 to 25.3 ± 1.9 Ma and the zircon binomial peak fitting ages ranged from 79 to 61 Ma, all younger than the stratigraphic ages (∼92–88 Ma) of their host rocks. One sample had similar fission track ages (apatite 76.0 ± 5.0 Ma and zircon 79.0 ± 3.0 Ma) within reasonable error, representing a magmatic event. The data were divided into four groups. (i) 79–76 Ma: magmatic cooling event, (ii) 69–61 Ma: uplift of the whole region and exhumation and erosion, (iii) 37–34 Ma and (iv) ∼25 Ma: various uplift events related to tectonic inversion, causing partial uplift, exhumation and erosion in the basin. This created favorable conditions for formation and storage of mineral resources, especially sandstone uranium ore deposits. Our results combined with previous research suggest that the variation in uplift and exhumation began in the basin’s SE part and propagated to the NW ∼5–8 Ma later. The tectonic inversion in the southern Songliao Basin at least began ∼37–34 Ma. This corresponds with the time of the Paleo-Pacific Plate shifting to NWW motion and the India–Asia collision. These regional-scale uplift, exhumation and inversion events were probably responses to the subduction and turning of the Paleo-Pacific Plate from the southeast and the collision of the Indian subcontinent from the southwest. It is important to study the tectonic inversion in the whole east of China since the Late Cretaceous and the change of the direction of the Pacific plate movement.

Teeth, fossil record and evolutionary history of the cowtail stingray Pastinachus Rüppell, 1829

Hypolophin ‘dasyatids’ are a common group of large stingrays today frequenting the Indo-Pacific inshores. Being often harvested in their restricted area, few are known about their biology and their evolutionary history despite a very peculiar dental pattern making it easy to track their fossil record. An abundant material consisting of isolated teeth from Late Bartonian (38–40 Ma) lagoonal deposits of Djebel el Kébar, Tunisia, allows to describe a new stingray, Pastinachus kebarensis nov. sp. This taxon represents the oldest occurrence for this genus but also the oldest fossil record for hypolophins. A dental comparison of these fossils with 3D rendered models of fresh specimens testifies that early hypolophin representatives had already a strongly arcuate and bulbous upper jaw, interlocking with a broad and elongated tooth plate on the lower jaw. This new fossil and its fossil relatives (here updated), indicate a pre-Bartonian origination for hypolophins in western Neotethys, and reveal a rapid and widespread colonization of the proto-Mediterranean Sea, western Atlantic and Indo-Pacific coasts during the late Paleogene–early Neogene. Finally, it is worth noting that early hypolophin representatives seemingly entered freshwater habitats occasionally as modern cowtail stingrays do.

Early Miocene herpetofaunas from the Greek localities of Aliveri and Karydia – bridging a gap in the knowledge of amphibians and reptiles from the early Neogene of southeastern Europe

We here describe new remains of amphibians and reptiles from the early Miocene (MN 4) of two different Greek localities, Aliveri and Karydia. The newly described material consists of urodelans, alytids, indeterminate anurans, turtles, crocodylians, lacertids, indeterminate scincomorphs, anguids, colubrids, viperids, and indeterminate snakes. The presence of the frog Latonia cf. gigantea in Greece is documented for the first time. Additionally, the presence of viperids in Aliveri implies a much wider distribution for these snakes during the early Miocene of Europe. Of special interest is the presence of a peculiar colubrid that seems to possess a hitherto unknown vertebral structure, which is herein defined as the ‘paracentral ridge’. Although incomplete, the new material has important taxonomic and biogeographic implications, as it enhances our understanding of southeastern European herpetofaunas from the early Miocene, a time period that was characterised by major dispersal and extinction events and climatic change that affected the whole continent.

Carbonate banks and ramps on the northern shore of Palaeogene and Early Neogene Borneo: Observations and implications on stratigraphy and tectonic evolution

Carbonate banks and ramps on the northern shore of Palaeogene and Early Neogene Borneo: Observations and implications on stratigraphy and tectonic evolution

Geological features and exploration fields of tight oil in the Cenozoic of western Qaidam Basin, NW China

Abstract Using a large amount of drilling and experimental analysis data, this paper evaluates four potential fields of tight oil exploration in western Qaidam Basin from comprehensive analysis of geological conditions such as sedimentary environments, source rock evaluations, reservoir characteristics, and source-reservoir relationships. Influenced by continuous uplift of Tibet Plateau since Paleogene, the sedimentary environment of the western Qaidam Basin exibits three characteristics: (1) a paleo-topographic configuration consisted of inherited slopes, depressions and paleohighs; (2) frequent alternation of relative humid and arid paleoclimate; and (3) oscillation of salinity and level of the paleo-lake water. Preferential paleo-environment resulted in two sets of large-scale source rocks with high efficiency and two types of large-scale tight reservoir rocks (siliclastic and carbonate), deposited during the late Paleogene to early Neogene. The above source and reservoir rocks form favorable spatial relationships which can be classified into three categories: symbiotic, inter and lateral. Based on sedimentary environments and reservoir types, tight oil resource in western Qaidam Basin can be divided into four types, corresponding to four exploration fields: salty lacustrine carbonate tight oil, shallow lake beach-bar sandstone tight oil, delta-front-sandstone tight oil and deep lake gravity-flow-sandstone tight oil. The temporal and spatial distribution of tight oil has characteristics of layer concentration, strong regularity and large favorable area, in which the saline lacustrine carbonate and shallow lake beach-bar sandstone tight oil are the best exploration targets in the western Qaidam Basin.

Influence of natural fractures on gas accumulation in the Upper Triassic tight gas sandstones in the northwestern Sichuan Basin, China

The Upper Triassic Xujiahe Formation in the northwestern Sichuan Basin, China, is a typical tight gas sandstone reservoir that contains natural fractures and has an average porosity of 1.10% and air permeability less than 0.1 md because of compaction and cementation. According to outcrops, cores and image logs, three types of natural fractures, namely, tectonic, diagenetic and overpressure-related fractures, have developed in the tight gas sandstones. The tectonic fractures include small faults, intraformational shear fractures and horizontal shear fractures, whereas the diagenetic fractures mainly include bed-parallel fractures. According to thin sections, the microfractures also include tectonic, diagenetic and overpressure-related microfractures. The diagenetic microfractures consist of transgranular, intragranular and grain-boundary fractures. Among these fractures, intraformational shear fractures, horizontal shear fractures and small faults are predominant and significant for fluid movement. Based on the Monte Carlo method, these intraformational shear fractures and horizontal shear fractures improve the reservoir porosity and permeability, thus serving as an important storage space and primary fluid-flow channels in the tight sandstones. The small faults may provide seepage channels in adjacent layers by cutting through layers. In addition, these intragranular and grain-boundary fractures increase the connectivity of the tight gas sandstones by linking tiny pores. The tectonic microfractures improve the seepage capability of the tight gas sandstones to some extent. Low-dip angle fractures are more abundant in the T3X3 member than in the T3X2 and T3X4 members. The fracture intensities of the sandstones in the T3X3 member are greater than those in the T3X2 and T3X4 members. The fracture intensities do not always decrease with increasing bed thickness for the tight sandstones. When the bed thickness of the tight sandstones is less than 1.0 m, the fracture intensities increase with increasing bed thickness in the T3X3 member. Fluid inclusion evidence and burial history analysis indicate that the tectonic fractures developed over three periods. The first period was at the end of the Triassic to the Early Jurassic. The tectonic fractures developed during oil generation but before the matrix's porosity and permeability reduced, which suggests that these tectonic fractures could provide seepage channels for oil migration and accumulation. The second period was at the end of the Cretaceous after the matrix's porosity and permeability reduced but during peak gas generation, which indicates that gas mainly migrated and accumulated in the tectonic fractures. The third period was at the end of the Eogene to the Early Neogene. The tectonic fractures could provide seepage channels for secondary gas migration and accumulation from the Upper Triassic Xujiahe Formation into the overlying Jurassic Formation.

Meso–Cenozoic lithospheric thermal structure in the Bohai Bay Basin, eastern North China Craton

The Bohai Bay Basin is a region where part of the North China Craton has been thinned and destroyed. It has experienced two periods of crustal thinning that occurred during the Cretaceous and Paleogene, but investigations of its Mesozoic and Cenozoic lithospheric thermal structure are limited. Therefore, in this study, the distributions of mantle heat flow, crustal heat flow, and Moho temperatures during the Meso–Cenozoic are calculated based on analyses of the thermal history of the Bohai Bay Basin. The results indicate that the ratio of mantle heat flow to surface heat flow peaked during the late stages of the early Cretaceous and during the middle to late Paleogene. The corresponding mantle heat flow was more than 65% of the surface heat flow. Moho temperatures reached three peaks: 900–1100 °C in the late stages of the early Cretaceous; 820–900 °C in the middle to late Paleogene; and (in the Linqing Depression, Cangxian Uplift, and Jizhong Depression) 770–810 °C during the early Neogene. These results reveal that the Bohai Bay Basin experienced significant geological change during the Cretaceous, including the transformation of lithospheric thermal structure from “cold mantle and hot crust” before the Cretaceous to “hot mantle and cold crust” after the Cretaceous. The results also indicate that the basin experienced two large-scale rifting events. Therefore, this work may provide the thermal parameters for further investigations of the geodynamic evolution of eastern China.

Cenozoic vegetation gradients in the mid- and higher latitudes of Central Eurasia and climatic implications

Cenozoic vegetation gradients in the mid- and higher latitudes of Central Eurasia are studied based on a total of 22 mega- (fruits and seeds, leaves) and 20 microfloras (pollen and spores) compiled from literature. Vegetation is interpreted at the level of plants functional types (PFTs) using a system including 26 classes and an aquatic functional type. The obtained ecospectra showing diversity of PFTs are interpreted in three time slices, namely the early Oligocene, early Miocene and late Pliocene/early Pleistocene. Our results confirm the presence of diverse mixed forests (Turgai type) in the study area throughout the late Paleogene and early Neogene, partly, raised diversity of herbaceous components, especially of dry herbs, and the presence of xeric shrub PFTs points to more open plant cover. The late Pliocene/early Pleistocene spectra from the central and southern latitudinal zones of the study area confirm the existence of open landscapes in general, but partly have a considerable arboreal diversity excluding the presence of mere steppe. Ecospectra obtained from the diversity of functional types have a characteristic representativeness depending on the organ types considered in each case, and therefore have a delimited comparability. Our results show that PFT diversities obtained from microfloras are most suitable in estimating the openness of landscape and in representing zonal biomes in general. The vegetational patterns reconstructed based on the ecospectra of fossil floras basically support the results obtained from previous palaeoclimate reconstructions evidencing cooling and drying of the continental interior of Eurasia throughout the later Neogene. Moreover, the PFT approach is proven more sensitive to identify seasonal drought when compared to other, taxonomy based climate reconstruction methods. Moreover, a first attempt is made to quantify latitudinal temperature gradients for the study area. Data indicate that the Oligocene and early Miocene gradients where shallow and almost identical while the late Pliocene/early Pleistocene gradient was intermediate between the earlier Neogene and the modern one.