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Significant breakthroughs have been achieved in the exploration of Paleogene reservoirs in the Lufeng Depression. However, as drilling depth is becoming greater, the discovered oil and gas reservoirs show signs of transition from conventional to unconventional accumulations, and the identification of conventional and unconventional reservoir boundaries is of particular significance. Herein, the hydrocarbon dynamic field boundaries in the Lufeng Depression are comprehensively identified by the geological drilling result method, the sandstone pore throat radius critical value discrimination method and the dry layer drilling rate variation method; then, the hydrocarbon dynamic field is divided and the characteristics and differences of hydrocarbon accumulations in each hydrocarbon dynamic field are compared. The results show that the buoyancy-driven hydrocarbon accumulation depth in the Lufeng Depression is between 3,500-4,000 m, and the hydrocarbon accumulation depth limit is about 5,800 m. The focus of research on Paleogene oil and gas exploration in the Lufeng Depression should be placed on conventional oil and gas reservoirs in the free dynamic field and tight oil reservoirs in the reformed dynamic field. As for the Enping Formation and Upper Wenchang Formation, efforts should concentrate on conventional oil and gas reservoir exploration, and the tight reservoir of Lower Wenchang Formation should be explored in the high fracture density area in C-4 and C-8 well blocks and the west of C-8 well block of the Lufeng 13 sag. The research results of this paper are of great value in further increasing oil and gas production and the explorarion of reservoirs in the Lufeng Depression. [ABSTRACT FROM AUTHOR]

Conventional and tight unconventional oil and gas resources in the Huizhou Depression have shown broad exploration prospects, which mainly originate fromWenchang Formation source rocks. Thus far, studies on Wenchang Formation source rocks mainly focused on the geochemical characteristics and conventional petroleum resource evaluation; however, the correlation of conventional, tight, and shale oil and gas, and their resources are still unknown. In fact, the formation of conventional, tight, and shale oil and gas are intrinsically related, which allows for a more objective evaluation to consider the three types of oil and gas resources simultaneously in the whole dynamic process of both hydrocarbon generation and expulsion, as well as reservoir tightness history. In this work, based on geological and geochemical analyses, the improved hydrocarbon generation potential method was utilized to establish a hydrocarbon generation and expulsion model of the Wenchang Formation source rocks. Then, combined with the reservoir tightness history, the conventional, tight, and shale oil and gas resources were evaluated. The results show that the Wenchang Formation source rocks are distributed in the whole depressions, with a thickness of 50-1850 m and an average total organic carbon content of 2.2%. The organic matter is mainly type II and is mature-high maturity. The Wenchang Formation source rocks reached hydrocarbon generation threshold and expulsion threshold at a vitrinite reflectivity of 0.43% and 0.65%, respectively, and the reservoir evolved completely tight at 2.3 Ma. Overall, the Lower and Upper Wenchang Formation contain a large amount of conventional, tight, and shale oil and gas resources. [ABSTRACT FROM AUTHOR]

As the focus of conventional oil and gas exploration is changing from shallow to deep layers, the identification of deep effective reservoirs is crucial to exploration and development. In this paper, based on the geological anatomy of oil and gas reservoirs, a new discriminatory criterion and evaluation method for effective reservoirs is proposed in combination with the analysis of reservoir formation dynamics mechanism. The results show that the hydrocarbon properties of the reservoir vary with the ratio of the capillary force between the sandstone reservoir and its surrounding rock. The effective reservoir is discriminated and the reservoir quality is evaluated based on the capillary force and depth of the surrounding media and the sandstone reservoir for adjacent plates. When the capillary force ratio is greater than 0.6, fewer effective reservoirs are developed. The effective reservoir is determined by the capillary force ratio of the sandstone reservoir and the surrounding rock medium to mechanically explain the geological phenomenon that low-porosity reservoirs can also accumulate hydrocarbons. Our findings have significant guiding value for Paleogene oil and gas exploration in the Zhu I depression of Pearl River Mouth Basin. [ABSTRACT FROM AUTHOR]

Fabaceae is one of the most diverse angiosperm families and is distributed across the globe in a variety of environments. The earliest evidence of the family, previous to this work, was from Paleogene sediments where it was found to be diverse in many fossil assemblages around the world. Here, we describe a fossil legume fruit from the Olmos Formation (upper Campanian) in northern Mexico. We designated the fossil fruit as Leguminocarpum olmensis Centeno-González, Martínez-Cabrera, Porras-Múzquiz et Estrada-Ruiz sp. nov., and related it with the Fabaceae family based on the presence of a dehiscent pod with two valves, an apex bearing stylar base, short stipe, and reticulated veins in the pericarp. We propose a new fossil species of Leguminocarpum for this fossil fruit. This fossil provides critical information on the long geologic history of Leguminosae around the world, significantly extending the record into the Cretaceous of Mexico. Naylet Centeno-González et al. report the discovery of the oldest legume fruit fossil at 73.5 million years old in the Olmos Formation of Mexico. This finding supports the hypothesis that Mexico is the center of radiation for Fabaceae. [ABSTRACT FROM AUTHOR]

Abstract The present paper address the occurrence of Venericardia shell concentrations distributed over hundreds of meters along terrigenous horizons as a typical sedimentary facies of the Wilcox Formation in the Burgos Basin. These extensive deposits overlie Paleogene sandstones so common around the municipality of China, Nuevo León, that they are almost overlooked. This report documents for the first time the ichnological assemblage and shell accumulations of the Paleogene in the Burgos Basin. Ophiomorpha cf. nodosa and Ophiomorpha isp. from Skolithos ichnofacies are the main identified trace fossils; the probable paleoenvironment is a near-shore shallow sea under high-energy conditions related to coastal bars. The analyzed taphonomic features suggest that Venericardia shell concentrated or accumulated as bioevents resulting from intermitent tempestites in the proximal zone. These accumulations are composed of the species Venericardia (Venicor) zapatai organized as regular and linear shell arrangements contained within a frail sedimentary matrix from which they are easily-extracted. Highlights • The Burgos basin records Thanetian-Ypresian transgressive and regressive sedimentary cycles with abundant shell concentrations. • Venericardia (Venericor) zapatai accumulated through sporadic shoreface environments. • The ichnogenus Ophiomorpha and its sedimentological association with Venericardia sp. shells is preserved in the Burgos basin. • Large benthic foraminifera (Discocyclina sp.) are abundantly preserved inside Venericardia shells. [ABSTRACT FROM AUTHOR]

Abstract The fossil crocodylomorph fauna of the Cenozoic of South America is very rich and diverse. Historically, few publications have been dedicated to providing an overall review of this fauna, with most reviews focusing on specific areas. However, the fact that many new species, taxonomic reviews and description of new specimens have been proposed in the last decade makes a comprehensive review of the fossil crocodylomorph fauna of the South American Cenozoic necessary. The only crocodylomorph lineages to have a fossil record comprising Late Cretaceous and Cenozoic deposits in South America is the Dyrosauridae. Sebecidae or its predecessors, however, are very likely to have inhabited the continent during the Cretaceous-Paleogene transition as well; both Dyrosauridae and Sebecidae are considered here to have survived the Cretaceous-Paleogene extinction while inhabiting South America. Caimaninae (Alligatoroidea) arrived either in the late Cretaceous or in the early Paleocene coming from North America. The fossil record of Caimaninae is present, however, only from the Paleocene. By the Eocene, there are no records of Dyrosauridae in South America; this group was globally extinct after the Eocene, possibly due to the global cooling that occurred by the end of the epoch. Sebecids and caimanines solely comprised the crocodylomorph fauna of the continent until the Miocene, where there are the first records of Gavialoidea (Gryposuchinae) and a possible first dispersion of Crocodyloidea, through the tentative tomistomines Charactosuchus and Brasilosuchus. Gryposuchinae likely arrived in the continent from Africa or from Asia during the Oligocene. Charactosuchus and Brasilosuchus may have come from North America where tomistomines lived from the Oligocene to the Pliocene. Sebecids were extinct after the middle Miocene; Charactosuchus , Gryposuchinae, Purussaurus , Mourasuchus and durophagous caimanines such as Gnatusuchus were extinct after the late Miocene. These extinctions are related to changes in the drainage basins caused by elevation of the Andes mountain range. Only the extant caimanine Caiman , Melanosuchus and Paleosuchus would survive the Miocene, being enriched by Crocodylus from the Pliocene onwards, which is likely that Crocodylus arrived in the American continents from Africa. The current fossil record indicates that these four genera comprise the extant crocodylian fauna of the continent since the Pliocene. Although our knowledge on crocodylomorph fossil fauna of the South American Cenozoic has increased continuosly, especially in the last decade, much yet must be done, especially on the taxonomy and phylogeny of Brasilosuchus and Charactosuchus , fieldworks in Paleogene and Pliocene localities, and the evolution of the specialized Caimaninae morphotypes. Highlights • This paper is a review of the South American fossil crocodylomorph fauna. • The fauna is comprised mainly by Dyrosauride, Sebecidae and Caimanine during the Paleogene. • Gavialoids arrived between the Paleogene and the Neogene. • End of Miocene: geomorphological changes in the continent caused the extinction of many taxa. • Caiman, Melanosuchus, Paleosuchus and Crocodylus solely comprise the fauna from the Pliocene onwards. [ABSTRACT FROM AUTHOR]

Abstract Undercompaction is an important mechanism for developing fluid overpressure in the mudstone strata. The main factors that affect undercompaction are the deposition rate (DR) and mudstone content (MC); however, the manner in which the DR and the MC influence the development of undercompaction is still unclear. To clarify the pressurization mechanism of undercompaction and the influence of DR and MC, the acoustic and density logging as well as the sonic-velocity–effective-stress schematic are used to identify the undercompaction overpressure. Furthermore, the PetroMod software is used to simulate the development of overpressure and to analyze the influence of the DR and MC on the undercompaction of Paleogene strata in the Baxian Depression of Jizhong Subbasin. The Baxian Depression causes the development of overpressure in the Dongying Formation, the first member of the Shahejie Formation, the third member of the Shahejie Formation, the fourth member of the Shahejie Formation, and the Kongdian Formation, whereas the undercompaction overpressure is observed to mainly develop in the Dongying Formation and in the first member of the Shahejie Formation. A prerequisite for performing the simulation is that the total thickness and deposition time of the formation should remain constant. Further, the effects of the varying DR and MC on the development of undercompaction are simulated. The results exhibit that the DR and MC are prerequisites for developing undercompaction overpressure. However, the DR only affects the undercompaction development period and exhibits little effect on the final overpressure amplitude. Meanwhile, the amount of MC not only increases the amplitude but also results in an early development of the undercompaction overpressure. Highlights • The starting depth of overpressure differs among different source rock intervals. • High deposition rate (DR) and mudstone content (MC) are necessary for developing undercompaction overpressure. • High DR advances undercompaction formation with negligible effect on the final overpressure amplitude. • The undercompaction overpressure amplitude increases as the MC and the formation period increase. [ABSTRACT FROM AUTHOR]

The aim of this study is to decipher the respective influences of geodynamic and climate disturbances at the Jurassic/Cretaceous boundary on sedimentary facies and carbonate diagenesis in a stable intracratonic basin using isotopic geochemistry and subsidence quantification. Fourteen lithofacies were deposited in a (1) carbonate platform and (2) a delta plain environment. Climate change from cool and wet to warm and semi-arid conditions during the early Tithonian influenced the syn-sedimentary dolomitization process within the carbonate platform during the mid-Tithonian. Architecture and facies reconstructions well-constrained the Jurassic-Cretaceous Unconformity (JCU), which was an important local structural episode marked by (1) an 80 m uplift in the eastern Paris Basin and by (2) the formation of a NW–SE low wavelength 15 km-wide and 30 km-long flexure. This first tectonic event tended to maintain brine ponds and supratidal marsh environments in the platform during the late Tithonian and early Berriasian, forming Purbeckian facies and associated dolomitic facies. A major depositional change occurred between the early and late Berriasian from shallow carbonate platform environments to fluviatile-deltaic clastic deposits (Wealden facies). This facies change is underlain by a major unconformity corresponding to the Ryazanian unconformity. It is marked (1) by erosion processes, karstification of the carbonate substrate, and the development of ferruginous weathering products (goethite), followed by (2) incision processes in a fluvial-deltaic environment. This unconformity is consecutive to a 40 m uplift in the eastern Paris Basin. The rifting phase in the Bay of Biscay, in the Pyrenean Zone, and in the Artic-North Atlantic together with the opening of the Ligurian Sea had a major influence on the northern part of France by causing uplifts (120 m from the Tithonian) and flexuring. Geodynamics played a major role in carbonate demise in the Paris Basin leading to exposure and karstification of the carbonate platform. Added to the generalized uplift, western Tethyan cool and humid conditions from the late Berriasian caused terrigenous influx into large-scale marine domains which was detrimental and unfavorable to carbonate growth. [ABSTRACT FROM AUTHOR]

The Upper Cretaceous and Lower Paleogene Table Mountain Shoshonite lava flows and their proposed source, the Ralston Buttes intrusions, provide insight into the volcanic history of the Colorado Front Range. This study affirms the long-held hypothesis linking the extrusive Table Mountain lava flows and their intrusive equivalents at Ralston Buttes through major- and trace- element geochemistry. Systematic 40Ar/39Ar geochronology from all flows and intrusive units refines the eruptive history, improves precision on previously reported ages, and provides tighter constraints on the position of the K-Pg boundary in this location. Four flows are recognized on North and South Table mountains outside of Golden, Colorado. Flow 1 (66.5 ± 0.3 Ma, all ages reported with 2σ uncertainty) is the oldest, most compositionally distinct flow and is separated from younger flows by approximately 35 m of sedimentary deposits of the Denver Formation. Stratigraphically adjacent flows 2 (65.8 ± 0.2 Ma), 3 (65.5 ± 0.3 Ma), and 4 (65.9 ± 0.3 Ma) are compositionally indistinguishable. Lavas (referred to here as unit 5) that form three cone-shaped structures (shown by this study to be volcanic vents of a new unit 5) on top of North Table Mountain are compositionally similar to other units, but yield an age almost 20 m.y. younger (46.94 ± 0.15 Ma). Geochemistry and geochronology suggest that the rim phase of the Ralston plug (65.4 ± 0.2 Ma) is a reasonable source for flows 2, 3, and 4. All units are shoshonites--potassic basalts containing plagioclase, augite, olivine, and magnetite phenocrysts--and plot in the continental-arc field in tectonic discrimination diagrams. A continental-arc setting coupled with Late Cretaceous to early Paleogene ages suggest the high-K magmatism is associated with Laramide tectonism. [ABSTRACT FROM AUTHOR]

The Dongsheng uranium district, located in the northern part of the Ordos Basin, contains the largest known sandstone-hosted uranium deposit in China. This district contains (from west to east) the Daying, Nalinggou, and Dongsheng uranium deposits that host tens of thousands of metric tonnes of estimated recoverable uranium resources at an average grade of 0.05% U. These uranium orebodies are generally hosted by the lower member of the Zhiluo Formation and are dominantly roll or tabular in shape. The uranium deposits in this district formed during two stages of mineralization (as evidenced by U–Pb dating) that occurred at 65–60 and 25 Ma. Both stages generated coffinite, pitchblende, anatase, pyrite, and quartz, with or without sericite, chlorite, calcite, fluorite, and hematite. The post-Late Cretaceous uplift of the Northern Ordos Basin exposed the northern margins of the Zhiluo Formation within the Hetao depression at 65–60 Ma, introducing groundwater into the formation and generating the first stage of uranium mineralization. The Oligocene (∼25 Ma) uplift of this northern margin exposed either the entirety of the southern flank of the Hetao depression or only the clastic sedimentary part of this region, causing a second gravitational influx of groundwater into the Zhiluo Formation and forming the second stage of uranium mineralization. [ABSTRACT FROM AUTHOR]

Phase equilibrium experiments have been performed on an extremely high-Ti (5.4 wt.% TiO2) picrite from the base of the Paleogene (~55 Ma) East Greenland Flood Basalt Province. This sample has a high CaO/Al2O3 ratio (1.14), a steep rare-earth elements (REE) profile, is enriched in incompatible trace elements, and is in chemical equilibrium with highly primitive olivine. This all suggests that the picrite is a near-primary melt that did not suffer major chemical evolution during ascent from the mantle source and through the crust. Near-liquidus phase relations were determined over the pressure range of 1 atm, 1 to 1.5 GPa and at temperatures from 1094 to 1400°C. They provide an important constraint on the petrogenesis of these lavas. The high-Ti picritic melt is multi-saturated with olivine (Ol) + orthopyroxene (Opx) at 1 GPa but has only Ol or Opx on the liquidus at lower and higher pressures, respectively. This indicates the primitive melt was last equilibrated with its mantle source at relatively shallow pressure (~ 1 GPa). Melting probably started at 2-3 GPa and the picritic melt was produced by 15-30% melting of the mantle source. Such a degree of partial melting requires a mantle with a high potential temperature (1480-1530˚C). The relatively low CaO content and high FeO/MnO ratios of the most primitive East Greenland picrites, the high Ni content of olivine phenocrysts and the presence of low-Ca pyroxene (i.e., pigeonite) at high pressure in our experiments all suggest that the mantle source contained a major component of garnet pyroxenite. Residual garnet in the source could adequately explain the low Al2O3 content (7.92 wt.%) and steep REE patterns of the picrite sample. However, simple melting of a lherzolitic source, even with a major pyroxenite component, cannot explain the formation of magmas with the very high Ti contents observed in some East Greenland basalts. We therefore propose that magmas highly-enriched in Ti were produced by melting of a metasomatized mantle source containing Ti-enriched amphibole and/or phlogopite. [ABSTRACT FROM AUTHOR]

Abstract: The Lower Cretaceous sections in northern Sinai are composed of the Risan Aneiza (upper Barremian‐middle Albian) and the Halal (middle Albian‐lower Cenomanian) formations. The facies reflect subtle paleobathymetry from inner to outer ramp facies. The inner ramp facies are peritidal, protected to open marine lagoons, shoals and rudist biostrome facies. The inner ramp facies grade northward into outer ramp deposits. The upper Barremian‐lower Cenomanian succession is subdivided into nine depositional sequences correlated with those recognized in the neighbouring Tethyan areas. These sequences are subdivided into 19 medium‐scale sequences based on the facies evolution, the recorded hardgrounds and flooding surfaces, interpreted as the result of eustatic sea level changes and local tectonic activities of the early Syrian Arc rifting stage. Each sequence contains a lower retrogradational parasequence set that constituted the transgressive systems tracts and an upper progradational parasequence set that formed the highstand systems tracts. Nine rudist levels are recorded in the upper Barremian through lower Cenomanian succession at Gabal Raghawi. At Gabal Yelleg two rudist levels are found in the Albian. The rudist levels are associated with the highstand systems tract deposits because of the suitability of the trophic conditions in the rudist‐dominated ramp. [ABSTRACT FROM AUTHOR]

The Niudong Buried Hill Field, which lies in the Baxian Depression of the Bohai Bay Basin, is the deepest oil/gas accumulation in eastern China. Its Precambrian dolomite reservoir occurs at burial depths of 5860 m–6027 m. This paper attempts to document the hydrocarbon charging and accumulation history in this field, which could greatly enhance the understanding of the mechanisms for the formation of deep hydrocarbon accumulations. Our previous study of oil trapped in fluid inclusions has demonstrated that the ratio parameters of the fluorescence spectral intensities at 425 nm and 433 nm (Q 425/433 ratio), and at 419 nm and 429 nm (Q 419/429 ratio) can be more effective for revealing hydrocarbon charging history than the previously-used fluorescence parameters such as Lambda max and red/green quotient as well as fluorescence colors. The hydrocarbon charging and accumulation history in the Niudong Buried Hill Field was studied with an integrated approach involving the application of these two spectral parameters of petroleum inclusion fluorescence as well as utilization of other data including homogenization temperatures of aqueous inclusions coeval with petroleum inclusions, and cross-cutting relationships of cements and “oil veins” in pores and fractures. The results indicate that the dolomite reservoir in the Niudong Buried Hill Field experienced three episodes of hydrocarbon charging. In the first two episodes (between 38.5Ma and 25Ma), the low mature and mature oils, which were derived from source rocks in the Sha-4 Member of the Eocene Shahejie Formation, migrated into the reservoir, but part of them leaked out due to normal faulting at the updip margin of the buried hill. These early-charged oils were preserved mainly in small pores in micritic dolomites by oil-wettability and capillary pressure. In the Neogene, the basin subsided as a whole and local faults at the updip margin became inactive and played a sealing role. By approximately 13Ma, the source rocks became highly mature and the generated hydrocarbons then migrated into the reservoir and accumulated. Therefore, the last charging is the most important for hydrocarbon accumulation in the Niudong Buried Hill Field. [ABSTRACT FROM AUTHOR]

A study on the sedimentary facies characterization and depositional environment interpretations for the K#Field (K-Oil Field) in Cambay petroleum basin of western onshore, India was conducted based on the sub-surface data from drilled wells, including well logs, borehole images, cores and the regional knowledge of the basin. In this work, an effort is made to integrate the current data from seismics and well logging, to study and analyze its depositional environments and establish the petroleum systems. The study regions for the present work are K45 and K48 blocks. The target strata includes 2 oil-bearing formations of Paleogene, which is about 3600 ft; they are M#Fm (M-Formation) of the Eocene and N#Fm (N-Formation) of Oligocene, subdivided into 11 zones. The sediment fill is mostly of Tertiary. The research attempts to decipher the oil - depositional source correlation problems of the basin. Sedimentary models were established referring to the core analysis, core photographs and well logs. Reservoir and heterogeneity study included reservoir lithology features, physical properties and pore structure features.Well facies analysis of oil well WELL-0297 and WELL-0129 was done and the results were analyzed for further drilling of new wells for oil and gas exploration. The study found that the Eocene, Oligocene, Miocene and Paleogene are fluviatile facies sand and mud interbed sediment with the thickness 2000-4000 ft, which are main oil-bearing formations in these areas. Studies concluded that the fluvial reservoirs of the K#Field are characterized by large variations from laterally extensive bodies with good interconnectedness and high net-to-gross ratios, multi-storey ribbon bodies with poor interconnections and low net-to-gross ratios. [ABSTRACT FROM AUTHOR]

Reservoir rocks at Gomba oilfield, located in the Hungarian Paleogene Basin, include fractured and karstified Triassic carbonates with significant fluid storage potential. However little information is available about the fracture network in these carbonates which has led to production problems at Gomba. The purpose of this study is to investigate the relationship between the spatial distribution of high porosity zones in the carbonates and the microfracture system. For this evaluation, individual fractures were studied and used in a discrete fracture network (DFN) modelling exercise at two wells, Gomba-1 and Gomba-3. The investigation took place at two different scales. Fracture length and aperture distributions were derived at the micro-scale (mm to cm), whereas fracture density and fracture orientation data were investigated at the reservoir scale. The results of both investigations were taken into consideration in the modelling. The results of the fracture network models were compared to reservoir lithologies which ranged from fractured carbonates to collapse breccias. Based on the results, it appears that the porosity associated with a significant proportion of the fractures was increased as a result of dissolution. Fracture distribution was not uniform along the studied well paths, and fracture orientation was chaotic at particular depth intervals. On the basis of the DFN models, three different fractured zones are predicted to occur in the reservoir, but only two of the zones have significant fracture porosity. Comparing these results with petrographic observations, an epigene karst phase is proposed which is older than (or the same age as) the time of hydrocarbon migration; karst-related voids were therefore important pathways for fluid migration. The void system and karst caverns partly collapsed during subsequent burial, resulting in karst-related traps. By analogy with modern cave systems, the karst cavern zones at Gomba probably extend horizontally rather than vertically, and are oriented NE-SW parallel to major structural lineaments. [ABSTRACT FROM AUTHOR]

The Río Chico Group in the San Jorge Basin of central Patagonia (Argentina) preserves some of South America's most significant Paleogene records of biotic and climatic change. Three of its constituent formations, the Peñas Coloradas, Las Flores, and Koluel-Kaike, host vertebrate faunas referred to the "Carodnia faunal zone," the Itaboraian South American Land Mammal Age (SALMA), and the Riochican SALMA. However, the precise absolute ages of these units, and thus their associated faunas and paleoclimate records, are poorly resolved. Herein, we report new paleomagnetic and geochronologic results from these formations in south-central Chubut Province, Argentina. U-Pb dating of four volcanic ashes, using both laser ablation-multicollector-inductively coupled plasma-mass spectrometry and high-resolution chemical abrasion-isotope dilution-thermal ionization mass spectrometry, indicates ages of igneous crystallization of 51.403 ± 0.037 (0.045) [0.071] Ma for a level within the middle Las Flores Formation and 46.714 ± 0.012 (0.026) [0.057] Ma, 44.579 ± 0.013 (0.026) [0.054] Ma, and 42.856 ± 0.017 (0.027) [0.054] Ma for levels in the lower, middle, and upper Koluel-Kaike Formation, respectively. Combining these with previous isotopic ages in our new magnetostratigraphic framework, we correlate the Peñas Coloradas Formation to chrons C27n-26r (ca. 62.5 to ca. 61.6 Ma; late Danian) and the section from the middle Las Flores to the uppermost Koluel-Kaike to chrons C23n to C19r (ca. 51.4-42.2 Ma; mid Ypresian-late Lutetian). We combine these data with other recently published chronostratigraphic results from Paleogene units in Patagonia to better constrain the ages of noteworthy Paleogene plant and mammal fossil sites in Patagonia and to develop a revised temporal calibration of the Las Flores, Vacan, and "Sapoan" faunas. [ABSTRACT FROM AUTHOR]

The Palaeogene lithostratigraphic units of the Swiss Helvetic Alps have been revised and in parts newly defined in order to harmonise the existing nomenclature. The resulting new classification scheme of the Helvetic Palaeogene includes (1) the basal Siderolithic Group, (2) the entire nummulite succession of Euthal Formation, Bürgen Formation, Klimsenhorn Formation, Wildstrubel Formation, Niederhorn Formation, and Sanetsch Formation, (3) the Stad Formation, (4) the Muot-da-Rubi Formation, (5) the North Helvetic Flysch Group, as well as (6) South Helvetic and Ultrahelvetic (to ?North Penninic) flysch formations. The new classification further aims at simplifying the often very confusing nomenclature and the multitude of local names. [ABSTRACT FROM AUTHOR]

In this paper, the type, vertical evolution, and distribution pattern of sedimentary facies of the Paleogene Dainan Formation in the Gaoyou Depression of the North Jiangsu Basin are studied in detail. Results show that fan delta, delta, nearshore subaqueous fan, and lacustrine facies developed during the Dainan Formation period and their distribution pattern was mainly controlled by tectonics and paleogeography. The fan delta and nearshore subaqueous fan facies predominantly occur in the southern steep slope region where fault-induced subsidence is thought to have created substantial accommodation, whereas the delta facies are distributed on the northern gentle slope which is thought to have experienced less subsidence. Finally, the lacustrine facies is shown to have developed in the center of the depression, as well as on the flanks of the fan delta, delta, and nearshore subaqueous fan facies. Vertically, the Dainan Formation represents an integrated transgressive-regressive cycle, with the E d being the transgressive sequence and the E d being the regressive sequence. This distribution model of sedimentary facies plays an important role in predicting favorable reservoir belts for the Dainan Formation in the Gaoyou Depression and similar areas. In the Gaoyou Depression, sandstones of the subaqueous distributary channels in the fan delta and the subaqueous branch channels in the delta are characterized by physical properties favorable for reservoir formation. [ABSTRACT FROM AUTHOR]

Although stemmed crinoids are well-known from modern oceans, the post-Palaeozoic Articulata represent a slender ‘twig’ that survived the demise of the many other clades forming a ‘bush’ of taxa that failed to survive the end-Permian mass extinction. Thus, although many aspects of form and ecology of extant stemmed crinoids can help explain the functional morphology and niche differentiation of Palaeozoic taxa, there are few close analogues among living members of the group. Most Palaeozoic crinoids have morphological features with no modern counterpart. This is particularly true of the stem – both column and attachment structure – which had a great variation of form, far wider than is recognized from the post-Palaeozoic. Primitive recumbent crinoids typically have a homeomorphic proxistele, which may also have been a feature of upright crinoids with only a weakly rheophilic habit. Primitive columns with broad, circular axial canals may be ‘hold overs’ from ancestral Hohlwurzeln (‘hollow roots’). This broad space may have been filled by perihaemal fluid, but it also may have included other, more ‘nutritious’ tissues attractive to predators and/or scavengers. Ordovician crinoid columnals had a greater range of symmetries than at any other time during the history of the group; many went extinct during or at the end of the period. Cyclic and pentagonal symmetry in the stems of extant crinoids may be due to the functional requirements of the crown. Attachment structures have a surprisingly poor fossil record, but it may be that some Palaeozoic crinoids were unattached as adults, yet retaining, at least in part, an erect attitude. [ABSTRACT FROM AUTHOR]

The Oligocene sedimentary succession in the eastern North Sea is revised and re-interpreted by applying new state-of-the-art reflection seismic data integrated with new bio- and Sr-stratigraphy data from three key wells in the study area. The Oligocene succession in the eastern North Sea is divided into four transgressive–regressive (T-R) sequences, characterized by non-accretional and/or aggradational transgressive systems tracts and prograding regressive systems tracts. Detailed studies of three wells, including biostratigraphy and Sr analysis, constrain the age relationships between the T-R sequences. Internal clinoform geometry indicates that the sediments were sourced from the present southern Norwegian mainland to the north of the depositional area. The direction of progradation shifted from being SE-directed in the earliest Rupelian (early Oligocene) to S- and SW-directed during Chattian time (late Oligocene). Rapid basin subsidence is indicated by the development of non-accretionary transgressive systems tracts, with subsequent progradation into water depths of hundreds of metres. The creation of accommodation space was out of phase relative to eustatic sea-level changes, and mainly controlled by regional-scale differential vertical movements where uplift and exposure of landmasses of the hinterland (southern Norway) occurred concurrently with basin subsidence. Halokinesis had an intra-basinal influence on the main sediment transport direction, but probably did not contribute much in creation of accommodation space. [ABSTRACT FROM AUTHOR]

The configuration and evolution of subduction zones in the Eastern Mediterranean region in Cretaceous time accommodating Africa–Europe convergence remain poorly quantitatively reconstructed, owing to a lack of kinematic constraints. A recent palaeomagnetic study suggested that the triangular Central Anatolian Crystalline Complex (CACC) consists of three blocks that once formed an ~N–S elongated continental body, underthrusted below ophiolites in Late Cretaceous time. After extensional exhumation and upon Palaeogene collision of the CACC with the Pontides of the southern Eurasian margin, the CACC broke into three fragments that rotated and converged relative to each other. Here, we date the extension and contraction history of the boundary between two of the rotating massifs of the CACC by studying the Upper Cretaceous–Palaeogene Ayhan–Büyükkışla basin. We report an40Ar/39Ar age of an andesite at the base of the sequence to show that the deposition started in an E–W extensional basin around 72.11 ± 1.46. The basin developed contemporaneously with regional exhumation of the CACC metamorphics. The lower basin sedimentary rocks were unconformably covered by mid-Eocene limestones and redbeds, followed by intense folding and thrust faulting. Two balanced cross-sections in the study area yield a minimum of 17–27 km of post-mid-Eocene ~N–S shortening. We thus demonstrate the Cenozoic compressional nature of the Kırşehir–Niğde-Hırkadağ block boundary and show that the extensional exhumation of the CACC predates collision-related contraction. A plate kinematic scenario is required to explain these observations that involves two Late Cretaceous–Palaeogene subduction zones to the north and south of the CACC, for which we show a possible plate boundary configuration. [ABSTRACT FROM PUBLISHER]

The Hualapai Plateau in northwest Arizona, the location of the western Grand Canyon, contains an unusually lengthy Tertiary stratigraphic record dominated by fluvial deposition and extending from at least late Paleocene through late Miocene time. The thickest and oldest Tertiary sections are best exposed in a system of partially re-exhumed Laramide paleocanyons. The Paleogene drainage system was locally disrupted and ponded by Laramide monoclines. In pre- Oligocene time, extensive alluvial fans spread southward from the Shivwits Plateau scarp across the current location of the modern Colorado River gorge to the northern margin of the Laramide drainage system at Hindu Canyon. Locally derived, fluvial Buck and Doe Conglomerate subsequently filled the disrupted Paleogene channels, spilled out over the local interfluves, and formed an extensive aggradational surface of low relief by late Oligocene time. Early Miocene volcanism filled in much of the relict Laramide relief. Erosional recession of the adjacent Shivwits Plateau escarpment shifted the northern Hualapai Plateau margin 8 km northeastward after the Laramide drainage episode and before the incision by the modern Colorado River. Partially exhumed tributaries to the Hindu Canyon paleochannel and associated sedimentary deposits bordering the southern edge of the Grand Canyon gorge demonstrate that local surface runoff flowed south, away from the modern Grand Canyon location, during early Paleogene time. Headwardly eroding Colorado River tributaries exhumed, captured, and reversed the flow of these tributaries to the Laramide canyon, beginning in late Miocene or Pliocene time. The geomorphic and stratigraphic records show no evidence of, and provide no space for, incision of a Late Cretaceous- Paleogene ancestral precursor to the modern Colorado River gorge. Instead, all the field evidence clearly supports a late Miocene- Pliocene origin for integration of the western Grand Canyon on the central Hualapai Plateau with the upper Colorado River. [ABSTRACT FROM AUTHOR]

The Paleogene and Neogene oil and gas in the western Qaidam basin have a regular distribution in three concentric zones from the edge to the center of the basin. Natural gas mainly occurs in the inner zone, and the gas-oil ratio of the northern area of the basin is significantly higher than that of the southern area. Large amounts of carbon isotope data of natural gas, plotted in X-shaped and comprehensive identification diagrams for the southern area and northern area, respectively, were used to identify the types of natural gas. The large-scale distribution of natural gas is highly consistent with the Ro values of major source rocks, but is poorly correlated with the type of organic matter. This indicates that the main controlling factor of natural gas distribution is organic matter maturity, and the kerogen types act as the basis for the formation of different types of natural gas. Paleouplifts and squeezed anticlines near hydrocarbon generation depression centers, which are major natural gas-rich regions, control the migration directions of natural gas, while hydrocarbon migration pathways and fault systems connecting gas sources are the most important factors for natural gas reservoir formation in the inner basin. Therefore, favorable zones for natural gas distribution can be predicted on the basis of the distribution of thermal evolution and the gas generation intensity of major source rocks as well as the structural map. The Shizigou-Youshashan-Yingdong-Dawusi, Youquanzi -Kaitemilike - Youdunzi, and Xiaoliangshan - Nanyishan - Dafengshan structural belts are favorable zones for natural gas accumulation. This study has important theoretical and practical significance for future natural gas exploration. [ABSTRACT FROM AUTHOR]

Gypsum-salt rocks and coccolith calcareous shale are widely deposited in the lower part of the Paleogene Shahejie Formation in the Dongying Sag, Shandong Province. The gypsum-salt rock is believed to be formed during the earlier deposition in salt lake, while the overlying coccolith shale in saline lake with relatively low salinity. By comparing the lake environment and lacustrine microbial communities between ancient and recent lakes, cyanobacteria are regarded as the main representative of productivity during the formation of gypsum-salt strata series, with the annual productivity of 1500-2000 gC m yr. Based on the research of ultramicrofossils in the calcareous shale, coccolith is considered as the main contributor to the productivity during the formation of calcareous shale. On the basis of statistic data of sedimentary rates, shale laminations, and coccolith fossils in each lamination, the quantitative value of productivity is calculated, with the annual productivity of 2250-3810 gC m yr (averagely 3120 gC m yr). Statistic data of large amount of pyrite framboids indicate that the lower water column was persistently in sulfidic or anoxic conditions during the deposition of gypsum-salt strata series, but it changed to be dysoxic when the coccolith calcareous shale was deposited. Both of these water conditions are favorable for the preservation of organic matter. It is estimated that the organic carbon burial efficiency of the Lower Paleogene salt lakes and saline lakes of Dongying Depression is about 10%-15%, which is calculated and analyzed using the multi-parameter geobiological model. [ABSTRACT FROM AUTHOR]

Deciphering the driving mechanisms of Earth system processes, including the climate dynamics expressed as paleoceanographic events, requires a complete, continuous, and high-resolution stratigraphy that is very accurately dated. In this study, a robust astronomically calibrated age model was constructed for the middle Eocene to early Oligocene interval (31-43Ma) in order to permit more detailed study of the exceptional climatic events that occurred during this time, including the middle Eocene climate optimum and the Eocene-Oligocene transition. A goal of this effort is to accurately date the middle Eocene to early Oligocene composite section cored during the Pacific Equatorial Age Transect (PEAT, IODP Exp. 320/321). The stratigraphic framework for the new timescale is based on the identification of the stable long eccentricity cycle in published and new high-resolution records encompassing bulk and benthic stable isotope, calibrated XRF core scanning, and magnetostratigraphic data from ODP Sites 171B-1052, 189-1172, 199- 1218, and 207-1260 as well as IODP Sites 320-U1333, and 320-U1334 spanning magnetic polarity Chrons C12n to C20n. Subsequently orbital tuning of the records to the La2011 orbital solution was conducted. The resulting new timescale revises and refines the existing orbitally tuned age model and the geomagnetic polarity timescale from 31 to 43 Ma. The newly defined absolute age for the Eocene- Oligocene boundary validates the astronomical tuned age of 33.89Ma identified at the Massignano, Italy, global stratotype section and point. The compilation of geochemical records of climate-controlled variability in sedimentation through the middle-to-late Eocene and early Oligocene demonstrates strong power in the eccentricity band that is readily tuned to the latest astronomical solution. Obliquity driven cyclicity is only apparent during 2.4myr eccentricity cycle minima around 35.5, 38.3, and 40.1 Ma. [ABSTRACT FROM AUTHOR]

Abstract: Low-temperature thermochronology data have been acquired from outcrop samples from the southeastern edge of the Paris Basin (Morvan). They provide indications about the former sedimentary cover, its denudation and about inversion tectonics in the Paris Basin. Apatite fission-track data acquired on Variscan granites and Triassic sandstones reveal that the basement was subjected to temperatures of about 70±10°C during the Late Cretaceous. We suggest that the peak temperature was generated by an Upper Cretaceous sedimentary cover of low thermal-conductivity chalk. Additional stratigraphic, sedimentological, paleogeographic, paleoweathering, and continental paleosurface data support the reconstruction of this chalk paleocover and of its erosion. This former blanketing sequence was removed during the Early Paleogene regional inversion episode which affected the southern edge of the Basin intensively and was related to far-field compression between Europe and Africa. This study shows that (i) for the SE border of the intracontinental Paris Basin, kilometer-scale vertical deformation occurred, (ii) the sedimentary sequences of the Paris Basin covered considerably larger areas than the present contours of the sediment fill, (iii) paleoweathering and erosion processes later removed the sedimentary cover rather quickly (<10My) due to inversion tectonics. [Copyright &y& Elsevier]

In order to describe the internal deformation of the northeast part of the Shan-Thai Block resulting from the penetration of the Indian plate into Asia, a paleomagnetic study was carried out on the Cretaceous and Paleogene strata in the southern part of the Simao Terrane. High-temperature magnetic components with unblocking temperatures around 680°C were isolated and positive fold test shows its primary nature of magnetization. The tilt corrected site-mean directions of the Lower Cretaceous and Upper Cretaceous from the Menglun area are Ds =46.2°, Is =45.9°, k=11.0, α95 =10.6° and Ds =33.2°, Is =30.9°, k=68.4, α95 =8.2°, respectively. The site-mean directions of the Upper Cretaceous and Lower Paleogene for the Mengban area are Ds =50.5°, Is =31.0°, k=207.6, α95 =6.4° and Ds =43.5°, Is =23.0°, k=26.1, a95 =13.4°, respectively. The results of the Lower Cretaceous and Upper Paleogene from the Mengla area are Ds =46.9°, Is =42.2°, k=27.3, α95 =7.7° and Ds =41.8°, Is =23.8°, k=38.9°, a95 =5.8°, respectively. In comparison with previous paleomagnetic data of the Simao Terrane, the rotational deformation can be divided into four stages. The Cretaceous and Paleocene sediments of the Simao Terrane experienced intensive folding before the early Oligocene. During the early Oligocene to early Miocene, the Shan-Thai and Indochina Blocks experienced southeastward extrusion with ~20° clockwise rotation relative to the South China Block. During the middle to late Miocene, the Shan-Thai Blocks experienced more 15° clockwise rotation. Since the late Miocene, the activity of strike-slip faults surrounding the Simao Terrane enhanced the internal differential rotations of the Terrane. These deformation processes finally resulted in a complex internal deformation of the Simao Terrane. [ABSTRACT FROM AUTHOR]

Abstract: This study of the hypabyssal kimberlite with particularly fresh olivine from the Palaeogene Koala pipe (Ekati cluster, Slave craton, Canada) is focused on reconstruction of the kimberlite parental melt. The Koala kimberlite sample is a typical ultramafic rock (archetypal or Group-I kimberlite) containing large abundance of forsteritic olivine set in a carbonate-rich matrix. The euhedral olivine-II shows significant zoning in terms of forsterite content and trace elements. Only the rims of olivine-II are considered to be magmatic — they are uniform in terms of Fo (91.5±0.2mol%) and host primary crystal (apatite, Cr-spinel) and melt inclusions. The magmatic spinel phenocrysts are strongly zoned from titanian magnesian chromite to pleonaste, with the cores having the same composition as spinel inclusions in olivine. The primary and pseudo-secondary melt inclusions in both magmatic Cr-spinel and olivine comprise a complex assemblage of daughter phases, dominated by carbonate minerals (dolomite, eitelite (Na2Mg(CO3)2), shortite Na2Ca2(CO3)3, nyerereite Na2Ca(CO3)2, zemkorite (Na,K)2Ca(CO3)2, and fairchildite (K2Ca(CO3)2)). In addition to the dominant carbonates, the melt inclusions contain phosphates, chlorides and sulphates (bradleyite (Na3Mg(PO4)(CO3), halite, sylvite, aphthitalite (Na0.25 K0.75)2SO4)), but the silicate component is represented by tetraferriphlogopite only. The melt inclusions in olivine studied in heating experiments show immiscibility of two carbonate liquids on heating and cooling, and homogenise at low temperature<700°C. The liquid immiscibility texture is also characteristic of the calcitic groundmass, and represented by irregularly shaped calcite segregations and near-spherical globules. The calcite in the globules is unusually enriched in Na2O, SrO and BaO (in wt.%, 0.37–0.65, 1.17–2.40, 2.37–4.18, respectively). Such compositions are compared to secondary calcite replacing nyerereite and shortite in the natrocarbonatite lavas of the modern Oldoinyo Lengai volcano. The results on mineralogy, composition and homogenisation temperature of melt inclusions and the groundmass of the Koala kimberlite imply that the parental kimberlite liquid was a Si-poor Ca–Mg carbonate, enriched in alkali elements, lithophile trace elements, phosphorus, chlorine and sulphur. [Copyright &y& Elsevier]

Abstract: Most of the 16 currently recognized astrapothere genera are well known through numerous specimens preserving at least almost complete dentition. One of the exceptions is the enigmatic genus Isolophodon Roth, 1903, based on very scant and fragmentary materials from Paleogene levels of central Patagonia. This taxon was ruled out from almost all taxonomic lists, although its validity has not been discussed by subsequent authors. We herein re-describe and discuss the taxonomic status of the species of Isolophodon. The type species, I. cingulosus Roth, 1903, is characterized by having lower cheek teeth with a much reduced hypoflexid, resembling derived uruguaytheriines, but lower-crowned and with three lower premolars, as in the species of Astraponotus Ameghino, 1901. This is the only astrapothere nominal species attributable to the Tinguirirican South American Land Mammal Age (SALMA, Early Oligocene). Isolophodon aplanatus Roth, 1903 (Casamayoran and Mustersan SALMAs, middle Late Eocene) has proportionally more elongated lower molars and a less developed paraflexid than the type species. Isolophodon would represent an early diverging lineage of astrapotheriids, in which some dental features evolved convergently with the more derived uruguaytheriines. Additionally, we describe other fragmentary but very significant specimens from Paleogene localities in central Patagonia (Argentina) attributable to the following taxa: cf. Scaglia kraglievichorum (Barrancan? subage), based on a partial upper molar nearly 60% larger than the type of Scaglia kraglievichorum Simpson, 1957; Astrapotheriidae gen. et sp. 1 (Barrancan? Subage, Middle Eocene), based on an isolated upper molar larger than any other Eocene astrapothere; Astrapotheriidae gen. et sp. 2, based on five isolated upper cheek teeth from “La Cantera” (Gran Barranca, Early Oligocene), characterized by a large, isolated hypocone and accessory cusps on P3-P4. These taxa enlarge the known diversity of Paleogene astrapotheres and document novel evolutionary patterns for these mammals. [Copyright &y& Elsevier]

Abstract: We compare Late Maastrichtian siliciclastic sandstone in northeastern Mexico with those representing the Cretaceous–Paleogene (K–Pg) boundary to reveal differences in provenance and depositional conditions between background sedimentation and K–Pg sand. Lithology and compositional variations are presented for the deep-water Burgos Basin and the shallow-water La Popa Basin. The Late Maastrichtian sandstones in the Burgos Basin have sharp lower contacts, contain abundant trace fossils and are separated by meter-thick marl layers. They represent sporadic mass flows from coastal areas separated by long phases of hemipelagic sedimentation. The K–Pg sandstone layers are amalgamated, contain thin marl intercalations only in the uppermost part and trace fossils are present in the top sandstone layer only. Also this succession represents mass-flow deposits, but the sand may have been deposited during a very short period. The La Popa Basin sandstones represent deltaic sedimentation interrupted by submarine channel deposition during the K–Pg boundary transition with abundant rip-up clasts and bioclasts at the base. The sandstones of the Burgos Basin are quartz to akosic wacke dominated by quartz (>90%) and some feldspar (<10%) in calcite cement and matrix. Lithic fragments are rare and dominated by chert and bioclasts. Ultra-stable heavy minerals (ZTR=50–80) and plutonic quartz grains (ca. 40% of the total quartz population) are particularly common in the K–Pg sandstones. In the Maastrichtian sandstones, metamorphic heavy minerals, particularly chlorite, clinozoisite, and tourmaline (20–50% of the heavy mineral population), and metamorphic quartz (80% of the quartz population) have higher abundances. The La Popa sandstones are subarkose to arkose and arkosic wacke and have a high abundance of feldspar (15–30%) and lithic fragments (5–20%), mainly of siltstone and carbonate. The sandstones from both basins have chemical compositions typical for recycling (Zr/Sc=12–27 and 17–140 in the Burgos and La Popa Basin, respectively) and influences from mafic source rocks (Th/Sc=0.4–1.1; Ti/Nb=350–510). Therefore we suggest that all studied successions share a common provenance with transport of recycled orogenic metasedimentary components from northwestern Mexico and magmatic arc material from western Mexico. Subsequently, longshore currents mixed the detritus with limestone clasts derived from the tectonically active Sierra Madre Oriental, which probably is the cause for compositional changes in the sandstones. Due to increased sediment input from western Mexico at the K–Pg boundary, provenance changes cannot be related to the Chicxulub impact. [Copyright &y& Elsevier]

Abstract: Tectonics is extremely important to the depositional record preserved in continental sedimentary basins, affecting both the formation of sequence boundaries and the filling characters of these sequences. This comprehensive analysis of Paleogene depositional patterns and the sequence compositional types in the Banqiao sub-basin of the Bohai Basin, Eastern China, shows that episodic rifting and differential activity on major faults have resulted in the formation of various types of transfer zones and structural slope-break zones, both of which played significant roles in the formation and distribution of sequence types and depositional systems. Transfer zones controlled the positions of sediment source areas, entry points for sediment into the basin and, as a result, the development of depositional systems. Structural slope-break zones are paleotopographic features where there is a sharp basinward increase in depositional slope that is controlled by fault geometry. The location of structural slope-break zones influenced the distribution of depositional systems and sand bodies. Areas where the structural slope-break zone overlapped with transfer zones were sites for major drainage systems and the preferred positions of delta fans and turbidite fans. The areas controlled by the transfer zone and the structural slope-break zone with the distribution of sand bodies are the favorable place for the prospecting of subtle stratigraphic traps in the Banqiao sub-basin. [Copyright &y& Elsevier]

Abstract: The Paleogene to Neogene San Julián and Monte León formations underlie the central and eastern parts of the Austral Basin (Patagonia, Argentina), and represent coastal plain to shallow shelf systems within a retroarc foreland basin east of the Andes. The formations are characterized by prominent occurrences of thin (<1 m) densely compacted fossil concentrations, including the large oyster Crassostrea? hatcheri. Formation ages have been problematic given macrofaunal provincialism effectively precluding precise extrabasinal correlations. A Sr-isotope chronostratigraphy based on fossil shell calcite from oysters, pectinids and brachiopods is presented for a regional NE–SW-oriented transect extending ∼200 km along strike of the Austral Basin. The Paleogene–Neogene boundary (∼23 Ma) may occur within the uppermost San Julián Formation (22.68 Ma, with a range between 22.22 and 23.22 Ma), coincident with a prominent glauconitic interval, or in a meteorically altered erosional paleosurface that caps this formation and may correlate with an eustatic sea level fall coincident with the global boundary. The younger Monte León Formation is entirely of early Neogene (Aquitanian to early Burdigalian) age, with ages of 22.12 Ma (21.68–22.58) at the base to 17.91 Ma (17.51–18.29) at the top. The proposed new chronostratigraphic framework forms a foundation for future differentiation of local, regional, and global sedimentary patterns in the Austral Basin during the Paleogene/Neogene transition; in particular, with contemporaneous basins and tectonic blocks across the southern polar region, such as in Australia, New Zealand, and Antarctica. [Copyright &y& Elsevier]

Abstract: Four facies associations representing, from sea to land, namely (1) tidal bars in distal delta front, (2) proximal tidal bar complexes, (3) tidal channel and tidal flat deposits, and (4) multi-episodic, tide-influenced channels, resulted from the bio- and lithofacies analysis of the siliciclastic Cretaceous/Paleogene Lefipán Formation (Patagonia, Argentina). Lithofacies analysis indicates the existence of coarse-grained, tide-dominated deltas fed with sediments of braided rivers, a rare type of delta that was developed at the western margin of a large marine embayment during the Cretaceous/Paleogene (K/Pg) boundary interval. Differences in taxonomic composition and ecological structure of the biofacies revealed variations in environmental factors, with salinity exerting the principal influence on biofacies. Salinity varied from oligohaline and mesohaline in the deltaic, high-stress environments, as typified by monospecific bivalve assemblages, to diverse and trophically more complex associations, indicating more normal marine and stable conditions. Thus, the biofacies provided an independent tool to check the results of the lithofacies analysis in complex transitional environments. A comparison of Maastrichtian and Danian faunas suggests that the K/Pg boundary event disrupted the stable Maastrichtian communities via the extinction of dominating species, leading to less diverse but more varied Danian assemblages. A shift in trophic structure to increased percentages of deposit-feeders in the Danian was not a direct consequence of impact-related environmental perturbations at the boundary in the studied onshore environment. This contrasts with previous studies of siliciclastic offshore settings, where such a shift in trophic composition was interpreted as the consequence of a productivity crisis at the boundary. [Copyright &y& Elsevier]

The synorogenic basins of central Cuba formed in a collision-related system. A tectono-stratigraphic analysis of these basins allows us to distinguish different structural styles along the Central Cuban Orogenic Belt. We recognize three distinct structural domains: (1) the Escambray Metamorphic Complex, (2) the Axial Zone, and (3) the Northern Deformation Belt. The structural evolution of the Escambray Metamorphic Complex includes a latest Cretaceous compressional phase followed by a Palaeogene extensional phase. Contraction created an antiformal stack in a subduction environment, and extension produced exhumation in an intra-arc setting. The Axial Zone was strongly deformed and shortened from the latest Cretaceous to Eocene. Compression occurred in an initial phase and subsequent transpressive deformation took place in the middle Eocene. The Northern Deformation Belt consists of a thin-skinned thrust fault system formed during the Palaeocene to middle Eocene; folding and faulting occurred in a piggyback sequence with tectonic transport towards the NNE. In the Central Cuban Orogenic Belt, some major SW–NE structures are coeval with the Cuban NW–SE striking folds and thrusts, and form tectonic corridors and/or transfer faults that facilitated strain-partitioning regime attending the collision. The shortening direction rotated clockwise during deformation from SSW–NNE to WSW–ENE. The synchronicity of compression in the north with extension in the south is consistent with the opening of the Yucatan Basin; the evolution from compression–extension to transpression is in keeping with the increase in obliquity in the collision between the Caribbean and North American plates. [ABSTRACT FROM AUTHOR]

The Alpine chain exposed in the Western Mediterranean area represents a front several kilometres in width, dismembered by more recent tectonics and by opening of the Tyrrhenian Basin. In most exposures of this mountain belt, relics of older metamorphic rocks occur. The deformational sequence of events may be revealed by the recognition of metamorphic records associated with different structures. Within a tract of the Alpine front cropping out in the Peloritani Mountains (NE Sicily), we distinguished two metamorphic complexes characterized by different tectonometamorphic histories. Their present tectonic juxtaposition is a cataclastic thrust linked to the recent Africa-verging Sicilian–Maghrebian fold-and-thrust belt. The Lower Complex is characterized by Hercynian metamorphism (P > 0.2 GPa and T ≈ 350°C) exclusively. It essentially consists of very low-grade metapelites and metavolcanic rocks overlain by an unmetamorphosed sedimentary cover. The Upper Complex, comprising different tectonic slices, consists of medium- to high-grade Hercynian metamorphic rocks (P = 0.3–0.8 GPa and T up to 650°C) with Alpine metamorphic overprint (T > 250°C) affecting also the Mesozoic–Cenozoic cover. Lithotypes, structures, and inferred P–T conditions of investigated rocks suggest the existence of an Alpine accretionary wedge during the Cretaceous deformational collision. Within the Upper Complex, a polyphase Palaeogene mylonitic horizon involving rocks belonging to different tectonic slices fully preserves the tectonometamorphic evolution. For this reason, we focused our attention on these sheared rocks in order to reconstruct the entire tectonic history of this geologically complex area. Our new basic model allows the complex structure of the nappe-pile edifice of the Peloritani Mountains to be simplified, casting new light on the tectonic evolution of this key sector of the southern Calabrian-Peloritani Orogen. [ABSTRACT FROM AUTHOR]

Serpentinite emplacement mechanisms along convergent plate boundaries are complex and not well understood. This investigation combined structural and stratigraphic data from serpentinite in Puerto Rico to suggest an emplacement mechanism along the North American-Caribbean plate boundary. Northward-dipping thrust faults and foliations along the southern margins of the Monte del Estado and Río Guanajibo serpentinite bodies in southwestern Puerto Rico indicate southwestward thrust movement of serpentinite. Structural analysis of faults, folds, and foliation recorded within the serpentinite bodies and analysis of contact relationships with volcano-sedimentary rocks lead to the interpretation that thrust movements record contractional deformations occurring during the Maastrichtian-Paleocene and late Eocene-early Oligocene intervals. The conclusion that serpentinite has been most recently emplaced above thrust faults during transpression between the Caribbean-North America plates is in contrast to the earlier hypothesis that serpentinite was emplaced in response to diapirism. Late Eocene transpression reactivated older faults and also displaced the serpentinite. Although the timing of the serpentinite emplacement in southwestern Puerto Rico is similar to emplacement events in Cuba and Hispaniola, there are differences in the origin, mechanism, and direction of emplacement of the serpentinite masses. The heterogeneity in the serpentinite emplacement mechanism and transport direction evokes reconsideration of the deformation history along the Caribbean-North American plate boundary. [ABSTRACT FROM AUTHOR]

Abstract: The division and analysis of the genetic types of slope breaks will be helpful in studying the enrichment regularity of hydrocarbon reservoirs because the enrichment of hydrocarbon reservoirs is closely related to the shelf-slope break types in continental lake basins or sags in China. This paper analyses the types of basin margins in Qikou Sag by assessing the sag boundary fault characteristics and spatial combination patterns using high-resolution three-dimensional seismic data, well logs and other data. Basin margins were divided into four types: steep slope fault belts, multi-level step-fault belts, steep slope step-fault belts and slope break flexure belts. Different types of depositional systems developed near the different basin margins, and correspondingly, four types of sequence stratigraphic patterns were developed. According to the study of trap types that occur adjacent to the different slope-break zones, fault-controlled lithologic traps were the predominant trap type in fault-controlled slope break zones, and lithologic traps occurred in the sag centre distant from the boundary faults. Along the slope break flexure belt, different types of traps developed in different slope break levels; stratigraphic unconformity traps occurred within the first slope break level, and stratigraphic–lithologic traps and up-dip pinchout lithologic traps were found in the second slope break level. So the deployment of future exploration should be conducted at different levels in Qikou Sag. [Copyright &y& Elsevier]

A palynological investigation of marine uppermost Maastrichtian to lower Paleocene strata in two New Zealand sections, mid-Waipara River and Fairfield Quarry, revealed well-preserved dinoflagellate cyst assemblages including three new dinoflagellate cyst species. A formal description of the new dinoflagellate cyst species are presented here. Furthermore a variation of Carpatella cornuta, named C. aff. cornuta is discussed. In the mid-Waipara River section the ranges of the new species Adnatosphaeridium regulatum sp. nov., Alterbidinium mcmillanii sp. nov. and Canningia fairfieldensis sp. nov. are calibrated directly with other microfossil groups including foraminifera, radiolarian and terrestrially derived spores and pollen. The last occurrence of Adnatosphaeridium regulatum sp. nov. is within the lowermost Danian foraminiferal zone Pα and this event is recorded in sections located in several New Zealand sedimentary basins. Alterbidinium mcmillanii sp. nov. has a very restricted range within the latest Maastrichtian to basal Danian with its last occurrence within foraminferal zone P0. Canningia fairfieldensis sp. nov. has so far only been recorded in lower Danian strata and occurs within the foraminiferal zones Pα to P1c and radiolarian zones RP1?–RP2. A morphological variation of Carpatella cornuta named Carpatella aff. cornuta is only observed in a very narrow interval across the Cretaceous–Paleogene (K-Pg) boundary in the mid-Waipara River section. Based on comparison with other New Zealand K-Pg boundary sections, A. mcmillanii sp. nov. and C. fairfieldensis sp. nov. seem to have a palaeoenvironmental affinity for shallow marine to inner neritic depositional environments. [ABSTRACT FROM AUTHOR]

Grimsdalea magnaclavata was first described by Germeraad, Hopping and Muller from Miocene and Pliocene deposits of northern South America, specifically Colombia and Venezuela. The specific epithet, ‘magnaclavata', was selected by the authors to draw attention to the distinctive clavate processes of the pollen. A revised taxonomic description is supported by illustrations of fossil specimens from outcrop and well sections that show the range in morphology not previously recorded in the original description; the key difference is the wide variation in process morphology from clavae to clavae with interspersed echinae. Based on the new observations of the pollen morphology we conclude that the records from Cretaceous and Paleogene sediments in North and West Africa are invalid. G. magnaclavata is clearly restricted to northern South America from the Miocene to Pleistocene. The parent plant of G. magnaclavata probably grew in upper coastal plain or around swamps, commonly associated with shrubs and herbaceous savannah plants. The botanical affinity of G. magnaclavata has always been in question. Based on a review of pollen from several palm genera presently extant in northern South America we consider that the nearest living relatives, if indeed G. magnaclavata is an ancient palm, are the genera Mauritia and Mauritiella. The basis for this conclusion is the distinctive foot layer morphology of the processes in the fossil and the modern examples. [ABSTRACT FROM AUTHOR]

Postcranial characters of South American native ungulates are important in order to analyze their relationships in the actual therian taxonomy, particularly to test their alleged afrotherian affinities. In this sense, the most primitive and oldest South American eutherians are represented by two endemic groups of "condylarths", the Kollpaniinae and Didolodontidae. These forms, characterized by lower crowned bunodont dentition, have never been found in direct association with their postcranial remains. Even though, several skeletal elements have been assigned to some of forms, following different assumptions and criteria. Two distinct astragalar remains (MACN-CA 10737 and AMNH 117457) have been referred to the genus Didolodus, one of the most common didolodontids from early and middle Eocene Patagonian outcrops. Here we describe in detail and illustrate these materials. A critical analysis is made of several regression equation models which have been used in other cases to associate by size isolated postcranial elements to taxa defined by teeth. A new model was formulated based on 19 modern bunodont mammals with directly associated skeletons in order to test the accuracy of the regression equations. Although the results of the equation models failed to accuratly assigned the isolated astragali to any of the Didolodus species, they can be used as a good tool to disprove the association hypothesis. A broad comparison with astragalar remains of South American native ungulates indicates that MACN-CA 10737 has notoungulate affinities, in contrast AMNH 117457 resembles the astragali assigned to didolodontids from São José de Itaboraí, Brazil, according to the models criticized here. The similitude is particularly due to the broad development of the cotylar fossa, a character proposed as an afrotherian synapomorphy, but probably developed independently in different groups. Improvement in knowledge regarding postcranial characters of the earliest South American native ungulates is necessary not only due to its importance in improving accuracy of phylogenetic relationships, but also for the inferences made on paleobiological features. [ABSTRACT FROM AUTHOR]

Abstract: A high-resolution palynological study carried out across the Cretaceous/Palaeogene (K/Pg) boundary in two sections (Knappengraben and Gamsbach) of the Gosau Group near Gams (Gams Basin, Northern Calcareous Alps, Austria) has identified over 178 dinoflagellate species and subspecies from 89 rock samples. In most samples, the dinocysts are moderately well to well preserved, but associated with reworked material. Some well-known marker species around the K/Pg boundary, such as Carpatella cornuta, Spongodinium delitiense, Trithyrodinium evittii, Palynodinium grallator, Manumiella druggii, Cordosphaeridium fibrospinosum, Membranilarnacia? tenella, Senoniasphaera inornata, Damassadinium californicum, and Dinogymnium acuminatum have been recorded from the samples studied. In addition to these, Trabeculidinium quinquetrum, Lejeunecysta izerzenensis, Batiacasphaera rifensis, Impagidinium maghribensis and Cyclonophelium compactum represent local markers. A Spongodinium delitiense acme is recorded in both sections above the K/Pg boundary and is interpreted to indicate a transient cooling event of oceanic surface waters. The stratigraphic distribution of the dinocyst species indicates that they were not seriously affected by the mass extinction event at the K/Pg boundary, but their diversity slightly increases above it. The composition of the assemblages, however, changes drastically. Six dinocyst assemblages and four palynofacies assemblages were identified by means of cluster analysis. Their distribution does not show any regular pattern. The increase of phytoclasts in the Danian clearly indicates enhanced terrestrially derived input into the basin. The palynological and sedimentological differences between the two sections can be explained by small scale local lateral variations. [Copyright &y& Elsevier]

Abstract: Shell remains of a new species of Polysternon (Chelonii, Bothremydidae) have been recently discovered in the new locality of Barranc de Torrebilles (late Maastrichtian, southern Pyrenees). The specimens studied share features with Polysternon provinciale and ‘Foxemys’mechinorum and reveal some exclusive characters such as: neural 1 with concave lateral margins; first marginal scutes trapezoidal; posterior margin of the second marginal very close to the suture between peripheral 1 and costal 1; anterior margin of the first vertebral rounded; and anterior lobe of the plastron emarginated. The shell morphology, taphonomy and sedimentology suggest that the proposed species, Polysternon isonae, was fully adapted to freshwater and inhabited fluvial meandering river environments. The Barranc de Torrebilles site is located in the uppermost part of the Maastrichtian succession in the Tremp Basin, only 35 m beneath the unit that contains the Cretaceous/Palaeogene boundary. Thus, P. isonae may be among the last representatives of this genus before its extinction at the end of the Cretaceous Period, according to the current knowledge of the fossil record. [Copyright &y& Elsevier]

Abstract: The Central Sumatra Basin (CSB) is a prolific oil producing basin in Indonesia where a single source rock has been identified, the Brown Shale Formation of the Paleogene Pematang Group. Despite the presence of a single source rock, the oils in the Central Sumatra Basin and particularly in the Aman Trough, exhibit variable molecular and isotopic compositions, previously described as reflective of lateral facies variations within the source rock. Analyses by gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS) and gas chromatography–isotope ratio mass spectrometry (GC–IRMS) of 15 oil samples from the Aman Trough allowed identification of vertical and lateral facies changes within the Brown Shale Formation as well as paleoproductivity and paleoclimatic changes that took place during deposition of this prolific source rock. The molecular and isotopic data indicate the source rock for these oils was deposited in a fresh to brackish water stratified lake in which CO2 limiting conditions prevailed. Compound specific isotopic data also indicate that changes in paleoclimatic conditions, possibly associated with the Eocene–Oligocene paleoclimatic transition, had an effect on the geochemical composition of the source rock in the Aman Trough. [Copyright &y& Elsevier]

Plesiadapidae are a family of Paleogene mammals thought to have phylogenetic affinities with modern Primates. We describe previously unpublished dentitions and the first skull and isolated petrosals of the plesiadapid Pronothodectes gaoi, collected from middle Tiffanian localities of the Paskapoo Formation in Alberta. Other species of Pronothodectes, traditionally considered the most basal members of the Plesiadapidae, occur at earlier, Torrejonian horizons in Montana, Wyoming, and Alberta. Classification of P. gaoi as a species of Pronothodectes has proved controversial; accordingly, we use the newly available samples and the more extensively preserved specimens to re-evaluate the generic affinities of this species. Included in our study are comparisons with craniodental material known for other plesiadapids and plesiadapiforms. Cladistic analysis of craniodental characters is used to assess the hypothesis that P. gaoi and other species in this genus are basal members of the Plesiadapidae. The new dental evidence confirms that P. gaoi lacks derived character states of other plesiadapids except for a variably present fissuring of the m3 hypoconulid. Moreover, several aspects of the cranium seem to be more primitive in P. gaoi (i.e., more like nonplesiadapid plesiadapiforms) than in later occurring plesiadapids, such as Plesiadapis tricuspidens and Plesiadapis cookei. Cladistic analysis of craniodental morphology supports a basal position of P. gaoi among species of Plesiadapidae, with the exception of other species of Pronothodectes. The basicranium of P. gaoi preserves a laterally placed bony canal for the internal carotid neurovascular system, suggesting that this was the ancestral condition for the family. Am J Phys Anthropol, 2012. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The La Popa Basin in north-eastern Mexico features outstanding, continuous three-dimensional exposures of the Cretaceous-Palaeogene boundary event deposit in shallow shelf environments pierced by salt stocks. In the area to the south-east of the El Papalote diapir, the Cretaceous-Palaeogene deposit consists of two superimposed sedimentary units and erosively overlies upper Maastrichtian sand-siltstones with soft-sediment deformation and liquefaction structures. The basal unit 1 is an up to 8 m thick chaotic, carbonate-rich bed that discontinuously fills incised gutters and channels. Besides abundant silicic and carbonate ejecta spherules from the Chicxulub impact, unit 1 includes large sandstone boulders and abundant shallow-water debris (for example, mud clasts, algae, bivalve shells, gastropod shells and vertebrate remains). Unit 1 is conformably overlain by unit 2. Distal to the diapir, unit 2 consists of a centimetre to decimetre-thick conglomeratic, coarse bioclast and spherule-bearing sandstone bed. Closer to the diapir, unit 2 becomes a metre-thick series of four to eight conglomeratic to fine-grained graded sandstone beds rich in shell debris and ejecta spherules. Unit 2 is conformably overlain by structureless to parallel laminated sandstone beds that may mark the return to the pre-event depositional regime. The sedimentary characteristics of the Cretaceous-Palaeogene deposit, including its erosive base, its sheet-like geometry, the presence of multiple, graded beds, evidence for upper flow regime conditions and the absence of bioturbation, support an origin by a short-term multiphase depositional event. The occurrence of soft-sediment deformation structures (for example, liquefaction) below the Cretaceous-Palaeogene deposit suggests that earthquakes were the first to occur at La Popa. Then, shelf collapse and strong backflow from the first tsunami waves may have triggered erosion and deposition by violent ejecta-rich hyperconcentrated density flows (unit 1). Subsequently, a series of concentrated density flows resulting from tsunami backwash surges may have deposited the multiple-graded bedding structures of unit 2. The specific depositional sequence and the Fe-Mg-rich as well as Si-K-rich composition of the ejecta spherules both provide a critical link to the well-known deep marine Cretaceous-Palaeogene boundary sites in the adjacent Burgos basin in north-eastern Mexico. Moreover, the pulse-like input of Chicxulub ejecta material at the base of the event deposit allows for correlation with other Cretaceous-Palaeogene boundary sites in the Gulf of Mexico and the Atlantic, as well as in Central and Northern America. The presence of diverse dinosaur and mosasur bones and teeth in the event deposit is the first observation of such remains together with Chicxulub ejecta material. These findings indicate that dinosaurs lived in the area during the latest Maastrichtian and suggest that the tsunami waves not only eroded deltas and estuaries but the coastal plain as well. [ABSTRACT FROM AUTHOR]

Abstract: The Latest Danian Event (LDE) has been recognized on the southern Tethyan margin (Egypt; Tunisia), and in the Atlantic (Zumaia, Spain) and Pacific Oceans (ODP Site 1209). Based on a supraregional carbon isotope excursion, and a negative shift in oxygen isotopes in the Pacific it has been suggested that the LDE is an early Paleogene transient warming event. So far the environmental effects of the LDE have been observed in few sections and details on its impact and duration are scarce. We present a quantitative study of benthic foraminiferal assemblages retrieved from five sections along a depth transect on the Paleocene southern Tethyan shelf (Nile Basin, Egypt) to assess paleoenvironmental change during the LDE. The lithologic sequences and foraminiferal assemblages indicate that the onset of the LDE is related to widespread shelf dysoxia. The organic-rich laminated marls of lower LDE bed I contain levels devoid of benthic foraminifera. During the later stage of the LDE (dark-gray shales of bed II) the shelf is repopulated by a Neoeponides duwi benthic assemblage, occurring in all sections, initiating a gradual restoration of normal-marine shelf environments. Q-mode and R-mode correspondence analysis assist in the interpretation of the N. duwi assemblage, which is related to disturbed conditions at the sea floor following oxygen depletion and increased organic loading. The sharp lithologic boundary at the base of the LDE suggests that the event coincides with a rapid transgression following a sea-level fall, with an estimated amplitude of ~50m or less. Comparison with the Dan-C2 and ELPE/MPBE, two proposed transient warming episodes preceding and postdating the LDE, shows that the three Paleocene events have several characteristics in common. However, the duration of the LDE (~200kyr) exceeds the estimated duration of the other events, and a sea-level cycle is only reported from the LDE. [Copyright &y& Elsevier]

In recent years, deep water areas have become popular exploration fields because of their abundant hydrocarbon resource potential. There are only relatively poor planar seismic profiles and no wells for deepwater areas of the Lingshui Formation in the Qiongdongnan Basin. A lot of faults developed and strata are fragmented due to high temperatures and high pressure, and this has resulted in dim sequence boundaries. Based on seismic data of the deepwater area and well data of bordering shallow water areas, Lingshui Formation was divided into four third class sequences; namely SI, SII, SIII and SIV, and the three-dimensional isochronous stratigraphic framework of the Lingshui Formation in the studied area was shaped. Based mainly on seismic attributes such as amplitude, continuity, internal structure and external shape, six typical seismic facies were identified, including mat-shaped, filling, wedge-shaped, foreset, moundy-shaped and lenticular-shaped, and a seismic facies distribution map was subsequently drawn. With studies on wells of bordering shallow water areas, regional sedimentary characteristics, and isopach map as references, sedimentary planar distribution features were analyzed. The deepwater area of the Lingshui Formation has mainly developed littoral and shallow sea. Sandstone bodies of fan delta, braided river delta, slope fan, basin floor fan, and turbidite fan are at an interdigitate junction to marine hydrocarbon source rocks and thus are favorable prospecting targets. [ABSTRACT FROM AUTHOR]

Abstract: Based on the formation mechanism of water-soluble gas, combined with the geological conditions of the Palaeogene Huizhou Sag, the resource potential and utilization of water-soluble gas in the Palaeogene source rock in the Huizhou Sag are analyzed quantitatively using grid calculation method. The Palaeogene Wenchang and Enping formations of the Huizhou Sag are major source rocks that generate significant quantities of gas and the sandstone reservoirs are weakly overpressured to overpressured on the whole. Calculated according to the thickness, sandstone content, porosity, water saturation, strata pressure, temperature, and mineralization of the Wenchang and Enping Formations, the resource volume of water-soluble gas is about 1 791.49×108 m3 and 2 688.5×108 m3, 1.19 and 3.46 times that of the conventional gas, respectively. If the strata pressure is relieved to normal pressure, the degasification volume is 80.84×108 m3 and 97.04×108 m3. The water-soluble gas is an unconventional resource with great potential, and can provide substantial gas source for conventional pools through degasification. [Copyright &y& Elsevier]

Abstract: The Qikou Sag is a complex Cenozoic faulted basin at the center of the Bohai Bay Basin. The Paleogene sediments in the basin show a maximum thickness of 11,000m in Paleogene representing intense crustal extension. The sag has a typical dish-like structure in the upper part, with the central domain represented by a deep half graben, and surrounded by different types of gentle slopes and sub-sags linked with the basin-margin uplifts. The inner structure of the sag is jointly controlled by the basin-margin extensional faults, intrabasinal extensional tectonics and transfer tectonics. The sag is divided into four different extensional tectonic domains by the basement fault along the coastline, the Haihe–Xingang Fault and the Qidong Fault. These sub-sags are in turn controlled by different detachment systems. The listric Cangdong and Hangu faults mark the major boundary faults controlling the extensional structure of the basin. The structure and tectonics of the Qikou Sag provide a direct record of the late stages of rifting and destruction of the North China Craton. The Mesozoic basement structures of the sag determine the tectonic styles in different sub-sags. The complete inversion of the structures in Mesozoic profoundly influenced the development and evolution of the basin during Paleogene. We identify three main stages in the tectonic evolution of the Qikou: the Oligocene faulting stage, the Miocene–Pliocene thermal subsidence stage and the Pleistocene–Quaternary depression stage. In the Oligocene, fault activities and the basin architecture were mainly controlled by the listric boundary fault system of the basin and the secondary fault system in the hanging wall under the detachment and extension in the upper crust. Since Miocene, the boundary fault of the basin underwent weak extension. The upwelling of the upper mantle and the formation of corresponding shallow depressions contributed to the evolution and tectonic architecture of the Qikou Sag. [Copyright &y& Elsevier]