Objective The genetic mechanism and sedimentary filling process of the Dongying Formation sublacustrine fan are unclear in the slope zone of the southeastern part of Bozhong Depression， which restricts the fine study of sublacustrine fan and deployment of well location in the study area， Methods From the perspective of source-sink system and three-dimensional seismic data， we semi-quantitatively analyzed the denude capacity and transportation path of the Bonan low uplift provenance. In addition， we clarified the characteristic sedimentary response and source coupling mechanism of a large-scale sublacustrine fan. We established the sedimentary filling process of a sublacustrine fan and summarized the development mode of a sublacustrine fan. Results （1） the Dong 2 subsequence is in the stage of lake-basin fracture-sink transition， which can be divided into two third-order sequences， in which the sublacustrine fan is developed in the highstand systems tract period of the lower Dong 2 subsequence； （2） during the period of lower Dong 2， the flux of denudation of the eastern section of the Bonan low uplift is larger than that of a sublacustrine fan. The detrital material provided by near provenances in the western part of the Bonan low uplift is unloaded under the depositional break of the slope along seven ancient gullies and five restricted ancient gullies. The coupling of near source supply， transport channel， and sedimentary slope break formed a large contiguous lacustrine fan deposit； and （3） the sedimentary filling process of asublacustrine fan is controlled by the location of restricted paleogeomorphology and the amount of space. Among them the early restricted paleogeomorphic formation can create large accommodating space， the sublacustrine fan sand body is preferentially unloaded. It formed the three major fan deposits， A， B and C. Owing to the spatial restriction of the two sides， the strong hydrodynamic conditions and seismic phases exhibit a chaotic down-cut channel superimposed on the lateral migration， and the formed fans are more sand-rich. With the entry of gravity flow with continuous replenishment in the later stage， the accommodating space gradually decreases， while the gravity flow along the replenishment channel overflows to the center of the open lake basin， forming two fans， D and E. Owing to the energy gradually weakening， the seismic phases have the characteristics of laminar strong-amplitude reflections， with the characteristics of the watercourse being inconspicuous， and the sand-richness is moderate. Late-stage source supply and energy is weak， and localized erosion and modification of seismic relative to early fan bodies exhibits weak amplitude reflections dominated by muddy watercourses. The large lake bottom fan has a spatiotemporal distribution and evolution pattern of early restrictive filling， middle overflow adjustment and late erosion and modification， which constitutes a developmental feature of lateral contiguous and vertical multi-phase superposition. Conclusions The three sectors， A， B， and C， below the first terrace are sand-rich and shallowly buried， with good conditions for oil and gas transportation and aggregation and excellent reservoir-cover combinations. The sweet spot area of sector C sector is large and has been an important target for the exploration of rocky reservoirs in the Bohai Sea in recent years.

Objective The levels of oxygen in shallow waters and the atmosphere during the Mesoproterozoic period （approximately 1.8-1.0 Ga） have raised controversy. Currently， it is widely believed that there may have been fluctuating high and low oxygen levels at that time. However， the spatiotemporal heterogeneity of the ancient planet during this period limits our understanding of the redox state of the ancient oceans， but accumulated evidence tends to indicate dynamic fluctuations in the oxygen content of shallow seas. Methods This study， which focused on the carbonate strata of the Longjiayuan Formation in the Guandaokou Group， western Henan province （oldest age 1.59 Ga）， carried out petrological， elemental geochemical and C and O isotope geochemical analyses， mainly using Ce anomalies δ. Indicators such as δ¹³C and Y/Ho restored the redox state of the shallow sea in the region. Results Microscopically， the formation lithology consisted mainly of relatively pure fine-grained， powdery， and mud crystalline dolomite， with main structures containing different forms of laminated stones and siliceous bands. The main geochemical data indicated overall Th content <0.5 µg/g， Y/Ho > 26， ΣREE <12 µg/g， and Ce/Ce^*， Pr_（N）/Yb_（N） and Y/Ho. There was no significant correlation between ΣREE and Th concentration， indicating that the sample material was not affected by terrestrial debris interference to any great extent. Mn/Sr was generally low （average<6），δ¹⁸O>-10‰， and there was no significant correlation between Ce/Ce^*， Eu/Eu^* and Dy_（N）/Sm_（N）， indicating that the original seawater signal was relatively well preserved during diagenesis. The rare earth element distribution indicated significant negative Ce anomalies （0.53-0.94） and positive Y anomalies in the region around 1.54 Ga， similar to the value for modern seawater rare earth elements. This was accompanied by a significant increase in Y/Ho （mean 64）， followed by δ¹³C， which experienced a significant positive deviation and later recovered to the original level of the Mesoproterozoic era. Conclusions These findings indicated that there may have been a brief oxidation event in the region during the Mesoproterozoic. The range （0.53-0.94） and time （~1.54 Ga） of negative Ce anomalies in the Longjiayuan Formation were reasonably consistent with values in the second and third segments of the Gaogaozhuang Formation， and in the lower part of the Yangzhuang Formation. These indicated that the atmosphere and shallow sea environment in the North China Craton underwent an overall oxygenation process of common amplitude during this period. The negative Ce anomaly and its rapid rebound indicated that the low oxygen state in the shallow sea and atmosphere of the Mesoproterozoic continued to dominate， interspersed with a pulse-type oxygenation process that may have been widespread throughout the North China Craton at that time. This study provided direct evidence of pulse oxygenation events during the Mesoproterozoic， which was useful in determining the redox state of shallow waters during this period， and to explore the impact of oxygen level on the evolution of eukaryotes.

Objective To discuss the high-frequency sequence division and its control on reservoirs in carbonate strata. Methods This study used the Th/U curve in natural gamma ray spectrum logging as the indicator curve. combined with the Fischer diagram and lithological assemblage sequence， high frequency sequence of Ma{}_{\mathrm{5}}^{\mathrm{1}\mathrm{⁃}\mathrm{5}} sub-member of Majiagou Formation was divided quantitatively in the Tao 7 block of the Ordos Basin. Results The research shows that the Th/U value in natural gamma-ray spectroscopy logging can be used as an indirect alternative index of astronomical orbit in carbonate strata. The high-frequency sequence can be effectively divided by quantitative and qualitative analysis methods such as spectrum analysis combined with the Fischer diagram and lithologic lithofacies analysis. The Ma{}_{\mathrm{5}}^{\mathrm{1}\mathrm{⁃}\mathrm{5}} sub-member in the Tao 7 block can be divided into one third-order sequence， six fourth-order sequences， and twenty fifth-order sequences. It is estimated that the average deposition rate of the Ma{}_{\mathrm{5}}^{\mathrm{1}\mathrm{⁃}\mathrm{5}} sub-member is 5.03 cm/kyr， and the deposition time is approximately 2.43 Ma. The gypsum pseudocrystal dolomite， which developed in the upper part of the intertidal zone and in the top of the high-frequency sedimentary cycle with upward shallowing， is the dominant facies belt for reservoir development. Near the high-frequency sequence boundary of the fourth-order sequence is the favorable interval for reservoir development. The early karst caused by frequent changes of sea level was the main driving force for the formation of model pores in the Ma{}_{\mathrm{5}}^{\mathrm{1}\mathrm{⁃}\mathrm{4}} sub-member and laid the foundation for the krast in later supergene stage. Conclusions Quantitative identification and division of high-frequency sequence is important for reservoir prediction in carbonate strata.

Objective The Yuzhou area is the most highly studied Upper Paleozoic coal-bearing strata of the southern part of North China Block， which has abundant sedimentological and stratigraphic paleontological research basis； however， owing to the lack of absolute chronology data， the division of chronostratigraphy， and regional large-scale stratigraphic correlation are affected. Methods In this study， laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS） was applied to date the U-Pb age of detrital zircon of two mudstone samples near the stratigraphic boundary of the Taiyuan Formation-Shanxi Formation and Xiashihezi Formation-Shangshihezi Formation in the Yuzhou area and determine their maximum depositional ages. Results （1） The 40 detrital zircons from the bottom sample of the Shanxi Formation （ZK1006-5） constitute a continuous young component spectrum ranging from 283-343 Ma， with the youngest single zircon age （YSG age） is 283±9.4 Ma. The 18 detrital zircons from the bottom sample of the Shangshihezi Formation （ZK2387-3） constitute a continuous young component spectrum ranging from 257-299 Ma， with the YSG age is 257±6.8 Ma. They represent the maximum deposition age of the sample strata， indicating that the deposition time is no earlier than 283±9.4 Ma and 257±6.8 Ma. （2） The deposition of the Shanxi Formation and Shangshihezi Formation in the Yuzhou area began in Kungurian and Wuchiapingian， respectively， which is consistent with regional biostratigraphic data. （3） The Upper Paleozoic coal-bearing strata of the North China Block have a large span of penetrating rock strata， and the overall performance is characterized by inward penetration of the plate edge gradually through the new characteristics. Conclusions Based on the previous studies on volcanic events in the Late Paleozoic basin of the North China Block， the eastern margin of the basin was found to be strongly active in which the same sedimentary period， and the induced magmatism， tectonic activity， biological succession， and transgression may be related to the formation of the ancient continent of Laurisia land at the same time.

Objective Since 2019， CNPC has conducted exploration on the Upper Cretaceous Donga strata in the Trakes slope of the Termit Basin， Niger. Several wells obtained industrial oil flows， demonstrating good exploration potential. Compared to the Paleogene fluvial-deltaic Sokor1 Formation， the detailed characteristics of the Upper Cretaceous marine sandstones of the Donga Formation have not yet been fully examined. Methods In the present study， based on seismic， wireline， and mud logging data， 53 side wall cores and cutting samples from four wells were analyzed with thin sections， casting thin sections， X-ray diffraction， scanning electron microscopy， gamma-ray spectral logging， etc. Therefore， this study investigated the marine sandstone reservoir characteristics of DS1 member and DS3 member in the Donga Formation and analyzed their controlling factors. Results The results show that the rock type of the DS1 member is mainly fine-medium grained quartz sandstone with high component maturity， whereas the DS3 member is dominated by fine grained lithic quartz sandstone with mass calcareous mineral cement. The reservoir rock quartz grain is sub-round to round with moderate to poor sorting in the Donga Formation， the rock matrix is mainly composed of kaolinite and calcite， and most of quartz grains have point to line contact. Reservoir rock diagenesis have strong compaction and cementation， with common dissolution， and the pores are primarily intergranular with medium to ultra-low porosity and permeability. The high quality reservoirs in the Donga Formation are mainly distributed in the DS1 member， and reservoir physical property improves from west to east in Trakes slope. The analysis results show that the development of marine quartz sandstone in the Donga Formation is controlled by three factors. Firstly， vertical distribution of the sedimentary face and marine quartz sandstone was controlled by sea level changes， which manifested widespread marine distributary channel sandstones in the DS1 member that deposited in the early stage of marine transgression， whereas the DS3 member， in the highest sea level of marine deposit with high salinity， formed high contents of carbonate cement and poor reservoir physical property. Secondly， the stable gentle slope geomorphology in the Late Cretaceous was favorable for the development of marine sand bodies， and the intense strike-slip fault activities in the Paleogene induced the formation of micro-fractures in reservoir rock， which effectively improved the reservoir physical properties. Thirdly， the rigid construction of marine quartz sandstone granules was favorable for the preservation of rock primary pores， and the dissolution of unstable minerals such as feldspar and calcareous minerals improved the pore structure of the reservoir rock. Conclusions The development of a regional cap rock of marine mudstone and shale was conducive to the formation of self-generation and self-preservation reservoir in the Donga Formation. Compared with the lower slope zone of the Trakes slope， marine quartz sandstone has better reservoir physical properties and widespread distribution in the middle and high slope zones closer to the eastern sediment source area and are favorable for further exploration in the Donga Formation.

Objective This study aimed to define the high-quality reservoir development model of the Xu3 member in the source rock stratum， that is， the tight sandstone gas exploration in the Xu3 member of the Xujiahe Formation， Western Sichuan Depression， and provide theoretical guidance. Methods The core， thin section， scanning electron microscope， fluid inclusion， situ stable carbon and oxygen isotopes， porosity， and permeability data were integrated. Based on the basic characteristics of Xu3 member tight sandstone reservoirs in the Western Sichuan Depression and the types of diagenesis， the heterogeneity of the reservoirs and the development model of high-quality reservoirs were analyzed systematically. Results The results show that lithic quartz sandstone and lithic sandstone were the main rock type of the Xu3 member， and the reservoir space was primarily composed of intragranular dissolution pores and fractures， with porosity less than 7% and permeability less than 1×10^-3μm². Therefore， the sandstone reservoirs could be divided into intragranular dissolution pore and fracture- intragranular dissolution pore types. The diagenesis of the Xu3 member sandstones included compaction， cementation， and dissolution and experienced early humic acid， middle organic acid， and late hydrothermal fluids during the evolution process. In addition， two types of vertical sedimentary cycles， sandstone with sandstone and sandstone with mudstone， were identified in the Xu3 member. Conclusions The results indicated that the tight sandstone was altered by the early humic acid and middle organic acid continuously via the intergranular pore throat and fracture and in favour of reservoir formation. However， the late hydrothermal fluid acted solely in the late large scale fracture and had an insignificant effect on reservoir quality. In addition， the high-quality reservoir of the sandstone with the sandstone vertical sedimentary cycle mainly developed in the lower part of the cycle which characterized by relatively coarse-grain， but the high-quality reservoir of the sandstone with mudstone vertical sedimentary cycle mainly developed in the lower part of the cycle with relatively coarse-grain； the upper part of the cycle is adjacent to the mudstone.