Abstract:A pterosaur-bird track assemblage from a sandstone-siltstone-mudstone sequence of the Lower Cretaceous Tugulu Group of Xinjiang comprises the first pterosaur track record from this province and the largest specimen thus far known from China. The pterosaur tracks are assigned to the ichnogenus Pteraichnus based on the triangular overall-shape, the four elongate digit traces and the robust manual digit trace III. Supposed trackmakers were dsungaripterid pterodactyloids whose skeletal remains are well known from the Tugulu Group. The bird tracks that occur on the same surface, are those of typical shorebirds, known from different other localities in southeast Asia. The congruence with Koreanaornis dodsoni described from the same stratigraphic level justifies an assignment to this ichnospecies. This is a further evidence of the co-occurrence of pterosaurs and birds in a typical lakeshore environment with possible seasonal alteration of water supply and aerial exposure indicated by wave ripples, mudcracks and repeated cycles of coarse to fine sediment. Pterosaurs and birds frequented the shoreline and may have fed also on the numerous invertebrates such as the Scoyenia tracemaker that left abundant burrows.

Abstract:Two new species of wasps belonging to the family Ephialtitidae, Praeproapocritus flexus sp. nov. and Proapocritus parallelus sp. nov., from the Middle Jurassic Jiulongshan Formation of southeastern Inner Mongolia, China, are described and illustrated. Praeproapocritus vulgates Rasnitsyn & Zhang, 2010 and six species of Proapocritus, P. densipediculus, P. sculptus, P. longantennatus, P. formosus, P. atropus, and P. elegans, all described by Rasnitsyn and Zhang in 2010, are first record from the Middle Jurassic of China. These two new findings supplement the morphological understanding of ephialtitids in the Middle Jurassic of China and broaden the diversity of ephialtitids in their by-gone ecosystems.

Abstract:One new genus with a new fossil species, Declinimodus setulosus gen. et sp. nov. which was found in the Middle Jurassic Jiulongshan Formation of Daohugou, Inner Mongolia, China, are described and illustrated. The new species is assigned to the Rhyacophilidae according to button-shaped of the 2nd segment of maxillary palp, and the forked R1 (in the forewing, located near apex). These new discovery are the earliest fossil records of Rhyacophilidae, which providing important evident for the study of the origin and early evolution of Trichoptera.

Abstract:Two new tetrapod burrow casts from the Naobaogou Formation (Middle or Late Permian) of Nei Mongol, China are described. It marks the first pre-Cenozoic tetrapod burrow from China, and one of the earliest records of tetrapod burrows. Comparison to other Permian and Triassic burrows suggests that these burrows were created by tetrapod slightly smaller than Lystrosaurus. Deduced from the morphology and sizes of two burrows and known tetrapods of the Naobaogou Formation, the burrow should be the production of a therapsid, most likely a dicynodon. These burrows indicate a seasonal climate and this area was semiarid or arid during that time.

Abstract:Twenty-seven moss specimens collected from the Guangfayong section (Early Miocene, 22.1 Ma) of the Weichang District, North China were investigated in the present study. Based on the morphological and anatomical features of gametophytes, all specimens were found to belong to three species: Leptodictyum riparium, Drepanocladus subtrichophyllus sp. nov., and Amblystegium varium, all of which belong to the family Amblystegiaceae. The microhabitats and living environments of fossil mosses were also investigated based on comparison with living mosses. The results suggest that these mosses grew primarily at the edges of rivers, streams, and lakes and favored being submerged in streams or lakes in the Weichang District in the Early Miocene.

Abstract:Outcrop and microscopic studies have been applied in this research paper in order to find out the Asmari Formation depositional sequences in the Shajabil Anticline section located at the north of the Izeh Zone, Zagros Basin, Iran. Five depositional sequences were identified based on 11 facies types (bioclast Nummulitidae Lepidocyclinidae packstone, bioclast perforate foraminifera Nephrolepidina Miogypsinoides wackestone-packstone, bioclast perforate foraminifera Corallinacea wackestone-packstone, bioclast echinoid Neorotalia Brachiopoda wackestone-packstone, coral floatstone-rudstone, bioclast Corallinacea imperforate foraminifera wackestone-packstone, bioclast imperforate foraminifera Archaias wackestone-packstone, bioclast imperforate foraminifera Dendritina wackestone-packstone-grainstone, bioclast imperforate foraminifera Borelis wackestone-packstone and very fine sandy mudstone) corresponding to the tidal flat, restricted and semi-restricted lagoon and open marine environments of an inner and middle shelf areas.

Abstract:A new section at Jebel Gorraa, in northern Tunisia, contains the Paleocene–Eocene transition interval. Sample analysis of the section delivers abundant and diverse microfauna of planktonic and benthic foraminifera. Biostratigraphically, the Acarinina sibaiyaensis index-species is identified for the first time in this region, which allows us to specify the location of the Paleocene–Eocene boundary as well as the first E1 biozone of the lower Eocene. Samples from this biozone contain calcitic tests poorly preserved with an enrichment of iron oxide signifying a period of upheaval in local marine environments linked to the global warming of the Paleocene–Eocene Thermal Maximum (PETM), the marker for the P/E boundary.

Abstract:The Qingbaikouan System is the lowest unit of the Neoproterozoic Erathem in Chinese stratigraphic succession, and it now provides a precise geochronological framework and geological time scale for mapping and stratal correlation in China. However, a sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon age date (1368±12 Ma) obtained from a bentonite in the Qingbaikouan Xiamaling Formation indicates that it belongs to the Mesoproterozoic Erathem instead. This change is a milestone in understanding the Precambrian Stratigraphic Time Scale in China, and it has had great influence on Precambrian correlations in Asia. Otherwise, a large amount of geochronological work has been done in the “Jiangnan Orogen Belt” of South China, and new isotopic data have redefined the traditional recognition of metamorphosed Mesoproterozoic strata from the Sibao orogeny to the Neoproterozoic Erathem. Based on SHRIMP zircon U-Pb age data, the authors regard the Sibao orogeny (equal to the Wuling orogeny) as a movement at ca 820 Ma, meaning that the Sibao orogeny was not equivalent to the Grenvillian orogeny. Finally, we report here the first SHRIMP U-Pb age of the boundary between the top of the Qingbaikouan Gongdong Formation (786.8±5.6 Ma) and the bottom of the Chang’an (diamictite) Formation (778.4±5.2 Ma), which is the age of the lowest diamictite of the Nanhuan System in China.

Abstract:The early stage of Sichuan Basin formation was controlled by the convergence of three major Chinese continental blocks during the Indosinian orogeny that include South China, North China, and Qiangtang blocks. Although the Late Triassic Xujiahe Formation is assumed to represent the commencement of continental deposition in the Sichuan Basin, little research is available on the details of this particular stratum. Sequence stratigraphic analysis reveals that the Xujiahe Formation comprises four third-order depositional sequences. Moreover, two tectono–sedimentary evolution stages, deposition and denudation, have been identified. Typical wedge-shaped geometry revealed in a cross section of the southern Sichuan Basin normal to the Longmen Shan fold–thrust belt is displayed for the entire Xujiahe Formation. The depositional extent did not cover the Luzhou paleohigh during the LST1 to LST2 (LST, TST and HST mean lowstand, transgressive and highstand systems tracts, 1, 2, 3 and 4 represent depositional sequence 1, 2, 3 and 4), deltaic and fluvial systems fed sediments from the Longmen Shan belt, Luzhou paleohigh, Hannan dome, and Daba Shan paleohigh into a foreland basin with a centrally located lake. The forebulge of the western Sichuan foreland basin was located southeast of the Luzhou paleohigh after LST2. According to the principle of nonmarine sequence stratigraphy and the lithology of the Xujiahe Formation, four thrusting events in the Longmen Shan fold–thrust belt were distinguished, corresponding to the basal boundaries of sequences 1, 2, 3, and 4. The northern Sichuan Basin was tilted after the deposition of sequence 3, inducing intensive erosion of sequences 3 and 4, and formation of wedge-shaped deposition geometry in sequence 4 from south to north. The tilting probably resulted from small-scale subduction and exhumation of the western South China block during the South and North China block collision.

Abstract:Altyn Tagh fault controls the deformation characteristics of the northern margin of the Qinghai-Tibet Plateau. The sinistral slip rate of the eastern segment of the fault reduces gradually where the reduction transforms into the deformation within Qilian Mountain, forming a series of thrust faults and strike-slip faults. Among them, the Yema River-Daxue Mountain fault is one of the important structural transform faults in the study area. Based on the differences of the geometrical characteristics and activities, the fault is divided into four segments, the Yema River segment, the Shibandun segment, the Liushapo segment and the Baishitougou segment, among which the former three are Holocene active faults, and the Baishitougou segment belongs to late Pleistocene fault. The excavated trenches imply a total of 6 paleoearthquake events, and at least 4 events have occurred during Holocene, whose occurrence times are 8300±700 yr BP, 6605±140 yr BP, 4540±350 yr BP, 2098±47 yr BP, respectively. The recurrence interval is 2600±600 yr BP that is close to the lapsed time of the last one, 2098±47 yr BP, which suggests that the Yema River-Daxue Mountain fault is in a high risk of major earthquakes in the future. The vertical coseismic displacements of the four Holocene paleoearthquake events are 100 cm, 42 cm, 40 cm and 50 cm, respectively, the horizontal coseismic displacements are 5 m, 4.5–5.5 m, 5–8 m and 4–5.5 m, separately, and then the reference magnitude of the paleoearthquake events is conjectured to be M7.6±0.1.

Abstract:The Boziguoer A-type granitoids in Baicheng County, Xinjiang, belong to the northern margin of the Tarim platform as well as the neighboring EW-oriented alkaline intrusive rocks. The rocks comprise an aegirine or arfvedsonite quartz alkali feldspar syenite, an aegirine or arfvedsonite alkali feldspar granite, and a biotite alkali feldspar syenite. The major rock-forming minerals are albite, K-feldspar, quartz, arfvedsonite, aegirine, and siderophyllite. The accessory minerals are mainly zircon, pyrochlore, thorite, fluorite, monazite, bastnaesite, xenotime, and astrophyllite. The chemical composition of the alkaline granitoids show that SiO2 varies from 64.55% to 72.29% with a mean value of 67.32%, Na2O+K2O is high (9.85%–11.87%) with a mean of 11.14%, K2O is 2.39%–5.47% (mean = 4.73%), the K2O/Na2O ratios are 0.31–0.96, Al2O3 ranges from 12.58% to 15.44%, and total FeOT is between 2.35% and 5.65%. CaO, MgO, MnO, and TiO2 are low. The REE content is high and the total SREE is (263–1219) ppm (mean = 776 ppm), showing LREE enrichment and HREE depletion with strong negative Eu anomalies. In addition, the chondrite-normalized REE patterns of the alkaline granitoids belong to the “seagull” pattern of the right-type. The Zr content is (113–1246) ppm (mean = 594 ppm), Zr+Nb+Ce+Y is between (478–2203) ppm with a mean of 1362 ppm. Furthermore, the alkaline granitoids have high HFSE (Ga, Nb, Ta, Zr, and Hf) content and low LILE (Ba, K, and Sr) content. The Nb/Ta ratio varies from 7.23 to 32.59 (mean = 16.59) and the Zr/Hf ratio is 16.69–58.04 (mean = 36.80). The zircons are depleted in LREE and enriched in HREE. The chondrite-normalized REE patterns of the zircons are of the “seagull” pattern of the left-inclined type with strong negative Eu anomaly and without a Ce anomaly. The Boziguoer A-type granitoids share similar features with A1-type granites. The average temperature of the granitic magma was estimated at 832–839°C. The Boziguoer A-type granitoids show crust–mantle mixing and may have formed in an anorogenic intraplate tectonic setting under high-temperature, anhydrous, and low oxygen fugacity conditions.

Abstract:The wedge shaped Dong Tso ophiolitic block is distributed near the transition point from the western to the middle sub–belt of the Bangong–Nujiang suture zone. The ophiolite is characterized by well–developed cumulate rocks that are mainly composed of cumulate and massive gabbros. In the cumulate gabbros, the adcumulate amphiboles are distributed extensively around the plagioclase and residual pyroxene grains; hence, the rocks are named adcumulate amphibole–gabbro. In this study, the formation age of the ophiolite has been estimated to be 166 ± 4 million years (Ma) by the sensitive high–resolution ion microprobe (SHRIMP) II U–Pb isotopic analysis of the zircons from the adcumulate amphibole–gabbro; the 40Ar/39Ar plateau age was estimated to be 148.19 ± 1.53 Ma, which should represent the emplacement time of the ophiolite, by isotopic dating of the pure amphibole mineral from the amphibole–schist. Two different suits of volcanic lavas have been recognized in this work. The purple colored pillow basalts have high TiO2 and P2O5 contents, and are rich in light rare earth elements (LREEs), large–ion lithospheric elements (LILEs) and high–field–strength elements (HFSEs), the characteristics that are the typical of the oceanic island basalt (OIB). On the other hand, other massive basaltic andesites of celadon color are poor in MgO; rich in Fe2O3, LREEs, LILEs, and HFSEs; and especially characterized by negative Nb and Ta anomalies, the properties that establish the andesites as continental arc volcanic rocks. It is concluded that hotspots had developed in the old Dong Tso basin, the oceanic basin that had been developing from middle Jurassic (166 Ma) or even before and emplaced northward in late Jurassic (about 148 Ma).

Abstract:In the vicinity of Konya (Turkey), mafic, micro-porphyritic sub-volcanic rocks intrude into the Mesozoic units, which represents the only example of such a rock type in the region. 40Ar/39Ar dating of two whole rock samples from the sub-volcanics gave ages of 13.72±0.13 and 12.40±0.11 Ma, suggesting temporal association to the Late Miocene-Pliocene high-K calc-alkaline volcanism in the region. The mineral chemistry and geochemical data permit us to classify the rocks as “minette” lamprophyres. They include diopside and phlogopite phenocrysts in a microcrystalline groundmass composed of sanidine, phlogopite, diopside and titano-magnetite. Segregation and ocelli-like globular structures occur commonly in the samples. In terms of major elements, the lamprophyres are calc-alkaline, and potassic to ultrapotassic rocks. All the lamprophyres display strong enrichments in LILE (Rb, Ba, K, Sr), radiogenic elements (Th, U) and LREE (La, Ce) and prominent negative Nb, Ta, and Ti anomalies on primordial mantle-normalized trace element diagrams. Geochemical data suggest that the lamprophyres and high-K calc-alkaline rocks in the region derived from a subduction-modified lithospheric mantle source affected by different metasomatic events. Lamprophyric magmatism sourced phlogopite-bearing veins generated by sediment-related metasomatism via subduction, but high-K calc-alkaline magmas are possibly derived from a mantle source affected by fluid-rich metasomatism.

Abstract:The bauxites in central Guizhou are hosted by the Lower Carboniferous Jiujialu Formation. Geochemistrial characteristics of the Lindai bauxite deposit indicate that the underlying Shilengshui Formation dolomite is the precursor rock of mineral resources. Weathering simulation experiments show that Si is most likely to migrate with groundwater, the migration rate of which is several magnitude higher than Al and Fe under nature conditions (pH=3–9). The neutral and acid non-reducing condition is the most conducive to the Al rich and Si removal, while the acid reducing conditions is the most conducive to the Al rich and Fe removal. In the process of bauxite formation, coal beds overlying the Al-bearing rock series or other rock formation rich in organic materials can produce acid reducing groundwater, which are important for the bauxite formation. Finally, propose the metallogenic model of the bauxite in central Guizhou Province and put forward three new words which are “original bauxite material”, “bauxite material” and “original bauxite”.

Abstract:Based on the CCD images, IIM data and DEM data of China’s lunar exploration project (Chang’E-I) and related processed and analytic results, an integrated study of regional geology of Sinus Iridum and its adjacent area was conducted, and a series of relevant researches and analyses were carried out, including analysis of impact craters and their extrusive and accumulative materials, division of stratigraphic and tectonic units and classification of rock types, integrated analysis of chronology and lunar evolution history. In consideration of crater’s shape features，quantity and preserving status of filling materials, the lunar impact craters can be divided into 7 types and 11 sub-types, and the accumulative materials of craters are divided into 6 types and 9 accumulative groups. According to the content and distribution of TiO2 and image characteristics, the basalts are divided into high-TiO2, medium-TiO2 and low-TiO2 basalts. Discussion was made on division of tectonic units and evolution features in the study area. The geological map of the Sinus Iridum Quadrangle (LQ-4) at a scale of 1:2.5 M was preliminarily compiled with the ArcGIS system, and the spatial database of the map was established. Related technical specification, procedure and method for lunar geological mapping have been worked out, so as to lay a foundation for the forthcoming geological mapping of the global Moon in China by using the data of Chang’E-II and also for comprehensive study and geological mapping of other celestial bodies in the future.

Abstract:The Jinshan gold deposit is located in the Northeast Jiangxi province, South China, which related to the ductile shear zone. It contains two ore types, i.e. the alteration-type ore and the gold-bearing quartz vein ore. Rb-Sr age dating is applied to both gold-bearing pyrite in the alteration-type ore and fluid inclusion in the gold-bearing quartz vein to make clear the time of the gold mineralization of the Jinshan deposit. Analytical results of this study yielded that the age of the alteration-type ore bodies is about 838±110Ma, with an initial 87Sr/86Sr value of 0.7045±0.0020. However, the age of the gold-bearing quartz vein-type ore is about 379±49Ma, and the initial 87Sr/86Sr is 0.7138±0.0011. Based on the age data from this work and many previous studies, the authors consider that the Jinshan gold deposit is a product of multi-staged mineralization, which may include the Jinninian, Caledonian, Hercynian, and Yanshanian Periods. Among them, the Jinninian Period and the Hercynian Period might be the two most important ore-forming periods for Jinshan deposit. The Jinninian Period is the main stage for the formation of alteration-type ore bodies, while the Hercynian Period is the major time for ore bodies of gold-bearing quartz vein type. The initial values of the 87Sr/86Sr from this study, as well as the previous isotope and trace element studies, indicate that the ore-forming materials mainly derived from the metamorphic wall rocks, and the ore-forming fluids mainly originated from the deep metamorphic water.

Abstract:According to the compositions of the underground gasfield brines in the west of Sichuan Basin, the phase equilibria in the ternary systems KBr–K2B4O7–H2O and KCl–K2B4O7–H2O at 373 K were studied using the isothermal dissolution equilibrium method. The solubilities of salts and the densities of saturated solutions in these ternary systems were determined. Using the experimental data, phase diagrams and density-composition diagrams were constructed. The two phase diagrams were simple co-saturation type, each having an invariant point, two univariant curves and two crystallization regions. The equilibrium solid phases in the ternary system KBr–K2B4O7–H2O are potassium bromide (KBr) and potassium tetraborate tetrahydrate (K2B4O7·4H2O), and those in the ternary system KCl–K2B4O7–H2O are potassium chloride (KCl) and potassium tetraborate tetrahydrate (K2B4O7·4H2O). Comparisons of the phase diagrams of the two systems at different temperatures show that there is no change in the crystallization phases, but there are changes in the size of the crystallization regions. As temperature increases, the solubility of K2B4O7·4H2O increases rapidly, so the crystallization field of K2B4O7·4H2O becomes smaller.

Abstract:Following the 2008 Wenchuan M8 earthquake, the seismic risk of the northeastern section of the Longmenshan fault zone and the adjacent Hanzhong basin has become an issue that receives much concern. It is facing, however, the problem of a lack of sufficient data because of little previous work in these regions. The northeastern section of the Longmenshan fault zone includes three major faults: the Qingchuan fault, Chaba-Lin’ansi fault, and Liangshan south margin fault, with the Hanzhong basin at the northern end. This paper presents investigations of the geometry, motion nature, and activity ages of these three faults, and reveals that they are strike slip with normal faulting, with latest activity in the Late Pleistocene. It implies that this section of the Longmenshan fault zone has been in an extensional setting, probably associated with the influence of the Hanzhong basin. Through analysis of the tectonic relationship between the Longmenshan fault zone and the Hanzhong basin, this work verifies that the Qingchuan fault played an important role in the evolution of the Hanzhong basin, and further studies the evolution model of this basin. Finally, with consideration of the tectonic setting of the Longmenshan fault zone and the Hanzhong basin as well as seismicity of surrounding areas, this work suggests that this region has no tectonic conditions for great earthquakes and only potential strong events in the future.

Abstract:To reveal the geochemical characters of water coproduced with coalbed gas and shallow groundwater, water samples were collected from 12 wells of coalbed methane and 7 wells of shallow groundwater. The pH, CODMn, fCO2, total dissolved solids (TDS), total hardness, and concentrations of metasilicic acid, sodium and kalium, calcium ion, magnesium ion, ammonium iron, bicarbonate ion, carbonate, chloride, sulfate ion, nitrate ion, fluoride, lithium, zinc, nickel, manganese, iron, boron, barium, etc. of the samples were measured. Research results showed the following: (1) Concentrations of TDS, chloride, fluoride, sodium and kalium, ammonium, iron, and barium in the water coproduced with coalbed gas exceeded the national standards of China; however, physical, chemical, and biological properties of shallow groundwater could meet the national standard. (2) The water produced from coalbed contained mainly Na–Cl·HCO3, with average TDS of 4588.5 ppm, whereas shallow groundwater contained a mixture of chemicals including Na·Mg·Ca-HCO3·SO4 and Na·Mg-HCO3·SO4, with average TDS of 663.8 ppm. (3) In general, it was observed that bicarbonate and sodium accumulated in a reducing environment and deeper system, while depletion of hydrogen ions and dissolution of sulfate, calcium, and magnesium occurred in a redox environment and shallow system. (4) Sodium and kalium, ammonium, chloride, and bicarbonate ions were the main ions found in the study area.

Abstract:Geochronology of oil-gas accumulation (OGA) is a challenging subject of petroleum geology in multi-cycle superimposed basins. By K-Ar dating of authigenic illite (AI) and fluid inclusion (FI) analysis combined with apatite fission track (AFT) thermal modeling, a case study of constraining the OGA times of the Permian reservoirs in northeast Ordos basin (NOB) has been conducted in this paper. AI dating of the Permian oil-gas-bearing sandstone core-samples shows a wide time domain of 178–108 Ma. The distribution of the AI ages presents 2-stage primary OGA processes in the Permian reservoirs, which developed in the time domains of 175–155 Ma and 145–115 Ma with 2-peak ages of 165 Ma and 130 Ma, respectively. The FI temperature peaks of the samples and their projected ages on the AFT thermal path not only present two groups with a low and a high peak temperatures in ranges of 90–78°C and 125–118°C, respectively corresponding to 2-stage primary OGA processes of 162–153 Ma and 140–128 Ma in the Permian reservoirs, but also appear a medium temperature group with the peak of 98°C in agreement with a secondary OGA process of c.~30 Ma in the Upper Permian reservoirs. The integrated analysis of the AI and FI ages and the tectono-thermal evolution reveals that the Permian reservoirs in the NOB experienced at least 2-stage primary OGA processes of 165–153 Ma and 140–128 Ma in agreement with the subsidence thermal process of the Mid-Early Jurassic and the tectono-thermal event of the Early Cretaceous. Then, the Upper Permian reservoirs further experienced at least 1-stage secondary OGA process of c.~30 Ma in coincidence with a critical tectonic conversion between the slow and the rapid uplift processes from the Late Cretaceous to Neogene.

Abstract:In this study Chengdu Red Earth (CRE) from the Chengdu Plain (CP), Sichuan province, was analyzed for its elemental (major and trace elements) and isotopic (Sm-Nd) geochemistry and compared with Pleistocene loess and paleosol samples from the Chinese Loess Plateau (CLP) in Northern China. The geochemical composition of CRE is similar to north China loess, and also resembles the average UCC. This indicates that CRE, as loess deposits in Northern China, was derived from well-mixed sedimentary protoliths that have undergone numerous upper crustal recycling processes. However, obvious differences in the geochemical characteristics of CRE and the north China loess are also revealed in our results. For chemically stable elements, CRE has higher Ti, Zr, Hf and lower ΣREE, Ba contents in comparison with loess samples from the CLP. Further analysis shows that CRE has higher TiO2/Al2O3, SiO2/Al2O3, Ba/Rb and lower Ce/Yb, Eu/Yb, LaN/YbN and ΣLREE/ΣHREE ratios. In Sm-Nd isotopic geochemistry, Sm and Nd content and the εNd(0) value in CRE are significantly higher than those in north China loess. The higher TiO2 content in CRE coincided with a high background concentration of Ti in the Sichuan Basin and the surrounding regions. The lower ΣREE and higher Sm, Nd, εNd(0) values are related to the wide distribution of basalt in the southwest Sichuan Basin. The elemental and isotopic geochemistry of CRE indicates that eolian materials in the CP predominantly come from the Sichuan Basin and the surrounding regions, which differs from loess deposits in the CLP.

Abstract:Based on the latest submarine topography data of the China 908 Project (China offshore marine environmental comprehensive investigation and assessment), we analyzed the general China offshore submarine topographical characteristics and the factors influencing its development. The submarine topography off the coast of China follows the NW-SE trend of the land topography. The gradient of the submarine topography ranges from 0.2% to 1.6% with an average gradient of about 0.8%. The depth contours run mostly parallel to the coast, and extend out to sea in estuary areas. The submarine topography is dominated by the geological structure, which shows the typical characteristics of two uplifts and two subsidence events from north to south. The geological structure combined with the different sedimentary environments and complex hydrodynamic conditions produced topography that can be characterized by three types: sedimentary basins, compression-uplift, and transition form. In the sedimentary basin and compression-uplift regions, the topographical undulation is small, sediments are fine-grained, and the currents flow in a single direction, leading to bays with sedimentary plains and underwater accumulation slopes, which are of the same tectonic origin. Transition-type topography is characterized by strong undulations and mixed-size sediment particles, terraces and scarps inshore and shelf plains and erosion-deposition landforms offshore. This is a result of incomplete fault block development and repeated transgressions. In the deposition reformation regions (transition form type), the topography has strong undulations, the sediments are coarse, tidal sand ridges are well-developed at terrigenous-supplied estuaries and convergence zones, and the Holocene sediments are thick, transformed by tides, river runoff, and currents.

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