Proposed GSSP for the base of Cambrian Stage 9, coinciding with the first appearance of Agnostotes orientalis, at Duibian, Zhejiang, China

Exposed in natural outcrops near the Duibian Village, Jiangshan County, Zhejiang Province, China, the Duibian B section is proposed as the boundary stratotype for the base of an unnamed stage termed provisionally Cambrian Stage 9. The proposed position of the GSSP is 108.12 m above the base of the Huayansi Formation, at a horizon coinciding with the first appearance of the cosmopolitan agnostoid trilobite Agnostotes orientalis. This horizon coincides also with the first appearance of the cosmopoli-tan polym...     

Proposed GSSP for the base of Cambrian Stage 9, coinciding with the first appearance of <Emphasis Type="Italic">Agnostotes orientalis</Emphasis>, at Duibian,Zhejiang, China

Exposed in natural outcrops near the Duibian Village, Jiangshan County, Zhejiang Province, China, the Duibian B section is proposed as the boundary stratotype for the base of an unnamed stage termed provisionally Cambrian Stage 9. The proposed position of the GSSP is 108.12 m above the base of the Huayansi Formation, at a horizon coinciding with the first appearance of the cosmopolitan agnostoid trilobite Agnostotes orientalis. This horizon coincides also with the first appearance of the cosmopolitan polymerid trilobite Irvingella angustilimbata. The section fulfills all the requirements for a GSSP, and the horizon can be constrained not only by the primary stratigraphic marker (A. orientalis) but also with secondary biostratigraphic, chemostratigraphic, and sequence-stratigraphic correlation tools. The first appearance of A. orientalis is one of the most readily recognizable levels in Cambrian, and can be correlated with precision to all paleocontinents. Supported by Chinese Academy of Sciences (Grant No. KZCX2-YW-122), the Ministry of Science and Technology of China (Grant Nos. 2006FY120300, 2006CB806400), National Natural Science Foundation of China (Grant Nos. 40072003, 40023002, 40332018, 40672023, 40602002), and the U.S. National Science Foundation (Grant No. EAR-0106883)     

Conodont evolution and stratotype sign of carboniferous Tournaisian-Visean boundary in South China

Sediment-successive strata of the Carboniferous Tournaisian-Visean period, i.e. Aikuanian-Datangian, are widespread in South China, where it is most possi- ble to establish the GSSP of the T\V boundary. Owing to a global drop of sea-level in the period, when the dropping-range could reach to 150 m[1], sedimentary interruptions, sudden changes of facies and disjunc- tions of organic-evolutionary chains occurred com- monly and cause sharp conflicts on division and cor- relation of the bound…     

Criteria for defining and recognizing the various orders of sequences in outcrop sequence stratigraphy

Sequence stratigraphy which began in the late seventies of the previous century has not only enriched and widened the scope of stratigraphy, but also has been widely used in sedimentary geology, basin analy-sis, exploration of oil and gas, and other fields of ge-ology. In the last two decades and more, sequence stratigraphy, as a new branch of stratigraphical disci-pline, has become a cornerstone of modern stratigra-phy, and has produced more profound influences than all others. The currently …     

Some fundamental problems in outcrop sequence stratigraphy

Some fundamental problems in outcrop sequence stratigraphy are discussed, and the following ideas are obtained: (i) Detailed sedimentary facies analysis and study on stacking pattern of parasequences, careful and accurate study of biostratigraphy, and stratigraphical correlation of different facies areas are the essential conditions for proper identification of sequences. (ii) The first flooding surface may be an ideal sequence boundary in outcrop sequence stratigraphy, where the most distinct palaeontological and sedimentary changes take place and make the surface readily recognizable in outcmp. (iii) The distribution in space, specially in different facies belts, is regarded as an important criterion for defining and recognizing the various orders of sequences. The third-order sequence is probably global in nature, which may be discerned in various depositional facies belts at least on one continental margin, and can be correlated over long distances, sometimes worldwide. (iv) The first flooding surface may be used as a useful reference marker in optimizing chronostratigraphic boundaries. Project jointly supported by the SSER, the Ministry of Science and Technology of China, and the Ministry of Land and Natural Resources of China.     

Triassic integrative stratigraphy and timescale of China

The Triassic rocks are widespread in China, and both marine and terrestrial strata are well developed. The Triassic stratigraphic architecture of China is very complex in both spatial variation of the so-called "South Marine and North Continental", i.e. the southern areas of China occupied mostly by marine facies while the northern China by terrestrial facies during the Triassic Period, and temporal transition of the "Lower Marine and Upper Continental", i.e. the lower part of the Triassic System composed mainly of marine facies and the upper part of terrestrial strata especially in South China. Although the Global Stratotype Section and Point(GSSP) of the Permian-Triassic boundary is located in South China, the Triassic of China except for some marine Lower-Middle Triassic depositions shows significantly local characteristics and is hardly correlated with the global chronostratigraphic chart. Consequently, the Triassic of China contains not only the international research hotspots but also difficult points in stratigraphic study. This paper aims to present a brief review of the Triassic in China, including chronostratigraphy, biostratigraphy, magnetostratigraphy and chemostratigraphy, and summarize an integrated Triassic stratigraphic framework of China. Accordingly, a stratigraphic correlation is proposed for the lithostratigraphic sequences among the three tectono-paleogeographic stratigraphic regions. The comprehensive study indicates that ammonoids are the classic index fossils in Triassic biostratigraphy but conodonts are more advantageous in the study and definition of the Triassic chronostratigraphic boundaries. China still has the potential to optimize the GSSPs of the Induan-Olenekian boundary and Olenekian-Anisian boundary. The correlation of the Permian-Triassic boundary between marine and terrestrial facies might be achieved with the help of the Permian-Triassic "transitional bed" and its related biotic and environmental events in association with the biostratigraphic study of conchostracan, vertebrate and plant fossils. In addition, the carbon isotopes have been proved to be one of the powerful methods in marine Triassic stratigraphic study, whereas the oxygen and strontium isotopes may be additional important bridges to establish the correlation between the marine and terrestrial strata, but as yet lacking of relevant studies in terrestrial strata. Considering the most stratigraphic intervals of the Triassic and the terrestrial Triassic in China are difficult to be correlated to the global chart, the proposed Chinese(regional) Triassic chronostratigraphic chart of marine and terrestrial stages would be of importance to the study of Chinese Triassic stratigraphy and related aspects, but the stages must be conceptually in line with international standards and studied as soon as possible in order to finalize the definition.     

Depositional sequence architecture and filling response model of the Cretaceous in the Kuqa depression, the Tarim basin

The Cretaceous system of the Kuqa depression is a regional scale (second order) depositional sequence defined by parallel unconformities or minor angular unconformities. It can be divided into four third-order sequence sets, eleven third-order sequences and tens of fourth- and fifth-order sequences. It consists generally of a regional depositional cycle from transgression to regression and is composed of three sets of facies associations: alluvial-fluvial, braided river-deltaic and lacustrine-deltaic facies associations. They represent the lowstand, transgressive and highstand facies tracts within the second-order sequence. The tectonic subsidence curve reconstructed by backstripping technique revealed that the Cretaceous Kuqa depression underwent a subsidence history from early accelerated subsidence, middle rapid subsidence and final slower subsidence phases during the Cretaceous time, with the correspondent tectonic subsidence rates being 30-35 m/Ma, 40-45 m/Ma and 5-10 m/Ma obtained from northern foredeep. This is likely attributed to the foreland dynamic process from early thrust flexural subsidence to late stress relaxation and erosion rebound uplift. The entire sedimentary history and the development of the three facies tracts are a response to the basin subsidence process. The slower subsidence foreland gentle slope was a favorable setting for the formation of braided fluvial deltaic systems during the late period of the Cretaceous, which comprise the important sandstone reservoirs in the depression. Sediment records of impermanent marine transgression were discovered in the Cretaceous and the major marine horizons are correctable to the highstands of the global sea level during the period.     

The species diversity of fusulinaceans and high-frequency sea-level changes in the Carboniferous-Permian boundary section at Xikou, Zhen’an County, Shaanxi Province, China

The study on the interrelation between sea-level changes and biodiversity with its evolution has great significance for understanding the impact of global changes on organic evolution and exploring the inherent laws of life-environment coevolution in geological history. In this paper, the stratigraphic distribution of fusulinacean fauna in the Carboniferous-Permian boundary section at Xikou, Zhen’an County, Shaanxi Province, is analyzed quantitatively, and the relationship between the species diversity of fusulinaceans and relative sea-level changes is discussed. As a whole, the species numbers of fusulinacean fauna experience a rapid increase and an obvious decline in Xikou, Zhen’an County, from the Late Carboniferous to the Early Permian. There is a significant increase in species diversity around the Carboniferous-Permian boundary, which is one of the biggest bio-events of the fusulinacean fauna, and represents the radiation of Pseudoschwagerininae subfamily in the studied area. Integrated fusulinacean species diversity into sequence stratigraphic framework, detailed study suggests that the species diversity of the fusulinaceans is closely related to its relative stratigraphic location, and is essentially controlled by the sea-level changes, especially by the high-frequency sea-level changes. Generally, the species diversity of fusulinaceans is low, and the number of first and last appearance datum is small in the lower unit of high-frequency depositional cycle formed during the quick rise of the sea level; whereas the species diversity of fusulinaceans is high, and the number of first and last appearance datum is large in the upper unit of high-frequency cycle formed during the slow fall of the sea level. Within the third-order depositional sequence, the species diversity of the fusulinaceans at the first flooding surfaces and the maximum flooding surfaces is low, and it increases upward. The fusulinacean species diversity is low within the transgressive systems track, and it is high within the highstand systems track. The second-order rise and fall in sea level coincide with the bloom and decline of high order taxa of fusulinaceans.     

Fluvial to bay sequence stratigraphy and seismic facies of the Cretaceous to Paleogene successions in the MITI Sanriku‐oki well and the vicinities,the Sanriku‐oki forearc basin,northeast Japan

This paper describes the significant depositional setting information derived from well and seismic survey data for the Upper Cretaceous to Lower Eocene forearc basin sediments in the central part of the Sanriku‐oki basin, which is regarded as a key area for elucidating the plate tectonic history of the Northeast Japan Arc. According to the results of well facies analysis utilizing cores, well logs and borehole images, the major depositional environments were of braided and meandering fluvial environments with sporadically intercalated marine incursion beds. Seismic facies, reflection terminations and isopach information provide the actual spatial distributions of fluvial channel zones flowing in a north–south trending direction. The transgression and regression cycles indicate that the Upper Cretaceous to Lower Eocene successions can be divided into thirteen depositional sequences (Sequences SrCr‐0 to SrCr‐5, and SrPg‐1 to SrPg‐7). These depositional sequences demonstrate three types of stacking patterns: Types A to C, each of which shows a succession mainly comprising a meandering fluvial system, a braided fluvial system with minor meandering aspects in the upper part, and major marine incursion beds in the middle part, respectively, although all show an overall transgressive to regressive succession. The Type C marine incursion beds characteristically comprise bay center and tidal‐dominated bay margin facies. Basin‐transecting long seismic sections demonstrate a roll up structure on the trench slope break (TSB) side of the basin. These facts suggest that during the Cretaceous to Eocene periods, the studied fluvial‐dominated forearc basin was sheltered by the uplifted TSB. The selective occurrences of the Type C sequences suggest that when a longer‐scale transgression occurred, especially in Santonian and early Campanian periods, a large bay basin was developed, creating accommodation space, which induced the deposition of the Cretaceous Kuji Group along the arc‐side basin margin.     

The age of the Permian-Triassic boundary

The 5 cm boundary clay bed in the Chinese stratotype section through the Permian-Triassic boundary has been recognised as a bentonite. SHRIMP ion microprobe dating of zircons in the bentonite indicates a magmatic age of 251.2 ± 3.4 Ma (2σ); this is the first direct constraint on the numerical age of the Permian-Triassic boundary.Future refinements of ages at this important, but poorly constrained, level of the Phanerozoic timescale may depend on re-analysis of this uniquely placed volcanic horizon, and other bentonites in the fossiliferous Chinese Upper Permian and Lower Triassic. The utility of defining the Permian-Triassic boundary in the Chinese stratotype section, in the vicinity of known dateable horizons, should be considered.     

Fourth‐ to third‐order cycles in the Hakobuchi Formation: Shallow‐marine Campanian final deposition of the Yezo Group,Nakagawa area,northern Hokkaido,Japan

The Yezo Group has a wide longitudinal distribution across Hokkaido, northern Japan. It represents a Cretaceous (Early Aptian–Late Maastrichtian) and Late Paleocene forearc basin‐fill along the eastern margin of the paleo‐Asian continent. In the Nakagawa area of northern Hokkaido, the uppermost part of the Yezo Group consists of the Hakobuchi Formation. Along the western margin of the Yezo basin, 24 sedimentary facies (F) represent 6 facies associations (FA), suggesting prevailing storm‐dominated inner shelf to shoreface environments, subordinately associated with shoreface sand ridges, outer shelf, estuary and fluvial environments. The stacking patterns, thickness and facies trends of these associations allow the discrimination of six depositional sequences (DS). Inoceramids Sphenoceramus schmidti and Inoceramus balticus, and the ammonite Metaplacenticeras subtilistriatum, provide late Early to Late Campanian age constraints to this approximately 370‐m thick final stage of deposition and uplift of the Yezo forearc basin. Six shallow‐marine to subordinately non‐marine sandstone‐dominated depositional sequences include four 10 to 110‐m thick upward‐coarsening regressive successions (FS1), occasionally associated with thin, less than 10‐m thick, upward‐fining transgressive successions (FS2). The lower DS1–3, middle DS4–5 and upper DS6 represent three depositional sequential sets (DSS1–3). These eastward prograding and westward retrograding recurring shallow‐marine depositional systems may reflect third‐ and fourth‐order relative sealevel changes, in terms of sequence stratigraphy.     

An accurately delineated Permian-Triassic Boundary in continental successions

The Permian-Triassic Boundary Stratigraphic Set (PTBST), characteristic of the GSSP section of Meishan and widespread in marine Permian-Triassic Boundary (PTB) sequences of South China, is used to trace and recognize the PTB in a continental sequence at Chahe (Beds 66f―68c). Diversified Permian plant fossils extended to the PTBST, and a few relicts survived above that level. Sporomorphs are dominated by fern spores of Permian nature below the PTBST, above which they are replaced by gymnosperm pollen of Triassic aspect. In the nearby Zhejue Section, the continental PTBST is charac- terized by the fungal 'spike' recorded in many places throughout the world. The boundary claybeds (66f and 68a,c) of the PTBST are composed of mixed illite-montmorillonite layers analogous with those at Meishan. They contain volcanogenic minerals such as β quartz and zircon. U/Pb dating of the upper claybed gives ages of 247.5 and 252.6 Ma for Beds 68a and 68c respectively, averaging 250 Ma. In con- trast to the situation in Xinjiang and South Africa, the sediment sequence of the Permian-Triassic tran- sition in the Chahe section (Beds 56―80) become finer upward. Shallowing and coarsening upward is not, therefore, characteristic of the Permian-Triassic transition everywhere. The occurrence of relicts of the Gigantopteris Flora in the Kayitou Fm. indicates that, unlike most marine biota, relicts of this pa- leophytic flora survived into the earliest Triassic. It is concluded that Bed 67 at Chahe corresponds to Bed 27 at Meishan, and that the PTB should be put within the 60-cm-thick Bed 67b④, now put at its base tentatively. This is the most accurate correlation of the PTB in continental facies with that in the marine GSSP.     

Petrography, diagenesis and provenance of Eocene Tyee Basin sandstones, southern Oregon Coast Range: New view from sequence stratigraphy

Abstract Sandstone petrography considered within a sequence stratigraphic framework provides a better understanding of the characteristics of the Eocene Tyee Basin, an accretionary and forearc sequence, southern Oregon Coast Range. Detailed comparison of the relative abundance of major framework grains documents a marked difference in the sandstone composition of each depositional sequence. Such a difference is mainly due to an abrupt change in provenance, from a local Klamath Mountains metasedimentary source to a more distant extrabasinal Idaho Batholith‐Clarno volcanic arc source. Furthermore, the composition of framework grains varies systematically from the lowstand systems tract to the highstand systems tract within a depositional sequence. This suggests that relative sea level change in the depositional basin, and tectonics in the source area, can affect the patterns of sedimentation and sandstone composition. In addition, the Eocene Tyee Basin sandstones have a down‐section distribution of authigenic minerals, consisting of early formed zeolites and late‐stage quartz, as well as a change in the abundance of smectite to mixed‐layer chlorite/smectite with increasing burial depth. The down‐section distribution of authigenic minerals is also causally linked to the compositional variation of framework grains in each depositional sequence with increasing burial temperature. Much primary porosity has been filled with these authigenic minerals, which diminishes the permeability of potential reservoir rocks. Reservoir‐quality porosities and permeabilities, however, are present locally in the basin. The development of these reservoir‐quality sandstones within the Eocene Tyee Basin sequence is due to a complex burial diagenesis, which is directly related to temporal and spatial variations in original detrital mineralogy, in sedimentation pattern, and in burial temperature in the basin.     

Sequence stratigraphic framework and distribution of depositional systems for the Paleogene in Liaodong Bay area

With a comprehensive geological and geophysical data base,the Paleogene in the Liaodong Bay area,which consists of the Kongdian,Shahejie and Donghying Formations from the base to top,was divided into 4 second-order sequences and 8 third-order sequences based on the characteristics of the se-quence boundaries. Each third-order sequence is subdivided into the lowstand,lake transgressive and highstand systems tracts. The Lowstand systems tract (LST) is mainly composed of progradational parasequence sets,while the lake transgressive systems tract (TST) largely consists of the retrograda-tional parasequence sets and the highstand systems tract (HST) is dominated by the progradational parasequence sets. The main types of depositional systems include the shallow lake,semi-deep lake,deep lake,delta,fan delta,braided fluvial delta and nearshore subaqueous fan. The braided fluvial delta and fan delta depositional systems are mainly confined to the sequences of the lower SEs4-Ek,SEs3 and SEs1 2,while the sequences of SEd3,SEd2 and SEd1 are dominated by the delta and nearshore subaqueous fan depositional systems with the latter being developed at the downthrown side of the basin-bounding fault in each sequence. The evolution of the depositional systems is always con-trolled by the paleo-tectonic setting and the ancient landform in the space and geological time. It is concluded that the most favorable reservoirs are distributed in the Liaoxi low uplift and the central Liaozhong sag.     

The marine Triassic sequence stratigraphy of Lower Yangtze

Based on detailed field observation and multidisciplinary studies of integrated stratigraphy, the marine Lower and Middle Triassic of Lower Yangtze region is divided into five third-order sequences, the general approach of the outcrop sequence stratigraphical study of carbonate ramp is proposed, the pattern in the development of the Early and Middle Triassic sequence under the major regression is summarized, and the sequence stratigraphical and chronostratigraphical frameworks across various paleogeographical facies zones on the marginal platform are established. Project supported by the Stake Key Project “SSLC” and the National Natural Science Foundation of China (Grant Nos. 49502022, 49632070).     

华南二叠系卡匹敦阶高分辨率浮点年代标尺

基于详细的生物地层学研究,以磁化率为古气候替代指标,对广西来宾铁桥剖面卡匹敦阶地层开展时间序列分析,建立高分辨率浮点年代标尺(FPTS).结果表明,磁化率记录了铁桥剖面中二叠世晚期沉积序列中的米兰科维奇旋回,卡匹敦阶上部磁化率突然增加与峨眉山玄武岩喷发和卡匹敦晚期全球性海退有关,这些事件导致同期沉积物中碎屑物质增加.铁桥剖面瓜德鲁普—乐平统界线附近磁化率和蓬莱滩剖面(乐平统底界GSSP)表现出一致的变化趋势,具可对比性.利用多窗谱法(MTM)和傅里叶变换(FT)从磁化率序列中识别出五个米兰科维奇周期:长偏心率周期(E2,405ka)、短偏心率周期(E1,100ka)、长地轴斜率周期(O2,44.1ka)、长岁差周期(P2,20.95ka)和短岁差周期(P1,17.7ka).对比基于E2周期建立的磁性地层磁化率(MSS)带和标准参考带(SRZ),建立整个沉积序列的高分辨率(200ka)FPTS,提出卡匹敦阶的时限为3.85 Ma(存在+0~0.28 Ma误差),整段沉积序列的平均沉积速率为2.91cm·ka-1.同时计算出卡匹敦阶内部七个牙形石带的时限,从最短26.6ka到最长2.3 Ma.另外,估算出峨眉山大火成岩省喷发启动时间为262.67 Ma,位于瓜德鲁普—乐平统界线之下1.42 Ma.     

A potential stratotype for the regional lowermost stage of the continental Paleocene in China

Phanerozoic chronostratigraphic units can only be defined through their lower boundary stratotypes.The lowermost stage of the Paleocene of China,which mainly consists of terrestrial deposits,can only be defined through its lower boundary stratotype,i.e.the continental Cretaceous/Paleogene boundary stratotype.There is no section yet found which contains continuous terrestrial deposits and biostratigraphic records of the Cretaceous-Paleogene transition in Nanxiong,Guangdong and Jiayin,Heilongjiang,there is no evidence for establishing the continental stratotype of the Cretaceous/Paleogene boundary in either area.Therefore,both the"Shanghuan stage"and"Furaoan stage"are not good candidates for the lowermost stage of the Paleocene of China.From the viewpoint of charophytes,the outcrop section of the Dangyang,Hubei Province(Central China)contains the most continuous,abundant and diverse terrestrial biostratigraphic records of the Cretaceous-Paleogene transition,in particular the early Paleocene,known so far in the world.The biostratigraphic records of ostracods in the transition are also continuous,rich,and diverse.The Dangyang outcrop section is the only section known so far in China that is a possible candidate for a continental stratotype of the Cretaceous/Paleogene boundary in China and the section is the only potential section identified to date for establishing the regional lowermost stage of the Paleocene,Paleogene and Cenozoic in China or stratotype section for the stage.     

Indicator of paleosalinity: Sedimentary sulfur and organic carbon in the Jurassic–Cretaceous Tetori Group,central Japan

A simple geochemical technique using the ratio of total sulfur (TS) to total organic carbon (TOC) was successfully used to reconstruct paleoenvironments in the Jurassic–Cretaceous Tetori Group, central Japan. The TS to TOC ratio is often employed as an effective parameter to separate modern marine or brackish sediments from freshwater deposits. To test the TS/TOC method for paleoenvironmental interpretation of the Tetori Group, we first analyzed TS/TOC for samples for which depositional conditions (i.e. marine, brackish or freshwater) had been recognized paleontologically. The results indicate that the method can effectively separate sedimentary rocks deposited under freshwater from marine and brackish settings. Once we had established the effectiveness of this method, we applied it to three sections of the Tetori Group, central Japan. Stratigraphic fluctuations in TS/TOC values revealed episodic incursions of marine or brackish conditions in the dominantly freshwater depositional sequence in the middle of the Jobu Formation of the Itoshiro Subgroup at the Izumi section, Fukui Prefecture. The same paleoenvironment is also suggested to occur at the top of the Tetori Group in the Tateyama section, Toyama Prefecture. This research provides important information to paleogeographers who currently lack evidence from facies fossils to indicate if the uppermost part of the Tetori Group represents marine or brackish settings. A chemostratigraphy of TS/TOC parameters potentially could provide a correlation among Jurassic–Cretaceous sequences along continental margins over East Asia.     

Sequence framework of two different kinds of margins and their response to tectonic activity during the Middle-Late Triassic,Ordos Basin

Two kinds of margin respectively occur in the Ordos Basin during the Middle-Late Triassic (Yanchang Age), one is foreland margin developed under the background of flexural subsidence by thrusting intensively in the southwest margin, and the other is intracratonic basin margin by stable subsidence in northern and central parts of the basin. The Middle-Late Triassic Yanchang Formation can be divided into four regional third-order sequences, which are separated by gentle angular unconformity or regional erosion surface, made up of lowstand system tract (LST), expanding system tract (EST) and highstand system tract (HST) from lower to upper within a sequence. But there are distinct differences of the sequence framework between the southwest margin and northern and central parts of the basin. The southwest margin develops heavy conglomerate layer and unconformity as a result of orogeny by thrusting, and the intracratonic basin margin by stable subsidence in the northern and central parts grows aggradational sandstone, conglomerate in fluvio-delta system and parallel unconformity. The depositional framework of southwest margin reflects the tectonic evolution from flexural subsidence by thrusting to rebounded uplift. The formation of sequence boundary is related to the resilient uplift and erosion. The sequence stratigraphic framework and depositional system tract configuration in the foreland basin are controlled by structural activity of the fold and thrust belt, and the sequence succession reflects episodic thrusting of the Middle-Late Triassic toward the foreland basin. The sequence evolution in northern and central parts reflects the depositional succession of fluvio-delta system under intracratonic background, composed of coarse-grained sediment in braided channel deposit at the lower, meandering channel deposit in the middle and fine-grained sediment in the flood plain at the upper, dominated by lake level fluctuation. During the deposit of the LST in the intracraton basin, accommodation space is limited, and results in abundant fluvial sediment migration laterally, erosion and transport, forming laterally sandstone composite and aggradational deposit on the alluvial plain, which constitutes specific erosion unconformity boundary.