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The tectonic evolution of the Lishui Sag in the East China Sea Shelf Basin significantly influences its sequence stratigraphy. By integrating seismic reflections, well logs and core data, this study examines the quantitative activity of the Lingfeng fault, sequence framework and sequence architecture in the Lishui Sag. The Paleocene succession is divided into one second-order sequence (SSQ1), three third-order sequences (SQ1–SQ3) and nine system tracts, representing a complete syn-rift evolution consisting of initial syn-rift, rift climax and late syn-rift stages. The results indicate that the differential activity of the Lingfeng fault shapes the basin structure and controls the subsidence centre, leading to prominent variations in the spatial distribution and filling of the sequence stratigraphy during different tectonic stages. The initial syn-rift sequence (SQ1), characterised by a low activity of the segmented Lingfeng fault, is primarily found in isolated small sub-sags. The rift climax sequence (SQ2), with increasing displacement and longer segmented fault zones, exhibits a wedge-shaped filling pattern with substantial topographic elevation differences. The late syn-rift sequence (SQ3) shows a gradual decrease in tectonic activity and uniform filling, with all system tracts within the sequences fully developed. The sequence architecture of the hanging wall in the Lishui Sag can be classified into fault-scarp and fault-slope type, whereas the sequence architecture of the hanging wall dip-slope can be classified into sedimentary slope-break and faulted slope-break. The Lingfeng fault controlled the tectonic evolution, sedimentary subsidence centre and sequence filling and architecture in the Paleocene rifted Lishui Sag. The Paleocene succession is divided into one second-order sequence (SSQ1), three third-order sequences (SQ1–SQ3) and nine system tracts, representing a complete syn-rift evolution consisting of initial syn-rift, rift climax and late syn-rift stages. The sequence architecture of the hangingwall can be classified into fault-scarp and fault-slope type, and hanging wall dip-slope sequence architecture can be divided into sedimentary slope-break and faulted slope-break types. [ABSTRACT FROM AUTHOR]

The provenance evolution of Paleocene is a main factor controlling the sedimentary filling characteristics of the East China Sea Shelf Basin, and is of great significance in the exploration and development of petro-bearing basins. Based on the core samples of the Paleocene of the Lishui Sag, East China Sea Shelf Basin, the systematic analysis of petrological and mineralogical characteristics was carried out. Through the study of the spatial and temporal distribution of sandstone clastic components, light and heavy mineral assemblages and related parameters, the evolution of the Paleocene provenance system in the study area and its significance for the sedimentary filling of the basin were discussed. The Paleocene clastic rocks in the Lishui Sag are mainly lithic feldspar sandstone, feldspar lithic sandstone and lithic sandstone. The sandstone is mainly moderately well-sorted, and the grains are mostly subangular or subrounded, with poor overall rounding, indicating that the structural maturity and compositional maturity are relatively lower. The light mineral assemblages of the Guifeng and Lingfeng formations of Peleocene are obviously different and show zoning features in different parts of the basin. In the central and northern parts of the western subsag, there are mainly parent rock types of cycle orogenic belts, while in the south of the western subsag, there are mainly parent rock types of cycle orogenic belts and magma arc. In the eastern subsag, there are mainly parent rock types of cycle orogenic belts. The characteristics of heavy mineral assemblages in the main horizons of the Paleocene in the study area change little. The Zhejiang-Fujian uplift belt in the west and the Yandang uplift in the east are the most important provenance areas of the Lishui Sag. The Lingfeng low uplift in the center of the basin suffered serious denudation before the deposition of the lower member of the Mingyuefeng Formation, providing local provenance for the basin. The provenance system analysis showed that when the Yueguifeng and Lingfeng formations were deposited, they were in the early and peak stages of fault depression, and the intra-basin provenance area was formed by the intra-basin fault uplift. As the upper member of the Lingfeng Formation was deposited, the basin entered the late stage of fault depression, local intra-basin provenance was no longer developed, and the main provenance system was extra-basin provenance.

Analysis of the sedimentary environment during the clastic formation process is of great significance for reservoir evaluation and desert prediction. This paper focused on the Paleocene in the West Lishui Sag, East China Sea Basin. XRF fluorescence diffraction and carbon and oxygen isotope tests were carried out on core samples from four wells. Based on the geochemical characteristics of the samples and the changes in the elemental ratios, combined with the lithologic characteristics and sedimentary structure of the samples, the paleoclimate, paleosalinity, paleobathymetric, paleoredox, paleotemperature, and other paleoenvironmental characteristics were analyzed. The results show that the characteristics of major and trace elements were similar in the lower Mingyuefeng Formation (E1m2), Upper Lingfeng Formation (E1l1), Lower Lingfing Formation (E1l2), and Yueguifeng Formation (E1y). The Paleocene in the West Lishui Sag was mainly in the reducing environment of brackish-salt water with weak water stratification. The water depth showed a trend of becoming deeper, then shallower, and then deeper. The paleoclimate in the West Lishui Sag was warm on the whole. However, the content of Sr became smaller after later deposition, so the calculated paleowater temperature was higher. In addition, oxygen isotopes were affected by diagenesis, resulting in a negative oxygen isotope value. The paleoproductivity was low, and the hydrocarbon generation potential was poor. The content of nutrient elements mainly came from terrigenous input rather than biological origin, and terrigenous intrusion characteristics gradually increased from E1y to E1m2. The study also shows that paleoproductivity was affected by the paleoclimate and paleowater depth. Warm and humid climate and deep water body were conducive to the accumulation of paleoproductivity. [ABSTRACT FROM AUTHOR]

The Lishui Sag on the southwest margin of the East China Sea Shelf Basin (ECSSB) is a relatively new oil and gas exploration area, with the Paleocene being one of the most potential oil-bearing intervals in the sag. In this study, combined with the principles of element geochemistry and mineralogy, the salinity characteristics of the paleowater body are reconstructed and discussed using the Sr/Ba ratio, B/Ga ratio, equivalent boron content and Couch's method. The results show that (1) the highest salinity indicated by Sr/Ba and B/Ga ratios appears in the Upper Lingfeng Formation; (2) the equivalent boron content ranges from 62 to 254 ppm, with an average of 122 ppm, showing the existence of fresh water and brackish deposition settings; and (3) the paleosalinity calculated quantitatively by Couch's method is between 4.9 and 13.1‰. To ensure the reliability of the study, paleosalinity results from the different methods are cross-plotted, and the effects of provenance and diagenesis on the paleosalinity analysis are negligible. The comparison results show that Couch's method, equivalent boron content and B/Ga ratio are more reliable among all paleosalimeters. The identified paleosalinity type of paleowater body is mainly brackish water, which is exactly mesohaline water. The paleosalinity of the Paleocene stratigraphic interval in Lishui Sag is consistent with the sedimentary facies distribution. Our comprehensive comparison provides a basis for inferring the source of fresh water, the genesis of transitional water bodies and the evolution of sedimentary facies. [ABSTRACT FROM AUTHOR]

Estimation of base level changes in geological records is an important topic for petroleum geologists. Taking the Paleocene Upper Lingfeng Member of Lishui Sag as an example, this paper conducted a base level reconstruction based on Basin Filling Modelling (BFM). The reconstruction was processed on the ground of a previously interpreted seismic stratigraphic framework with several assumptions and simplification. The BFM is implemented with a nonlinear diffusion equation solver written in R coding that excels in shallow marine stratigraphic simulation. The modeled results fit the original stratigraphy very well. The BFM is a powerful tool for reconstructing the base level, and is an effective way to check the reasonableness of previous interpretations. Although simulation solutions may not be unique, the BFM still provides us a chance to gain some insights into the mechanism and dynamic details of the stratigraphy of sedimentary basins. [ABSTRACT FROM AUTHOR]

Influenced by episodic tectonic activity and multiple sediment sources, the source-to-sink systems in rifted basins are relatively complex. Based on seismic data, well logging, cores, thin sections, and heavy mineral data, the growth and linkage of the Lingfeng fault were reconstructed and its influence on the sedimentary responses of the Palaeocene-rifted Lishui Sag in the East China Sea Shelf Basin was examined. The researchers conducted a fault throw-distance analysis on the Lingfeng fault and found that it displayed an overall weak-strong-weak evolutionary process. During the early syn-rift stage, the Lingfeng fault exhibited a segmented geometry consisting of seven fault segments with low fault activity along its strike, and small-scale source-to-sink systems developed in both the hanging wall dip-slope and footwall. As the main syn-rift stage progressed, strong fault activity induced large-scale exposure of the source area, resulting in a high sediment-supply rate and large-scale source-to-sink systems. During the late syn-rift stage, the fault weakened and evolved into a connected basin-boundary fault, and proximal source-to-sink systems in the footwall gradually disappeared. Semi-quantitative measurements of the geomorphic parameters of these source-to-sink systems indicated wide and shallow sediment transport pathways in hanging wall dip-slope areas (average width and depth of approximately 6.34 kmand 0.13 km, respectively) and narrow and deep sediment transport pathways in the footwall (average width and depth of approximately 3.75 km and 0.15 km, respectively). The semi-quantitative statistical analysis implies that the cross-sectional area of the transport channels was positively correlated with the corresponding fan/delta complexes in a rift basin. • The Lingfeng fault controlled the source-to-sink systems in the Palaeocene rifted Lishui Sag. • Fault activity led to tilting the hanging wall dip-slope in the syn-rift basin, which controlled the transport pathway and sediment supply. • The dimension of the sedimentary transport pathways were positive to sediment flux, providing a good approximation of source dimensions. [ABSTRACT FROM AUTHOR]

The Lishui Sag, in the East China Sea Shelf Basin, is rich in hydrocarbons, with the major hydrocarbon-bearing layers being the Paleocene Mingyuefeng clastic rocks. Analysis of the implicit geologic background information of these Paleocene clastic rocks using petrological and geochemical methods has significant practical importance. These Paleocene sandstones are mainly lithic arenite, lithic arkose and greywacke, composed of K-feldspar, plagioclase, authigenic clays, silica and carbonates. As continental deposits, Yueguifeng clastic rocks have high aluminosilicate and mafic detritus contents, while the Lingfeng and Mingyuefeng Formations are rich in silica due to an oscillating coastal marine depositional environment The major element contents of these Paleocene sandstones are low and have a concentrated distribution, indicating that the geochemical composition is non-epigenetic, transformed by sedimentary processes and diagenesis. The Yueguifeng detritus comprises recycled sediments, controlled by moderate weathering and erosion, while the Lingfeng and Mingyuefeng detritus is interpreted as primarily first-cycle materials due to low chemical weathering. In the Late Cretaceous to Early Paleocene, the Pacific Plate began subducting under the Eurasian Plate, causing an orogeny by plate collision and magma eruption due to the melting of subducted oceanic crust This resulted in the dual tectonic settings of 'active margin' and 'continental island arc' in the East China Sea Shelf Basin. During the Late Paleocene, the Pacific Plate margin migrated eastward along with development of the Philippine Ocean Plate, and the tectonic setting of the Lishui Sag gradually turned into a passive continental margin. Detrital sources included both orogenic continental blocks and continental island arcs, and the parent rocks are primarily felsic volcanic rocks and granites. [ABSTRACT FROM AUTHOR]

The East China Sea Shelf Basin (ECSSB) is a typical back-arc rift basin and is divided further by a series of sags and basement ridges. The Lishui Sag on the southwest margin of the ECSSB, is underlain by a productive, gas-prone, marine Paleocene section. In combination with sequence stratigraphy and seismic geomorphology, an integrated approach was applied to map the high-frequency sequences and systems tracts of the Lower E1m (57.2–56.5 Ma) and Upper E1l strata (60–57.2 Ma) by using well, two-dimensional and three-dimensional seismic data. Our approach involves documentation of seismic stratal geometries, seismic facies and core lithofacies. Seismic truncation, offlap, onlap and downlap geometries were used for identifying two depositional sequences with four systems tracts in the Upper E1l and Lower E1m strata. Two sedimentary facies were recognized from core and log data and identified as tidal sand ridges and delta mouth bar deposits. The depositional facies were imaged from a series of strata slices obtained by 3D survey. Five types of depositional systems were recognized based on the geometry change expressed on strata slices. In stratigraphic order these are (a) incised channels on the inner shelf and subaqueous fans on the middle shelf, (b) diffuse, elongated linear tidal sand ridges on the continental shelf and turbidity flows on the slope, (c) incised valley, prograding shelf edge delta on the continental shelf and shelf edge and delta front turbidites on the slope, (d) incised valley fills, fluvial aggradation and fluvial dominated mouth bar on the continental shelf, and (e) shoreface barrier bar and sand ridges that are parallel to the shoreline. This integrated analysis provides us an opportunity to evaluate the exploration significance in the stratigraphic framework and improve the accuracy of petroleum plays prediction. [ABSTRACT FROM AUTHOR]