Seasonal responses of monthly mean sea levels in the Bohai Sea to hydrometeorological forcing and their double screening regression models

-In this paper, the maximum entropy spectral, the cross-spectral and the frequency response analyses are madeon the basis of the data of monthly mean sea levels at coastal stations in the Bohai Sea during 1965-1986. The results show that the annual fluctuations of the monthly mean sea levels in the Bohai Sea are the results of the coupling response of seasonal variations of the marine hydrometeorological factors. Furthermore, the regression prediction equation is obtained by using the double screening stepwise regression analysis method . Through the prediction test , it is proved that the obtained results are desirable.

Sequence palaeogeography and coal accumulation of inland faulting basin： an example from late Triassic Yangtze platform of China

To unveil formation mechanism of key sequence boundaries of inland faulting basin and coal accumulation charac- teristics of coal seams in isochrohal stratigraphic framework, sequence stratigraphy, palaeogeographic recovery and other methods were used to research the sequence stratigraphy and coal accumulation in the example of Banding Basn in the west margin of Yangtze Platform, and the authors advanced a coal accumulation model of Faulting basin on the basis of accommo- dation space changes in the background of palaeogeography of sequence framework. The results show that： normal lacustrine regression and forced lacustrine regression are the main driving forces for the formation of sequence boundaries of Faulting ba- sin; basement subsidence is the main source of accommodation space of Faulting basin; and subsidence disequilibrium is the main cause for the difference in generation rate of accommodation space of Faulting basin. Coal accumulation in Faulting basin is obviously controlled by accommodation space changes in sequence framework and basin evolution. As Faulting basin evolves into depression basin, both subsidence rate of basin basement and generation rate of accommodation space decrease vertically, it appears as a progradational reverse-graded sedimentary sequence, coal accumulation in secondary sequence framework intensifies first and then weakens, and coal accumulation at the middle stage of highstand system tract is the best. During steady rifting period, minable coal seams were mostly developed in initial lacustrine flooding surface of fourth-order sequence and at the middle-late period of highstand system tract, and coal accumulation center lay in palaeogeographic unit of delta plain with moderate available accommodation space. During shrinking period, minable coal seams gradually migrated to the maximum lacustrine flooding surface and coal accumulation center lay in palaeographical unit of lacustrine with large available accommodation space.

High-frequency lacustrine sequence stratigraphy of clastic lakes:lessons from ancient successions

Sequence stratigraphic concepts and methods provide novel tools for performing stratigraphic analysis,allowing us to improve our understanding of depositional models and basin evolution.Main controls and depositional elements(e.g.,surfaces,systems tracts,parasequences,etc.)recognized in conventional sequence stratigraphy are designed for marine-related systems.In contrast,the sequence stratigraphy of lacustrine successions is much more complex and poorly understood,because it is not driven by sea-level changes,but by a complex interaction between tectonics and high-frequency climatic cycles.The comprehensive analysis of the water balance of lacustrine systems allows the recognition of three types of lake conditions:Underfilled,balanced-fill and overfilled lakes.Understanding the lake conditions in ancient successions is fundamental for unraveling lacustrine sequence stratigraphy,since these conditions effectively control water salinity,internal stacking pattern and the characteristics of systems tracts.Underfilled lakes are hydrologically closed lakes,and consequently,the lake-level can highly fluctuate,driven by high-frequency wet-dry climatic cycles.During wet periods,rivers supply water and sediments,resulting in fining-and thinning-upward elementary depositional sequences(EDS's)accumulated during the transgressive systems tract(TST).In contrast,dry periods are characterized by a relative lake-level fall with the subaerial exposure of lake margin areas during the regressive systems tract(RST).Lake water salinity can fluctuate from brackish to hypersaline.Balanced-fill lakes are partially closed lakes,and consequently,they have characteristics of both underfilled and overfilled lakes.During the TST,the lake is in underfilled condition,and consequently,the introduction of water and sediment will accumulate a fining-upward interval until reaching the spill point during the maximum flooding.The RST is accumulated under an overfilled lake condition,with coarseningupward progradational littoral deltas and related subaqueous delta deposits.Lake water salinity fluctuates from brackish to freshwater.Overfilled lakes are hydrologically open lakes.Most deposits accumulate during the RST,forming coarsening-upward progradational littoral deposits,with associated subaqueous deltas.All overfilled lakes are freshwater lakes.Subsidence is crucial for allowing the long-term preservation of lacustrine deposits.Lakes can temporarily store water and sediments in areas that lack subsidence,but these deposits will not be preserved in the stratigraphic record.Consequently,two types of lakes are recognized:1)subsiding lakes,which have permanent accommodation space and 2)hanging lakes,having temporary accommodation space.Although they cannot permanently store sediments,hanging lakes are fundamental for lacustrine sequence stratigraphy,since they can flood subsiding lakes with the near-instantaneous release of a substantial volume of water,creating favorable conditions for the accumulation of organic-rich shales.This rapid flooding from hanging lakes induced a forced transgression(FT),which is a large-scale rapid transgression(xenoconformity)not related to the normal sediment and water supply from local source areas.