Sequence Stratigraphy and Tectonic Environment of the Chartai Group,Inner Mongolia

The Middle Proterozoic Chartai Group separated by two unconformities consists of three depositional se-quences: the Shujigou Formation-Zenglongchang Formation (DS Ⅰ), the Agulugou Formation (DS Ⅱ), andthe Liuhongwan Formation (DS Ⅲ). The carbonate platform and back-platform basin are the basic environ-ment model of the Chartai Group. The syndepositional faults on the oceanward side of the carbonate platformand large-scale slumping in the soft sediments are important marks of facies tracts. The newly establishedZenglongchan uplifting, an epeirogenetic uplifting, plays an important role in the formation of thepalaeogeographic framework of the Chartai Group. The stratigraphic correlation between the Chartai Groupand the Bayan Obo Group is made for the first time by using sequence stratigraphic principle and model estab-lished by P.R. Vail. The Chartai Group, which was deposited on the northern passive continental margin of theNorth China platfom, represents the platform cover.

Dynamical Process and Genesis of Late Triassic Sediment Filling in Ordos Basin

Coupling relationship exists in development time of the Qinling orogen and the neighboring Ordos basin, implying that they are connected genetically, that is, the formation and evolution of the Ordos basin are response to orogeny. The present Ordos basin is a residual part of the Late Triassic large Ordos basin. The primary large Ordos basin was featured by four types of boundaries, i.e. (1) southern thrusting boundary; (2) southwestern strikeslip thrusting boundary; (3) northwestern rifting boundary; and (4) northeastern and northern passive gentle slope type boundary. This basin was composed of sequences A and B. These sequences consist of three parts, i.e. lower alluvial systems tract, middle expanding lacustrine systems tract and the upper contracting lacustrine systems tract. A systems tract is actually a parasequence set. Based on division of sequences stratigraphic units and reconstruction of depositional systems tracts, the present paper proposes that: (1) two episodes occurred during Late Triassic Qinling collision orogeny; (2) collision is stronger in western Qinling than in eastern Qinling.

Carbon and oxygen isotope variation and its implication for marine sequence: A case study of Ordovician in Tarim Basin

Carbon and oxygen isotopes of marine carbonate rocks or fossil shells could indicate global sea-level relative change.Generally,heavier carbon isotopes or lighter oxygen isotopes reflected rise of global sea-level relative changes,and vice versa.For carbonate rocks deposited before Tertiary,carbon isotope was more stable than oxygen isotope,and thus it was more suitable to indicate global sea-level relative fluctuation.Within time limit of the 3rd-order sequence(1-10Ma),large scale migration of carbonate platforms would not occur and carbonate productivity would not change greatly,therefore,a research method of marine tectonic sequence(i.e,a contrastive analysis method of carbon and oxygen isotopessedimentary cycles)was proposed.Thus,the marine 3rd-order sequences were divided the global sealevel sequence which was controlled by global sea-level change and the tectonic sequence which was controlled by regional tectonic subsidence and uplift.The global sea-level fluctuation indicated by carbon and oxygen isotopes were consistent with variation of sedimentary cycles and water depth of the global sea-level sequence,but were not consistent with variation of sedimentary cycles and water depth of the tectonic sequence.As a case study of Ordovician in Tarim Basin,two 3rd-order global sea-level sequences were identified in the Lower Ordovician,while six 3rd-order tectonic sequences controlled by collision and compression between Arkin island arc,Kudi active continental margin uplift and Tarim Plate were identified in the Middle and Upper Ordovician.Particularly,OSQ6 in the Upper Ordovician(Lianglitage Formation)was a typical tectonic sequence.