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The Bohai Bay Basin, located on the eastern Asian margin, is the second largest oil-production basin in China. It contains numerous depressions and sags, among which Nanpu Sag has become particularly important because of signifi cant oil discoveries in recent years. Geologically and tectonically, however, the rifting mechanism and geodynamic evolution of the basin remain uncertain. This paper uses detailed volcanic and stratigraphic records obtained through extensive drilling and sampling in Nanpu Sag to interpret tectono-stratigraphic sequences and discuss basin dynamic evolution and crustmantle interactions of the Bohai Bay Basin. Nanpu Sag contains voluminous volcanic rocks of dominantly alkaline basalts. Drill core samples, well logs, and seismic profi les reveal three volcanic cycles between the Eocene and Miocene Epochs. These basalts were created during a transition from garnet-to spinel-peridotite. Five tectono-stratigraphic sequences produced by episodic continental rifting have been identifi ed, each composed of a basal coarse clastic sequence, a lower volcanic sequence, a middle deep-water clastic sequence, and an upper infi lling sequence.Tectonically, Nanpu Sag experienced four evolutionary phases. The fi rst three corresponded to three rifting events revealed by cyclic volcanism and sedimentary depositional features. The fourth phase was marked by extreme thermal subsidence and prograding fl uvial deposition followed by tectonic inversion. A diapiric upper-mantle upwelling model is proposed to explain the dynamics that controlled the multiple rifting processes, the cyclic volcanism, and the periodic tectonic evolution of Nanpu Sag and the greater Bohai Bay Basin.

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Four neogondolellid conodont interval zones were recognized across the Changhsingian stage at Ganxi section, western Hubei Province, south China. They are in ascending order: the Clarkina wangi Zone, the Clarkina changxingensis changxingensis Zone, the Clarkina changxingensis yini Zone, and the Clarkina meishanensis meishanensis Zone. The present study suggests that the base of the Changhsingian can be defined by the first appearance datum (FAD) of Clarkina wangi within an evolutionary lineage from Clarkina longicuspidata to Clarkina wangi. The Wuchiapingian–Changhsingian boundary can be placed at the base of bed 104 at Ganxi section, south China because of the first occurrence of Clarkina wangi.

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