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Storm-induced deposits in the sedimentary record can now be easily identified on account of a better understanding of processes of unidirectional and oscillatory flow. Thin-bedded sandstone, siltstone, and interlayered mudstone deposits of the Oligocene Jianquanzi Member in the Yaxi Area of the Jiuxi Basin along the northeastern margin of the Tibetan Plateau were formed by shallow lacustrine storm-generated flows. Petrologic analysis reveals that the sandstones exhibit moderate to high compositional maturity but are texturally sub-mature to immature. Based on investigation of drill cores, six storm-deposit lithofacies are identified, including massive or graded sandstone, parallel and trough cross-bedded sandstones, hummocky cross-stratified sandstone, wave-rippled sandstone and siltstone, massive or horizontal bedded mudstone, and structurally deformed sandstone and mudstone. In a vertical succession, these lithofacies occur as three fining-upward lithofacies associations, each of which represents different architectural elements (and depositional processes) of proximal to distal storm deposits. The relatively coarse proximal architectural element is formed by strong density flows and unidirectional-dominated combined flows; the transitional architectural element is dominated by unidirectional- and oscillatory-dominated combined flows to pure oscillatory flows, resembling Tb-e divisions of the classic Bouma sequence; the relatively fine distal architectural element is dominated by unidirectional-dominated combined flows with a very weak oscillatory flow component. The origin of storms responsible for these deposits is attributed to Asian winter monsoons associated with the paleoclimatic and paleogeographic setting.

We use digital seismic reflection profiles within a 1° × 1° survey area on the Cocos Ridge (COCOS6N) to study the extent and timing of sedimentation and sediment redistribution on the Cocos Ridge. The survey was performed to understand how sediment focusing might affect paleoceanographic flux measurements in a region known for significant downslope transport. COCOS6N contains ODP Site 1241 to ground truth the seismic stratigraphy, and there is a seamount ridge along the base of the ridge that forms a basin (North Flank Basin) to trap sediments transported downslope. Using the Site 1241 seismic stratigraphy and densities extrapolated from wireline logging, we document mass accumulation rates (MARs) since 11.2 Ma. The average sediment thickness at COCOS6N is 196 m, ranging from outcropping basalt at the ridge crest to ~ 400 m at North Flank Basin depocenters. Despite significant sediment transport, the average sedimentation over the entire area is well correlated to sediment fluxes at Site 1241. A low mass accumulation rate (MAR) interval is associated with the ‘Miocene carbonate crash’ interval even though COCOS6N was at the equator at that time and relatively shallow. Highest MAR occurs within the late Miocene–early Pliocene biogenic bloom interval. Lowest average MAR is in the Pleistocene, as plate tectonic motions caused COCOS6N to leave the equatorial productivity zone. The Pliocene and Pleistocene also exhibit higher loss of sediment from the ridge crest and transport to North Flank Basin. Higher tidal energy on the ridge caused by tectonic movement toward the margin increased sediment focusing in the younger section.

The division and analysis of the genetic types of slope breaks will be helpful in studying the enrichment regularity of hydrocarbon reservoirs because the enrichment of hydrocarbon reservoirs is closely related to the shelf-slope break types in continental lake basins or sags in China. This paper analyses the types of basin margins in Qikou Sag by assessing the sag boundary fault characteristics and spatial combination patterns using high-resolution three-dimensional seismic data, well logs and other data. Basin margins were divided into four types: steep slope fault belts, multi-level step-fault belts, steep slope step-fault belts and slope break flexure belts. Different types of depositional systems developed near the different basin margins, and correspondingly, four types of sequence stratigraphic patterns were developed. According to the study of trap types that occur adjacent to the different slope-break zones, fault-controlled lithologic traps were the predominant trap type in fault-controlled slope break zones, and lithologic traps occurred in the sag centre distant from the boundary faults. Along the slope break flexure belt, different types of traps developed in different slope break levels; stratigraphic unconformity traps occurred within the first slope break level, and stratigraphic–lithologic traps and up-dip pinchout lithologic traps were found in the second slope break level. So the deployment of future exploration should be conducted at different levels in Qikou Sag.