Mechanism of sand body prediction in a continental rift basin by coupling paleogeomorphic elements under the control of base level

Abstract

In view of the complex sandbody distribution in continental rift basins, a sandbody prediction method is proposed based on the coupling of three core paleogeomorphic elements, provenance system, channel system, and slope break system, which composes the process of “provenance-transport-sedimentation” controlled by base level. The sand body prediction method takes the base level as the lever, the equilibrium position near the lake basin edge as the supporting point, and the core paleogeomorphic elements as study objects, lays stress on the fact that dynamic factors controlling static factors, and takes full consideration of flow state conversion and sandbody genesis. The core paleogeomorphic elements have eight types of theoretical coupling modes, corresponding to coupling deposition effect from the worst to the optimal. During fluctuations of base level, the coupling modes of the core paleogeomorphic elements in continental rift basins change under the “seesaw effect”, as a result, the migration pattern, sedimentary environment, and genesis of sand body change significantly, which control sand body distribution in turn. The sand body development regularity of the Gaoyou Sag in Northern Jiangsu Basin and the Weixinan Sag in Beibu Gulf Basin has been analyzed based on this sand control mechanism and a good prediction result of sand body is achieved, which confirms the validity and practicality of the sand control mechanism. Key words: continental rift basin, base level, ancient landform, coupling mode, sand control mechanism, Northern Jiangsu Basin, Beibu Gulf Basin