Sedimentary filling characteristics and controlling factors of lacustrine microbial carbonates sequence in the Santos Basin, Brazil

Abstract

Based on comprehensive analysis of seismic, logging, core, thin section data, and stable isotopic compositions of carbon and oxygen, the sedimentary filling characteristics of the Lower Cretaceous Barra Velha Formation sequence in H oil field, Santos Basin, are studied, and the high-frequency sequence stratigraphic framework is established, and the spatial distribution of reef-shoal bodies are predicted and the controlling factors are discussed. During the depositional period of the Barra Velha Formation, the study area is a slope-isolated platform-slope sedimentary pattern from southwest to northeast and the change of climate background from rift to depression periods has resulted in the variation of sedimentary characteristics from the lower third-order sequence SQ1 (BVE 300 Member) of low-energy deep water to the upper third-order sequence SQ2 (BVE 200 and 100 members) of high-energy shallow water in the Barra Velha Formation. The activities of extensional faults and strike-slip faults in rift period and the sedimentary differentiation from platform margin to intra-platform in depression period made the sedimentary paleogeomorphology in these two periods show features of “three ridges and two depressions”. The reef-shoal bodies mainly developed in the SQ2-LHST period, with vertical development positions restricted by the periodic oscillation of the lake level, and developed on the top of each high-frequency sequence stratigraphic unit in SQ2-LHST in the platform. The strike-slip fault activity controlled the distribution of the reef-shoal bodies on the plane by changing the sedimentary paleogeomorphology. The positive flower-shaped strike-slip faults made the formation of local highlands at the margins of and inside the shallow water platforms and which became high-energy sedimentary zones, creating conditions for the development of reef-shoal bodies.