Lufeng depression is a proven rich-hydrocarbon accumulation area in the Pearl River Mouth Basin and has caught lots of attentions from petroleum
geologists.The drilling of oil and gas mainly focused on the Wenchang Formation in the southern area in the past years.The southern part of Lufeng depression is an active-fault bounded basin with an area of approximately 2200 Km2.The spatial distribution and temporal evolution of depositional systems were significantly influenced by tectonic momvments.In this study,the sequence architecture,depositional systems and the control of tectonics on temporal evolution were investigated using seismic profiles,cores and well logs.The results show that the Wenchang Formation is a second-order sequence, which can be subdivided into six third-order sequences(from base to top：SQ1,SQ2, SQ3,SQ4,SQ5 and SQ6)based on the study of the characteristics of seismic reflection relationship and wireline logging changes.The six third-order sequences correspond to three distinct stages of rift evolution,namely the early syn-rift,rift climax and late syn-rift stages.Based on seismic facies,cores and well logs, several depositional systems were distinguished in different types of lacustrine sequences:(1)the early syn-rift sequence(SQ1+SQ2),which mainly consists of fan delta, braided river delta and shallow lacustrine depositional system;(2)the rift climax sequence(SQ3),which is mainly composed of nearshore subaqueous fan,deep lacustrine and turbidity fan and(3)the late syn-rift sequence(SQ4+SQ5+SQ6),which comprises mainly braided river delta and shallow lacustrine.The depositional systems and facies dispersal patterns are believed to be a function of the interaction between tectonic movements and sediment supply.Various subsidence rates along the boundary faults at different stages can create distinct accommodation space and palaeogeomorphologies, leading to diverse stacking patterns and different sediment inputs.Besides, several types of transfer zones and structural slope-break zones developed during rifting stages and they both controlled the distribution of depositional systems. For example, transfer zones usually control the entry points of sediments into the basin,as a result,the development of depositional system. Magmatic diapirism is quite common in Lufeng depression, creating topographically higher area,which significantly influenced the position of drainage system,thus leading to the migrated sedimentary facies from early to late.This study provides insights into tectonic control on depositional system and may aid in the prediction of potential reservoir distribution in rift basins such as Lufeng depression.
Topics: Lacustrine sedimentation , Topics: Sequence stratigraphy
