惠西南地区古近系转换带型源-汇系统研究及其勘探意义

Study of source-sink system of transfer zone type of Palaeogene in southwestern area of the Huizhou sag and its exploration significance

珠江口盆地惠西南地区隆洼间发育一系列转换带型沟谷源-汇系统,勘探程度较低,一直以来主要依靠地震资料进行沉积相刻画。本文基于最新的高分辨率三维地震资料,以区域古地貌为基础,定量表征了惠州25、27转换带分水岭、分水线、汇水单元等沟谷体系的基本要素。作为沟通物源区与惠州26洼的重要输砂通道,转换带汇聚了物源汇水区的碎屑物质,并沿转换带沟谷再次搬运入湖,这一过程中碎屑物质经过强水动能改造,成熟度进一步提高。基于源-汇系统认识,对惠州27转换带地震相进行了分析,认为碎屑物经两级沟谷体系入湖,形成了文四段早期的进积型扇三角洲与文四段晚期的退积型辫状河三角洲,完善了该地区物源、搬运、沉积三要素之间的源-汇耦合关系,对深挖转换带型沟谷体系潜力具有参考价值,推动了惠西南地区惠州27转换带古近系的勘探进程。

Sedimentary facies of several source-sink systems of transfer zone type developed between uplift and sag,southwestern area of the Huizhou sag,Pearl River Mouth basin,where the exploration maturity is low,are mainly characterized by using seismic data.Based on the regional palaeo-geomorphology,such basic elements of gully-valley system as watershed,divide line and catchment units were quantitatively characterized according to the latest high-resolution 3 D seismic data in Huizhou 25&27 transfer zone.As an important bypass for the sediments from provenance to the Huizhou 26 sub sag,the transfer zone converged fragmentary materials from the catchment area of the provenance,which would be transported along the gully-valley of the transfer zone to lake again.In this process,the maturity of fragmentary materials would be further improved under the effect of strong water kinetic energy.Based on the understanding of source-sink system,the seismic facies of Huizhou 27 transfer zone were analyzed and it is believed that the process of fragmentary materials flowing into lake via two-level gully-valley system helped the formation of the progradational fan delta of lower 4th member of Wenchang Formation and the retrogradational braided river delta of upper 4 th member of Wenchang Formation and improved the source-to-sink coupling relationship among provenance,transportation and deposition in this area.It can serve as a reference for tapping the potential of gully-valley system of transfer zone type and has promoted the exploration progress of Palaeogene of Huizhou 27 transfer zone in southwestern area of the Huizhou sag.