珠江口盆地荔湾凹陷北部早中新世沟槽特征及其成因

沟槽及其成因是近年来沉积学和古海洋学的研究热点。本研究基于珠江口盆地荔湾凹陷内的高精度三维地震资料,在研究区早中新世地层中首次识别出延伸千米的沟槽。这些沟槽形成时研究区位于远离陆架坡折的深水盆地,其走向大致平行于早中新世南海北部陆架坡折走向,可细分为4个亚区,形态呈直线形、拱形或似波痕状,几何学参数在不同分区各有特点。另外,在部分沟槽底部具有规模较大的条带状高振幅异常,可能对应粗粒沉积或富含天然气。根据沟槽特征推测其成因可能与盆内广布的中层水环流影响下的底流活动有关。古地貌控制下的早中新世古底流,通过其水体对海底产生侵蚀进而形成侵蚀沟槽。此研究不仅有助于南海北部超深水区的油气勘探,同时可为南海早中新世古海洋学研究提供新证据。

Features and origin of the early Miocene grooves in northern Liwan sag,Pearl River Mouth Basin

Grooves and their origin are the research hotspots in sedimentology and palaeooceanography in recent years. Based on the high resolution 3D seismic data in Liwan sag of Pearl River Mouth Basin,multi-kilometer scale grooves are identified, for the first time, in the early Miocene strata of the study area. These grooves are located in deep-water basin away from the shelf slope break roughly parallel to the strike of northern South China Sea shelf margin break during the early Miocene. They can be subdivided into four sub-zones. They are straight or arched,or ripple-like in shape and their geometry parameters have different characteristics in different sub-zones. In addition,there are large bands of high amplitude anomalies at the bottom of some grooves,which may correspond to coarse-grained sediments or be rich in natural gas. According to their features,it is inferred that their origin may be related to bottom currents,which was influenced by the intermediate water circulation widespread in the basin. The bottom currents,which were mainly controlled by palaeogeomorphology during the early Miocene,eroded the seabed and formed the grooves. This study not only contributes to the hydrocarbon exploration in ultra-deep water area in northern part of South China Sea,but also provides new evidence for the early Miocene palaeooceanographic research in South China Sea.