Intracanyon Sands Delivery and Distribution of the Baiyun Submarine Canyon System: An Integrated Study Using Piston Cores, 3-D Seismic Data and Numerical Modeling

Abstract

Located on the central part of the northern South China Sea margin, the Baiyun submarine canyon system comprises eighteen N-S oriented, slope-confined canyons. Using high-resolution 3D seismic data, two newly-acquired piston cores and numerical modeling, this study aims to investigate the sand delivery and distribution pattern within canyon and reconstruct the depositional processes by the anatomy of the fifth submarine canyon in the west of the canyon system. Piston core P1, located in the canyon head, displays three separate sand layers in the top, middle and bottom intervals. Among them, the middle sand layer is thickest (250cm) and comprises multiple sand layers interbedded with clay and foraminifera beds. Comparingly, P2 is located in the canyon’s lower reach and mainly comprises muddy sediments.

Observations from seabed morphology and seismic coherence slices reveal a high-gradient, large-scale headwall scarp together with some secondary scarps in the vicinity of P1. This implies that the genesis of sand layers of P1 might be closely related to the slump process associated with preexist shelf margin. In contrast, P2 lies within a small deep-water channel flowing across the east flank of a prominent MTD, indicating a dominant formative process of turbidity currents. Hence, it is reasonable to speculate that a flow transformation might occur during the downslope transport of canyon head’s sediments. Besides, it also suggests that most of the sands in the canyon head don’t reach its lower mouth. Here, we hypothesize that local topographic irregularities might play an important role in capturing sands and hampering further downslope delivery.

To test the hypothesis, we involved 3D numerical simulation by using Dionisos software. To achieve a high-resolution, we used the modern seabed as the initial topography input with a presumption that the morphology barely changed in the recent 21 ka (dating results of the base of P2). Modeling tests confirmed the observation that most sandy sediments are captured by local accommodations during the sand delivery within the topographically complex canyon. This study indicates that large canyons with sands in their heads don’t necessarily develop sandy submarine fans in their mouths, especially when sand supply is not significantly enough. And, local topographic irregularities can be favorable zone in accumulating deep-water sands within the canyon and should be paid more attention in future hydrocarbon explorations.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018