CHARACTERISTICS AND DEPOSITIONAL MODEL OF THE FAULT-CONTROLLED BOTTOM-CURRENT DRIFT DEPOSITS IN THEBEIKANG BASIN, SOUTHERN SOUTH CHINA SEA
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摘要:
深海底流为深水沉积过程的重要要素之一，其可直接搬运或间接改造沉积物，并在海底形成沉积型地貌，即底流漂积体。在底流漂积体的8个沉积亚类中，受断层活动影响的断控型漂积体研究程度较低，全球范围内相关实例较少，其形态特征及沉积模式并无统一的描述。笔者以南海南部北康盆地为例，基于高分辨率多波束及地震反射资料解释，系统总结了断控漂积体的形态参数和在地震资料中的识别标志；确定了同沉积断控型漂积体和后沉积断控型漂积体；探讨了不同类别对应的断层活动、沉积过程及其沉积模式。断层活动和深海底流沉积作用同时期发生时，可形成具有不规则丘状结构的同沉积断控型漂积体；而当断层活动发生于底流作用之前时，前期断层活动形成的陡坎使得底流流速增加，从而有效地改造海底地貌，形成后沉积断控型漂积体。然而，目前的研究仅限于正断层活动与底流作用的耦合关系，其他类型的断层运动（如逆断层、走滑断层等）有必要在未来底流沉积研究中给予重点关注。
Abstract:Bottom current is a significant depositional process in deep sea, by which sediments can be directly transported to form contourite drifts on seafloor. Among the different types of contourite drifts, fault-controlled drifts are not well constrained and few studies have been devoted to their morphological features and depositional patterns. This study is to summarize the features for seismic identification of fault-controlled drifts based on high-resolution multibeam bathymetric and seismic data from the Beikang Basin, southern South China Sea. Two sub-types of fault-controlled drifts, i.e. the syn-depositional and post-depositional fault-controlled drifts are recognized. Their formation mechanism and relationships with faulting are discussed in this paper. According to the interaction between faulting and bottom-current processes the bottom currents can be divided into two types: 1) bottom currents simultaneous to the fault movement, generating the synchronous fault-controlled drifts; 2) bottom currents after the fault movement generating the post-depositional drifts. However, the researches conducted so far are limited to the drift deposits related to normal faults. More researches are required for the drifts formed in other active tectonic settings, such as those related to strike-slip faults and reverse faults.
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Key words:
- normal fault /
- bottom current /
- contourite drift /
- sedimentary depositional pattern /
- Beikang Basin /
- South China Sea
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表 1 北康盆地地震反射界面及所对应的地质事件[21]
Table 1. Seismic reflection discontinuities and correspondent geologic events[21]
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表 2 断控漂积体形态沉积特征及其与断层运动的交互关系
Table 2. Fault-controlled drift characteristics and associated fault-contourite interactions
断控型漂积体 发育水深/m 面积/km2 坡度角 几何形态 交互关系 沉积类型 1 1 470～1 910 21 7°～13° 不明显丘状 底流作用与断层活动同时发生 同沉积 2 1 290～1 660 40 14°～28° 不规则丘状 底流作用与断层活动同时发生 同沉积 3 1 230～1 480 74 7°～15° 丘状 底流作用发生在断层活动之后 后沉积 4 1 420～1 810 107 9°～17° 丘状 底流作用发生在断层活动之后 后沉积 5 1 380～2 040 32 6°～10° 不规则丘状 底流作用与断层活动同时发生 同沉积 6 1 190～1 630 40 15°～28° 不明显丘状 底流作用与断层活动同时发生 同沉积
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