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1 引 言 台湾西南部岸外陆坡有几个峡谷。从北到南,这些峡谷是澎湖、高雄、高屏和枋寮(图1)。它们已被知道了60多年。因为没有充分的由现代海洋地球物理和地质方法所取得的资料,它们中的没有一个被很好了解。例如,这些峡谷的沉积过程被了解很少,因为从这些峡谷中没有取得为沉积分析用的沉积岩芯。这些峡谷的一般地质评述已由Yu和Lu(1994)给出。 枋寮峡谷(据海岸城市命名)切割了海岸线之南的陆架约20km(图1)。直到现在,仅有一篇出版的文章专门涉及了枋寮峡谷(YU等,1991)。根据有限的测深资料和穿过枋寮峡谷的3.5Hz回声图,Yu等(1991)没有辨认出下峡谷分支成由南北向底辟侵入造成的两段。因此,他们的关于枋寮峡谷的地貌和成因的结论仅是部分正确的。 本文详细地描述了枋寮峡谷的地貌,并把地貌与页岩底辟体的局部上升关联起来,然后利用新取得的测深资料和多道地震反射剖面讨论此峡谷的成因。
1 Introduction There are several canyons off the coast of Taiwan’s southwest coast. From north to south, these canyons are Penghu, Kaohsiung, Gao Ping and Fangliao (Figure 1). They have been known for more than 60 years. None of them is well understood because there is not enough information available from modern marine geophysical and geological methods. For example, the deposition of these canyons is poorly understood as sedimentary cores for sediment analysis are not available from these canyons. Geological reviews of these canyons have been given by Yu and Lu (1994). The Cecilia Canyon (named after the coastal city) cut about 20 km of shelf on the south coastline (Figure 1). Until now, only one published article specifically addressed the Fangliao Gorge (YU et al., 1991). Based on the limited sounding data and the 3.5 Hz echoes passed through the Fangliao Gorge, Yu et al. (1991) did not identify two sections of the lower canyon branching into the north-south diapir. Therefore, their conclusions about the physiognomy and genesis of the Fangliao Gorge are only partially correct. This paper describes in detail the landform of the Ceoliao Canyon and correlates the topography with the local uplift of the shale diapirism. The origin of this canyon is then discussed using newly acquired sounding data and multi-channel seismic reflection profiles.