남극 남쉐틀랜드 군도 북부 대륙주변부의 후기 제 4기 퇴적작용

Late Quaternary Sedimentary Processes in the Northern Continental Margin of the South Shetland Islands, Antarctica

  • 윤석훈 (제주대학교 해양고학부/해양과학환경연구소) ;
  • 윤호일 (한국해양연구원 극지연구소) ;
  • 강천윤 (한국해양연구원 극지연구소)
  • 발행 : 2004.02.01

초록

남쉐틀랜드 군도 북쪽 대륙주변부에 분포하는 후기 제 4기 퇴적층에 대한 퇴적상과 고해상 탄성파상 분석을 통하여 빙하 발달기 해저퇴적작용을 규명하였다. 중력시추기를 이용하여 채취된 퇴적물은 퇴적구조와 조직 특성을 달리하는 6개의 퇴적상으로 구분되었으며, 3.5 KHz 고해상 탄성파 특성은 반사파들의 명확성(또는 반사강도), 측면연속성, 형태 및 해저지형에 따라 6개의 탄성파상으로 분류되었다. 이들 퇴적상과 탄성파상, 그리고 해저지형의 특성은 마지막 빙하최대발달기와 그 이후 빙하 쇠퇴기 동안에 상당한 퇴적작용의 변화가 있었음을 지시한다. 마지막 빙하기 동안 현재의 대륙붕 지역에는 극빙하가 확장하여 대부분의 지역을 덮었고, 기저빙하의 유동으로 침식된 깊은 해곡이 대륙붕 상에 형성되었으며, 이 당시 퇴적된 조립질 빙퇴석 퇴적체가 대륙붕 지역에 우세하게 분포한다. 이후 빙하기가 종식되어 남극 대륙빙하가 후퇴하면서, 빙하말단에서 저온의 음빙수가 다량 방출되어 고탁도의 밀도류를 형성하였고, 이러한 고탁도의 수류는 이전 빙하기에 형성된 대륙붕의 해곡을 따라 대륙사면까지 이동하면서 상당량의 퇴적물을 해곡 내의 수로와 대륙사면의 협곡에 집적시켰다. 아울러 대륙사면에서는 드물지만 해저사태와 일시적인 해저류에 의한 퇴적활동도 일어났으며, 남쉐틀랜드 해구에서는 대륙사면으로부터 유입된 저탁류가 간헐적으로 해 구축을 따라 이동하였다. 그러나 빙하가 완전히 후퇴한 현재에는 반원양성의 퇴적이 대륙붕과 대륙사면 전반에 걸쳐 우세하며, 남쉐틀랜드 해구에서는 저탁류가 간헐적으로 발생하여 해구축을 따라 이동된다.

Sedimentary facies and high-resolution echo facies were analyzed to elucidate sedimentation pattern of the late Quaternary glacial-marine deposits in the northern continental margin of the South Shetland Islands. Six sedimentary facies are classified, based on grain texture and sedimentary structures in gravity cores. The high-resolution (3.5 ㎑) echo characters are classified into 6 echo facies on the basis of clarity, continuity, and shape of bottom and subbottom echoes together with seafloor topography. Distribution of the echo and sedimentary facies suggest that there was a significant change in sedimentation pattern between the Last Glacial Maximum (LGM) and subsequent glacier-retreating period. When the grounded glaciers extended to the present shelfbreak during LGM, coarse-grained subglacial tills were widespread in the shelf area, and deep troughs in the shelf were carved beneath the fast-flowing ice steam. As the glacial margin retreated landward after LGM, dense meltwater plumes released from the retreating ice-front were funneled along the glacier-carved troughs, and accumulated channel- or cannyon-fill deposits in the shelf and the upper to mid slope. At that time, slope sediments seem to have been reworked by slope failures and unsteady contour currents, and further transported by fine-grained turbidity currents along the South Shetland Trench. After the glacial retreat, sediments in the shelf and slope areas have been mainly introduced by persistent (hemi) pelagic settling, and fine-grained turbidity currents frequently occur along the axis of the South Shetland Trench.

키워드

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