Tectonic and climatic controls on the paleoceanographic evolution of the southeastern South Orkney Microcontinent (Scotia Arc, Antarctica)

Abstract

The opening, widening and deepening of the Drake Passage, framed in the development of the Scotia Arc, impacted the oceanic circulation of the Southern Ocean and facilitated the establishment of the modern Antarctic Circumpolar Current. The South Orkney Microcontinent (SOM), located in the southern Scotia Arc, is one of the largest continental blocks resulting from the separation of South America and the Antarctic Peninsula. Given its key location, studying the sedimentary cover of the SOM can provide new insights into early paleoceanographic reorganization before and during the opening of the surrounding oceanic basins. In this study, we analyzed the sedimentary record of the southeastern SOM (SE SOM) using multichannel seismic reflection profiles. Five main seismic units were identified and dated through correlation with Ocean Drilling Program Leg 113 Sites 695 and 696, providing a basis for lithological interpretation. Results reveal that the southeastern margin of the SOM records the influence of Weddell Sea water masses and associated bottom contour currents from the late Eocene onwards, with a marked development of contourite deposits during the early and middle Miocene. This process was facilitated by continued subsidence associated to the development of the Powell Basin, followed by the initial opening of the Jane Basin, which likely created a new deep -water pathway for water masses exchange. The cessation of bottom current deposition in the SE SOM during the late Miocene coincides with the onset of widespread development of contourite deposits in the southern Scotia Sea basins. After the middle Miocene, sedimentation patterns in the SE SOM suggest the advance of an ice sheet onto the continental shelf, consistent with the establishment of a more permanent glaciation on the Antarctic Peninsula region at around 5 Ma.