Deep tow studies of the Vema Fracture Zone: 2. Evidence for tectonism and bottom currents in the sediments of the transform valley floor

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Abstract
The Deep Tow geophysical instrument package has been used to survey a 65‐km segment along the principal transform displacement zone (PTDZ) of the Vema Fracture Zone, away from either ridge‐transform intersection. The surface trace of the PTDZ is a small groove, 5–80 m deep and 20–200 m wide, incised in the otherwise flat‐lying turbidites of the transform valley floor. The fault trace cuts across the transform valley diagonally from ridge crest to ridge crest, hugging the southern flank of the median ridge. The groove is straight or gently sinuous, relatively free of the splays and bifurcations which characterize the transform fault zone near the ridge‐transform intersection (Macdonald et al., this issue). A pull‐apart basin was observed at the location of a slight clockwise bend in the fault trace. Vertical offsets of turbidites suggest that the west end of the median ridge and the east end of the south wall are rising relative to the transform valley floor at rates of the order of millimeters per year. Sediment waves were observed buried under 10–20 m of sediment, suggesting that Antarctic Bottom Water may have flowed through the transform valley more vigorously several tens of thousands years ago than at present.

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