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Geostrophic sand ridge, dune fields and associated bedforms from the Northern KwaZulu‐Natal shelf, south‐east Africa
Author(s) -
RAMSAY PETER J.,
SMITH ALAN M.,
MASON THOMAS R.
Publication year - 1996
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1046/j.1365-3091.1996.d01-17.x
Subject(s) - geology , bedform , ridge , geostrophic current , geomorphology , sediment transport , geostrophic wind , sand dune stabilization , pleistocene , paleontology , sedimentary rock , sedimentary structures , sediment , sedimentary depositional environment , oceanography , structural basin
Subaqueous dunes are formed on the KwaZulu‐Natal outer‐shelf due to sediment transport by the Agulhas Current (geostrophic current). These dunes occur within two dune fields at depths of − 35 to − 70 m. The net sediment transport direction is south, but short‐period reversals form northward‐migrating bedforms. The dune fields are physically bounded by late Pleistocene beachrock and aeolianite ledges. A bedform hierarchy has been recognized in the dune fields comprising a system of three generations of climbing bedforms. The outer dunefield has given rise to a sand ridge ( H =12 m; L =4 km; W =1.1 km; and an 8° lee slope) whereas the inner dune fields have achieved large‐scale dune status. Bedload parting zones within the dune fields occur where the sediment transport direction switches from north to south due to reversals in the geostrophic flow; these zones occur at depths of − 60, − 47 and − 45 m. An interpretative stratigraphic model is presented on what such geostrophite deposits would look like in the ancient sedimentary record.