Print this pageArchitectural Changes within Channel Depositional Settings of a Fine-Grained Turbidite, Tanqua Karoo, South Africa
KIRKOVA, JULITTA T., and ARNOLD H. BOUMA
One of the submarine fans belonging to the Tanqua Karoo Subbasin in South Africa, represents a complete basin floor fan, characterized in downfan direction by a variety of channel settings, such as nested-channel complex at the base-of-slope, and channel-levee-overbank sets in the adjacent basin-floor fan area. The uniqueness of these exposures is a combination of small grain- size variations (Lvf-Uvf, occasionally up to Lf) of the sediments and the size of the outcrops (up to 1.5 km long and 20 m thick). Regardless of the fine grain size these turbidites display erosive as well as depositional behavior.
The channels within the channel complex are characterized by: 1) lateral change from channel to levee to overbank deposits, 2) relative vertical fining and thinning of the sediment fill, 3) many erosional surfaces, rip-up clasts, and plant fragments, 4) erosional remnants within amalgamated sandstones, and 5) soft sediment deformation of the sediment below the channel surface. These channels are relatively shallow and range in lateral extent. Overall, it seems that they exhibit good lateral and vertical sandstone connectivity.
The channels belonging to the channel-levee-overbank depositional environments cut through thin-bedded turbidite facies, which represent levee-overbank deposits of another channel. Sandstone amalgamation, slumping sediment deformation, rip-up clasts, and plant fragments are common. The environment of deposition is interpreted to represent channel switching in the middle-fan area. These channel complexes display good lateral and rather poor vertical sand-on-sand connectivity.