Thin-Bedded Turbidites of the Tanqua Karoo: Physical and Depositional Characteristics
Thin-bedded turbidites (TBTs, 5–60 cm in bed thickness) constitute a common lithofacies in fine-grained deepwater clastic environments. Field and laboratory data from the present study reveal systematic differences between the various deepwater depositional settings. Grain-size and bed-thickness distribution in the TBTs are the result of varying flow velocity and sediment load. The finest grain-size and thinnest beds are developed in the midfan levee-overbank and midfan passive channel-fill deposits. The coarsest grains and thickest beds are observed in the distal sheet sandstones. The data indicate bedform type and bedform stacking, in several scales, to vary with subfacies. Levee-overbank and passive channel-fill TBTs are dominated by base truncated Bouma Sequences (Tc, Tcd, Tcde), but channel-sheet transition and distal sheet deposits are characterized by top-truncated Bouma Sequences (Ta, Tab, Tabc). The TBTs were deposited as a result of “bodyspill” from channelized turbidity currents or as deposits from the lagging tails of degenerating turbidity currents.