Evolution and Stratigraphic Architecture of the Wonoka
Submarine Canyons in Salt-Withdrawal Mini-Basins, Northern Flinders Ranges, South Australia
Dyson, Ian A., Salt
Neoproterozoic submarine canyons of the Wonoka Formation outcrop in the northern Flinders Ranges.
Individual canyons are exposed in synclines overlying or contained within
salt-withdrawal mini-basins of the Adelaide Geosyncline.
The 1500 meter-deep Patsy Springs canyon was cut during
salt-withdrawal adjacent to the Christmas-tree diapir
at Pinda Springs. Its base is a deep-water sequence
boundary with no shallow-water equivalent. The canyon fill contains
high-frequency, fining-upward sequences of the forced transgressive
systems tract, punctuated with unconformity-based channel complexes passing
laterally into mudflows off the canyon wall. The basal, several meter-thick
carbonate breccia of each channel complex is overlain
by vertically amalgamated, laterally interconnected, narrow and sinuous
channel sands. The sinuous Fortress Hill canyon displays similar architecture.
Mudflows generated from instability on the outside of each bend were reworked
into channel breccias at the base of successive channel complexes, with
fine-grained overbank facies
deposited on the inside of each bend. The Nankabunyana Canyon overlies the salt-withdrawal
mini-basin at Beltana diapir.
Unconformity-based channel breccias were deposited adjacent to and on
downthrown side of growth faults. An angular unconformity, formed by slumping
of transgressive shale in the canyon axis, is
overlain by channel breccia with onlap
of an overall fining-upward succession of thin-bedded turbidites.
Correlation of a
mega-slump unit in each canyon indicates sedimentation could not keep pace with
subsidence, with overlying unconformity-based channel breccia
marking next fin-ing-upward cycle. Overall
fining-upward canyon fills are characterized by low net to gross. Channel
complexes are encased within background sedimentation comprising fine-grained turbidites that provide excellent seal.