--> Rift-Lake Turbidity-Flow-Dominated Sediments: Puysegur Group (Middle Cretaceous), Fiordland, New Zealand, by J. K. Lindqvist; #90986 (1994).

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Abstract: Rift-Lake Turbidity-Flow-Dominated Sediments: Puysegur Group (Middle Cretaceous), Fiordland, New Zealand

Jon K. Lindqvist

The Puysegur Group in southwest South Island, New Zealand, represents part of a rift basin system that extended across southern New Zealand during the middle Cretaceous separation of Australasia and Antarctica.

Six facies associations (A-F) are recognized in coastal exposures of the 1500+ m thick succession. Terrestrial and shallow lake margin deposits consist of: (A) a basal conglomeratic alluvial fan-alluvial plain association; and (B) a delta-top association of Gilbert-delta sandstone and shale, distributary channel sandstone, pedoturbated mudstone, and thin coal. Coarse-grained deep-water facies associations: (C) boulder breccia and graded sandstone; and (D) cobble conglomerate and mudstone, probably accumulated as talus aprons adjacent to border faults. The bulk of the succession comprises (E) a delta-slope channel and levee association of 10-50 m thick, crudely stratified, channelized coarse sandstones enclosed by mudstone and thin sandstone-mudstone couplets; and (F) a prodelta associ tion of 'classic' graded sandstone-mudstone turbidites, typically arranged in 20-50 m thick fining and thinning-upward cycles.

Turbidity currents probably originated as river-generated underflows or by liquefaction of delta-slope sediment. Mudstones contain abundant terrestrial plant debris, as do many sandstone beds. Possible analog of the delta-slope and prodelta deposits in Puysegur Group are found in axial margin and shoal margin deltas of East African rift lakes Malawi and Tanganyika. Fining upward successions in associations E and F are interpreted as lake low-stand to high-stand cycles.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994