Middle Cambrian slope deposits in northern Victoria Land, Antarctica: Fingerprinting small carbonate platforms dominated by grainy carbonates and microbial reefs

초록

Carbonate-bearing slope strata are reported from the upper Miaolingian-lower Furongian Spurs Formation in northern Victoria Land, Antarctica, deposited in a backarc basin during the Ross Orogeny. The Spurs Formation consists mainly of shale interbedded with conglomerate and sandstone. It overlies the middle Miaolingian Glasgow Volcanics and volcaniclastic Molar Formation and is overlain by the lower Furongian sandstone-dominated Eureka Formation. The Spurs conglomerate is composed of randomly-oriented, granule- to boulder-sized, polymictic clasts of shale, sandstone and various limestone. These limestone clasts are variable in texture, such as microbial boundstone composed of calcimicrobe Epiphyton and subordinate microbial crust, oolitic-peloidal packstone to grainstone, and minor lime mudstone to wackestone. These are collectively interpreted as slope deposits, in which limestone clasts may have been derived from missing platform margin carbonate, analogous to Cambrian to Lower Ordovician slope successions elsewhere. On the other hand, the rarity of thinly bedded micritic limestones in the Spurs slope successions is markedly distinctive, and possibly reflects subdued production of lime muds behind the platform edge. It suggests that the vanished carbonate platform may have formed within a narrow shelf margin, dominated by coarse-grained carbonate and microbial reefs. Such style of carbonate platforms would contribute to understand how syn-orogenic carbonates initiated and developed in back-arc basins along the pacific margin of Gondwana (i.e., southern Australia and New Zealand).

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