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Abstract

The Carboniferous La Capilla Fm. of the Calingasta-Uspallata basin of western Argentina contains a low diversity fauna inhabiting a continental shelf under glacial ice fronts advancing from the east. Distal glaciomarine sediments on these ice-influenced shelves of Gondwana are most commonly interpreted as being deposited under quiet, low-energy conditions. Ta­phonomic and paleoecologic analysis of a sample of the fauna reveals the following: low species richness, yet comparable equitability to coeval, tropi­cal faunas; low articulation ratios and high pedicle valve dominance for brachiopods; diverse corrasion modes, about half relatively high categories; one hundred percent fracturing of brachiopod shells, with carinate fracture types dominant, and no evidence of epibiont coverage ofbrach.iopod shells, despite presence of encrusting organisms in the fauna. Collectively, the data indicate long residence time on the seafloor, with strong episodes of rework­ing - contrary to the low-energy hypothesis. Modem analogues of continental shelves reworked by currents to depths of 250 meters exist in Antarctica. The existence of similarly preserved faunas in the coeval, marginal basins of southern Gondwana needs to be confirmed.

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