HOW UNUSUAL IS THE EARLY TRIASSIC SHALLOW MARINE FAUNA?

The Early Triassic has been characterized as a time of low diversity, dwarfed (Lilliputian) faunas with a depauperate and rather uniform community structure. To test these predictions we have recollected and analysed the fauna of the Virgin Limestone Formation (Spathian, southwestern Utah), one of the few shallow marine carbonate deposits of this age, comparing it with faunas from similar marginal marine settings in the Triassic and Jurassic (Muschelkalk, Penarth Group, Great Estuarine Series). The Virgin Limestone shows marked lateral and vertical variations in facies and faunal composition, and a repeated crinoid- to brachiopod- to bivalve-dominated succession in fining-upwards parasequences. Beta diversity contribution has been calculated both for sampling localities and for beds within a single outcrop. Maximum size for specific taxa is compared with that of congeneric or confamilial taxa from similar environmental settings. Although there are some unusual aspects about the Virgin Limestone fauna (e.g. overwhelming predominance of Spirorbis-like microconchids among the encrusting guild), preliminary indications are that the fauna is not significantly different from other Triassic and Jurassic faunas in similar marginal marine settings.