Abstract
The distribution of Nurnmulites fabianii fabianii and Nummulites fabi.anii reti.dtas in the Mortisa sandstone is discussed. The Monisa sandstone is a terrigenous unit of late Priabonian age occurring south of the Asiago Plateau (Venetian Alps, northern Italy). The facies analysis allowed to recognize thickening-coarsening upward cycles interpreted as shallowing upward parasequences corre- sponding to depositional regressions. In each cycle five different fa- cies were recognized. The first and the last facies of every cycle con- tain larger foraminiferal assemblages with numerous specimens of Nummulites fabianii. Two different morphotypes of this species were attributed to the subspecies N. fabianii fabianii (Prever) and N. /a- bianii retiatus Roveda. Their distribution was influenced by the pa- leoenvironmental conditions. The flat subspecies N. fabianii retia- lrs occurs in the base-cycle marly facies, deposited under low-energy, lowlight conditions. The more inflated N. fabianii fabianii charac- terises the shallower top-cycle limestone, deposited under high-energn highlight conditions. Our observations suggest there is no obvious link between the morphology and the stratigraphic position, so the biostratigraphic si- gnificance of the two subspecies (currently used to divide the Pria- bonian in a lower and an upper part) remains uncertain.
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