Dasycladalean algae distribution in ammonoid-bearing Middle Triassic platforms (Dolomites, Italy)

This paper gives an account of distribution of Dasycladales in ammonoid-bearing Middle Triassic carbonate platforms of the Dolomites. A ca. 600-m-thick section was investigated within the Latemar platform interior and Dasycladales from correlated ammonoid-bearing samples of the Marmolada platform were studied for comparison. At Latemar, the dense sampling allowed, with some confidence, the identification of the first occurrences of Diplopora nodosa and Gyroporella ladinica, and the last occurrences of D. annulatissima and D. comelicana. Their stratigraphic range was found to be in agreement with literature. Other first or last occurrences could not be reconciled with known distributions, and were considered as environmentally or palaeogeographically controlled. All four algal events occur within a narrow interval of two Illyrian (Upper Anisian) ammonoid subzones (avisianum and crassus subzones). This study demonstrates the biostratigraphic potential of Dasycladales in platform settings, and highlights the necessity of detailed stratigraphic studies to determine their distribution.