Spectral Analysis of the Middle Triassic Latemar Limestone

Abstract

ABSTRACT The Middle Triassic Limestone in the Dolomites region, northern Italy, consists of hundreds of vertically stacked, meter scale, platform carbonate cycles. Each cycle is composed of a shallow marine subtidal carbonate unit with a thin (centimeter scale) vadose diagenetic dolomite cap. These Latemar are the products of repeated episodes of submergence/emergence with durations estimated at 20,000 yr. The couplets are arranged in upward thinning bundles of five, indicating the presence of a 100,000 year modulating component. We examined this high frequency cycling in the platform buildup using a variety of classical and advanced spectral analysis techniques. We found si nificant evidence for the presence of a Milankovitch forcing signal in this cycling. We also present evidence that the adjacent coeval basinal facies, the Livinallongo Formation, exhibits a similar bundling pattern in its cm-scale hemipelagic carbonate/shale alternations. We conclude that Milankovitch-forced, small amplitude sea-level oscillations were the most likely cause of these Middle Triassic carbonate rhythms.