Rhaetian (Late Triassic) Milankovitch Cycles in the Tethyan Dachstein Limestone and Laurentian Passaic Formation Linked by the g2-g5 Astronomical Metronome

Abstract

Milankovitch cycles have long been suspected of having been recorded in the shallow marine Lofer cyclothems of the Rhaetian Dachstein Limestone of the European Northern and Southern Calcareous Alps. However, sufficient evidence has not yet been forthcoming to make a compelling case for Milankovitch control on the cyclothems. At the same time, there is overwhelmingly strong evidence that Milankovitch cycles were influencing the paleoclimates of Rhaetian Laurentia and the wet-dry playa lake deposits of the Passaic Formation (Newark Basin, USA). The strongest cycles in these deposits, the McLaughlin cycles, have been linked to the metronomic g2-g5, or 405 kyr orbital eccentricity cycle. Thus, Milankovitch cycles were operating throughout the Rhaetian, and being global in nature, likely played a role in the genesis of the coeval Lofer cyclothems. The Dachstein Limestone in the Julian Alps, relatively undisturbed by tectonics, exhibits strong Milankovitch-like cyclicity, including evidence for g2-g5 cycling. The shallow marine Dachstein and continental Passaic formations provide evidence for complementary forcing mechanisms and active aquifer-limno-eustasy: low sea level in Lofer exposure facies is reflected in wet Passaic playa lake deposits, and high sea level in Lofer subtidal facies in dry Passaic playa lake deposits. The Dachstein and Passaic formations are further linked by the g2-g5 metronome; a provisional correlation is proposed, subject to future validation by additional, as yet undeveloped chronostratigraphic constraints.