Facies architecture of an isolated carbonate platform: tracing the cycles of the Latemàr (Middle Triassic, northern Italy)

Abstract

The 720‐m‐thick succession of the Middle Triassic Latemàr Massif (Dolomites, Italy) was used to reconstruct the lagoonal facies architecture of a small atoll‐like carbonate platform. Facies analysis of the lagoonal sediments yields a bathymetric interpretation of the lateral facies variations, which reflect a syndepositional palaeorelief. Based on tracing of lagoonal flooding surfaces, the metre‐scale shallowing‐upward cycles are interpreted to be of allocyclic origin. Short‐term sea‐level changes led to subaerial exposure of wide parts of the marginal zone, resulting in the development of a tepee belt of varying width. Occasional emergence of the entire lagoon produced lagoon‐wide decimetre‐thick red exposure horizons. The supratidal tepee belt in the backreef area represented the zone of maximum elevation, which circumscribed the sub‐ to peritidal lagoonal interior during most of the platform’s development. This tepee rim, the subtidal reef and a sub‐ to peritidal transition zone in between stabilized the platform margin. The asymmetric width of facies belts within individual metre‐scale cycles was caused by redistribution processes that reflect palaeowinds and storm paths from the present‐day south and west. The overall succession shows stratigraphic changes on a scale of tens of metres from a basal subtidal unit, overlain by three tepee‐rich intervals, separated by tepee‐poor units composed of subtidal to peritidal facies. This stacking pattern reflects two third‐order sequences during the late Anisian to early middle Ladinian.