--> Sedimentary and Diagenetic Record of Ladinian-Carnian Carbonate Platforms (Southern Alps) and its Implications for Mid-Triassic Climatic Changes, by M. Mutti and H. Weissert; #90986 (1994).

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Abstract: Sedimentary and Diagenetic Record of Ladinian-Carnian Carbonate Platforms (Southern Alps) and its Implications for Mid-Triassic Climatic Changes

Maria Mutti, Helmut Weissert

The evolution of Ladinian-Carnian platform carbonates of the Southern Alps is controlled by regional subsidence and sea-level changes and strongly reflect paleoeclimatic fluctuations. Numerous climatic models predict that the geography of the Pangean continent was conducive to the establishment of a "megamonsoonal" circulation. We use diagenetic events and their isotopic record in Ladinian-Carnian platforms to understand the impact of Triassic climate on sedimentation and to evaluate changes in climate.

Late Ladinian to early Carnian stratigraphy in the investigated areas consists of shallow water carbonates with peritidal cycles, repeatedly affected by subaerial exposure and karsting. Marine micritic limestones have an oxygen composition of -4 to -7.4^pmil PDB. These values are depleted relative to the Triassic sea water by 3 to 6^pmil and reflect reequilibration by meteoric waters. Meteoric calcites of the same age associated with paleokarst episodes have oxygen isotopic compositions (^dgr18O= -4.6 to -6.7^pmil PDB) progressively more depleted upward in the section. These isotopic data reflect either precipitation at progressively cooler temperatures or progressive increase of meteoric recharge. Shallow water carbonates with evaporites and dolomites overlie in the late C rnian the sequence affected by meteroic water. Oxygen isotopes document precipitation from normal and evaporation concentrated seawater, reflecting an overall decrease in moisture abundance.

Facies distribution, petrographic and isotopic data provide evidence for a strong seasonality in the sedimentary record, expressed at different temporal hierarchies, supporting the hypothesis of a climate dominated by monsoonal circulation. Moisture abundance reaches a maximum in the late Ladinian-early Carnian, testifying to the intensification of monsoonal circulation.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994