DIAGENETIC EVOLUTION OF THE CARNIAN WETTERSTEIN PLATFORMS OF THE EASTERN ALPS

The carbonate platforms of the Wetterstein Formation of the Eastern Al ps (Drau Range and Northern Calcareous Alps) show a distinct facies zo nation of reefs and lagoons. While some lagoonal areas were episodical ly emerged and formed lagoonal islands, others remained permanently fl ooded. The scale of near surface, meteoric or marine diagenesis was re lated to this lagoonal topography. At shallow burial depth, cementatio n was dominated by altered marine solutions, which additionally caused recrystallization of metastable constituents of the sediment and earl ier marine cements (high magnesian calcite, aragonite) connected with a carbon and oxygen isotopic change to more negative values. Deeper bu rial cementation shows a succession with two types of saddle dolomite and three types of blocky calcite. Carbon and oxygen isotopic values o f these cements show a trend towards more negative values from the fir st to the last generation, in the following succession: clear saddle d olomite-zoned blocky calcite-cloudy saddle dolomite-post-corrosion blo cky calcite-replacive blocky calcite. Fluid inclusion studies of the c arbonate cements are interpreted to indicate a deeper burial temperatu re development that first increases from 175 to 317-degrees-C, followe d by a temperature decrease to 163-260-degrees-C, and subsequent incre ase up to 316-degrees-C, whereby the samples of the Drau Range always show the lowest values. Calculations of the isotopic composition of th e water, from which the carbonate cements were precipitated, yielded p ositive deltaO-18 values from 6.66 to 17.81 parts per thousand (SMOW), which are characteristic for formation and/or metamorphic waters. Als o, the isotopic compositions of the palaeofluids probably changed duri ng deeper burial diagenesis, following the temperature development.