EARLY DIAGENESIS OF PLITVICE LAKES WATERFALL AND BARRIER TRAVERTINE DEPOSITS

Travertine forms spectacular waterfalls, barriers, and subaqueous fine -grained lake-fill accumulations throughout the Plitvice National Park , Croatia, north-western Yugoslavia. Barrier deposits form dams, behin d which, the lakes of the Plitvice complex are situated. Three generat ions of low-magnesian calcite spar comprise the waterfall and barrier forming travertines. The initial precipitates generally are composed o f cloudy, very finely to medium crystalline equant to bladed spar. A l ater generation is composed of clear, isopachous layers of medium to c oarsely crystalline bladed crystals. Additionally, centimeter-thick la minated speleothem-like crusts, composed of clear, bladed to columnar spar, are the common precipitates around micritic accumulations within the older travertine. In comparison, the lake-fill deposits are prima rily composed of moderately (recent lake-fill deposits) to well-develo ped (relict lake-fill deposits) 3-8 mum calcite rhombohedrons. Petrogr aphic analyses clearly show that cyanobacteria, fungi, and/or other mi crobial organisms bore into the spar and micritize it. This sparmicrit ization is pervasive throughout the waterfall and barrier deposits. Bl aded spar crystals range from those which are pristine to those whose original bladed morphology can only be interpreted by comparison with laterally adjacent crystals. Individual samples display multiple gener ations of spar which have undergone various degrees of sparmicritizati on. Sparmicritization results in a thoroughly micritized accumulation in which evidence of the original spar composition has been completely obliterated.