Geochemical and petrographic evidence of meteoric diagenesis in Tufa deposits in Northern Dalmatia (Zrmanja and Krupa rivers, Croatia)

Holocene tufa deposits in the Northern Dalmatia region of Croatia occur along the banks and at present sites of waterfalls of the Zrmanja river and its tributary the Krupa river. Petrographic, geochemical and statistical analyses have been used to relate textural features and trace element composition to the degree of meteoric diagenesis. Trace metal concentrations associated with carbonate phase were determined by sequential extraction procedure. The insoluble residue (I.R.) is predominantly of primary origin and its amount ranges from 3 % to 29 %, averaging 13.75 %, thus permitting variable water/rock ratios of the stabilazing meteoric system. All the evidence points to a scarcity of post-depositional recrystallization and cementation, but where present these features are accompanied by I.R., Mg, Sr and Zn depletion and Fe enrichment.