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Authigenic iron minerals as indicators of early-dolomitization in the Sandy Dolomites (uppermost Permian–Lower Triassic, Velebit Mt., Croatia)

Sedimentation from the uppermost Permian to the Lower Triassic deposits in the Velebit Mt. area is continuous (SALOPEK, 1948), and occurs within the lowest part of the informal lithostratigraphic unit of Sandy Dolomite. Lower Triassic deposits are mostly represented by early-diagenetic dolomites characterized by scarce fossil findings and frequent siliciclastic grains. Their composition indicate shallow-water marine depositional environment strongly influenced by the hinterland. Authigenic Fe-mineral association present in these dolomites, mainly pyrite and siderite, can therefore help in reconstruction of diagenetic and geochemical conditions of the dolomitization environment. Dolomitization of the studied sediments containing characteristic mineral association of pyrite, siderite, ankerite and dolomite, occurred in the mixing zone of sea and fresh water. Such dolomitization model is typical for the transgressive sequences (e.g. WRIGHT et al., 1997), which is in line with the ongoing transgression recorded within the Sandy Dolomite unit and continuous siliciclastic input to the shallow-water environment during Early Triassic. Fe-mineral associations and thermodynamic stability of authigenic iron minerals studied within uppermost Permian to Lower Triassic Sandy Dolomites of the Velebit Mt. provided a new tool to reveal diagenetic environment.

Fe-authigenic minerals; early-dolomitization; Lower Triassic; Velebit Mt.

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