Duje Smirčić

Stratigraphic Definition and Correlation of Middle Triassic Volcaniclastic Facies in the External Dinarides: Croatia and Bosnia and Herzegovina

Middle Triassic volcaniclastic depositsin the External Dinarides of Croatia and Bosnia and Herzegovina are related to the rifting of the Tethyan Ocean. Three localities in the External Dinarides: Donje Pazarište, Bosansko Grahovo and Zelovo were biostratigraphically analysed in this study. The Middle Triassic carbonate deposits with volcaniclastic interlayers in Donje Pazarište were defined by means of conodonts. Rare ammonoid specimens were collected.Recovered conodont and ammonoid taxa suggest these sections are of Early Illyrian to Early Fassanian Age. The section studied in Bosansko Grahovo is dominantly composed of volcanic and volcaniclastic rocks. Limestone peperites were collected for conodont analysis. Two conodont zones were defined, suggesting volcanic activity in the same, from Lower Illyrian to Fassanian, time interval. The Zelovo Section was biostratigraphically investigated by several authors. The pietra verde deposits from Zelovo are referred as late Fassanian to Early Longobardian Age. Biostratigraphic correlation from mentioned three localities imply that the magmatic activity in the External Dinarides, and formation of different volcaniclastic facies lasted from Illyrian to Longobardian, similar as in the surrounding western Tethyan territories.

Western Tethyan Epeiric Ramp Setting in the Early Triassic: An Example from the Central Dinarides (Croatia)

In the central part of the External Dinarides in Plavno, Croatia, near Knin, a remarkably thick (927.5 m) Early Triassic depositional sequence was investigated. The Plavno sequence starts in the EarlyGriesbachian and ends with a continuous transition into the Anisian strata. A complete 13C isotope curve has been achieved and combined with conodonts, bivalves and ammonoids to establish and correlate stage and substage boundaries. The δ13C curve is consistent with former studies. It displays a general increase from the Griesbachian to a prominent maximum beyond the +8‰ amplitude around the Dienerian-Smithian boundary (DSB), followed by a steep and continuous decline to low, negative values in the Smithian. Around the Smithian-Spathian boundary (SSB) a steep rise to a second maximum occurred. It is followed by a saw-tooth shaped decline in the Spathian and a similar increase to a peak at the Spathian-Anisian boundary (SAB).Sedimentologically, the Plavno sequence is interpreted as having been deposited on an extensive epeiric ramp under long-term transgressive conditions, sharing depositional characteristics of both the epeiric platform and the carbonate ramp. The entire Plavno sequence was deposited above the storm-wave base and was storm influenced. Three informal members are differentiated: 1) the dolostone member (Early Griesbachian); 2) the siliciclastic member (red-coloured shale, siltstone, sandstone with oolitic/bioclastic grainstone intercalations), which can be further divided into lower, middle and upper intervals (Late Griesbachian, Dienerian and Smithian); and 3) the mudstone member (grey lime mudstones, marls and calcisiltites with common ammonoids and gastropods-Spathian). The Plavno sequence is compared with other western Tethyan sections. Observed differences stem from local controls on deposition in the overall shallow marine environment.