The interplay of carbonate systems and volcanics: Cues from the 3D model of the Middle Triassic Sciliar/Schlern platform (Dolomites, Southern Alps)

In the Dolomites (Southern Alps), the original stratigraphic relationships and depositional geometries of Middle Triassic carbonate systems are exceptionally preserved and exposed, and well-constrained in a high-resolution sequence stratigraphic and bio-chronostratigraphic framework. During the late Ladinian, the region experienced a strong tectono-magmatic event, leading to local uplifts and sinks, partial collapses of carbonate edifices and large submarine landslides, as well as the emplacement of thick volcanic and volcanoclastic deposits. The relationships between carbonate and magmatic bodies can be observed in detail in the area between the Sciliar/ Schlern mountain group and the Alpe di Siusi/Seiser Alm. In order to better constrain the distribution, geometries and relationships between carbonate, volcanic and volcanoclastic facies, a 3D geological model of the Anisian-Ladinian platform-to-basin system of the Sciliar and Catinaccio carbonate platforms has been developed. The input data set is composed by a net of geological sections built on an updated geological map, field data and formation boundaries digitized on a high-resolution DTM. The resulting pre-volcanic, platform-to-basin system shows a slightly arcuate shape of the margin part facing a starved basin. The volcanic stage is accompanied by strong tectonic subsidence in local sectors of the investigated area, with infilling by mass flow deposits, volcanic rocks, and volcanoclastic material. Major fault-scarps related to the collapse of pre-volcanic carbonate platforms have been modeled. The distribution and thickness of magmatic bodies in the area is however quite variable. The modeled post-volcanic platform-to-basin system shows the impact of the Late Ladinian irregular sea bottom on the distribution and thickness of the younger (mixed carbonate and volcanoclastic) basinal sediments. The model also show that the post-volcanic edifices extended beyond the collapsed portions and occupied an area slightly larger than their pre-volcanic predecessors. The last interval documents the development of lowstand fringing reefs around the older carbonate platform and possibly around demised volcanic areas.