Stratigraphy and palaeoenvironment of the early Jurassic volcaniclastic strata at Djupadalsmölla, central Skåne, Sweden

Abstract: From the almost 200 volcanic outcrops in the Central Skåne Volcanic Province (CSVP), only three are of volcaniclastic material. These volcanoclastics, and the transition to the underlying crystalline basement, have been investigated for the first time in a drill core (KBH2) from Djupadalsmölla in order to understand the stra-tigraphy, depositional process, age of deposition, and depositional environment. The core constitutes three rock units, in ascending order: the kaolinite weathered crystalline basement, a thin dark coloured mudstone, and a mas-sive lapilli tuff (volcaniclastics). From the degraded state of the crystalline basement, it is clear that extensive che-mical weathering tock place implying a wet and humid climate. Through palynological studies of the mudstone unit the depositional environment was likely a restricted bay or lagoon with limited marine influences surrounded by a forest covered wetland at the time of volcanism. The age of the mudstone could be determined to late Pliensbachian through the palynomorphs. Petrographic analysis shows that all but the lowermost part of the volcaniclastic deposit has a lapilli tuff texture. The material is, however, highly degraded and replaced by swelling clay minerals and highly affected by diagenetic processes. The depositional process could only be narrowed down to two alternatives. Either directly deposited by a pyroclastic flow or secondarily deposited by a lahar.