Abstract
Upper Cretaceous deposits in Medvednica Mt. are composed of coarse-grained conglomerates, sandstones, shales and the pelagic Scaglia Limestones. Such deposits in the wider region possess reservoir potential, not previously studied in Northern Croatia. Modal composition of conglomerates, size and distribution of clasts, porosity and permeability were studied from one new exposure in Medvednica Mt., and the results were compared with previously published data from neighboring successions. Conglomerates are polymictic, clast- to matrix-supported, with clasts and matrix entirely composed of local bedrocks. Porosity varies between 4.98 to 10.89% and permeability from 1.13 to 43.3 mD. Overlying pelagic Scaglia Limestones contain pelagic foraminifera of the latest Santonian to Early Campanian age (83 to 85 Ma). Clasts were eroded from the local hinterland, probably transported to the beach by short-term torrents and deposited along the shelves of the proto-Medvednica Island. Previously presumed alluvial transport is not likely. Deposition took place in a Gosau-type basin during the subsidence phase, additionally controlled by a third-order sea-level change at the Santonian-Campanian boundary. According to this study, Upper Cretaceous clastites possess possible reservoir potential, and deserve more attention in future hydrocarbon research in Croatia.
Highlights
Cretaceous deposits from the Medvednica Mt. have been studied since the beginning of the 20th century [1,2,3,4,5], in some cases as stops in field guides [6,7,8] or within unpublished doctoral and master theses, e.g., [9,10,11].Polymictic conglomerates within the Late Cretaceous succession are composed of clasts of local origin [4,7,8,10]
Upper Cretaceous deposits in Medvednica Mt. are composed of coarse-grained conglomerates, sandstones, shales and the pelagic Scaglia Limestones
Size and distribution of clasts, porosity and permeability were studied from one new exposure in Medvednica Mt., and the results were compared with previously published data from neighboring successions
Summary
Cretaceous deposits from the Medvednica Mt. have been studied since the beginning of the 20th century [1,2,3,4,5], in some cases as stops in field guides [6,7,8] or within unpublished doctoral and master theses, e.g., [9,10,11].Polymictic conglomerates within the Late Cretaceous succession are composed of clasts of local origin [4,7,8,10]. Cretaceous deposits from the Medvednica Mt. have been studied since the beginning of the 20th century [1,2,3,4,5], in some cases as stops in field guides [6,7,8] or within unpublished doctoral and master theses, e.g., [9,10,11]. Geosciences 2018, 8, 456 deposits, while in the southwestern (SW) and southern (S) parts they lie over the Paleozoic-Triassic rocks [3,12,13] (Figure 1). These rocks predominate as clasts in conglomerates (Figure 1). Cobbles, and sporadically boulders are, in most cases elongate-oval, Geosciences
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