Abstract
Fresh-water, coarse-grained and detritus-dominated Mura Formation in North- Eastern Slovenia includes pyroclastic and volcaniclastic deposits originating from Upper Pliocene volcanic activity of basaltic geochemical character. Although localized in occurrence at the hamlet Grad, these pyroclastic and volcaniclastic sediments form a distinctive depositional unit, for which the term “Grad Member" is proposed and introduced in this paper. In the Grad area no lavas or cinder cones are preserved, and the origin of volcaniclastic fragments still uncertain. For this reason, Chemical composition of basaltic rock fragments from the Grad Member volcaniclastics has been studied and compared with basaltic rocks from the neighboring locations at Klöch, Kindsberg, Dölling and Neuhaus. The Grad Member pyroclastic and volcaniclastic deposits seem to be fed from the same source which is different from the occurrences in Austria. That supports the idea about the existence of a local volcanic centre in the present Grad area. The old volcanic edifices were possibly destroyed by the late-stage hydrovolcanic eruptions, and pyroclastic and volcaniclastic deposits subjected to constant reworking by fluvial currents in a dynamic sedimentary environment of alluvial fan and braided river systems.
Highlights
Fresh-water, coarse-grained and detritus-dominated Mura Formation in NorthEastern Slovenia includes pyroclastic and volcaniclastic deposits originating from Upper Pliocene volcanic activity of basaltic geochemical character
Upper Pliocene Grad Member consists of pyroclastic, syn-eruptive resedimented volcaniclastic and mixed volcaniclastic-fluvial deposits. Their formation is closely related to Continental alkali basaltic volcanism which was active about 3 million years ago in the area of the present medieval castle and the surrounding hamlet Grad in Goričko, NorthEastern Slovenia
Based on the content of alkali oxides and silica, the samples from Austria and the Grad Member volcaniclastics do not vary significantly, the samples from the Grad Member tend to be more rich in silica at a given Na20 + KzO content
Summary
Fresh-water, coarse-grained and detritus-dominated Mura Formation in NorthEastern Slovenia includes pyroclastic and volcaniclastic deposits originating from Upper Pliocene volcanic activity of basaltic geochemical character. Upper Pliocene Grad Member consists of pyroclastic, syn-eruptive resedimented volcaniclastic and mixed volcaniclastic-fluvial deposits. Their formation is closely related to Continental alkali basaltic volcanism which was active about 3 million years ago in the area of the present medieval castle and the surrounding hamlet Grad in Goričko, NorthEastern Slovenia. No lavas are preserved in the Grad area, but only their fragmented remains (Plate 1 - Fig. 1) in volcaniclastic debris flow deposits. For this reason, doubts have been posed again recently about the existence of local volcanic centre in the Sotinsk tre 'Juskova
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