A Geophysical-Geochemical Approach to the Study of the Paleogene Julian—Slovenian Basin “Megabeds” (Southern Alps—Northwestern Dinarides, Italy/Slovenia)

Kei Ogata,Gian Pini,Željko Pogačnik,Andrea Festa,Giorgio Tunis,Kim Senger

doi:10.3390/geosciences9040155

Abstract

The Paleogene “megabeds” of the Julian-Slovenian Basin are regional, basin-wide deposits, produced by catastrophic carbonate platform collapses. They record the emplacement of a bipartite slide mass behaving as a cohesive blocky/debris flow in the lower part, and as a grain to turbulent flow in the upper part. Several types of primary (sedimentary) soft sediment deformation structures testify fluid overpressure conditions during emplacement. Such structures are identified within a brecciated, fine grained matrix that encloses and intrudes slide blocks and clasts, characterized by NE-, NW- and SW-directed paleo-transport directions, indicating a depositional setting close to the basin margins. Here we present an updated review of some representative megabeds, exposed in the open-pit quarry outcrops of Anhovo (SW Slovenia). In particular, we here discuss new interpretations based on X-ray fluorescence spectrometry (XRF), thermo-gravimetry (TG) and electric resistivity tomography (ERT). Our results indicate that basal marly clasts of the megabeds are markedly different from the uppermost draping marls, suggesting two different coeval sources. The relationships with the underlying successions are strongly erosive, with deep localized scouring of the substrate and amalgamations between different megabeds, and the depositional units inside individual megabeds, supporting the geochemical differences.

Highlights

The Paleogene carbonate “megabeds” or “megabreccias” of eastern Friuli (Italy) and westernSlovenia are very thick and laterally extensive composite stratigraphic units that originated from the simultaneous accumulation of multi-sized carbonate debris from repeated catastrophic submarine landslide events [1,2]
We here discuss new interpretations based on X-ray fluorescence spectrometry (XRF), thermo-gravimetry (TG) and electric resistivity tomography (ERT)
In order to decipher the processes related to the formation of the megabeds we present revised interpretations here based on new geochemical X-ray fluorescence spectrometry (XRF) and thermo-gravimetric (TG) analyses, and on a series of 2D electrical resistivity tomography (ERT) profiles acquired as part of the exploration mining operations at the Anhovo quarry

Summary

Introduction

Slovenia are very thick (up to 260 m) and laterally extensive (up to 50 km wide) composite stratigraphic units that originated from the simultaneous accumulation of multi-sized carbonate debris from repeated catastrophic submarine landslide events [1,2]. These ancient mass transport deposits, identified in literature as sedimentary mélanges and olistostromes [3,4], testify that large. The Friuli Carbonate Platform was located at the southern boundary of the Julian—Slovenian Basin, forming a passive, distal margin relatively close to the paleo-Dinaric deformational front on the opposite NE side [1,2]

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