Mélanges and broken formations at the boundary zone of the Magura and Silesian nappes (Gorlice area, Polish Outer Carpathians) - a result of sedimentary and tectonic processes

Krzysztof Starzec,Aneta Wronka,Ewa Malata,Luiza Malina

doi:10.7306/gq.1173

Krzysztof Starzec, Aneta Wronka + Show 2 more

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https://doi.org/10.7306/gq.1173

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Abstract

Based on geological ﬁeld mapping, analyses of cores from explanatory wells, and foraminiferal age control data, we have differentiated a few types of mélanges and broken formations at the bordering zone between the Magura and Silesian nappes (Gorlice area in the Polish Outer Carpathians). These mélanges and broken formations differ in composition and structure due to different settings and processes of their formation. Several levels of broken formation within the uppermost part of the Krosno Beds were formed as mass-transport deposits at the southern slope of the Silesian Basin. They may record tectonic pulses related to advancing accretionary wedge within Magura area and directly predate the stage of the larger-scale sedimentary mélange formation at the front of the wedge. This mélange is composed mainly of the material representing the Magura succession (Siary Subunit) and the Krosno type sediments of the Silesian succession. It was emplaced within the Silesian basin in the Early Miocene time. The so-called “Harklowa peninsula”, whose geological structure has been the subject of discussions and various interpretations in the past years, is built of this type of mélange. The other recognized type of broken formation and mélange represents the chaotic bodies formed at the base of the Magura Nappe.The results of our studies contribute to better understanding of the structural evolution of this part of the Outer Carpathians.

Highlights

Chaotic rock bodies characterized by disorganized internal structure and named most commonly as mélange or olistostrome have been the subject of many studies
In our paper we follow the definitions presented by Festa et al (2012). These authors argue that the term mélange should be used only in a descriptive meaning as suggested by Berkland et al (1972), Silver and Beutner (1980), Raymond (1984), Cowan (1985), Wakabayashi (2011) or Wakabayashi and Dilek (2011), instead of genetic definitions such as those of Hsü (1968), Cowan (1974), Gansser (1974) or Sengör (2003) that restricted the term only to Krzysztof Starzec, Ewa Malata, Aneta Wronka and Luiza Malina chaotic rocks originated by tectonic strain
The Middle–Late Eocene and latest Eocene/Early Oligocene calcareous benthic and planktonic foraminifera might have derived from marly, pelagic sediments that accumulated on the slopes above the local CCD

Summary

Introduction

Chaotic rock bodies characterized by disorganized internal structure and named most commonly as mélange or olistostrome have been the subject of many studies Several other terms, such as wildflysch (e.g., Bird, 1969; Behr et al, 1982), megabreccias (e.g., Di Stefano et al, 1996; Bosellini, 1998), broken formation (e.g., Hsü, 1968; Codegone et al, 2011), argille scagliose (e.g., Ogniben, 1953; De Libero, 1998; Pini et al, 2004), tectonosomes (Pini, 1999) or mud volcanoes (Camerlenghi and Pini, 2009) have been used to designate chaotic deposits. Such definitions of mélange and broken formation do not imply any process of their origin, i.e. tectonic or sedimentary

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