Quaternary environmental evolution in the South Carpathians reconstructed from glaciokarst geomorphology and sedimentary archives

Laura Tîrlă,Virgil Drăgușin,Petra Bajo,Silviu Covaliov,Nicolae Cruceru,Vasile Ersek,Diana Hanganu,John Hellstrom,Dirk Hoffmann,Ionuț Mirea,Tiberiu Sava,Gabriela Sava,Ionuț Şandric

doi:10.1016/j.geomorph.2020.107038

Abstract

The Carpathian island-type glaciokarst has a great potential of preserving signals of past environments, archived in cave deposits like speleothems and clastic infills. We present here the geomorphology and structural control of several relict alpine caves and the surrounding glaciated marble karst in the Făgăraș Mountains. Four truncated and partially unroofed caves remained on the ridge-top of Mușeteica Mountain, above the glacial cirque, while a ponor cave that developed on the cirque bottom could be related to the Last Glacial Period. Structural measurements and cave morphology showed that the conduits formed at the intersection of foliation planes and tectonic fractures on the NE-SW and NW-SE directions. Cave development reflects three speleogenetic stages: 1) texture- and fabric-controlled dissolution and distension; 2) structurally-controlled breakdown; and 3) truncation, unroofing, and cave infilling with sediments. Slow diffuse dissolution was typical for the ridge-top caves, whereas M1 Cave developed by pressure flow.Further, we report the first UTh speleothem ages, related to the evolution of alpine caves and island glaciokarst in the South Carpathians during the Middle and Late Pleistocene. Dating results show a minimum estimated age of ~560 ka for the ridge-top caves, and that speleothem deposition met optimal conditions only during warmer periods, largely corresponding to interglacials. Stable carbon isotope values in speleothems range between −9.96‰ and −4.11‰, indicating the presence of plant and soil organic activity at the time of deposition. In total, five speleothem growth phases were distinguished during the last ~560 ka.We excavated the sediment infill of a ridge-top doline down to a 2-m depth. Radiocarbon dating revealed that it was deposited during the Late Holocene, and preliminary pollen analysis identified a plant assemblage dominated by grasses.Using the relationships between karst development, glaciation, and cave sedimentary archives, we present a time slice chronology of alpine landscape evolution at >560 ka, ~400 ka, ~330 ka, the Last Glacial Period (70–12 ka), and the Late Holocene. Our geomorphological, isotopic, and geochronological results also support the existing hypothesis that the South Carpathians may have experienced at least two glacial phases during the Pleistocene. Glacial erosion rate during the Last Glacial Period, and most likely during the penultimate glaciation, averages around 0.6 mm yr−1.

Highlights

Glacial activity leaves geomorphological imprints on carbonate rock bodies isolated at high altitudes, resulting in what is known as the island type glaciokarst (Veress et al, 2019)
This study provides new geomorphological and geochronological information on the evolution of the Făgăraș Mountains (Romania) marble karst and gives new insights into the relationship between karstification and Pleistocene environmental changes in the central South Carpathians
Our results show how the alpine karst and sedimentary archives such as speleothems and clastic infills have recorded these changes in an isolated high-altitude setting

Summary

Introduction

Glacial activity leaves geomorphological imprints on carbonate rock bodies isolated at high altitudes, resulting in what is known as the island type glaciokarst (Veress et al, 2019). Caves can be either truncated or completely removed by glaciation (Mais, 1999; Klimchouk et al, 2006), or be buried and preserved by infilling with glacial till (Cooper and Mylroie, 2015). They can preserve morphological traits and sediments that could offer information useful for the reconstruction of mountain uplift (Meyer et al, 2011). Alpine caves and their associated sedimentary deposits brought more light onto the Quaternary evolution of the Alps (Spötl et al, 2002, 2007; Häuselmann et al, 2015), Apennines (Columbu et al, 2015), Norwegian Alps (e.g., Lauritzen, 1995; Berstad et al, 2002), or the Cantabrian Mountains (Ballesteros et al, 2015, 2019)

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Results

Conclusion