No Valley Deepening of the Tatra Mountains
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https://doi.org/10.1130/G47635.1 Manuscript received 29 December 2019 Revised manuscript received 15 May 2020 Manuscript accepted 15 May 2020 © 2020 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Published online 19 June 2020 No valley deepening of the Tatra Mountains (Western Carpathians) during the past 300 ka Jacek Szczygieł1*, Helena Hercman2, Gregory Hoke3,4, Michał Ga¸siorowski2, Marcin Błaszczyk2 and Artur Sobczyk4 1 Institute of Earth Sciences, University of Silesia, Be¸dzin´ska 60, 41-200 Sosnowiec, Poland 2 Institute of Geological Sciences, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland 3 Department of Earth Sciences, Syracuse University, Syracuse, New York 13244-1070, USA 4 Institute of Geological Sciences, University of Wrocław, Pl. Maksa Borna 9, 50-204 Wrocław, Poland ABSTRACT sive. During MIS 6, the climate conditions were Wet-based mountain glaciers are efficient agents of erosion, which leads to the assumption milder, Tatra glaciers had a smaller range than that each glacial episode results in successive valley deepening. The tendency of subsequent during the LGM (Lindner et al., 2003), and con- glaciations to obscure evidence of previous events makes it difficult to study the work done ditions were conducive to speleothem growth by past glacial episodes. Epiphreatic and paleophreatic caves that developed at or under the (Hercman, 2000; Kicin´ska et al., 2017). There water table and dried out in response to valley deepening can serve as recorders of the val- is no direct evidence of pre–MIS 12 glaciation ley incision history. U-series data from speleothems in the cave networks at the base of the within the Tatra, however perched glaciofluvial present-day valleys in the Tatra Mountains (Western Carpathians) consistently yield the oldest deposits are interpreted to represent MIS 16–22 ages of ca. 325 ka. While speleothem ages are typically phreatic-vadose transition minimum and older glacial episodes (Lindner et al., 2003). ages, they nonetheless unequivocally demonstrate that neither glacial valley deepening nor In this study, we examine the history of glacial fluvial incision occurred over the past 300 ka, unlike the successive valley deepening over the valley deepening using nine localities across same period in the adjacent Alps. three adjacent valleys by determining the ages of speleothems from the modern, active cave INTRODUCTION however, remains difficult to prove, especially system at the base of the valley and from paleo- Wet-based mountain glaciers are docu- given a glacier’s tendency to rework deposits phreatic caves perched above the valley. mented to be efficient agents of erosion (Stern and reshape landforms developed in previous et al., 2005) that commonly create dramatic, glacial episodes. Geochronology studies pro- STUDY AREA high-relief landscapes. Indeed, mountain gla- vide evidence for abrupt valley incision during The Tatra are a fold-and-thrust belt composed ciers have been invoked as both limiting and the early and Middle Pleistocene (e.g., Shuster of Paleozoic crystalline basement covered by amplifying relief creation (e.g., Brozović et al. et al., 2005; Häuselmann et al., 2007). Given the Mesozoic sedimentary rocks (Jurewicz, 2005). [1997] versus Molnar and England [1990]) as extensive modification of the surficial environ- The Tatra constitute a horst exhumed from a well as exhumation (Stern et al., 2005; Thom- ment with successive glacial episodes, glacial depth of at least 5 km since the Miocene. Ex- son et al., 2010; Meyer et al., 2011). Yet the valleys developed in carbonates that favor the humation rates are on the order of 100–500 m/ cyclic variation between hothouse and icehouse development of cave systems have the potential Ma, with the highest rates in the southeastern conditions during the Quaternary makes deci- to reveal the chronology and magnitude of valley corner of the range (Anczkiewicz et al., 2015; phering the magnitude of erosion attributable deepening with U-series dating. Śmigielski et al., 2016). to any single glacial episode difficult to quan- The Tatra Mountains (Slovakia and Poland; The Tatra landscape was sculpted by the tify. The general assumption is that each glacial also referred to as simply “the Tatra”), the north- Pleistocene glaciations and periglacial process- episode deepens and widens the valleys occu- ernmost portion of the central Western Carpath- es. All valleys in the Tatra were occupied by pied by glaciers (Harbor, 1992). In the case of ian Mountains (Fig. 1), rise on average 1.4 km glaciers during the LGM and the total ice extent mountain glaciers, the evidence supporting the above the surrounding Central Carpathian Pa- is well mapped, with the largest glaciers extend- idea of successive valley deepening are typi- leogene Basin, and the northern side of the range ing as much as 3 km from the mountain front cally relative chronologies on terrace or moraine contains deep and extensive cave networks. The (Zasadni and Kłapyta, 2014). Nearly all glacial sequences with little, if any, absolute age con- Tatra are thought to have experienced eight gla- geochronology in the Tatra is LGM or young- trol (Ehlers et al., 2011). Early work in glacial ciations, which we refer to using Marine Isotope er (Kłapyta and Zasadni, 2018). Cosmogenic landscapes posited that the initial glacial episode Stages (MIS): MIS 2, 6, 8, 10, and 12, and three nuclide ages on moraines and the valley walls was responsible for the majority of landscape poorly constrained glaciations correlated with above the trimlines yield LGM or younger ages modification and that work by subsequent gla- the Alpine Günz, Donau, and Biber glaciations (Makos et al., 2013, 2018; Engel et al., 2015). ciers was minimal (Tarr, 1893). This hypothesis, (Lindner et al., 2003). The glaciations associ- While eight glacial episodes extending as far ated with MIS 2 (Last Glacial Maximum, LGM) back as the Pliocene Biber composite event are *E-mail: [email protected] and MIS 12 are thought to be the most exten- described in the literature (Lindner et al., 2003; CITATION: Szczygieł, J., et al., 2020, No valley deepening of the Tatra Mountains (Western Carpathians) during the past 300 ka: Geology, v. 48, p. 1006–1011, https:// doi.org/10.1130/G47635.1 1006 www.gsapubs.org | Volume 48 | Number 10 | GEOLOGY | Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/48/10/1006/5146608/1006.pdf by guest on 23 September 2021 A B C Figure 1. (A) Location of the Tatra Mountains in the Carpathian belt (white rectangle shows location of B). (B) Tectonic sketch of the Tatra (after Jurewicz, 2005) (black rectangle shows area of C). (C) Shuttle Radar Topography Mission 1 arc-second shaded relief with digital eleva- tion model (masl—meters above sea level). Black labels show caves with U-series ages (in ka) of speleothem basal layers. Black line marks the extent of the Last Glacial Maximum, after Zasadni and Kłapyta (2014). Kłapyta and Zasadni, 2018), the oldest reported we explored the potential for valley overdeepen- Kościeliska, and Bystra Valleys on the northern age on a glaciofluvial terrace in the Tatra is a ing and subsequent aggradation by estimating side of the Tatra (Fig. 1) and collected 16 spe- thermoluminescence age of 443 ± 36 ka (MIS the maximum possible thickness of Quaternary leothems for U-series dating from nine caves 12; Lindner et al., 1993). deposits based on valley profile morphology and ( Table 1). Ideal samples are speleothems depos- The karstic caves of the Tatra are developed bedrock outcrops in the valley floor (Figs. S5, ited immediately after the transition between in levels sensu Palmer (1987) and serve as water- S12, and S13 in the Supplemental Material1). phreatic and vadose conditions. We focused on: table indicators. Thus, as valley incision pro- Prior to this study, the oldest reported age for L0, the active (epi)phreatic level; and the L1 and gresses, the cave network lowers in response to L1 was 300 ± 12 ka by U-series on a flowstone L2 paleophreatic levels (Fig. 2). Samples were the falling water table, resulting in the transi- deposit (Szczygieł et al., 2019). analyzed by standard 230Th/234U disequilibrium tion of karst conduits from phreatic to vadose. techniques (Ivanovich and Harmon, 1992), allow- This transition is reflected in a shift from clastic U-SERIES DATING ing precise age determinations of up to 0.55 Ma. fluvial deposition to speleothem precipitation. We explored a total of 30 paleophreatic or ep- Details regarding sample locations, geomorpho- This study targets caves in the (epi)phreatic zone iphreatic caves spread across the Chochołowska, logical context, and U-series geochronology, in- that developed under the water table and subse- cluding correction for detrital Th, are given in quently dried out in response to valley deepen- Table S1 in the Supplemental Material. 1 ing (Ford et al., 1981). In the Tatra, we distin- Supplemental Material. Methods, sample loca- Our samples are typical of other speleothems tion, and their geomorphological context. Please visit guished five vertically stacked cave levels, L0 https://doi .org/10.1130/GEOL.S.12456302 to access from the Tatra, with low U concentrations and to L4 (Fig. 2). There are no direct constraints on the supplemental material, and contact editing@geo- admixtures of detrital contamination (Kicin´ska the depth to bedrock in the valley floors; thus, society.org with any questions. et al., 2017). Detrital contamination correction Geological Society of America | GEOLOGY | Volume 48 | Number 10 | www.gsapubs.org 1007 Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/48/10/1006/5146608/1006.pdf by guest on 23 September 2021 are younger than those from the L0 Kasprowa Niz˙nia and Bystra caves; however, this does not imply that they were drained later, only that the onset of speleothem growth began later.