Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | The Cryosphere Discuss., 4, 1011–1034, 2010 The Cryosphere www.the-cryosphere-discuss.net/4/1011/2010/ Discussions TCD doi:10.5194/tcd-4-1011-2010 4, 1011–1034, 2010 © Author(s) 2010. CC Attribution 3.0 License. Cryogenic and This discussion paper is/has been under review for the journal The Cryosphere (TC). non-cryogenic pool Please refer to the corresponding final paper in TC if available. calcites D. K. Richter et al. Cryogenic and non-cryogenic pool calcites reflect alternating permafrost and Title Page interglacial periods (Breitscheid-Erdbach Abstract Introduction Cave, Germany) Conclusions References Tables Figures D. K. Richter1, P. Meissner1, A. Immenhauser1, U. Schulte1, and I. Dorsten2 J I 1Ruhr-University Bochum, Institute for Geology, Mineralogy and Geophysics, Universitatsstr.¨ 150, 44801 Bochum, Germany J I 2Am Schleidt 9, 35745 Herborn, Germany Back Close Received: 4 June 2010 – Accepted: 11 June 2010 – Published: 15 July 2010 Full Screen / Esc Correspondence to: D. K. Richter ([email protected]) Published by Copernicus Publications on behalf of the European Geosciences Union. Printer-friendly Version Interactive Discussion 1011 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract TCD Weichselian cryogenic calcites collected in what is referred to as the “Ratselhalle”¨ of the Breitscheid-Erdbach Cave were structurally classified as rhombohedral crystal and 4, 1011–1034, 2010 spherulitic crystal sinters. The carbon and oxygen isotopic composition of these pre- 5 cipitates corresponds to those of known cryogenic calcites of slow genesis of Central Cryogenic and 13 18 European caves (δ C=+0.6 and −7.3‰; δ O=−6.9 to −18.0‰). The variant carbon non-cryogenic pool and oxygen isotope pattern differing between different caves is attributed to cave spe- calcites cific ventilation. Particularly, Breitscheid cryogenic calcites reflect mean levels of cave ventilation. By petrographic and geochemical comparisons of Weichselian cryogenic D. K. Richter et al. 10 calcite with recent to sub-recent precipitates as well as Weichselian non-cryogenic cal- cites of the same locality, a model for the precipitation of these calcites is proposed. While the recent and sub-recent pool-calcites isotopically match the geochemistry of in- Title Page terglacial speleothems (stalagmites, etc.), isotope ratios of Weichselian non-cryogenic Abstract Introduction pool-calcites reflect cooler conditions. Weichselian cryogenic calcites show a trend to- 18 15 wards O-depleted values with higher carbon isotope ratios reflecting slow freezing Conclusions References of the precipitating solution. In essence, the isotope geochemistry of the Weichselian Tables Figures calcites reflects the climate history changing from overall initial permafrost (glacial) con- ditions to an interglacial and subsequently to renewed permafrost conditions. The last stage then grades into the present-day warm period. Judging from the data compiled J I 20 here, the last permafrost stage is followed by only one interglacial. During this inter- J I glacial, the cave ice melted and non-cryogenic Weichselian calcite precipitates were deposited on the cave ground or on fallen blocks, respectively. Back Close Full Screen / Esc 1 Introduction Printer-friendly Version Cryogenic cave calcites (CCC sensu Zˇ ak´ et al., 2004) form during freezing of car- Interactive Discussion 25 bonate saturated cave waters. This process takes place when seepage waters enter a cave or cave system characterized by mean temperatures below 0 ◦C. Alternatively, 1012 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | the 0 ◦C isotherm might fluctuate over time. Due to evaporation effects, rapid freezing of cave waters leads to 13C-enriched values of precipitated calcites (Lacelle, 2007; Spotl,¨ TCD 2008). In contrast, slowly freezing waters and related preferential 18O incorporation 4, 1011–1034, 2010 into the ice, leads to a low δ18O of calcite precipitates from this fluid (Zˇ ak´ et al.,2004). 5 In recent years, Quaternary cryogenic calcites formed by slow growth conditions from Central European caves were described in a series of publications (locations between Cryogenic and Scandinavian and Alpine ice shields; Zˇ ak´ et al., 2004, 2008; Richter and Niggemann, non-cryogenic pool 2005; Richter and Riechelmann, 2008; Richter et al., 2008, 2009). The genesis of calcites these calcite particles is essentially bound to water pools on top of ice bodies in caves D. K. Richter et al. 10 during the transition periods between warm and cold periods. Conversely, the precip- itation of similar calcites from pool waters on the cave floor is not yet documented. Nevertheless, during these transition periods, mean annual temperatures outside of Title Page the cave gradually decrease and then fall below the freezing point. Following a subse- quent temperature warming, cave ice, formed during cold periods, melts and different Abstract Introduction 15 types of cryogenic calcites are accumulated on the cave ground or on collapsed blocks covering the cave floor. Conclusions References Unconsolidated sediments of calcite particles with a broad range of structures Tables Figures are locally accumulated on the cave floor and on blocks in the “Ratselhalle”¨ of the Breitscheid-Erdbach Cave in NW Hesse (“Herbstlabyrinth-Advent” cave system sensu J I 20 Grubert (1996) and Hulsmann¨ (1996); for location refer to Fig. 1). These deposits were sampled in 2004 and 2009 for detailed structural and geochemical analysis and are the J I topic of this present publication. Back Close The age of the main type of the calcite particles found, namely aggregates of euhe- dral calcite crystals, was dated 29 170 ± 480 yrs based on the U/Th method (Kempe Full Screen / Esc 25 et al., 2005). These precipitates were interpreted as having formed as rafts on pool water situated on cave ice bodies (Kempe, 2008). The less commonly found types of Printer-friendly Version calcite aggregates, here referred to as composite spherulites, were petrographically compared with known cryogenic calcites described by Richter and Niggemann (2005). Interactive Discussion The later ones were attributed to a precipitation setting in slowly freezing pools on ice 1013 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | bodies due to their 18O depleted signature (−14 to −18‰ VPDB). The genetic relation between before-mentioned types of “crystal sands” present in TCD the “Ratselhalle”¨ was previously poorly constrained. Here, the petrographic and geo- 4, 1011–1034, 2010 chemical properties of the different types of these crystal sands are documented in 5 detail and a contrast comparison with recent/subrecent calcite formations in a sinter basin of the “Ratselhalle”¨ is presented. The aim of this publication is to improve the un- Cryogenic and derstanding of cryogenic calcites as novel archives of cold continental climate phases. non-cryogenic pool calcites 2 Geographical and geological setting D. K. Richter et al. The “Breitscheid-Erdbach” Cave formed in the Upper Devonian Iberger Limestone of 10 Breitscheid (Kayser, 1907; Krebs, 1966) on the NE margin of the Tertiary Westerwald Title Page vulcanite (Fig. 1). The reefal deposits of the Iberger Limestone, located on a volcano Abstract Introduction basement in the Rhenoherzynic trough of the Rhenish Slate Mountains (Krebs, 1971), is well known for its abundant upper Cenozoic karst phenomena (Stengel-Rutkowski, Conclusions References 1968). Conversely, the “Herbstlabyrinth-Adventhohlen”¨ cave system was first discov- Tables Figures 15 ered in winter of 1993/94 during quarry works (Grubert, 1996). Following Dorsten et al., (2005), this cave system formed in a shallow phreatic system. Several of the cave levels reflect the palaeo-position of ancient long-lasting ground water tables. Kaiser J I et al. (1998) identified four karst levels, which today are situated in the vadose zone, J I and three subsequent stages of sinter formation have been identified but not yet dated. 20 The “Herbstlabyrinth-Adventhohlen”¨ cave system is located between the villages of Back Close Erdbach and Breitscheid (Fig. 2). With an overall length of more than 5300 m, it is Full Screen / Esc the largest cave system in Hesse and one of the most significant ones in Germany. The “Ratselhalle”¨ (altitude 363 m a.s.l.) providing the sampling material for this study belongs to the western part of the EW trending main cave area. The thickness of the Printer-friendly Version 25 hostrock above the “Ratselhalle”¨ reaches about 31 m. Interactive Discussion 1014 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 3 Methodology TCD “Crystal sand” accumulations covering the cave floor or lying on collapsed blocks (Figs. 3 and 4) were sampled at five locations. In addition, specimens of recent and 4, 1011–1034, 2010 sub-recent rafts of sinter deposits in a pool located in the NW-part of the “Ratselhalle”¨ 5 (Fig. 4) were collected for comparative studies. Cryogenic and The sample material was cleaned in an ultrasonic bath in the laboratory prior to non-cryogenic pool a manual separation of the various sinter types under the binocular. The detailed ex- calcites ternal structure of small sinter precipitates was photographed under a high-resolution field emission scanning electron microscope (HR-FEM) of type LEO/Zeiss 1530 Gem- D. K. Richter et al. 10 ini. For this purpose, selected samples have been sputtered