The Cryosphere, 4, 501–509, 2010 www.the-cryosphere.net/4/501/2010/ The Cryosphere doi:10.5194/tc-4-501-2010 © Author(s) 2010. CC Attribution 3.0 License. Cryogenic and non-cryogenic pool calcites indicating permafrost and non-permafrost periods: a case study from the Herbstlabyrinth-Advent Cave system (Germany) D. K. Richter1, P. Meissner1, A. Immenhauser1, U. Schulte1, and I. Dorsten2 1Ruhr-University Bochum, Institute for Geology, Mineralogy and Geophysics Universitatsstr.¨ 150, 44801 Bochum, Germany 2Haarstraße 22, 35745 Herborn, Germany Received: 4 June 2010 – Published in The Cryosphere Discuss.: 15 July 2010 Revised: 9 November 2010 – Accepted: 11 November 2010 – Published: 30 November 2010 Abstract. Weichselian cryogenic calcites collected in what 1 Introduction is referred to as the Ratselhalle¨ of the Herbstlabyrinth- Advent Cave system are structurally classified as rhombo- In contrast to most carbonate speleothems (e.g. stalagmites) hedral crystals and spherulitic aggregates. The carbon and which precipitate from supersaturated waters above 0 ◦C oxygen isotopic composition of these precipitates (δ13C = (e.g. Hill and Forti 1997) cryogenic cave calcites (CCC sensu +0.6 to −7.3‰; δ18O = −6.9 to −18.0‰) corresponds to Zˇ ak´ et al., 2004) form during freezing of cave waters. This those of known slowly precipitated cryogenic cave calcites process takes place when seepage waters enter a cave char- under conditions of isotopic equilibrium between water and acterized by mean temperatures below 0 ◦C. In present-day ice of Central European caves. The carbon and oxygen iso- ice caves of the temperate zone with high ventilation, wa- topic composition varies between different caves which is at- ter freezes in a thin film on the surface of ice. Due to rapid tributed to the effects of cave air ventilation before the freez- kinetic escape of CO2 from the solution, rapid freezing of ing started. cave waters leads to high δ13C values of precipitated calcites By petrographic and geochemical comparisons of Weich- (Lacelle, 2007; Spotl,¨ 2008). In contrast, slowly freezing wa- selian cryogenic calcite with recent to sub-recent precipitates ters and related preferential 18O incorporation into the ice in as well as Weichselian non-cryogenic calcites of the same lo- more or less isolated cavities within permafrost, leads to low cality, a model for the precipitation of these calcites is pro- δ18O values of calcite precipitates from this fluid (Zˇ ak´ et al., posed. While the recent and sub-recent pool-calcites isotopi- 2004). cally match the composition of interglacial speleothems (sta- In recent years, Quaternary cryogenic cave calcites formed lagmites, etc.), isotope ratios of Weichselian non-cryogenic by slow growth conditions from Central European caves have pool-calcites reflect cooler conditions. Weichselian cryo- been described in a series of publications (locations between genic calcites show a trend towards low δ18O values with Scandinavian and Alpine ice sheets; Zˇ ak´ et al., 2004, 2008, higher carbon isotope ratios reflecting slow freezing of the 2009; Richter and Niggemann, 2005; Richter and Riechel- precipitating solution. In essence, the isotope geochemistry mann, 2008; Richter et al., 2008, 2009, 2010). The genesis of the Weichselian calcites reflects the climate history chang- of these calcite particles is essentially bound to water pools ing from overall initial permafrost conditions to permafrost- on top of ice bodies in caves during the transition periods be- free and subsequently to renewed permafrost conditions. tween glacial/stadial to interglacial/interstadial. Conversely, Judging from the data compiled here, the last permafrost the precipitation of similar calcites from pool waters on the stage in the Ratselhalle¨ is followed by a warm period (in- cave floor is not yet documented. Nevertheless, during these terstadial and/or Holocene). During this warmer period, the transitional periods, mean annual temperatures outside of the cave ice melted and cryogenic and non-cryogenic Weich- cave gradually decreased and then fell below freezing point. selian calcite precipitates were deposited on the cave ground Because of the low heat conductivity of rocks this decrease or on fallen blocks, respectively. in temperature reached the subsurface with some delay (as described by Pielsticker, 2000) so that low-frequency tem- perature changes are not recorded in cryogenic cave calcite Correspondence to: D. K. Richter records, depending on the overburden of the cave. Follow- ([email protected]) ing a subsequent temperature rise, cave ice formed during Published by Copernicus Publications on behalf of the European Geosciences Union. 502 D. K. Richter et al.: Cryogenic and non-cryogenic pool calcites indicating permafrost and non-permafrost periods Fig. 2. Sketch map of Herbstlabyrinth-Advent Cave system show- ing the location of Ratselhalle¨ as well as a speleological map of this chamber with sampling locations. Fig. 1. Map showing the position of the Herbstlabyrinth-Advent Cave system as well as other caves of Central Europe from which 2 Geographical and geological setting cryocalcite has been described (light brown – Rhenish Slate Moun- tains, light grey – Weichselian glaciated areas). See lower left inset The Herbstlabyrinth-Advent Cave system formed in the for more details. Upper Devonian Iberg Limestone of Breitscheid on the NE margin of the Tertiary Westerwald volcanic complex (Fig. 1). The reefal deposits of the Iberg Limestone (Kayser, previous cold periods, melted and different types of cryo- 1907; Krebs, 1966), located on a volcano basement in genic cave calcites accumulated on the cave ground or on the Rhenohercynian trough of the Rhenish Slate Mountains collapsed blocks covering the cave floor. (Krebs, 1971), is well known for its abundant epi- and endo Unconsolidated sediments of calcite particles with a broad karst phenomena of Late Cenozoic age (Stengel-Rutkowski, range of structures are present on the cave floor and on blocks 1968). The Herbstlabyrinth-Advent Cave system was first in the Ratselhalle¨ of the Herbstlabyrinth-Advent Cave system discovered in the winter of 1993/1994 during quarry works (sensu Grubert (1996) and Hulsmann¨ (1996)) in NW Hesse (Grubert, 1996). Deposits with bones of small mammals as (see Fig. 1). These deposits were sampled in 2004 and 2009 well as some remains of cave bears indicate at least episodic for detailed structural and geochemical analyses and are the connections to the surface in the past. A second artificial topic of the present publication. entrance was built in order to develop a touristic cave. Fol- The age of the main type of the calcite particles found, lowing Dorsten et al. (2005), this cave system formed in a namely aggregates of euhedral calcite crystals, was dated to shallow phreatic system. Several of the cave levels reflect the 29 170 ± 480 years based on the U/Th method (Kempe et al., palaeo-position of ancient long-lasting ground water tables. 2005). These precipitates were interpreted as having formed Kaiser et al. (1998, 1999) identified four karst levels, which as rafts on pool water situated on cave ice bodies (Kempe, today are situated in the vadose zone with a temporal active 2008). The less commonly found types of calcite aggregates, fluvial system in the lowest part of the cave, and three sub- here referred to as composite spherulites, were petrographi- sequent stages of speleothem formation have been identified cally compared with cryogenic calcites described by Richter but not yet dated. The Herbstlabyrinth-Advent Cave system and Niggemann (2005) and Richter and Riechelmann (2008). is located between the villages of Erdbach and Breitscheid The later ones were attributed to a precipitation setting in (Fig. 2). With an overall length of more than 5300 m, it is the slowly freezing pools on ice bodies due to their low δ18O largest cave system in Hesse and one of the most significant signature (−14 to −18‰ VPDB). ones in Germany. The Ratselhalle¨ (altitude 363 m above sea The genetic relation between before-mentioned types of level) providing the sampling material for this study belongs “crystal sand” present in the Ratselhalle¨ was previously to the western part of the EW trending main cave area and is poorly constrained. Here, the petrographic and geochemi- 20 m long, 15 m wide and 5 m high on average. This part of cal properties of the different types of these crystal sands are the cave can be accessed via a narrow passage. Because of documented in detail and a comparison with recent/subrecent its remote location the average annual air temperature in this calcite formations in a pool in the Ratselhalle¨ is presented. chamber is about 9 ◦C. The thickness of the hostrock above The aim of this publication is to improve the understanding the Ratselhalle¨ reaches about 40 m. of cryogenic cave calcites as novel archives of cold continen- tal climate phases. The Cryosphere, 4, 501–509, 2010 www.the-cryosphere.net/4/501/2010/ D. K. Richter et al.: Cryogenic and non-cryogenic pool calcites indicating permafrost and non-permafrost periods 503 4 Data presentation and interpretation 4.1 Speleothem particles Samples of speleothem particles are composed of nearly sto- ichiometric calcite (d(104) 3.034–3.036 A)˚ as documented by diffractometer analysis. This outcome is not unexpected given that the host rock of the cave is mainly composed of low Mg-calcite (d(104) 3.030–3.034 A).˚ Only small amounts of secondary dolomite are present in the hostrock carbonate. Below, speleothem particles sampled from the (i) cave floor and collapsed blocks and (ii) from pools are described sep- arately, because different modes of formation are proposed based on field observations. 4.1.1 Speleothem particles collected from the cave floor Fig. 3. “Crystal sand” on collapse block (arrows) in the Ratselhalle.¨ and on collapsed blocks The most common form of speleothem particles are aggre- Calcite-cemented debris on the cave walls marks the for- gates and individual crystals with rhombohedral faces which mer presence of ice attached to the cave wall (Pielsticker, occur at all sampling points (Fig.