CLASTIC CAVE DEPOSITS IN BOTOVSKAYA CAVE (EASTERN SIBERIA, RUSSIAN FEDERATION) JAROSLAV KADLEC 1 ,MARTIN CHADIMA 1 ,LENKA LISA ´ 1 ,HELENA HERCMAN 2 ,ALEXANDR OSINTSEV 3 , AND HEDI OBERHA ¨ NSLI 4 Abstract: Botovskaya Cave is a typical example of a two-dimensional maze with a total length of explored passages exceeding 60 km, which represents the longest limestone cave system in the Russian Federation. The clastic cave sediments filling the cave passages differ in both mineral and mineral magnetic properties and were deposited under different hydrological conditions. The older portion of the clastic cave fills was derived from overlying sandstones, whereas the properties of younger cave sediments show closer affinity to the soils and weathering products originating on the plateau above the cave. The cave sediments underwent repeated periods of deposition and erosion during the Tertiary (?) and Pleistocene. The last catastrophic erosion event occurred in the cave more than 350 ka based on flowstone dating. Water seeping through the overlying sandstone body causes collapses of sandstone slabs from the cave passage ceilings, forming the youngest portion of the clastic cave fills. INTRODUCTION It has been demonstrated that the study of the clastic cave deposits can contribute to better understanding of the cave system development as well as to the local hydrolog- ical processes. Sedimentological and mineralogical studies together with radiometric or paleomagnetic datings of both clastic and chemogenic deposits have commonly been applied in cave sediment research (e.g., Ha ¨uselmann et al., 2007; Kadlec et al., 2001). The mineral magnetic approach has been used only occasionally to understand climatic, hydrological and anthropogenic processes controlling sediment deposition in caves (Ellwood et al., 1996, 2004; Sroubek et al., 2001, 2007). The assemblage of magnetic minerals found in sediments is controlled by the character of the source rocks, weathering, mode and energy of transporting medium, and by depositional as well as post- depositional processes. The aim of this paper is an examination of Botovskaya Cave deposits using methods operating with magnetic and heavy minerals and with quartz grain exoscopy. Obtained mineral characteristics were used for correlations from the point of view of sediment source and mode of transpor- tation into the cave passages. Radiometric and paleomag- netic datings of the cave carbonate bed allowed us to estimate the age of both depositional and post-depositional processes. GEOGRAPHICAL AND GEOLOGICAL SETTINGS Botovskaya Cave (55u 189 N, 105u 209 E) is located on the Angarsko-Lensky Plateau of the southern Siberian Craton about 500 km north of Irkutsk City (Fig. 1). The area reaches altitudes of 1100 m a.s.l., and belongs to the Zhigalovo District of the Irkutsk Area. The plateau is dissected by river valleys up to 400 m deep. Cave entrances lie at a relative elevation of 310 m above the Lena River level, in a valley of the Garevogo Creek, the left tributary of the Boty River, which joins the Lena River. The cave system, dipping gently to the north, has developed in an Early Ordovician limestone formation with a thickness of 6 to 12 m. The limestone bed is underlain by Middle and Late Cambrian sandstone, siltstone, marl and gypsum and overlain by Middle Ordovician sandstone, limestone and argillite (Filippov, 2000). The cave system developed under confined (artesian karst) settings (Klimchouk, 2000, 2003; Filippov, 2000). The speleogenesis of the Botovskaya Cave system was interpreted by Filippov (2000) and is due to two different processes, (i) corrosion involving meteoric artesian water and (ii) ascending deep circulating artesian water spanning the time period between Late Mesozoic and Early Neogene. The clastic cave deposits fill the bottom portion of the cave passages and are not usually exposed sufficiently for study. The deposits from the cave were preliminarily described by Filippov (2000). Breitenbach (2004) described in detail a recently excavated section of cave sediments (the same section is labeled Section 1 in this paper). The cave is divided into two parts: the Old World and the New World. All studied sections of cave sediments are situated in the Old World, 200–400 m east of the Central and Medeo entrances (Fig. 2). The key Section 1 and Section 2 are exposed in two test-pits excavated in the sedimentary fill close to survey stations PK0122 and PK042. The smaller Section 3 and Section 4 are located 1 Institute of Geology AS CR, v.v.i., Rozvojova 269, CZ-165 00 Praha 6, Czech Republic, kadlec@gli.cas.cz 2 Institute of Geological Sciences, PAN, Warszawa, Poland 3 Speleoclub Arabica, Irkutsk, Russia 4 GeoForschungsZentrum Potsdam, Germany J. Kadlec, M. Chadima, L. Lisa ´, H. Hercman, A. Osintsev, and H. Oberha ¨ nsli – Clastic cave deposits in Botovskaya Cave (Eastern Siberia, Russian Federation). Journal of Cave and Karst Studies, v. 70, no. 3, p. 142–155. 142 N Journal of Cave and Karst Studies, December 2008