Cave Deposits and their Potential in Geological Sciences

 A void where a drop of water breaks the silence of its secrets, the veil of dusk masks the beauty of its reality, called "Cave" - the hidden architecture of nature. Spreading beyond the territory of sunlight, these natural openings vary in size from tiny passages to interconnected corridors profuse several miles - often large enough to accommodate humans and other lives within. Caves usually emerge by extensively diverged geological processes in various terrains like calcareous realm, bluffs situated at the edge of coastlines, glacial and volcanic regions by the subsequent interaction with water. Since prehistoric times, caves have been a natural, safe ambience to attract early humans, animals, and birds for shelter. Globally, prolific evidence of early humans has been discovered in the natural caves, which are evident by the fossil remains. The skeletons of early human Australopithecines have been unearthed from the cave deposits in South Africa, and the earliest testimony of primitive Neanderthal Man was also discovered from a cave in the Meander Valley of Germany. In 1927-1928, an American anthropologist, Prof. H.E. Terra from Yale University traveled to western Central Asia and wrote an article about his journey to the natural prehistoric caves dwelling at about 9,000 to 13,000 feet above mean sea level, in the north of mighty Himalaya. Therein he describes the art of interpreting petroglyphs and old rock inscriptions. The shreds of evidence of scorched ground, charcoal, and plant remains have been recovered from the central Indian limestone caves (Kotumsar and Dandak) by Yadav et al. (2007). The chronology suggests that these caves were dwelling places for prehistoric humans from 6940 to 4030 years ago. 

The multidisciplinary research of caves has enormous scope in advanced geological investigations under speleology. The term speleology derives from the Greek word spelaion for cave and logos for study, which means the scientific study of all perspectives of caves and their environment. French spéléologie and spélæologie are nearly analogous with the French attorney and caving pioneer Édouard-Alfred Martel, who used this term on several occasions during the 1890s, he credits its coinage to the Émile Rivière, a physician and paleoanthropologist. Although the term speleology is also often interconnected with venturing to explore caves, referred to as caving; however, spelunking or potholing sounds more appropriate for caving. Speleology is the amalgamation of geology, hydrology, biology, ecology, and archaeology, enduring particular curiosity for geologists, archaeologists, environmentalists, and ecologists. The natural caves often manifest karst geomorphology - a landscape that forms in the carbonate or calcareous (limestone, dolomite) and gypsum rocks by the gradual dissolution. The carbonate rocks are primarily composed of calcium carbonate (caco3), an aggregate of calcite and aragonite.

The cave develops when the rainwater combined with atmospheric carbon dioxide falls to the earth's surface and picks up extra gas and acids (humic and fulvic) as it trickles into the soil. This weak acidic droplet then percolates through the carbonate bedrocks and dissolves the carbonate minerals, creating wider cavities and conduits. Due to this process, various deposits and features are formed inside the caves, such as stalactite, stalagmite, limestone columns, flowstone, botryoidal forms, pool spar, crystals, rimstone dams, waterfall, ponds, and cave pearls, etc. these deposits are collectively called speleothem. The icicle growths with pointed tips that hang down from the cave ceiling are called stalactites, precipitated by the mineral-rich water that drips through the cave ceiling. The upward growth with round or flattened tops of a stratified mineral pile is called stalagmite, which forms by water dripping onto the cave's floor. Over thousands to millions of years, by the dripping of each droplet, every single layer of these deposits gradually expands, holding the record of their environment and chemical composition. As a result, speleothems have a great potential to resolve various scientific puzzles like spatial and temporal variations in past climate, vegetation changes, dependent microbiology, history of preceding earthquakes, geochemistry of minerals, structures, and other associated factors on annual to millennial timescales. Past climatic information from speleothems is obtained largely by using the ratio of oxygen isotope (δ18O) and trace element distribution, which primarily depends on several climatic factors, including temperature and precipitation. In recent years, advanced dating techniques (Uranium–Thorium series) provide more immeasurable opportunities to refine the records of cave research. Several studies have been conducted in the Indian subcontinent and nearby regions using cave deposits, specifically stalagmites - as the natural climate proxy (Bar-Matthews et al., 1999; Breitenbach et al., 2012; Cheng et al., 2009; Denniston et al., 2000; Dykoski et al. 2005; Fairchild and Treble, 2009; Fleitmann et al., 2007; Kathayat et al., 2018; Kotlia 2012; Liang et al., 2015; Neff et al., 2001; Sanwal., 2013; Sinha et al., 2005; Sinha et al., 2018; Yadava et al., 2004). 

Apart from climatic studies, speleothems also have the capability of sorption of actinide radionuclides and are relevant in the natural analog study, which is being approved for the repository’s safety assessment studies. As we know, isolating the long-lived radioactive wastes is one of the growing concerns of nuclear power plants worldwide. In the last few years, a number of studies from India (Sengupta et al., 2015; Sanwal et al., 2015; Sengupta et al., 2017) have proven that the speleothems provide a long-term execution and safety evaluations of the deep geological repositories designed to dispose of nuclear waste.

Deposits in a limestone cave 

References

• Bar-Matthews, M., Ayalon, A., Kaufman, A. and Wasserburg, G.J., 1999. The Eastern Mediterranean paleoclimate as a reflection of regional events: Soreq cave, Israel. Earth and Planetary Science Letters, 166(1-2), 85-95.
• Breitenbach, S.F.M., Adkins, J.F., Meyer, H., Marwan, N., Kumar, K.K., Haug, G.H., 2010. Strong influence of water vapor source dynamics on stable isotopes in precipitation observed in Southern Meghalaya, NE India. Earth and Planetary Science Letter 292 (1–2), 212–220. 
• Cheng, H., Fleitmann, D., Edwards, R.L., Wang, X., Cruz, F.W., Auler, A.S., Mangini, A., Wang, Y., Kong, X., Burns, S.J. and Matter, A., 2009. Timing and structure of the 8.2 kyr BP event inferred from δ18O records of stalagmites from China, Oman, and Brazil. Geology, 37(11), 1007-1010.
• Denniston, R.F., González, L.A., Asmerom, Y., Sharma, R.H. and Reagan, M.K., 2000. Speleothem evidence for changes in Indian summer monsoon precipitation over the last∼ 2300 years. Quaternary Research, 53(2), 196-202.
• Dykoski, C.A., Edwards, R.L., Cheng, H., Yuan, D., Cai, Y., Zhang, M., Lin, Y., Qing, J., An, Z. and Revenaugh, J., 2005. A high-resolution, absolute-dated Holocene and deglacial Asian monsoon record from Dongge Cave, China. Earth and Planetary Science Letters, 233(1-2), 71-86.
• Fairchild, I.J. and Treble, P.C., 2009. Trace elements in speleothems as recorders of environmental change. Quaternary Science Reviews, 28(5-6), 449-468.
• Fleitmann, D., Burns, S.J., Mangini, A., Mudelsee, M., Kramers, J., Villa, I., Neff, U., Al-Subbary, A.A., Buettner, A., Hippler, D. and Matter, A., 2007. Holocene ITCZ and Indian monsoon dynamics recorded in stalagmites from Oman and Yemen (Socotra). Quaternary Science Reviews, 26(1-2), 170-188.
• Joshi, L.M., Kotlia, B.S., Ahmad, S.M., Wu, C.C., Sanwal, J., Raza, W., Singh, A.K., Shen, C.C., Long, T. and Sharma, A.K., 2017. Reconstruction of Indian monsoon precipitation variability between 4.0 and 1.6 ka BP using speleothem δ 18 O records from the Central Lesser Himalaya, India. Arabian Journal of Geosciences, 10(16), 1-16.
• Kathayat, G., Cheng, H., Sinha, A., Berkelhammer, M., Zhang, H., Duan, P., Li, H., Li, X., Ning, Y. and Edwards, R.L., 2018. Evaluating the timing and structure of the 4.2 ka event in the Indian summer monsoon domain from an annually resolved speleothem record from Northeast India. Climate of the Past, 14(12), 1869-1879.
• Kotlia, B.S., Ahmad, S.M., Zhao, J.X., Raza, W., Collerson, K.D., Joshi, L.M. and Sanwal, J., 2012. Climatic fluctuations during the LIA and post-LIA in the Kumaun Lesser Himalaya, India: evidence from a 400 y old stalagmite record. Quaternary International, 263, 129-138.
• Kotlia B.S. and Joshi L.M., 2013. Late Holocene climatic changes in Garhwal Himalaya. Current Science 104(7), 911–919.
• Liang F, Brook G.A., Kotlia B.S., Railsback LB, Hard B, Cheng H, Edwards RL, Kandasamy S. 2015. Panigarh cave stalagmite evidence of climate change in the Indian Central Himalaya since AD 1256: Monsoon breaks and winter southern jet depressions. Quaternary Science Reviews 124:145–161.
• Neff, U., Burns, S.J., Mangini, A., Mudelsee, M., Fleitmann, D. and Matter, A., 2001. Strong coherence between solar variability and the monsoon in Oman between 9 and 6 kyr ago. Nature, 411(6835), 290-293.
• Sanwal, J., Kotlia, B.S., Rajendran, C., Ahmad, S.M., Rajendran, K. and Sandiford, M., 2013. Climatic variability in Central Indian Himalaya during the last∼ 1800 years: Evidence from a high resolution speleothem record. Quaternary International, 304, 183-192.
• Sanwal, J., Dudwadkar, N.L., Thirumurugan, A., Tripathi, S.C., Gandhi, P.M., Satyam, P.V. and Sengupta, P., 2016. Adsorption of Ru, Ce and Eu radionuclides within naturally precipitated polycrystalline calcium carbonate under acidic environment. Journal of Radioanalytical and Nuclear Chemistry, 309(2), 751-760. 
• Sengupta, P., Sanwal, J., Mathi, P., Mondal, J.A., Mahadik, P., Dudwadkar, N. and Gandhi, P.M., 2017. Sorption of Cs and Sr radionuclides within natural carbonates. Journal of Radioanalytical and Nuclear Chemistry, 312(1), 19-28. 
• Sengupta, P., Sanwal, J., Dudwadkar, N., Tripathi, S., and Gandhi, P. 2016 Adsorption of actinides within speleothems. Mineralogical Magazine, 80(5), 765-780. 
• Sinha, A., Cannariato, K.G., Stott, L.D., Li, H.C., You, C.F., Cheng, H., Edwards, R.L. and Singh, I.B., 2005. Variability of Southwest Indian summer monsoon precipitation during the Bølling-Allerød. Geology, 33(10), 813-816.
• Sinha, N., Gandhi, N., Chakraborty, S., Krishnan, R., Yadava, M.G. and Ramesh, R., 2018. Abrupt climate change at~ 2800 yr BP evidenced by a stalagmite record from peninsular India. The Holocene, 28(11), 1720-1730.
• Yadava, M. G., Sarswat, K. S., Singh, I. B., & Ramesh, R., 2007. Evidence of early human occupation in the limestone caves of Bastar, Chhattisgarh. Current Science, 92(6), 820–823. 

       

           Mrs. Jaishri Sanwal Bhatt

           Women Scientist, Geodynamics Unit

          Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore

write to her at jaishrigeology@gmail.com