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Dating caves using speleothems, sediments & guano

DATING CAVE SAMPLES

An increasing amount of scientific research is being done on cave samples, to determine the age of the cave deposits such as sediments and speleothems, which gives information on paleoenvironmental conditions, as well as to investigate ancient climatic changes from speleothems. Caves have been shown to offer an environment that is able to preserve material from being eroded away. Compared to the surface environment outside, caves are less exposed to erosional processes.

GEOLOGY

Malaysia has a tropical climate which means a lot of rain. The limestone in the Peninsula originates from the Silurian, 438-408 mya, to Permian 286-248. The tropical climate has has produced tower karst in various locations, mostly on latitudes north of Kuala Lumpur. However KL and the Klang Valley is also of a karstic nature as it has subsurface limestone.

Many of the karst towers have caves, and these caves have preserved cave deposits and speleothems that may contain clues for understanding the karst landscape. The tower karst mostly appears as isolated limestone hills surrounded by plains of alluvial or detrital material. These hills are remnants of much larger limestone deposits that have been denuded and are now covered under more recent alluvium.

DATING CAVES

Speleothems are formed from minerals deposited by water that has dripped through over many thousands of years to grow. The chemistry of the minerals show the environmental conditions when they were deposited. Stalactites grow in a similiar way to tree trunks, in that concentric rings are deposited over the years, with the oldest rings being on the inside. Therefore speleothems provide paleoenvironmental records as they have been protected from erosion and destruction, yet they respond to changing conditions on the earth's surface. It is possible to reconstruct monsoon rainfall variations over the last 10,000 years. These variations and other aspects of climate are recorded by the geochemistry of speleothems as they grow.

Initial research in the peninsula was done in the 1980s by using the Electron Spin Resonance and Uranium series dating techniques to date cave material. This was done in caves in Perlis, Smart et al. (1984). ESR dating was applied on younger looking samples whereas the U-series involved older ones. ESR detects the amount of radiation damage stored in a solid material. U-series dating detects uranium concentration to estimate age from the radioactive decay. The U-series method has been used for dating sites in Europe and Asia. It has been shown that results showing ages of 400,000 years to 12,000 years B.P are consistent with estimates based on archeological and geological evidence. Generally geological material remains undisturbed for several million years. These dating techniques are being used to estimate the age of speleothem deposition. Caves act as traps, amassing samples of organic debris, broken rocks etc. These ancient sediments are mostly preserved from further erosion, thereby preserving records of the past environment.

In the last few years much more research is being done on speleothems and sediments, particularly in caves in Asia. Decoding geochemical records in stalagmites has been widely recognized as a powerful tool for the elucidation of paleoclimate/environment of the terrestrial areas. Stable isotope data (oxygen and carbon) of carbonate minerals (mostly calcite, but sometimes aragonite) in stalagmites have been the most commonly and widely used proxies for paleoclimatic research. This is based upon the assumption that carbonate minerals precipitated in isotopic equilibrium with dripping waters from stalactites, thus should reflect paleoclimatic variations. Complex chemical analysis of the mineral composition at varying distances from the centre of the statactite not only dates the deposition but also gives other information. For example testing the properties of the oxygen atoms within the minerals can give clues about the temperature in the cave at the time of deposition, which is related to the mean annual temperature on the surface above the cave system.

Ancient climatic and vegetation changes can be seen from the growth rate of cave speleothems. The growth of stal depends on the climate, depending on how wet or dry it is. As the climate and temperature changed over the thousands of years, this affected the size and structure of the stals being deposited in the caves below.

Stalagmites were collected from Gunung Buda in 2003, 2005 and 2006 to study climatic changes. In Mulu in 2009 research was done to date speleothem and sediment samples, using 3 techniques (cosmogenic, uranium-lead and paleomagnetic dating). The studies were focused on the Whiterock Cave system which is part of the Clearwater system. See more on dating Mulu's caves. The studies were funded by BCRA Cave Science and Technology Research Initiative (CSTRI).

CLIMATIC CHANGES FROM GUANO

Studies are also been done on ancient guano to determine climatic changes. Some caves contain thick deposits of guano from bats and swiftlets, and testing the sequences should reveal these changes. It is hypothesised by researchers that the climate of SE Asia was drier and more seasonal during the Last Glacial Period. This affected the grasslands and forests. The guano is deposited and fresh layers cover the older layers which are rapidly degraded, resulting in an earthy residue which appears to undergo little disturbance and over millennia, deposits of guano several metres thick build up on the cave floor. This guano represents a source of palaeoenvironmental information on glacial - interglacial timescales.
Abstracts of studies done at Batu Caves and Niah Cave can be seen at Wurster et al.

CLIMATIC CHANGES FROM CARBON DIOXIDE

In the past decade or so there has been a lot of talk internationally about the greenhouse effect, carbon dioxide emissions etc. Carbon dioxide is one of the greenhouse gases found in the earth's atmosphere. Human activity has increased the concentration of CO2 and other greenhouse gases. Natural sources of CO2 are greater than sources due to human activity, but over periods longer than a few years natural sources are closely balanced by natural sinks such as weathering of continental rocks and photosynthesis of carbon compounds by plants and marine plankton. Caves are formed by the dissolution of the limestone bedrock by carbonic acid from water laden with atmospheric CO2. Dissolved carbon in the water flows out of the caves if there is a streamway, and may end up in the oceans. Scientists are now studying how this dissolution affects the levels of CO2 in the atmosphere. It is thought the overall impact is small, especially compared to the human impact of burning fossil fuels etc.

SEA LEVEL CHANGES

Researchers are now working on determining the changes in sea levels over the years. Geologists have always given different figures regarding how high the sea level rose, and fell in the late Quaternary. Several geologists have postulated that in the late Quaternary sea levels rose to 50m (or even 70m) above present day levels in the Malay peninsula area. However this is not accepted by more recent researchers who who suggest a rise of a mere 6m. Now accurate dating methods means more accurate results can be obtained.

Radiocarbon dating can be done on shells, corals, peat and wood from estuarine environments. The average results of researchers since the 1980s show that in the Strait of Melaka, sea levels declined from + 2.5 m aMSL at 4600y BP to + 1.25 m aMSL at 1400y BP. At Tioman the relative sea level was around 1.4 and 2.7 m above the present MSL during the period 5500-1900 BP.

In fact Sahul Time (Monash University) suggests that the sea levels have been more or less the same for the last 6000 years. They were at their lowest around 25,000 years ago (135m below today's level) but since then having been rising. In the last 6000 years they have only risen by 2m.

Refs :

ANON (2007) Borneo ice cores in underground caves give clues to climate change. Scientific Blogging, Science 2.0. Sept 26.
MUHAMMAD, R.F; Yoshida, D; Tani, A. & Smart, P.L. (2002) Implications of Electron Spin Resonance and Uranium-series Dating Techniques on Speleothems in the Kinta and Lenggong Valleys, West Malaysia. Advances in ESR Applications, vol.18 pp.19-26.
SMART, P.L., Andrews, J.N. and Batchelor, B., (1984). Implications of Uranium series dates from speleothems for the age of landforms in northwest Perlis, Malaysia: A preliminary study. Mal. Jour. Trop. Geog. 9, 59-68.

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Liz Price 2008-2011

Page last updated 1 May 2011