PhD Theses from #PUBLISHER# / 2006-03-01 12:36:39
by Siti Zulaikah, S3 – Mathematics and Natural Sciences
Promotor : Prof. Dr. The Houw Liong
Co-Promotor : Dr. Satria Bijaksana
Co-Promotor : Dr. rer.nat. Umar Fauzi
Keyword : Magnetic properties, stalagmite, paleosecular variation, paleoclimate
Nomor Panggil (DDC) :
T 538. 727 ZUL
Sumber pengambilan dokumen : 20051515
Research on rock magnetism has been performed for many purposes. In this study, rock magnetic properties especially those observed in stalagmite are used to determine the past geomagnetic field secular variation or paleosecular variation (PSV). Furthermore, magnetic properties of stalagmites in this study are also used as proxy data indicator of past climate change or paleoclimate.
The global paleosecular variation can not be determined in great detail as the PSV data are available mostly high latitude regions but lacking those from low latitude regions such as Indonesia. In this study, PSV for low latitude is constructed from stalagmites. Compared to ordinary sediments, stalagmites and other cave deposits have an advantage that they show no sign of inclination error as sediments generally do. Cave deposits and stalagmites are abundant in Indonesia encompassing wide range of age and rate of sedimentation that is faster that those from temperate climate. These allow for greater number of data and higher resolution.
The wide range age (up to teens of thousand years) is also beneficial for paleoclimatic study. Its unique and chaotic climate change makes Indonesia a key area in regional and global changes. This is one of the main reasons for this research. Although still limited in quantity, proxy paleoclimatic data are already available for Indonesia, for example O 8 variation in corals, tree ring in teak as well as pollen and charcoal abundance in lake sediments. Every proxy data provides a specific range of age and resolution. These proxy data are still insufficient to build a reliable climatic record. Stalagmites have been shown to act as multi proxy recorders. In this research, magnetic properties are studied as potential proxy data for pelaoclimate. The magnetic data of the stalagmit in this study, can records the climate change of Java and generally Indonesia at least in the last of thousand years.
Measurements were carried out on several magnetic parameters notably magnetic susceptibility and magnetic remanence in various forms, such as NRM (natural remanent magnetization), ARM (anhysteretic remanent magnetization) and IRM (isothermal remanent magnetization). Other supporting analyses to characterize the magnetic minerals were also performed, such as visual observation using SEM (scanning electron microscope) equipped with EDX, compositional analysis using X-ray diffraction (XRD) and absolute age determination using radiocarbon method.
In this study, sample collection includes 6 stalagmites from Trenggalek, East Java (one of the region that is sensitive to ENSO or El-Nino Southern Oscillation), 2 stalagmites from Purworejo and Bantul and 1 stalagmite from the Island of Muna in Sutheast Sulawesi. Two stalagmites from Trenggalek yield absolute ages of 3320+100 years old (STG-NDL) and 6300+470 years old (STG-NJL). It is known that the deposition rate of stalagmite is lower for the younger part. From mineralogical point of view, these stalagmites are dominated by calcite (CaCO3) and low magnetic mineral content. Grain size of magnetic mineral, predominantly multi-domain magnetite (Fe304), varies from 10-2 to 102 gm. Variation of magnetic parameter in stalagmite is controlled by the concentration of magnetic minerals. The grains appear to be interacting but no compositional variation along the stalagmites.
Magnetic susceptibility observed in stalagmites show no special pattern. Magnetic susceptibility of each sample varies averaging between -3.0 x 10-6 to 5.0 x 10-m3fkg. Meanwhile, two stalagmites that grew in flooding free enclosure show similar pattern of susceptibility variation. Anisotropy of magnetic susceptibility (AMS) analysis shows that the degree of anisotropy varies from 2 to 16% although most samples have degree of anisotropy that are less than 10%. The maximum axes of susceptibility tend to be parallel with bedding plane, even though some samples show the opposite.
NRM intensities generally show no specific pattern along these stalagmites. The initial NRM intensity varies from 10-6 to 104 Am2/kg. while the median destructive field (MDF) varies from 5 to 25 mT, although some have MDF of up to 40 mT. Some of samples show unstable record of remanence as indicated by C C95
more than 10Â°. PSV record nevertheless show local consistency especially in inclination with coefficient of similarity (r) of up to 0.97. PSV data obtained in this study is similar to that of Xingwen, China with r value varied from 0.6 up to 0.98.
Based on susceptibility pattern found in stalagmites that grew in flooding-free enclosure, magnetic mineral abundance is related to wet condition. This agrees with sunspot data as well as the CO2 abundance, which is an indicator of greenhouse effect. Comparison of the above parameters shows that there has been an increase in global warming for the last ± 150 years. Comparison between magnetic and delta C14 data shows similar pattern are found for the years of 1175, 1400, 1600 and 1675. These findings prove that magnetic data can be used as a proxy data for climate change, where high susceptibility value indicates wet condition and low susceptibility value indicates dry condition.