Geochemistry and petrography of speleothems from Turkey and Iran : palaeoclimate and diagenesis
Year: 2013
Type: dissertation
Abstract: \nSpeleothems contain key archives of palaeoclimatic information, which can be interpreted \nthrough multiple geochemical and petrographic proxies, and precisely dated by Uranium \nSeries dating. As U/Th dating is only viable for samples up to approximately 700 kyr of age, \nU/Pb dating must be used to date older samples. In this study, U/Pb methods were used to \ndate an aragonite layer in a speleothem from Iran, following the use of autoradiography to \nselect samples with appropriately high uranium. \nAragonite is metastable at earth surface conditions, and is therefore prone to \nrecrystallisation as calcite if it comes into contact with a fluid that is undersaturated with \nrespect to aragonite. This process affected two speleothems from Dim Cave, SW Turkey, \nand one speleothem from Torang Cave, Iran. The older Dim Cave stalagmite, which \nprecipitated during MIS 5e, was not identified as a recrystallised stalagmite at first, as the \nmineralogy of the growth axis appeared to show a change in primary mineral rather than \nrecrystallisation. Despite the fact that recrystallisation had occurred, it was possible to \ncreate an age model, as the system had not opened to a great degree. The persistence of \nan aragonite layer in this speleothem, as well as several other geochemical proxies, \nindicates that an arid phase occurred during early MIS 5e in SW Turkey. The second \nrecrystallised speleothem from Dim Cave provides useful insights into the geochemical and \npetrographic character of recrystallised speleothems. The recrystallised speleothem from \nTorang Cave produced a record of climatic instability in southern Iran during MIS period 9- \n7, although the age model was not precise enough to draw precise conclusions. \nA small aragonitic Holocene growth from Dim Cave grew during a time which corresponds \nto an early Holocene pluvial period that affected the entire eastern Mediterranean Basin, \ncoinciding with the deposition of Sapropel 1. \n \n*[N.B.: Additional data was attached to this thesis at the time of its submission. Please refer to the author for further details.]
Author: Leretta Wickens
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W806172727