Vollmer, Thorsten (2005) Paleoclimatology of Upper Triassic Playa Cycles. New Insights Into an Orbital Controlled Monsoon System (Norian, German Basin). PhD thesis, Universität zu Köln.
Paleoclimatology of Upper Triassic Playa Cycles: New Insights Into an Orbital Controlled Monsoon System (Norian, German Basin) Abstract The main purpose of the project was to study the rhythmic sediments of the Steinmergel Keuper playa system in the North and South German basin in order to test the hypothesis of possible climate control on sedimentation. Furthermore, in case of there being orbital control on sedimentation, the North/South correlation was tested based on high-resolution cyclostratigraphy. This needed a detailed facies study taking into account paleogeography and paleoclimatology. Moreover, additional geophysical and geochemical parameters were used as proxy parameters for paleoclimatology. Time series analysis provided the necessary information about the orbital controlling factors on cyclicity. Colour logging provided a very high-resolution paleoclimatic proxy parameter as it is a good indicator of changes of the reduction/oxidation conditions and especially cyclic changes from green/grey to red are shown well by colour logging. Cyclic changes in the lightness give reliable information about dolomite formation in the playa lake. Therefore, changes in lightness reflect lake level changes. Stable oxygen and carbon isotopes furnished indications about paleoclimatology and paleohydrology of the playa system. Covariance of the isotopes suggests a hydrological closed basin. Trends of lightening of the isotopes show the climatic trends toward more humid periods. Further climatic proxy parameters were given by XRF-analysis. The K/Al ratio, for example, provides information on the weathering pattern of the hinterlands. Thus, low K/Al ratios suggest an increased chemical weathering of the hinterlands and high K/Al ratios an increased physical weathering of the hinterlands. Susceptibility data were used besides colour data for frequency analysis. Petrographic data were provided by XRD, thin section and cathode luminescence. The integrated study of drill cores, outcrops distributed all over the German basin and samples results in a detailed facies model of the playa system. Three different main cycle types were recognized depending on their position within the playa. The most central part of the playa system (i.e. playa lake) is characterized by repeated successions of dark grey mudstones, dolomite beds and displacive gypsum within the dolomite. A more marginal (playa lake to wet mudflat) cyclic facies is a succession of dark grey mudstones, dolomite beds followed by red mudstones. The most marginal facies (mudflat) is a cyclic pedogenetic dolocrête facies. Because of the close relationship between the sediments and cyclic changes in the monsoonal activity the cyclicity within the sediments is interpreted to be initiated by changes in the orbital parameters, i.e. Milankovitch cycles. Playa mudflats change cyclically with playa lakes reflecting cyclic changes between drier and wetter periods in an overall semi-arid setting. The overall climate control on sedimentation and the results of evolutionary spectral analysis allow an interpretation in terms of Milankovitch cycles: - A basic wet dry cycle is interpreted as having its origin in the precession (20kyr). The very high-resolution of the colour logging show further that this cycle is composed of two sub-cycles, which are most likely hemi-precessional cycles (10kyr). - Five basic cycles are bundled into a lower frequent cycle representing the eccentricity of 100 kyr (E1-E2). - These cycles are bundled again to form the eccentricity of 400kyr (E3). - The lowest-frequency cycle is the 2Myr cycle formed by bundling of E3 cycles.
|Item Type: ||Thesis (PhD thesis)|
|Subjects: ||Earth sciences|
|Uncontrolled Keywords: |
|Palaeoklimatologie , Milankovitch-Zyklen , Playa , Farben , Trias||German|
|Paleoclimatology , Milankovitch-Cycles , Playa , Colours , Triassic||English|
|Faculty: ||Mathematisch-Naturwissenschaftliche Fakultät|
|Divisions: ||Mathematisch-Naturwissenschaftliche Fakultät > Geologisches Institut|
|Date Type: ||Completion|
|Date of oral exam: ||06 December 2005|
|Full Text Status: ||Public|
|Date Deposited: ||28 Jun 2006 10:54|
|Ricken, Werner||Prof. Dr.|
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