Cyclostratigraphy and the Milankovitch TheoryBy
- W. Schwarzacher, The Queen's University of Belfast, Department of Geology, Belfast, BT7 1NN, UK
Cyclostratigraphy is concerned primarily with measuring geological time and the time units used in this approach are sedimentary cycles. Milankovitch cycles mark time intervals of tens of thousands to several millions of years. Such cycles are the result of variations in the Earth's position in relation to the Sun and these in turn determine the climatic variations. The Milankovitch theory was resurrected in the 1960's when evidence from Pleistocene deep sea sediments linked orbital variations and climate.
This monograph discusses sedimentary cycles and their use in measuring geologic time. There is considerable effort made to clarify the term "sedimentary cycle", in particular, the two opposing concepts of cyclic stratification and event stratification. The recognition of sedimentary cycles and of Milankovitch cycles specifically, is considered and care is taken with the question of relating sediment thickness to time. Several examples from the Carboniferous to the Cretaceous are given to show how cyclostratigraphy can be applied to current geological problems. This volume should be of interest to geologists involved with stratigraphical analysis and basin analysis.
Developments in Sedimentology
Published: August 1993
- 1. Introduction. Definition of cycles. The quantitative description of cycles. The complexity of cycles. The regularity of cycles. The origin of cycles. Conclusions. 2. Oscillating Systems. Linear systems. Non-linear systems. Stochastically driven oscillators. Examples of oscillating systems. Climatic oscillators: the Ghil oscillator. The Saltzman oscillator. Geological oscillators. Concluding remarks. 3. The Milankovitch Theory. The planetary system. The precession. The frequency stability of the orbital elements. The insolation. Milankovitch cycles and climate. The Pleistocene climate. 4. Methods of Analysis. Stratigraphical sections as stochastic processes. The spectral analysis. The estimation of spectra. Cospectral analysis. Power spectra in stratigraphical analysis. Walsh spectra. The Walsh spectrum in stratigraphy. The role of spectral analysis in cyclostratigraphy. The filtering of sections. The effects of non-stationarity. Complex demodulation. Conclusions. 5. The Relation between Time and Sediment Accumulation. The random walk model. The rate of sedimentation. The completeness of the record. Cycles with precise time periods. Cycles with changing lithology. The effect of random variations on a periodic signal. Bioturbation. Methods of finding a mapping function z,t. 6. Stratification and Stratification Cycles. Marl-limestone sedimentation. Stratification patterns. Stratification cycles. The numerical description of bedded sequences. Stratigraphic trends. The recognition of stratification cycle boundaries. 7. Examples from the Carboniferous. The Lower Carboniferous. The Carboniferous limestones of north-west Ireland. The Benbulbin shale and Glencar limestone. The Dartry limestone. The cyclostratigraphic interpretation of the Sligo sequence. The cyclicity of Yorkshire and North Wales. The Pennsylvanian (Upper Carboniferous) cycles. 8. Triassic: Carbonate Platforms. The Northern Calcareous Alps. The cyclicity of the Dachstein limestone. Quantitative studies. The Trans-Danubian Central range. The Dolomites. Absolute time estimates. The similarity of cycles. Subsidence. Sea level fluctuations. The geometry of cycle formation. The platform-basin interaction. Concluding remarks. 9. Some Jurassic Examples. The lower Jurassic in Britain. The Kimmeridge clay. The German Upper Jurassic. Examples from Tethyan regions. 10. Examples from the Cretaceous. The Umbria and Marche region of Italy. The Maiolica. The Scisti a Fucoidi. The Scaglia Bianca. The western Tethis and the Atlantic. The epicontinental seas. The Cretaceous-Tertiary boundary. Concluding remarks. 11. Non-Carbonate Cycles. The Permian evaporites. Lacustrine environments: the Lokatong and Passaic formations. The Green River Formation. Shallow marine environments. Fluviatile environments. Prodelta turbidites. 12. Cyclostratigraphy and Milankovitch Cycles. Practical cyclostratigraphy. The recognition of Milankovitch cycles. The causes of sedimentary cycles. References. Subject Index.