Category:Cyclostratigraphy of the Chalk Group
In recent years, research on Cenomanian successions across Europe has sought to explain the often distinctly rhythmically bedded nature of these strata, and to elucidate a controlling mechanism for this apparent cyclicity. Leary et al. (1989) showed that the chalk component of chalk-marl couplets in the Cenomanian reflected cyclical abundances of calcarious microfossils that were coincident with higher surface water temperatures. Gale (1989) recognised this apparent climatic fluctuation as Milankovitch Cyclicity, the frequency of the chalk-marl couplets corresponding most closely to changes in the Earth's solar budget induced by precession.
Subsequently, Gale (1995) examined Cenomanian successions in the Anglo-Paris Basin, NW Germany and SE France, and produced a composite succession of chalk-marl couplets for the whole of the Cenomanian. Gale (1995) used the sequence stratigraphical framework of Robaszynski et al. (1998) to subdivide the Cenomanian successions of these different regions into five intervals, denoted A to E (oldest to youngest). The couplets of each interval were then numbered sequentially from oldest to youngest, prefixed by the identifying letter of the sequence they were contained in. Correlation of chalk-marl couplets between basins was tested using biostratigraphy, sequence stratigraphy and carbon isotope stratigraphy, and showed that in some basins erosion or non-deposition had produced gaps in the couplet succession, and that elsewhere the succession was greatly expanded (Gale, 1995).
Gale (1995) concluded that if the chalk-marl couplets were assumed to be precession cycles with a periodicity of 21 000 years, as suggested by studies of other successions showing similar features (Fischer, 1991), then the length of the Cenomanian calculated from the composite succession of couplets was 2.24 million years. The closeness of this value to the radiometrically determined length of the Cenomanian (2.2 million years) supports the precession cycle hypothesis (Gale, 1995).
In the course of constructing the composite chalk-marl couplet succession for the Cenomanian, Gale (1995) recognised that some couplets were extremely widespread, with persistent lithological and/or faunal characteristics.
FISCHER, A G. 1991. Orbital cyclicity in Mesozoic strata. In EINSELE, G, RICKEN, W & SEILACHER, A. (eds). Cycles and events in stratigraphy (Springer-Verlag: Berlin.), 48-62.
GALE, A S. 1989. A Milankovitch scale for Cenomanian time. Terra Nova, 1, 420-425.
GALE, A S. 1995. Cyclostratigraphy and correlation of the Cenomanian Stage in Western Europe. In HOUSE, M R & GALE, A S (eds.), Orbital Forcing Timescales and Cyclostratigraphy, Geological Society Special Publication, No. 85, pp. 177-197.
LEARY, P N, COTTLE, R A & DITCHFIELD, P. 1989. Milankovitch control of foraminiferal assemblages from the Cenomanian of southern England. Terra Nova, 1, 416-419
Pages in category ‘Cyclostratigraphy of the Chalk Group’
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