Abstract: Cyclostratigraphy: Is it Ready to do Something?

Timothy D. Herbert, I. Premoli Silva, E. Erba, S.L. D'Hondt

Cyclostratigraphy, defined here as the stratigraphic use of Milankovitch rhythms imprinted on some aspect of sedimentation, has much promise for improving quantitative stratigraphy. The success of Pliocene-Pleistocene orbital chronologies encourages stratigraphers to look at older sequences in the same light. We describe here two case studies of Cretaceous cyclostratigraphy in which sufficient data now exist to suggest that the method can yield important new stratigraphic information.

Many DSDP cores and Campanian to Paleocene pelagic sediments outcropping on land display carbonate cycles and have paleomagnetic polarity data. The large number of sites and a paleomagnetic framework allow a rigorous test of the proposed orbital origin of the sedimentary cycles. Where detailed paleomagnetic determinations have been made, reversal boundaries occur in a consistent position in the carbonate-cycle sequence (as is the K/T extinction boundary). For some intervals of Late Cretaceous time, a 20 kyr cycle-by-cycle correlation is possible across the South Atlantic Ocean and into the pelagic sections of Spain. The results have implications for rates of processes across the K/T extinction level and for the nature of the hemispheric response to orbital forcing. Another use of cycl c sedimentation is to improve chronology during the Cretaceous Long Normal Interval. Time series analyses will be presented of Aptian through Cenomanian cyclic sediments of Italy, which have been zoned by planktonic foraminiferal and calcareous nannofossils. Cyclostratigraphy seems capable of precisely defining zonal durations and gives elapsed chronologies between stage boundaries consistent with, but considerably more precise than, available radiometric tie points.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994