Abstract The mid-Cretaceous (Albian) deep-water sediments (coccolith-globigerinacean marls) of the Umbria-Marche Apennines show complex rhythmic bedding. We integrated earlier work with a time-series study of a digitized and image-processed photographic log of the Piobbico core. A drab facies is viewed as recording normal stratified conditions, and a red facies as the product of downwelling warm saline (halothermal) waters. Both are pervaded by orbital (Milankovitch) rhythms. These reflect fluctuations in the composition and abundance of the calcareous plankton in the upper waters. The drab facies is overprinted by redox oscillations on the bottom, including episodic precessional anaerobic pulses (PAPs). Contrasts between the individual beds representing the alternate phases of the precessional rhythm rose and fell with orbital eccentricity, in the classical pattern of Berger’s climatic precession or precession index curve, varyingly complicated by the obliquity rhythm. We conclude that greenhouse oceans in general, and perhaps this area in particular, were very sensitive to orbital forcing. Our count of 29 406-ky eccentricity cycles yields an Albian duration of 11.8 ± 0.4 My.

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Abstract Changes made to the Pliocene and Pleistocene portions of the Geomagnetic Polarity Time Scale (GPTS) by matching paleoclimatic oscillations in marine sediments to variations in the earth’s orbital elements have been validated by recent 40 Ar/ 39 Ar dating. We explore here the potential for orbital chronology to improve and refine the Cretaceous and early Paleocene portion of the GPTS. Because orbital cycles mark off time in geologically short increments, their sedimentary imprint may be used to measure elapsed time between events such as magnetic reversals or biostratigraphic datums very precisely. A large number of Deep Sea Drilling Project drill sites of late Cretaceous to early Paleocene age display carbonate cycles whose mean period, estimated by paleomagnetically determined sedimentation rates, is close to 20 ky, the expected mean period of the precessional cycle. Because the cycles can be detected before and after the Cretaceous-Tertiary boundary, they offer a new tool to date the position of the extinction level within magnetochron C29R and to measure the rates of environmental and evolutionary changes across the boundary. Cycle-by-cycle correlations appear possible between South Atlantic sites; recent information from sections in Spain suggests that interhemispheric correlations can be made. We also present an astronomical time scale for the durations of the Cenomanian, Albian, and Aptian stages as defined by marine microfossil datums and the top of reversed polarity chron M-0. The durations of these stages are estimated to be 6.0 ± 0.5 my, 11.9 ± 0.2 my, and 10.6 ± 0.2 my, respectively. A cumulative cyclo-chronology from the well-dated Cenomanian-Turonian boundary places the top of polarity chron M-0, a tie point for the calibration of the M-series anomaly sequence, at 121.6 Ma.