57 ALBIAN CYCLOSTRATIGRAPHY CYCLOSTRATIGRAPHY AND CHRONOLOGY OF THE ALBIAN STAGE (PIOBBICO CORE, ITALY) ALESSANDRO GRIPPO Department of Earth Sciences, University of Southern California, Los Angeles, California 90089-0740, U.S.A. e-mail: grippo@earth.usc.edu ALFRED G. FISCHER Department of Earth Sciences, University of Southern California, Los Angeles, California 90089-0740, U.S.A. LINDA A. HINNOV Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218, U.S.A. TIMOTHY D. HERBERT Department of Geological Sciences, Box 1846, Brown University, Providence, Rhode Island 02912, U.S.A. AND ISABELLA PREMOLI SILVA Dipartimento di Scienze della Terra, Università di Milano, via Mangiagalli 34, 30133 Milano, MI, Italy 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. Cyclostratigraphy: Approaches and Case Histories SEPM Special Publication No. 81, Copyright © 2004 SEPM (Society for Sedimentary Geology), ISBN 1-56576-108-1, p. 57–81. INTRODUCTION The Umbria–Marche arc of the Apennines, in the region west of Ancona, contains a continuous history of pelagic–hemipelagic sedimentation extending from Early Jurassic times into the Mi- ocene (Cresta et al., 1989). It is here (at Gubbio) that the impact nature of the Cretaceous–Tertiary boundary was discovered, and that continuous stratigraphic profiles of Cretaceous–Paleogene magnetic zonation were developed. The Cretaceous biostratig- raphy of the region is summarized in Premoli Silva and Sliter (1995). The Albian Stage is here represented by 50–60 m of pelagic sediment, initially coccolith–globigerinid ooze and marl, now compacted into rhythmically alternating beds of marlstone and limestone that form the Scisti a Fucoidi (Fucoid Marls) and the basal beds of the succeeding Scaglia Bianca Limestone. History of Study The rhythmicity was first studied in discontinuous outcrops by de Boer (1982,1983) and de Boer and Wonders (1984). A strati- graphic thickness of 50–60 m, representing a stage with an esti- mated duration of ca. 12 million years, implies a mean accumu- lation rate of 4–5 Bubnoff units (mm/ky, m/My). That made the ca. 8 cm bedding couplets likely candidates for the precessional cycle, and their grouping into bundles of five a likely expression of the short-eccentricity cycle. Schwarzacher and Fischer (1982) had reached similar conclusions about cyclic patterns in the underlying Barremian and overlying Cenomanian limestones. Continuity of sequence was obtained in the Piobbico core, drilled by Premoli Silva, Napoleone, and Fischer through the Scisti a Fucoidi at the Le Brecce farm northwest of Piobbico (Fig. 1). Pratt and King (1986) described the composition of the organic matter. Detailed studies mainly directed at an 8 m core segment (cycles 8–12, Fig. 16) yielded calcium carbonate pro- files and a gray-scale scan by densitometry of diapositives (Herbert and Fischer, 1986, Herbert et al., 1986). These yielded new insights into rhythmicity and sedimentation, and the gray- scale scan showed reflectivity to be an excellent proxy for calcium carbonate content, save for a step function from gray to black associated with black marlstone beds (the PAPs of this paper). Spectral studies by Park and Herbert (1987), Premoli Silva et al. (1989a), and Premoli Silva et al. (1989b) confirmed the assignment of cyclicities and discovered the presence of an obliquity signal. The stratigraphy of the core was described by Erba (1988) and Tornaghi et al. (1989). The chemical and gray-scale analyses employed had proved too tedious for large-scale application to cyclostratigraphic stud- ies. The visual count of the short-eccentricity bundles in core and outcrop by Herbert et al. (1995) yielded an Albian duration of 11.9 My, but it remained undocumented. By then, digitization of photographs and programs for time- series analysis had brought the entire core into reach of study and documentation. Fischer and Grippo, with the aid of Hinnov, undertook a restudy of the core photographs (for details, see Appendix). By means of a photolog, gray-scale log, and spectral analyses we were able to document the cyclicity in the ca. ten million years of history recovered by the core, and we extended this to the full Albian by extrapolation to the surface data of Herbert et al. (1995). While these studies were in progress, Fiet et al. (2001) mea- sured a surface section of the Albian on Monte Petrano, some 13