FROM SAPROPEL TO RED MARL–ORBITALLY DRIVEN BEHAVIOR OF A CRETACEOUS SEA

Albian deep-water sedimentation in the Umbria-Marche facies of Italy (Mediterranean Tethys) shows complex rhythmic interbedding. Throughout Albian time the 20-ka precession drove cycles in primary productivity which resulted in marl-limestone couplets, of which the limestones, peaks in coccolith productivity, signal less fertile blue-water times. Eccentricity highs in the 95 ka short eccentricity cycle brought monsoonal regimes, upwelling, eutrophy, and bottom stagnation, punctuating the record with cm-scale sapropels. Prolonged eccentricity lows in parts of the long (406 ka) eccentricity rhythm brought dominance of zonally-driven warm, saline, nutrient-depleted waters and downwelling, resulting in episodes of red marl or red clay deposition. Episodes of strong obliquity forcing inserted additional sapropels. These sapropels are markedly distinct from the 300-ka episode of anoxia that produced oceanic anoxic event OAE 1b (the Urbino member).