U–EF vs. Mo–EF crossplot of samples from the Tithonian-Berriasian. The top inset diagram illustrates the general patterns of U–EF vs. Mo–EF covariation in modern marine environments. The grey field represents “unrestricted marine” environments, characteristic of the eastern tropical Pacific, whereas the yellow field represents the “particulate shuttle” trend, characteristic of depositional systems such as the Cariaco Basin, where intense redox cycling of metal oxyhydroxides (especially Mn-bearing) occurs within the water column. XEF = [(X/Al)sample/(X/Al)PAAS], and X and Al stand for the weight concentrations of element X and Al, respectively. Samples are normalized against the post-Archean average shale (PAAS) compositions of Taylor and McLennan (1985). The trace-element distribution indicates that Sample #1 recorded peculiar, probably euxinic, conditions of deposition, while samples #2 to 40 recorded conditions of depositions under oxic waters and with reducing conditions developing at shallow depth below the sediment-water interface. Samples #41 to 59 recorded fully oxygenated, normal-marine conditions of depositions.