Primary production, isotopes, extinctions and the atmosphere

A Comparison of the Stable Oxygen and Carbon Isotope Composition of Early Cretaceous and Late Jurassic Carbonates from DSDP Sites 105 and 367

“…In fact, the scatter over a given geologic period is so large (as can easily be visualized from Figure 4) that two co-authors, using the same data, reached opposite conclusions as to the actual existence of such variations (Keith and Weber, 1964;Weber, 1967). Explanations for these long-period fluctuations range from periodic diastrophism (Jeffery et al, 1955;Compston, 1960) to the evolution of land plants (Weber, 1967) to changes in nutrient supply from the continents because of topographic and climatic changes (Tappan, 1968). All of these explanations seem to require too long a time to operate to be responsible for the variations observed here.…”

“…Jeffery et al (1955), Compston (1960), Weber (1967), and Tappan (1968) all discussed variations based on average values for geologic periods. Thus the average carbon isotope composition of marine limestone of Cretaceous age is heavier than the average composition of similar limestone of Jurassic age (Weber, 1967).…”

Facies Evolution, Carbonate Dissolution Cycles in Sediments from the Eastern South Atlantic (DSDP Leg 40) Since the Early Cretaceous

“…The lysocline is much more elevated in high productivity zones and is therefore not directly comparable to the lysocline in the central ocean basins (Bramlette, 1965;Tappan, 1968;Broecker, 1971;Berger and Roth, 1975).…”

Summary and Conclusions

“…During the latter Tertiary, this fluctuation would be in the order of 1 kilometer. An extreme fluctuation is postulated for the end of the Cretaceous-early Paleocene, at which time the two compensation levels indicated here are thought to have risen well into the photic zone (Tappan, 1968;Worsley, 1970).…”