Workshop on Cretaceous Climate and Ocean Dynamics

Campanian isotope events, sea level and climate change

The general shapes of the Campanian carbon isotope curves exhibit remarkable similarities in all areas. A positive excursion spans the Santonian / Campanian boundary (~83.7 Ma), a second positive carbon isotope event occurs in the mid-Campanian (~78.7 Ma), and a negative excursion characterises the upper Campanian (~74.8 Ma). These events, together with smaller peaks, troughs and inflection points in the isotope profiles enable precise inter-regional correlations that are consistent with nannofossil data. Major shifts in profiles coincide with changes in eustatic sea-level, and provide robust chronostratigraphic trends that offer potential for bed-scale inter-continental correlation independent of biostratigraphy. Relatively stable values in the lower Campanian and their long-term fall through the upper Campanian reflect high and then falling eustatic sea-levels, and increased carbonate production on late Campanian platforms and in epicontinental seas. Short-term (~600 kyr) positive excursions record greater organic productivity and/or organic matter preservation and decreased carbonate fluxes during periods of rapid sea-level rise and the drowning of carbonate platforms. Excursions were terminated by falling nutrient supply and increased carbonate fluxes associated with epicontinental sea expansion and renewed carbonate platform growth during the late transgression and highstand. Negative excursions are linked principally to reworking of marine and terrestrial organic matter during rapid sea-level fall. Oxygen isotopes exhibit a wide range of values in the different study sections. Stratigraphic trends in Tunisia are inconsistent with other areas, indicating a substantial local diagenetic overprint. However, shows no covariance with , confirming that the carbon isotopes preserve primary stratigraphic trends. Rising values through the Campanian in the other sections reflect falling sea-surface temperatures accompanying Late Cretaceous global cooling. Gradient changes in the isotope profiles and short-term peaks and troughs may reflect short-term climate events. Cooling was most rapid during the early to mid-Campanian accompanying eustatic sea-level rise, but slowed and may even have reversed during the late Campanian regression. Strontium isotopes record a remarkable linear increase through the Campanian and, although insensitive to short-term sea-level change, provide an independent means of dating and correlation. The combination of sedimentological, biostratigraphic and chemostratigraphic data provides a powerful tool for constraining Late Cretaceous environmental change.