Ice Sheet Proxies from Seismic Stratigraphy and Deep Sea Isotopes

As the results of the MSSTS-1 and CIROS-1 records were being studied, two significant papers were published. One was by Haq et al. (1987), a better documented update of the Vail et al. (1977) monograph with a more detailed sea level curve based on coastal advance and retreat histories extracted from seismic imaging of continental margins around the world. It still showed a sharp and substantial mid-Oligocene shallowing, ostensibly from Antarctic Ice Sheet formation, along with some isolated shoaling events in the Paleogene and Cretaceous. The paper emphasized the cyclic sea level changes with a frequency of 1-3 million years, third-order cycles, inferred to be glacioeustatic. This link between ice sheets and sea level was invoked to explain cyclic patterns in Cenozoic strata in Australasia by Loutit and Kennett (1981).

The other paper was a compilation of deep-sea isotope data from numerous DSDP and Ocean Drilling Program (ODP) sites in the Pacific and Atlantic Oceans by Miller et al. (1987) - the smoothed curves for both oceans were a little different in detail but their main features included both the earliest Oligocene and middle Miocene positive isotope shifts first seen by Shackleton and Kennett (1975). At the time, no cyclicity comparable to that proposed by Haq et al. (1987) was recognized in the deep-sea isotope record, but the record plainly indicated continental ice build-up in the earliest Oligocene, not the mid-Oligocene indicated by the Haq et al. (1987) analysis. A comparison of the two curves is shown in Fig. 3.5. Which was correct? CIROS-1 cores had the oldest significant diamictites in the late Oligocene, but the Transantarctic Mountains, with their origins around 55 Ma (Gleadow and Fitzgerald, 1987), could well have been a barrier to earlier continental ice.

0 0

Post a comment