Abstract:
Several studies examining isotopic records (d18O) aim to demonstrate the correlation of positive shifts in oxygen isotopes with erosions (sequence boundaries) in continental margins, which suggest glacioeustacy as the mechanism for such erosions. Application of consistent statistical and mathematical methods results in a quantitative evaluation of signal content in individual isotope profiles, from which we propose a composite oxygen isotope curve. Primary evidence is drawn from the Alabama coastal plain. Filtered core and outcrop data are correlated to test qualitative placement of sequence boundaries. Processing and comparison of results from offshore Brazilian data and from several DSDP/ODP records then provide a broader spatial correlation of frequencies and events. Auto correlation functions verify and estimate signal presence in each profile. Cross-correlation functions between the sampling sites give an initial estimate of the consistency of response to climatic events and common mechanisms. Power spectral analysis permits identification of common events and cyclicities despite temporal and spatial separation. A matched filter technique enhances signal-to-noise ratios in the data producing estimates of signal and noise power. Finally, nonparametric methods establish if and to what confidence level the data from disparate sources are independent or may arise from underlying processes producing isotope values of the same population, i.e., test the comparability of paleoclimatic processes that generate each of the datasets. Significantly, the oxygen isotope evidence when analysed in a depositional sequence framework appears consistent with glaciation from the late Cretaceous through the Paleogene.