Correlation of Late Jurassic and Early Cretaceous zonation events in ODP and DSDP Atlantic and Indian Ocean sites (Table 5)

A database was built of 378 stratigraphic events, including first and last stratigraphic occurrences (FO/LO) of calcareous nannofossils, foraminifers, and dinocysts, and geomagnetic reversal occurrences in Latest Jurassic through Early Cretaceous deep-marine strata of 10 Atlantic and three Indian Ocean drilling sites. A total 136 different events are included, about one-third of which are unique to either ocean; however, this number may decrease when more Indian Ocean ODP sites become available for study. Using the complete data set, with the quantitative stratigraphy methods STRATCOR and RASC, we calculated closely comparable optimum sequences of average first and last occurrence positions. The preferred zonal solution, based on the STRATCOR method, includes 56 events, each of which occurs in 3 or more sites and comprises 6 geomagnetic reversal events, 25 nannofossils, 5 planktonic and 8 benthic foraminifers, and 12 dinocysts. Eight assemblage zones of Tithonian through Albian age have been recognized that correlate most of these sites. The nannofossil events, Cruciellipsis cuvillieri FO, Tubodiscus verenae FO, Rucinolithus wisei LO, and Chiastozygus litterarius FO, in the Atlantic Ocean are half a stage or more older than those in the Indian Ocean. Stratigraphic ranges of the benthic foraminifers Haplophragmium inconstans, Trochammina quinqueloba, and Dorothia praehauteriviana, differ significantly among sites. The same is true for the dinocyst events Phoberocysta neocomica LO and Druggidium apicopaucicum LO, rendering these taxa less useful for zonation and correlation.