INTEGRATED CHRONOSTRATIGRAPHIC DATABASE FOR DEFINING CRETACEOUS GSSPS: ALBIAN CASE STUDY

Stratigraphic research since 1976 has focused on selecting criteria to define stratotypes for each age/stage of the geologic column. More than half of the chronostratigraphic units are now so defined by Global Stratotype Sections and Points (GSSPs). However, achieving consensus on some boundaries has long been stalemated. For example, since 1995 no agreement has been reached for base of the Albian Age/Stage, uppermost unit of the Early/Lower Cretaceous. A major issue is that the traditional criterion, ammonites, are distributed regionally. Thus the ability to correlate base Albian defined by ammonites outside of Europe is impossible.

The European ammonites are integrated with planktic foraminifera, nannoplankton, dinoflagellates, and geochemical events in a quantitative, testable database. This dataset enables the projection of a stratotype point into marine sections across paleogeographic boundaries. Correlation hypotheses are formulated by comparing quantitatively first and last occurrences of taxa in a section with ranges compiled in many sections. The Cretaceous Chronostratigraphic Database (CRETCSDB) is composed of more than 3400 fossil taxa and marker beds calibrated to a mega-annum scale. These events are integrated from nearly 300 published worldwide sections that span from the Jurassic/Cretaceous boundary to the Cretaceous/Paleogene boundary. The ranges of first and last occurrences are calibrated to standard Cretaceous stages defined by Global Stratotype and Section Points or to reference sections where GSSPs are not yet designated. Thus the ages and stratigraphic order of taxa, event beds and of key sequence contacts in defined reference sections can be tested and objectively analyzed. Base Albian candidate boundary criteria are first occurrences of: 1) Leymeriella (Proleymeriella) schrammeni anterior at 113.07 Ma; 2) Leymeriella tardefurcata at 112.68 Ma; 3) Prediscosphaera columnata at 114.50 Ma; 4) Paraticinella eubejaouaensis at 113.11 Ma; and 5) base of black shale bed Niveau Paquier at 112.72 Ma. The last occurrence of Globigerellinoides algerianus is a potential accessory at 112.88 Ma.