The middle Cretaceous recorded major depositional and biotic events in carbonate shelves, epeiric seaways, and deep oceans. Global sea level rise in the Early Aptian and in the Late Cenomanian preceded OAEs, and evolutionary diversifications followed major turnovers in benthic and planktic biota. These environmental, depositional and biotic changes are more significant than those across the Albian-Cenomanian boundary that separate the Early and Late Cretaceous series. We propose that the Cretaceous Period/System be formally divided into Early/Lower, Middle, and Late/Upper ages/series. The base of the Early/Lower unit is the base of the Berriasian Age/Stage. The base of the Middle Age/Series would be the base of the Aptian Age/Stage when its definition is agreed upon. The base of the Late/Upper interval would be the base of the Turonian Age/Stage. Traditionally the base of the Tethyan Aptian is the first appearance (FO) of the ammonite Deshayesites. Ammonites diversified following the mid Aptian extinction associated with OAE1a when sixteen new families evolved in the late Aptian to Albian. The base of the Turonian is the FO of Watinoceras. During the Turonian five new families appeared. Planktic foraminifera, nannofossils, and dinoflagellates bracket the base of the Aptian. The FO of Leupoldia cabri is above the FO of Deshayesites. The FO of Hayesites irregularis is slightly before Deshayesites. Key dinoflagellates datums are the FOs of Pseudoceratium securigerum and Aptea polymorpha and the last occurrence (LO) of Hystrichodinium ramoides. Magnetochron CM0R is close to these bioevents. In some sections deepening is recorded about 1 m.y. after the FO of Deshayesites. OAE1a is recorded about 1.5 m.y. later. The base of the Turonian is bracketed by the LO of Rotalipora cushmani and the FO of Helvetoglobotuncana helvetica, and is very close to the FO of Quadrum gartneri. The FO of the basal Turonian Watinoceras is in OAE2. In carbonate platforms, drowning is considered to be closely associated with OAE2. This proposal defines three Cretaceous epochs/series by bioevents closely allied to global oceanic drowning and anoxic events. These epochs are characterized by evolutionary diversification of planktic foraminifers, nannofossils, dinoflagellates, and rudists.
|Titolo:||Three-Fold division of the Cretaceous Period: A proposal|
PREMOLI SILVA, ISABELLA (Penultimo)
|Settore Scientifico Disciplinare:||Settore GEO/01 - Paleontologia e Paleoecologia|
|Data di pubblicazione:||set-2005|
|Enti collegati al convegno:||Subcommission on Cretaceous Stratigraphy IUGS|
|Tipologia:||Book Part (author)|
|Appare nelle tipologie:||03 - Contributo in volume|