Agglutinated Foraminifera Morphogroups - Insights to the Late Cretaceous Paleoenvironments from Two Tethyan Sections: Contessa Highway, Italy and Dambovita Valley, Eastern Carpathians, Romania
Agglutinated foraminifera morphogroups have proved lately (e.g. Kaminski & Gradstein, 2005) to represent an important tool in providing useful information about bathymetry and organic carbon fluxes to the sea floor. An extended and improved scheme of morphogroups of agglutinated foraminifera is used in the present study in order to determine if this group of foraminifera reflects and can be used as a proxy for paleoenvironmental changes in the Late Cretaceous.
This method was attempted in two land sections from Tethys which can be very well correlated by integrated biostratigraphy: the Contessa Highway Section, Umbria-Marche region, Italy, and Dambovita Valley sections, Eastern Carpathians, Romania.The role of morphogroups as paleoenvironmental indicators is proven in the Upper Cretaceous of the two mentioned settings where the results of the morphogroup analyses were integrated with sedimentological, carbon isotope data, and regional sea-level curves.
The Upper Cretaceous carbon isotope stratigraphy based on the work of Jarvis et al., 2002, 2006 in the Tethyan area led to the definition of “events” in this record. They represent positive or negative peaks in the δ13C curve that are correlated throughout the Tethys and are related with sea-level shifts in regional curves. High sea-level are implied for positive excursions in the δ13C curve while low sea-levels in the Tethyan area are assumed for negative excursions during Late Cretaceous. All these “events” can be traced also using the morphogroups of agglutinated foraminifera.
All the positive peaks in the Thetyan δ13C curve identified by Jarvis (2002, 2006) and the local δ13C curves (e.g. Jenkins et al. 1994) correspond with higher values of the deep infaunal morphogroup in the Contessa Highway section. Late Turonian, Late Coniacian, Early Santonian positive peaks but mostly the Santonian/Campanian Boundary Event and the mid Campanian Event determined an increase in the values of the M4b and M4a morphotypes up to 40% of the agglutinated assemblages. Negative values in the δ13C curve as the middle Coniacian or Upper Campanian event are reflected by the greatest values of the M1 morphotype of agglutinated foraminifera. The Santonian/Campanian Boundary Event and the mid Campanian Event can also be identified in the Dambovita Valley, Eastern Carpathians where the same increase in the deep infaunal morphogroup up to 50% of the whole agglutinated assemblage can be seen from the morphogroup analysis.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009