HR: 1340h
AN: PP33B-0941    [Abstracts]
TI: Aptian Facies Diversity Around The Tethys Realm: Global Oceanic Factors Vs. Local Physiographic Conditions
AU: * Ponton, C
EM: cpont001@fiu.edu
AF: Department of Earth Sciences, Florida International University, 11200 SW 8th Street, PC-344, Miami, FL 33199 United States
AU: Maurrasse, F J
EM: maurrass@fiu.edu
AF: Department of Earth Sciences, Florida International University, 11200 SW 8th Street, PC-344, Miami, FL 33199 United States
AB: Comparison of Aptian stage succession in southeastern France, northeastern Mexico, and central Italy, indicates that deposits of C$_{org}$-rich facies are diachronous and may show sharply contrasting successive conditions of deposition. For instance, the La Pe\~{n}a Formation in northeastern Mexico spans the interval that includes OAE 1a (Selli/Goguel event), and is mostly organic rich marls, but the section at La Huasteca Canyon also shows conspicuous red to purplish-colored carbonate-poor layers intercalated with the dark gray C$_{org}$-rich shales and marly limestones. While the marls average 68.74%wt of CaCO$_{3}$ and TOC values of 0.59%wt, the reddish beds show CaCO$_{3}$ values as low as 17.04%wt and high TOC values up to 2.63%wt. The apparent discrepancy between these layers questions the origin of the reddish layers that have been overlooked. Although initial EDS analysis on these reddish beds confirms a high iron oxide content (8-9%wt), it remains uncertain whether they represent true oxic conditions at that time, or whether they have been modified by subsequent diagenesis. In southeastern France, the Provencal platform shows in the Early Aptian Urgonian facies a light gray, discontinuous and locally diachronous marly interval, which is a weak indication of possible relation with the worldwide anoxic event. Exact chronological correlation of this layer with the Selli-Goguel Event, and relative timing of these conditions with the northeastern Mexican platform is still pending. Previous studies show considerably high TOC values of 2-2.5%wt for the lower Aptian series at other section within the Provencal platform. In the Umbria-Marche Basin of central Italy, the well-known Selli level or OAE1a is characterized by a regional C$_{org}$-rich marker bed indicative of anoxic/dysoxic conditions. However, in the Gubbio sections, intermittent maroon to red-colored intervals that strike out within the predominantly black shale series are compatible with oxic environments. Geochemical analyses report iron content with values up to 9.15%wt of Fe$_{2}$O$_{3}$ in these red shales, values that are strikingly similar to the reddish beds from NE Mexico. The reddish-brown beds present within the black shale facies in the Aptian series clearly indicate periods of local variations to well-oxygenated conditions within the recurrent low-oxygen waters. Thus, facies differences with variations of coeval oxic and dysoxic conditions, imply that in certain areas, local factors controlled sediment type, and overprinted global forcing mechanisms that depleted oxygen level elsewhere.
DE: 9609 Mesozoic
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting