Mathematics – Logic
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusmpp24a..01m&link_type=abstract
American Geophysical Union, Spring Meeting 2008, abstract #PP24A-01
Mathematics
Logic
0404 Anoxic And Hypoxic Environments (4802, 4834), 0459 Macro- And Micropaleontology (3030, 4944), 0460 Marine Systems (4800), 0473 Paleoclimatology And Paleoceanography (3344, 4900)
Scientific paper
Lower Aptian series at the la Huasteca Canyon, Nuevo Leon, NE Mexico, include the uppermost part of the Cupido Formation, a shallow-platform facies (TIC > 60%) succeeded by the La Peña Formation (TIC very variable 17 - 92 %). The change indicated a long-term shift in sedimentation characterized by distinct periodic increase in terrigenous, organic matter and abundant occurrence of ammonites. The interbeds of marls, calcareous shales, marly calcilutites and calcirudites of the La Peña facies contain abundant thin-shelled ammonites, and few planktonic foraminifera. The change occurred in the Dufrenoya justinae ammonite Zone, coeval with the Dufrenoya furcata Zone of the standard ammonite biochronostratigraphy of the Mediterranean province for the uppermost Early Aptian (Barragan-Manzo and Mendez-Franco, 2005; Barragan and Maurrasse, 2008). These zones differentiate the upper part of the Lower Aptian, therefore posterior to OAE1a. Nonetheless, while microfacies of the La Peña Fm show also intermittent belemnites, small pelecypods other than rudists, and sea urchins, benthic foraminifera are mostly absent occurring toward younger levels in the Gargasian coincident with highest taxonomic diversity. Benthic foraminifers are conspicuously absent particularly at the levels closest to the transition zone with the infrajacent Cupido facies. Also, despite increase in TOC (up to 2.6 %) in the La Peña facies, ∂13 Corg curve shows little co-variation with increasing OM, which we interpret to represent a regional phenomenon related to super-productivity in the isolated sub-basin of the Mexican platform (Maurrasse et al., 2006). In contrast, typical Cupido Fm microfacies exhibit abundant miliolids (20-30 %), fragments of rudists, echinoids, ostracods (> 30-40%), very few thin ammonite shell debris, and oolites at intermittent levels. Rich benthic foraminifer assemblages are indicative of well-oxygenated bottom conditions. However, there are three horizons about 60 cm-thick each that are remarkably devoid of benthic foraminifers. They occur at 5. 72 m, 11.45m and 29.6 m, respectively, below the La Peña Fm. Variations within the Cupido Fm are consistent with fluctuating high- productivity, well-oxygenated neritic environment punctuated by development of hypoxic to anoxic bottom waters (Maurrasse et al., 2006). These recurrent episodes of severe oxygen depletion fall within the time interval that may be correlational with the infrajacent D. deshayesi to possibly the D. wessi zones in the Mediterranean ammonite biozonation scheme. We interpret these horizons to represent recurrent hypoxic to anoxic bottom conditions that are local expression of global forcing factors during Cretaceous greenhouse conditions that lead to well-defined OAE-1a and the subsequent anoxic events. Barragan-Manzo, R., and Maurrasse, F., (2008) Revista Mexicana de Ciencias Geologicas, v. 25, 1, p. 145-157. Barragan-Manzo, R., and Mendez-Franco, 2005, Towards a standard ammonite zonation for the Aptian (Lower Cretaceous) of northern Mexico. Revista Mexicana de Ciencias Geologicas, v. 22, 1, p. 39-47. Maurrasse, F. J-M. R., Barragan-Manzo, R., and Ponton, C. 2006, Cupido- La Peña Formations: High-Productivity to Super-Productivity during the Cretaceous Enhanced Greenhouse Conditions, GSA Abst.with programs v. 38, no 7, p. 491.
Barragan-Manzo R.
Maurrasse F. J.
Ponton Camilo
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