GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 223-3
Presentation Time: 2:00 PM


PAEZ-REYES, Manuel1, GUERREDIAGA, Ashley1, REA, Rebecca1, SILVA-TAMAYO, Juan Carlos1, JUNIUM, Christopher K.2, MILLER, Brent V.3 and CARVAJAL-ORTIZ, Humberto4, (1)Department of Earth and Atmospheric Sciences, University of Houston, Science & Research Building 1, 3507 Cullen Blvd, Houston, TX 77204-5007, (2)Department of Earth Sciences, Syracuse University, Syracuse, NY 13244, (3)Dept. of Geology & Geophysics, Texas A&M University, College Station, TX 77843, (4)Petroleum Services Division, Core Laboratories, 6316 Windfern Road, Houston, TX 77040,

Secular episodes of enhanced anoxia in the Mesozoic ocean, collectively termed oceanic anoxic events-OAEs, led to the deposition of organic-rich sediments in a wide range of marine environments. A cause-effect relationship between volcanism, ocean anoxia, enhanced organic carbon burial, and carbon cycling disruption has been proposed for the OAEs. Among these events, the Oceanic Anoxic Event 2 is characterized by a well-developed positive d13C anomaly both in carbonate and organic substrates. Recently, the evolution of the d13CTOC excursion has been presented in a highly-resolved chronostratigraphic framework along the Western Interior Seaway. Stratigraphic correlations between this area and other localities worldwide enable the identification of a typical d13CTOC anomaly consisting of a first positive d13CTOC maximum interrupted by a sudden return to more negative d13CTOC values, a return to heavier and sustained d13CTOC values, and finally a gradual return to pre-excursion values. Less well-studied are the precursor events, periods of fluctuating positive and negative peaks in d13CTOC, prior to the main positive anomaly. Two Cenomanian-Turonian organic-rich mudstone successions from the Upper Magdalena Valley, Colombia display d13CTOC variability that is typical of OAE 2, in addition to the precursor events. Thin ash beds are commonly found (ca. 60 beds) and provide clues to the coupling between carbon cycling and regional volcanism. The coincidence of the d13CTOC variability prior to OAE 2 and the increasing occurrence of ash layers suggests a link between volcanic activity and the carbon cycle preceding the onset of the isotopic anomaly. Interestingly, after its onset, the remaining isotopic anomaly and its short-term fluctuations seem to not be fully driven by volcanism. We suggest that internal feedback dynamics in the climate-ocean system are most likely the responsible mechanism leading to the return of the carbon cycle to pre-event levels.