Orbitally tuned C and N isotopic records of Aptian oceanic anoxic event 1a in northeastern Mexico and Deep Sea Drilling Project Site 398, north Atlantic Ocean

Author(s): Montanez, I. P.; Li, Y.; Osleger, D. A.; Bralower, T. J.
Author Affiliation(s): Primary:
University of California, Davis, Department of Geology, Davis, CA, United States
Other:
Pennsylvania State University, United States
Volume Title: AGU 2006 fall meeting
Source: Eos, Transactions, American Geophysical Union, 87( Fall Meeting Suppl.); American Geophysical Union 2006 fall meeting, San Francisco, CA, Dec. 11-15, 2006. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0096-3941 CODEN: EOSTAJ
Note: In English
Summary: High-resolution and expanded records of early Aptian Oceanic Anoxic Event (OAE) 1a (120 Ma) were recovered from outer shelf and slope deposits from the Sierra Madre Oriental of northeast Mexico and from hemipelagic deposits at Deep Sea Drilling Project Site 398 on Vigo Seamount in the North Atlantic Ocean. OAE1a is recognized in these deposits by minor increases in organic carbon content (up to 2 wt%) and widely-recognized, characteristic δ13Corg and δ13Ccarb variations that record significant changes in global carbon cycling. Here we present continuous dm-scale records of grain size distributions, wt% TOC and carbonate, C/N ratios, and C and N isotopes for these stratigraphically-expanded sections. Our high-resolution rock magnetic study of the same stratigraphic intervals establishes orbital timescales for OAE1a at these sites. The highly expanded records reveal significantly more structure in isotopic and TOC variation throughout OAE1a than contemporaneous condensed deep-sea records. Our data define an initial prominent negative excursion followed by repeated and short-lived (103 to 104 yr) fluctuations and a final interval of near invariant δ13Ccarb and δ13Corg values. Elevated TOC, a significant increase in C/N ratios from background marine values, rapid shifts in C and N isotopic compositions and sustained decoupling of δ13Corg and δ15Norg occur throughout the interval of short- lived isotopic fluctuations. Anhysteretic remanent magnetization (ARM) measurements were used as proxies for terrigenous influx during OAE1a. Spectral analyses of ARM depth series reveal dominant cycles with wavelength ratios resembling those of modern orbital periodicities, implying that orbital variations may have modulated depositional processes. These orbitally tuned geochemical proxy records indicate that the Aptian deposits from northeastern Mexican and Site 398 on Vigo Seamount hold promise for refining phase relationships between geochemical and isotopic proxies throughout OAE1a, and, in turn, constraining the mechanics of addition of light carbon to the ocean-atmosphere system.
Year of Publication: 2006
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Anaerobic environment; Anhysteretic remanent magnetization; Aptian; Atlantic Ocean; C-13/C-12; Carbon; Carbon cycle; Climate forcing; Cores; Cretaceous; DSDP Site 398; Deep Sea Drilling Project; Geochemical cycle; Grain size; IPOD; Isotope ratios; Isotopes; Leg 47; Lower Cretaceous; Magnetization; Marine environment; Marine sediments; Mesozoic; Mexico; N-15/N-14; Nitrogen; North Atlantic; Northeastern Mexico; OAE 1a; Oceanic anoxic events; Orbital forcing; Organic carbon; Organic compounds; Paleo-oceanography; Paleomagnetism; Remanent magnetization; Seamounts; Sediments; Sierra Madre Oriental; Stable isotopes; Total organic carbon; Vigo Seamount
Coordinates: N405736 N405736 W0104306 W0104306
Record ID: 2008070676
Copyright Information: GeoRef, Copyright 2018 American Geosciences Institute.