Determining paleoredox conditions across the Cretaceous-Paleogene mass extinction at Blake Nose; evaluation of carbon and nitrogen isotopes and trace metal profiles

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Author(s): Quan, T. M.; Nelson, A.
Author Affiliation(s): Primary:
Oklahoma State University, Boone Pickens School Geology, Stillwater, OK, United States
Volume Title: AGU 2012 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2012; American Geophysical Union 2012 fall meeting, San Francisco, CA, Dec. 3-7, 2012. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The Cretaceous-Paleogene (K-Pg) boundary (≈65 Mya) is marked by a major mass extinction for a wide range of terrestrial and marine organisms. In addition, there is significant evidence for disruptions in the carbon and nutrient cycles, productivity, paleoclimate, and bottom water oxygen levels, but the exact temporal and spatial extent of the disruptions are still unknown. In order to assess changes in nitrogen cycling and post-extinction anoxia, we have been measuring sedimentary nitrogen isotopes (δ15N), carbon isotopes (δ13C), and redox-sensitive trace metal concentrations in several cores across the K-Pg boundary. Since the sedimentary δ15N record can provide information on bottom water oxygen levels as well as nitrogen cycling, we can also investigate the use of bulk sedimentary δ15N as a proxy for paleoredox conditions by comparing the isotope record with that of the redox-sensitive trace metals. We obtained samples from Blake Nose in the North Atlantic (ODP 171B), a site that is proximal to the Chicxulub impact location. The cores at this site have an excellent record through the K-Pg boundary and contain clear evidence of both the impact and subsequent mass extinction. We measured δ15Nbulk, δ13Corg, total organic carbon (TOC), total nitrogen (TN) and trace metal concentrations in samples dating from the Late Maastrichtian (R. fructicosa foraminiferal zone) through to the Early Paleogene (foraminiferal zone P1c). Unlike our previous findings at the more distal Bass River (ODP 174AX) and Demerara Rise (ODP 207) sites, there is no obvious increase in δ15N values through the mass extinction, although there is a slight enrichment in redox-sensitive trace metals after the boundary. As a result, there appears to be no evidence for increased denitrification/anammox activity (and therefore no significant change in deep water redox state) immediately after the K-Pg boundary at Blake Nose based on the δ15N profiles; however, the trace metal profiles suggest there was a change in redox conditions in the deep water column and/or sediment column. The dissimilarity of the Blake Nose record to those from Bass River and Demerara Rise indicates that post-boundary anoxia appears to be a localized occurrence, and that local conditions play an important role in shaping the geochemical records.
Year of Publication: 2012
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Atlantic Ocean; Blake Nose; Blake Plateau; C-13/C-12; Carbon; Cenozoic; Cretaceous; Demerara Rise; Equatorial Atlantic; Isotope ratios; Isotopes; K-T boundary; Leg 171B; Leg 174B; Leg 207; Lower Paleocene; Marine environment; Mass extinctions; Mesozoic; Mid-Atlantic Ridge; N-15/N-14; Nitrogen; North Atlantic; Northwest Atlantic; Ocean Drilling Program; Paleocene; Paleoecology; Paleoenvironment; Paleogene; Stable isotopes; Stratigraphic boundary; Tertiary; Upper Cretaceous; West Atlantic
Coordinates: N295500 N300900 W0760600 W0763800
N224500 N224700 W0460400 W0460700
N090200 N092800 W0541100 W0544400
Record ID: 2014044814
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