TY - JOUR
T1 - The Northern Gulf of Mexico During OAE2 and the Relationship Between Water Depth and Black Shale Development
AU - Lowery, Christopher M.
AU - Cunningham, Robert
AU - Barrie, Craig D.
AU - Bralower, Timothy
AU - Snedden, John W.
N1 - Funding Information:
The authors are grateful to Ramon Trevino of the Texas Bureau of Economic Geology (BEG) for informing us of the existence of the Spinks Core and to James Donnelly of the BEG Core Repository in Austin for assistance in laying out and sampling the core. We are also indebted to GeoMark Research LTD for running TOC and organic car bon isotopes. Finally, we are grateful for the support by members of the Gulf Basin Depositional Synthesis Project research project at the UT Institute for Geophysics, including Jon Virdell, Tim Whiteaker, and Patricia Ganey-Curry. T. J. B. acknowledges support from NSF grant EAR-1338316. A detailed core description is included as Supporting Information S1, full micropaleontological count data are included as supporting information S2, geochemical data are included as supporting information S3, and wireline log data and Delta Log R calculations are included as supporting information S4.
Publisher Copyright:
©2017. American Geophysical Union. All Rights Reserved.
PY - 2017/12
Y1 - 2017/12
N2 - Despite their name, Oceanic Anoxic Events (OAEs) are not periods of uniform anoxia and black shale deposition in ancient oceans. Shelf environments account for the majority of productivity and organic carbon burial in the modern ocean, and this was likely true in the Cretaceous as well. However, it is unlikely that the mechanisms for such an increase were uniform across all shelf environments. Some, like the northwest margin of Africa, were characterized by strong upwelling, but what might drive enhanced productivity on shelves not geographically suited for upwelling? To address this, we use micropaleontology, carbon isotopes, and sedimentology to present the first record of Oceanic Anoxic Event 2 (OAE2) from the northern Gulf of Mexico shelf. Here OAE2 occurred during the deposition of the well-oxygenated, inner neritic/lower estuarine Lower Tuscaloosa Sandstone. The overlying organic-rich oxygen-poor Marine Tuscaloosa Shale is entirely Turonian in age. We trace organic matter enrichment from the Spinks Core into the deepwater Gulf of Mexico, where wireline log calculations and public geochemical data indicate organic enrichment and anoxia throughout the Cenomanian-Turonian boundary interval. Redox change and organic matter preservation across the Gulf of Mexico shelf were driven by sea level rise prior to the early Turonian highstand, which caused the advection of nutrient-rich, oxygen-poor waters onto the shelf. This results in organic matter mass accumulation rates 1–2 orders of magnitude lower than upwelling sites like the NW African margin, but it likely occurred over a much larger geographic area, suggesting that sea level rise was an important component of the overall increase in carbon burial during OAE2.
AB - Despite their name, Oceanic Anoxic Events (OAEs) are not periods of uniform anoxia and black shale deposition in ancient oceans. Shelf environments account for the majority of productivity and organic carbon burial in the modern ocean, and this was likely true in the Cretaceous as well. However, it is unlikely that the mechanisms for such an increase were uniform across all shelf environments. Some, like the northwest margin of Africa, were characterized by strong upwelling, but what might drive enhanced productivity on shelves not geographically suited for upwelling? To address this, we use micropaleontology, carbon isotopes, and sedimentology to present the first record of Oceanic Anoxic Event 2 (OAE2) from the northern Gulf of Mexico shelf. Here OAE2 occurred during the deposition of the well-oxygenated, inner neritic/lower estuarine Lower Tuscaloosa Sandstone. The overlying organic-rich oxygen-poor Marine Tuscaloosa Shale is entirely Turonian in age. We trace organic matter enrichment from the Spinks Core into the deepwater Gulf of Mexico, where wireline log calculations and public geochemical data indicate organic enrichment and anoxia throughout the Cenomanian-Turonian boundary interval. Redox change and organic matter preservation across the Gulf of Mexico shelf were driven by sea level rise prior to the early Turonian highstand, which caused the advection of nutrient-rich, oxygen-poor waters onto the shelf. This results in organic matter mass accumulation rates 1–2 orders of magnitude lower than upwelling sites like the NW African margin, but it likely occurred over a much larger geographic area, suggesting that sea level rise was an important component of the overall increase in carbon burial during OAE2.
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U2 - 10.1002/2017PA003180
DO - 10.1002/2017PA003180
M3 - Article
AN - SCOPUS:85037356322
SN - 0883-8305
VL - 32
SP - 1316
EP - 1335
JO - Paleoceanography
JF - Paleoceanography
IS - 12
ER -