Benthic Faunal Baselines in the Gulf of Mexico: A Precursor to Evaluate Future Impacts

This chapter provides a comparison between recently developed, post-oil spill baseline measurements throughout the Gulf of Mexico (GoM) and previous, pre-oil spill baselines for benthic foraminifera, meiofauna, and macrofauna for areas impacted by the Deepwater Horizon (2010) and Ixtoc 1 (1979–1980) oil spills. This comparison will provide two primary outcomes: (1) assessment of any lasting changes in benthic faunal assemblages caused by the Deepwater Horizon and Ixtoc 1 oil spills in the Gulf of Mexico and (2) augmentation of pre-oil spill baselines or establishment of “new normal” post-oil spill baseline measurements that can be utilized to quantitatively assess impact, response, and recovery of benthic fauna in the event of a future oil spill

SEISMIC REFLECTORS AND UNCONFORMITIES AT PASSIVE CONTINENTAL MARGINS

Vail and co-workers1-3 have recently suggested, based on seismic reflection data available to Exxon, that more than 25 global unconformities occur in Mesozoic-Tertiary age passive continental margins around the world. These data have been used to subdivide the stratigraphical record into several cycles, each of which is controlled by oscillatory changes in sea-level. The resulting scheme has been used as a basis to predict the stratigraphy of passive margins where there is little or no well control4 or where few reflector terminations can be found5. We report here four difficulties with this scheme: (1) during times of minimal continental ice cover changes in the relative rate of sea-level are generally not sufficient to cause unconformities, except in old, slowly subsiding, margins; (2) seismic and biostratigraphical resolution restricts the identification of unconformity-bounded stratigraphical sequences to relatively few in continental shelves; (3) sequence boundaries appear to be best defined on slopes or in regions of active tectonic tilting; and (4) limitations in the sequence analysis technique preclude its use in predictive stratigraphy, especially in shelf and slope regions of margins. © 1984 Nature Publishing Group

Characterizing the Variability of Benthic Foraminifera in the Northeastern Gulf of Mexico following the Deepwater Horizon Event (2010-2012)

Following the Deepwater Horizon (DWH) event in 2010 subsurface hydrocarbon intrusions (1000-1300 m) and an order of magnitude increase in flocculent hydrocarbon deposition caused increased concentrations of hydrocarbons in continental slope sediments. This study sought to characterize the variability [density, Fisher\u27s alpha (S), equitability (E), Shannon (H)] of benthic foraminifera following the DWH event. A series of sediment cores were collected at two sites in the northeastern Gulf of Mexico from 2010 to 2012. At each site, three cores were utilized for benthic faunal analysis, organic geochemistry, and redox metal chemistry, respectively. The surface intervals (∼0-10 mm) of the sedimentary records collected in December 2010 at DSH08 and February 2011 at PCB06 were characterized by significant decreases in foraminiferal density, S, E, and H, relative to the down-core intervals as well as previous surveys. Non-metric multidimensional scaling (nMDS) analysis suggested that a 3-fold increase in polycyclic aromatic hydrocarbon (PAH) concentration in the surface interval, relative to the down-core interval, was the environmental driver of benthic foraminiferal variability. These records suggested that the benthic foraminiferal recovery time, following an event such as the DWH, was on the order of 1-2 years