228TH AS AN ANNUAL-SCALE GEOCHRONOLOGICAL TOOL: APPLICATIONS TO THE 2010 BP BLOWOUT EVENT

²²⁸Th, part of the ²³²Th decay series, is delivered to marine systems primarily by rivers and in situ production, and has been shown to have a strong particle affinity, which should make it an ideal geochronological tool. It has not received wide use as a geochronological tool, however, primarily due to the short half-life (~1.91 years), which is too short for most depositional systems.

²¹⁰Pb and ²³⁴Th analyses have shown that surficial Gulf of Mexico sediments following the 2010 BP blowout event accumulated at extremely rapid rates, up to 100x greater than rates of underlying, “natural” sediments. Since over two years has passed since the BP event, the time frame is now ideal for investigating the utility of ²²⁸Th as a geochronological tool.

Using gamma spectroscopy, ²¹²Pb and ²⁰⁸Tl are used as proxies for ²²⁸Th, and are detected to depths of 5-6 cm in cores collected almost 2 years following the event. Down-core ²²⁸Th profiles are consistent with decay profiles and support ²¹⁰Pb and ²³⁴Th data indicating extremely rapid sediment accumulation following the 2010 BP blowout event.

While work is still in progress, ²²⁸Th appears to be a promising tool for bridging the gap between ²¹⁰Pb (half-life ~22.3 years) and ²³⁴Th (half-life ~24 days) geochronometers, thereby allowing for the investigation of sedimentary processes over a range of time scales.