247
to identify recent sedimentation, as well as sedimentological, chemical, and biological indicators that are susceptible to degradation, rapid modification/change, and/or
low preservation potential in the sedimentary record. Also, as mentioned, impacted
sedimentation was expected to be at the very sediment surface, and this allowed for
targeted analysis for rapid determination of oil-contaminated sedimentation.
14.7.2 Time Series
The continued collection of sediment cores over the subsequent years following
DWH provided the ability to define how the sedimentary signature was distinctly
different from non-event sedimentation and how the sedimentary signature evolved
over the following months to years. This was particularly critical to be able to use
the same chronometer (
234
Th xs ) for direct comparison of sedimentation rates (event
vs post-event) (Sadler 1981). The time series defined the duration of the event and
timing of the post-event response and if/when the benthic system stabilizes and/or
recovers following such an event. It also provided the opportunity to investigate
how the sedimentary system, including the signature of oil-contaminated sediments,
evolved over subsequent years and the preservation potential of oil-contaminated
sediments in the sedimentary record.
14.7.3 Sampling Resolution
Due to the short duration (months) of the blowout event and subsequent rapid collection of cores, the appropriate sub-sampling resolution to detect sedimentation on
a monthly time scale was also of critical importance. The utilization of highresolution sampling (2 mm sub-sampling) of cores allowed for the highest temporal
resolution to detect the sedimentary signature of the blowout event with multiple
sample intervals that represented the depositional pulse. It also allowed for the utilization of
234
Th xs as an indicator of short-term (months) sedimentation rates of the
depositional pulse, as well as a direct comparison to post-event rates. This provided
post-event baselines to define the deviation in sedimentation rates associated with
the depositional pulse. The continued use of 2 mm sampling resolution was critical
for determining the post-event sedimentation rates using
234
Th xs as this indicator was
often only detectable in the upper 2–10 mm. Coarser sampling resolution would not
have been able to define post-event sedimentation rates using
234
Th xs .
Factors to consider with respect to sub-sampling resolution for detection of an
event in the sedimentary record are the thickness of the depositional event and the
required sensitivity of the analytical measurements used to detect the sedimentary
signature of the event. Coarser sampling resolution may be appropriate for depositional events of greater thickness, often associated with long duration and/or high
magnitude/sedimentary responses. The thinner the depositional event the finer the
14 Characterization of the Sedimentation Associated with the Deepwater Horizon…
to identify recent sedimentation, as well as sedimentological, chemical, and biological indicators that are susceptible to degradation, rapid modification/change, and/or
low preservation potential in the sedimentary record. Also, as mentioned, impacted
sedimentation was expected to be at the very sediment surface, and this allowed for
targeted analysis for rapid determination of oil-contaminated sedimentation.
14.7.2 Time Series
The continued collection of sediment cores over the subsequent years following
DWH provided the ability to define how the sedimentary signature was distinctly
different from non-event sedimentation and how the sedimentary signature evolved
over the following months to years. This was particularly critical to be able to use
the same chronometer (
234
Th xs ) for direct comparison of sedimentation rates (event
vs post-event) (Sadler 1981). The time series defined the duration of the event and
timing of the post-event response and if/when the benthic system stabilizes and/or
recovers following such an event. It also provided the opportunity to investigate
how the sedimentary system, including the signature of oil-contaminated sediments,
evolved over subsequent years and the preservation potential of oil-contaminated
sediments in the sedimentary record.
14.7.3 Sampling Resolution
Due to the short duration (months) of the blowout event and subsequent rapid collection of cores, the appropriate sub-sampling resolution to detect sedimentation on
a monthly time scale was also of critical importance. The utilization of highresolution sampling (2 mm sub-sampling) of cores allowed for the highest temporal
resolution to detect the sedimentary signature of the blowout event with multiple
sample intervals that represented the depositional pulse. It also allowed for the utilization of
234
Th xs as an indicator of short-term (months) sedimentation rates of the
depositional pulse, as well as a direct comparison to post-event rates. This provided
post-event baselines to define the deviation in sedimentation rates associated with
the depositional pulse. The continued use of 2 mm sampling resolution was critical
for determining the post-event sedimentation rates using
234
Th xs as this indicator was
often only detectable in the upper 2–10 mm. Coarser sampling resolution would not
have been able to define post-event sedimentation rates using
234
Th xs .
Factors to consider with respect to sub-sampling resolution for detection of an
event in the sedimentary record are the thickness of the depositional event and the
required sensitivity of the analytical measurements used to detect the sedimentary
signature of the event. Coarser sampling resolution may be appropriate for depositional events of greater thickness, often associated with long duration and/or high
magnitude/sedimentary responses. The thinner the depositional event the finer the
14 Characterization of the Sedimentation Associated with the Deepwater Horizon…