Environmental Statement - Maersk Oil

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Balloch Field Development Environmental Statement
Section 3 Baseline Environment
The Mapping European Seabed Habitats (MESH) project categorised seabed sediments in the UKCS
area. From this, a predictive map of European sediment types was developed (Figure 3‐8). The
sediments in the vicinity of the Balloch development are predominantly sublittoral mud and sandy
mud.
Within Block 15/20, very soft clays occur as pockets and ribbons up to about 1.5 m deep in some
areas, with more extensive deposits also occurring. Sediments underlying the surface cover of sandy
mud comprise the very soft clays of the Witch Ground Formation and the firmer clays of the
Swatchway Formation. Superficial deposits in areas where the Witch Ground Formation is absent are
underlain by the Swatchway Formation. Swatchway deposits are firmer silty or sandy clays that vary
in thickness between about 7 m to 26 m (Fugro, 2010 and Gardline, 2004).
Seabed sediments in the Balloch area were observed as relatively homogeneous across the site and
consisting of very poorly sorted coarse silt, with a silt/mud component of 66.9 % (Fugro, 2010) (Figure
3‐9).
Figure 3‐9 Example seabed photographs from the Fugro (2010) site survey.
Organic matter primarily comprising of detrital matter and naphthenic materials, i.e. carboxylic acids
and humic substances, performs an important role in marine ecosystems by providing a source of
food for suspension and deposit feeders which may then be predated by carnivores. This has led to
the suggestion that variation in benthic communities is, in part, caused by the availability of organic
carbon (Snelgrove and Butman, 1994). Organic carbon is also an important adsorber (scavenger) of
heavy metals and may be of use when interpreting the distribution of metals (McDougall, 2000).