Slopes - Trace Fossils as Indicators of Sedimentary Environments - page 603

systems in a manner similar to the North Sea Basin. In the Vøring Basin, the
Nise Formation may exceed 1200 m in thickness and is mainly interpreted as
deep-sea submarine fan deposits (e.g., Fjellanger et al., 2005; Knaust, 2009;
Martinsen et al., 2005 ). Successions in those localities are dominated by sedi-
ment gravity-flow deposits, with thoroughly bioturbated zones interstratified
with bedded turbidites and other mass-flow units.
By contrast, theNise Formation in theEllida area (6405/7-1), lying further to the
south within the Vøring Basin, possesses few turbidites or turbiditic/contouritic
mudstones. Facies associations there are dominatedbypervasively bioturbated silty
mudstones, sandy mudstones, and muddy sandstones ( Fig. 6 ). These successions
are interpreted to record upper to lower slope settings, dominated by background
or ambient (non-event) conditions. These ambient facies contrast markedly with
the few intercalated turbidite and contourite heterolithic mudstone units.

4.3.1 Event-Generated Heterolithic Facies
The event-style deposits in the Ellida well are characterized by thin (cm-scale)
heterolithic sandstone/siltstone and claystone composite bedsets (e.g., Fig. 6 B),
as well as graded to stratified lamina-sets displaying a characteristic pinstriped
appearance. The sandstone layers are of mm-scale, and are delicately parallel
laminated with minor current ripples. Traction structures are generally attrib-
uted to dilute turbidity currents, although some may record contour-current
reworking. Sandstones are characterized by BI

0-1, with isolated fugichnia
and Phycosiphon , and normally grade to largely unburrowed silty claystones
to silt-poor claystone layers, interpreted as rapidly emplaced T e turbidite divi-
sions. Trace fossils are sporadically distributed (BI

¼

0-2) and occur as thin
bands of diminutive Chondrites , small- and large-diameter Planolites , and
minor Phycosiphon . Locally, mud-filled Zoophycos , Schaubcylindrichnus
( S. freyi ), and diminutive Asterosoma are also present. Overall, trace-fossil
suites are characterized by a low diversity and record rapid reoccupation of
newly available muddy substrates by opportunists following event sedimenta-
tion. Prevailing elements are predominantly shallow-tier forms.

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4.3.2 Ambient, Bioturbated Mudstone Facies
Ambient (background) facies of the Nise Formation, by contrast, consist of
thoroughly biogenically admixed clay, silt and sand, predominantly expressed
as silty and sandy mudstones ( Fig. 6 A and B) that locally pass into muddy sand-
stones ( Fig. 6 C and D). Sandy and silty mudstones are pervasively bioturbated
(BI 4-5), and no primary sedimentary structures are preserved. The ichnolo-

gical suite comprises Phycosiphon , Chondrites , Planolites , Zoophycos , robust
Scolicia , Helminthopsis , Cosmorhaphe , Taenidium , Thalassinoides , Schaubcy-
lindrichnus ( S . freyi ), and Rhizocorallium . Locally, these suites also include iso-
lated Asterosoma , Spirophyton , Phoebichnus , and Nereites . These ambient
suites constitute highly diverse expressions of the Zoophycos Ichnofacies.
The bioturbated mudstone facies are interpreted to reflect the slope margin

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