Abstracts: High
Resolution Sequence Stratigraphy of Deltaic, Slope, and Turbidite Depositional
Systems
in the Upper Carboniferous of Northern Europe
ELLIOTT, TREVOR
The Upper Carboniferous
in northern Europe was characterized by a humid--tropical climate, high
magnitude--high frequency fluctuations in sea
level
forced by the Gondwanan
glaciation, and a copious sediment supply. Faunal concentrate condensed
horizons (marine bands) produced during periods of rising
sea
level
provide
a high-resolution chronostratigraphic framework in which intervals of approximately
60,000 yr can be analyzed at a regional scale. These conditions render
Upper Carboniferous successions an ideal testing ground for the methods
and concepts of high-resolution sequence stratigraphy. Extension in the
Lower Carboniferous was followed by thermally-driven subsidence in the
Upper Carboniferous, and in the early part of the Upper Carboniferous the
basins were characterized by a stepped bathymetry that was inherited from
the extensional
phase
. The basins comprised river-fed deltas, a basin slope,
and deeper basin turbidite
systems
. Re-examination of classic sections
in these basins using an integrated sedimentological and sequence stratigraphic
approach has challenged many long-held views of Upper Carboniferous sedimentation.
These points can be illustrated
by reference to a well exposed remnant of an Upper Carboniferous basin
in western Ireland, the Clare Basin. The basin comprises a 1.6-km succession
that commenced with a deepening, sediment-starved phase
and was followed
by a basin-fill succession of turbidites, slope, and deltaic deposits.
Examination of the deltaic deposits has led to the recognition of regional-scale
incised valleys dominated by sand-rich fluvial deposits, lowstand shelf-edge
deltas that differ sedimentologically from highstand and transgressive
systems
tract deltas, and a pronounced bias in preserved
systems
tracts
to those associated with lowstand conditions. In the slope an ordered,
sea
level
--driven stratigraphy that includes the creation and filling of
slope channels in a single
sea
level
cycle
has been recognized. In the
deeper basin, discrete sand-rich lowstand turbidite units can be identified
between regionally extensive condensed horizons. Although this succession
accumulated in an intracratonic basin, it shares many similarities with
the stratigraphy and sedimentation of clastic-rich, delta-driven passive
margins such as the Gulf of Mexico, Nigeria, and Angola.
AAPG Search and Discovery Article #90938©1997-1998 AAPG Distinguished Lecturers