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S5, the clinothems are inferred to grade into WDBE
silty mudstones, as no associated incision surface
has been recorded.
The allostratigraphic unit 5 is truncated beneath
the SU2/TS5 surface both north and south of
locality S5. The scale of truncation is up to 20 m to
the south and up to 40 m to the north (Fig. 7).
Subaerial unconformity SU2 and
transgressive surface TS5
Description
South of locality S5, the bounding surface between
silty mudstones of allostratigraphic unit 5 and
overlying sandstones of allostratigraphic unit 6 is
characterised by a few decimetres-thick conglom-
erate bed with quartz and quartzite pebbles, marine
body-fossil debris (belemnites) and decimetre-
scale wood fragments (Fig. 11C and D). In places,
the bed is extensively bioturbated by
Diplocraterion
parallelum
(Fig. 10C). Mapping of the surface
underneath the conglomerate bed defines up to
20 m-deep incision into underlying WDBE ele-
ment strata (allostratigraphic unit 5; Figs 5A and
7). From locality S5 to S6, the same unconformity
cuts 9 m into underlying WDBE element strata
(allostratigraphic unit 5) and is draped by a centi-
metre-thick, gravelly sandstone bed with abun-
dant shell imprints and oyster fragments. In the
northern area, the unconformity is defined by the
overlying i) 10 cm thick lithic conglomerate bed
with locally abundant marine body fossils (
belem-
nite rostra
) and/or ii) mud pebble beds, or iii) an
up to 1 m thick matrix-supported conglomerate
bed with lithic pebbles and cobbles (up to 9 cm in
diameter) composed of quartz, quartzite and gneiss
(similar to locality N3, section 28; Figs 5C, 13A
and D). Along the northern area, the erosional sur-
face records an incision up to 40 m deep.
Interpretation: Allostratigraphic unit 5
Based on the change in facies and palynomorph
surface TS4 beneath, allostratigraphic unit 5 is
interpreted as having formed by marine ravine-
ment during regional transgression. Allostrati-
graphic unit 5 is unique in the Neill Klinter Group
because it contains contemporaneous deposits of i)
silty mudstone units formed in a wave-dominated
brackish-marine embayment (WDBE architectural
element; Figs 7 and 10A to B; Table 3) and ii) stacked
units of tide-dominated delta clinothems (TDDC
architectural element; Figs 7, 12A to C and 12E;
Table 3). The association of these two architectural
elements is restricted to the southern area and can
be explained by the formation of different adja-
cent paralic subenvironments in response to coast-
parallel differences in sediment input subsequent
to transgression across TS4.
A major tide-dominated delta system, defined by
the TDDC element, was established on top of the
underlying distributary system (allostratigraphic
unit 4, locality S5) during the rise in relative sea-
level. The contemporaneous embayments with low
sedimentation rates hosted the brackish to normal
marine silt-rich mud (WDBE element). The TDDC
element shows lateral sediment migration, as sug-
gested earlier by Dam & Surlyk (1998). The mud
fraction of the sediment load was distributed basin-
ward and into bays adjacent to distributary mouths
by suspension plumes, whereas coarser sediments
were deposited as prograding delta lobe clinothems
or mouth bars by bottom currents.
Picking the maximum flooding surface MFS4 is
difficult due to a lack of well-defined distal facies.
The MFS4 surface is placed within the lower part
of the WDBE element. In the area of locality S5,
MFS4 is cut by the lower boundary of the clino-
them element TDDC and is therefore inferred to
have been located in a more distal position on the
downlap surface of the lowermost progradational
clinothem. Only the silty shales of the WDBE ele-
ment were eroded along the succeeding subaerial
unconformity SU2 (see below) south and north of
locality S5 that formed during a fall in relative
sea-level.
Interpretation: Subaerial unconformity SU2
and transgressive surface TS5
This basinwide unconformity is interpreted as a
combined subaerial unconformity and transgres-
sive surface SU2/TS5. The subaerial unconformity
surface is interpreted to have formed by fluvial ero-
sion and marine regressive ravinement during a
fall in relative sea-level. Fluvial gravel was subse-
quently deposited onto the SU2. During the follow-
ing rise in relative sea-level, marine transgressive
ravinement and sedimentation obliterated much
of the previous fluvial erosional and depositional
features formed along the unconformity. The strata
above the transgressive surface TS5 thus record a
change from progradational depositional archi-
tecture, formed during the regressive stage, into
retrogradational architecture, formed during the
transgressive stage. Lateral variation in incision was
controlled by the interplay between rate of fall and
rise in relative sea-level, slope gradient variation
along the coast, rate of sediment supply, distance
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