Depositional dynamics and sequence development in a tidally influenced marginal marine basin: Early Jurassic Neill Klinter Group, Jameson Land Basin, East Greenland - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 312

amount of plant debris, mixed siderite-cemented
mudstone and clastic pebble-filled shallow
channel-formed sandstone beds increase signifi-
cantly towards the top of allostratigraphic unit 2.
Along the southern area (S2 to 6), the muddy to
sandy basal part of the allostratigraphic unit 2 is
5 to 15 m thick and composed of tide-influenced
heterolithic prodelta mudstone facies associa-
tion (FA5b) overlain by tide-influenced sandy
heterolithic delta front facies association (FA5a),
forming together a single upward coarsening unit
(Fig. 9B to D; Table 2). The prodelta silty mud-
stones of FA5b directly above the FSa contain
small bivalves, marine and terrestrial shell debris
and brackish to open marine microfossils. The
upward-coarsening unit is topped by an erosive
unconformity lined with thin, discontinuous and
gravelly conglomerate along the base of a tide-dom-
inated fluvial channel-fill facies association (FA1b;
Table 2). This, up to 9 m thick, upward-fining sand-
stone unit is topped by a flooding surface (FSb).
Above the FSb in the southern area, the rest of
the sandy heterolithic allostratigraphic unit 2
records laterally shifting upward-fining subtidal
inclined heterolithic strata facies association
(FA2a), upward-coarsening mudstone dominated
to sandstone dominated inclined heterolithic strata
facies association (FA2b), tide-influenced fluvial
channel-fill facies association (FA1a) and sandy
heterolithic tidal channel infill facies associations
(FA3c, 3d and 3e) (Fig. 9B and D; Table 2). At locali-
ties S2 to 6, the 8 to 32 m thick uppermost part of
allostratigraphic unit 2 thickens northward and is
composed of up to 10 m thick upward-fining sandy
tidal channel infill facies associations (FA3b and
3c) and sand-dominated inclined heterolithic strata
facies association (FA2b) (Figs 7 and 9A; Table 2).
Marine trace fossils (for example, Diplocraterion
parallelum ) are observed in the uppermost part of
the allostratigraphic unit 2. The top of the
allostratigraphic unit 2 is defined at the base of an
up to 2 m thick structureless sandy facies transi-
tion into shale-dominated heterolithic beds.
In the northern area, the allostratigraphic unit 2
is thicker than in the southern area. Similarly to
the southern area the lower part of allostratigraphic
unit 2 is defined by a single upward-coarsening
sandstone unit whereas the remaining part of the
allostratigraphic unit 2 records superimposed
upward-coarsening and upward-fining facies asso-
ciations bounded by flooding surfaces. Dominance
of terrestrial palynomorphs increases upwards in
allostratigraphic unit 2 (Koppelhus & Dam, 2003;
Ahokas et al ., 2014; this study). The up to 9 m thick

upward-coarsening units are composed of mixed
tide-influenced and wave-influenced heterolithic
delta front to prodelta facies associations (FA5a
and 5b, respectively) and tidal inclined hetero-
lithic strata facies associations (FA2a and 2b;
Table 2). The up to 6 m thick upward-fining units
are composed of fluvial-tidal transition facies asso-
ciations (FA1a and 1b; Table 2).
Several unconsolidated intervals containing
chlorite-coated grains (Fig. 6A) are observed
within the allostratigraphic unit 2 at locality N4.
These 2 to 3 m thick greenish coloured intervals
rarely include recognisable sedimentary struc-
tures. At all the northern localities, allostrati-
graphic unit 2 is terminated above by an erosive
conglomeratic bed marking the shift from sandy
heterolithic facies associations into locally shale-
dominated facies associations with brackish-water
palynomorphs (Ahokas et al ., 2014).

Interpretation: Allostratigraphic unit 2

At all localities, the basal upward-coarsening unit
of the allostratigraphic unit 2, directly above the
FSa, is interpreted as a tide-dominated prodelta
and delta front (TDDF) architectural element
(Figs 7 and 9; Table 3). The morphology of the
bivalve shells above the FSa suggests that they
lived in relatively shallow water, burrowing in
sediments close to the sea bed where light condi-
tions and amount of sediment in suspension have
been sufficiently high. At all the southern local-
ities, the first maximum flooding surface (MFS1)
is picked within a condensed interval of silty
mudstones of the TDDF element (Fig. 7). At the
northern localities, the FSa flooding surface amal-
gamates with the MFS1; and this surface is
picked at the transition from the brackish archi-
tectural element WIBE into the sandy heterolithic
and mixed tide-influenced and wave-influenced
deltaic strata of the element TDDF (Figs 7 and 8B).
The superimposed upward-coarsening and
upward-fining units forming the bulk of the sandy
heterolithic allostratigraphic unit 2 are interpreted
as the tide-dominated delta platform (TDDP) and
tide-dominated subtidal sandy shoal (TDSS) archi-
tectural elements (Fig. 9; Table 3). The erosive sur-
face separating the distal TDDF from the proximal
TDDP element is interpreted as a regressive marine
ravinement surface (MRS1) based on the locally
developed gravel lag and its erosive character along
the base of tide-influenced channel-fill facies
association. The mineralogical immaturity of the
coarse fraction suggests short transport distances.