Shorefaces - Trace Fossils as Indicators of Sedimentary Environments - page 560

sandstones to show little or no burrowing (cf. MacEachern and Pemberton, 1992 ).
Unfortunately, discerning whether their absence corresponds to high intensity
storms (greater erosional amalgamation) or to high-frequency storms (minimal
time for reestablishment of benthic communities) is virtually impossible.
Like the offshore complex, the lower to middle shoreface complex consists
of sediments accumulated during both fair-weather and storm conditions. In
contrast to the offshore, however, the preserved depositional record of the
lower-middle shoreface complex of many successions is characterized by a pre-
dominance of tempestite beds, with fair-weather sediments constituting a com-
mon, though subordinate, component of the interval ( Kumar and Sanders, 1976;
Niedoroda et al., 1984 ).
2.3 Upper Shoreface-Foreshore-Backshore Complex
2.3.1 Upper Shoreface
The upper shoreface is situated in the high-energy build-up and surf zones and
lies between the breaker zone and the low-tide mark ( Clifton et al., 1971;
Davidson-Arnott and Greenwood, 1976; Greenwood and Mittler, 1985; Hunter
et al., 1979 ). The zone corresponds to the “Outer Rough”, “Outer Planar”, and
possibly part of the “Inner Rough” zones of Clifton et al. (1971) , where the bulk
of sediment transport is related to multidirectional current flow ( Davis, 1978 ).
Within the upper shoreface, wave- and storm-driven currents paralleling the
shoreline (e.g., longshore drift) interact with shore-normal currents generated
by translatory flow (combined-flow oscillation and current interference) asso-
ciated with plunging waves, producing multidirectional, sinuous-crested sub-
aqueous dunes ( Figs. 8A, B and 9A ).
Under intermediate barred states (cf. Davidson-Arnott and Greenwood, 1976;
Greenwood and Davidson-Arnott, 1979; Hunter et al., 1979; Thom et al., 1986;
Wright et al., 1979 ), wave- and storm-induced currents run obliquely shoreward
over the bar, turn shore-parallel along the longshore troughs, and ultimately return
seaward through rip channels. Greenwood and Mittler (1985) pointed out that
there is generally little depositional record of a bar complex, based on their study
of the Kouchibouguac Bay barred system of New Brunswick. Preserved sedi-
ments correspond to the fill of the longshore troughs and those associated with
the seaward slope of the bar itself.
Hunter et al. (1979) studied a barred coastline in Oregon and pointed out
that, under a barred configuration, an erosional discontinuity, reflecting the
base of the deepest rip channels or longshore troughs, tends to separate the
opportunistic colonization of the upper surface with robust O. borneensis ( Ob ). Rare O. irregulaire
( Oi ) are present as well. Note the subtle fugichnion (fu) in the lower left side of the core.
(D) Granule-bearing sandstone with low-angle planar-parallel laminae, interpreted as large-scale
SCS. Isolated zones of Rosselia socialis ( R ) represent tempestite colonization. Scale bars in
centimeters.