Shorefaces - Trace Fossils as Indicators of Sedimentary Environments - page 573

FIGURE 14 Resin peels and line interpretations from three modern tide-influenced shorefaces
(TIS) in the Juan de Fuca Strait, Canada. Images from Frey and Dashtgard (2011) , and Dashtgard
et al. (in press) . For all images, the landward direction is to the left of the page and the oceanward is
to the right. (A) Upper shoreface to foreshore transition: rhythmically interbedded plane-bedded and
combined flow/current-rippled sandwith isolatedpebbles (darkgray) and shell fragments (light gray).
Note the absence of bioturbation. (B)Middle to upper shoreface transition: wave-rippled and current-
ripped sand interbedded with plane-bedded (possibly hummocky cross-stratified) sand. These sedi-
ments overlie hummocky cross-stratified sand. Note the lack of bioturbation in this core. Cross-hatch
pattern defines area of distorted core. (C) Lower shoreface: current-rippled and plane-bedded
medium-grained sand (BI ¼ 2) overlying intensely bioturbated (BI ¼ 5-6) sand (gray pattern).
(D) Lower shoreface: intensely bioturbated (BI ¼ 5-6), medium-grained sand belowa current-rippled
surface. Burrows are mainly simple vertical and horizontal tubes. (E) Upper offshore: partial preser-
vationof current ripples near topof core, with increasing sediment reworkingwithdepth. Bioturbation
indexvalues increase fromBI ¼ 2-3 near the top of the core toBI ¼ 6 near the base. Acronyms used for
sedimentary structures: current ripples (cr), combined-flow ripples (cfs), hummocky cross-
stratification (hs), plane bedding (pb), and wave ripples (wr). Acronyms used for identifiable traces:
Arenicolites (Ar), Planolites (P), Skolithos (Sk), and lined- Skolithos (lSk). Scale bar ¼ 3 cm.
normally used to identify the middle shoreface (e.g., SCS, trace-fossil suites of
the archetypal Skolithos Ichnofacies) become interbedded with structures typ-
ically attributed to the upper shoreface and/or lower shoreface. Consequently, a
“middle shoreface” zone cannot be differentiated in the TMS, and the lower
shoreface appears to grade landward into the upper shoreface.