Shorefaces - Trace Fossils as Indicators of Sedimentary Environments - page 546

Chapter 19
Shorefaces
S. George Pemberton, * ,1 James A. MacEachern, † Shahin E. Dashtgard, †
Kerrie L. Bann, ‡ Murray K. Gingras * and John-Paul Zonneveld *
*Ichnology Research Group, Department of Earth & Atmospheric Sciences, University of Alberta,
Edmonton, Alberta, Canada, † Applied Research in Ichnology and Sedimentology (ARISE),
Department of Earth Sciences, Simon Fraser University, Burnaby, British Columbia, Canada,
‡ Ichnofacies Analysis Inc., Calgary, Alberta, Canada
1 Corresponding author: e-mail: [e-mail]
1. INTRODUCTION
The marine shoreface complex consists of a steeply seaward-sloping sediment
ramp (1:200) that extends from then low-tide mark to a nearly flat (1:2000)
inner shelf or basin floor, typically corresponding to approximately 10-20 m
of water depth ( Clifton, 2003; Immenhauser, 2009; Johnson, 1919 ). Strand-
plains are more typical of regressive coasts; however, shorefaces may occur
on both regressive and transgressive coasts ( Fig. 1 ). The shoreface setting
is dominated by wave energy and, as a result of decreasing wave interaction
with the substrate in a seaward direction, shows a pronounced basinward fin-
ing. The shoreface is classically divided into three subenvironments (from
seaward to landward): the lower, the middle, and the upper shoreface. The
boundaries between these zones, and between the lower shoreface and the off-
shore, are not always clearly defined ( Reinson, 1984 ). For example, with
greater storm domination, the effective wave base is lowered to depths
approaching the storm-wave base. As a result, erosively amalgamated tempes-
tites erroneously attributed to “lower shoreface” conditions may actually have
been deposited well below fair-weather wave base. Although the large-scale
regional context may vary, the specific subenvironments of the shoreface are
not significantly different whether they occur as part of a strandplain, barrier
island, or wave/storm-dominated delta free from interference from active dis-
tributary channels (cf. MacEachern and Bann, 2008; MacEachern et al., 2005;
Tonkin, 2012 ). The shoreface grades distally into offshore units and landward
into foreshore deposits. A complete shoreface progradational succession
reflects offshore through to foreshore environments; consequently, these
adjacent environments bear inclusion in any discussion of shoreface deposits
per se .