Estuaries - Trace Fossils as Indicators of Sedimentary Environments - page 448

Chapter 16
Estuaries
Murray K. Gingras, * ,1 James A. MacEachern, † Shahin E. Dashtgard, †
John-Paul Zonneveld, * Jesse Schoengut, ‡ Michael J. Ranger } and
S. George Pemberton *
*Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta,
Canada, † Department of Earth Sciences, Simon Fraser University, Burnaby, British Columbia,
Canada, ‡ Canadian Natural Resources Limited Calgary, Alberta, Canada, } 808 West Chestermere
Drive, Chestermere, Alberta, Canada
1 Corresponding author: e-mail: [e-mail]
1. INTRODUCTION
Our understanding of the ichnology of modern and ancient estuaries has con-
siderably advanced since the 1970s. The foundation of estuary ichnology is built
on the extensive neoichnological studies conducted in estuaries of Georgia,
USA ( Dorjes and Howard, 1975; Howard and Frey, 1975; Howard et al.,
1975; Mayou and Howard, 1975 ). This is notwithstanding an immensely impor-
tant body of work produced previously from North Sea sites (e.g., H¨ntzschel,
1939; Reineck, 1956 ), focused on marginal-marine neoichnology. In 1982, the
neoichnological observations from the North Sea and the estuaries of Georgia
were used to formulate the brackish-water ichnological model, providing the
initial key for the identification of estuaries in the rock record (cf. Pemberton
et al., 1982 ).
The ichnological model for estuaries developed alongside a rapidly expand-
ing ability to identify tidally influenced sedimentation, in concert with a grow-
ing understanding of seismic data and sequence stratigraphy ( Bubb and
Hatlelid, 1977; Dobrin, 1976; Mitchum, 1977; Mitchum and Vail, 1977; Vail
and Mitchum, 1977; VanWagoner et al., 1987 ). From this stratigraphic research
came a growing awareness that incised valleys were cut during relative lowstands
of sea level but were dominantly filled with strata deposited during the
subsequent marine transgression (e.g., Allen and Posamentier, 1993; Dalrymple
and Zaitlin, 1994; MacEachern et al., 2012 ). Basal transgressive strata represent
the leading edge of marine incursion, and as such, ichnologically discernible,
brackish-water deposits are strongly associated with many incised valley-fill
deposits (e.g., Beynon et al., 1988; Karvonen, 1989; MacEachern and Gingras,
2007; MacEachern and Pemberton, 1994; Pemberton et al., 1982; Rahmani,