Tidal Flats and Subtidal Sand Bodies - Trace Fossils as Indicators of Sedimentary Environments - page 513

Chapter 18
Tidal Flats and Subtidal
Sand Bodies
Patricio R. Desjardins, * ,1 Luis A. Buatois † and M. Gabriela M ´ngano †
*Shell International Exploration and Production Inc., Houston, Texas, USA, † Department of
Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
1 Corresponding author: e-mail: [e-mail]
1. INTRODUCTION
During the past two decades, the number of publications dealing with the
ichnology of wave-dominated shallow-marine systems has outpaced those on
tide-dominated settings. In addition, most of the research dealing with tide-
influenced or tide-dominated environments is actually focused on marginal-
marine brackish-water environments, such as estuaries, bays, and deltas (e.g.,
Carmona et al., 2009; Gingras and MacEachern, 2012; Gingras et al., in press;
MacEachern and Gingras, 2007; McIlroy, 2007 ) and, even more recently,
tidally influenced and modulated shorefaces ( Dashtgard et al., in press ), rather
than open-marine tide-dominated settings. Despite these shortcomings, a num-
ber of key contributions have outlined some of the most relevant characteristics
of ichnofaunas in fully marine environments where tides play a major role in
mobilizing and depositing sediments, namely, tidal flats, subtidal sandbar com-
plexes, and tidal dunes and sand ridges in open shelf settings (e.g., Desjardins
et al., 2010b, 2012a; M´ngano and Buatois, 1999, 2004a,b; M´ngano et al.,
2002a; Sch¨fer, 1972 ).
A major difference between wave-dominated and tide-dominated systems is
that the former display a clear onshore-offshore trend in energy conditions
( Buatois and M´ngano, 2011; Pemberton et al., 2012 ), whereas the energy gra-
dient in tide-dominated shallow-marine environments is not straightforward
( Yoshida et al., 2007 ). Despite all these complexities, tide-dominated shore-
lines, in particular those developed in macrotidal settings, can be subdivided
into supratidal, upper, middle, and lower intertidal, and subtidal environments
( Klein, 1971, 1977 ), the associated depositional profile displaying clear ichno-
logical trends ( Buatois and M ´ ngano, 2011; M ´ ngano and Buatois, 1999,