Porosity and Permeability in Bioturbated Sediments - Trace Fossils as Indicators of Sedimentary Environments - page 809

Chapter 27

Porosity and Permeability in
Bioturbated Sediments

Murray K. Gingras, * ,1 Greg Baniak, * John Gordon, † Jussi Hovikoski, ‡
Kurt O. Konhauser, * Andrew La Croix, } Ryan Lemiski, } Carl Mendoza, *
S. George Pemberton, * Camilo Polo * and John-Paul Zonneveld *
*Department of Earth & Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada,
† Husky Energy, Calgary Alberta, Canada, ‡ Geological Survey of Denmark and Greenland (GEUS),
Copenhagen, Denmark, } Department of Earth Sciences, Simon Fraser University, Burnaby, British
Columbia, Canada, } Talisman Energy Inc., Calgary, Alberta, Canada
1

Corresponding author: e-mail: [e-mail]

1. INTRODUCTION
It is generally believed that bioturbation reduces the permeability of sedimen-
tary strata. This is because biogenic churning of laminated sediment lowers
the sorting of the sediment preserved within laminae. Also, bioturbation
is commonly overlooked in intensely bioturbated media because of a lack of
lithological definition and because of the complex fabrics that are sometimes
present. However, several examples of bioturbation-enhanced bulk permeabil-
ity have been reported in the literature (e.g., Cunningham et al., 2009, 2012;
Dawson, 1978; Gingras et al., 1999, 2004a,b; Gordon et al., 2010; Gunatilaka
et al., 1987; La Croix, 2010; Lemiski et al., 2011; McKinley et al., 2004;
Mehrtens and Selleck, 2002; Sutton et al., 2004; Tonkin et al., 2010; Zenger,
1992 ). These range from biogenic modifications of the primary depositional
fabric to diagenetic alterations (typically recrystallization) of the sedimentary
matrix.
Permeability fabrics and the distribution of porosity result from physical
heterogeneities in sedimentary rocks. Physical heterogeneity may result from
the presence of laminae, the arrangement of grains or fossils, fabric-retentive
and fabric-destructive diagenesis, and structural deformation. Bioturbation
alters local grain distributions in the hosting sedimentary rock, and trace fossils
commonly possess geochemical characteristics that differ from the surrounding
sedimentary rock (e.g., Konhauser and Gingras, 2011; McIlroy et al., 2003;
Over, 1990; Petrash et al., 2011 ). Thus, trace fossils can influence the distribu-
tion of porosity and permeability in sedimentary rocks by physically changing