Lacustrine Environments - Trace Fossils as Indicators of Sedimentary Environments - page 368

Chapter 13
Lacustrine Environments
Jennifer J. Scott, * ,‡,1 Luis A. Buatois † and M. Gabriela M ´ ngano †
*Department of Earth & Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada,
† Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan,
Canada, ‡ Present address: Department of Earth Sciences, Mount Royal University, Calgary,
Alberta, Canada
1 Corresponding author: e-mail: [e-mail]
1. INTRODUCTION
Lakes are extremely complex systems in which animal and plant distribution
is controlled by a delicate interplay of abiotic (e.g., energy, light, oxygen,
temperature, salinity, substrate, and nutrients) and biotic factors (e.g., competition,
grazing, predation, and symbiosis) ( Buatois and M ´ ngano, 2011; Cohen, 2003;
Miller andWhite, 2007; Renaut and Gierlowski-Kordesch, 2010 ). Lacustrine sys-
tems differ from oceans in several ways, including the smaller volumes of sedi-
ment and water in lakes, the direct link between lake level and sediment supply,
and the fact that shoreline migration may be due to not only progradation but also
due towithdrawal ofwater ( Bohacs et al., 2000 ). The vertical relationships of litho-
facies commonly reflect abrupt changes, particularly when the changes are due to
tectonics or climate-controlled fluctuating water levels. The chemistry of ground-
water and lake water can be highly variable, even within a single basin, and can
change over relatively short time periods. In general, the impacts of environmental
changes in continental basins are more pronounced than in oceanic basins. Simi-
larly, the variability of organisms living in adjacent environments can lead to pro-
nounced lateral heterogeneity in trace-fossil assemblages.
Ichnology can be applied to the interpretation of sedimentary successions in
lake basins at several scales. Detailed information about sedimentary processes
and substrate conditions can be interpreted using the evidence provided by bio-
genic traces, together with sedimentology. Features showing substrate consistency
(e.g., deeply impressed vertebrate footprints), changing sedimentation rates (e.g.,
escape traces), and depositional hiatuses (e.g., intensely bioturbated horizons), for
example, increase the ability to interpret sedimentary processes affecting individ-
ual beds and bedsets. By considering the specific types of biogenic structures pro-
duced (e.g., vertebrate footprints, insect nests), it may be possible to recognize
whether a substrate was subaerially exposed, to interpret the relative duration of