Palynology and geochemistry of channel-margin sediments across the tidalefluvial transition, lower Fraser River, Canada: Implications for the rock record Joanna M. Czarnecki a, * , Shahin E. Dashtgard a , Vera Pospelova b , Rolf W. Mathewes c , James A. MacEachern a a Applied Research in Ichnology and Sedimentology (ARISE) Group, Department of Earth Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada b School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia V8W 2Y2, Canada c Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada article info Article history: Received 24 August 2013 Received in revised form 10 December 2013 Accepted 13 December 2013 Available online 21 December 2013 Keywords: Dinoflagellate cyst Pollen Carbon isotopes Estuary Delta Marginal-marine McMurray Formation abstract In the tidally influenced Fraser River, Canada, palynological and carbon isotope (d 13 C org ) signatures of channel- margin sediments are compared to environmental parameters (e.g., grain size, water salinity) to establish how the signatures vary across the tidalefluvial transition. Palynological assemblages in the Fraser River are dominated by tree pollen, which constitutes between 85% and 95% of all assemblages. Dinocyst abundances do not exceed 2% of the total palynological assemblage, and the number and diversity of dinocysts gradually decreases landward. The calculated landward limit for dinocysts is at approximately 83 river km, which is relatively close to the upstream limit of the tidal backwater (at w100 km). d 13 C org values show minimal variability across the tidalefluvial transition, and the average value is approximately 26&. The d 13 C org signature of river sediments indicates a dominance of terrestrially sourced organic matter regardless of brackish-water and tidal influence on sediment deposition. Six palynological and geochemical trends are identified as relevant to the rock record. 1) In deltaic environments, palynological and geochemical characteristics are less useful than sedimentological and ichnological characteristics for establishing depositional conditions. 2) In marginal-marine settings, low abundances and low species diversities of dinocysts, coupled with a “terrestrial” geochemical signature (d 13 C org < 25&) do not necessarily indicate deposition in a terrestrial environment. 3) Dinocyst abundances above 1% of the total palynomorph population can indicate a significant marine influence on sediment deposition. 4) Mud beds, preferably bioturbated, should be preferentially sampled in order to maximize palynomorph recovery. 5) Marine palynomorphs can occur, albeit in very low concentrations, to the landward limit of the tidalebackwater zone. 6) Palynological and geochemical data should be compared across the paleo-depositional environment in order to establish general trends and remove local variations caused by biases such as grain size. Ó 2013 Published by Elsevier Ltd. 1. Introduction Palynology is recognized as a valuable tool for refining paleo- environmental interpretations of ancient sedimentary deposits. This is because palynomorphs are ubiquitous in marine and con- tinental settings, can be transported significant distances into connected water bodies, and most importantly, have high preser- vation potential owing to the chemically and erosionally resistant composition of their outer walls (e.g. Dale, 1983; de Vernal et al., 2001; de Vernal et al., 1998; Mudie and Harland, 1996; Wall and Dale, 1966). The deposition of allochthonous palynomorphs in marginal-marine settings such as estuaries and deltas provides a mechanism for differentiating continental, transitional (i.e., brackish-water), and fully marine deposits (Loboziak et al., 2005; MacDonald, 1990). In addition, when palynomorph distributions are compared to the corresponding carbon isotope values for organic carbon (d 13 C org ) in the same deposits, there is greater cer- tainty in differentiating the relative position of sediment deposition along the continental-to-marine continuum. At present, there is a paucity of research that demonstrates the integration of palynology * Corresponding author. Tel.: þ1 587 439 3292. E-mail addresses: jczarnec@sfu.ca, jczarnecki@shaw.ca (J.M. Czarnecki). Contents lists available at ScienceDirect Marine and Petroleum Geology journal homepage: www.elsevier.com/locate/marpetgeo 0264-8172/$ e see front matter Ó 2013 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.marpetgeo.2013.12.008 Marine and Petroleum Geology 51 (2014) 152e166