Quantitative Techniques in Ichnology and Sedimentology with Examples from the Cretaceous McMurray Formation, NE Alberta, Canada

• Author / Creator

  Timmer, Eric R.D.

• Process ichnology is a relatively new ichnological tool whereby trace fossils are interpreted as the product of changing infaunal stresses including: salinity fluctuation, reduced oxygenation, high sedimentation rates, reduced nutrient availability, and elevated hydraulic energy. In this paradigm, trace fossils can be used as proxies for paleoenvironmental changes and thus provide excellent support for depositional interpretations. This body of work explores the spatial and temporal relations between the physical/chemical environment and infauna preserved in paleo-estuarine deposits of the Cretaceous McMurray Formation in NE Alberta, Canada using a quantitative process sedimentology and process ichnology approach. The purpose of this work is to develop techniques for promoting the use of the process ichnology framework among ichnologists while coincidentally evaluating tidal depositional interpretations of McMurray Formation inclined heterolithic stratification (IHS). Visual and quantitative time-series analysis of laminae thickness measurements was performed to evaluate tidal depositional interpretations of IHS. Analyzed laminae provided evidence for tidal modulation during IHS deposition and offered insight on the preservation potential of tidal signatures in moderately bioturbated units. In order to visualize a process ichnology dataset comprising bioturbation index (a proxy for sedimentation rates and salinity fluctuations) and sizediversity index (a proxy for salinity fluctuation) in 3D, a geomodeling workflow was proposed. This workflow, along with a 3D facies model offered a glimpse at the spatial and temporal variability of sedimentation rates and salinity affecting communities inhabiting IHS sediment. A software application, PyCHNO, was designed to optimize the data collection aspects of the process ichnology method. This desktop application allows an ichnologist to collect bioturbation index, size-diversity index and ichnogenera abundances on a bed-by-bed basis from core photographs efficiently and systematically. Collected data can be input into geomodels, visualized as process ichnology logs, or analyzed statistically. Fluctuations in physical and chemical stresses, proxied using data collected with PyCHNO, temporally and spatially affected McMurray Formation deposition. Spatially, ecological stresses were interpreted to represent small-scale (i.e. point-bar scale) ecological variability and estuarine-scale ecological variability. Estuarine-scale, cyclical ecological stress patterns are temporally coincident with El Ni˜no cyclicity and were interpreted to represent responses to changes in precipitation during McMurray Formation deposition. Point-bar scale ichnological variability was examined using a dataset collected within a seismically-constrained point-bar geobody. From ichnonetwork analysis, bed scale ichnogeneric composition measured throughout the point-bar’s growth and evolution remained relatively stable, suggesting relatively stable ecological conditions. Time-series analysis of ichnological data did not yield definitive spatial or temporal signals, which further reinforced interpretations of relatively stable ecological conditions during the point-bar’s deposition. Computer simulations and engineering analogues of helical burrowing behavior, similar to Gyrolithes, which is locally preserved in dense, monogeneric assemblages in McMurray Formation IHS were programmed to better understand the ecological advantages of this ethology. Resulting computations suggest that helical burrowing behavior can represent a technique for avoiding existing burrows and that this behavior performs best in homogeneous food distribution landscapes when compared to other deposit feeding strategies.

• Subjects / Keywords

  • McMurray Formation
  • Ichnology
  • Process Ichnology
  • Sedimentology

• Graduation date

  Spring 2018

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3FJ29T71

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.