Burrow Cementation Trends in Shoreface Sediments of the Upper Cretaceous Horseshoe Canyon Formation, Alberta, Canada

Zorn, Marilyn E.¹, George Pemberton¹, Murray Gingras¹, Kurt O. Konhauser¹, Karlis Muehlenbachs¹ (1) University of Alberta, Edmonton, AB

Isotopic analyses of authigenic siderite and calcite cements within in situ and transported Rosselia socialis burrows from shoreface deposits in the Upper Cretaceous Horseshoe Canyon Formation, Alberta, Canada reveal the early cementation history of the burrow and geochemical conditions of the initial sedimentary environment. Transverse, incremental sampling of the bulbous, in situ and spindle-like, transported forms reveals systematic isotopic deviation of d¹³C and d¹⁸O around the burrow core, representing accretionary records of evolving pore-water conditions. As the number of isotopic deviations recorded in bulbous specimens is equal to those observed in spindle-shaped burrows, both the in situ and transported burrows likely underwent similar periods of cementation. Transportation of the spindle-like burrows without disaggregation indicates that cementation occurred in close proximity to the sediment water interface prior to entrainment, but before lithification of the surrounding sediments. These findings suggest that burrow-facilitated cementation can occur during very shallow burial or even at the sediment-water interface.  Similar conditions are inferred in Ophiomorpha networks in the proximal offshore to distal lower shoreface where accumulated organic matter is prevalent and the degree of anaerobisis increases. This results in early cementation that affects permeability and porosity trends that can be detrimental to reservoir properties. This early siderite cementation is not present in Ophiomorpha systems in the proximal lower shoreface to foreshore zones where the burrows would be an integral part of the reservoir dynamics. This "toe of the shoreface" early cementation should be evaluated in any reserve estimations.