PALAEOENVIRONMENTAL ANALYSES OF THE SURNBURST FORMATION (LOWER CRETACEOUS) IN THE MANYBERRYES FIELD, SOUTHERN ALBERTA, CANADA: PRELIMINARY RESULTS

SEBASTIÁN RICHIANO; MURRAY GINGRAS

Congreso; XVI Reunion Argentina de Sedimentología; 2018

The Sunburst Sandstone (Lower Cretaceous) was defined fromsubsurface boreholes in northern Montana (USA). In southern Alberta, Canada,the term Sunburst applies to quartzose fluvial sandstones that reachthicknesses of up to 30 m, of light grey to light brown, fine- to coarse-grained,well to poorly sorted sub-litharenites and occasionally quartzarenites, in whichchert is the main lithic grain constituent. The lower contact is unconformableupon Mississippian, Jurassic or older Cretaceous strata. The upper contact isdisconformable with the Ostracod Beds. The Sunburst Ribbon Sandstone iswidely distributed in central and southern Alberta, and trend northwest followingpaleovalleys. The study area centers on the Manyberries Oil Field in southeastAlberta. All data presented in this contribution was collected through a detailedsedimentological and ichnological analysis of 15 cores totaling 222 m. Thethickness of the cores analyzed varies between 9 and 35 m. A total of 10sedimentary facies were grouped into 6 facies associations (FA1 to 6). FAs1-2are characterized by heterolithic facies with trace fossils (small Skolithos,Cylindrichnus, Planolites, Palaeophycus, Teichichnus) that are emblematic ofbrackish-water settings. The widespread occurrence of these faciesassociations supports the interpretation of transgressive lagoon. FA3 iscomposed of low-angle cross-stratified sandstones that are interpreted as ashoreface barrier. FA4 comprises sandstones and silty-sandstones containingPsilonichnus and rhizoliths belonging to the backshore. Finally, FA5 (channels)and FA6 (palaeosols) are taken to be intermixed fluvial and continental plaindeposits. The deposits of the Sunburst Fm. in the study area represent a singleunconformity bound transgressive-regressive cycle.