Cretaceous forensic podiatry: big game tracking with a microresistivity image log on a McMurray Formation scroll bar

Abstract

Abstract For the first time, a subaereal scroll bar setting is described for the McMurray Formation. It is made up of ridge and swale features capping point bar deposits. Occurring in the same narrow stratigraphic zone, scroll bars appear as either a vertical section of low-angle dips corresponding to ridges, or flat-lying bedding deposited in swales. These features were deposited from suspension during flooding events; the orientation of one set of ridges parallels point bar development, while the ridges overlying a second point bar are oriented obliquely. The orientation of the oblique ridges was locally controlled by superelevation of the river. Newly interpreted vertical loading structures up to 60 cm deep and 50 cm across are interpreted to be dinosaur footprints. These footprints are limited to a narrow stratigraphic zone above the point bars in the associated ridge and swale setting of the scroll bar. These are the first dinosaur footprints discovered in the McMurray Formation and the first to be interpreted from image logs. Although these footprints were identified in image logs, the image log features now permit the identification of footprints in core. The scroll bars and dinosaur footprints each provide direct evidence for a floodplain environment in the McMurray Formation, but combined provide compelling documentation of a subaereal setting and the complete point bar –scroll bar cycle. This new interpretation expands the depositional framework for future mapping in the McMurray Formation.