Dinosaur tracks in a Cretaceous (lower Albian) braid delta system (Basque–Cantabrian Basin, western Pyrenees): linking trace fossils suites and short-term preservation windows

Abstract

Abstract Albian dinosaur tracks from the Monte Grande Formation (Basque–Cantabrian Basin) are described. Sedimentary succession shows seven different facies associations (FAs) with four track-bearing levels (levels 1–4) of a braid delta system. FA 4, a proximal crevasse subdelta, preserves in levels 2 and 3 theropod, possibly sauropod and undetermined dinosaur tracks, as well as Ophiomorpha and Skolithos traces. FA 5, a middle crevasse subdelta, presents undetermined cross-section tracks in levels 1 and 4, besides Ophiomorpha , Skolithos and locally Teichichnus in other layers. Both FAs have the same general ichnoassociation, although with preservational variations. The sedimentary succession represents an area with periods of crevasse subdelta progradation and colonization of opportunistic organisms, and other periods of subdelta abandonment represented by short sedimentary hiatuses in which the water sheet would be shallow or even absent and where dinosaurs would be roaming. Particularly, the traces of levels 2 and 3 represent the same ichnocoenosis constituting two different suites and may be envisaged as penecontemporaneous, produced within a short-term preservational window. This tracksite is one of the scarce Albian dinosaur ichnological records in the southwestern European island palaeoarchipelago and one of the few worldwide localities where Albian dinosaur tracks have been found in deltaic facies.