Updated stratigraphy and structure of the Barmur Group (Tjörnes beds, Iceland) and implications for the opening of the Bering Strait

The Barmur Group (Tjörnes beds) sedimentary sequence onshore Iceland records the first opening of the Bering Strait oceanic gateway, and late Miocene–early Pliocene cooling that preceded intensification of the Northern Hemisphere glaciation. The stratigraphy of the Barmur Group is not known in detail because of difficulties in correlating coastal and inland exposures. To address this issue, we carried out remotely piloted vehicle (drone-based) mapping of the entire 11 km outcrop. We correlated the processed ‘virtual outcrop’ image with previously logged sections and constructed a 3D structural model. The composite thickness of the Barmur Group in the model is 442 m, which is 16% thinner than previously estimated. This discrepancy reflects earlier difficulties in correlating coastal and inland exposures and the recognition of faulting at the base of the succession. We recently showed that the bioevent signalling the first Pacific-to-Atlantic faunal migration through the Bering Strait occurred during magnetic chrons C3n.4n–C3n.3r (5.235–4.896 Ma); the new model suggests that it occurred near the chron boundary ( c. 5.0 Ma). Thus, we show that a 3D virtual outcrop is a useful tool to quantify uncertainty when assembling a composite section. We also provide the complete workflow used to plan, acquire and process the virtual outcrop.