Lagið fylgir efstu hraunum Grjótárólivínbasaltsyrpunnar og er byggt á segultímatali sem birt var í grein eftir Duncan, R. A. & Helgason, J.1998, Precise dating of the Holmatindur cooling event in eastern Iceland: Evidence for mid-Miocene bipolar glaciation, J. Geophys. Res., American Geophysical Union, 103(B6), 12, 397-12, 404.
[The layer is drawn following the upper parts of the Grjótá olivine basalt group where the base of Chron 5 is located. The geomagnetic profile was based on Duncan, R. A. & Helgason, J.1998, Precise dating of the Holmatindur cooling event in eastern Iceland: Evidence for mid-Miocene bipolar glaciation, J. Geophys. Res., American Geophysical Union, 103(B6), 12, 397-12, 404.]