Sedimentary documentation of the break-up of Rodinia, Offerdal Nappe, Swedish Caledonides

(1) The ∼1500 m thickness of the Offerdal succession, (2) the occurrence of >300 m thickness of the pebble- to boulder-bearing continental-basement derived alluvial fan conglomerates, (3) the high sediment input rates, and (4) the high subsidence rates suggest an actively subsiding basin and a relatively uplifted hinterland. Furthermore, the arkosic composition of the Offerdal metasandstones, as well as the Precambrian porphyry, syenite and quartzite clast composition of the lithic conglomerates, recognised from the subjacent continental basement of Baltica, suggest a continental sediment source. The rapid accommodation changes, and especially the simultaneous subsidence of downdip areas and uplift of updip areas in UTU2 suggest syn-depositional extensional block rotation. Collectively, this evidence suggests that the Offerdal succession was deposited in a continental rift basin related to break-up of Rodinia.