Abstract Nineteen large (2348–4285 m above sea level) central polygenetic alkaline shield-like composite volcanoes and numerous smaller volcanoes in Marie Byrd Land (MBL) and western Ellsworth Land rise above the West Antarctic Ice Sheet (WAIS) and comprise the MBL Volcanic Group (MBLVG). Earliest MBLVG volcanism dates to the latest Eocene (36.6 Ma). Polygenetic volcanism began by the middle Miocene (13.4 Ma) and has continued into the Holocene without major interruptions, producing the central volcanoes with 24 large (2–10 km-diameter) summit calderas and abundant evidence for explosive eruptions in caldera-rim deposits. Rock lithofacies are dominated by basanite and trachyte/phonolite lava and breccia, deposited in both subaerial and ice-contact environments. The chronology of MBLVG volcanism is well constrained by 330 age analyses, including 52 new 40 Ar/ 39 Ar ages. A volcanic lithofacies record of glaciation provides evidence of local ice-cap glaciation at 29–27 Ma and of widespread WAIS glaciation by 9 Ma. Late Quaternary glaciovolcanic records document WAIS expansions that correlate to eustatic sea-level lowstands (MIS 16, 4 and 2): the WAIS was +500 m at 609 ka at coastal Mount Murphy, and +400 m at 64.7 ka, +400 m at 21.2 ka and +575 m at 17.5 ka at inland Mount Takahe.

Two major Neoproterozoic sedimentary basins that probably formed in response to an early pulse of Iapetan rifting along the Laurentian margin are well exposed in the East Greenland Caledonides. The Hekla Sund Basin is exposed at the northern termination of the East Greenland Caledonides, and it is represented by the Rivieradal and Hagen Fjord Groups, which attain a cumulative thickness of 8–11 km. The evolution of this basin reflects deposition during active rifting and a postrift thermal equilibration stage. The Eleonore Bay Basin of East Greenland includes the deposits of the Eleonore Bay Supergroup of early Neoproterozoic age overlain by Cryogenian (mid-Neoproterozoic) glacial deposits of the Tillite Group, which have a combined thickness in excess of 14 km. Four stages of basin evolution may be distinguished based on paleogeographic reorganizations of the shelf and a change from siliciclastic to carbonate deposition, and the final stage was dominated by glacigenic deposition. Major regional stratigraphic breaks seem to be absent, as is other evidence of rift-related sedimentation, suggesting deposition in one or a series of connected ensialic basins. A comparison with other Neoproterozoic basins along the Laurentian margin of the Iapetus Ocean shows similarities between the Eleonore Bay Basin and coeval deposits on Svalbard and the Central Highlands of Scotland. The development of an extensive carbonate platform during the later stages of both the Eleonore Bay and Hekla Sund Basins testifies to a period of tectonic stability prior to onset of Iapetus rifting. The extent of this carbonate platform may have been even larger, since similar successions are present in the Caledonides of Scotland and Ireland.