The Cape Melville Formation (CMF), exposed on southeastern King George Island, South Shetland Islands, provides rare evidence of extensive earliest Miocene glaciation in the Antarctic Peninsula region. The formation records the presence of regional marine-based grounded ice on the continental shelf. It overlies disconformably the upper Oligocene Destruction Bay Formation, which consists of sandstones recording nonglacial shallow marine conditions. Four units have been identified within the approximately 150 m thickness of the CMF. The basal unit (A) consists of coarse glacigenic debris-flow facies interbedded with glaciomarine mudstone and sandstone. The overlying unit (B) is mainly fine-grained. This succession may represent relatively ice-proximal deposition followed by glacial retreat and/or relative sea-level rise. The upper CMF (units C and D) was deposited in an ice-distal marine environment, with intermittent input of coarse glacigenic debris, mainly from ice rafting. Thin beds of pelagic carbonate ooze within unit C indicate periods of low terrigenous sediment input and high productivity. Lithologically diverse glacigenic gravel clasts (mainly ice-rafted debris) in the CMF had a wide regional source area, suggesting that ice cover was widespread regionally and included calving ice margins. For a small proportion of clasts the nearest known source is the mountains fringing the southern Weddell Sea. Such clasts were presumably transported north in debris-laden icebergs by a strong, cold Weddell Sea surface current. A temperate glacial setting is tentatively inferred from the CMF. Palynological results confirm and enhance the paleoenvironmental interpretation from the sedimentology, and include the first early Miocene dinoflagellate cyst assemblages recorded on the Antarctic Peninsula. This reappraisal of the glacial record from the CMF provides valuable constraints on the Antarctic cryosphere and regional paleoenvironments in the mid-Cenozoic.