The Penobscot orogeny in the Appalachians, the Grampian orogeny in the British Isles, and the Finnmarkian orogeny in the Scandinavian Caledonides are Late Cambrian–Early Ordovician events that characterize terranes having similar pre- and post-deformation features. Together they record a major orogen-wide closing of the Cambrian Iapetus Ocean basin. The Penobscottian is the principal pre-Acadian deformation event in the Gander and related terranes of the Appalachians. The upper Proterozoic–Cambrian rocks deformed by it include subduction-related mélanges. In the northern Appalachians its timing is best constrained in northern Penobscot County, Maine, where polydeformed slate and sandstone (Grand Pitch Formation), dated Cambrian(?) by Oldhamia, are overlain by the singly deformed Arenig-age Shin Brook Formation. Basal conglomerate of the Shin Brook contains Grand Pitch clasts, and higher tuff contains Early Ordovician (late Arenig) Celtic province shelly fossils that indicate deposition around a volcanic island in cool waters of moderate to high latitude, remotely distant from contemporaneous warm equatorial waters of the North American (Laurentian) continental margin. The Grampian, in the Scottish–Irish orthotectonic Caledonides, deformed and metamorphosed miogeoclinal, upper Precambrian to lower Middle Cambrian Dalradian rocks that were largely derived from the Laurentian craton. An early tectonothermal phase, probably associated with subduction that produced blueschists, was followed by the main Barrovian metamorphism (510 to 480 Ma). Fossils in the Arenigian post-tectonic rocks of the South Mayo trough have strong North American affinities. Dalradian equivalents in the paratectonic Caledonides (Howth Peninsula, Ireland; Anglesey, Wales) suggest rifting of the Cambrian miogeocline, confirmed by the cool-water Celtic province Arenig shelly fauna of Anglesey. The Finnmarkian event deformed and metamorphosed rocks of the Late Proterozoic–Cambrian(?) Baltic continental-rise prism of Baltic provenance and obducted slabs of ophiolite. The minimum of its isotopic age range, 540 to 480 Ma, is confirmed by the Llanvirnian Otta serpentinite conglomerate that unconformably overlies an ophiolite remnant. Fossils from the conglomerate suggest cool-water Baltic and ocean-island affinities. The sequences deformed by these penecontemporaneous events record a complex history of the Late Proterozoic–Cambrian Iapetus Ocean, including miogeoclinal sedimentation on the margins of Laurentian, Baltic, and Armorican cratons, and the rifting and closing of intervening oceanic tracts. At the time of their deformation, these sedimentary sequences occupied the margins of a very large Early Ordovician Iapetus Ocean.

There is evidence in northeastern Maine for at least two glacial phases represented by two tills. The older till unit is the St. Francis, a blue-gray deposit observed in the St. John and Hammond Brook Valleys. At Golden Rapids, the St. Francis till is overlain by a younger brown till with a different clast lithology. The surface of the St. Francis till section at Hammond Brook exhibits a weathered zone, 30 to 45 cm thick, and is overlain by approximately 6 m of stratified sediments. Erratics of Canadian Shield provenance in the surface till indicate advance of the Laurentide Ice Sheet into Maine at least in late Wisconsinan time. Indicator fans, stoss-and-lee forms, drumlins, and striae imply southerly to southeasterly ice flow during the late Wisconsinan maximum. Moraines in southern Aroostook and northern Penobscot Counties and associated outwash and eskers record the northward to northwestward recession of the ice sheet from coastal Maine. Deglaciation in the study area occurred after the formation of the Pineo Ridge Moraine in southern Maine and after the emplacement of the St. Antonin segment of the Highland Front moraine complex of the St. Lawrence Valley in Quebec. A relict ice cap occupied northeastern Maine during the last phase of late Wisconsinan deglaciation. This ice cap had a northeast-southwest trending axis and occupied a perimeter defined by the Aroostook River Valley and by the Fish River, St. Froid, Eagle, Square, Cross, Mud, and Long Lakes. Late Wisconsinan ice flow south of the Aroostook River Valley was generally southeastward. In northern Aroostook County, the flow eventually became northwestward as a consequence of ice drawdown following the incursion of the marine waters into the St. Lawrence Lowland. The radiocarbon age (averaged from several samples) of a sheared and convoluted peat layer associated with a diamicton near Oxbow, Maine, suggests that deglaciation of the area was complete by approximately 10,500 years B.P.