Quaternary geology of Port Saunders map area, Newfoundland
Authors: Grant D R 
Published: October 2014

Pre-Quaternary uplift and differential planation cut lowlands and submarine deeps on sedimentary rocks, leaving Long Range Mountains as an isolated tilted Tertiary peneplain on an upthrust crystalline basement block, with a locally exhumed sub-Cambrian
unconformity with glacial topography. Three major Quaternary glaciations by two ice domains, the Laurentide Ice Sheet and the Newfoundland Ice Cap complex, are documented by morphostratigraphy (terrain maturity), ice flow patterns, glacial trimlines, and relative sea-level changes. During an early
maximal glaciation, represented by a mature summit glacial terrain (St. John zone), Laurentide and Newfoundland ice extended beyond Grey Islands. Relative rock dissection suggests a Middle Pleistocene age. Coastal cirques, now submerged 40 m, were probably initiated then and occupied during the
onset of later glaciations. During a second major glaciation (Doctor's zone) of presumed late Middle Pleistocene age, ice overran Groais Island, Horse Islands and Baie Verte Peninsula and left seaward-sloping trimlines at 600 m on nunataks. A Long Range ice cap dominated then and during later
glaciations judging by an ice divide area preserving preglacial landforms surrounded by a scoured belt and radiating troughs. A fresh glacial terrain (Long Range zone) with trimlines at 400-550 m records six Late Wisconsinan events. Laurentide abutted Long Range ice, extended eastward to Atlantic
Ocean and converged southwestward on Esquiman Channel calving bay 14 ka. Highland nunataks divided western Long Range ice into confluent piedmont lobes which deposited calcareous till with seaward-decreasing highland erratics. Tidewater lobes stabilized in Goldthwait Sea 12.8 ka, building the
Piedmont Moraines which grade laterally to glaciomarine drift and mark the lift-off line. During retreat, seasonal pulses plowed up marine sediment into De Geer or "winter" moraines, while icebergs and meltwater discharge deposited stony deepwater mud. A Long Range ice readvance, probably during a
climatic reversal 11-10 ka, built Leg Pond Moraine and ice-contact marine deltas. Remnant plateau ice left the Cloud River Moraines (9.7 ka?). Cirque moraines and talus glaciers may be Neoglacial. Nivation and cryoturbation continue above the mean annual 0 degree C isotherm at 400 m. Marine limit
rises northwestward from 70 m to 142 m, reflecting Laurentide loading. Shorelevel displacement curves and a shoreline-profile diagram with l000-year intervals illustrate postglacial sea-level recovery. In the north sea level fell continuously, except for a possible stillstand induced
gravitationally by the 11 ka readvance, whereas in the south, it fell below present level by 8 ka and continues to rise because of subsidence, causing coastal erosion. A low fossil cliff may reflect a fluctuation 2 ka due to forebulge migration. Fractures which displace glacial pavements suggest
deglacial faulting, perhaps by release of glacially stored compressive crustal stress. Practical applications include adapting the radial dispersal model to mineral exploration, contending with unstable marine clay and karstic terrain in foundation sites, rationalizing development of scarce granular
resources, taking account of coastal erosion, and monitoring the effects of possible crustal movement on hydroelectric installations.