ABSTRACT: Etat des connaissances sur la ligne de ravage Micma de J.W. Goldthwait (estuaire du Saint-Laurent). [A review of the Micmac shoreline of J.W. Goldthwait (St.Lawrence estuary].

CGRG Bibliography of Canadian Geomorphology
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Abstract

The Micmac shoreline of Goldthwait (1911) is a complex feature common to both shores of the St. Lawrence estuary. As described 90 years ago, the Micmac shoreline is composed of three units: 1) a former cliff (Micmac cliff) cut into Cambro-ordovician bedrock for the south shore islands, and/or in Quaternary/Holocene unconsolidated deposits, which extends almost continuously from Levis to Sainte-Anee-des-Monts on he south shore; it occurs also at many localities on the north shore between Quebec City and Blanc-Sablon, on most islands including Anticosti, and in the upper St. Lawrence estuary; 2) a low accretion terrace(Mitis terrace), a few hundred metres wide, built at the foot of the cliff; 3) an intertidal shore platform cut alternatively in shales or slates or in Quaternary unconsolidated deposits. In addition, these units present many morpho-sedimentological aspects from place to place. The low terrace has been radio cabon dated in 36 localities from both shores of the St. Lawrence estuary. The median age (n=43) is 2030+/-80 years BP. At that time the relative sea level (RSL) was 3.5 to 4.5 m above present day. The cliff and the adjacent intertidal platform cut into unconsolidated deposits, are undoubtedly mid- to late-Holocene erosional features formed during two episodes of RSL fluctuations. The rock cliff and related shore platform are inherited features of Sangamonian age or older which have been slightly modified by glacial and shore processes during the Wisconsin and the Holocene. At many sites, glacial erosion features have been preserved on the shore platform whereas at a few localities the platform is partially covered by Wisconsinan deposits, giving evidence of its existence before the last glaciation.

Bibliography of Canadian Geomorphology