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The Merigomish Subbasin occurs along the southern Hank of the composite Late Devonian Permian Maritimes Basin of Atlantic Canada. The subbasin consists predominantly of Visean to Westphalian clastic rocks that overlie Middle to Late Devonian basalt and continental clastic rocks of the McArras Brook Formation. The McArras Brook Formation is unconformably overlain by a 120 meter thick Late Visean clastic sequence of the Martin Road Formation, which represents the oldest rocks deposited in the Merigomish Subbasin. Geochemical and isotopic attributes of representative samples of the clastic rocks in the McArras Brook and Martin Road formations were investigated in order to constrain their respective provenance and to investigate the regional tectonic significance of the angular unconformity that separates them. The clastic rocks selected for analysis have clast sizes ranging from 1 to 4 mm in diameter. The geochemistry and isotopic signatures of the clastic rocks in these formations are so similar that they are interpreted to have been derived from the same source region. Both formations are characterized by a limited range in Si 2 : (65 78 wt. %), wider ranges in other major elements such as MgO and Fe 2 0 3 relatively constant Tb/Nb. moderate LREE enrichment (La/Sm n - 3 6 1.1), relatively flat HREE patterns (Tb/Yb n = 1.3-1.4) strongly negative e Nd values (-6 5 to -7.7. calculated for a 320 Ma depositional age), and high T DM values (ranging from ca.1.5 to 16 Ga) Taken together, the geochemical and isotopic signature of the McArras Brook and Martin Road formations suggest that they were predominantly derived from local Silurian siliciclaslic rocks of the Arisaig Group in the Antigonish Highlands. The isotopic data also suggest an important contribution from the Meguma terrane to the south The data are compatible with local sources, and ihe geochemical similarity between ihc McArras Brook and Martin Road formations suggests that the angular unconformity that separates them is of local, rather than regional, significance.  RESUME  Le sous-basstn de Merigomish longe le flanc meridional du bassin composite du Devonien tardif-Permien des Maritimes dans les provinces de l'Atlantique le sous-bassin est principalement constitue de roches clastiques du Viseen au Weslphalien recouvrant des roches clastiques connentales et des basaltes du Devonian moyen a tardif de la Formation de McArras Brook. La Formation de McArras Brook est recouverte de facon discordante d'une sequence clastique de 120 metres d'epaisseur du Viseen tardif de la Formation de Martin Road, qui represente les roches les plus agees s'etant deposees dans le sous-bassin de Merigomish. On a analyse les attributs geochimiques et isotopiques d'echantillons representatifs des roches clasiiques des formations de McArras Brook et de Martin Road pour circonscrire leurs provenances respectives el eludier la portec tectonque regionale de la discordance angulaire les separant. Les roches clastiques selectionnees aux fins de I'analysr presentent des clastes done la taille vane entre un el quatre millimetres de diametre Les signatures geochimiques el isotopiques des roches clastiques de ces formations sonl tellement similaires qu'on les intcrpele comme des roches provenant de la meme reegion d'ongmc. Les deux formations se caracterisent par un ecart de valeurs limile de SiO 2 ; (65 a 78% pds), des ecarts de valeurs plus importants des aulres principaux elements comme 1e MgO et le Fe 2 O 3 une teneur relativement constanle en Tb/Nb, un ennchisscment modere en elements de terres rares legers (La/Sm n , -3.6 1.1), des concentrations relativemcnt stables d'elements de terres rares lourds (Tb Yb n 1.3 1.4), des valeurs de e Nd fortement negatives (de 6.5 a 7.7. d'apres un age de sedimentation de 320 Ma), et des valeurs de T DM elevees (variant entre environ 1.5 et 1.6 Ga). Lorsqu'on les considere ensemble, les signatures geochimiques et isotopiques des fotmations de McArras Brook et de Martin Road pennettent de supposer que le materiel des formations provient principalemenl de roches siheoelastiqucs silunennes du groupe d'Arisaig dans les massifs d'Antigonish. Les donnees isotopiques evoqucnl en outre une contribution importante du terrane de Mcguma au sud. Les donnees sont compatibles avec les sources locales et la similarie geochinuque entre les formations de McArras Brook et de Martin Road larsse supposer que la discordance angulaire qui les separe a une portee locale plulot que regionale   Traduit par la redaction

atlantic geology

Geochemistry, provenance, and tectonic significance of sedimentary rocks of the Middle to Late Devonian McArras Brook and Visean Martin Road formations, Merigomish Subbasin, northern Antigonish Highlands, Nova Scotia