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STRUCTURAL GEOLOGY OF NORTH AMERICA 



The Arisaig region of Nova Scotia was affected by folding and in- 

 trusives at the close of Lower Ordovician and probably again at the close 

 of the period, when the Taconic orogeny spread over much of the Mari- 

 time Provinces. Numerous plutons, mostly of Middle Devonian age, were 

 emplaced in the Nova Scotian Precambrian and in the pre-Devonian 

 strata of central New Brunswick as previously described. Similar in- 

 trusions occurred in the Gaspe Peninsula. The strata of New Brunswick 

 and Nova Scotia were cast into northeasterly trending folds at this time, 

 which probably paralleled former structures. Figure 12.7 shows the folds 

 and faults of the St. John area in New Brunswick. 



Normal faults are shown in a number of cross sections in the literature 

 but are not much discussed. They are evidently later than the compres- 

 sional orogenies or due to late adjustments of the individual orogenies. 

 Some may be related to the Triassic basin faults and some even to 

 Tertiary faulting. 



TECTONIC HISTORY 



Most writers emphasize two great orogenies in the Maritime Provinces, 

 the Taconic at the close of the Ordovician and the Acadian or Shicksho- 

 kian that ran its course through middle and late Devonian time. If the 

 geologist is not influenced unduly by the interpretations and conclusions 

 of numerous writers and considers only the numerous coarse conglom- 

 erates, unconformities, and volcanic series without previous impressions, 

 it would be natural to conclude that a long succession of compressional 

 impulses with accompanying intermittent volcanic and magmatic ac- 

 tivity affected the Maritime Provinces. At intervals from Proterozoic to 



late Triassic time, vigorous deformation occurred from place to place. 

 It does not seem altogether sound to the writer to conclude that two 

 orogenies stand apart as clear-cut and distinct. Perhaps orogenic events 

 reached maxima, and these maxima are to be considered the Taconic and 

 Acadian orogenies. The great angular unconformity at the base of the 

 Carboniferous emphasizes the superior nature of the orogenic phases 

 that preceded the Mississippian. 



The Mississippian beds are folded in places, and so are the Penn- 

 sylvanian, but the phases of Carboniferous orogeny are not so severe as 

 the earlier ones. Over the New Brunswick lowlands the beds are fairly 

 flat. Bordering highlands were intermittently and sharply elevated, how- 

 ever, throughout the Mississippian and Pennsylvanian to supply the great 

 amounts of coarse elastics that make up the thick deposits. One of these 

 source areas probably was the Precambrian area of Nova Scotia; another 

 possibly lay to the northeast along the St. Lawrence. 



During the succession of orogenies that beset the Maritime Provinces, 

 several ranges were undoubtedly elevated and several troughs of deposi- 

 tion undoubtedly sank, and this activity was accompanied by voluminous 

 volcanism. With the sea extensively invading the cordillera, a condi- 

 tion is visualized much like the partially submerged Andean system of 

 southern Chile, Patagonia, and Tierra del Fuego. The changing geo- 

 graphic scene during the Paleozoic has not been set down on maps — 

 perhaps the geological information is not yet sufficient to perform such a 

 snythesis. 



The fronts of the orogenic belts, however, seem clear by now, and after 

 the geology of Newfoundland has been presented, an attempt will be 

 made to relate the orogenic belts of Greater Acadia. 



