Grosses Roches Area, Matane Electoral District P

RP 339(A) PRELIMINARY REPORT ON STE-FELICITE - GROSSES ROCHES AREA, MATANE ELECTORAL DISTRICT P. R. NO. 339 PROVINCE OF QUEBEC. CANADA DEPARTMENT OF MINES HON, W. M. COTTINGHAM. MINISTER A-O. DUFRESNE. DEPUTY MINISTER GEOLOGICAL SURVEYS BRANCH E W. JONES, CHIEF PRELIMINARY REPORT ON STE-FÉLICITÉ-GROSSES ROCHES AREA MATANE ELECTORAL DISTRICT BY JACQUES BÉLAND QUEBEC 1957 P- R. NO. 339 M-0-4298 PRELIMINARY REPORT on the Ste. Félicité-Grosses Roches Area Matane Electoral District by Jacques Béland INTRODUCTION The Ste. Félicité-Grosses Roches Area, which was mapped by the writ- er during the summer of 1956, is in northwestern Gaspé Peninsula. It is bounded on the north by the St. Lawrence river, on the south by latitude 48945`, and on the east and west by longitudes 67°00" and 67°30`.. The west boundary passes one mile east of Matane. The area covers a surface of about 280 square miles and includes parts of Dalibaire, Cherbourg, Leclercq, Cuoq, St, Denis and Tessier town- ships and part of Matane Seigniory. It is fairly well settled except in the southeast, which is under forestry concessions to Hammermill Paper Company of Erie, Pennsylvania, and Price Brothers of Quebec. The principal settlements are, from west to east along the shore, Petite Matane, Ste. Félicité, and Grosses Roches; and, inland, St. Luc St. Adelme, St. Jean de Cherbourg, and St, Thomas. Access to practically any point in the region is provided by a network of good gravel roads which joins Provincial Route No. 6 at various points along the shore. A power line con- structed a few years ago crosses the northern part of the area, Physiography Physiographically, the area can be divided into three units, from south to north: a mountain range, a dissected plateau, and a coastal plain,. In the southeastern corner of the area is a small portion of the Shickshock range, here rising to 1,900 feet above sea level, Northwest of this range is a dissected plateau, about 15 miles wide, which crosses the whole area northeasterly, The plateau varies in elevation from 1,700 feet to 500 feet sloping northwesterly toward the St. Lawrence and, in part, southwesterly toward Matane river The coastal plain occupies a narrow band along the shore in the western half of the area and is bounded southerly by an escarpment which marks the edge of the plateau above described, The escarpment bordering the coastal plain extends along the shore in the eastern part of the area Its summit more or less coincides with the maximum elevation reached by the Champlain Sea towards the end of the Wisconsin glacial episode as is indicated by fairly well preserved gravel terraces and wave-cut cliffs.. Wave-cut cliffs were noted up to an elevation of about 550 feet. Within the dissected plateau certain rock types have definite topo- graphic expressions. A belt of hummocky ground in the north-central part of the area is occupied by hard sandstones, Long ridges with even crests are generally made up of regularly dipping beds of limestone conglomerate or quartzite or boch. Gently rolling ground generally characterizes areas underlain by slates and siltstones. Drainage in the northern part of the area is effected by a series of short and steep streams flowing northerly into the St. Lawrence. The largest of these streams are, from west to east, Petite Matane, Cap de la Baleine, Jaco Hughes, Grosses Roches, Brouillé, Sem and Vapeur. Along most of their courses these streams cut across the structural trends of the area. In their lower parts they flow through deep, narrow gorges which point to fairly recent and rapid downcutting of the land by these streams. Drainage in the southern part of the area is directed southwesterly to Matane river via a large tributary named Petite Matane river (1) whici. branches into several lesser streams in the southeastern part of the area, These lesser streams do not follow the general structural trend but Petite Matane river along most of its course is parallel to this trend, In its lower part, Petite Matane river flows through a deep narrow gorge with a moderately steep gradient, Rejuvenation is also indicated here, The upper part of the river is character- ized by gentle valley slopes pointing to a former more mature stage. A few small lakes, less than 14 mile across, are scattered over the area. Most are formed by water impounded along stream courses or in shallow de- pressions at or near the heads of streams. GENERAL GEOLOGY The consolidated rocks in the area may be divided into five units as follows: metavolcanics and sandstones of the Shickshock group, impure sandstones; slates, siltstones and limestones; limestone conglomerates and quartzites; basic volcanic rocks. The last four units probably are of Ordovician age.. The age of the Shickshock group is inferred here to be Ordovician, although it has previously been considered to be Cambrian or older. The metavolcanics and sandstones of the Shickshock group occupy a very small portion in the southeastern corner of the area where they form a steep and high hill, part of the Shickshock range, The relations of the Shicks- hock group to the Ordovician belt to the northwest are not clear. The contact here appears to be transitional and conformable, but whether the Ordovician is above or below the Shickshock group is not apparent. The impure sandstones which constitute one rock unit in the Ordovi- cian belt are found in the north-central part of the area over a length of about 10 miles and a width of 2 miles, They also occupy a small portion near the western boundary„ Several structural features within the Ordovician belt tend to indicate that these sandstones in the northern part of the area are at the base of the exposed Ordovician section. (1) There are in this area two rivers named Petite Matane., One, the larger, is a tributary of Matane river; the other empties directly into the St Lawrence at the village of Petite Matane, - 3 - They are lithologically similar to the "Pillar sandstone" of the Tourelle area (1), considered on paleontological evidences to be Lower Ordovi- cian (Deepkill) . The stratigraphie position of the sandstones near the western boundary is less clear. There are vague indications that they are above part of the series of slates, siltstones and limestones that extend between the sandstones in the northern part of the area and the Shickshock range, Within these slates,siltstones and limestones are also zones of limestone conglomerate and quartzite and lenses of basic volcanic rocks, With the sandstones, all these rocks actually form one series. Areal extents as shown on the map are in many cases based on predominance of rock types, and boundaries are more or less arbitrary:, Slates and siltstones similar to those found over most of the area are interbedded with the sandstones and with the limestone conglomerates and quartzites. The southern contact of the sandstone belt in the northern part of the area, for instance, is one of transition, the slates and siltstones becoming more and more abundant as one proceeds southward The slates, siltstones and limestones are much alike from the northern to the southern boundary of the area except that they show an increase in metamorphism southward toward the Shickshocks range,The slates become more phyllitic. The limestone conglomerate and quartzite similarly show a distinctive increase in degree of metamorphism. Near the Shickshocks the limestone pebbles are sheared, the matrix is phyllitic, and the quartzites are glassy. There is, therefore, no abrupt change in the metamorphism shown by the rocks of the Shickshock group and those considered to be of Ordovician age. Lenses of basic volcanic rocks occur within the Ordovician assemblage, The largest, located at about the centre of the area, is 2t miles long and y mile wide. Nearby is another lens about 1 mile long and !2 mile wide, Three other small occurrences, at respectively 1!%, 4 and 101 miles northeast, fall on a line which is the prolongation of the long axis of the largest lens. A fault might have controlled the emplacement of all these volcanic bodies. Various types of glacial deposits including till, stratified gravel and sand, and a segment of an esker are found in the area, Glacial striae generally trending northerly or northwesterly were noted on many outcrops Distri- bution of erratics points to successive movements of ice northward and southward Deposits of possibly marine clay occur above sea-level at the mouths of some of the streams emptying into the St, Lawrence, Sand and gravel terraces and elevated beaches are found in the escarpment bordering the dissected plateau and on the narrow coastal plain., All these marine deposits are related to the Champlain Sea episode. Recent deposits include sand and gravel accumulations along flat segments of streams, beach deposits on the shore, and weathered rock material and soil on hill slopes. (1) McGerrigle, H.W.: The Tourelle and Courcelette Areas, Que. Dept. of Mines., Geol„ Rept., 62, 1954, The stratigraphie succession previously outlined is condensed in the following table of formations. Table of Formations Recent Stream and beach deposits Pleistocene Marine (Champlain) Clay, sand and gravel; beach deposits. Glacial Till, glacial outwash, esker Basic volcanics., Limestone conglomerates and quartzites. Ordovician Slates, siltstones and limestones. Impure sandstones. Metavolcanics and impure OrdovicianShickshock group or older sandstones. Shickshock Group The Shickshock group in the area includes green metavolcanics or greenstones interlayered with green and grey arkosic sandstones. Also near the contact with the Ordovician assemblage are green—grey, fine—grained rocks that may be of volcanic or sedimentary origin.

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