CHAPTER 1 INTRODUCTION Y Tinted Version of High Elevations)
Total Page：16
File Type：pdf, Size：1020Kb
CHAPTER 1 INTRODUCTION This report is a synthesis of the results of reconnais- by smooth patterns correlating with the floor of the rift, con- sance geological mapping projects in eastern Labrador in trasting with hackly patterns representing the flanking pre- which the author has been involved, starting in 1979 and rift basement rocks. Sandwich Bay, a smaller, subparallel collectively extending over more than 30 years. It includes indentation to the southeast also owes it origin to the same the eastern part of the Makkovik Province (Cape Harrison rifting event, as do the fault-controlled northeast-trending domain) and the eastern part of the Grenville Province in margins of the Strait of Belle Isle. Two straight sections of southern Labrador. The region mapped covers an area of coastline (overall) are also evident between St. Lewis River roughly 80 000 km2, which is about 20% of the Province of and Black Bear River, trending north-northwest and north- Newfoundland and Labrador. It is equivalent to about 72% northeast. Seismic and gravity data (cf. Gower et al., 1997a) of the area of insular Newfoundland, or 0.8% the area of suggest the existence of north‒south offshore basins (proba- Canada. Twenty-five geological maps, at 1:100 000-scale, bly Phanerozoic), so these stretches of shoreline may also be plus a 1:500 000-scale compilation of the whole area, have fault controlled. Farther north, the orientation of the coast- been published by the Government of Newfoundland and line is very dependent on the structural orientation of the Labrador (Figure 1.1A). These collectively represent the bedrock. Most of the coastline comprises crystalline base- final cartographic products of the mapping project (Gower, ment rocks, but spectacular sandy beaches exist north of 2010a, b, 2011). The maps and this report are supported by Sandwich Bay (Porcupine Strand; Plate 1.1A). a digital database to be released later. Major rivers are labelled in Figure 1.2A, B. Of particu- 1.1 LOCATION lar note are the Kenamu and Eagle rivers in Labrador and the south-draining rivers in eastern Québec, which discharge Eastern Labrador, for present purposes, is that part of into the Gulf of St. Lawrence, including the labelled St. Labrador east of longitude 60° west (which is roughly 30 km Augustin and St. Paul rivers. All these are eroding back into east of Goose Bay), excluding some parts in the northwest of the plateau area and have become deeply incised. This is a the region (Makkovik area), but including a relatively small consequence, at least in part, of isostatic rebound following area west of longitude 60° west, situated north of Lake the last glaciation. The incised rivers are not markedly influ- Melville (Figure 1.1A, B). It includes all of NTS map areas enced by bedrock structural trends, except the Kenamu 3D, 3E, 13A, 13B, 13G, 13H and 13I, most of 13J, parts of River, which follows a splay fault of the Lake Melville rift 12P and 13K, and small segments of 13O and 2M. Each of system. In contrast, the southeast-draining rivers (Hawke, the 1:100 000-scale geological map regions delineated in Gilbert, Alexis and St. Lewis rivers) are all strongly con- Figure 1.1A has been assigned a geographical name by the trolled by a complex system of southeast-trending strike-slip author, based on a prominent geographic feature in that dis- faults dating from at least 1000 Ma (Ma = 1 million years). trict, but having no formal significance otherwise. Except for the largest water courses, the rivers are mostly fairly shallow, boulder-strewn, have numerous rapids, and a 1.2 PHYSIOGRAPHY few small waterfalls (rarely more than a few metres high; Plate 1.1B). They are swift flowing during spring runoff, but Three key physiographic elements are the coast, rivers by late summer are much reduced in flow rate. The rivers are and uplands (Figure 1.2). The most striking feature of the mostly unnavigable in small craft beyond a few kilometres coast is the 200-km-long, southwest-penetrating indentation from their mouths. defined by Groswater Bay and Lake Melville. Although termed a ‘lake’, Lake Melville is a saltwater tidal extension The overall topography of eastern Labrador is that of an of Groswater Bay. Together with Double Mer, which is a east-sloping plateau, modified by the Lake Melville and parallel saltwater tidal indentation, Lake Melville and Sandwich Bay rift basins. The highest area, which rises Groswater Bay define a northeast-trending region that owes above the plateau, is the Mealy Mountains, south of Lake its origin to late Neoproterozoic–early Phanerozoic rifting Melville, reaching a height of 1097 m (3599 feet). The (Lake Melville rift system). The faulted margins of the rift mountains in this area partly owe their existence to the are evident in the grey-shaded digital elevation model and resistant nature of the bedrock (massive anorthosite). A its hypsometrically tinted colour version (Figure 1.2A, B) smaller area of mountainous terrain is present in the north 1 REGIONAL GEOLOGY OF EASTERN LABRADOR CHARLES F. GOWER LEGEND B o 55 N Study area Makkovik Postville Highway Secondary / Woods road Proposed road Transmission line 0 km 50 Rigolet Park boundary Gannet Islands Ecological Reserve North West River Cartwright & Sheshatshiu Mealy Mountains National Park Paradise River Black Tickle Happy Valley Hwy 516 - Goose Bay Hwy 510 Cartwright Junction Proposed Eagle River Charlottetown Pinsent’s Waterways Provincial Park Arm Hwy 514 13O Adlavik 55o N Islands A Big River Byron Bay St. Port Benedict Lewis Mountains Hope Hwy 513 13J 13I Nipishish Simpson Lake Double Mer Rigolet Groswater Bay 13K Mary’s Harbour Table Bay Grand Lake Sandwich Lake English Lodge Melville River Bay Bay 13G 13H 03E Kenemich Southeast Sand Hill Labrador River Mealy Paradise River Mountains River 25A Québec 60 24P 14M LABRADOR Port Hope Crooks Lake Eagle Alexis INDEX MAP Simpson 24I 14L 1:250,000 N.T.S. sheets River River 58 24H 14E 14F 050100 150 13B 13A 03D km Upper Upper 24A 14D 14C St. Augustin St. Paul Kyfanan St. Lewis 56 23O Red Bay River River Lake River 23P 13M 13N 13O 52o N Labrador 23J 23I 13L 13K 13J 13I Pinware River Québec 54 Pinware 23G 3E Pinware 23H 13E 13F 13G 13H Provincial Park River 3D 0 km 50 23B 23A 13D 13C 13B 13A L’Anse-au-Loup 52 2M o 22P 12P o o Forteau 56 W 60 W 12P 56 W 68 64 60 56 Figure 1.1. Eastern Labrador showing area addressed in this report. A. Names and locations of 1:100 000-scale geological maps for eastern Labrador, B. Major communities and cultural features (present and proposed roads, parks and power trans- mission line). 2 CHAPTER 1 Figure 1.2. Physiographic features of eastern Labrador showing area addressed in this report. A. Digital elevation model, B. Hypsometrically tinted version of INTRODUCTION same data (pale-green ‒ low elevations; brown ‒ high elevations). Highest point is in Mealy Mountains at 1097 m. 3 REGIONAL GEOLOGY OF EASTERN LABRADOR CHARLES F. GOWER Plate 1.1. Selected physiographic features in southeast Labrador. A. Porcupine Strand looking north from Cape Porcupine, B. ‘Staircase’ Falls; tributary of St. Paul’s River, C. Wetlands southeast of Mealy Mountains, D. Battle Island and the settle- ment of Battle Harbour. part of the region, termed the Benedict Mountains. The graphic features have strongly influenced the interpretations highest point is ca. 730 m (2395 feet). The mountains are embodied in the author’s geological maps. massive granitoid rocks. 1.3 INFRASTRUCTURE AND LAND USE The plateaux are generally characterized by low, round- ed, wooded hills with intervening wetlands, including string In addition to providing information on current infra- bogs, and numerous shallow lakes and ponds (Plate 1.1C). structure, this section also addresses some current and Most bedrock in interior regions is covered in a blanket of potential developments likely to affect eastern Labrador in various types of surficial deposits. Progressing toward the near future (Figure 1.1B). It is an update of that given by coastal areas, the hills lose their forest covering, showing, Gower (2010c). first of all, bare-rock-outcropping hilltops, and eventually, within a few kilometres of the coast, losing their forest cov- 1.3.1 HIGHWAYS ering (Plate 1.1D), except for scrubby, stunted trees in shel- tered hollows and taller trees in valleys. In coastal areas, 1.3.1.1 Trans-Labrador Highway outcrop is good, albeit lichen covered. On 16th December, 2009, the provincial government A brief summary, such as this, must ignore the wealth of announced the opening of Phase III of the Trans-Labrador valuable detail that the physiography offers to the field geol- Highway. Phase III involved highway construction between ogist. Apart from a subtle east-southeast ‘grain’ due to gla- Cartwright Junction and Happy Valley–Goose Bay. Further cial dispersion, almost every feature is explicable in terms of work was carried out during the summer of 2010 to official- rock type or structure, and repeated reference is made to ly complete the highway. Upgrading and paving of the such features in the ensuing text. Undoubtedly, physio- highway is currently in progress. 4 CHAPTER 1 INTRODUCTION The Trans-Labrador Highway stretches approximately national park reserve in the Mealy Mountains area of 1150 km from southeasternmost Labrador to southwest Labrador. Final agreement was reached and the Mealy Labrador, passing through Happy Valley–Goose Bay, Mountains National Park was declared on July 31st, 2015. Churchill Falls and Labrador City–Wabush. The highway The park will protect 10 700 km2. This represents roughly (Hwy 510) in southeast Labrador links various communities 50% of the 22 000 km2 area earlier designated as the Mealy between Blanc-Sablon and Red Bay, then, north of Red Bay, Mountains National Park study area, which included, not passes by Lodge Bay, Mary’s Harbour and Port Hope only the Mealy Mountains and much of the Eagle River Simpson.