Geology of the Goose Arm Hughes Brook Area

Lilly, H. D. (Hugh Dalrymple) (1961) Geology of the Goose Arm Hughes Brook Area. Masters thesis, Memorial University of Newfoundland.

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Abstract

The regional setting for this thesis is in the central part of West Newfoundland. -- The examination is concerned with an area of approximately 250 square miles more or less lying between North Mountain, in the Bay of Islands, inclusive of the southern part of the mountain, and the Humber River west of Limestone Station. A small area located south of the river is also included. -- The bedrock of the area consists primarily of clastic and carbonate sediments ranging in age from Cambrian to Upper Ordovician which lie with unconformity upon earlier, more or less metamorphosed, Cambrian or Precambrian argillaceous and arenaceous rocks. -- The younger clastic rocks, which may have upper members of Silurian age, are in part overlain by and, to a lesser extent, intercalated with still younger volcanic rocks. Both the volcanic rocks and upper members of the clastic rocks have been intruded by large masses of ultrabasic and basic rocks and lesser bodies of granite. -- The clastic rocks are largely deltaic in character and consequently poorly fossiliferous. Moreover, the carbonate rocks have been largely recrystallized and well preserved fossils, suitable for identification, are few. Age determinations were, therefore, made by lithological correlations with adjacent areas where fossils have been better preserved. Large, easily recognized, exposures of the St.George group of Lower Ordovician age, which are abundantly fossiliferous to the south of the thesis area, provided the chief markers for these correlations. -- Evidence for an early phase of orogeny occurs in the upper beds of the main sequence of Ordovician carbonate sediments. The widespread occurrence of the younger clastic sediments and subsequent volcanic activity indicate that orogeny comprised a number of phases which took place over a rather prolonged period of time. -- A further orogenic phase is evidenced by the deformation of the younger clastic sequence and widespread metamorphism. -- A thrust of more than 6 miles is noted, and evidence for it is submitted on the basis of the superposition of pre-St.George rocks over Lower to Middle Ordovician rocks and their relationships to the nearest possible source facies. -- The occurrence of galena and sphalerite-bearing horizons in the carbonate rocks, and their possible origin, is briefly discussed. -- Generalized references are made to additional work outside the area in as much as it is necessary to show the overall relationship to the environment. A brief outline of some of the problems encountered in determining the relationships of the basal metamorphic rocks to the main carbonate sequences is also provided.

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