Lakehead University Geology - Journal Yearbook (Thunder Bay, Ontario Canada)

Page 18 text:

chlorite, illite and an interbedding of chlorite and illite. The difference in colour is probably- caused by the higher oxidation state of the dark yellowish brown silts. Varved sediments, probably of Pleistocene age, underlie the Recent sediments in the area of study. North of Coppermine Point the varved sediments are greenish gray in colour whereas to the south of Coppermine Point the varves have been oxidized to pale brown in colour. The mineralogical composition of the varved sediments consists of orthoclase, microcline, quartz, chlorite, illite, an interbedding of chlorite and illite, dolomite and calcite. It was noted that there is a decrease in the percentage of calcite in the varved sediments northward of St. Mary ' s River. JOHN S. MOTHERSILL LIMNOGEOLOGICAL STUDIES OF THE EASTERN PART OF THE LAKE SUPERIOR BASIN. 16

Page 17 text:

Dr. J. Mothersill, B.Sc, (Physics) Carleton; B.Sc. (Geological Engineering) Queen ' s; Ph.D. Queen ' s . Background Exploration Geologist for Standard Oil (N.J.) Senior Geologist for Mobil International Oil Co. Exploring for petroleum in Turkey, Nigeria, France and Colombia. LIMNOGEOLOGICAL STUDIES OF THE EASTERN PART OF THE LAKE SUPERIOR BASIN The bottom topography of the eastern part of the Lake Superior basin consists of a lake-shelf two to four miles wide and a series of north-south aligned, topographical deeps and highs three to four miles wide lakeward, which is in marked contrast to the east-northeast and east-southeast trends of the onshore Precambrian rocks. The temperature of the bottom sediments is related to water- depth. The high pH values of the bottom sediments in Goulais Bay and Batchawana Bay appear to be caused by the alkaline waters of the Goulais and Batchawana rivers respectively. The pH measure- ments of the bottom sediments elsewhere in the area of study do not appear to be related to either water-depth or to the lake-bottom sedimentary types. The Recent sand deposition is restricted to the lake-shelf and to the offshore topographical high areas. Based on grain-size analyses the sands of the topographical highs are normally coarser- grained and better sorted than the sands of the adjacent lake-shelf area suggesting stronger current action offshore. In addition the sands of these two environments can be differentiated on the basis of total heavy mineral content as the sands of the topographical highs never contain more than 3»1 per cent heavy minerals whereas the sands of the lake-shelf area may contain from 4.1 to 26.0 per cent heavy minerals. The main area of provenance for the sands would appear to be the rocks along the shoreline and the drainage area of the eastern Lake Superior basin. The reason for the relative decrease in the percentage of heavy minerals present along the topographi- cal highs would appear to be that most heavy minerals are unstable in a fresh water environment and therefore would tend to be chemically decomposed before being transported to the offshore topographical high areas. The sands south of Coppermine Point are generally coarser-grained, better sorted and less positively skewed than the sands north of Coppermine Point regardless of environment of deposition. This is probably the result of stronger current action along the shallower waters of the topo- graphical highs and lake-shelf area south of Coppermine Point. The occurrence of a thicker sand sequence in progressively shallower water from north to south across the area of study could be related to the post-glacial isostatic tilting of the Lake Superior basin to the southwest as the Michipicoten area has been raised 20 meters relative to the Sault Ste. Marie area since the Nipissing stage (Farrand, i 960 ). The Recent sediments in the central parts of Batchawana and Goulais Bay and in the offshore topographical lows consist of coarse silts to coarse clays. These Recent silt-clays form a consistent sequence of the following three units: an upper thin veneer ( 4 cm. ) of coarse to very fine-grained dark yellowish brown silt; an intermediate, relatively thin (2-12 cm.), unit con- sisting of olive gray, fine-grained silt to coarse-grained clay; a lower thick unit of coarse to very fine-grained, dark yellowish brown silt. The thickness of this sequence is greatest in the central parts of the topographical deeps where it is in excess of 180 cm. thick. The mineralogical composition of the three units is very similar and consists of orthoclase, microcline, quartz, 15

Page 19 text:

Dr. Henri Loubat Geological Engineer, PhD., Geneva Assistant Professor, Lakehead University I became particularly attracted by petrology in 19ol when I found the opportunity of studying a set of metamorphic rocks from California. These rocks belonged to the glaucophane-schist and eclogite facies of metamorphism. At that time, I was fascinated by two problems exhibited by these classic Californian types: the process of diaphtoresis , and the phenomenon of converging facies. The glaucophane-schist may be due to a particular regional metamorphism acting on greywackes and ophiolites; but frequently it results from a retrograde process of modification from a high degree of metamorphism (amphibolite or eclogite) toward lower degrees of alteration. Both these glaucophane-bearing types are to be found, closely associated, in California, and they exemplify very well the retroinorphosis ( diaphthoresis) and facies convergence . It is easy to realize the interest of the study of those facies, if we know that eclogite themselves are not always considered as metamorphic rocks.... Soon after, receiving a grant from the University of Geneva I studied briefly greenstones, sediments and serpentines from Cuba. The degree of alteration of my samples was somewhat discouraging for a sucessful petrographical and geochemical investigation, but this was a first contact with igneous submarine rocks. During the next four years my main petrographic activity was devoted to surveying the Versoyen region - this area of the Alps is geologically very attractive. We should know that the Alps are subdivized longitudinally by a major tectonic thrust plane, the trace of which is called the Pennic front thrust . This line runs parallel to the chain, subdivizing it into two equal bands: the internal Alps (toward Italy) and the external Alps (toward France and Switzerland). The former is very rich in ophiolites, strongly metamorphic and intensely disturbed by the tectonic. The latter is not metamorphic, lacking ophiolites, and gently folded. The Versoyen, which is located exactly on the border between France and Italy, is the last ophiolitic area we could find when leaving the internal Alps going toward France, ’with this marginal location, this area offers the weakest degree of metamorphism we could have in the Alps for submarine volcanic rocks. A study based on field, microscopic and chemical investigations leads to the following conclusions: ' We have there a well-preserved submarine volcanic complex composed of the piling of various related units; at the bottom, along with slabs of aplitic granites and gneiss (fragments of the Alpine basement?), thin layers of serpentinites . Above, thick lenses of diff erenciated gabbros; still above, a set of sills, inter-bedded with black schists. At the top, an enormous amount of pillow-lavas. This rather logical sequence so well known by anglo-saxon geologists, was never recognized before anywhere in the Alps, although it is quite probable that it is actuall ' omnipresent, but was always disturbed by complex diastrophism. Petrology 17