Silurian Strata of Notre Dame Bay and Exploits Valley, Newfoundland by W
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BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA SILURIAN STRATA OF NOTRE DAME BAY AND EXPLOITS VALLEY, NEWFOUNDLAND BY W. H. TWENHOFEL AND R. R. SIIROCK CONTENTS Page Introduction................................................................................................................................. 1744 Previous investigations............................................................................................................. 1745 Outline of Silurian geology...................................................................................................... 1747 Regional distribution........................................................................................................ 1747 Regional structure............................................................................................................. 1747 Metamorphism................................................................................................................... 1747 Stratigraphy........................................................................................................................ 1749 Igneous rocks...................................................................................................................... 1750 Silurian conglomerates..................................................................................................... 1751 Sections in Notre Dame Bay and vicinity......................................................................... 1753 Botwood............................................................................................................................... 1753 General statement.................................................................................................... 1753 Wigwam Point to Peter Arm................................................................................ 1753 Botwood to Northern Arm.................................................................................... 1756 Upper Black Island........................................................................................................... 1757 Yellow Fox and Indian islands...................................................................................... 1757 General statement.................................................................................................... 1757 Yellow Fox Island.................................................................................................... 1758 Indian islands............................................................................................................. 1759 Change Island..................................................................................................................... 1760 Long Tickle......................................................................................................................... 1761 Goldson and Pike arms.................................................................................................... 1761 General statement.................................................................................................... 1761 Burnt Island............................................................................................................... 1761 South shore of Goldson Arm................................................................................. 1763 Southeast shore of Herring Neck, southwest end........................................... 1763 Herring Head............................................................................................................. 1764 Pike Arm..................................................................................................................... 1765 Grand Falls......................................................................................................................... 1766 Summary of sections................................................................................................................. 1767 Correlation of Silurian of Notre Dame Bay and the Exploits Valley........................ 1769 Pleistocene deposits................................................................................................................... 1770 Conclusions.................................................................................................................................. 1770 ILLUSTRATIONS Figure Page 1. Map of a portion of Notre Dame Bay and the Bay of Exploits........................... 1748 2. Map of the Botwood region, Bay of Exploits........................................................... 1754 3. Map of several large islands in Notre Dame Bay.................................................... 1758 4. Map of a portion of New World Island...................................................................... 1764 ( 1743) Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/48/12/1743/3415489/BUL48_12-1743.pdf by guest on 24 September 2021 1744 TWENHOFEL AND SIIROCK----SILURIAN STRATA, NEWFOUNDLAND INTRODUCTION The occurrence of Silurian strata in White and Notre Dame bays and the Exploits Valley has been known since the explorations of Murray and Howley more than sixty years ago. These explorations, reconnais sance in nature, yielded little information concerning thicknesses, litho- logical characters, and faunal contents of the sedimentary rocks. The few Silurian fossils reported were of such general or uncertain identifica tion as to have little value for precise age determination and specific correlation. It was not until 1910, when Charles Schuchert examined the collections of the Geological Survey of Newfoundland at St. John’s, that the fossils were more definitely identified and the stratigraphie posi tion of the fossiliferous Silurian strata of Newfoundland was somewhat more exactly determined. Since the Silurian strata of northern Newfoundland are the most east ern known on the North American continent, the contained fossils are of paramount importance for correlation with the European Silurian. The meager information available in 1935 precluded determination of the exact position of the Newfoundland strata in the Silurian system; did not show whether the Silurian faunas of Newfoundland were related to those of Anticosti, as seemed probable, or to those of the Acadian geosyncline as developed at Arisaig, Nova Scotia; and failed to demon strate whether the sediments had been deposited in the Appalachian or the Acadian geosyncline. The need for more definite information concerning the Silurian of New foundland became apparent in 1934 when the senior writer began the preparation of a contribution on the Silurian strata of the St. Lawrence region for a projected memoir on the stratigraphy of North America. As a step toward acquiring additional information, the writers requested a grant from the Grants-in-Aid Committee of the United States National Research Council. This request was approved, and the grant made pos sible the field work done in the summer of 1935 along the coast and on the islands of Notre Dame Bay and along the Exploits River. The writers were assisted in the field by W. S. Twenhofel, son of the senior writer, and by Adam Peckford, owner and operator of the motor boat used during much of the work. Unfortunately, one of the most important exposures was not seen in 1935 because there are two islands in Notre Dame Bay bearing the name of Yellow Fox, and the strata of the wrong one were studied. Another important exposure was not seen because its existence was then unknown to the writers. This had been discovered by George R. Heyl, in the midst of a flow breccia on Upper Black Island in the Exploits Estuary. The region of White Bay was not visited at the time because a party Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/48/12/1743/3415489/BUL48_12-1743.pdf by guest on 24 September 2021 INTRODUCTION 1745 of the Geological Survey of Newfoundland was working in that area, and it did not seem wise to duplicate effort. Subsequently, A. K. Snelgrove, Director of the Geological Survey of Newfoundland, expressed the wish that the strata of White Bay be examined, and this led to the senior writer’s again visiting the island in the summer of 1936. This later work, partly supported by the Geological Survey of Newfoundland, included a study of the strata in Notre Dame Bay not seen in 1935, a re-study of some of the sections seen that year, and a brief examination of the Silurian strata of the White Bay region which were then being studied by Heyl. The Silurian fossils collected at various times by Snelgrove and his associates were given to the writers for study, and they take this oppor tunity of expressing their gratitude for the courtesy. These fossils will be described in another paper. PREVIOUS INVESTIGATIONS The earliest published studies of the Silurian of Newfoundland were made by Murray and Howley.1 In 1864, Murray studied the geology of the eastern coast of the great northern peninsula and parts of the coasts of White, Hall, and Notre Dame bays. The strata of Exploits Valley and Notre Dame Bay were investigated by Murray and Howley in 1871. Murray gave most of his attention to the former, whereas Howley studied the rocks along the coasts and on the islands of Exploits and Notre Dame bays. The strata assigned by these authors to the Silurian were discussed under the heading, “Upper Formations, Trap Dykes and Overflows.” They commented briefly con cerning the distribution and nature of the rocks but gave