The Surficial Geology and Pleistocene History of Vermont
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THE SURFICIAL GEOLOGY AND PLEISTOCENE HISTORY OF VERMONT By DAVII) P. STE\V\RT AND PATJL MAcCLINTOCK VERMONT GEOLOGICAL SURVEY ChARLES G. I)oIL, Slate Geologist 1)EPART lENT OF WATER RESOURCES MONTPELIER, VERMONT BULLETIN No. 31 1969 TABLE OF CONTENTS PAGE INTRODUCTION ...................... 15 Early Studies ...................... 15 The Scope of the Mapping Program ............ 19 Geomorphic and Tectonic Setting ............. 21 Acknowledgments .................... 23 SURFACE MATERIAL .................... 25 Till .......................... 25 Basal Till ...................... 26 Ablation Till ..................... 26 Glacio-Fluvial Deposits ................. 29 Kame Terraces .................... 29 Kame Moraines .................... 31 Eskers ........................ 31 Spillwav Gravel (Valley Trains) ............. 33 Lacustrine Sediment ................... 33 Local Origin I lvpothesis for the Lake Sediment....... 37 Marine Sediment . . . . . . . . . . . . . . . . . . . 39 GLACIAL AND GLACIO-FLUVIAL ERosIoN ........... 39 Glacial Erosion ..................... 39 Relative I lardness and Fabric of the Rock ........ 40 Major Topographic Features .............. 40 Erosional Topography ................. 40 Lake Basins ..................... 41 Mountain Gaps .................... 41 The Connecticut Valley ................ 41 The Vermont Valley .................. 42 Yellow I3og ...................... 12 Glacio-Fluvial Erosion .................. 42 Streams Beyond the Ice Margin . . . . . . . . . . . . 42 Subglacial, Englacial and Superglacial Streams ...... 13 Potholes ....................... 43 The Shattuck Mountain Channels ............ 43 PROBLEMS OF IDENTIFICATION AND CORREI.ATION OF l)RIFT SHEETS 44 Effects of Mountain Terrain ............... 44 Effects of Complex Bedrock ............... 45 Effects of Multiple Glaciation ............... 46 PAGE PAGE \ Conventional Field lethods that Proved Unsuccessful in Ver- Champlain Lowland ................... 111 ........................ 47 mont THE I3ITRLINGTON STAnK .................. 111 Physical Characteristics of the I)rift ........... 47 The Extent of the Burlington Glaciation .......... 113 Features Resulting from Glacial Erosion ......... 48 The Border of the Burlington Drift Sheet.......... 118 Features Resulting from Glacial Deposition ......... 48 Out\vash Deposits of the Burlington Stade ......... 125 Moraines ....................... 49 I linesburg Name Terraces ............... 125 Outwash Aprons . 49 Buck Hollow Name Terrace .............. 127 Boulder Trains and Indicator Fans ............ 49 Name Gravel of the Enoshurg Falls Quadrangle ...... 127 Organic Remains, I aleosol s, Interglacial Gravels and I3laek River Name Complex ............... 137 Weathering Profiles Between l)rift Sheets Name Deposits of the Newport Region ......... 137 TILL FAHRI(. ....................... 51 The Bristol-East Middleburv Name Terraces ....... 137 MULTIPLE GLAcI,TIox ................... Name Gravel in the Barre Area ............. 138 THE PLEISTOcENE SEIQI - ENCE IN Viiiox .......... 56 Name Terraces on the Green Mountain Slopes ...... 138 A lh)5SIHLE PEE-BENNINGTON GLAcI..L STADF ........ hIGH-LEVEL LAKES OF THE BURI.INGTON STADF ........ 139 THE BENNINGTON GLAcIAL STAnK .............. 61 high-Level Lakes of North Central Vermont ........ 139 Lake Bascom in the Bennington Region .......... 68 Stage I ....................... 143 THE \\E5T NORiVICH INTERSTAI)E .............. 70 lemphrcmagog Basin ................ 143 THE SIIELIIURNE GLAcIAL STADE .............. 70 Lamoille and Sto\ve Valleys ............. 143 Possibility of Two Northeast Tills ............. 79 Winooski \allev .................. 143 Alternate Interpretation I ............... 80 Stage II ....................... 145 Alternate Interpretation II ............... 80 Memphremagog Basin ................ 146 Alternate Interpretation III .............. 80 Lamoille Valley ................... 146 \ loraincs (.omposcd of Shelburne Till ........... 80 Sto\ve Valley .................... 146 loraines of the St. Johnshurv Region .......... 81 Winooski Valley .................. 149 Shelburne Moraines of the Rutland Region ........ 85 Stage III ....................... 149 \ loraines of the \ lanchester-l3ennington Region ..... 85 Memphremagog Basin ................ 15 1 Outwash l)eposits of Shelburne Age ............ 88 The Lamoille and Sto\ve Valleys ........... 152 Name Gravel 1)eposits ................. 88 \\inooski Valley .................. 1 53 Eskers ........................ 89 Stage IV ....................... 151 The Connecticut Valley Eskers ............ 91 Memphremagog Basin ................ 154 The Passumpsic Valley Esker ............. 91 Lamoille, Stowe and \Vinooski Valleys ......... 155 High-Level Ice-Contact Lakes of Shelburne Age ....... 93 Stage V ....................... 157 I Ugh-Level Lakes of the Connecticut River Valley 93 \1emphremagog Basin ................ 157 I ugh-Level Lakes of the Manchester-Bennington Region 95 Lamoille, Stowe and Winooski Valleys ......... 158 Eastern Margin of the Shelburne Drift ........... 97 The End of the hugh-Level Lakes ............ 158 Origin of the Northeast Fahric Along the Eastern Margin.. 98 I high-Level Lakes of Southern Vermont ........... 159 Piggy-Back-Ride Hypothesis ............. 98 LAKE \ERMONT ...................... 160 \Iarginal Shear I lvpothesis .............. 101 The Calving Retreat of the Burlington Glacier ....... 160 THE LAKE IIITcHCOCK INTERSTADF ............. 101 The Quaker Springs Stage ................ 163 PAGE PAGE FIGURE 1. Index map showing the area of Bennington surface till and the The Coveville Lake Stage 169 Shelburne drift border ................. 60 ................... The Fort Ann Stage 174 2. Lake Bascom in Vermont ................ 69 POST LAKE \ERMONT EROSION INTERVAL ........... 177 3. Moraines of Shelburne age in the St. Johnsbury region 81 THE CHAMPLAIN SEA INTERVAL ............... 179 4. Moraines and high-level lakes of the Shaftsbury-Manchester POST-GLACIAL TILTING OF THE LAKE AND SEA SHORELINES 183 region 86 ......... CORRELATION OF THE \ERMONT 1LEISTOCENE 184 5. Lake Shaftsbury in Vermont ............... 96 Probable Correlation with the St. Lawrence Lowland and ....... 99 6. Probable eastern border of the Shelburne drift ................ 184 Southeastern Quebec 104 7. Profile plot of the littoral sediments of Lake Hitchcock ................... 185 Burlington Till 186 8. Crests of the Green Mountains and gaps through which Burl- Shelburne Till 110 ington ice advanced Bennington Till .................... 187 9. Index map showing the Burlington drift border in the Rutland Conclusions 187 and Lake St. Catherine regions 112 Correlation with Other Areas of New England 188 10. Index map showing the Burlington drift border in the Bethel- .................... 189 Bennington Till 114 Brandon region ... ................. Shelbume Till 189 11. Index map showing the Burlington drift border in the Mont- Middletown-Cambridge Readvance 189 pelier region 115 BII3LIOGRAPHY 239 12. Index map showing the Burlington drift border in the Hard- wick-Morrisville region ................. 116 Appendices PAGE 13. Index map showing the Burlington drift border in the APPENDIX Memphremagog region ................. 117 Field data and calculated vector mean of fabrics of the Benning- A. 140 14. High-level lakes of north-central Vermont—Stage I . ton till ......................... 191 15. High-level lakes of north-central Vermont—Stage II . 142 B. Field data and calculated vector mean of fabrics of the Shel- 16. High-level lakes of north-central Vermont—Stage III . 144 burne till 200 17. High-level lakes of north-central Vermont—Stage IV . 147 Field data and calculated vector mean of fabrics of the Burling - C. 148 18. Iligh-level lakes of north-central Vermont—Stage V . ton till ......................... 215 D. Discussion of the glacial sequence in North America and New TABLE PAGE England. Reprinted from The Glacial Geology of Vermont 1. Field assistants that participated in the mapping program, the (Stewart, 1961) ..................... 224 year they worked and their present status 24 E. VECMAC program used to compute vector mean ...... 236 PLATE PAGE Illustrations I—Figure 1. FIGURE PAGE The crest of the Green Mountains in southern I. Index map showing the areas mapped by the participants in the Vermont. Hancock Mountain in foreground (Roches- mapping program 14 ter Quadrangle) ................ 20 2. Index map showing quadrangle names and locations . 17 Figure 2. 3. Index map showing the Physiographic Subdivisions of Vermont 18 The crest of the Green Mountains in the vicinity of 4. Stratigraphic units of the sections exposed along Stannard Mt. Snow (Mt. Pisgah). Picture taken looking north Brook 59 PLATE PAGE PLATE PAGE from the summit of Mt. Snow, elevation 3556 feet, VIII across the Somerset Reservoir (\Vilmington Quad- Fabrics of the Bennington till beyond the Shelburne rangle) 20 till border in the Wilmington-Brattleboro region . 65 11—Figure 1. Ix Slumping structure in lake sediment caused by the Fabrics of the Bennington till beyond the border of melting of ice in the underlying kame gravel. Two the Shelburne till in the Bennington area ...... 67 miles cast-southeast of Jericho Center (Camels X Hump Quadrangle) ............... 30 Northwest striae crossing northeast striae and Figure 2. earlier northwest striae. One-half mile west of The Four Varved and laminated lake sediment capped by Corners (Lyndonville