OFFICE OF THE STATE GEOLOGIST VERMONT GEOLOGY MARCH 1988 VOLUME 5 GUIDEBOOK 2 CONTENTS Stratigraphy and Structure of the Camels Hump Group along the Lamoille River Transect, Northern Vermont Barry Doolan Cl-C33 The Beekmantown Group in the Central Champlain Valley Paul A. Washington Steven A. Chisick Fl-Fl? Taconic Geology near Fair Haven, Vermont Brewster Baldwin Andrew V. Raiford G1-G13 Pleistocene Glaciation at Lake Willoughby, Vermont Ballard Ebbett Hl-H32 Structural Character of the "Pre Silurian" and "Silurian" Rocks and the Nature of the Boundary between them in Central Vermont David S. Westerman 11-19 EDITOR Jeanne C. Detenbeck VERMONT GEOLOGICAL SOCIETY, INC. P.O. Box 304 Montpelier, Vermont 05602 FORE WORD About the Guidebook The Vermont Geological Society is pleased to present the second in its series of Guidebooks, containing field trip guides of trips sponsored by the Society in its 14 year history. Each guide has the date of the original field trip on the first page, but the contents of each represents the most recent field work done in that area. Not all leaders of Vermont Geological Society field trips have been willing and/or able to publish guides, but, in the future, when enough manuscripts for a guidebook have accumulated, we will publish another volume. Credits Thanks to Charlotte Mehrtens and Rolfe Stanley for reviewing one field trip guide. Camera-ready copy was prepared by Jeanne Detenbeck. About the Society The Vermont Geological Society was founded in 1974 for the purpose of: 1) advancing the science and profession of geology and its related branches by encouraging education, research and service through the holding of meetings, maintaining communications, and providing a common union of its members; 2) contributing to the public education of the geology of Vermont and promoting the proper use and protection of its natural resources; and 3) advancing the professional conduct of those engaged in the collection, interpretation and use of geologic data. For more information about Society membership, meetings, and publications, write to: Secretary, Vermont Geological Society, Box 304, Montpelier, Vermont 05602. Officers 1987-1 988 President Jeffrey Pelton Vice President John Malter Secretary Alan Liptak Treasurer David Westerman Board Shelley Snyder 1 88 of Donald Wernecke 1 88 Directors Ray Coish 1 89 Committee Chairpersons Advancement of the Science Rolfe Stanley Geological Education Sharon O'Loughlin Public Issues Eric Lapp Publications/Editorial Jeanne Detenbeck October 6, 1984 STRATIGRAPHY AND STRUCTURE ( OF THE CAMELS HUMP GROUP VERMONT ALONG THE LAMOILLE RIVER GEOLOGY TRANSECTI NORTHERN VERMONT MOLU1LE 5 Barry L. Doolan Department of Geology University of Vermont VGS GUIDEBOOK 2 Burlington, Vermont 05405 FIELD TRIP GUIDE C STOP PAGE 1 • Fairfax Falls Power Station Lower Pinnacle Formation C19 2. Beaver Meadow Conglomerate C20 3. Pinnacle and Fairfield contact C22 4. Volcanic Breccia of the Pinnacle Formation C24 5. Fairfield Pond Formation C24 6. West Fletcher fault C25 7. Amphibolitic greenstone member of Tibbit Hill C25 8. Tibbit Hill Formation C30 9. Underhill Formation C30 VERMONT GEOLOGICAL SOCIETY BOX 304 MONITPELIER, VERMONT 05602 October 6, 1984 STRATIGRAPHY AND STRUCTURE OF THE CAMELS HUMP GROUP ALONG THE LAMOILLE RIVER TRANSECTS NORTHERN VERMONT Barry Doolan Department of Geology University of Vermont Burlington, Vermont 05405 with additional stops provided by: Timothy Mock and Allen McBean* Department of Geology, University of Vermont INTRODUCTION REGIONAL SETTING OF THE CAMELS HUMP GROUP The purpose of this excursion is to pre- The Camels Hump Group was first defined by sent the stratigraphic and structural relation- Cady (1956) in the Camels Hump quadrangle of Ver- ships of the Camels Hump Group in northern Ver- mont and subsequently subdivided into formations mont. The excursion crosses the Georgia Mountain by Doll and others (1961). The Camels Hump Group anticline and Hinesburg thrust in the Milton 7 1/2 are almost entirely rift related rocks which pre- minute quadrangle, the Enosburg Falls - Fletcher date the development of the passive continental anticline of the Gilson Mountain quadrangle and margin along the ancient "western" boundary the Richford syncline of the Jeffersonville 7 1/2 (present coordinates) of the lapetus Ocean quadrangle. The eastern part of the Jefferson- (Williams and Stevens, 1975). The Group thus ville quadrangle lies just to the west of the includes most of the rocks stratigraphically over- Green Mountain anticlinorium (Fig. 1.) lying the Grenville basement and underlying plat- form slope or rise sequence rocks of the ancient Significant problems to be addressed on margin. this trip are the correlation of stratigraphy and comparisons of structure west and east of the In the western outcrop belts of the Camels Enosburg Falls - Fletcher anticline, correlation Hump Group and correlative lower Oak Hill Group of the Underhill Formation with the established rocks of Quebec (Clark, 1934) the sequence is western stratigraphy, and the origin of the Rich- overlain by rift-drift transition "basal" quartz- ford syncline exposed in the adjacent Jefferson- ites of the Cheshire Quartzite and drift stage ville 7 1/2 minute quadrangle to the east. dolomites, quartzites and carbonate breccias of the shelf and slope facies. To the east the rocks of the Camels Hump Group are overlain by slope and MAPPING AND ACKNOWLEDGMENTS rise facies rocks of the Sweetsburg and Ottauque- chee formations. Significant facies differences The mapping conducted by the author in the on both local and regional scales are noted by Gilson Mountain and Jeffersonville quadrangles previous workers and should be expected in rift during the period of 1985 to the present has been environments both parallel and perpendicular to funded by the Vermont Geological Survey under the the basin. Detailed stratigraphic comparisons of direction of Charles Ratte'. Mapping was done rocks in the rift basin have been hampered by a directly on 1:5000 orthomap aerial photographs and lack of detailed mapping within the Camels Hump compiled at 1:12000. The author has benefited Group and deformation which postdates the forma- from able assistance in the field by students tion of the basin. This excursion attempts to completing field camp projects in the Gilson Moun- detail the stratigraphic relationships of the tain and Jeffersonville quadrangles. The early Camels Hump Group in the vicinity of the Lamoille projects were conducted on 1:12000 enlargements of River transect. the topographic base and include the following students: Dave Marshall, Chris Miksic and Todd The Lamoille River transect from the Worsfold (1982); Debra Merrill, Steve Schope, Milton to the Jeffersonville quadrangle, provides Scott Schulein, and Dan Dowling (1983); Dave an excellent array of exposures which help to Iseri, Doug Friant, Doug Graham, Robert Myers and define the across strike nature of the ancient Jeffrey Slade (1984). Later projects were com- rifted basin. The western sequence of the Camels pleted on the 1:5000 base by Dave Greenwalt, Greg Hump Group displays a thin stratigraphic sequence Koop and Hugh Rose (1985) and Michael Landsman with at least one erosional unconformity and (1986). Peter Thompson's (1975) work in the Enos- rift-drift to platform cover rocks. The eastern burg Falls and Jeffersonville quadrangles is shown sequence involves a greater percentage of volcanic in part in the northeastern corner of Figure 3B. rocks, thicker rift-clastic sequences and slope to The author has also benefited greatly by ongoing rise cover rocks (Fig. 2). The increased rift studies by his graduate students Maurice Colpron related subsidence to the east supports the model and Bill Dowling whose work in the Oak Hill Group of formation of "instantaneous" eastward facing in Quebec has helped to focus on the regional rift basins by lithospheric stretching and Airy- relationships discussed in this report. type subsidence synchronous with rifting (e.g., McKenzie, 1978). 0 Present address: Agency of Transportation Significantly, the Lamoille River section Division of Materials and Research differs in detail from that observed to the north State Street in Quebec (e.g., Clark, 1934; Dowling and others, Montpelier, Vermont 05602 1987; Colpron and others, 1987) and in the Enos- Cl U •-1 o. - — _•S% _/, —- -- —\ •_,_/ ''c' t 2. — — — \ - —171 - ID \•• S. to / 1- - .•S_-_I'S- CD . - •IIII j - — - -. 1,. I - - CA — _\ — — -. ._II (p P •:-'. i — ail I - I -, .IiIIII — I -I\ — -.,' 1•/ CA — I _•_ \' __I 1551 /I "5''/ -- N1 .j I sS 'S.:.. • i 1 II C1 a VT An 1.3 !, 09&ed)C..///" i\\ 5 L' 0 C2 1 • The Tibbit Hill is Interbedded with elastic burg Falls quadrangle (Dennis, 1964). To the rocks in the Enosburg Falls quadrangle (Pinna- south, in the Lincoln Mountain quadrangle, the cle fades of the Tibbit Hill of Dennis, 1964); Camels Hump Group is considerably shortened and only the westernmost and easternmost parts of the 2. The White Brook dolomite is a discontinuous Lamoille River section are lithically comparable. horizon in Vermont and when found does not pre- The missing section to the south lies mostly cisely define the boundary between the equiva- within the Gilson Mountain quadrangle and the lents of the Pinnacle and Fairfield Pond forma- western part of the Jeffersonville quadrangle. tions in Quebec (Booth, 1950; Dennis, 1964). These rocks and their cover presumably have been removed from the Lincoln Mountain area during 3. More coarse-grained conglomeratie facies are allochthon emplacement along thrust faults rooted found in the Pinnacle Formation of Vermont and below and within the Underhill Slice of Stanley an overall increase in thickness of the Pinna- and Ratcliffe (1985; Fig. 1). cle is noted southward (Dowling and others, 1987). STRATIGRAPHY OF THE CAMELS HUMP GROUP 4. The Call Mill Slate, and West Sutton Forma- tion as mapped in Quebec are only locally ALONG THE LAMOILLE RIVER TRANSECT definable in Vermont (Booth, 1950; Dennis, In this section the stratigraphy of the 1964).