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The Bedrock Geology of the Hamburg Quadrangle With Open Map STATE GEOLOGICAL AND NATURAL HISTORY SURVEY OF CONNECTICUT A DIVISION OF THE DEPARTMENT OF AGRICULTURE AND NATURAL RESOURCES The Bedrock Geology of the Hamburg Quadrangle WITH MAP BY LAWRENCE LUNDGREN, JR. University of Rochester 1966 QUADRANGLE REPORT NO. 19 ------ ---------------~----- STATE GEOLOGICAL AND NATURAL HISTORY SURVEY OF CONNECTICUT A DVISION OF THE DEPARTMENT OF AGRICULTURE AND NATURAL RESOURCES HONORABLE JOHN N. DEMPSEY, Governor of Connecticut JOSEPH N. GILL, Commissioner of the Department of Agriculture and Natural Resources COMMISSIONERS HON. JOHN N. DEMPSEY, Governor of Connecticut DR. J. WENDELL BURGER, Department of Biology, Trinity College DR. RICHARD H. GooDWIN, Department of Botany, Connecticut College DR. ]OE WEBB PEOPLES, Department of Geology, Wesleyan University DR. JOHN RODGERS, Deparament of Geology, Yale University DR. JAMES A. SLATER, Department of Zoology and Entomology, University of Connecticut DIRECTOR }OB WEBB PEOPLES, Ph.D. Wesleyan University, Middletown, Connecticut EDITOR MAP EDITOR Lou WILLIAMS PAGE, Ph.D. HENRY R. ALDRICH, Ph.D. DISTRIBUTION AND EXCHANGE AGENT WALTER BRAHM, State Librarian State Library, Hartford 11 TABLE OF CONTENTS Page Absttact 1 Inttoduction .................................................................................................................. 1 Rock units ..................................................................................................................... 3 Descriptive procedures ......................................................................................... 3 Outcrop locations ................................................................................................. 4 Hebron Formation ............................................................................................... 4 Canterbury Gneiss ............................................................................................... 6 Brimfield Formation ............................................................................................. 7 Nomenclature and areal distribution ............................................................ 7 Biotite-muscovite schist (Ohm) ................................................................... 8 Amphibolite (Oba) ............................................................................ 8 Garnetiferous quartz-biotite schist and gneiss (Obqb) ................................. 10 Cale-silicate gneiss ....................................................................................... 10 Biotite-garnet-orthoclase-sillimanite schist (Obm, Ot-b) ............................. 10 Tatnic Hill Formation 10 Areal distribution ........................................................................................ 10 Upper part (Otm, Otcm) ............................................................................ 11 Lower part (Otm) ....... .. ......................................................................... 11 Blastomylonitic rocks ..................................................................................... 13 Rock units in the Hunts Brook syncline (Otm, Otc, Otg, Ot-b) ................. 13 lvoryton Group ................................................................................................... 14 Nomenclature ..................................... .......................................... 14 Middletown Formation (Omig, Omia) ....................................................... 15 Monson Gneiss (Om, Oma, Omga) ........................................................... 16 New London Gneiss ..................................................................................... 17 Areal distribution ................................................................................. 17 Joshua Rock Gneiss Member (nj) ....................................................... 17 Granitic gneisses ( n) ........................................................................... 18 Amphibolite (na) ................................................................................. 18 Section at Hamburg Cove ..................................................................... 18 Section near Cedar Lake ....................................................................... 20 Mamacoke Formation ........................................................................................... 21 Nomenclature ............................................................................................... 21 Candlewood Ledge belt .............................................................................. 21 Beaver Brook belt ........................................................................................ 22 Grassy Hill belt ........................................................................................... 22 Biotitic quartz-feldspar gneiss (mb) ......................................................... .. 22 Cale-silicate ensemble (me) ......................................................................... 24 General description ............................................................................... 24 Amphibolite and calc-silicate rocks (ma) ............................................ 24 Nodular gneiss (mn) ........................................................................... 24 Sillimanitic and garnetiferous biotite schist (ms) .............................. .. 25 Plainfield Formation ............................................................................................. 25 Nomenclature and distribution ..................................................................... 25 Quartzite (pq, pcq) ..................................................................................... 27 Sillimanitic biotite schist (ps) ..................................................................... 28 Garnetiferous biotitic schist and gneiss (pgs) ............................................. 28 iii Nodular gneiss (pen) .................................................................................... 28 Biotitic quartz-feldspar gneiss (pb, pbc) ............................. ........................ 28 Sterling Plutonic Group . .. .. .. 28 Nomenclature ................................................................................................ 28 Biotite granite-gneiss ( sgb) . .. .. .. .. .. .. .. .. .. 29 Hornblende granite-gneiss ( sgb) . .. .. .. .. .. .. .. 29 Alaskite gneiss (sga) .................................................................................... 29 Mixed granite gneisses (sgm) ...................................................................... 29 Pegmatite . .. .. .. .. ... ... .. .. .. .. .. 31 Stratigraphic sequence and age relationships .. .. .. 31 Structural relationships . ... .. .. .. .. .. .. .. .. 34 Bedrock control of topography ...................................................................................... 38 Geologic history ............................................................................................................ 39 Economic geology . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 40 References . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .... .. .. .. 40 ILLUSTRATIONS Page Plate 1. Geologic map of the Hamburg quadrangle (in pocket) Figure 1. Map of Connecticut showing location of the Hamburg quadrangle and of other published quadrangles .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 2 2. The division of the Hamburg quadrangle into ninths .. .. .. .. .. .. .. .. .. .. .. 4 3. Configuration of the surface separating the Ivoryton Group from the mantle of younger rocks ...... ........... ... ................ ........... 35 TABLES Page Table 1. Modal analyses and mineral assemblages of the Hebron Formation .. 5 2. Modal analyses of the Canterbury Gneiss .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ...... 6 3. Modal analyses and mineral assemblages of the Brimfield Formation .. .. .. .. 9 4. Modal analyses of the Tatnic Hill Formation................... .............................. 12 5. Modal analyses and mineral assemblages of the Middletown Formation ...... 15 6. Modal analyses of the Monson Gneiss . ................. .................. 16 7. Modal analyses of the New London Gneiss . ...................... 18 8. Optical properties of the aegerine-augite in the Joshua Rock Gneiss Member of the New London Gneiss . .... ... .. .. ....... .................... 19 9. Modal analyses of the Mamacoke Formation ............... 23 10. Modal analyses of the Plainfield Formation . .. .. .. .. .. .. .. 26 11. Modal analyses of the Sterling Plutonic Group .......................... 30 12. Stratigraphic sequence and possible ages of rock units in the Hamburg quadrangle ............................... 32 iv The Bedrock Geology of the Hamburg Quadrangle by Lawrence Lundgren, Jr. ABSTRACT Bedrock in the Hamburg quadrangle comprises the following units, from oldest to youngest: Plainfield Formation (quartzite, schist, gneiss) ; Mamacoke Formation (schist, marble, cak-silicate rocks, biotitic quartz-feldspar gneiss); Ivoryton Group (new name), which includes the New London Gneiss (granitic gneisses including the Joshua Rock Gneiss Member, an aegerine-augite granite gneiss), the Monson Gneiss (plagioclase-quartz gneiss and alaskite gneiss) , and the Middletown Formation ( anthophyllitic gneiss and amphibo­ lite); Tatnic Hill and Brimfield Formations (laterally equivalent fades of a major biotite­ muscovite schist unit) ; Canterbury Gneiss ( biotitic
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