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Conglomerate, sandstone, siltstone, argillite, and melaphyre. Consists of Brookline, Dorchester, and Squantum Members. Roxbury Conglomerate forms base of Boston Bay Group. Divided into Brookline, Dorchester, and Squantum Members. Conglomerate in Brookline Member contains clasts of Dedham Granite, quartzite (possibly from Westboro Formation), and volcanic rock from underlying Mattapan Volcanic Complex. Dorchester Member consists of interbedded argillite and sandstone and forms an intermediate unit between Brookline Member and overlying Cambridge Argillite. Uppermost Squantum Member is a distinctive diamictite which appears to pinch out in northern part of basin. Brighton Melaphyre lies within Brookline Member and consists of mafic volcanic rocks (quartz keratophyre, keratophyre, and spilite). Roxbury clearly lies nonconformably on Dedham Granite near Hull, MA; can be traced continuously over Mattapan Volcanic Complex. Age is Proterozoic Z and possibly Early Cambrian (Goldsmith, 1991).
State |
Massachusetts |
Name |
Roxbury Conglomerate |
Geologic age |
Proterozoic Z to earliest Paleozoic |
Lithologic constituents |
Major
Sedimentary > Clastic > Conglomerate
Sedimentary > Clastic > Sandstone
Sedimentary > Clastic > Siltstone
Minor
Igneous > Volcanic > Mafic-volcanicmelaphyre
Metamorphic > Metasedimentary > Metaclastic > Argillite
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Comments |
Part of Milford-Dedham Zone (Tertiary and Older Rocks). Secondary unit description per MA023. |
References |
Zen, E-An (ed.), Goldsmith, R. (comp.), Ratcliffe, N.M. (comp.), Robinson, P. (comp.), Stanley, R.S. (comp.), Hatch, N.L., Jr., Shride, A.F., Weed, E.G.A., and Wones, D.R., 1983, Bedrock Geologic Map of Massachusetts: U.S. Geological Survey, Reston, VA, scale 1: 250,000.
https://pubs.er.usgs.gov/publication/70046713 Goldsmith, Richard, 1991, Stratigraphy of the Milford-Dedham zone, eastern Massachusetts; an Avalonian terrane, Chapter E, IN Hatch, N.L., Jr., ed., The bedrock geology of Massachusetts: U.S. Geological Survey Professional Paper, 1366-E-J, p. E1-E62.
https://pubs.er.usgs.gov/publication/pp1366EJ
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NGMDB product |
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Counties |
Middlesex - Norfolk - Plymouth - Suffolk
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