Chamberlain's Brook Formation

{{Infobox rockunit

| name = Chamberlain's Brook Formation

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| type = Formation

| age = Middle Cambrian
~{{Geological range|509|506}}

| period = Cambrian

| prilithology = Green, purple and red siliciclastic marine mudstones{{cite journal|doi=10.1666/0022-3360(2002)076<0822:MCASCA>2.0.CO;2|year=2002|volume=76|issue=5|pages=822|title=Middle Cambrian (Acadian Series) Conocoryphid and Paradoxidid Trilobites from the Upper Chamberlain's Brook Formation, Newfoundland and New Brunswick|journal=Journal of Paleontology|last1=Kim|first1=Dong HEE|last2=Westrop|first2=Stephen R.|last3=Landing|first3=ED}}

| otherlithology =

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| region = Atlantic coast

| country = United States
Canada

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| unitof = Adeyton Group{{cite book|url=http://www.nr.gov.nl.ca/nr/mines/geoscience/publications/report06_02.pdf|title=Bedrock Geology of the Cap St. Mary's Peninsula. Southwest Avalon Peninsula, Newfoundland|author=Terrence Patrick Fletcher|date=2006|publisher=Department of Natural Resources Geological Survey Newfoundland Labrador|location=St. John's Newfoundland|isbn=1-55146-031-9}}

| subunits = Fossil Brook Member (and others)

| underlies = Manuels River Formation (unconformably?)

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| thickness = up to {{convert|14|m|ft|abbr=on}}

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| map = Chamberlains Brook Formation map.svg

| map_caption = Occurrence of the Chamberlain's Brook Formation in southeastern Newfoundland

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The Chamberlain's Brook Formation is a thin but distinctive geologic formation of dark red calcareous mudstonesNormore, L. S. 2012: GEOLOGY OF THE RANDOM ISLAND MAP AREA (Nts 2C/04), Newfoundland. Current Research (2012) Newfoundland and Labrador Department of Natural Resources Geological Survey Report 12-:121–145. that crops out from Rhode Island to Massachusetts and, Nova Scotia, New Brunswick and Newfoundland. It preserves fossils, including trilobites, dating back to the lower mid-Cambrian period. Its lowermost member is the Braintree Member (lowest Middle Cambrian) and the uppermost member is the Fossil Brook Member.