Gull River Formation

{{Infobox rockunit

| name = Gull River Formation

| image = Gull River formation1.jpg

| caption = Gull River Formation exposed along the shore of Lake St. John, Ramara

| type = Formation

| age = Caradoc
~{{Fossil range|460.9|449}}

| period = Sandbian

| prilithology = Limestone, dolomite

| otherlithology = Shale, sandstone

| namedfor = Gull River

| namedby = V. J. Okulitch

| year_ts = 1939

| region = Ontario
New York
Pennsylvania

| country = Canada
United States

| coordinates =

| unitof = * Simcoe Group

• Black River Group

| subunits =

| underlies = * Bobcaygeon Formation

• Coboconk Formation

| overlies = Shadow Lake Formation

| thickness =

| extent =

| area =

| map =

| map_caption =

}}

The Gull River Formation is a geological formation of Middle Ordovician age (Caradoc Stage), which outcrops in Ontario, Canada.{{cite web|title=Gull River formation|url=http://weblex.nrcan.gc.ca/html/006000/GSCC00053006056.html|publisher=Natural Resources Canada|accessdate=January 4, 2015|date=January 9, 2008}} Lithologically, the formation is dominated by light grey to brown limestones and greenish gray dolomites with thin shale and sandstone interlayers.{{cite book|last1=Armstrong|first1=Derek K.|last2=Dodge|first2=J. E. P.|title=Paleozoic Geology of Southern Ontario|date=2007|publisher=Ontario Geological Survey|isbn=978-1-4249-4526-9|pages=4|url=http://maps.niagararegion.ca/Metadata/md/DocumentUpload/2007-08-08%2014-44-38.pdf}}{{cite book|last1=Armstrong|first1=D. K.|title=Paleozoic Geology of the Northern Lake Simcoe Area, South-Central Ontario|date=2000|publisher=Ontario Geological Survey|isbn=978-0--7778--9451--4|pages=9–15|url=http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/OFR6011/OFR6011.pdf}}