The Boyle Formation consists principally of cherty limestones / dolostones. Chert nodules can be cored by visible sponge fossils.
Stratigraphy: Casey Member, Boyle Formation, Givetian Stage, upper Middle Devonian
Locality: Drowning Creek West outcrop - roadcut along the northern side of Route 52, ~1.2 miles west of Drowning Creek, far-eastern Madison County, east-central Kentucky, USA
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Info. at:
Schieber, J. & R. Lazar (eds.). 2004. Devonian black shales of the eastern U.S. New insights into sedimentology and stratigraphy from the subsurface and outcrops in the Illinois and Appalachian Basins. Field Guide for the 2004 Annual Field Conference of the Great Lakes Section of SEPM. Indiana Geological Survey Open-File Study 04-05. 90 pp.
Tags: chert nodule nodules limestone Boyle Formation Casey Member Drowning Creek roadcut Estill County Kentucky
The structure below the camera lens cap is a stylolite, a pressure dissolution feature that frequently has the appearance of a hospital EKG reading. These occur in many limestones, dolostones, and marbles, especially in or near orogenic belts.
The host rock here is limestone, a biogenic sedimentary rock composed of calcite (CaCO3 - calcium carbonate). Most limestones form in ancient, warm, shallow ocean environments.
Stratigraphy: Casey Member, Boyle Formation, Middle Devonian
Locality: Drowning Creek West roadcut, eastern Kentucky, USA
Tags: stylolite stylolites limestone limestones Casey Member Boyle Formation Devonian Drowning Creek West roadcut Kentucky
Weathered shales unconformably overlying dolostone in the Devonian of Kentucky, USA.
The upper part of this overgrown roadcut consists of weathered dark shales of the Portwood Member, an offshore marine succession at the base of the New Albany Shale / Ohio Shale. The lower Portwood has linguloid and orbiculoid brachiopods and Zoophycos trace fossils. Intervals with deformed bedding interpreted as seismites are present in the lower Portwood. The base of the middle Portwood is an unconformity. The basal bed of the middle Portwood is a dolostone with a burrowed lower surface. Brachiopods identical to forms in the Tully Limestone of New York State occur in the middle Portwood.
The lower part of the cut consists of carbonates (less than 1 meter thick) that are the lateral equivalent of the Beechwood Member of the North Vernon Limestone (= Middle Devonian crinoidal limestones). At this site, the equivalent beds are called the Boyle Dolomite or Boyle Formation.
Stratigraphy: Portwood Member of the basal New Albany Shale / Ohio Shale (middle Polygnathus varcus zone, Givetian Stage, upper Middle Devonian) over the Beechwood Member of the Boyle Dolomite / Boyle Formation (lower Polygnathus varcus zone, Givetian Stage, upper Middle Devonian)
Locality: Waco Cut - roadcut along the northern side of Route 52, ~0.2 miles east of the Route 52-Route 977 intersection at the town of Waco, eastern Madison County, east-central Kentucky, USA (37˚ 44.471’ North latitude, 84˚ 08.566’ West longitude)
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Info. at:
Schieber, J. & R. Lazar (eds.). 2004. Devonian black shales of the eastern U.S. New insights into sedimentology and stratigraphy from the subsurface and outcrops in the Illinois and Appalachian Basins. Field Guide for the 2004 Annual Field Conference of the Great Lakes Section of SEPM. Indiana Geological Survey Open-File Study 04-05. 90 pp.
Tags: Boyle Dolomite dolostone Formation Portwood Member New Albany Shale Ohio Devonian Givetian Waco Roadcut cut Madison County Kentucky Beechwood
Weathered shales unconformably overlying dolostone in the Devonian of Kentucky, USA.
The upper part of this overgrown roadcut consists of weathered dark shales of the Portwood Member, an offshore marine succession at the base of the New Albany Shale / Ohio Shale. The lower Portwood has linguloid and orbiculoid brachiopods and Zoophycos trace fossils. Intervals with deformed bedding interpreted as seismites are present in the lower Portwood. The base of the middle Portwood is an unconformity. The basal bed of the middle Portwood is a dolostone with a burrowed lower surface. Brachiopods identical to forms in the Tully Limestone of New York State occur in the middle Portwood.
The lower part of the cut consists of carbonates (less than 1 meter thick) that are the lateral equivalent of the Beechwood Member of the North Vernon Limestone (= Middle Devonian crinoidal limestones). At this site, the equivalent beds are called the Boyle Dolomite or Boyle Formation.
Stratigraphy: Portwood Member of the basal New Albany Shale / Ohio Shale (middle Polygnathus varcus zone, Givetian Stage, upper Middle Devonian) over the Beechwood Member of the Boyle Dolomite / Boyle Formation (lower Polygnathus varcus zone, Givetian Stage, upper Middle Devonian)
Locality: Waco Cut - roadcut along the northern side of Route 52, ~0.2 miles east of the Route 52-Route 977 intersection at the town of Waco, eastern Madison County, east-central Kentucky, USA (37˚ 44.471’ North latitude, 84˚ 08.566’ West longitude)
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Info. at:
Schieber, J. & R. Lazar (eds.). 2004. Devonian black shales of the eastern U.S. New insights into sedimentology and stratigraphy from the subsurface and outcrops in the Illinois and Appalachian Basins. Field Guide for the 2004 Annual Field Conference of the Great Lakes Section of SEPM. Indiana Geological Survey Open-File Study 04-05. 90 pp.
Tags: Boyle Dolomite dolostone Formation Portwood Member New Albany Shale Ohio Devonian Givetian Waco Roadcut cut Madison County Kentucky Beechwood
Wallbridge Unconformity in Kentucky, USA.
The rocks in the upper part of the picture are cherty limestones of the Middle Devonian Boyle Formation. The gray rocks in the lower part of the picture are the Lower Silurian Estill Shale (also known as the Crab Orchard Shale). The entire Upper Silurian and Lower Devonian are missing at the contact, representing about 40 to 50 million years.
The Boyle-Estill contact is a megasequence boundary called the Wallbridge Unconformity - it's the Tippecanoe-Kaskaskia Megasequence boundary. Regionally recognizable packages of sedimentary rocks bounded by major unconformities are known as megasquences, or Sloss sequences (named after geologist L.L. Sloss, 1913-1996). The bounding unconformities were caused by erosion during regressions. Continental margins have more complete sedimentary successions, whereas craton interiors have more incomplete successions. The names for North America's megasequences are (from oldest to youngest): Sauk, Tippecanoe, Kaskaskia, Absaroka, Zuni, and Tejas.
Stratigraphy: Casey Member of the Boyle Formation (Middle Devonian) over the Estill Shale (Lower Silurian)
Locality: Drowning Creek West outcrop - roadcut along the northern side of Route 52, ~1.2 miles west of Drowning Creek, far-eastern Madison County, east-central Kentucky, USA
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Info. at:
Schieber, J. & R. Lazar (eds.). 2004. Devonian black shales of the eastern U.S. New insights into sedimentology and stratigraphy from the subsurface and outcrops in the Illinois and Appalachian Basins. Field Guide for the 2004 Annual Field Conference of the Great Lakes Section of SEPM. Indiana Geological Survey Open-File Study 04-05. 90 pp.
Tags: Boyle Formation Dolomite Crab Orchard Estill Shale Devonian Silurian unconformity unconformities disconformity disconformities Drowning Creek West roadcut Tippecanoe Kaskaskia Megasequence megasequences boundary contact contacts boundaries Madison County Kentucky Wallbridge