GEOLOGIC MAPPING AND THE GENERAL GEOLOGY OF CHATHAM COUNTY Phil Bradley - North Carolina Geological Survey
Why Geologic Mapping in Chatham County? NCGS - Our mission is to provide unbiased and technically accurate applied earth science scientific information to address societal needs. One way we collect geologic data is through the STATEMAP Program: The STATEMAP program is part of the National Geologic Mapping Program - Congressionally mandated program within the USGS. The NCGS receives STATEMAP funds through an annual competitive grant process. The primary objective of the STATEMAP is to establish the geologic framework of areas that are vital to the welfare of individual States.
Available Detailed Geologic Data in the Triangle Area Durham Chapel Hill Raleigh Pittsboro
Uses of Geologic Maps A geologic map records the distribution of rock and soil materials at and near the land surface. Geologic maps constitute a fundamental and objective scientific foundation on which land-use, water-use, and resource-use decisions are based. Examples: -Assist in finding and protecting groundwater resources -Identify potential areas of naturally occurring groundwater contaminants of radon and arsenic. -Transportation planning -Identify areas that may contain potential mineral hazards, such as arsenic, mercury, asbestos, or radon. -Identify potential geologic hazards such as landslides and sinkholes. -Mineral resources, sand and gravel resources, natural gas resources -Etc.
Tools in the Field Hand lens Rock hammer Brunton Compass Field computer Field book Field camera Topographic map Scale bar and photograph identification board
Collecting Geologic Data and Measurements -What are structural features and measurements? Bedding Joints Source of figure - http://earthsci.org/processes/struct/section/strike.gif Some Common Features: Bedding the original layering plane when the material was deposited Foliation planar features commonly formed from the growth of platy minerals during metamorphism Joint a fracture in rock where there has been no movement in the plane of the fracture Fault - a fracture in rock where there has been movement in the plane of the fracture
Making Geologic Maps Detailed Geologic Maps are based on observations and measurements collected in field
What the rocks tell us Central Piedmont Shear Zone
Hyco Volcanic Arc Stage Ca. 633 613 million years ago Sedimentary rocks: conglomerates, sandstone, siltstones, mudstones volcanic rocks (tuffs, lavas) Sedimentary rocks: conglomerates, sandstone, siltstones, mudstones granite, granodiorite, diorite, gabbro.
Lavas associated with the Hyco Volcanic Arc Stage Ca. 633 613 million years ago Haw River and HWY 64 MO-72: Haw River and HWY 64 area MO-422: Haw River and HWY 64 area Lavas Dome in Mt St Helens - USGS Photograph from the Hawaiian Volcano Observatory website - USGS
Tuffs associated with the Hyco Volcanic Arc Stage Ca. 633 613 million years ago PT-762: Robeson Creek PT-762: Robeson Creek PT-890: Pittsboro Christian Village Soufrière Hills: Photo by Richard Heard, 1997 (Montserrat Volcano Observatory). Tuffs (Ash consolidated into rock) USGS Mt. St. Helens
PT-1023: New Judicial Center - Pittsboro MO-272: Haw River near Robeson Ck. USGS Mt. Unzen, Japan Sedimentary rocks from the erosion of volcanic rocks (Volcanosedimentary rocks)
Geologic History of Part of the Carolina Zone Hyco Volcanic Arc Stage Ends Ca. 613 million years ago Hyco Formation Volcanism due to subduction Hyco Volcanic Arc: Deposition of the lower and upper portions of the Hyco Formation Lower portions of Hyco Formation: Ca. 633 629 million years ago Upper portions of Hyco Formation: Ca. 616-613 million years ago Figure modified from: Harris and Glover, 1985 1985 CGS Fieldtrip guidebook
Geologic History of Part of the Carolina Zone Renewed stage of volcanism Aaron Volcanic Arc Stage Begins Ca. 580 million years ago Aaron Formation Volcanics of the Virgilina member of the Aaron Formation Hyco Formation Apparent magmatic hiatus after the deposition of Hyco Formation Erosion of older Hyco Formation rocks and renewed volcanism - Aaron Arc: Deposition of the Aaron Formation and Virgilina member of Aaron Formation (Bowman, 2010) Ca. 588 579 million years ago Figure modified from: Harris and Glover, 1985 1985 CGS Fieldtrip guidebook
Geologic History of Part of the Carolina Zone Renewed stage of volcanism Aaron Volcanic Arc Stage Begins Ca. 580 million years ago Aaron Formation Volcanics of the Virgilina member of the Aaron Formation Hyco Formation Apparent magmatic hiatus after the deposition of Hyco Formation Erosion of older Hyco Formation rocks and renewed volcanism - Aaron Arc: Deposition of the Aaron Formation and Virgilina member of Aaron Formation (Bowman, 2010) Ca. 588 579 million years ago Figure modified from: Harris and Glover, 1985 1985 CGS Fieldtrip guidebook
Farrington pluton Farrington pluton Underlies: Southern Village Fearington Village Governors Club Legend Oaks Etc Ca. 579 million years old granite to diorite body Farrington pluton
Geologic History of Part of the Carolina Zone Aaron Volcanic Arc Stage Ends Sometime after Ca. 579 million years ago Heat and Pressure Virgilina Deformation Volcanics of the Virgilina member of the Aaron Formation Aaron Formation Hyco Formation Volcanic island arc collided with another island chain (perhaps the Charlotte terrane). Layers of tuffs and lavas, sediments and intrusive rocks were folded and weakly metamorphosed. The metamorphism turned the rocks into metatuffs, metamorphosed lavas, metagranodiorite, etc. Occurred sometime between Ca. 579 554 million years ago (Pollock, 2007) Figure modified from: Harris and Glover, 1985 1985 CGS Fieldtrip guidebook
Geologic History of Part of the Carolina Zone Renewed Volcanism Uwharrie Formation and Albemarle Group Rhyodacite domes (like Morrow Mtn.) Aaron Formation Hyco Formation Granites and granodiorites (like Roxboro pluton and Greensboro area) Beginning around Ca. 550 million years ago a new period of volcanism begins (today these rocks are present in the Asheboro and the Uwharrie Mountains (Morrow Mountain). New magma chambers form and feed extrusive volcanics. The new volcanic deposits are built on top of the extinct and deformed Hyco and Aaron Formations. This volcanic and associated deposition period lasts until Ca. 530 million years ago Figure modified from: Harris and Glover, 1985 1985 CGS Fieldtrip guidebook
Geologic History of Part of the Carolina Zone Figure from: Pollock, 2007
Geologic History of Part of the Carolina Zone Carolina Zone in process of colliding with ancient North America (Laurentia). Figure source: NCGS Figure source: Nance and Linnemann, 2008 GSA Today, v. 18, no. 12, doi: 10.1130/GSATG24A.1
Geologic History of Part of the Carolina Zone Heat and Pressure Deformation Uwharrie Formation and Albemarle Group Rhyodacite domes (like Morrow Mtn.) Aaron Formation Hyco Formation Granites and granodiorites (like Roxboro pluton and Greensboro area) Ca. 450 Carolina Zone collides with ancient North America (Laurentia). Layers of tuffs and lavas, sediments and intrusive rocks were folded and weakly metamorphosed. Older Hyco and Aaron Formations rocks were folded more and metamorphosed again. The metamorphism turned the rocks into metatuffs, metamorphosed lavas, metagranodiorite, etc. Figure modified from: Harris and Glover, 1985 1985 CGS Fieldtrip guidebook
PT-890: Pittsboro Christian Village PT-762: Robeson Creek PT-868: Chatham Park land
Geologic History of Part of the Carolina Zone After the Carolina Zone collided with ancient North America (Laurentia): Gondwana was slowing moving toward collision with Laurentia. Ca. 450 320 million years Figure source: Nance and Linnemann, 2008 GSA Today, v. 18, no. 12, doi: 10.1130/GSATG24A.1
Geologic History of Part of the Carolina Zone Ca. 300 million years ago Figure source: Nance and Linnemann, 2008 GSA Today, v. 18, no. 12, doi: 10.1130/GSATG24A.1
Geologic History of Part of the Carolina Zone Intrusion of Rolesvile Batholith and Deformation Rolesville Batholith Ca. 300 million years ago
Geologic History of Part of the Carolina Zone Intrusion of Rolesvile Batholith and Deformation Faults: Strike - Slip Rolesville Batholith Ca. 300 million years ago Figure source: Nance and Linnemann, 2008 GSA Today, v. 18, no. 12, doi: 10.1130/GSATG24A.1
Paleo-reconstruction ca. 240 million years ago Early to Middle Triassic. Source: created by Ron Blakey Northern Arizona University Department of Geology (http://jan.ucc.nau.edu/~rcb7/globaltext2.html) Source: Figure 84. The breakup of Pangaea and the formation of the Mesozoic rift basins. From: http://3dparks.wr.usgs.gov/nyc/mesozoic/mesozoicbasins.htm
Geologic History of Part of the Carolina Zone Begin of rifting of Pangea Jonesboro Fault forms Faults: Strike - Slip Rolesville Batholith Jonesboro Fault: Normal
Geologic History of Part of the Carolina Zone Continued rifting of Pangea Movement on Jonesboro Fault Erosion Faults: Strike - Slip Rolesville Batholith Jonesboro Fault: Normal
Geologic History of Part of the Carolina Zone Continued rifting of Pangea Continued movement on Jonesboro Fault Erosion Triassic basin sediments Fault: Strike - Slip Rolesville Batholith Jonesboro Fault: Normal
Paleo-reconstruction ca. 220 million years ago Late Triassic. Source: created by Ron Blakey Northern Arizona University Department of Geology (http://jan.ucc.nau.edu/~rcb7/globaltext2.html) Source: Figure 84. The breakup of Pangaea and the formation of the Mesozoic rift basins. From: http://3dparks.wr.usgs.gov/nyc/mesozoic/mesozoicbasins.htm
What would it have looked like looking East across the Jonesboro fault? (or West across the Chatham fault in the Dan River basin?) conglomeratic alluvial fans Fault trace View to east of alluvial fans fringing Lost River Mountains as seen from Burma Road above Mackay, Idaho, U.S.A. Source: http://www.gly.uga.edu/railsback/fieldimages/lostriveralluvialfans1.jpeg Badwater alluvial fan in Death Valley. Photo from NPS archives. http://geomaps.wr.usgs.gov/parks/deva/rfan.html
Artist rendition of flora and fauna of the Triassic basins. From the News and Observer Newspaper - Triassic Triangle poster. Dinosaurian footprints from the Sanford Triassic basin, NC. Photographs A and B from Olsen and Huber 1998. Roman numerals in A indicate nomenclature of animal s digits. Scale bar is 5 cm.
MO-543: Triassic sandstones - Stinking Creek area MO-454: Triassic Conglomerates on Jordan Lake MO-454: Triassic Conglomerates on Jordan Lake
Geologic History of Part of the Carolina Zone Continued rifting of Pangea Continued movement on Jonesboro Fault Erosion West Intrusion of diabase East Pittsboro Triassic basin sediments Cary Fault: Strike - Slip Raleigh Rolesville Batholith Jonesboro Fault: Normal
DIABASE INTRUDES THE PIEDMONT During the Jurassic (approximately 195-205 million years ago) dikes and sills of mafic composition intruded the sediments of the Triassic Basin and surrounding crystalline rocks. Diabase dike
Paleo-reconstruction ca. 200 million years ago Early Jurassic. Source: created by Ron Blakey Northern Arizona University Department of Geology (http://jan.ucc.nau.edu/~rcb7/globaltext2.html)
Paleo-reconstruction ca. 150 million years ago Late Jurassic. Source: created by Ron Blakey Northern Arizona University Department of Geology (http://jan.ucc.nau.edu/~rcb7/globaltext2.html) Source: Figure 84. The breakup of Pangaea and the formation of the Mesozoic rift basins. From: http://3dparks.wr.usgs.gov/nyc/mesozoic/mesozoicbasins.htm
Central Piedmont Shear Zone
Generalized block diagram showing hydrogeology of the Atlantic Coastal Plain, North and South Carolina. Source: Campbell, B.G., and Coes, A.L., eds., 2010, Groundwater availability in the Atlantic Coastal Plain of North and South Carolina: U.S. Geological Survey Professional Paper 1773, 241 p., 7 pls.
Chatham County Potential Time Table for Detailed Geologic Mapping Completed July 2010 June 2011 Liberty Crutchfield Crossroads Silk Hope Bynum 2012-2013 Farrington 2006-2007 Greenlevel 1996 Coleridge Siler City Siler City NE Pittsboro Merry Oaks In Progress (Portion) In Progress (Portion) New Hill Completed Bennett Bear Creek Goldston Colon Moncure Cokesbury 1994
NCGS Collected Data 2011 2012 Through 4/13/2012 Pittsboro and Merry Oaks Quadrangles
Source: NCGS, 1985