HISTORICAL GEOLOGY LECTURE 1. STRATIGRAPHY 1 Stratigraphy: Many past geologic events have resulted in strata or layers of sediment which have formed a stacked vertical sequence of sedimentary rocks. A good example is sediment in the form of mud and sand from a river accumulating on a sea-floor. The sediment forms a layer which eventually becomes or lithified into a sedimentary rock. Harry Williams,hardened Historical Geology The importance of stratigraphic sequences to historical geology is that they provide a rock record of past events e.g. a pebbly beach may be recorded as a CONGLOMERATE, a sandy river may be recorded as a layer of SANDSTONE; a clayey tidal flat as a layer of SHALE. Pebbly beach conglomerate Harry Williams, Historical Geology 2 3 Sandy beach Harry Williams, Historical Geology sandstone 4 Muddy marsh shale Harry Williams, Historical Geology Stratigraphy is the study of these layered rocks, especially their sequence, correlation from place to place, relative ages and interpretation. Several important stratigraphic principles emerged from the study of stratigraphy centuries ago by the early founders of the science of geology: Harry Williams, Historical Geology 5 6 Harry Williams, Historical Geology 1. Principle of Superposition: In any sequence of undisturbed strata, the oldest layer is at the bottom and higher layers are successively younger. 7 Harry Williams, Historical Geology 2. Principle of Original Horizontality: Most sedimentary rocks formed originally in close-to-horizontal layers (although many have since been moved from their original position). Undeformed strata Deformed strata (tilted) Harry Williams, Historical Geology 8 "The present is the key to the past" i.e. geologic processes operating today also operated in the past. e.g. river deposits forming today have a similar composition and character as their ancient counterparts; glacial erosional and depositional features are basically the same today as in the past...etc. Modern sand dune Harry Williams, Historical Geology Ancient sand dune 9 RESEARCH EARTH SCIENCE: EXAMPLE INFORMATION BEREA SANDSTONE History and description of the age of the of the sandstone you select Berea Sandstone AGE: Late Devonian – 416.0 to 359.2million years ago (mya) The Berea Sandstone formed from ancient streams in Canada that flowed to and filled ancient and stagnant (non-flowing) seas that sat over the states of West Virginia, Michigan, Ohio and Pennsylvania. Through this process, the ancient streams traveling south from the Canadian Shield dropped off sediments into the shallow seas located in what are now parts of the above states. When the seas eventually regressed (went away) due to climate and the building of the Acadia mountains to the east due to plate tectonics, the shallow seas disappeared and what were left were the rock layers such as the Berea Sandstone that had been deposited years earlier. Description of the formation (location, size, type of sandstone) • The Berea Sandstone is located throughout 4 states KY,MI,OH,WV and covers near 50,000 square feet. • Berea sandstone is a rock layer is a member of a number ofrock formations in the northeastern United States. It exists in the following formations • Berea Sandstone of Pocono Group (WV) Berea Sandstone of Waverly Group (OH) Berea Formation (MI) Berea Member of Pocono Sandstone (KY) Berea Member of Chattanooga Shale (KY) • The Berea Sandstone is a fine-grained quartz based sandstone. • It is primarily made of the following minerals: • 88.9% Quartz • 3.9% Cay • 3.4% Feldspar What have humans used the sandstone for as a resource? • Has been used for decades as an oil and gas producing formation in the states of Kentucky, Ohio, and Michigan • Berea Sandstone has been used as a building material; it has angular, opposed to rounded grains which makes it a strong abrasive. It has been used for buildings, sidewalks, foundations and bridges. • It has been famously used as a gridstone due to its consistent sandstone texture. Porosity and permeability of the sandstone What is Porosity and Permeability? • Porosity: consists of the tiny spaces in the rock that hold the oil or gas. • Permeability: is a characteristic that allows the oil and gas to flow through the rock. • Porosity: 2 studies conducted have shown that the Berea Sandstone has an average porosity of 22-23% (Zhan, 2010) • Permeability: Semi-permeable. At a 22-23% porosity, Berea is somewhat permeable and is capable on holding gas and oil. Types of fossils present • The Berea Sandstone does not contain many fossils due to the sandstone depositing during the late Devonian. • The Berea was deposited in an ancient, shallow ocean that was murky and did not have a flow (stagnant). Due to the environment of these anciet oceans, it was not a substantial environment for organism to thrive in. References 1. 2. 3. 4. 5. Berea Historical Society. Berea Historical Society, n.d. Web. 13 Sept. 2015. <http://www.bereahistoricalsociety.org/site/Sandstone.aspx>. Ohio History Central. Ohio History Connection, n.d. Web. 13 Sept. 2015. <http://www.ohiohistorycentral.org/w/Bedrock_Geology_of_Ohio>. Zhan, Xin, Lawrence M. Schwartz, M. Nafi Toksoz, Wave C. Smith, and F. Dale Morgan. “Pore-Scale Modeling of Electrical and Fluid Transport in Berea Sandstone.” GEOPHYSICS 75, no.5 (September 2010): F135–F142. © 2010 Society of Exploration Geophysicists National Geologic Map Database. U.S. Department of the Interior | Geological Survey, 15 July 2015. Web. 13 Sept. 2015. <http://ngmdb.usgs.gov/Geolex/Units/Berea_413.html>. Craig, Lawrence C. "Paleotectonic Investigations of the Mississippian System in the United States." Geological Survey Professional Paper(n.d.): 45+. Web. 13 Sept. 2015.