Download Notes - Rock Formation and Age File

FOSS: Earth History Geological Time •  The earth is es7mated to be about 4.5 billion years old. Our knowledge of its history comes from a number of sources. The geologic 7me scale is constructed through scien7fic methods and calcula7ons as well as from the interrela7onships of geological features as observed in the field. The principle of uniformitarianism (“the present is the key to the past”) is helpful in that we can accurately measure the rates of geologic processes we see today and apply them to the geologic past. •  For example, we know layers of sediment build up on the ocean floor at the rate of about 1 millimeter per year. Thus, it would take over one million years of sedimenta7on to form a unit of shale 1,000 meters thick. Evidence of the dynamic changes of Earth’s surface through 7me is found in the geologic record. Earth is approximately 4.6 billion years old. Earth history is based on observa7ons of the geologic record and the understanding that processes observed at present day are similar to those that occurred in the past (uniformitarianism). There are different methods to determine rela7ve and absolute age of some rock layers in the geologic record. Within a sequence of undisturbed sedimentary rocks, the oldest rocks are at the boRom (superposi7on). The geologic record can help iden7fy past environmental and climate condi7ons. Uniformitarianism “the present is the key to the past” •  the concept that the earth's surface was shaped in the past by gradual processes, such as erosion, and by small sudden changes, such as earthquakes, of the type ac7ng today. Law of Superposi7on •  the principle that in any sequence of sedimentary rocks which has not been disturbed, the oldest strata lie at the boRom and the youngest at the top Law of CrosscuWng •  if a fault or other body of rock cuts through another body of rock then it must be younger in age than the rock through which it cuts and displaces. These are thin syenite dikes that cut a fine-­‐grained gabbro, clearly aYer the gabbro was solid. The Law of Original Horizontality •  layers of sediment were originally deposited horizontally under the ac7on of gravity. •  The forces of nature beat up on the earth and break it into small pieces (weathering), which then wash down rivers (erosion) to the ocean and seRle out on the seafloor, in horizontal layers. Lots of excep7ons here! i.e. sand may be deposited at angles up to 15 degrees. Law of Lateral Con7nuity •  states that layers of sediment ini7ally extend laterally in all direc7ons; in other words, they are laterally con7nuous. As a result, rocks that are otherwise similar, but are now separated by a a valley or other erosional feature, can be assumed to be originally con7nuous. STATE OF OHIO
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DEPARTMENT OF NATURAL RESOURCES
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DIVISION OF GEOLOGICAL SURVEY
BEDROCK GEOLOGIC MAP OF OHIO
ASHTABULA
A
LUCAS
FULTON
WILLIAMS
LAKE
OTTAWA
GEAUGA
WOOD
HENRY
DEFIANCE
SANDUSKY
PAULDING
SENECA
TRUMBULL
CUYAHOGA
ERIE
LORAIN
PORTAGE
PUTNAM
HURON
MEDINA
SUMMIT
HANCOCK
MAHONING
VAN WERT
CRAWFORD
WYANDOT
RICHLAND
ASHLAND
WAYNE
STARK
ALLEN
COLUMBIANA
Glacial
Margin
HARDIN
MERCER
CARROLL
MARION
AUGLAIZE
LOGAN
SHELBY
HOLMES
MORROW
TUSCARAWAS
KNOX
UNION
JEFFERSON
COSHOCTON
DELAWARE
HARRISON
DARKE
LICKING
CHAMPAIGN
GUERNSEY
MIAMI
MADISON
BELMONT
MUSKINGUM
FRANKLIN
CLARK
PREBLE
FAIRFIELD
MONTGOMERY
GREENE
PERRY
NOBLE
PICKAWAY
MONROE
MORGAN
FAYETTE
WARREN
BUTLER
HOCKING
CLINTON
WASHINGTON
ROSS
ATHENS
VINTON
HIGHLAND
HAMILTON
A'
CLERMONT
PIKE
MEIGS
JACKSON
(cross section only)
Permian-Pennsylvanian
Serpent Mound
Impact Structure
BROWN
Key
Quaternary
ADAMS
GALLIA
SCIOTO
Pennsylvanian
Mississippian
Serpent Mound
Impact Structure
Devonian
PIKE
LAWRENCE
Silurian
Ordovician
ADAMS
ND
HIGHLA
Ordovician-Cambrian
(cross section only)
0
10
20
30
40 miles
Neoproterozoic
(cross section only)
0
10 20 30 40 50 kilometers
Mesoproterozoic
(cross section only)
Fault
1 mi
MICHIGAN BASIN
BELLEFONTAINE
OUTLIER
Glacial Margin
APPALACHIAN BASIN
A'
Bend in
section
A
GRANITE-RHYOLITE
PROVINCE
EAST CONTINENT RIFT BASIN
GRENVILLE PROVINCE
Recommended citation: Ohio Division of Geological Survey, 2006, Bedrock geologic map of Ohio: Ohio Department of Natural Resources, Division of Geological Survey Map BG-1, generalized page-size version with text, 2 p., scale 1:2,000,000.
This map is a generalization of the Bedrock Geologic Map of
Ohio (Slucher and others, 2006)—the first statewide 1:500,000-scale
bedrock-geology map compiled by the Ohio Division of Geological
Survey since 1920 and the first to properly portray the bedrock
geology that exists beneath the extensive deposits of Quaternary
sediments that cover much of the bedrock in the state. Overall,
the bedrock geology of Ohio consists of flat lying to gently dipping
carbonate, siliciclastic, evaporite, and organoclastic strata of sedimentary origin that range in age from Upper Ordovician to Upper
Carboniferous-Lower Permian. At depth, as illustrated in the cross
section, older sedimentary, igneous, and metamorphic rocks that
range from Lower Ordovician to Mesoproterozoic in age occur. At
the surface, an irregular veneer of mainly unconsolidated Quaternary sediments conceal most bedrock units occurring northward
and westward of the glacial margin.
Strata of the Ordovician System are the oldest exposed rocks
in Ohio and consist mainly of alternating shale and limestone sequences. Silurian System strata are mostly dolomites with lesser
amounts of shale. Rocks of the Devonian System consist of two contrasting types. Lower and Middle Devonian-age strata are mainly
carbonate rocks whereas Upper Devonian-age rocks consist mostly
of clastic rocks. In Champaign and Logan Counties, Devonian rocks
occur on a small erosional remnant referred to as the Bellefontaine
Outlier by geologists. Coincidentally, the highest topographic point
in Ohio (Campbell Hill–1,549 feet above sea level) occurs also in
this area.
The Carboniferous System is divided into two Subsystems, the
Mississippian and Pennsylvanian. Mississippian strata are mostly
shales and sandstones that occur locally in various proportions.
Pennsylvanian strata consist mainly of a diverse array of alternating sandstones, siltstones, shales, mudstones, limestones, and underclays; economic coal beds occur also in portions of this sequence.
The youngest interval of sedimentary rocks in Ohio, the Dunkard
Group, occurs only in southeastern Ohio and consists of strata
similar in composition to the underlying Upper Pennsylvanianage rocks; however, the age of the Dunkard Group has been debated since the late 1800s. Dunkard strata contain a well-studied
late Pennsylvanian-age assemblage of plant fossils with infrequent
early Permian-age forms. Yet, fossil plant spores found in coal beds
in the interval only support a late, but not latest Pennsylvanian
age. Thus, until more definitive fossils are found, geologist are unable to determine the exact age of the Dunkard Group beyond a
combined Permian-Pennsylvanian age assignment.
In west-central Ohio, the ancient Teays River system extended
across much of Ohio during the late Neogene to early Quaternary
Periods and sculptured an extensive network of deeply dissected
valleys into the bedrock surface. The spatial configuration of many
geologic units on this map clearly reflects the major channel networks of these former drainage systems. Also, four major regional
structural geology elements affect the spatial distribution of rocks
in Ohio: the Appalachian and Michigan basins, and the Cincinnati
and Findlay arches which occur between the two basins. Locally,
several high-angle normal faults displace rocks in the state.
The Serpent Mound Impact Structure in southern Ohio is a
circular area of deformed and broken rocks that is approximately
four and one-half miles in diameter. Recent investigations indicate
the feature is the result of a meteorite impact believed to have occurred between 256 and 330 million years ago.
Cross section A-A' traverses Ohio from the northwest to the
southeast and intersects the southern portion of the Michigan Basin, the area between the Cincinnati and Findlay arches, and the
western Appalachian Basin, respectively. The stratigraphic units
shown in this profile illustrate the broad, arching geometric distortion to the bedrock in Ohio created mainly by periods of tectonic
subsidence within these regional structural basins. For specific
details on the various rock units, economic commodities, and geologic hazards within Ohio, see either the printed or digital version
of the Bedrock Geologic Map of Ohio (Slucher and others, 2006).
Both products are available for purchase by contacting the ODNR
Geologic Records Center by calling 614-265-6576 or emailing:
[email protected].
Quaternary (about 1.8 million years ago to present)—Unconsolidated sediments: till, gravel, sand, silt, clay, and organic
debris. Continental origin. (Shown in cross section only)
Period of widespread erosion
Permian and Pennsylvanian (about 298 to 302 million years
ago)—Sedimentary rocks: mainly shale, sandstone, siltstone,
mudstone, and minor coal. Continental origin.
Pennsylvanian (about 302 to 307 million years ago) Sedimentary rocks: mainly shale, sandstone, siltstone, mudstone, limestone, and some coal. Continental and marine origin.
Pennsylvanian (about 307 to 318 million years ago)—Sedimentary rocks: mainly sandstone, siltstone, shale, and conglomerate, with some coal and limestone. Deltaic and marine origin.
Period of widespread erosion
Mississippian (about 322 to 359 million years ago)—Sedimentary rocks: sandstone, shale, siltstone, conglomerate, and minor limestone. Marine to marginal marine origin.
Devonian (about 359 to 385 million years ago)—Sedimentary
rocks: mainly shale and siltstone with some sandstone. Marine to marginal marine origin.
Devonian (about 385 to 407 million years ago)—Sedimentary
rocks: mainly limestone and dolomite with some shale, and
minor sandstone. Marine and eolian origin.
Period of widespread erosion
Silurian (about 416 to 423 million years ago)—Sedimentary
rocks: dolomite, anhydrite, gypsum, salt, and shale. Marine
and restricted marine origin.
Silurian (about 423 to 435 million years ago)—Sedimentary
rocks: dolomite and shale with some limestone. Marine origin.
Period of widespread erosion
Ordovician (about 446 to 450 million years ago)—Sedimentary
rocks: shale and limestone. Marine origin.
Ordovician (about 450 to 460 million years ago)—Sedimentary
rocks: limestone and shale. Marine origin.
Period of widespread erosion
Ordovician and Cambrian (about 486 to 510 million years ago)—
Sedimentary rocks: mainly dolomite, sandstone, shale, with minor limestone. Marine origin. (Shown in cross section only)
Period of widespread erosion
Neoproterozoic (between 900 million and 1 billion years
ago)—Metamorphic rocks: gneiss, schist, amphibolite, and
marble; and igneous rocks: granite. Form during collision of
tectonic plates. (Shown in cross section only)
Mesoproterozoic (between 1.0 and 1.2 billion years ago)—Sedimentary rocks: sandstone and siltstone; and igneous rocks: basalt and rhyolite. Form during rifting of continental landmass.
(Shown in cross section only)
Period of widespread erosion
Mesoproterozoic (between 1.45 and 1.52 billion years ago)—Igneous rocks: granite and rhyolite. Formed during crustal evolution and differentiation. (Shown in cross section only)
Geologists recognize two different kinds of 7me: rela7ve 7me and absolute age. Rela7ve 7me concerns the sequence of geologic events, and absolute age measurements concern the actual age of a rock or mineral. Rela7ve Da7ng •  Principles Of Rela7ve Age Rela7ve da7ng doesn't really give us an actual 'age,' but it does put things in sequen7al order. This allows geologists to determine the age of a rock or strata rela7ve to another rock or strata. So instead of saying 'when' something happened, it puts events in the 'order' they happened. It's basically the difference between saying 'I'm 25 years old and my sibling is 20 years old' and 'I'm older than my sibling.' Geologists use a variety of techniques, or principles, to determine the rela7ve age of a rock unit. Absolute Age •  Absolute da7ng is the process of determining an approximate computed age in archaeology and geology. •  Absolute da7ng provides a computed numerical age in contrast with rela7ve da7ng which provides only an order of events. Radiometric Da7ng •  Geologists use radiometric da7ng to es7mate how long ago rocks formed, and to infer the ages of fossils contained within those rocks. Radioac7ve elements decay. The universe is full of naturally occurring radioac7ve elements. Radioac7ve atoms are inherently unstable; over 7me, radioac7ve “parent atoms” decay into stable “daughter atoms.” •  When molten rock cools, forming what are called igneous rocks, radioac7ve atoms are trapped inside. AYerwards, they decay at a predictable rate. By measuring the quan7ty of unstable atoms leY in a rock and comparing it to the quan7ty of stable daughter atoms in the rock, scien7sts can es7mate the amount of 7me that has passed since that rock formed. Radiometric Da7ng Carbon •  hRp://vertpaleo.org/The-­‐Society/blog-­‐
oldbones/Old-­‐Bones-­‐Blog/September-­‐2013/
Romancing-­‐the-­‐isotopes-­‐-­‐radiometric-­‐
da7ng.aspx Luminescence Da7ng •  thermoluminescence, emission of light from some minerals and certain other crystalline materials. The light energy released is derived from electron displacements within the crystal laWce of such a substance caused by previous exposure to high-­‐energy radia7on. Hea7ng the substance at temperatures of about 450° C (842° F) and higher enables the trapped electrons to return to their normal posi7ons, resul7ng in the release of energy. The intensity of the emission can be correlated to the length of 7me that a given substance was exposed to radia7on; the longer the 7me allowed for the radia7on to build up an inventory of trapped electrons, the greater the energy released. Because of this feature, thermoluminescence has been exploited as a means of da7ng various minerals and archaeological ar7facts. Thermoluminescence Da7ng •  Video Rela7ve Age of Sedimentary Rocks •  Website •  •  Bracke7ng the fossils Fossils are generally found in sedimentary rock—not igneous rock. Sedimentary rocks can be dated using radioac7ve carbon, but because carbon decays rela7vely quickly, this only works for rocks younger than about 50 thousand years. •  So in order to date most older fossils, scien7sts look for layers of igneous rock or volcanic ash above and below the fossil. Scien7sts date igneous rock using elements that are slow to decay, such as uranium and potassium. By da7ng these surrounding layers, they can figure out the youngest and oldest that the fossil might be; this is known as “bracke7ng” the age of the sedimentary layer in which the fossils occur. Fun Facts About Ohio'S Geological History •  Fun Facts About Ohio'S Geological History 1. The oldest exposed rocks found in Ohio were deposited here 470 million years ago. 2.  Flint is the official gemstone of Ohio. It originated in sea sponges that fell to the sea floor in pre-­‐historic 7mes. The sponges' openings were filled with mud or sand and then compressed over 7me. Flint was used by Na7ve Americans to shape spear points, knives and other tools. 3.  Want to collect a million seashells? Pick up a piece of limestone rock. Limestone was formed from the remains of seashells. Many pres7gious and architecturally significant buildings and monuments in Ohio are made from limestone. 4.  The trilobite Isotelus is Ohio's state fossil. Many states have a state fossil. 5.  Sandstone found in Ohio's Berea layer of the earth is known for three amazing things. First, it holds oil between its course grains. (Oil is a substance formed by sea creatures that decomposed in the absence of oxygen.) By 1886 more that 2,000 wells were drilled in eastern Ohio. Second, sandstone is a perfect material to make grindstones. In the 1870s, the Berea layer produced more than 75 percent of the world's en7re supply. Grindstones were shipped to Australia, Japan and South America. Third, buildings throughout North American are made from this important stone. Fun Facts About Ohio'S Geological History 6. 
More than 80 percent of the electricity Ohioans use is made by burning coal, a fossil fuel. 7.  About 290 million years ago a huge rock from space cashed into what is now Adams County in southern Ohio, shaRering rocks in a five mile diameter. Rock layers at the center were pushed into the earth and then bounced back up. Those forma7ons are now a 1,000 feet above their original posi7on. 8.  Much to the disappointment of grade-­‐school dinosaur lovers everywhere in Ohio, the state can't boast of any dinosaur bones or fossils found here. During the age of dinosaurs, massive erosion occurred here, preven7ng bones from being buried and turning into fossils. But we have great trilobite fossils. 9.  Mammoths and mastodons, two elephant-­‐like creatures, roamed Ohio during the Ice Age. 10.  The rare and endangered Lakeside Daisy grows in only a few loca7ons near the Great Lakes shores of the United States and Canada. The plant can be seen at the Lakeside Daisy State Nature Preserve on the Marblehead Peninsula on Lake Erie. The flower grows on an alvar, a shallow soil system over limestone. • 
(SOURCE: Ohio Governor's Residence and Heritage Gardens; Geologic Walk Guide and Companion Educa7onal Materials) Ohio's Geologic Periods •  hRp://www.ohiohistorycentral.org/w/
Ohio's_Geologic_Periods?rec=1380