The geology of
Ohio
Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The sta ...
formed beginning more than one billion years ago in the
Proterozoic eon of the
Precambrian. The igneous and metamorphic crystalline basement rock is poorly understood except through deep boreholes and does not outcrop at the surface. The basement rock is divided between the Grenville Province and Superior Province. When the Grenville Province crust collided with Proto-North America, it launched the
Grenville orogeny
The Grenville orogeny was a long-lived Mesoproterozoic mountain-building event associated with the assembly of the supercontinent Rodinia. Its record is a prominent orogenic belt which spans a significant portion of the North American continent, f ...
, a major mountain building event. The Grenville mountains eroded, filling in rift basins and Ohio was flooded and periodically exposed as dry land throughout the
Paleozoic
The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon.
The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838
by combining the Greek words ''palaiós'' (, "old") and ' ...
. In addition to marine carbonates such as
limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
and
dolomite Dolomite may refer to:
*Dolomite (mineral), a carbonate mineral
*Dolomite (rock), also known as dolostone, a sedimentary carbonate rock
*Dolomite, Alabama, United States, an unincorporated community
*Dolomite, California, United States, an unincor ...
, large deposits of
shale and sandstone formed as subsequent mountain building events such as the
Taconic orogeny
The Taconic orogeny was a mountain building period that ended 440 million years ago and affected most of modern-day New England. A great mountain chain formed from eastern Canada down through what is now the Piedmont of the East coast of the Unit ...
and
Acadian orogeny led to additional sediment deposition. Ohio transitioned to dryland conditions in the
Pennsylvanian, forming large coal swamps and the region has been dryland ever since. Until the
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...
glaciations erased these features, the landscape was cut with deep stream valleys, which scoured away hundreds of meters of rock leaving little trace of geologic history in the
Mesozoic
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
and
Cenozoic.
Stratigraphy, Tectonics & Geologic History
The oldest igneous and metamorphic rocks in Ohio date to the
Precambrian. They remain poorly understood, except for a few deep boreholes. Central and eastern Ohio is underlain by the metamorphic rocks belonging to the Grenville Province—an ancient plate that collided with the Superior Province of Proto-North America in the
Proterozoic eon, beginning slightly more than one billion years ago.
In Ohio, the Grenville Province and Superior Province are separated by the Grenville Front, which underlies the Cincinnati Arch and Findlay Arch. West of the Grenville Front is a series of rifts, similar to the modern rifts in East Africa that form the Red Sea. The rifts in western Ohio form part of the East Continent Rift Zone, which is covered in six kilometers of undeformed sandstones and other silicate sedimentary rocks.
The collision of the Grenville Province with Proto-North America resulted in the long-lasting
Grenville orogeny
The Grenville orogeny was a long-lived Mesoproterozoic mountain-building event associated with the assembly of the supercontinent Rodinia. Its record is a prominent orogenic belt which spans a significant portion of the North American continent, f ...
, producing a tall mountain range. However, the mountain range eroded to an undulating plain, bounded by rift valleys in the west, by the start of the
Paleozoic
The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon.
The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838
by combining the Greek words ''palaiós'' (, "old") and ' ...
.
Paleozoic (539-251 million years ago)
The
Cambrian at the start of the Paleozoic marked the proliferation of multi-cellular life. By the
Late Cambrian
Late may refer to:
* LATE, an acronym which could stand for:
** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia
** Local-authority trading enterprise, a New Zealand business law
** Local average treatment effect, ...
, Ohio was covered in shallow seas, creating marine and delta deposits. Sandstone, mudstone,
shale,
limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
and
dolomite Dolomite may refer to:
*Dolomite (mineral), a carbonate mineral
*Dolomite (rock), also known as dolostone, a sedimentary carbonate rock
*Dolomite, Alabama, United States, an unincorporated community
*Dolomite, California, United States, an unincor ...
deposited atop the faulted Precambrian basement rocks. Periodic retreats of sea level during the Paleozoic eroded these rock units, leading to some unconformities in the sedimentary sequence, through the
Early Permian. During some of these periods of sea level retreat, beginning in the
Ordovician
The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya.
T ...
, the region experienced terrestrial erosion in the
Pennsylvanian and
Permian
The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last ...
. The drop in sea levels was related to the uplift of the region during the
Taconic orogeny
The Taconic orogeny was a mountain building period that ended 440 million years ago and affected most of modern-day New England. A great mountain chain formed from eastern Canada down through what is now the Piedmont of the East coast of the Unit ...
to the east.
In the
Middle Ordovician
The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya.
Th ...
, a renewed
marine transgression
A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, which results in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling ...
flooded the region, depositing limestone reefs. These rocks are only known from underground drilling and do not outcrop at the surface.
The
Point Pleasant Formation is the oldest rock unit exposed at the surface in Ohio and formed during the
Late Ordovician
The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya.
...
, outcropping along the Ohio River near Cincinnati. The formation records a transition from shallow-water limestone reef formation to a deeper water environment, marked by overlying shale and limestone, which form the
Cincinnatian Series. Clay shed from the rising mountains, associated with the Taconic orogeny formed the shale units. The warm sea water created perfect conditions for abundant biological activity and the Cincinnatian Series is highly fossil-bearing, outcropping across much of southwest Ohio in river beds, hillsides and road cuts. Ohio's State Invertebrate Fossil, is a
trilobite
Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...
found in the formation.
The Southern Hemisphere where Ohio was located at the end of the Ordovician experienced a widespread glaciation, around 438 million years ago. Sea level dropped due to the glaciation, accompanied by a subsidence of the land. Ordovician deposition ended, marked by a paraconformable break in the
Drakes Formation
The Drakes Formation is a geologic formation in Kentucky. It preserves fossils dating back to the Ordovician period .
See also
* List of fossiliferous stratigraphic units in Kentucky
This article contains a list of fossil-bearing stratigra ...
.
By the beginning of the
Silurian, sea levels advanced again. The shallow sea in the Silurian led to the formation of subtropical carbonates, which now outcrop to the east and west of the Cincinnati Arch and at the crest of the Findlay Arch. Some of the carbonates were deposited in reefs, such as the
Early Silurian Lockport Dolomite. Although they do contain some fossils, most of the Silurian rock units poorly preserve evidence of life. The units are separated by layers of
evaporite
An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocean ...
, including
anhydrite
Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the ...
,
gypsum
Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywal ...
and
halite
Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...
. Thick salt beds formed in connection with drops in sea level and land subsidence, generating the thick salt beds of the
Salina Group in eastern Ohio.
A new plate collision launched the
Acadian orogeny in the
Devonian and led to sediment deposition in the Appalachian Basin of eastern Ohio. The
Early Devonian
The Early Devonian is the first of three epochs comprising the Devonian period, corresponding to the Lower Devonian series. It lasted from and began with the Lochkovian Stage , which was followed by the Pragian from and then by the Emsian, ...
Helderberg Limestone and Oriskany Sandstone, which formed 408 million years ago, are known in the subsurface. Some Early Devonian rocks, of the Holland Quarry Shale, were briefly exposed at the quarry in Lucas County, before it was filled in and reclaimed. Most Devonian rocks date to the
Middle Devonian
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, w ...
and outcrop between southern Ohio and Lake Erie. A large
unconformity
An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...
separates Silurian and Middle Devonian dolomite and limestone. The overlying Devonian rocks include the Columbus Limestone to the east of the Findlay Arch and the Detroit River Group carbonates to the west. The angular unconformity between lower Silurian rocks is marked in some places by phosphate beds, that preserve bones and teeth.
The Columbus Limestone is especially fossil bearing and outcrops in a band between Columbus and Sandusky County, as well as on Kelleys Island in Lake Erie. The best fossil exposures are found at limestone quarries along the belt, which supply local concrete demand. Toward the end of the Middle Devonian, the marine environment shifted toward black marine shale deposition, of the Olentangy Shale and Ohio Shale. For the most part, these shale units are not fossiliferous. However, in some places, there are occurrences of
brachiopod
Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, w ...
,
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
,
arthrodire
Arthrodira (Greek for "jointed neck") is an order of extinct armored, jawed fishes of the class Placodermi that flourished in the Devonian period before their sudden extinction, surviving for about 50 million years and penetrating most marine eco ...
and shark fossils, as well as
Dunkleosteus
''Dunkleosteus'' is an extinct genus of large armored, jawed fishes that existed during the Late Devonian period, about 382–358 million years ago. It consists of ten species, some of which are among the largest placoderms to have ever lived: ...
armor plates.
At the start of the
Mississippian, in the
Carboniferous, 340 million years ago, river and delta sediments covered over the shales, producing the Bedford Shale, Berea Sandstone, Cuyahoga Formation and Logan Formation. The deposition of these units was briefly interrupted by a return to a stagnant marine environment, forming the Sunbury Shale. Outcrops of Mississippian rocks run parallel to Devonian rocks across central Ohio and paralleling the Lake Erie shore. In fact, Mississippian outcrops form a band of hills five to 10 miles south of the lake. In general the Mississippian rocks are moderately fossiliferous, with good
crinoid
Crinoids are marine animals that make up the class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, which are ...
preservation in Cuyahoga Formation.
Pennsylvanian rocks deposited in stream channels carved into older Mississippian rocks.
The
Middle Pennsylvanian Sharon sandstone and
Pottsville Group preserve evidence of uplift in the east, and subsidence in the west of the Appalachian Basin. The rocks that formed in the Pennsylvanian and Permian were mainly terrestrial in origin, including non-marine shale, sandstone, coal, ironstone and limestone, along with some marine rocks, such as flint and marine shale. River deltas in the Pennsylvanian, were covered in thick, swampy vegetation, helping to produce coal deposits.
Sedimentary rocks and fossil evidence suggests that Ohio has been a terrestrial environment since the Permian. For instance, the main subdivisions of the Pennsylvanian: the Pottsville Group, Alleghany Group, Conemaugh Group and Monongahela Group, along with the Early Permian Dunkard Group, are each more terrestrial than the last. The region was situated inland, experiencing terrestrial erosion as the Proto-North American continent of
Laurasia collided with
Gondwana to form the
supercontinent
In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which leav ...
Pangaea
Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...
. Rocks from the end of Paleozoic are best exposed in road cuts along I-77, between Canton and Marietta, I-77 from Cambridge to Bridgeport and cliffs on the Ohio River north of Marietta to East Liverpool.
Mesozoic-Cenozoic (251 million years ago-present)
For 245 million years, spanning the entirety of the
Mesozoic
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
in the
Paleogene, of the early
Cenozoic, Ohio experienced long-running uplift and weathering. Prior to the
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...
glaciations, the region was covered in large stream valleys, which are believed to have removed several hundred meters of rock, erasing most evidence of the Mesozoic and Cenozoic. Some bones and plant fossils, including
mastodon
A mastodon ( 'breast' + 'tooth') is any proboscidean belonging to the extinct genus ''Mammut'' (family Mammutidae). Mastodons inhabited North and Central America during the late Miocene or late Pliocene up to their extinction at the end of th ...
remains, have been found in recent sediments formed since the Pleistocene.
Natural resource geology
Ohio has varied natural resources. In 2016, 64.92 million tons of limestone and dolomite valued at $615 million was quarried, along with 12.23 million tons of coal, worth $541 million. Sand and gravel, salt, sandstone and conglomerate all have production over one million tons. Shale and clay are also quarried. Ohio produces three billion dollars worth of natural gas and $844 million of oil annually.
Coal deposits were first recognized in the 1740s by early settlers and were mapped as early as 1752. Decreased demand due to increased natural gas production has reduced coal mining in the 2010s, although one underground mine and three surface mines received expansion permits from the state in 2016. Mining and quarrying currently employs 3,546 people in the state.
The Salina Group is mined 500 meters beneath Lake Erie, in Cuyahoga County and Fairport Harbor.
Geological features
* The Auglaize Fault goes from
Darke County, Ohio
Darke County is a county in the U.S. state of Ohio. As of the 2020 census, the population was 51,881. Its county seat is Greenville. The county was created in 1809 and later organized in 1817. It is named for William Darke, an officer in the ...
to
Hancock County, Ohio.
* The
Sheriden Cave
Sheridan Cave is a Paleo-Indian archaeological site from the late Ice age in Wyandot County, Ohio. Glacial deposits sealed off the cave more than 10,000 years ago. Sheriden Cave is a karst sinkhole on a dolomite ridge that crosses Hancock and Wy ...
, a
karst sinkhole
A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are locally also known as ''vrtače'' and shakeholes, and to openi ...
in
Wyandot County, Ohio
Wyandot County is a county located in the northwestern part of the U.S. state of Ohio. As of the 2020 census, the population was 21,900. Its county seat is Upper Sandusky. It was named for the Wyandot Indians, who lived here before and after ...
.
* The Bowling Green Fault goes from
Findlay, Ohio
Findlay ( ) is a city in and the county seat of Hancock County, Ohio, United States. The second-largest city in Northwest Ohio, Findlay lies about 40 miles (64 km) south of Toledo. The population was 40,313 at the 2020 census. It is home ...
to southern Michigan.
References
{{Geology of the United States by political division
Ohio
Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The sta ...