The Midland Formation is a

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 Creta ...

(latest

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

to earliest

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

)

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

in the

Culpeper Basin The Culpeper Basin is one of the Newark Supergroup's Triassic rift basins. It lies east of the Appalachian Mountains and extends from the Madison County—Orange County line in Virginia to Frederick, Maryland.Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the East Coast of the United States, Atlantic Coast and the Appalachian Mountains. The geography an ...

. It is a

sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

unit which formed in a short period of time between the first two

basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of a ...

flows in the basin: the Hickory Grove and

Mount Zion Church Mount Zion Church may refer to the following churches: United States (by state, then city/town) * Mt. Zion Christian Church, Richmond, Kentucky * Mount Zion Church and Cemetery (Hallsville, Missouri), listed on the National Register of Historic Pl ...

basalts. The most common rocks in the formation are dark reddish

interbedded In geology, interbedding occurs when beds (layers of rock) of a particular lithology lie between or alternate with beds of a different lithology. For example, sedimentary rocks may be interbedded if there were sea level variations in their sedimen ...

sandstones Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

and

siltstones Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, pp ...

, representative of fluvial (stream) environments. Rare but fossiliferous

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an a ...

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especia ...

and

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 wh ...

also occurs, representing recurring lacustrine (lake) conditions. The Midland Formation is considered equivalent to the

Shuttle Meadow Formation The Shuttle Meadow Formation is a Mesozoic geologic formation in the Hartford Basin in Connecticut and Massachusetts, USA.Olsen, P.E., Schliesche, R.W., Gore, P.J.W. (Editors), 1989, Tectonic, Depositional, and Paleoecological History of Early Me ...

of the

Hartford Basin The Eastern North America Rift Basins are a series of sediment-filled ''rift, aborted rifts'' created by large-scale continental extension. Their positions closely mirror the eastern coast of North America. Sediments and volcanic material from the ...

, the

Feltville Formation The Feltville Formation is a mapped bedrock unit primarily in New Jersey, with one known outlier in Pennsylvania and another one in New York. It is named for the Deserted Village of Feltville in Watchung Reservation, New Jersey, which is near wh ...

of the

Newark Basin The Newark Basin is a sediment-filled rift basin located mainly in northern New Jersey but also stretching into south-eastern Pennsylvania and southern New York. It is part of the system of Eastern North America Rift Basins. Geology Approximat ...

, and the

Bendersville Formation Bendersville is a borough in Adams County, Pennsylvania, United States. The population was 736 at the 2020 census.https://data.census.gov/all?q=Bendersville+borough,+Pennsylvania Geography Bendersville is located at (39.982466, -77.249608). Ac ...

of the

Gettysburg Basin Gettysburg may refer to: Events * Gettysburg Campaign, a series of American Civil War military engagements in the Main Eastern Theater. ** Battle of Gettysburg, July 1–3 military engagements during the 1863 Gettysburg Campaign ** Retreat from ...

. Some sources prefer to classify the Midland Formation as part of the Shuttle Meadow Formation. Based on

conchostracan Clam shrimp are a group of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant and also known from the fossil record, from at least the Devonian period and perhaps before. They were originally classifi ...

biostratigraphy Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictionary of Bio ...

, the Midland Formation is believed to contain the Triassic-Jurassic boundary near its base. A prominent shale layer containing

Hettangian The Hettangian is the earliest age and lowest stage of the Jurassic Period of the geologic timescale. It spans the time between 201.3 ± 0.2 Ma and 199.3 ± 0.3 Ma (million years ago). The Hettangian follows the Rhaetian (part of the Triassi ...

-age fossilized fish, the Midland fish bed, is present about 10 meters above the base of the formation. Though now flooded by a manmade lake, it was formerly well-exposed along Licking Run, just north of

Midland, Virginia Midland is a census-designated place (CDP) in Fauquier County, Virginia, United States. The population as of the 2010 census was 218. Midland is home to a post office with the local ZIP code of 22728. Midland is the closest community to the bir ...

. Plant spores,

coprolites A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name is de ...

, and

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

footprints have also been recorded at nearby outcrops.Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607.

Paleobiota

Footnotes

References

* Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. . Geologic formations of Maryland Geologic formations of Virginia Triassic System of North America Triassic geology of Virginia Rhaetian Stage Sandstone formations Conglomerate formations Shale formations Siltstone formations Alluvial deposits Ichnofossiliferous formations Paleontology in Virginia {{US-geologic-formation-stub

Paleobiota

See also

Footnotes

References