View source for Mahantango Formation

{{Short description|Geological formation in the United States}}
{{Infobox Rockunit
| name = Mahantango Formation
| image = Mahantango_Formation_Rt522_PA.jpg
| type = [[Geological formation]]
| prilithology = [[Shale]]
| otherlithology = [[Limestone]], [[Siltstone]]
| namedfor = [[Mahantango Creek]]
| namedby = 
| region = [[Appalachian Basin]] of<br />eastern [[North America]]
| coordinates = 
| caption = Outcrop of the Mahantango on [[U.S. Route 522|Rt. 522]], [[Fulton County, Pennsylvania|Fulton County]], Pennsylvania
| unitof = [[Hamilton Group]]
| subunits = [[#Description|See: Description]]
| underlies = [[Harrell Shale]] and [[West Falls Formation]]
| overlies = [[Marcellus Formation]]
| thickness = 
| extent = [[Maryland]], [[Ohio]], [[Pennsylvania]], [[Virginia]], and [[West Virginia]]
| age = [[Givetian]], ~{{Fossil range|387}}
| period = Givetian
}}
The [[Devonian]] '''Mahantango Formation''' is a mapped bedrock unit in [[Pennsylvania]], [[West Virginia]], and [[Maryland]].<ref>Ryder, R.T., Swezey, C.S., Crangle, R.D., Jr., and Trippi, M.T., 2008, Geologic cross section E-E’ through the central Appalachian Basin from the Findlay Arch, Wood County, Ohio, to the Valley and Ridge Province, Pendleton County, West Virginia: U.S. Geological Survey Scientific Investigations Map SIM-2985, 2 sheets with 48-page pamphlet.  https://pubs.er.usgs.gov/publication/sim2985</ref><ref>Ryder, R.T., Crangle, R.D., Jr., Trippi, M.H., Swezey, C.S., Lentz, E.E., Rowan, 
E.L., and Hope, R.S., 2009, Geologic cross section D-D’ through the central Appalachian basin from the Findlay arch, Sandusky County, Ohio, to the Valley and Ridge province, Hardy County, West Virginia: U.S. Geological Survey Scientific Investigations Map SIM-3067, 2 sheets with 52-page pamphlet.  https://pubs.er.usgs.gov/publication/sim3067
</ref><ref>Ryder, R.T., Trippi, M.H., Swezey, C.S., Crangle, R.D., Jr., Hope, R.S., Rowan, E.L., 
and Lentz, E.E., 2012, Geologic cross section C-C’ through the central Appalachian basin from near the Findlay Arch, north-central Ohio, to the Valley and Ridge Province, Bedford County, south-central Pennsylvania: U.S. Geological Survey Scientific Investigations Map SIM-3172, 2 sheets with 70-page pamphlet.  https://pubs.er.usgs.gov/publication/sim3172
</ref> It is named for the North branch of the [[Mahantango Creek]] in [[Perry County, Pennsylvania|Perry]] and [[Juniata County|Juniata]] counties in Pennsylvania. It is a member of the [[Hamilton Group]], along with the underlying the [[Marcellus Formation]] Shale.<ref name="explanation"/> South of [[Tuscarora Mountain]] in south central Pennsylvania, the lower members of this unit were also mapped as the '''Montebello Formation'''.<ref>{{cite map|title=Geologic Map of the Mifflintown Qd.|id=A126|scale= 1:24,000|author1=Conlin, Richard R. |author2=Hoskins, Donald M. |publisher=[[Pennsylvania Geological Survey]], Fourth Series|cartography=[[United States Geological Survey]]}}</ref>
Details of the type section and of stratigraphic nomenclature for this unit as used by the U.S. Geological Survey are available on-line at the National Geologic Map Database.<ref>{{Cite web|url=https://ngmdb.usgs.gov/Geolex/Units/Mahantango_2597.html|title = Geolex — Mahantango}}</ref>

==Description==
The Mahantango Formation is a gray, brown, and olive [[siltstone]] and [[shale]],<ref>Berg, T.M., Edmunds, W.E., Geyer, A.R. and others, compilers, (1980). Geologic Map of Pennsylvania: Pennsylvania Geologic Survey, Map 1, scale 1:250,000.</ref><ref>Milici, R.C., and Swezey, C.S., 2014, Assessment of Appalachian Basin oil and gas resources: Devonian gas shales of the Devonian Shale-Middle and Upper Paleozoic Total Petroleum System, in Ruppert, L.F., and Ryder, R.T., eds., Coal and Petroleum Resources in the Appalachian Basin: Distribution, Geologic Framework, and Geochemical Character: U.S. Geological Survey Professional Paper 1708, chapter G.9, 81p.  http://pubs.usgs.gov/pp/1708/g9/pdf/pp1708_g9.pdf</ref> characterized by coarsening-upward cycles.<ref name="explanation">{{cite web |url=http://www.dcnr.state.pa.us/topogeo/map1/explanation.pdf |archive-url=https://web.archive.org/web/20030422135023/http://www.dcnr.state.pa.us/topogeo/map1/explanation.pdf |url-status=dead |archive-date=April 22, 2003 |title= Explanation of Geologic Units |access-date=2008-01-26 |publisher=Pennsylvania Geological Survey}}</ref> 

==Stratigraphic Setting==
[[Image:USGS 2006 1237 table2 Stratigraphy Middle Devonian.svg|thumb|right|350px|Generalized [[stratigraphy|stratigraphic]] nomenclature for the [[Middle Devonian]] strata in the [[Appalachian Basin]].<ref name="USGS2006-1237"/>]]

The Mahantango Formation is typically found conformably overlying the [[Marcellus Formation]], and underlying the '''Tully Limestone''' (where present).<ref name=USGS2006-1237/>

The Mahantango has been divided into four members:<ref>MacLachlan, D.B., Hoskins, D.M., Payne, D.F., (1995). Bedrock Geology of the Freeburg 7.5 minuet Quadrangle, Snyder County, Pennsylvania. ORF 95-04, The Pennsylvania Geologic Survey, Harrisburg, PA.</ref>  
*Tully Limestone: a fossiliferous calcareous shale. The Tully is a conspicuous formation, which separates the Mahantango from the Hamilton Group.<ref name=USGS2006-1237>{{cite web |url=http://pubs.usgs.gov/of/2006/1237/of2006-1237.pdf|title= Assessment of Appalachian Basin Oil and Gas Resources: Devonian Shale–Middle and Upper Paleozoic Total Petroleum System |author1=Milici, Robert C. |author2=Swezey, Christopher S. |year=2006|access-date=2008-04-05 |publisher=[[United States Geological Survey]]}}</ref>
*Sherman Ridge: Olive gray, fossiliferous, claystone and siltstone with interbedded fine [[sandstone]] coarsening upward.
*Montebello Sandstone: Olive gray, fossiliferous, coarse to fine-grained sandstone, interbedded with siltstone and claystone, in coarsening upward cycles.
*Fisher Ridge (also described as the Dalmatia and Turkey Ridge): silty [[claystone]], siltstone, and very fine-grained sandstone.

The Sherman Ridge and Fisher Ridge are [[ridge-former]]s.<ref name="url">{{cite web |url=http://www.bucknell.edu/Documents/Geology/PaleozoicStratigraphicColumn1.pdf |title= Paleozoic Stratigraphic Column of Central Pennsylvania |publisher= [[Bucknell University]]|access-date=2008-05-26}}</ref>

In south-central Pennsylvania, the Mahantango includes the Clearville, Frame, Chaneysville, and Gander Run Members.

==Fossils==
[[File:Phacops-enrolled.jpg|right|thumb|Enrolled ''[[Phacops rana]]'' from an outcrop of the Mahantango near [[Milesburg, Pennsylvania|Milesburg]], [[Pennsylvania]], with [[schizochroal eye]] visible]]
There are numerous marine fossils found in the Mahantango including [[brachiopod]]s, [[crinoid]]s, [[trilobite]]s, [[bivalve]]s, and [[bryozoa]]ns.

=== Brachiopods ===
* [[Athyris]]
* [[Chonetes]]
* [[Mucrospirifer]]
* [[Protoleptostrophia]]
* [[Tropidoleptus]]

=== Crinoids ===
* [[Ancyrocrinus]]

=== Trilobites ===
* [[Basidechenella]]
* [[Dipleura]]
* [[Eldredgeops]] (formerly Phacops)
* [[Greenops]]

=== Bivalves ===
* [[Actinodesma]]
* [[Grammysioidea]]
* [[Grammysia]]
* [[Leiopteria]]
* [[Modiomorpha]]
* [[Nuculites]]
* [[Orthonota]]

=== Bryozoa ===
Atactotoechus furcatus

=== Coral ===
* [[Pleurodictyum]]
* [[Thamnoptychia]] (Trachypora)

=== Gastropods ===
* [[Bembexia]]
* [[Crenistriella]]
* [[Dictyotomaria]]?
* [[Glyptotomaria]]
* [[Loxonema]]
* [[Paleozygopleura]]
* [[Platyceras]]

=== Cephalopods ===
* [[Tornoceras]]
* [[Agoniatites]]
* [[Spyroceras]]
* [[Michelinoceras]]
* [[Bactrites]]
* [[Striacoceras]]
* [[Koenenites]]?

==Age==
Relative age dating of the Mahantango places it in the Middle [[Devonian]] period, being deposited between 392 and 385 (±3) million years ago. It rests [[unconformity|conformably]] atop the [[Marcellus Formation]] shale. Its upper contact is also conformable to the Trimmers Rock Formation and Harrell Shale.<ref>Berg, T.M., et al., (1983). Stratigraphic Correlation Chart of Pennsylvania: G75, Pennsylvania Geologic Survey, Harrisburg, Pennsylvania.</ref> In 2012, Read and Erikson reported the formation as Givetian in Virginia.<ref>[http://hdl.handle.net/10919/19078 Paleozoic Sedimentary Successions of the Virginia Valley & Ridge and Plateau]</ref>

==Interpretation of Depositional Environments==
The Mahantango represents a terrestrial to marine transition zone that went through many [[transgressive-regression]] sequences. The fine-grained rocks represent a shallow sea environment and accounts for many of the fossils. Coarser grained sediments represent near-shore environments, beaches, or possibly [[River delta|delta]] lobes. These environments were tide-dominated and often had violent storms. The Montebello Sandstone member is an example of a storm dominated rock unit. [[Brachiopod]] fossils are scattered in massive sandstone beds throughout the rock unit, while the Sherman Ridge member is more laminated with fossilized ripple marks often indicating tidal current directions.<ref>Prave, A.R., Duke, W.L., Slattery, W. (1996). A depositional model for storm- and tide-dominated prograding siliciclastic shorelines from the Middle Devonian of the central Appalachian foreland basin, USA. Sedimentology, 43, 611-629.</ref>

==See also==
*[[Geology of Pennsylvania]]

==References==
<references/>

==External links==
{{Commons category|Mahantango Formation}}

{{Navboxes
|title = Chronostratigraphic context of the Mahantango Formation by state
|list =
{{Chronostratigraphy of Maryland}}
{{Chronostratigraphy of Ohio}}
{{Chronostratigraphy of Pennsylvania|abbreviated=yes}}
{{Chronostratigraphy of Virginia}}
{{Chronostratigraphy of West Virginia}}
|state=collapsed}}

[[Category:Geologic formations of Maryland]]
[[Category:Geologic formations of Pennsylvania]]
[[Category:Devonian System of North America]]
[[Category:Devonian Maryland]]
[[Category:Devonian Pennsylvania]]
[[Category:Devonian geology of Pennsylvania]]
[[Category:Givetian Stage]]
[[Category:Shale formations of the United States]]
[[Category:Limestone formations of the United States]]
[[Category:Siltstone formations of the United States]]
[[Category:Shallow marine deposits]]
[[Category:Deltaic deposits]]
[[Category:Beach deposits]]
[[Category:Tidal deposits]]
[[Category:Cliff-formers]]
[[Category:Devonian southern paleotemperate deposits]]