Eagle Ford Formation

[[File:Austin Chalk -Eagle Ford Contact.JPG|thumb|225px|right|Outcrop of the Eagle Ford and Austin Chalk Contact off Kiest Blvd, 1/2 mile east of Patriot Pky in Dallas County]] The '''Eagle Ford Formation''' (also called the '''Eagle Ford Shale''') is a [[Sedimentary rock|sedimentary]] [[rock formation]] from the [[Late Cretaceous]] age underlying much of [[South Texas|South]] and [[East Texas]] in [[United States]], consisting of [[organic matter]]-rich [[fossil]]iferous marine [[shale]]. It derives its name from the old community of [[Eagle Ford]], now a neighborhood in [[West Dallas]], where [[outcrop]]s of the Eagle Ford Shale were first observed. Such outcrops can be seen in the [[geology of the Dallas–Fort Worth Metroplex]], and are labeled on images with the label "Kef". The Eagle Ford Shale is one of the most actively drilled targets for oil and gas in the United States in 2010. == Depositional environment == [[Image:DFWsection.jpg|thumb|right|225px|Schematic E-W section showing the Eagle Ford Shale among the geological strata beneath the DFW Metroplex]] [[Transgression]] continued to occur after complete deposition of the [[Woodbine]] around 92 million years ago (mya). Creation of the Colorado Group, which first created the Eagle Ford Shale, occurred between ~92 and 88 mya. The Eagle Ford is mostly confined within the subsurface but outcrops on west side of Dallas and continues at a 1 degree easterly prograding tilt. The Eagle Ford Shale had sea level depths about 100 meters or 330 feet, and deposited about 20-50 kilometers from the shore. The depositional environment in the lower beds was low energy and slightly [[Hypoxia (environmental)|anoxic]]. This anoxic setting of the deeper oceanic waters was a result of increased amounts of CO₂ during deposition in the Cretaceous. The lower section of the Eagle Ford consists of organic-rich, [[pyrite|pyritic]], and fossiliferous marine shales which mark the maximum flooding surface, or the deepest water during Eagle Ford deposition. The different [[fauna]] present in the Eagle Ford suggest the waters were calm and within the [[photic zone]]. A small member of the Eagle Ford that consists of a thin [[limestone]] unit between shales is known as the Kamp Ranch. A small regressive highstand formed this [[carbonate]] layer towards the top of the Eagle Ford, identifiable by high energy features, such as ripple marks from storm generated waves and interbedded carbonaceous [[siltstones]]. The overall thickness of the undivided Eagle Ford Group is 200–300 feet thick. == Eagle Ford unconformity == [[File:Eagle Ford Unconformity.JPG|thumb|225px|right|This cross-section illustrates how the reactivation of the Sabine Uplift in the East developed the Woodbine/Eagle Ford Unconformity that is present in the subsurface of Far East Texas]] In the Cretaceous after the Woodbine and Eagle Ford formations were deposited, the [[Sabine Uplift]] started to become elevated again due to its reactivation ~88mya. A decrease in the effective elastic plate thicknesses caused the basin to subside, as the uplift became increasingly elevated. As a result, an estimated 150m of uplift over the Sabine region caused the eastern parts of the Woodbine and Eagle Ford formations to have a subaerial exposure, which eventually resulted in their easterly erosion. Deposition of the [[Austin Chalk]] after this erosional occurrence caused a sealing of the well known East Texas petroleum reservoir, and creation of a middle Cretaceous unconformity. Currently the Sabine Uplift is in the subsurface, and the middle Cretaceous unconformity is not seen since as it is buried below a massive wedge of [[Clastic rock|clastic]] sediments from the Late Cretaceous to the present. == Eagle Ford Group undivided == North of [[Hill County, Texas|Hill County]], shale, [[sandstone]], and limestone; shale, [[bituminous]], [[selenitic]], with calcareous concretions and large [[septaria]]; sandstone and sandy limestone in upper and middle parts, platy, burrowed, medium to dark gray; in lower part [[bentonitic]]; hard limestone bed marks base in [[Ellis County, Texas|Ellis]] and [[Johnson County, Texas|Johnson]] Counties; locally forms low [[cuesta]]; thickness 200–300 feet. ==Oil and natural gas== The Eagle Ford Shale is a [[hydrocarbon]] producing formation rich in [[oil field|oil]] and [[natural gas field]]s. The shale [[Petroleum play|play]] area starts at the Texas-[[Mexico]] border in [[Webb County, Texas|Webb]] and [[Maverick County, Texas|Maverick]] counties and extends 400 miles toward East Texas. The play is 50 miles wide and an average of 250 feet thick at a depth between 4000 and 12,000 feet. The shale contains a high amount of [[carbonate]] which makes it brittle and easier to use [[hydraulic fracturing]] to produce the oil or gas. The oil reserves are estimated at 3 billion barrels with potential output of 420,000 barrels a day. == External links == * [http://utdallas.edu The University of Texas at Dallas] - [http://utdallas.edu/geosciences/ Geosciences Department] * [http://energyindustryphotos.com/eagle_ford_shale__formation_of_s.htm Energy Industry Photos] {{coord missing|Texas}}