The West Falls Group is a geologic group in the Appalachian Basin . It dates back to the Devonian period . Also stratigraphically equivalent to the Portage Group.
13-855: The West Falls Group is a geologic group in New York. It dates back to the Devonian period . Also stratigraphically equivalent to the Portage Group. The West Falls formation is bounded above by the Java Formation and below by the Sonyea Formation . It comprises the Angola Shale and Rhinestreet Shale Members. It was deposited during the Acadian Orogeny and is part of the Salina thrust sheet. Also known as
26-521: A characteristic manganese -rich zone 30 meters thick near its upper contact with the Hondo Group that characterizes the uppermost Vadito Group throughout the region. It may have formed by syngenetic deposition from hydrothermal fluids, or a more general manganese enrichment of basin waters at the close of Vadito volcanism. Another possibility is that it is a weathering horizon. Either possibility would make it an important regional time marker. The unit
39-632: A significant unconformity. It is overlain by the Ortega Formation . Based on Uranium–lead dating of zircons , the age of the formation is 1.693 Mya , and it is interpreted as metamorphosed rhyolites from the waning stage of back arc rifting associated with the Yavapai orogeny . It likely correlates with the Burned Mountain Formation in the Tusas Mountains . The formation has
52-611: Is a gray to greenish-gray shale, easily distinguished by its consistent low gamma ray signature , which is typical of this shale type. The West Falls Formation was deposited during the Frasnian stage of the Upper Devonian . Two distinct community types are observed in the group: "a shallower water spiriferacean - rhynchonellide - bivalve species ensemble, and a deeper water assemblage of unattached epibenthic and sessile semi- infaunal brachiopods " (Sutton, McGee). Both members of
65-419: Is notable for tourmaline -rich zones containing accessory fuchsite , purple muscovite, epidote , clinozoisite , zoisite , thulite , tremolite , sillimanite , kyanite , cyprine , allanite , and stibiotantalite . It shows indications of high simple shearing strain. It is at least 300 m (980 ft) in thickness. The formation is thought to be separated from the underlying lower Vadito Group by
78-571: The Glenwoody Formation , other strata (particularly in the lower part of the group) remain undivided into formations. Some well known groups of northwestern Europe have in the past also been used as units for chronostratigraphy and geochronology . These are the Rotliegend and Zechstein (both of Permian age); Buntsandstein , Muschelkalk , and Keuper ( Triassic in age); Lias , Dogger , and Malm ( Jurassic in age) groups. Because of
91-531: The Picuris Mountains . Its minimum age from detrital zircon geochronology is 1.693 Mya , corresponding to the Statherian period . The formation is composed of homogeneous feldspathic quartz - muscovite or quartz-eye schist containing quartz and feldspar megacrysts. Beds are typically light in color, ranging from pink to white to green. The modal composition is 50-70% quartz and 25-50% muscovite. It
104-820: The Wingate Sandstone , the Moenave Formation , the Kayenta Formation , and the Navajo Sandstone . Each of the formations can be distinguished from its neighbor by its lithology , but all were deposited in the same vast erg . Not all these formations are present in all areas where the Glen Canyon Group is present. Another example of a group is the Vadito Group of northern New Mexico . Although many of its strata have been divided into formations, such as
117-858: The West Falls Formation have been assessed for oil and gas exploration. The USGS has determined that the average total organic carbon (TOC) in the Rhinestreet Shale is 0.89%; the TOC in the Angola Shale is 1.47%. The Rathbone shale field in Rathbone , Steuben County , New York was discovered in 1931. 31 wells were drilled in this field, targeting the Angola and Rhinestreet members. Of these, 24 produced natural gas, 4 were dry holes, 2 were plugged and abandoned, and one produced oil. The wells were typically 900 to 1,500 feet (270 to 460 m) in depth, reservoir pressure
130-466: The West Falls Formation in New York. The West Falls is recognized in the subsurface from western New York to eastern Tennessee . The predominant lithology of the West Falls Group is shale . The Rhinestreet Member can be further subdivided into two shale types: a thick, fissile black shale underlies a gray to greenish-gray shale that likely indicates a transitional environment. The Angola member
143-513: The confusion this causes, the official geologic timescale of the ICS does not contain any of these names. As with other lithostratigraphic ranks, a group must not be defined by fossil taxonomy. Glenwoody Formation The Glenwoody Formation is a geological formation that is exposed in the cliffs southeast of the Rio Grande Gorge near the town of Pilar and in a few other locations in
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#1732851374450156-460: The stratigraphy of large regions. Geologists exploring a new area have sometimes defined groups when they believe the strata within the groups can be divided into formations during subsequent investigations of the area. It is possible for only some of the strata making up a group to be divided into formations. An example of a group is the Glen Canyon Group , which includes (in ascending order)
169-604: Was 225 pounds per square inch (1,550 kilopascals ) and flow rates ranged from 100 to 2,000 thousand cubic feet (2,800 to 56,600 m ) per day. Loyalsburg Formation Group (geology) In geology, a group is a lithostratigraphic unit consisting of a series of related formations that have been classified together to form a group. Formations are the fundamental unit of stratigraphy. Groups may sometimes be combined into supergroups . Groups are useful for showing relationships between formations, and they are also useful for small-scale mapping or for studying
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