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Geology of Urban Watersheds
Published in Daniel T. Rogers, Urban Watersheds, 2020
There are several types of unconformities (Wicander and Monroe 2007): Disconformity: An unconformity that exists between parallel layers of sedimentary rocks.Nonconformity: An unconformity where horizontal strata or layers of sedimentary rock overlie crystalline rock, either igneous or metamorphic.Angular unconformity—An unconformity where horizontal strata or layers of sedimentary rock are deposited on tilted and eroded strata. The result produces an angular discordance with the overlying horizontal layers.
Understanding the Geologic Framework of the Vadose Zone and Its Effect on Storage and Transmission of Fluids
Published in L.G. Wilson, Lorne G. Everett, Stephen J. Cullen, Handbook of Vadose Zone Characterization & Monitoring, 2018
An unconformity is a surface of erosion or nondeposition — usually the former — that separates younger strata from older rocks (Billings, 1954). An example is illustrated in Figure 10.7, a photograph of colluvial deposits superimposed on the step-shaped sides of an ancient river canyon cut into horizontal strata. Within sequences of sedimentary rocks, or at depositional contacts of sedimentary rocks over crystalline rocks, an unconformity may correspond to a significant change in physical properties. In the vadose zone, such a contact may represent a change from primary flow in the overlying material to secondary flow below. This may be accompanied by a permeability contrast associated with the contact itself. In practical terms, an unconformity involving unconsolidated alluvial deposits overlying consolidated rocks is often referred to as “soil” over “bedrock.” Vadose zone monitoring may be performed in a straightforward manner in the unconsolidated material, but may be very difficult in the consolidated rocks below. Figure 10.8 presents a hypothetical cross section showing several possible unconformity-related changes of flow pathways in the vadose zone. The geologist must be alert to the potential for such complications.
Introduction
Published in Sukumar Laik, Offshore Petroleum Drilling and Production, 2018
Stratigraphic traps are mainly classified based on their association with unconformity and the others not associated with unconformity. Unconformity is a time gap (break) in stratigraphy. The presence of unconformity indicates a time period of nondeposition or erosion. The time gap may be in terms of several million years. Unconformity is very important to petroleum geologists as it generates a stratigraphic gap as well as it is mostly associated with formation of conglomerates (Figure 1.15). Unconformity may be of different kinds based on the relation of the overlying and underlying beds. Angular unconformity is a type of unconformity where parallel strata of sedimentary rock are deposited on eroded inclined rock layers. Nonconformity is another kind of unconformity where the unconformity plane is lying above the plutonic body (Ghosh, 1993). In case of paraconformity, older sequences of a rock strata may be overlain by a set of much younger parallel units without an erosional surface (Ghosh, 1993). Finally, in the case of disconformity both the underlying and overlying beds show a parallel relationship with the unconformity plane (Ghosh, 1993).
Correlation of the lithostratigraphic facies relationships and depositional environments of the uppermost Silurian through Lower Devonian strata across the central Darling Basin, western New South Wales, SE Australia
Published in Australian Journal of Earth Sciences, 2021
The Winduck Interval is a sequence of sedimentary strata at the base of the Darling Basin, a siliciclastic backarc basin to the west of the Lachlan Fold Belt in eastern Australia (Figures 1 and 2). The Winduck Interval is bound above and below by unconformities. At the lower unconformity the Winduck strata overlies metamorphic rocks affected by the middle to late Cambrian Delamerian Orogeny and in parts some post-Delamerian upper Cambrian to Ordovician sediments, in the west, and by Silurian Benambran Orogeny metamorphic and igneous rocks in the east. The upper unconformity separates the Winduck Interval from the overlying Darling Basin strata of the Snake Cave Interval (e.g. Blevin et al., 2007; Khalifa et al., 2015, 2017, 2019; Willcox et al., 2003). The Snake Cave Interval has been replaced by the term Wana Karnu Group cropping out in the Mutawintji National Park, the Coturaundee Range, Menamurtee Hills and Scropes Range (e.g. Sharp, 2004; Vickery et al., 2010).
Sedimentary copper mineralization in the upper red formation, Yakhab area, central Iran
Published in Geosystem Engineering, 2019
Kaveh Pazand, Ali Behzadinasab, Mohammad Reza Ghaderi, Mohammad Reza Rezvanianzadeh
The Yakhab area in central Iran is located 20 km to the East of the town of Kashan (Figure 1). The Central Iranian Terrene is a composite of fold and thrust belts with basement blocks covered by thick sedimentary sequences. The Laramide orogeny (late Cretaceous) created a regional unconformity at the base of Eocene deposits throughout a vast part of Iran. Following this orogeny, and as a result of extensional movements, active basins formed in which a great thickness of basaltic lava to acidic flows and pyroclastic rocks were deposited (Parsapoor, Khalili, & Mackizadeh, 2009). The study area is mainly composed of Eocene volcanic and pyroclastic rocks (Figure 1). In the Oligocene–Miocene, marl, limestone, sandstone, shale and gypsum units known as Qom Formation widespread in the area, becoming even more extensive in depressions. In the Late Miocene, deposition of sandstone, marl, conglomerate and evaporate rocks known as the URF developed in a molasses-type condition of a sedimentary environment as a result of slow positive movement of the basin (Babaahmadi et al., 2010). The Upper Red Formation covers an extensive area in Central and NW Iran.
Genesis of the Archean–Paleoproterozoic Tabletop Domain, Rudall Province, and its endemic relationship to the West Australian Craton
Published in Australian Journal of Earth Sciences, 2018
N. M. Tucker, L. J. Morrissey, J. L. Payne, M. Szpunar
The ca 810–650 Ma D3–D4 Miles Orogeny occurred in response to southwest-directed compression and resulted in southeast–northwest-trending, upright to inclined folding, extensive greenschist facies retrogression of Paleo–Neoproterozoic rocks, and re-activation of both the Camel–Tabletop Fault (Czarnota, Gerner, Maidment, Meixner, & Bagas, 2009) and the Southwest Thrust–McKay Fault that bounds the southwestern margin of the Rudall Province (Hickman & Bagas, 1998, 1999). The Miles Orogeny has been linked to development of sediment-hosted copper deposits and unconformity-related uranium mineralisation (Huston et al., 2012). The ca 650–550 Ma D5 event resulted in localised, northeast-trending open folding in the Talbot Domain (Bagas, 2000, 2004). North-northeast-directed compression during the D6 Paterson Orogeny (ca 550 Ma) resulted in strike-slip movement along north-northwest and east-northeast-striking faults, east-southeast-trending open folding and dextral reactivation of D4 structures (Bagas, 2000, 2004; Hickman & Bagas, 1998). Thrusting and transpressional movement along the Camel–Tabletop Fault during D4–D6 also resulted in localised graben development that was infilled by rocks of the ca 800 Ma Karara Formation (Bagas & Smithies, 1998). The Paterson Orogeny in the Rudall Province was contemporaneous with the Petermann Orogeny in the Musgrave Inlier, which potentially implies the juxtaposition of these two regions by the Neoproterozoic–Cambrian (Bagas, 2004; Raimondo et al., 2008).