Jurassic

For example, the many deepwater fields located in the Gulf of Mexico are of Tertiary age and are comprised of complex sand bodies which were deposited in a deepwater turbidite sequence. The BP Prudhoe Bay sandstone reservoir in Alaska is of Triassic/ Cretaceous age and was deposited by a large shallow water fluvial-alluvial fan delta system. The Saudi Arabian Ghawar limestone reservoir is of Jurassic age and was deposited in a warm, shallow marine sea. Although these reservoirs were deposited in very different depositional environments they all contain producible accumulations of hydrocarbons, though the fraction of recoverable oil varies. In fact, these three fields are some of the largest in the world, containing over 12 billion barrels of oil each ... 

Other Deposits. Those deposits which cannot be classified as one of the previous 14 deposit types are called other. These include the uranium deposits in the Jurassic Todilto Limestone in the Grants district in New Mexico (17). 

Most commercial marine diatomite deposits exploit accumulations resulting from large blooms of diatoms that occurred ia the oceans during the Miocene geological epoch. Diatomite sediments older than the Jurassic period are rare in the fossil record. Commercial deposits of diatomite are accumulations of the fossil skeletons, which can occur in beds as thick as 900 m in some locations (5). Marine deposits must have been formed on the bottom of protected basins or other bodies of quiet water, undisturbed by strong currents, in an environment similar to the existing Santa Barbara Channel or Gulf of California (3,6). 

Jura-. Geol.) Jura, Jurassic, jurassisch, a. Geol.) Jurassic. 

Jurazeitalter, n. Jurassic period, just, adv. just, just now exactly. — a. right, saje. 

Jurassic 195 Myr Two large continents form Laurasia (north) and Gondwana (south). Dinosaurs diversify first birds and mammals evolve gymnosperms dominate terrestrial vegetation ammonites radiate into diverse forms... 

Fig. 9-11 Photograph of Ayun Tepui, taken from Canaima, Venezuela. The cliffs, which are about 2000 m high, consist of orthoquartzite. The irregular top is a karst topography formed by the slow dissolution of the quartz. It is estimated that the top of this tepui, and similar ones elsewhere on the Guayana Shield, have been exposed since the Jurassic.

Petersen, H.I., Depositional environments of coals and associated siliclastic sediments in the Lower and Middle Jurassic of Denmark, Geological Survey of Denmark, series 33, Copenhagen, 1994. 

Important metallic ore deposits include Besshi (Kieslager)-type (strata-bound cupriferous pyritic deposits), strata-bound Mn-Fe-type, skam-type, Kuroko-type and vein-type. Dominant non-metallic deposits are limestone, clay, native sulfur, zeolite, silica and gypsum deposits. The deposits are divisible into three groups, based on their ages of formation Carboniferous-Jurassic, Cretaceous-Paleogene and Tertiary-present. 

Jurassic—Cretaceous Besshi-type and Mn-Fe strata-bound deposits are present in Hidaka, Hokkaido (Fig. 1.2). Geochemical data and geological evidence all point to a midoceanic ridge environment of ore formation. values of Shimokawa Besshi-type... 

The Yamizo Mountains are mostly occupied by Paleozoic-Mesozoic sedimentary rocks, mainly of Jurassic age (e.g., Sashida et al., 1982) with a small amount of intrusive granitoids of unknown ages. The Paleozoic-Mesozoic sedimentary rocks have been called the Yamizo Formation (Kanomata, 1961). It is composed chiefly of shale, sandstone, alternating beds of shale and sandstone, and a small amount of limestone and chert. The succession of the geologic units and geologic structure of the Yamizo Formation have been left pending due to complex structure such as upturned beds (Kasai, 1978) and submarine land sliding (Aono et al., 1985). 

Sashida, K., Igo, H., Takizawa, S. and Hisada, K. (1982) On the Occurrence of Jurassic radiolarians from the Kanto Region and Hida Mountains, central Japan. Ann. Rept. Inst. Geosci. LI. Tsukuba, 8, 74-77. 

Isozaki and Itaya (1990) suggested from biostratigraphic data that the age of Minawa Formation is Triassic to Jurassic, indicating Besshi-subtype (mostly Group A) formed at these ages. 

Age of formation of Group B of Besshi-subtype are variable, early Cretaceous (Shimokawa), late Early Cretaceous to early Late Cretaceous (Makimine) and Triassic to Jurassic (Minenosawa, Kune). 

Fig. 2.52. Histograms showing sulfur isotope data for sulfide minerals from the major volcanogenic Cu sulfide deposits within the Jurassic to Cretaceous accretionary terrains in Japan (Sato and Kase, 1996).

Sandstone The tertiary, Jurassic and Triassic sandstones of the western Cordillera of the United States account for most of the uranium production in that country. Cretaceous and Permian sandstones are important host rocks in Argentina. Other important deposits are found in carboniferous deltaic sandstones in Niger in Permian Lacustrine siltstones in France and in Permian sandstones of the Alpine region. The deposits in Precambrian marginal marine sandstones in Gabon have also been classified as sandstone deposits. 

The Ebro headwaters flow on calcareous substratum, specifically sandstone and calcium marls, from the Triassic, Cretacic, and Jurassic. During the Quaternary, at the plain of La Virga (Reinosa), a shallow lake accumulated the deposits of siliceous sandrocks. This old highland lake is now the Embalse del Ebro reservoir. From that point downstream to Conchas de Haro the main channel flows on calcareous rocks from the Cretacic, highly resistant to the erosion. 

Bedrock and surficial Geology At Shiko Lake (Fig. 1) a Jurassic complex composed of diorite, monzonite, and syenite intrudes basalt and volcaniclastic rocks. Chalcopyrite, bornite, and gold occur disseminated and in veins mainly within the syenite (Fig. 2). 

Central and Eastern England is almost entirely underlain by sedimentary rocks that young from west to east. Four major geological sub-divisions are presented in Figure 1. Permian and Triassic mudstone and sandstone dominate the East Midlands and parts of Yorkshire Jurassic clays crop out within the centre of the study area and Cretaceous chalk underlies most of Central East Anglia. 

The Middle Jurassic consists mainly of marls. The Upper Jurassic formations are massive (over 100 m thick) and are made up exclusively of limestones. During Upper Jurassic and Lower Cretaceous the limestone deposits have been uplifted and resulted in a paleo-karst surface that hosts discontinuous bauxite deposits. Lower... 

The kimberlites in this study are located in the James Bay Lowlands and are in close proximity to the DeBeers Victor Mine. The kimberlites are mid Jurassic ( 170 Ma) in age and have been emplaced into... 

JURASSIC Kingak Shale l Milne Point Barrow... 

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