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[en] This contribution presents a geological map of the basaltic flows of Arapey formation (Mezosoic) cropping out in Road 30 between the Bella Union round point (27 Km) and Pena s cuesta (225 Km) together with the description of the petrographic features of the different portions of the 20 recognized flow units
[en] The Uruguay and magmatic associations with alkaline affinity are locally developed related either to final distensional events of the Brasiliano Cycle or to the Mesozoic tectonics. Preliminary results correspondent to the plutono-volcanic activity recognized in the Valle Chico Alkaline Massif, focusing petrographical and geochemical variations from Shoshonitic Associations to potassic transitional alkaline, associations, are presented in this paper.(author)
[en] In the germany mission framework were carried out a tour in agates and amethyst quarries with the aim to visit the following exploitation quarries La Cordillera, La Soberana y el Coquero
[en] Petrographic and geochemical features of porphyroblastic hornblendites in Piedra Alta Terrene of Uruguay are described. Their spatial and genetic relationships whith hornblendic gabbros and other basic plutonic rocks is also stablished. Their association with low grade metamorphic supracrustals inmagmatic mingling structures and late development, suggests an origin related to high vapour pressure that take off stability to gabbro paragenesis and favours Deer's reaction:pyroxene+ plagioclase +water= hornblende + SIO2. The silica produced is expressed as quartz dikes frequently mineralized with gold and platinum group elements. San Carlos gabbro is an uruguayan exemple of such proposed model.
[en] A sequence of conglomerates, sandstones, siltstones, clay stones carbonaceous shales and mud stones which rims the Oban Massif in the Calabar Flank, constitutes the early Cretaceous (probably Aptian) Awl Formation in the southeastern Nigeria. Field studies and laboratory analyses were conducted on these sediments to determine their provenance and depositional environment. Field observations show that the sediments are gently dipping (.<16 degrees) in a southwesterly direction. They vary in thickness from thin to very thick beds and are laterally discontinuous. The pattern of sedimentation is cyclic with fining upward sequences. The sediments are textually immature with angular to sub angular grains dominating, thus indicating short distance transportation. The sandstones are medium to coarse-grained, poorly sorted, mostly leptokurtic, fine skewed and uni modal in distribution . They are subarkosic with more 70% quartz which are of igneous and metamorphic origin while the associated claystones contain kaolinite. Heavy mineral assemblages show the presence of predominantly zircon, tourmaline, rutile, garnet and saurolite with a range of 66.7 to 96%. This indicates mature to super nature sandstones and can be attributed to wet climatic conditions. The carbonaceous shales which grade into mud stone in some cases are non-fossiliferous, poorly laminated, pyritized and rich in lignitised wood. All these indicate that sediments of Awl Formation were derived from the Oban Massif and deposited in environments ranging from channel lag and point bar to flood plain
[en] The mid-Cenomanian Mishrif Formation (Fm.) is considered as one of the most important rudist-bearing reservoir horizons in the Sirri Oil Fields of the Persian Gulf. Due to the general heterogeneity of carbonate reservoirs, the use of an integrated approach is helpful for investigating porosity and permeability distribution along with recognizing controlling pore system factors in the reservoir. Thus, for the reservoir characterization of the Mishrif Fm., an integrated approach including facies analysis, diagenetic history and sequence stratigraphic analysis is considered. Detailed petrographic studies showed a total of eight microfacies and seven facies belts, related to inner ramp to the basin of a homoclinal carbonate ramp. Humid climatic condition and tectonic activity, associated with eustatic sea-level fluctuations during the mid-Cretaceous, led to meteoric diagenesis of the Mishrif carbonates during subaerial exposures (mid-Cenomanian and Cenomanian-Turonian disconformities). General diagenetic overprints and modifications include micritization, cementation, dissolution, compaction, dolomitization, pyritization and fracturing. Considering this reservoir in the sequence stratigraphic framework reveals that the reservoir zones development is basically related to the Cenomanian–Turonian sequence boundary, recognized in the three studied wells, and also to the mid-Cenomanian boundary, identified only in one well. In addition, pore system properties were inspected by differentiation of Hydraulic Flow Units (HFUs) within the reservoir. The identified flow units, based on their capability for fluid flow, can be classified into four main rock types with very high- (HFUD), high- (HFUC), medium- (HFUB) and low-quality (HFUA). Accordingly, this study shows that the main part of the Mishrif Reservoir is affected by diagenetic processes related to subaerial exposures, resulting in zones with higher storage capacity and fluid flow rates. So, the study of depositional and diagenetic characteristics of the Mishrif carbonates in the sequence stratigraphy framework is essential to unravel the reservoir heterogeneity, and to describe the reservoir zones and their distribution in the field and regional scale. In addition, observed changes in the thickness of hydrocarbon column are attributed to the different location of the studied wells on the anticline structures, which show a tilted oil-water contact with a slope to the North.
[en] In the south of the Sierra de San Luis is recognized a basement composed by La Escalerilla and Los Puquios granites, accompanied by schist, mylonite s and mafic-ultramafic rocks. The schists, La Escalerilla granite and the mafic -ultramafic rocks are affected by a regional metamorphism in anphibolites facies, the two first present a N-S foliation di ping to east. The mylonite s correspond to a second event of deformation, distributed in thin belts of NNE-SSO direction and inclination to east, developed in green schist to anphibolites facies. Los Puquios granite represents the more young of the basement rocks and the intrusion was associated with a shear zone. Los Puquios granite forms dikes and small plutons cutting La Escalerilla granite and micas chits in high cortical levels