Geology _ Geophysics in Oil Exploration

Mudrockssuchasmudstoneandshalecomprisesome65ofall

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Unformatted text preview: from breccias, which consist of angular clasts Made up mainly by Qz Pebbles, Flint, Chert, & Jasper Both conglomerates and breccias are characterized by clasts larger than sand (>2 mm) There are many types of Conglomerate: • • • • • Limestone Conglomerate: Polymictic Conglomerate: Variety of Pebbles & Boulders are contained Monomictic Conglomerate: Consists of one pebble type Intraformational Conglomerate: composed of Clasts derived from the basin of deposition Extra formational Conglomerate: composed of Clasts derived from Beyond area of Sedimentation C‐Breccia: Sedimentary breccias are a type of clastic sedimentary rock which is composed of angular to sub angular, randomly oriented clasts of other sedimentary rocks. They are formed by submarine debris flows, avalanches, mud flow or mass flow in an aqueous medium. Technically, turbidities are a form of debris flow deposit and are a fine‐grained peripheral deposit to a sedimentary breccia flow. Breccias are common along fault zones Slumping Breccias: consist of broken beds derived from down slope slumping Solution Breccias: resulting from Dissolution of Evaporites & collapse of overlying strata Breccia 7 Geology & Geophysics in Oil Exploration Mahmoud Sroor Geology & Geophysics in Oil Exploration D‐Mud Rocks: Mudstone (also called mud rock) is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platy clay minerals may become aligned, with the appearance of facility or parallel layering. This finely bedded material that splits readily into thin layers is called shale, as distinct from mudstone. The lack of facility or layering in mudstone may be due either to original texture or to the disruption of layering by burrowing organisms in the sediment prior to lithification. Mud rocks, such as mudstone and shale comprise some 65% of all sedimentary rocks. Mudstone looks like hardened clay and, depending upon circumstances under which it was formed, it may show cracks or fissures, like a sun‐baked clay deposit. They can be...
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