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Unformatted text preview: the same volume • Roundness: Degree of grain rounding (Rounded, Sub rounded, Angular) • Grain surface texture: • Rough: indicates that the rock is Brocken & transport for short distance • Smooth: indicates that the rock was broken & transport for long distance • Printed: indicates that the rock supposed to wind with sands • Particle orientation Sedimentary Fabric: • Fabric: is the arrangement of grains (‐Oriented ‐Disoriented) • Packing: is grain to grain relationships & controlled by Digenesis • Sorting: is the grain size distribution • Well sorted: Narrow size range • Medium Sorted: Wide size range • Poorly Sorted: Large size range Terms to describe texture of most Sedimentary Rocks: • • • • • Fragmental texture: in Clastic or Mechanical sediments from very fine Clay to Blocks Crystalline texture: in Evaporites & Rock precipitated from Aqueous solutions Oolitic: in Limestone which is spherical or non spherical grains concentrated around nucleus Pisolitic: exactly like Oolitic but the grains have bigger size > 2mm diameter Colloform texture: result from coagulation of Colloid or Gel, which loose water, Shrinks & hardness Sedimentary Structures: • Primary Sedimentary Structures: • Stratification: the arrangement of sediments in layers or strata • Cross Bedding: produced due to the rapid deposition Graded bed • Graded bedding: occur when a mixture of particles deposited • Lenticular Bedding: Massive beds decrease rapidly in thickness (ex: S.S & L.S) • Mud Cracks: occurs due to shrinkage of Mud • Ripple Marks: formed by waves over bottom of shallow water • Rill Marks: as the tide retreats, water left the beach finds its way back to the sea producing a little Rivulets Ripple Mark • Wave Marks: formed on sloping Sands of a beach by Spent wave • Biogenic Sedimentary Structures: is fossil traces • Secondary Sedimentary Structures: • Concretions: ‐Spherical or irregular masses occur in sedimentary rocks • Septaria: occur when Concretion is cracked then cracks possible to be filled of Mud Cracks materials • Geodes: are cavities partially filled with crystals(composed of Qz or Calcite) 5 Geology & Geophysics in Oil Exploration Mahmoud Sroor Geology & Geophysics in Oil Exploration Sedimentary Structures: (due to Tukar book) • Erosional Sedimentary Structures: • Flute Marks: • Groove Marks: • Impact Marks: • Depo...
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