15-11 Structures

15-11 Structures - Structures and Structural Traps...

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Unformatted text preview: Structures and Structural Traps Petroleum System Geologists must find impermeable rock (~shale) or structure that prevents oil and gas from escaping naturally. This is a trap . Both the trap (cap rock) and a porous and permeable reservoir rock are critical to successful exploration. Types of Stress Compression Tensional Shear stresses applied unequally in different directions . 1. compressional stress- differential stresses that shorten a rock body . 2. tensional stress- stresses acting in opposite directions that tend to elongate, or pull apart , a rock body. 3. shear - slippage of slabs of rock or minerals past each other, like a deck of cards. Differential Stress Types of Stress tensional compressional shear Limbs Axis Axial plane Plunge Compression - Fold Anatomy ! anticline- a type of fold in which the rocks are arched upwards . syncline- a type of fold in which the rock layers are bowed downwards . Compression - Folds symmetrical: if limbs on either side of axial plane diverge at the same angle asymmetrical: if the limbs do not diverge at the same angle overturned: if one limb is tilted beyond the vertical. Compression - Folds Outcrop pattern of a Plunging anticline (the nose) points in the direction that it is plunging. Outcrop pattern of a Plunging syncline (the nose) points in the opposite direction of the plunge Compression Folds Plunging syncline Plunging anticline dome- upwarping of layers to produce a circular or elongate structure. basin- downwarping of layers to produce a circular or elongate low. Regional Folding Dome Basin Regional Folding Black Hills SD Definition: fractures in the crust along which significant displacement has taken place. Faults have displacement, gouge (ground up rock) and slickenlines. Faults sometimes occur in fault zones . Faults fault zone Dip-Slip Faults - Normal - Reverse Strike-Slip Faults ...Classified by sense of motion relative to the dip of fault surface. Fault Types Normal Fault Reverse Fault Types of Dip-Slip Faults based on direction of motion of the- hanging wall & - footwall two terms inherited from prospectors and miners....
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15-11 Structures - Structures and Structural Traps...

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