Lab 4D Geo Dimensions Part B- Study Notes

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Oct 30, 2023

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Frida Galvan Lab 4D Geo Dimensions Part B: Study Notes B6- GEOLOGIC STRUCTURES Original Horizontality and Superposition Stratigraphy is the study of layered sedimentary rocks. The 2 principles of stratigraphy:  The principle of superposition: an otherwise undisturbed sequence of sedimentary strata, or rock layers, the layers on the bottom are the oldest and layers above them are younger.  The principle of original horizontality: layers of rocks deposited from above, such as sediments and lava flows, that are laid down horizontally. Tilted Beds & Strike and Dip Geologists use a special symbol called strike and dip to represent inclined beds. Strike and dip map symbols look like the capital letter T, with a short trunk and extra-wide top line. The short trunk represents the dip, and the top line represents the strike. Dip is the angle that bed or layer plunges into earth from the horizontal.

Rules of strike and dip 1. Strike is always parallel to the bedding direction at that location. 2. The dip is always drawn perpendicular to strike in map view. 3. The dip can be labelled with the dip angle, or only the direction can be indicated. 4. Special symbols are used for horizontal beds and vertical beds. Tilted beds Tilted beds or layers occur when plate tectonic forces cause horizontal layers to be pushed up or dropped unevenly. Faults Faults are places in the crust where brittle deformation occurs as 2 blocks of rocks move relative to one another. Types of faults  Normal faults

 Reverse faults  Transform or strike-slip faults Folds Fold is geologic structure that is formed by layers or beds of rock being bent or folded. Types of folds  Anticlines

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 Synclines  Monoclines Plunging Folds Is a fold that is tilted downwards in space, parallel to the fold hinge plane.  Plunging anticline

 Plunging syncline Domes and Basin Dome is a circular structure in which the center is uplifted compared to its surroundings. The oldest layers are exposed in the center of the dome. Basin is a circular structure in which the center is depressed compared to its surroundings. The youngest layers are exposed in the center of the dome.

B7- READING A GEOLOGIC MAP Distance scale Shows that a certain length on the map equals a certain length in a real place. Most scales show distance in miles and kilometers. Latitude and longitude Geologic maps also have latitude and longitude marked along the edges of the map, as a way to help to locate positions on the map. Topographic contour lines The topographic map is essentially super-imposed on top of the geologic map. Legend with rock units/ formations The rock units are organized stratigraphically, with the oldest rock unit on the bottom and the youngest rock unit on top. Geologic time scale abbreviations

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