![]() ![]() Thus the principle of original horizontality is widely, but not universally, applicable in the study of sedimentology, stratigraphy, and structural geology. Also, sedimentary beds may pinch out along strike, implying that slight angles existed during their deposition. Similarly, sediments may drape over a pre-existing inclined surface: these sediments are usually deposited conformably to the pre-existing surface. The Law of Original Horizontality suggests that all rock layers are originally laid down (deposited) horizontally and can later be deformed. Superposition indicates that, where undisturbed, older. This is known as the angle of repose, and a prime example is the surface of sand dunes. The principle of original horizontality states that sediments originally form in horizontal layers. For instance, coarser grained sediments such as sand may be deposited at angles of up to 15 degrees, held up by the internal friction between grains which prevents them slumping to a lower angle without additional reworking or effort. However, it is now known that not all sedimentary layers are deposited purely horizontally. Īs one of Steno's Laws, the principle of original horizontality served well in the nascent days of geological science. Picture from Glen Canyon National Recreation Area, Utah.įrom these observations is derived the conclusion that the Earth has not been static and that great forces have been at work over long periods of time, further leading to the conclusions of the science of plate tectonics that movement and collisions of large plates of the Earth's crust is the cause of folded strata. From top to bottom: Rounded tan domes of the Navajo Sandstone, layered red Kayenta Formation, cliff-forming, vertically jointed, red Wingate Sandstone, slope-forming, purplish Chinle Formation, layered, lighter-red Moenkopi Formation, and white, layered Cutler Formation sandstone. These strata make up much of the famous prominent rock formations in widely spaced protected areas such as Capitol Reef National Park and Canyonlands National Park. ![]() The Permian through Jurassic stratigraphy of the Colorado Plateau area of southeastern Utah is a great example of Original Horizontality. It was first proposed by the Danish geological pioneer Nicholas Steno (1638–1686). The third principle states that layers of sedimentary rock are continuous, and anything that interrupts the layer. So, any tilting or folding of the rock occurred after it was deposited (Figure 3.3). The principle is important to the analysis of folded and tilted strata. The principle of original horizontality states that sediments are deposited by gravity in layers parallel to the Earth’s surface. The second rule is the principle of original horizontality, which says that layers of sediment are originally deposited horizontally (Figure 3.2). The principle of original horizontality states that layers of sediment are originally deposited horizontally under the action of gravity. ![]()
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