Principles of StratigraphyBy Syed Waheeb Akhter D-13-Pg-17

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What is Stratigraphy?• The branch of geology that seeks to understand the geometric

relationships between different rock layers (called strata), and to interpret the history represented by these rock layers.

• William 'Strata' Smith (23 March 1769 – 28 August 1839) was an English geologist and surveyor who generated the first geological map of England. When one thinks of how little had been published on formalized sedimentary stratigraphy and how little was known of the relationship of fossils to depositional setting and time

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Steno's Laws of Stratigraphy• Nicholas Steno (1638-1686) was a Danish-born pioneer of

geology, and is considered to be the father of stratigraphy.• Nicholas Steno's observations of rocks layers suggested that

geology is not totally chaotic. Rather, the rock layers preserve a chronological record of Earth history and past life.

• He developed three fundamental principles of stratigraphy, now known as Steno's Laws:

• Law of Original Horizontality.• Law of Superposition.• Law of Lateral Continuity.

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principles of stratigraphy• He established three principles still accepted today. The first

was the principle of superposition, the crucial discovery that old rock layers underlie new rock layers. The second was the principle of original horizontality, that sediments are deposited as liquids, and like water, they are deposited horizontally, filling in irregularities at the bottom, but making a smooth surface at the top. The third was the principle of lateral continuity, that layers of sediment are continuous, unless a barrier prevents the sediments from spreading during deposition, or subsequent changes in the landscape break those sediment layers apart.

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Law of Original Horizontality• Beds of sediment deposited in water form as horizontal (or nearly

horizontal) layers due to gravitational settling.

• In most situations where sedimentary layers are deposited (for example, on the floor of the ocean or a lake or on the floodplain of a stream), the layers are horizontal or close to horizontal. This observation is expressed as the Law of Original Horizontality. There are exceptions to the law (for example, layers deposited on a steeply inclined surface), but they are relatively few.

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Law of Superposition• In undisturbed strata, the oldest layer lies at the bottom and

the youngest layer lies at the top.

• The Law of Superposition states that in a layered, depositional sequence (such as a series of sedimentary beds or lava flows), the material on which any layer is deposited is older than the layer itself. Thus, the layers are successively younger, going from bottom to top. The convention in geology is to number the layers (beds) within a sequence such that the oldest layer has the lowest number. Such sequences (from oldest to youngest) might be 1, 2, 3, 4….etc. or 23, 24, 25, 25, 25…. etc.

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Law of Lateral Continuity• Horizontal strata extend laterally until they thin to zero thickness

(pinch out) at the edge of their basin of deposition.

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Other Important Principles of Stratigraphy

• Law of Cross-Cutting Relationships– An event that cuts across existing rock is younger than that disturbed rock. This law was developed by Charles Lyell (1797-1875).

• Principle of Inclusion – Fragments of rock that are contained (or included) within a host rock are older than the host rock.

• Principle of Fossil Succession – Another law important to the field of stratigraphy is the principle of fossil succession. This law goes hand in hand with the law of superposition and basically states that animals change through time.

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Unconformities• Unconformity – A surface that represents a very significant gap in

the geologic rock record (due to erosion or long periods of non-deposition).There are 4 main types of unconformities:

• Disconformity – A contact representing missing rock between sedimentary layers that are parallel to each other. Since disconformities are parallel to bedding planes, they are difficult to see in nature.

• Angular Unconformity – A contact in which younger strata overlie an erosional surface on tilted or folded rock layers. This type of unconformity is easy to identify in nature.

• Nonconformity – A contact in which an erosion surface on plutonic or metamorphic rock has been covered by younger sedimentary or volcanic rock.

• Paraconformity- A contact between parallel layers formed by extended periods of non-deposition (as opposed to being formed by erosion). These are sometimes called "pseudounconformities").

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Relative age dating• Relative age dating is a way to use geometric relationships

between rock bodies to determine the sequence of geologic events in an area. Relative dating is different from absolute dating in which specific dates are assigned to geologic events .

• Relative dating is based on the principles of stratigraphy discussed above.

• Relative ages are not numbers. They are descriptions of how one rock or event is older or younger than another. Relative age dating has given us the names we use for the major and minor geologic time periods we use to split up the history of Earth. When you talk about the Precambrian, Paleozoic, Mesozoic, and Cenozoic on Earth, these are all relative ages

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Absolute age dating• People love absolute ages. An absolute age is a number. When

you say that I am 38 years old or that the dinosaurs died out 65 million years ago, or that the solar system formed 4.6 billion years ago, those are absolute ages. We use a variety of laboratory techniques to figure out absolute ages of rocks, often having to do with the known rates of decay of radioactive elements into detectable daughter products.

• Unfortunately, those methods don't work on all rocks, and they don't work at all if you don't have rocks in the laboratory to age-date.

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How grand canyon’s formed ?• when all the world was submerged Waterworld-style (a new

record: two Kevin Costner references in one post!). These soft layers of sediment were then rapidly cut by the withdrawal of the Flood waters. This rapid erosion allegedly took only days or weeks to carve the entire chasm of Grand Canyon as we know it today.

• According to some calculations, the Flood began in the year 2348 B.C. In Grand Canyon: Monument to Catastrophe, creationist Steve Austin describes what happened next:

• Massive erosion occurred as the upheaval moved and flexed great bodies of earth’s crust including [Grand Canyon Super group] strata.

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Grand Canyon’s Sets of Rocks• The geology of the Grand Canyon area includes one of the

most complete and studied sequences of rock on Earth. The nearly 40 major sedimentary rock layers exposed in the Grand Canyon and in the Grand Canyon National Park area range in age from about 200 million to nearly 2 billion years old. Most were deposited in warm, shallow seas and near ancient, long-gone sea shores in western North America. Both marine and terrestrial sediments are represented, including fossilized sand dunes from an extinct desert

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The EndThanks for your time

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