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Relative Age Dating.  Students will: 1) understand how the age sequence of rocks can be determined from strata 2) conduct stratigraphic investigations.

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Presentation on theme: "Relative Age Dating.  Students will: 1) understand how the age sequence of rocks can be determined from strata 2) conduct stratigraphic investigations."— Presentation transcript:

1 Relative Age Dating

2  Students will: 1) understand how the age sequence of rocks can be determined from strata 2) conduct stratigraphic investigations (interpret strata)

3  Students will: 1) understand the scientists who developed the principles of Stratigraphy. 2) understand Steno’s 4 principles of Stratigraphy 3) use Steno’s principles to interpret rock sequences.

4 The Father’s of Modern Geology

5  This principle, developed by the British Geologist William Smith, suggests that the landscape developed over longer periods of time through very slow geological processes instead of one big catastrophic event.  This principle gave Darwin the basis for his theory of evolution. Darwin suggested that evolutionary change occurs very slowly, requiring generations.  Smith’s theory of slow deposition of rock layers (strata) conformed well to this scientific idea. William “Strata” Smith

6  An example of the slow processes of Geology can be seen at Niagara Falls. The erosion of the edge of the waterfall can be traced since its discovery by Europeans in  Early Geologists referred to this slow rate of change as Uniformitarianism.

7  A Scottish farmer known as the “Father of Modern Geology”  Lived during a time when natural phenomena were being explained by natural causes.  Hutton observed unconformities, and believed in cycles in science.  Hutton proposed the Rock Cycle and explained earth's natural phenomena by natural causes which he could see operating today such as uplift of rock layers, erosion, transportation, deposition, lithification and volcanism. A classic unconformity – two layers of rock meeting at an angle. The boundary between the Permian Yellow Sands Formation (above), and the Carboniferous Pennine Upper Coal Measures (below)

8  This led to what we call THE PRINCIPLE OF UNIFORMITARIANISM  THE CONCEPT REVELED IN THE CONCEPT OF DEEP TIME  He viewed the Earth and Earth history as having, "no vestige of a beginning, no prospect of an end."

9 Geologic Process: In One Year: deposition of deep-sea sediment cm deposition of continental-shelf sediments cm erosional lowering of continents cm uplift of mountains 0.3 cm plate movement 4 cm slip on San Andreas fault 4.5 cm For Comparision: growth of fingernails 10 cm growth of a sapling 18 cm From Bucke, David, Physical Geology

10  Age of canal building - Smith was a canal engineer.  Smith discovered that different rock formations contain distinct fossil assemblages and that even isolated areas of rocks could be identified in their sequence by the fossils they contained.  Made a map of England published in  Strata identified by organized fossils

11  Smith developed the Principle of Biotic Succession: The sequence of life forms in the stratigraphic record follows a specific order.  This principle allowed rocks in distant areas to be ordered.  20 years of intense work by geologists in Europe and North America ordered rock sequences and resulted in the naming of most "time periods".

12  Lyell’s stratigraphic principles, geological evidence, and results were published brilliantly in "Principles of Geology" 1830; went through 11 editions.  Very strong Uniformitarian.  Felt that speed of Geological Processes had not changed.  Earth must be very old.  All the big changes in Earth History were all due to the sum of small effects.

13  Applied Lyellian Uniformitarianism to organisms.  Theorized that evolution occurred by natural selection and that vast amounts of time were needed for evolutionary changes to occur.  Wrote the groundbreaking, influential On the Origin of Species in  His theory provided a mechanism to explain William Smith’s PRINCIPLE OF BIOTIC SUCCESSION.  Today Geologists USE SIMILARITY IN THE FOSSIL ASSEMBLAGES TO INFER PROXIMITY IN TIME.

14  Stratigraphy is the study of the rock layers and the order of events that happened to them.  Not only does this include deposition of the layers and the order that they were deposited BUT ALSO anything that happened to the rocks, like faults, folding, tilting, metamorphism, and eroding.

15 This is one of the simplest things to do in basic geology and usually one of the more enjoyable things since it is like a big puzzle that needs to be put together.

16  Steno was a Danish scientist of anatomy & geology.  He is thought to be the originator of geology and stratigraphy and was beatified by Pope John Paul II in  Steno was also something of a theologist, having being brought up a Lutheran he later converted to Catholicism as he considered this branch of Christianity to better facilitate his curiosity in the natural world.  He was eventually ordained as a priest in Florence.  He was memorialized by Google on January 11, 2012.

17 In 1669 Niclaus Steno postulated 4 principles of stratigraphy: 1) Principle of superposition of strata  In a sequence of strata, any stratum is younger than the sequence of strata on which it rests, and is older than the strata that rest upon it. 2) Principle of initial horizontality of strata  Strata are deposited horizontally and then deformed to various attitudes later. 3) Principle of stratal continuity  Strata can be assumed to have continued laterally far from where they presently end. 4) Principle of cross cutting relationships  Things that cross-cut layers probably postdate them. (i.e. they are younger than them)  since then we have added the Principle of Biotic Succession and the Principal of Inclusions.

18  The law states that strata that are younger will be deposited on top of strata that are older, given normal conditions of deposition.

19  In a sequence of strata, any stratum is younger than the sequence of strata on which it rests, and is older than the strata that rest upon it.

20 This figure shows both the Principle of Superposition (younger layers form on top of older layers) and the Principle of Original Horizontality (layers are deposited horizontally Strata are deposited horizontally and then deformed to various attitudes later. The Law of Original Horizontality states that when strata such as sediments (sand, silt, or clay) are formed, they are laid down in horizontal, flat-lying layers. If you pour sand into a tub of water, the layers will build up more or less horizontally and will be basically flat

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22 Drill core samples allow geologist to trace the layers of rock across vast distances.  Strata can be assumed to have continued laterally far from where they presently end.  This principle allows geologist to follow layers of rock that are kilometers apart often using drill core samples.

23 Stratal Continuity of rock layers in 3 national parks found near each other in the Southwest USA. 3)Principle of Stratal Continuity

24 Stratal Continuity of rock layers in 3 national parks found near each other in the Southwest USA. 3)Principle of Stratal Continuity

25 Determine the cross-cutting layers in the sequences above  Things that cross-cut layers probably postdate them. (i.e.they are younger than them)  Often sedimentary rocks have intrusions of younger rocks that cut through them  Often faults displace rocks from the original sequence of events

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27  Since Steno’s time we have added the principle of biotic succession  A layer of rock will transition from limestone to shale to sandstone as you move down a continental shelf

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29  Since Steno’s time we have added the Principle of Inclusions  Chunks of rocks can fall into igneous lavas or glacial eratics can be included in older sediments  Inclusions are older than the layers

30 Stratigraphy of the Grand Canyon

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32 What happened here? Interpret the geological processes that would produce this strata?

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34 1) Stratigraphy does not only include deposition of the layers and the order that they were deposited but also anything that happened to the rocks, for example: a) faulting b) folding c) tilting d) metamorphism e) eroding. 2) This is one of the simplest things to do in basic geology and usually one of the more enjoyable thing since it is like a big puzzle that needs to be put together.

35  An unconformity is a buried erosional surface.  What this means is that an old surface that was exposed to the surface for an extended period of time was eroded then buried.  It usually means the structures below it are truncated in some variety.  There are 3 types of unconformities:  1)Angular Disconformities  2)Disconformity  3)Nonconformity

36  Angular Disconformity - This is an unconformity between strata that are not parallel with one another. Usually when one set is folded or tilted and the above layers are not.

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38  Disconformity - This is an unconformity between parallel layers. It indicates a gap in time and is often hard to identify. Some identifying features are an irregular surface (wavy instead of flat) and inclusions (portions of the underlying rock within the above rock).

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40  Nonconformity - This is an unconformity between igneous/metamorphic rocks and sedimentary rocks.

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42  Erosion - The current surface that is actively being eroded. This is always the last thing to be added on a stratigraphy section.  Tilting - Rock strata always form horizontally, so anything not horizontal has been acted upon. If they are straight but at an angle they have been tilted.  Folding - If the rocks are bent, they have been folded.  Faulting - If there is a break and movement within the rocks this is a fault.

43  suggest the sequence of events that led to this cross-section:  What knowledge and terms do we need to understand? 1) Steno’s principles of stratigraphy (+ 2 more) 2) terminology – unconformities, faulting, folding intrusions, etc. So let’s fill in the gaps! Look at the Stratigraphy exercise that was distributed earlier!

44  Each layer is labeled (A through K)  Determine which layer is youngest  1 (youngest):  2:  3:  4:  5:  6:  7:  8:  9:  10:  11 (oldest):

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51  Principles of Stratigraphy and Cross-Cutting Relationships: znK4&feature=related znK4&feature=related  Law of Superposition: =related =related  3D Seismic: elated elated  Folds, Dips and Strike: lSQ&feature=rellist&playnext=1&list=PL2B2C1DA2EECFE20 F lSQ&feature=rellist&playnext=1&list=PL2B2C1DA2EECFE20 F


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