2Learning Goals Students will: understand how the age sequence of rocks can be determined from strataconduct stratigraphic investigations (interpret strata)
3Success Criteria Students will: understand the scientists who developed the principles of Stratigraphy.understand Steno’s 4 principles of Stratigraphyuse Steno’s principles to interpret rock sequences.
4Review of Early Geology The Father’s of Modern Geology
5The Principle of Uniformitarianism 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
6Niagara FallsAn 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 1678.Early Geologists referred to this slow rate of change as Uniformitarianism.
7James HuttonA 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)
8James HuttonThis led to what we call THE PRINCIPLE OF UNIFORMITARIANISMTHE CONCEPT REVELED IN THE CONCEPT OF DEEP TIMEHe viewed the Earth and Earth history as having, "no vestige of a beginning, no prospect of an end."
9From Bucke, David, Physical Geology A Little PerspectiveGeologic Process: In One Year: deposition of deep-sea sediment cm deposition of continental-shelf sediments 0.004 cm erosional lowering of continents uplift of mountains 0.3 cm plate movement 4 cm slip on San Andreas fault 4.5 cmFor Comparision: growth of fingernails 10 cm growth of a sapling 18 cmFrom Bucke, David, Physical Geology
10William SmithAge 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 inStrata identified by organized fossils
11William SmithSmith 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".
12Charles LyellLyell’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.
13Charles Darwin 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 1859.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.
14StratigraphyStratigraphy 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.
15The Puzzle of Stratigraphy 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.
16Nicolas Steno – Father of Stratigraphy 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 1987.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.
17StratigraphyIn 1669 Niclaus Steno postulated 4 principles of stratigraphy:Principle of superposition of strataIn 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.Principle of initial horizontality of strataStrata are deposited horizontally and then deformed to various attitudes later.Principle of stratal continuityStrata can be assumed to have continued laterally far from where they presently end.Principle of cross cutting relationshipsThings 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.
181) Principle of Superposition The law states that strata that are younger will be deposited on top of strata that are older, given normal conditions of deposition.
191) 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.
202) Principle of initial horizontality of strata 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 flatThis 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
223) Principle of Stratal Continuity 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.Drill core samples allow geologist to trace the layers of rock across vast distances.
233) Principle of Stratal Continuity Stratal Continuity of rock layers in 3 national parks found near each other in the Southwest USA.
243) Principle of Stratal Continuity Stratal Continuity of rock layers in 3 national parks found near each other in the Southwest USA.
254) Principle of cross cutting relationships 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 themOften faults displace rocks from the original sequence of eventsDetermine the cross-cutting layers in the sequences above
27New principles – 5) Principle of Biotic Succession Since Steno’s time we have added the principle of biotic successionA layer of rock will transition from limestone to shale to sandstone as you move down a continental shelf
29New principles – 6) Principles of Inclusions Since Steno’s time we have added the Principle of InclusionsChunks of rocks can fall into igneous lavas or glacial eratics can be included in older sedimentsInclusions are older than the layers
31The Diagram at left shows how geophysical testing techniques such as Seismology can be used to determine strata found below the surface. This technique is used to determine layers associated with oil and gas deposits. Geophysics is essential tool in Oil and Gas Exploration.
32What happened here?Interpret the geological processes that would produce this strata?
34New TerminologyStratigraphy 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:faultingfoldingtiltingmetamorphismeroding.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.
35Unconformities 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 Disconformities2) Disconformity3) Nonconformity
361) Angular Disconformity 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.
371) Angular Disconformity 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.
382) DisconformityDisconformity - 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).
392) DisconformityDisconformity - 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).
403) NonconformityNonconformity - This is an unconformity between igneous/metamorphic rocks and sedimentary rocks.
413) NonconformityNonconformity - This is an unconformity between igneous/metamorphic rocks and sedimentary rocks.
42Other Stratigraphy Terms we need to know: 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.
43Sample Stratigraphy Exercise suggest the sequence ofevents that led to thiscross-section:What knowledge andterms do we need tounderstand?Steno’s principles of stratigraphy (+ 2 more)terminology – unconformities, faulting, folding intrusions, etc.So let’s fill in the gaps! Look at the Stratigraphy exercise that was distributed earlier!
44Stratigraphy Exercises Each layer is labeled (A through K)Determine which layer is youngest1 (youngest):2:3:4:5:6:7:8:9:10:11 (oldest):
51Video LessonsPrinciples of Stratigraphy and Cross-Cutting Relationships: znK4&feature=relatedLaw of Superposition: =related3D Seismic: elatedFolds, Dips and Strike: lSQ&feature=rellist&playnext=1&list=PL2B2C1DA2EECFE20 F