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Chapter 6

Chapter 6. Sedimentary Archives. The characteristics of sediment deposited in an area depend on: . Tectonic setting Physical, chemical, and biological processes in the depositional environment Method of sediment transport Rocks in the source area from which the sediment is derived

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Chapter 6

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  1. Chapter 6 Sedimentary Archives

  2. The characteristics of sediment deposited in an area depend on: • Tectonic setting • Physical, chemical, and biological processes in the depositional environment • Method of sediment transport • Rocks in the source area from which the sediment is derived • Climate (and its effect on weathering) • Post-depositional processes of lithification (cementation, compaction) • Time

  3. Tectonics • The forces controlling deformation or structural behavior of a large area of the Earth's crust over a long period of time.

  4. An area may be: • Tectonically stable - Midwestern U.S. • Subsiding (sinking) - New Orleans or Mexico City • Rising gently - New England and parts of Canada after glacial retreat • Rising actively to produce mountains and plateaus - parts of Oregon in the Cascade mountains

  5. Tectonics influences the grain size and thickness of sedimentary deposits. Recentuplift of the source area leads to rapid erosion of coarse-grained sediment. Subsidence in the depositional basin leads to the accumulation of great thicknesses of sediment.

  6. Principle tectonic elements of a continent • Craton - Stable interior of a continent; undisturbed by mountain-building events since the Precambrian. • Craton - the most stable part interior of a continent. • Shields - Large areas of exposed crystalline rocks. • Platforms - Ancient crystalline rocks covered by flat-lying or gently warped sedimentary rocks.

  7. Principle tectonic elements of a continent • Orogeny • Orogeny refers to forces and events leading to a large structural deformation of the Earth's lithosphere due to the engagement of tectonic plates.  • Orogenic belts - Elongated regions bordering the craton which have been deformed by compression since the Precambrian. Mountain belts

  8. Old Orogenic belts ▼ Fig. 12.1 Present-day distribution of Precambrian shield areas. Orogens and localities described in the text are shown. Early Proterozoic: ZW: Zunhua-Wutaishanophiolite. J: Jormuaophiolite. P: Purtuniq ophiolite. T: Trans-Hudson orogen. W: Wopmayorogen. Middle Proterozoic: G: Grenville orogen. Panafricanorogenic belts (Late Proterozoic):A: Arabian-Nubian Shield. D: Damara-Katanga orogen. M: Mozambique belt. TS: Trans-Sahara belt.

  9. Principle tectonic elements of a continent • Craton - Shield - Platform • Orogenic belt

  10. Cross-Beds animation

  11. Depositional Environments • We defined a depositional environment as any area where sediment accumulates, but more specifically it entails a particular area where physical, chemical, and biological processes operate to yield a distinctive kind of deposit.

  12. DEPOSITIONAL ENVIRONMENTS • Geologists recognize three broad areas of deposition— • continental, transitional, and marine—each of which has • several specifi c environments (• Figure 6.11).

  13. FLUVIAL • BRAIDED STREAM • MEANDERING STREAM

  14. DESERT • Alluvial Fan • Sand Dune • Playa Lake

  15. Outwash • Moraines

  16. Transitional • Deltas • Beach • Barrier Island • Beach • Sand Dunes • Tidal Flat

  17. Origin of a Delta

  18. Interpreting Depositional Environmets

  19. Paleogeography

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