SEDIMENTS & SEDIMENTARY ROCKS: EARTH'S HISTORICAL RECORD

• Controls on Sediment Type
• Type of sedimentary rock that forms in a particular site depends upon:
• Method of transport (wind, water, ice, biological)
• Physical, chemical & biological processes operating in a particular environment of deposition (E.O.D.)
• Climate under which weathering & erosion occur
• Diagenesis - post-depositional chemical & physical interactions
• Influences on Deposition
• Entire accumulation of sediments influenced by regional tectonics depositional rate in abasin, coupled with tectonic activity, results in either an underfilled or overfilled basin.
• Cratons
• Shields - Large areas of exposed ancient crystalline rocks.
• Platforms - Surrounding regions over which sedimentary cover accumulates.
• Orogenic belts - elongate regions bordering cratons deformed by compressional forces.
• Environments of Deposition
• Physical, chemical, biological & geographic conditions under which sediments are deposited.
• Characterized by geographic & climatic parameters.
• There are three principal depositional settings:
• Continental
• Transitional
• Marine
• Sedimentary Rocks Classes
• CLASTIC (DETRITAL) SEDIMENTS
• CHEMICAL SEDIMENTS
• ORGANIC SEDIMENTS
• VOLCANOGENIC SEDIMENTS
• CLASTIC SEDIMENTARY ROCKS
• Produced as solid byproducts of weathering
• Granite weathers to lithic fragment (quartz., feldspar, & amphibole)
• Lithic fragment of quartz weathers to quartz
• CHEMICAL SEDIMENTARY ROCKS
• Produced as chemical or biochemical precipitates from ions in solution (e.g., halite, gypsum, diatomite, chert, ironstones).
• Limestones
• Evaporites
• Chert
• Ironstones.
• OTHER SEDIMENTARY ROCKS
• ORGANIC SEDIMENTS
• Non-skeletal & non-mineral including
• Coal
• Diatomite
• VOLCANOGENIC SEDIMENTS
• Airfall deposits related to explosive volcanism
• Tuff
• Bentonites
• Concept of Facies
• General appearance or aspect of a rock from which its E.O.D. can be inferred
• Lithofacies -distinguishing characteristics are based on rock characteristics
• Concept of Biofacies
• Fossil assemblages are distinguishing characters that reflect original environment
• Facies Fluctuations
• Offlap Sequences (Regression)
• Withdrawal of the ocean and development of new coastal settings
• Coarser-grained sediments prograde and overlie finer-grained marine deposits.
• Onlap Sequences (Transgression)
• Shoreline advances over coastal areas
• Coarser sediments are covered by finer- grained marine deposits.
• Why Does Sea Level Change?
• Eustacy - Global change in sea-level related to fluctuations in ice caps.
• Ocean Floor Upwarping - Oceanic basalts forming at mid-ocean ridges thermally expand, take up space otherwise occupied by water causing eustatic rise.
• Tectonics - Regional uplift (regression) and subsidence (transgression)
• Vail Cycles - Global cycles appear to be on orders of 10-80 million years

GE142