Lecture 6 Sedimentary Rocks
Veronica McCann・63 minutes read
Lecture focuses on sedimentary rocks with classifications into plastic, chemical, and biochemical categories, discussing formation processes like lithification, erosion, and weathering. Various types of sedimentary rocks are explored, including conglomerate, sandstone, shale, coquina, and limestone, with examples of rock formations and economic importance of materials like halite and gypsum highlighted.
Insights
- Weathering breaks down rocks into sediments, which, when compacted and cemented, form sedimentary rocks through lithification.
- Sedimentary rocks involve terms like lithification, deposition, sediment, transportation, erosion, and weathering.
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Recent questions
What are the three main types of rocks?
Igneous, metamorphic, sedimentary.
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Summary
00:00
Types and Formation of Sedimentary Rocks
- Lecture on sedimentary rocks, focusing on classification and identification.
- Three main types of rocks: igneous, metamorphic, and sedimentary.
- Igneous rocks formed from cooling, volcanism, melting, magma, and lava.
- Weathered igneous rocks become sediment, leading to sedimentary rocks.
- Metamorphic rocks transform under heat and pressure, undergoing metamorphosis.
- Sedimentary rocks involve terms like lithification, deposition, sediment, transportation, erosion, and weathering.
- Sedimentary rocks recycle materials through dissolution, weathering, accumulation, and cementation.
- Process of breaking down rocks involves deposition, lithification, and uplift.
- Classification of sedimentary rocks into plastic, chemical, and biochemical categories.
- Plastic texture in sedimentary rocks involves compacting grains for cementation.
20:57
Weathering, Erosion, and Sedimentary Rocks: A Summary
- Quinoa resembles oats but consists of gels glued together, found in Utah salt flats with salt deposits from evaporation, quartz, and sand.
- Next week's focus will be on sand formation, weathering processes (mechanical, chemical, biological), and sedimentary rocks' role in understanding environments.
- Weathering initiates with rocks' cracks allowing rain and wind to break them, leading to erosion and transportation by wind, water, or ice.
- Eroded material carried by water can round grains, change shapes, and eventually reach the ocean, contributing to landscape flattening and salty water creation.
- Chemical weathering's dissolution of ions in water leads to salty oceans, vital for organisms like corals, crabs, and bivalves to build homes.
- Weathering breaks down rocks into sediments, which, when compacted and cemented, form sedimentary rocks through lithification.
- Shale formation involves wet mud compacting, water removal, and dissolved minerals cementing grains, creating a solid rock.
- Biochemical rocks form from plant material or fossils, while chemical rocks result from evaporite minerals formed by evaporation.
- Clastic detrital rocks are categorized by grain size (gravel, sand, silt, clay), with rounded vs. angular shapes and well vs. poorly sorted grains.
- Chemical rocks, like halite and gypsum, are economically important, used in various applications from seasoning food to lining smokestacks for reducing pollutants.
48:53
Grain Sizes and Rock Types Explained
- Gravel is the largest grain size, exceeding two millimeters.
- Sand falls between two millimeters and one sixteenth of a millimeter.
- Silt, finer than sand, ranges from one sixteenth to one 256th of a millimeter.
- Clay is anything less than one 256th of a millimeter.
- Clay and silt are both categorized as mud, with clay being less than silt.
- Rock types vary based on grain size: shale for clay, siltstone for silt, sandstone for sand, conglomerate or breccia for gravel.
- Conglomerate has smooth edges on pebbles, while breccia is angular with sharp edges.
- Conglomerate consists of rounded grains, while breccia has angular grains.
- Sandstone is rough to the touch, made of glued-together sand grains.
- Shale, with very fine grains, feels smooth and is difficult to differentiate under a microscope.
01:10:56
Formation of Various Rocks and Minerals
- Coquina resembles oatmeal and is powdery like chalk, both examples of limestone.
- Chalk is powdery like the cliffs of Dover, formed from microscopic organisms called coccoliths.
- Coal, like bituminous coal, is made from compressed plant material in a low-oxygen swamp or lagoon environment.
- Rock salt forms from evaporation, while chert and flint can form from water traveling through rocks or organisms pulling materials from the ocean.
- Coquina is easily breakable, resembling a granola bar, and fizzes when acid is applied due to its calcium carbonate content.
- Limestone shows stacked shells, while Coquina is more easily broken but also fizzes due to its calcium carbonate composition.
- Bedded gypsum forms from evaporated lake beds, while rock salt from Detroit is mined under the city for roads and preservation.
- Chert is smooth and made of quartz, while bituminous coal is less shiny and lighter than anthracite coal.
- Rock salt drill cores help locate materials underground, like the rock salt mined in Detroit.
- Fossils in rocks like trilobites and leaf imprints indicate past life and the formation of calcite from dissolved calcium and bicarbonate.
01:32:14
Formation and Identification of Sedimentary Rocks
- Bedded chert contains microscopic organisms that accumulated quartz from water, appearing smooth but actually a graveyard of tiny organisms like diatoms.
- Chert can also form as nodules from quartz dissolved in water flowing through rock openings, known as chemical chert.
- Chert can form biochemically or chemically, with nodules historically used by Native Americans for tools like arrowheads.
- Rock salt and gypsum form from evaporation, seen in Death Valley where borax was mined using mules.
- Iron deposits in the Upper Peninsula of Michigan come from banded iron formations formed billions of years ago by iron precipitation from seawater.
- Sedimentary rock identification involves examining grain size and texture, with examples like conglomerate, sandstone, and shale.
- Non-clastic rocks can be chemical or organically formed, with examples like dolomite, rock salt, and rock gypsum, and dolostone forming only during certain time periods.
