Chapter 5 & 16: Surface Processes (Weathering, Erosion, & Sedimentary Rocks)

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1. Mechanical— physical disaggregation of the rock or mineral into particles that are then subjected to erosion and transport by wind, water and glacier. 2. Chemical—the disintegration of the rock or mineral into its constituent cations and anions. These ions constitute the dissolved loads of rivers, lakes, soil waters, groundwaters, rainwater, and the salt of the sea.

Mechanical weathering—what goes up must come down. Freeze/thaw opens up cracks

Chemical weathering

Feldspar Magnetite Biotite Quartz Granite is made up of several minerals that decay at different rates. Cracks form along crystal boundaries. The dissolution progresses, and the rock weakens and disintegrates. Chemical weathering

2 cm 1 cm Large rocks have less surface area for chemical weathering… …than small rocks do, so smaller rocks weather more quickly.

Lower temperatures and decreases in atmospheric CO 2 reduce weathering. Lowered CO 2 leads to climate cooling. Reduced weathering rate… Weathering reduces CO 2 in atmosphere as CO 2 HCO 3 –. …leads to an increase in atmospheric CO 2,… …which leads to climate warming, which increases weathering. Chemical weathering uses CO 2 (g) from the atmosphere Chemical weathering of silicate rocks affects climate and climate affects the weathering of rocks—feedback loop Variability in atmospheric carbon dioxide leads to variability in the rate of weathering.

CO 2 release from volcanism CO 2 uptake by silicate weathering Weathering of silicates removes carbon dioxide from the atmosphere. Carbon dioxide is added to the atmosphere during volcanic eruptions.

Carbonic acid forms when CO 2 and H 2 O molecules combine. Feldspar KAlSi 3 O 8 Al 2 Si 2 O 5 (OH) 4 Kaolinite clay + Hydrogen ions (H+) react with feldspar. NaAlSi 3 O 8 CaAl 2 Si 2 O 8 …makes shales Carbonic acid ionizes to form hydrogen (H + ) and bicarbonate ions.

Pyroxene (Fe, Mg)SiO 3 Pyroxene dissolves, releasing silica, Mg And ferrous iron. Silica Ferrous iron Ferric iron Ferrous iron is oxidized, forming ferric iron. Iron oxide (hematite) Fe 2 O 3 Ferric iron precipitates a solid, iron oxide (rust). Olivine (Fe,Mg)SiO 4 Soluble Mg 2+ to the ocean

…which makes deserts red

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The salt of the sea—product of chemical weathering of continental igneous minerals Na and Ca from plagioclase K from K-feldspar (orthoclase) H 4 SiO 4 is excess Si not needed to form clay minerals Mg from mafic minerals (amphiboles, pyroxenes and olivines)

Sedimentary rocks Metamorphic rocks Plutons Desert Playa lake Delta Glacier The sedimentary stages of the rock cycle Weathering breaks down rocks. Erosion carries away particles. Transportation moves particles downhill. Deposition occurs when particles settle out or precipitate. Diagenesis lithifies the sediment to make sedimentary rocks. Burial occurs as layers of sediment accumulate.

Click video to begin playing Sedimentary Bedding 1

Classification of Sedimentary Rocks 1. Clastic—disaggregated rocks consisting of minerals and rock fragments 2. Chemical—minerals precipitated from seawater and freshwaters. They formed where they are found. 3. Biological/Bioclastic—minerals precipitated from seawater and freshwaters through the action of organisms (shells and skeletons) that may have been subjected to transport (as clasts) and re- deposition.

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Deep sea carbonate deposition since the early Jurassic (microscopic plankton with calcite shells)—forams and coccoliths.

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Heating of lithosphere Faulted valleys Rift valley Volcanics and nonmarine sediments Continental crust Continental lithosphere Asthenosphere A rift develops as the ancient continent stretches and thins.

Transportation Seafloor spreading begins. Subsidence Former position of lithosphere

Evaporites, deltaic sediments, and carbonates are deposited. Former position of lithosphere Carbonate platform Deposition Burial and diagenesis

Thermal sag basin These deposits are then buried and undergo diagenesis. Abyssal plain Continental margin Continental crust sags from weight of sediments and cooling of lithosphere

SEDIMENTARY ENVIRONMENTS Geographic location and plate tectonic setting Transport agent and medium Organic processes and organisms that modify sediments Climate Sedimentary environment Sediments deposited Desert Turbidity currents Turbidity currents

CONTINENTAL ENVIRONMENTS Geographic location and plate tectonic setting Transport agent and medium Organic processes and organisms that modify sediments Climate Sedimentary environment Sediments deposited Lake 1 Desert Lake Desert Lake 3 Glacier 4 Rivers 2 Desert Turbidity currents Turbidity currents

SHORELINE ENVIRONMENTS Geographic location and plate tectonic setting Transport agent and medium Organic processes and organisms that modify sediments Climate Sedimentary environment Sediments deposited Lake 1 Desert Lake Desert Lake 3 Glacier 4 Rivers 2 Desert Turbidity currents Turbidity currents Delta 5 Beach 6 Tidal Flat 7

MARINE ENVIRONMENTS Geographic location and plate tectonic setting Transport agent and medium Organic processes and organisms that modify sediments Climate Sedimentary environment Sediments deposited Lake 1 Desert Lake Desert Lake 3 Glacier 4 Rivers 2 Desert Turbidity currents Turbidity currents Delta 5 Beach 6 Tidal Flat 7 Deep sea 8 Continental shelf 9 Organic reef Organic reef 10 Continental margin/slope 11

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Photograph of alluvial cycle section Interpretive drawing Cycle below Deep channel: coarse-grained sediments, large-scale cross- bedding Shallow channel: fine-grained sand, small-scale cross-bedding Floodplain: mud and silt One cycle Increasing grain size Cycle above 1 m

Sediments are buried, compacted, and lithified at shallow depths Diagenesis

…or subducted, where they are subjected to higher pressure and heat.

Compaction by burial squeezes out water. Diagenesis

Precipitation or addition of new minerals cements sediment particles. Cementation Lithification Diagenesis

Different sediments result in different sedimentary rocks. Fine Silt and siltstone, mudstone and shale, clay and claystone Course Mud Gravel Shale SandSandstone Conglomerate Pressure

Oil and gas Organic Matter Coal Pressure Heat to 90° - 120° C Heat to 90° - 120° C

Sandstones that reveal information about transport processes and depositional setting

1 mm Deep-sea fanBeachDeltaAlluvial fan Arkose: feldspar-rich Lithic sandstone: rock fragment-rich Quartz arenite: pure quartz Graywacke: matrix-rich

Coral reef Light LagoonOpen ocean Carbonate platforms are built by reef- building organisms that precipitate calcium carbonate as calcite aragonite. …whereas outside the reef, sedimentation is much slower. If the sea level rises, the reef continues to grow toward the light at sea level… …and lagoon sedimentation outpaces sedimentation in the open ocean. Within the lagoon, growth of these organisms is rapid, and sediment forms quickly,... Light Carbonate platform Eventually, a carbonate platform Grows, with steep sides. Inorganic carbonate also precipitates Out of the supersaturated lagoon Water and adds to the platform sedimentation. Atolls

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Salt water from open ocean Gypsum and halite crystals Evaporite sediments Spain Italy France ATLANTIC OCEAN MEDITERRANEAN SEA Evaporation Freshwater inflow (small) During the Miocene epoch (5-20 million years ago), the Mediterranean Sea became a shallow evaporite basin. A short geological history of the Mediterranean Sea

Salt water from open ocean Gypsum and halite crystals Evaporite sediments Spain Italy France ATLANTIC OCEAN MEDITERRANEAN SEA Evaporation Freshwater inflow (small) Salt water entered through a narrow channel.

Salt water from open ocean Gypsum and halite crystals Evaporite sediments Spain Italy France ATLANTIC OCEAN MEDITERRANEAN SEA Evaporation Freshwater inflow (small) Salt water entered through a narrow channel. Evaporation removed more water…

Salt water from open ocean Gypsum and halite crystals Evaporite sediments Spain Italy France ATLANTIC OCEAN MEDITERRANEAN SEA Evaporation Freshwater inflow (small) Salt water entered through a narrow channel. Evaporation removed more water… …than was replaced by freshwater inflow.

Salt water from open ocean Gypsum and halite crystals Evaporite sediments Spain Italy France ATLANTIC OCEAN MEDITERRANEAN SEA Evaporation Freshwater inflow (small) Salt water entered through a narrow channel. Evaporation removed more water… …than was replaced by freshwater inflow. As the basin became more saline, gypsum and halite precipitated…

Salt water from open ocean Gypsum and halite crystals Evaporite sediments Spain Italy France ATLANTIC OCEAN MEDITERRANEAN SEA Evaporation Freshwater inflow (small) Salt water entered through a narrow channel. Evaporation removed more water… …than was replaced by freshwater inflow. As the basin became more saline, gypsum and halite precipitated… …forming evaporite sediments.