Lecture 15 - Sedimentary notes PDF

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Lecture 15: Climate- Tectonic processes (mainly eustatic sea level change) and Climatic processes- Climate: defined as average weather — time length is normally around 30 years- Will dictate 3 main factors:- a) Temperature — which will affect reaction rates, primary productivity, evaporation rates,c...

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Lecture 15: Climate

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Tectonic processes (mainly eustatic sea level change) and Climatic processes Climate: defined as average weather — time length is normally around 30 years Will dictate 3 main factors: a) Temperature — which will affect reaction rates, primary productivity, evaporation rates, changes in aqueous state (stream, water and ice) b) Light — important in photosynthesis, more organic material, orbital forcing changes, dictates the length of growing seasons c) Precipitation — drive amount of sediment in transport, chemical reactions, annual run off, supply of nutrients

- Tectonic processes that drive climate include: volcanoes, flood basalts and position of the continents relative to each other 1) Volcanoes: - Major eruptions can introduce fine particulates — cool the earth as less sun radiation reaching the earths surface - Cooling is far more common - If ejected into the troposphere — they rain down affecting the weather not the climate - Case study: Laki and Grimsvotn — had a major outpouring of lava in 1783, caused winter to be 0.5 degrees lower average — caused from dust and gases generating a haze — crop failures also occurred in Europe - Case study: Tambora 1815 — had snow in June, July, August in Europe, - Case study: Krakatau 1883 — 20x tephra released by mount St Helens, caused a haze, generated red sunsets - Large eruptions cause around 0.1-0.5 lower temperature change on average 2) Flood basalts - Large scale, long lasting effusive eruptions - Long term increase in addition of co2 to the atmosphere - e.g. Deccan and Siberian traps - This cause greenhouse gas warming of 3-8 degrees - This increases chances on mass extinction e.g. Siberian traps caused the Permian — Triassic ME 3) Position of continents - Continental climate is obviously dependent on the latitude the continent is at - Global climate is affected by position of the continents - Distribution of land and sea is important - Higher sea levels — form more shallow seas = increases carbonate productions Climate and siliciclastic sediment supply: - Climate has an effect on siliciclastic sediment - If take sediments into hot arid conditions or warm humid conditions - Chemical weathering depends on factors that are controlled by climate - These factors include: - Amount of insoluble residue produced - Rate of physical weathering — tend to be climatically driven e.g. freeze thaw, run off from ocean - State of saturation of pore waters — need good porosity - Rate of water flow through - Temperature: 10°C rise will double reaction rate ! !

- Black areas are mountainess and are very variable - Little weathering in very arid/ dry conditions: e.g. deserts - In most tropical areas and humid: very intense weathering, silicates

- High latitudes — little weathering - Both latitudes and altitudes affect weathering

Climate and soils: - Rainwater reacts with CO2 to produce carbonic acid H2CO3 - Process lowers atmospheric CO2 and causes atmospheric cooling - vWeathering of siliciclastics uses 50% of H2CO3 consumed in weathering i.e as much as congruent weathering of carbonates - Feldspar weathering removes CO2 from the atmosphere - Plants are very important in soil production and soil stability

- In mountain areas weathering will increase — due to high precipitation rates as the water vapour will condense at higher altitudes - Draws down CO2 as mountain rainfall is increased - Deep-sea cores record reduction in CCD 50-10ma: correlates with appearance of Himalayas -

and increased flux of Ca2+ to the oceans. Marked increase in CO2 drawdown at same time caused global cooling.

Soils as climate markers: - Soils provide faithful recorders of climate change - Palaesols are fossil soils — different regions have different soils present - Increase mechanical strength if illuviated duricrusts present — e.g calcretes forming, more resistant to erosion - If extreme conditions — duricrusts form: in areas of very low rainfall and high pH: calcite and gycrete form, whereas, in areas of high rainfall and low pH: Ferricrete and alcrete - Carbonates are affected by climate: - can have cool water carbonates, warm water carbonates and pelagic carbonates - e.g. Need >18 degrees to form marine voids and lime muds - Greenhouse eras correspond to times of high sea level (no water trapped in ice caps), and ice-house to times of low sea level....