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Marine Geology Lecture Notes
Sea Level
Importance o Affects property and coastal development o Shift coastal/ margin environments o Open and close tectonic gateways, which affect circulation Local VS. Global Sea Level o Relative sea level- local change o Eustatic sea level- global change Accommodation space is a space for sediments Shoreline Movement o Retrogradation - landward movement o Aggradation - no horizontal movement/ vertical change o Progradation - seaward movement Eustatic Sea Level Changes o Volume of basin (affects size of container) o Plate tectonics – 100's m, basin size, ridge length, and spreading rate o Sediments- 100's m, infilling basin, removal of sediment o Volume of water (affects water in container) o Glacial ice formation- 100's m, Antarctic (100m), Artic (10m), and mountain (1m) o Terrestrial water- 10's m, aquifers, lakes, and rivers o Water temperature- 10's m Regional Sea Level Changes o Loading and unloading- 10's m, glacial, sediment, and seawater Long Term Sea Level
o Major sea level changes due to ridge volume and glacial changes o Cyclic variations Ridge Volume o Displaces water o Related to Wilson cycle (500 my) o >30% increase in Jurassic when ocean basins forming Glaciation o Removes water o We need cold summers to allow ice to build because when the summers are too hot the ice melts and we need the ice and snow to stay long enough for the cold weather to come back, this allows the glacier to maintain itself Milankovitch cycles o Earth’s tilt, wobble, and orbit fluctuate in regular patterns that appear to correspond to cycles of Quaternary glaciations o Insolation- Measure of incident solar radiation o Changes in tilt amplify or suppress the seasons, particularly at the poles o Obliquity - change in tilt of pole (21.5 derrees-24.5 degrees) 41 ky o Eccentricity - shape of the orbit around the sun, change in orbit from elliptical to more circular, 100 ky o Precession - wobble of axis and rotation of orbital ellipse, 23 ky, change in orientation of pole Sea Level Periodicity o 200-400 my- ridge number or length o 1-100 my- ridge spreading rates
o Fractionation- unequal separation o Fractionation occurs when- H2O16 is evaporated and heavier H2O18 is initially “rained out” Changes in Oxygen Isotopes o When clouds reach high latitudes, H2O16 rains out and... If it's cold, H2O16 freezes in glaciers, which >18 O:16 O in oceans If it's warm, flows back into oceans, which <18 O:16 O in oceans Calculating Oxygen Values o Oxygen isotopes are measured with respect to PDB (Pee Dee Belemnite) o >more 18 O- more ice and cooling o <less 18 O- less ice and warming
Deltas and Estuaries
What is a Delta? o A discrete shoreline protuberance Where a river enters a water body forming prograding clinoforms River supplies sediments by currents, waves and tides Influences on Delta Development o Water Precipitation, drainage area o Sediment Climate, local geology, relief
o Marine processes Waves, tides, sea level Delta Plain o Channels and Levees o Swamps o Marshes and bays Delta Front Processes o Rivers carry sediment as bed load and suspended load o Deposition by river slowing o Forms prograding deposition Delta Front Animation o Inertia Shallow plume Turbulence slows plume Deposition seaward of channel o Buoyancy Fresh water over marine water Secondary flow created Maintains a narrow zone of deposition Narrow linear bar More seaward o Bottom friction Bottom friction rapidly slows water Deposition at channel Water spreads laterally Delta Classification o 3 types of processes River Wave
Delta Cycle o 1. Delta plain aggradation o 2. shelf progradation o 3. Capture of channel elsewhere o 4. beaches (rework delta front) o 5. Barrier Island o 6. Shoals Holocene Sea Level o Sea level slowed, sediments caught up; retrogradational to aggradational to progradatioinal What is an Estuary? o A flooded river valley o A coastal embayment subject to freshwater runoff Types of Estuaries o Salt wedge o Partially mixed o Well mixed Divisions of an Estuary o 1. Head Riverine processes and sandier sediments o 2. Main Estuary Traps sediment and muddier sediments o 3. Mouth Ocean processes and sandier sediments Processes- Mud o Flocculation Attraction of negative Clays with positive salt ions o Turbidity maximum Null point sedimentation bottom currents meet
o Biologic organisms Binding to sediments into fecal pellets Classification (Geomorphic) o Wave Mouth bar Narrow entrance Ebb/flood deltas o Tide Large entrance-v shape Tidal sand banks o River – bay head deltas o All flanking salt marshes
Beaches and Barrier Islands
Beach o Berm- high point where beach slopes seaward and landward o Longshore transport- river of sand moving along beach o Storms waves move sand offshore o Fairweather swells move bars back onshore Beach Slope o Higher energy = flatter slope o Finer material= flatter slope What is a Barrier Island? o Sandy, shore-parallel islands separated from the mainland by estuary, lagoon, or tidal environments
lengthens islands Mixed Energy Barriers o Short, wide, higher islands o Numerous large inlets; large ebb tidal deltas o “drum-stick” shape Wider updrift and thinner downdrift o Tides cause ebb tidal delta to extend seaward “Drum-Stick” Shape o Larger ebb deltas o Wave refraction over ebb delta o Local updrift reversal of alongshore current o Updrift beach ridges prograde Barrier Island Formation o Emerging bar (traps sand) o Breached spit (cut-through spit) o Drowned coastal storm ridge (rising sea level) Barrier Island Migration o Erosion along the beach o Deposition landward by: Overwash Wind-blown sediments Flood delta incorporation Retrogradational/ Transgressive o Seaward over landward environments Progradational/ Regressive o Landward over seaward environments Holocene Sea Level o Sea level slowed; sediments caught up o Switch from retrogradation to aggradation or progradation
Preservation o Slow sea level rise allows for removal of sand by waves and longshore current o Rapid sea level rise can drown the island o Preservation is very rare, more likely sand shoal
Margins – Shelves
Shelf Deposits o Nearshore sand to offshore mud o More complicated Wave/Storm o Hummocky bedforms Shelf Processes o Tides Deposit sand waves or ribbons o Glaciers Erode surface Deposit moraines Authigenic Form by chemical reactions, biochemical on shelf Low sediment deposition Phosphorite o Indicate upwelling o Phosphater eplaces CaCO o Black color Gluconate
Latitude Atmospheric Movement o Heat transfer (by latent heat) Warm- rising (lows/rain) Cool- sinking (highs/dry) o Cells Vertical motions in the atmosphere Major Winds (2%) o Trade winds o Westerlies o Polar easterlies Water Movement o Wind causes drag on water o Form east-west currents o Form gyres (circular form in large semi-enclosed oceans) Ekman Spirals o Winds drag top layer o Transfer of lower layers by drag o Downward turning due to the Coriolis o Loses momentum due to friction o Forms a spiral Ekman Transport o Net flow of 90 degrees to wind direction Vertical Movement o Convergence- downwelling o Divergence- upwelling Divergence o Higher productivity at upwelling Temperature
o Warm at equator and cool toward poles Salinity o Increase: evaporation and ice o Decrease: Precipitation and run-off o Highest at the center of gyres Ocean Structure o Upper(<500 m) Mixed by winds and waves; variable o Lower (mid to bottom) Density driven (temp and salinity) Thermohaline Flow (56%) o Density driven flow Temperature and salinity Atlantic Ocean Currents o Intermediate: Antarctic Mid Waters Med. Waters o Deep/Bottom Antarctic Bottom Water (AABW) North Atlantic Deep Water (NADW) Deep Ocean Currents- Importance o Deep ocean chemistry o Global climate Primary Production o Produced by: Photosynthesis (Phytoplankton) Chemosynthesis (bacteria) Primary Production (33%) o Primary production:
High at nutrient zones (near poles and equator)
Deep Sea Sediments
Slope/Rise Processes o Gravity Slides/slump (mass movement) Flows (sediment movement; distinguished by support mechanism) Turbidity Current o Causes: Sediment failure o Earthquakes o Rivers floods o Consists of: Head, body, and tail o Head contains sediment; denser than water; flows by gravity o Turbulence; friction with still water (slows head); body runs into head; creates turbulence o Keeps sediment up and flowing Climatic Affect o Mechanical weathering (cold) Chlorite and Illite o Chemical weathering (warm) Kaolinite Ice Rafted o Carried by icebergs; melt and sediment sink o drop stones
Lysocline o Where calcium carbonate sediments begin to dissolve o Effected by shell mineralogy, organic coating; thickness and shape Calcareous Oozes – Diagenesis o Diagenesis is recrystallization and cementation after burial o Changes to Chalk – 300 m depth Limestone – 1 km depth Organic Material o Sapropels Preserved organic material under anoxic conditions (no deep turnover) Transport of Fine Particles o Turbulence keeps fine particles suspended Manganese Nodules o What are they made of? Manganese Iron oxides o Where found? Across Pacific Between ridge and abyssal plains in Atlantic o How formed? Form around a nucleus (biogenic grains) Grow as rings Slow growth o Why not be buried? Currents Sweep sediments or turn nodules over
Geologic history “Laws of Stratigraphy o Superposition o Original horizontality o Lateral continuity o Cross-cutting relationships o Faunal succession Unconformities o Erosion o Longterm non-deposition o Types: Angular unconformity Nonconformity Disconformity Paraconformity Recognizing Unconformities o Sediments- abrupt change Coarse lag Bedding truncation Surface of burrowing Soil horizon o Missing faunal zones o Age dates gaps What Are Facies? o Sediments or sedimentary rock that share some aspect of appearance Walther’s Law
o Facies occurring in conformable (no break in deposition) vertical successions also occurred in laterally adjacent environments o Cautions: Underlying topography Not true for unconformities Lithostratigraphy o Useful for: Correlating local environments Determining geologic development o Limitations: Not global Diachronous (boundaries are not time boundaries) Event Themes o Sudden depositional events Volcanoes- Ash (tephra) Meteorites- tektites Meteorite impact near the Yucatan, Mexico Core is from ODPD drilling off eastern Florida Note change from ocean sediments to ejecta to ocean sediments Margin events- tsunamis or storms Useful since: Instantaneous Can be over wide regions Limitations: Not global Post depositional change
