Sedimentation. Ocean Sediments Chapter 5. Paleoceanography. Lecture #6 Week #4. A.K. Morris, Ph.D.

Transcription

1 Sedimentation Ocean Sediments Chapter 5 A time capsule to the past Principle of superposition going deeper in the sediment means looking further into the past Oceanography Lecture #6 1 2 Fig. 5.1 Paleoceanography Study of ancient oceans by looking at sedimentation Do this with sediment cores 3 4 Oregon State U. Oregon State U. 5 Oregon State U. 6

2 Inspecting Sediment Cores Sediment layers formed from: dust volcanic ash river sediments underwater mudslides plant and animal skeletons precipitated calcium carbonate salts left behind by an evaporated sea Inspecting Sediment Cores Looking at Oxygen: First proposed by Cesare Emiliani ( ) Climate change investigations Heavy vs Light oxygen Showed that Earth climate changes Foraminifera 7 8 marum.de Sediment Cores in Marina Del Rey Harbor 9 S. Anghera H.M.S. Challenger Expedition First real ocean sediment investigation Sampling the Bottom RECALL: Only 300 deep water measurements Thomson found the bottom was as varied as on land

3 Forams all over the bottom Thick and thin distributions Kullenberg piston corer Breakthrough in coring Could core up to 25 m CLIMAP Project (1971 ( ) 1982) Climate: Long Range Investigation, Mapping, and Prediction (CLIMAP) Deep cores going back 700,000 years Lead to our understanding of Milankovitch Cycling Earth Cycles Milankovich Cycling #1 Eccentricity (100,000 year cycle) #2 Axial tilt (41,000 year cycle) #3 Precession (26,000 year cycle) Graphing Milankovich Cycling Heinrich Events Very fast onset of ice ages 6 in the past 75,000 years Demo Dansgaard Oeschger Events Not mentioned in your book Refers more to drastic climate fluctuations (VERY rapid warming) 25 or so in the past 110,000 years 17 18

4 New Approaches Ice cores and shallow sediment cores can only tell us so much Ocean Drilling Program (ODP) and R/V JOIDES Resolution! R/V JOIDES Resolution Fig. 5.5 Marine Sediment Classification Descriptive visual analysis comes first. What is it? Size Classification How big is it? Genetic Classification Who/what made it? Fig Descriptive Classification Data Logging divided into: Granular Granular Mud, silt, sand, shells, tests Formed by weathering, bio activity, volcanism biogenous vs. lithogenous Chemical Hydrogenous vs authigenic Got there over slower processes Limestone secretions, mineralize bio remains, evaporites,, metals deposits 24

5 Fig. 5.8 Lithogenous granular Classification based on size Uden-Wentworth scale Fig. 5.9 Biogenous granular Chemical Classification based on source Sediment Cycling Erosion, raining of particles Metamorphosis and melting Reincorporation Fig Links to the Hydrologic Cycle Inextricably linked Sediment Mobilization To dislodge A, current speed > 20 cm/s (8 in/s). Fig Continental Weathering Mechanical vs. Chemical vs. Biological Below 1 cm/s, particle falls out 29 30

6 Sediment Transport Moved by wind and water Fig Biological Sedimentation Fig Threshold Velocity relates to grain size Rolling, saltation,, and suspension Well-sorted = dominated by one size class Poorly-sorted = even mix of all size classes Sediment Traps Transport of C faster than predicted Biological Pump Carbon Affected by: Activity of sed producing orgs (e.g. high productivity = more sed n) Factors affecting sed n rate (e.g. aggregations) Factors affecting solubility (e.g. temp., pressure, chemistry) CaCO 3 Compensation Depth Lysocline vs. CCD = difference is determined by the productivity above Bioturbation by infauna Fig Fig Ecotoxicology and Sediment (example = Port of Los Angeles) Sediment Toxicity Testing Finer sediments sequester toxins better 35 36

7 New Orleans Consulting Work Aug 2007 Photos not shown here 37