9/20/2012 Crustal Age Review Review: What Drives Plate Motions: Bathymetry (1) Density vs. Gravity: causes oceanic crust to sink in subduction zones, causes crust to extend at spreading ridges (called ridge push, but the ridge is not pushing, the crust is pulling as it sinks into subduction zones)… (2) Thermal Convection: exerts drag force to base of crust, circulates heat and mantle material... Figure 2.10 Plate Boundary Motion Review •Ocean Basin Structure • Bathymetric • Bathymetry • Topography Mapping (echo CHAPTER 3 • Plate Boundaries sounding, sonar, Ocean Basins satellite gravimetry): measuring submarine topography. • Sea floor physiography driven by plate tectonic processes. • Abyssal Plain, Ridges, Basins, Continental Margin (Slope / Shelf). 1 9/20/2012 Modern Acoustic Instruments • Side scan SONAR – GLORIA (Geological Long‐range Inclined Acoustical instrument), Sea MARC (Sea Mapping and Remote Characterization): use the properties of acoustic reflection to characterize the seafloor material properties. • Multi‐beam Echosounders/SONAR – Pole mounted, towed, or hull mounted. – Collect Bathymetric data, as well as acoustic data that can be processed to characterize the seafloor material properties (eg. for habitat classification for the US Territorial Sea). •Echo Soundings –Echo sounder or fathometer: Reflection of sound signals – German ship Meteor identified mid‐Atlantic ridge in 1925 •Lacks detail Beam angle: deeper water = wider swath Beam angle http://annaroseandthesea.blogspot.com/ 2 9/20/2012 Beam angle: deeper water = wider swath http://www.bbc.co.uk/news/science‐environment‐12911806 • Satellite measurements of gravity. • Measure sea floor features based on gravitational bulges in the sea surface (equipotential surface). VIDEO: http://environmentalresearchweb.org/cws/article/yournews/49837 http://www.guardian.co.uk/science/video/2011/mar/31/gravity‐map‐earth‐surface‐goce 3 9/20/2012 • Humboldt Bay Bathymetry and Topography related to tectonic deformation and sedimentation. • Seismic Reflection Profiles reveal subsurface stratigraphy and geologic structures. • Seismic Reflection Profiles – Air guns – Strong, low‐frequency sounds – Details ocean structure beneath sea floor Hypsographic Curve: Shows relations between elevation of land and ocean • 70.8% of Earth covered by oceans • Uninterpreted (top) vs. Interpreted (bottom) seismic • Average ocean depth is 3729 meters reflection profiles offshore Humboldt Bay. • Average land elevation is 840 meters • Seismic Reflection Profiles reveal subsurface stratigraphy • Uneven distribution of areas of different depths/elevations and geologic structures. • Variations suggest plate tectonics at work 4 9/20/2012 Three Major Ocean Provinces: • Passive or Active Margins Continental margins: Shallow‐water areas close to shore • Passive Deep‐ocean basins: Deep‐water areas farther from land – Not close to any plate boundary Mid‐ocean ridge: Submarine mountain range – No major tectonic activity – Example: East coast of United States • Active – Associated with convergent or transform plate boundaries – Much tectonic activity Convergent or Transform • Convergent Active Margin – Oceanic‐continent convergent plate boundaries – Active continental volcanoes – Narrow shelf – Offshore trench – Example: Western South America • Transform Continental Margin – Less common – Transform plate boundaries – Linear islands, banks, and deep basins close to shore – Example: Coastal California along San Andreas Fault 5 9/20/2012 Continental Shelf • Flat zone from shore to shelf break – Shelf break is where marked increase in slope angle occurs • Slope generally <5° • Average width is 70 km (43 miles) but can extend to 1500 km (930 miles) • Average depth of shelf break is 135 meters Margins are dominated by (443 feet) sedimentation through glaciostatic sea‐ level fluctuations. Eel River has the largest annual sediment discharge (per km^2) in the continental US. 6 9/20/2012 • The type of continetnal margin determines the shelf features. Continental Slope • Passive margins have wider shelves. • California’s transform active margin has a continental • Steep slope between the shelf and the deep sea borderland. • Topography similar to land mountain ranges • Steeper slope than continental shelf – Averages 4° but varies from 1–25° gradient • Marked by submarine canyons Turbidity Currents • Submarine Landslides • Sediment from continental shelf and slope • Move under influence of gravity and bouyancy driven flow • Sediment deposited at slope base 7 9/20/2012 Adams, 1990; Goldfinger, et.al. 2009 Cross Section Mosher, et.al. 2008 Prothero, 1989 RR0705‐96PC Submarine Canyons • Narrow, deep, v‐shaped in profile • Steep to overhanging walls • Traverse the slope to the base • Carved by turbidity currents 8 9/20/2012 Abyssal Plains • Extend from base Continental Rise of continental rise/slope • Some of the • Transition between slope and abyssal plain deepest, flattest • Marked by turbidite deposits from turbidity parts of Earth • Suspension currents settling of very • Deposits generate deep‐sea/submarine fans fine particles • Sediments cover • Distal ends of submarine fans transition to flat ocean crust irregularities abyssal plains (e.g. Bengal fan!) • Well‐developed in Atlantic and Indian oceans Mid‐Ocean Mid‐Ocean Ridges Ridges and Transform Faults • Longest • East Pacific Rise mountain chains • Saturn Moon Enceladus • On average, 2.5 km (1.5 miles) above surrounding sea floor • Wholly volcanic • Basaltic lava • Divergent plate boundary http://www.nasa.gov/mission_pages/cassini/multimedia/pia11138.html http://www.pmel.noaa.gov/pubs/outstand/embl2063/structural.shtml 9 9/20/2012 Hydrothermal Vents • Sea floor hot springs, originally found by Oregon State Oceanographers in 1977. • Foster unusual deep‐ocean ecosystems able to survive Seamount Pillow lava without sunlight • Warm water vents –temperatures below 30°C (86°F) • White smokers –temperatures from 30–350°C (86–662°F) • Black smokers –temperatures above 350°C (662°F) http://volcano.oregonstate.edu/submarine‐volcanic‐ecosystems CHAPTER 4 Marine Sediment Classification: A. Shape, Size, Variation B. Formation Processes: • Lithogenic (rock) • Biogenic (organic based) • Authogenic/Hydrogenous (precipitated from water) • Volcanic • Cosmogenic (outer space) http://www.pmel.noaa.gov/vents/gallery/smoker‐images.html 10 9/20/2012 Sediment Transport Sediment Texture Fluid velocity • Grain size sorting determines – Indication of selectivity of transportation and the deposition processes size of the particles that • Textural maturity can be moved – Increasing maturity if • Clay content decreases • Sorting increases • Non‐quartz minerals decrease • Grains are more rounded (abraded) 11 9/20/2012 Sediments Terrigenous & Lithogenic sediments • Reflect composition of rock from which derived (from land) •Coarser sediments closer to shore • Rivers • Finer sediments farther from shore •Mainly mineral quartz (SiO2) • Winds (aeolian) • Glaciers (ice-rafted debris, IRD) • Turbidites • Sea level changes Terrigenous Sediments: • derived from weathering of rocks at or above sea level (e.g., 9 continents, islands) River sediment loads (~10 tons/yr) • two distinct chemical compositions – ferromagnesian, or iron‐ magnesium bearing minerals – non‐ferromagnesian minerals –e.g., quartz, feldspar, micas • largest deposits on continental margins (less than 40% reach abyssal plains) • transported by water, wind, gravity, and ice • transported as dissolved and suspended loads in rivers, waves, longshore currents 12 9/20/2012 Sediment Distribution Neritic Lithogenous Sediments • Neritic • Beach deposits – Shallow‐water deposits – wave‐deposited sand – Close to land • Continental shelf deposits – Dominantly lithogenous • Turbidite deposits – Typically deposited quickly • Glacial deposits • Pelagic – High latitude continental shelf – Deeper‐water deposits – Currently forming by ice rafting – Finer‐grained sediments – Deposited slowly • Dust (LANDSAT image). Pelagic Deposits • Dust comprise much of the fine‐grained deposits in remote open‐ocean • Fine‐grained material areas (red clays) • Accumulates slowly on deep ocean floor • primary dust source is • deserts in Asia and North Pelagic lithogenous sediment from Africa – Volcanic ash (volcanic eruptions) – Wind‐blown (aeolian) dust – Fine‐grained material transported by deep sea currents 13 9/20/2012 Seafloor Features: Distribution of Sediment on Continental Margins Continental Shelf by Grain Size Submarine canyons (cut into the c. slope) Abyssal plain Continental shelf Continental rise Abyssal plain Continental slope • boulder to clay size Glacial (Ice-rafted debris) particles also eroded and transported to oceans via glacial ice • glacier termination in circum‐polar oceans results in calving and iceberg formation • as ice (or icebergs) melt, entrained material is deposited on the ocean floor • termed 'ice‐rafted' debris 14 9/20/2012 Biogenic sediments Calcareous (CaCO3) Foraminifera -- animals Biogenic Sediment (from living things) Coccolithophores -- plants Siliceous (SiO2) Radiolaria -- animals • Two major types: Diatoms -- plants Forams –Macroscopic Diatoms Radiolarian • Visible to naked eye • Shells, bones, teeth –Microscopic • Tiny shells or tests • Biogenic ooze • Mainly algae and protozoans m = micron = millionth of a meter! m = micron = millionth of a meter! 15 9/20/2012 m = micron = millionth of a meter! m = micron = millionth of a meter! • siliceous oozes Biogenic Sediments: (primarily diatom oozes) cover ~15% • composed primarily