Review: What Drives Plate Motions: (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... Crustal Age Review Bathymetry Figure 2.10 Plate Boundary Motion Ocean Basin Structure Bathymetry Topography Plate Boundaries Review Bathymetric Mapping (echo sounding, sonar, satellite gravimetry): measuring submarine topography. Sea floor physiography driven by plate tectonic processes. Abyssal Plain, Ridges, Basins, Continental Margin (Slope / Shelf). CHAPTER 3 Ocean Basins 1
Echo Soundings Echo sounder or fathometer: Reflection of sound signals German ship Meteor identified mid Atlantic ridge in 1925 Lacks detail 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). Beam angle: deeper water = wider swath Beam angle http://annaroseandthesea.blogspot.com/ 2
Beam angle: deeper water = wider swath Satellite measurements of gravity. Measure sea floor features based on gravitational bulges in the sea surface (equipotential surface). http://www.bbc.co.uk/news/science environment 12911806 http://environmentalresearchweb.org/cws/article/yournews/49837 VIDEO: http://www.guardian.co.uk/science/video/2011/mar/31/gravity map earth surface goce 3
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 Uninterpreted (top) vs. Interpreted (bottom) seismic reflection profiles offshore Humboldt Bay. Seismic Reflection Profiles reveal subsurface stratigraphy and geologic structures. 70.8% of Earth covered by oceans Average ocean depth is 3729 meters Average land elevation is 840 meters Uneven distribution of areas of different depths/elevations Variations suggest plate tectonics at work 4
Three Major Ocean Provinces: Continental margins: Shallow water areas close to shore Deep ocean basins: Deep water areas farther from land Mid ocean ridge: Submarine mountain range Passive or Active Margins Passive Not close to any plate boundary 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
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 (443 feet) Margins are dominated by sedimentation through glaciostatic sealevel fluctuations. Eel River has the largest annual sediment discharge (per km^2) in the continental US. 6
The type of continetnal margin determines the shelf features. Passive margins have wider shelves. California s transform active margin has a continental borderland. Continental Slope Steep slope between the shelf and the deep sea 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
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
Continental Rise Transition between slope and abyssal plain Marked by turbidite deposits from turbidity currents Deposits generate deep sea/submarine fans Distal ends of submarine fans transition to flat abyssal plains (e.g. Bengal fan!) Abyssal Plains Extend from base of continental rise/slope Some of the deepest, flattest parts of Earth Suspension settling of very fine particles Sediments cover ocean crust irregularities Well developed in Atlantic and Indian oceans Mid Ocean Ridges Longest mountain chains On average, 2.5 km (1.5 miles) above surrounding sea floor Wholly volcanic Basaltic lava Divergent plate boundary Mid Ocean Ridges and Transform Faults East Pacific Rise Saturn Moon Enceladus http://www.nasa.gov/mission_pages/cassini/multimedia/pia11138.html http://www.pmel.noaa.gov/pubs/outstand/embl2063/structural.shtml 9
Seamount Pillow lava Hydrothermal Vents Sea floor hot springs, originally found by Oregon State Oceanographers in 1977. Foster unusual deep ocean ecosystems able to survive 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
Fluid velocity determines the size of the particles that can be moved Sediment Transport Sediment Texture Grain size sorting Indication of selectivity of transportation and deposition processes Textural maturity Increasing maturity if Clay content decreases Sorting increases Non quartz minerals decrease Grains are more rounded (abraded) 11
Sediments Reflect composition of rock from which derived Coarser sediments closer to shore Finer sediments farther from shore Mainly mineral quartz (SiO 2 ) Terrigenous & Lithogenic sediments (from land) Rivers 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., continents, islands) River sediment loads (~10 9 tons/yr) two distinct chemical compositions ferromagnesian, or ironmagnesium 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
Sediment Distribution Neritic Shallow water deposits Close to land Dominantly lithogenous Typically deposited quickly Pelagic Deeper water deposits Finer grained sediments Deposited slowly Neritic Lithogenous Sediments Beach deposits wave deposited sand Continental shelf deposits Turbidite deposits Glacial deposits High latitude continental shelf Currently forming by ice rafting Pelagic Deposits Fine grained material Accumulates slowly on deep ocean floor Pelagic lithogenous sediment from Volcanic ash (volcanic eruptions) Wind blown (aeolian) dust Fine grained material transported by deep sea currents Dust (LANDSAT image). Dust comprise much of the fine grained deposits in remote open ocean areas (red clays) primary dust source is deserts in Asia and North Africa 13
Distribution of Sediment on Continental Shelf by Grain Size Submarine canyons (cut into the c. slope) Seafloor Features: Continental Margins Abyssal plain Continental rise Continental shelf Abyssal plain Continental slope Glacial (Ice-rafted debris) boulder to clay size 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
Biogenic sediments (from living things) Forams Diatoms Calcareous (CaCO 3 ) Foraminifera -- animals Coccolithophores -- plants Siliceous (SiO 2 ) Radiolaria -- animals Diatoms -- plants Radiolarian Biogenic Sediment Two major types: Macroscopic 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
m = micron = millionth of a meter! m = micron = millionth of a meter! Biogenic Sediments: composed primarily of marine microfossil remains median grain size typically less than 0.005 mm (i.e., silt or clay size particles) characterized as CaCO3 (calcium carbonate) or SiO2 (silica) dominated systems sediment with biogenic component less than 30% termed calcareous, siliceous clay calcareous or siliceous 'oozes' if biogenic component greater than 30% siliceous oozes (primarily diatom oozes) cover ~15% of the ocean floor distribution mirrors regions of high productivity common at high latitudes, and zones of upwelling radiolarian oozes more common in equatorial regions 16
calcareous oozes (foraminifera, coccolithophores) cover ~50% of the ocean floor level below which no CaCO3 is preserved is the 'carbonate compensation depth (CCD) This change in dissolution rate is called the lysocline. Below the lysocline, more and more calcium carbonate dissolves, until eventually, there is none left. The lysocline typically occurs at a depth of 3000 to 4000 m Sediment Accumulation Calcium Carbonate Content in Pelagic Oceanic Sediment 17
Rates of Deposition of Marine Sediment Temporal Succession of Pelagic Sediment at Spreading Centers Sediment Succession in Absence of Siliceous Ooze 18
Cosmogenous Marine Sediments Macroscopic meteor debris Microscopic ironnickel and silicate spherules (small globular masses) Tektites Space dust Overall, insignificant proportion of marine sediments Marine Sediment Mixtures Usually mixture of different sediment types Typically one sediment type dominates in different areas of the sea floor. Distribution of Marine Sediments: sediments thickest along continental margins, thin at midocean ridges coastlines dominated by river borne and wave reworked terrigenous sediments shelf and slope characterized by turbidites and authigenic carbonate deposits glacial deposits and ice rafted debris common at high latitudes high input of terrigenous sediments 'dilutes' biogenous components deep sea (pelagic) basins abyssal clays (wind blown deposits) common lower quantities of biogenic material distribution of biogenous sediments dependent upon three primary factors production in surface waters dissolution in deep waters dilution by other sediments types 19