OCNG 251 Exam 2 Study Guide Chapter 4 Marine Sediments Marine sediments give us a detailed record of Earth s history Sediment cores are examined to determine sediment origin clues to sediment origin are found in its mineral composition and its texture Through sediment analysis scientists can infer past conditions such as sea surface temperature nutrient supply abundance of marine life atmospheric winds ocean current patterns volcanic eruptions major extinction events changes in Earth s climate and the movement of tectonic plates Key Concept Marine sediments accumulate on the ocean floor contain a record of recent Earth history including past environmental conditions Variety of technologies used to obtain sediment cores from the ocean floor o Dredge a bucket like device used to scoop up sediment from the deep ocean floor for analysis sediments are filtered out so chunks remain o Piston corer is used for more shallow samples a surface sample for RECENT data o Drilling vessels are used to collect cores from the deep ocean TAMU operates one The drilling pipe is flexible like cooked spaghetti and extends 40 m down o IODP International Oceanic Drilling Program examined the Chicxulub impact site 65 mya Provides evidence for dinosaur extinction meteorite w 10 km diameter buried deep down in East TX remains of small microscopic skeletons color variations within the same sections of the core large chunk of material from the Yucatan Peninsula sand small glass balls evidence for extraterrestrial materials layer rich in iridium extraterrestrial material 65 mya Lithogenic Sediment material derived from land sources lithogenous sediment begins as rocks on continents or islands erosion transport deposition o Sources weathering agents wind water ice Rivers areas of high rainfall drainage Erosion is the mode of transport Wind low rainfall desert Erosion as transport mechanism great distances possible for transport Glacial grind stuff up over continents oceans Erosion for transport occurs in high latitudes Gravity cliff erosion steep slopes Erosion for transport driving force for erosion o Sediment texture Grain size is proportional to the energy of transportation deposition clay mud silt clay sand pebble Requires little energy to transport fine materials clay high energy to move larger sediments o Composition minerals esp quartz o Found mostly around margins of the continents where it is constantly moved by high energy current along the shoreline in deeper turbidity currents lower energy currents distribute finer components that settle in deep ocean basins microscopic particles can be carried far out over the ocean by strong winds Biogenous Sediment material derived from living sources o Key Concept Biogenous sediment is produced from the hard remains of onceliving organisms Microscopic biogenous sediment is especially widespread forms deposits of ooze on the ocean floor Ooze material composed of at least 30 biogenous source o Commonly either calcium carbonate CaCO3 or silica SiO2 or SiO2nH2O usually planktonic free floating o Silica sediments Diatom photosynthesis microscopic plants many little holes to bring nutrition in eliminate waste connected like a pill box Radiolarians eat bacteria microscopic animals Siliceous ooze causes breakdown of these sediments over time o Calcium carbonate sediments Only a few microns thick Foraminifera protozoans animals tennis ball shaped not easily broken up o Distribution of Biogenous Sediments Most common as PELAGIC deposits Factors controlling distribution Productivity the organisms present in the surface water above the ocean floor o Surface waters w HIGH biologic productivity contain many living reproducing organisms conditions likely to produce biogenous sediments those w LOW biologic productivity contain too few organisms to produce biogenous ooze Destruction dissolution process in which skeletal remains dissolve in seawater at depth o Sometimes biogenous sediment dissolves before ever reaching the sea floor sometimes it is dissolved before it has a chance to accumulate into deposits on the sea floor Dilution process where the deposition of other sediments decreases the percentage of biogenous sediment found in marine deposits o Dilution occurs most often b c of abundance of coarsegrained lithogenous material in neritic environments biogenous oozes are uncommon along continental margins o Siliceous Ooze contains at least 30 of the hardened remains of silica secreting organisms Ocean is UNDERSATURATED w silica at all depths destruction of siliceous biogenous particles by dissolving in seawater occurs continuously slowly at all depths Siliceous ooze is commonly associated w areas of high biologic productivity of silica secreting organisms accumulate siliceous tests faster than seawater can dissolve them so many tests sinking at once once buried beneath other siliceous tests they are no longer exposed to the dissolving effects of seawater o Calcareous Ooze the CCD Calcite Compensation Depth Does not immediately dissolve in solution CaCO3 dissolves at an increasing rate w increasing depth below the lysocline until the CCD is reached avg 4 500 m at below the CCD sediment does not consist of much calcite b c it readily dissolves Scarce calcareous ooze below 5 000 m today in ocean dissolution CCD Ancient calcareous oozes at greater depths Calcareous ooze deposited on top of the mid ocean ridge will not be dissolved Sea floor spreading causes the newly created sea floor calcareous sediment on top of it to move into deeper water away from the ridge below CCD where calcareous sediment will dissolve UNLESS it is covered by a deposit that is unaffected by the CCD siliceous ooze abyssal clay Hydrogenous Sediment derived from dissolved material in water o Key Concept Hydrogenous sediment is produced when dissolved materials precipitate out of solution producing a variety of materials found in local concentrations on the ocean floor o Minerals precipitate directly from seawater usually when there is a change in conditions change in temperature or pressure addition of chemically active fluids Manganese nodules high concentration central nucleation object layered internal structure formation requires extremely LOW RATES of lithogenous or biogenous input so the nodules are not buried source is not certain but nodules do NOT form continuously over time but in spurts that are related to specific conditions like low sedimentation rate strong deep water currents Evaporite