Sea Floor Lecture 2/4/09

GEOL 302 Lecture 2-4-09 Chapter 4 (Sea floor), Pt.1: Parts & Processes Changes in sea floor bathymetry Erosion: Removal of rocks or debris by transport removal of rocks or debris by dissolution Mostly slow (currents, wave action) Deposition: emplacement of debris by settling emplacement of minerals by chemical precipitation Deposition on the sea floor: continuous ?rain? of sediment falling through the water, blanketing the sea floor. Sediment: pieces of rock or other materials that can be transported ( is eroded; can be deposited) Continental margin Continental margin is the sea floor region closest to land Continental shelf Along active margins are (narrow, wide) and shelves along passive margins are narrow, wide average depth at seaward edge is about 130 m Continental shelf break Continental slope Steep! 70 km/m Turbidity current ? mix of seawater mud, silt, sand and its denser than seawater 1929 Newfoundland, Canada, earthquake: Transoceanic telephone cables broken (15-50 mph) 1976 Canadians dump mine tailings into Rubert Inlet, BC Turbidity current flows for 1.5 hours; sonar recordings of it! (NOT IN THE TEXT) Continental rise Gentler gradient than continental slope (9 m/km) Area of sediment deposition ~ 500 km wide (300 mi) (not found on active margins) Ocean basin floor ? 30% of Earth?s surface! Abyssal plain Relatively flat, flattest portion of the ocean floor as well as the smoothest (smoothed by sediment settling on basalt) Abyssal hills More than 50% of the Atlantic and 80% of the Pacific has these hills Seamounts Is an island if above water, volcanic in origin Guyots A flat topped seamount, looks like it?s had its top cut off Fringing reefs Barrier reefs