The Sea Floor

Origin of the Ocean

• Water vapor released during degassing of early earth–volcanism

• Salt from chemical weathering

Methods of Studying the Sea Floor

• Rock Dredge• Corer• Sea-Floor Drilling• Submersibles• Echo Sounder

• Seismic Profiler

• Surveys - Magnetic, Gravity, Seismic Refraction

• Deep Sea Cameras

Features of the Sea Floor

• Continental Margins– Passive – Active

• Oceanic trench• Mid-oceanic ridge• Seamounts

Continental Shelves and Continental Slopes

• Vertical exaggeration in diagrams• Continental shelf• Continental slope• Continental rise

Active Continental Margins

• On land- earthquakes, young mountain belt, volcanoes

• Continental shelf, continental slope, oceanic trench

• Oceanic Trenches– Earthquakes of the Benioff seismic Zones– Volcanoes – Low Heat Flow– Negative Gravity Anomalies

Submarine Canyons

• Abyssal Fans• Bottom Currents• Down-canyon movement of sand• Bottom currents• River erosion• Turbidity Currents

– Graded bedding– Shallow water fossils

Passive Continental Margins

• Continental shelf, slope, rise• The Continental Rise

– Types of Deposition• From turbidity currents• From contour currents

• Abyssal plains

Fracture Zones

• Offset rift valleys• Transform Fault

– Portion that has earthquakes

Seamounts, Guyots, and Aseismic Ridges

• Seamounts• Guyots• Aseismic ridges

Reefs

• Fringing Reefs• Barrier Reefs• Atolls

Sediments of the Sea Floor

• Terrigenous Sediment• Pelagic Sediment

– thickness increases away from crest of mid-oceanic ridge

Deep-sea sediments, those found at depths greater than about 500 m, cover roughly two-thirds of the Earth. The predominant deep sediment is carbonate ooze, which covers nearly half the ocean floor

The Mid-Oceanic Ridge

• Rift Valley• Geologic Activity on the Ridge

– Shallow-focus Earthquakes– High Heat Flow– Basalt Eruptions– Hot springs

• Black Smokers

• Biologic Activity on the Ridge– Geomicrobiology

Oceanic Crust and Ophiolites

• Evidence for composition of the oceanic crust

• Ophiolite (from top to bottom)– Marine sedimentary rock– Pillow basalt– Sheeted dike complex– Gabbroic intrusions– Ultramafic rock

The Age of the Sea Floor

• Younger than 200 million years old• Parts of continents much older