Methods of studying the sea floor

rock dredge

cover

sea-floor drilling

submersibles

echo sounders

seismic profiler (similar to echo sounder but better mig louder noise at lower frequency)

magnetic, gravity & seismic refractor
 

Features of the Sea Floor
 

Shelf, Slope, Rift valley, Slope Shelf
 

sketch of the sea floor.....(diagram)
 
 
 
 
 
 

Rise, Abyssal Plain, 5 km Mid-oceanic Ridge, Sea Mounts, Trench
 

Continental shelf are topographic features that are defined by their depth, flatness and gentle seaward tilt slope <1
 

Topographic Oceanic Basin is divided into 3 major units

1. Continental Margins (2 types- active and inactive)

Continental Shelf

Continental Slope

Continental Rise

2. Oceanic Floor

3. Mid ocean ridges
 

Continental Slope is relatively steep slope that extends from a depth of 100-200 m at the edge of the continental shelf. Angle of depth ~ 4-5
 

Submarine canyons - V-shaped valleys that cut across continental shelves and down continental slope
 

Abyssal fans - found at the base of many submarine canyons
 

Canyons are erosional features and turbidity current is a great factor.
 

Passive continental margins - include a continental shelf, slope and rise. These develop on geologically quiet coasts (No earthquakes, volcanoes or young mountain ranges) found in Atlantic, Arctic, and Indian Oceans.
 

Continental rise has slope ~ 0.5 rests upon oceanic crust
 

Types of deposition

Sediments are deposited two ways - through turbidity current and contour current
 

Abyssal plains - very flat regions
 

Active Continental Margins - characterized by Earthquake
 

Oceanic trench - Average depth 8-10 km. Associated with oceanic trenches are earthquakes of the Benioff seismic zones - these areas are marked by abnormally low heat flow compared to normal ocean crust.
 

Mid-Oceanic Ridges - giant undersea mountain range > 80,000 km long, 1500-2500 km wide and 2-3 km high above the ocean floor
 

Fracture zones - 'major' lines of weakness in the earth's crust that cross the mid-oceanic ridge at approximately right angle.
 

Sea mounts, Guyots and Aseismic Ridges

. Sea mounts - conical undersea mountain 1000 m or more above sea floor
 

. Guyots - flat-topped sea mounts
 

. Aseismic Ridges - the alignment of sea mounts and or guyots with some ridges which have no earthquake activities
 

Reefs - wave-resistant ridges of coral, algae & other calcereous organisms and warm, shallow sunlit water with low suspended sediments
 

3 types of reefs

i. fringing reefs - flat and attached directly to shore
 
 
 

ii. Barrier reefs - parallel to shore separated by wide deep lagoons
 
 
 

iii. Atolls - circular reefs that rim lagoons
 
 
 
 
 

Sediments of the floor - Terrigenous (land derived), Pelagic Sediment (clay skeleton)
 

Terrigenous

Biogenous

Hydrogenous

Limestone

Manganese nodules

(economic protection)
 

Oceanic crust and ophiolites
 

Age of sea floor not older than 200 million years old as opposed to 4.5 billion years of earth
 

Geologic Riches in the sea

Oil & gas

Phospherite

Gold, Diamonds

Heavy black sands

Manganese nodules