Today Chapter 17 part I Earth beneath the

Today: Chapter 17, part I Earth beneath the Ocean Study guide Techniques of mapping the ocean floor Which parts make up a continental margin, and what is the difference between passive and active margin? · How are submarine canyons formed? · How does the continental rise get most of its sediment (turbidity currents) · The three major provinces of the ocean floor (ocean basins, continental margins and mid-ocean ridges). · Features of deep-ocean basins: Trenches, seamounts, abyssal plains · Types of seafloor sediments. · When is a biogenic sediment called an ooze (at least 30%contribution to sediment)? What are the two main biogenous sediments (calcareous and siliceous oozes) · What are features of erosional and depositional shore • Sand budget of a beach • Example of shoreline subsidence and emergence • Cause of sealevel rise ·

Today: Chapter 17, part I Earth beneath the Ocean 1. Mapping the ocean floor 2. Oceanic provinces 3. Seafloor sediments 4. Sampling the ocean floor

1) Mapping the ocean floor Methods (modern) Submersibles, Sonar (echoes of sound waves), Drill Ships, Seafloor Observatory Fig. 17. 2

1) Mapping the ocean floor Methods (modern, contd) l satellite radar (microwave beams)

1) Mapping the ocean floor Methods (old) l depth sounding lines (weighted line) First exploration of deep-sea floor with HMS Challenger (1872 -1876)

2) Marine provinces 1. Continental margin boundary between continent and ocean rift blocks of continental crust that are covered by sediment passive or active margin 2. Mid-ocean ridges sea-floor spreading center 3. Deep-ocean basins Abyssal plain (Pacific: abyssal hill province) deep ocean floor away from continental margins

2) Marine provinces Passive and active continental margins Passive margin = Atlantic type margin Active margin = Pacific type margin *no plate boundary *no seismic activity *sediments accumulate to 10 -20 km thick layer *wide continental margin *convergent plate boundary *trenches mark the boundary of continent and ocean, strong earthquakes *sediment accumulation few km *narrow continental margin Note vertical exaggeration! Fig. 17. 8

How are submarine Canyons created? Turbidity currents move downslope and erode submarine canyons in the continental slope. Deep sea fans are created by turbidite deposits at the mouths of the canyons, merge at the base of the continental slope and make up most of the sediments of the continental rise. These turbidity deposits exhibit graded bedding. See Fig. 17. 9

2) Marine provinces 1. Continental margin boundary between continent and ocean rift blocks of continental crust that are covered by sediment passive or active margin 2. Mid-ocean ridges sea-floor spreading center 3. Deep-ocean basins Abyssal plain (Pacific: abyssal hill province) deep ocean floor away from continental margins

Oceanic divergent plate boundaries: Oceanic ridges and rises Axial valley Atlantic: Mid-Atlantic Ridge Pacific: East-Pacific Rise

2) Marine provinces 3) Mid-ocean ridges l longest topographic feature on Earth (70, 000 km!) l 2 -3 km above ocean basins l. Rift valley along ridge axis l basaltic rocks

2) Marine provinces Features of Deep-Ocean basins l deep ocean trenches: - narrow… deep…. where oceanic plates are subducted…dominant bathymetric feature of the Pacific Ocean. l abyssal plains: l seamounts:

Features of Deep-Ocean basins NOT ridges, NOT margins 30% of Earth’s surface l deep ocean trenches: - narrow, deep, where oceanic plates are subducted, dominant bathymetric feature of the Pacific Ocean. l abyssal plains: - incredibly FLAT areas, thick sediments l seamounts:

Features of Deep-Ocean basins l deep ocean trenches: narrow, deep, where oceanic plates are subducted, dominant bathymetric feature of the Pacific Ocean. l abyssal plains: - incredibly FLAT areas, featureless, thick sediments l seamounts: - volcanoes, formed at ridge, or by hot spots, below sea-level, most are in the Pacific

3) Seafloor sediments Types Derived from: l terrigenous land Mineral grains from cont. rocks l biogenous organisms Marine animal shells, skeletons l hydrogenous water Minerals crystallize out of water

Terrigenous sediments Most lithogenous sediment is made up of quartz (Si. O 2 ) and clay Transport media include Rivers, glaciers, and wind.

Biogenous sediments Biogenic ooze contains at least 30% of skeletons from single celled microscopic algae and protozoa. Calcareous ooze Siliceous ooze

3) Seafloor sediments Carbonate oozes are only found above the calcium carbonate dissolution depth (CCD). Deeper water is more acidic (has more dissolved CO 2) and will dissolve the calcite shells. Fig. 17. 11

Calcium carbonate in modern surface sediments in the world oceans. The distribution follows the relatively shallow mid-ocean ridge that is above the CCD.

Hydrogenous sediments • Limestones • Evaporite salts • Manganese nodules Ancient evaporites (halite, Na. Cl and gypsum, Ca. SO 4)

Manganese nodules on the Pacific Ocean Floor Cross section through a manganese nodul Mining of nodules SEM of the surface of a nodule, evidence for microbial mediation of nodule formation? c. Contain Mn, Fe, Co, Cu, N

Manganese nodules distribution in the world ocean’s.

4) Sampling the ocean floor JOIDES Resolution (Joint Oceanographic Institutions for Deep. Earth Sampling) Can drill 1 km long sediment cores from over 8, 000 m water depth Cores represent millions of years of Earth’s history

4) Sampling the ocean floor Sediment core taken with drill-ship Joides Resolution in 1997 off Florida reveals first complete K-T deposits with meteor-debris Tertiary Only after 5000 yrs, biogenous sediment is being deposited Fireball and fallout, iridium anomaly Impact ejecta, tektites, spherules, shocked quartz K-T Boundary Cretaceous