In the profile (Fig. 6), what are the width and average depth of the Blake Plate
ID: 153929 • Letter: I
Question
In the profile (Fig. 6), what are the width and average depth of the Blake Plateau? What is the depth
of the sea floor to the east of the plateau?
a. Width 260 km; Blake Plateau depth 1,000 m, seafloor depth 5,000 m.
b. Width 210 km; Blake Plateau depth 100 m, seafloor depth 4,000 m.
c. Width 340 km; Blake Plateau depth 1,500 m, seafloor depth 4,000 m.
d. Width 300 km; Blake Plateau depth 1,000 m, seafloor depth 2,000 m.
e. Width 540 km; Blake Plateau depth 1,200 m, seafloor depth 5,000 m.
ESSC 320 – Lab 3
6
- Read the handout
S.E. Atlantic Continental Margin
(posted online).
15. Below is a list of geologic events that contributed to the formation of the Blake Plateau. Place them
in chronological order from 1 to 6, with 1 being the oldest and 6 being the most recent one.
___ Periodic flooding by Atlantic waters, and deposition of carbonates and evaporites.
___ Northward movement of North America results in cooler conditions. Carbonate production slows down and
cannot keep up with subsidence. Sediments change from shallow (5-100 m) to deep water (>500 m)
carbonates.
___ Continued growth of the Atlantic Ocean and associated subsidence allow the formation of coral reefs and
the deposition of shallow-water limestone and dolomite.
___ Development of a narrow, elongated depression similar to the modern Red Sea.
___ Rifting of Pangea.
___ A strong surface current began scouring the Florida Straits and Blake Plateau, cut off the supply of
continent-derived sediment to the plateau, preventing most deposition and deeply scouring the bottom.
16. Name the current that scours the Blake Plateau preventing sediment deposition. Where is it coming
from? Is it a warm or cold water current? (You will have to search the web to answer the second part of
this question; start from
http://oceancurrents.rsmas.miami.edu/atlantic/atlantic.html
)
17. Along the Blake Escarpment, where is the steepest region located and what process is responsible
for the presence of this cliff?
18. In the southern part of the Blake Plateau, immediately N of the Bahamas Islands, there is a series of
canyons. What is their origin?
19. Which of the following processes is ultimately responsible for the formation of the Blake
Escarpment?
a. subsidence; c. presence of an ancient reef;
b. erosion at the base by deep ocean currents;
d. normal faulting.
20. Geologic evidence indicates that until about 100 million years ago the Blake Plateau was a shallow
water area. Which of the following processes most likely moved the plateau to its modern depth?
a. Erosion by local currents removed the top part of the old shelf.
b. Thermal subsidence linked to the continued opening of the North Atlantic, similar to the process that
produces deeper ocean floor as you move away from the crest of ocean ridges.
c. Subduction at the convergent plate boundary.
d. Dissolution of carbonate sediments by cold sea water.
7
E. SEAMOUNTS AND ABYSSAL PLAINS
In the western North Atlantic, about 500 miles offshore the east coast of North America, there is a series of
seamounts named New England Seamounts. In this part of
the online expedition you will "surf" the Woods
Hole Oceanographic Institution (WHOI) web site to investigate their origin and characteristics. Go to the WHOI
Dive and Discover
website, and choose the
Expedition 7, New England Seamounts
(tab "Expeditions" in the
upper right part of the screen). Hunt for answer to the following questions:
21. What was the goal of this expedition, and why is this area particularly suitable for this purpose?
a. Sail across the area to construct a bathymetric map.
b. Investigate differences in the biology of shallow and deep water corals.
c. Reconstruct the flow of a deep ocean current that is thought to have changed with past climate changes.
d. Test the reliability of Alvin.
22. Which of the following best describes a seamount?
a. A mountain of volcanic origin, more than 1,000 m high, that does not reach to the surface of the ocean.
b. A mountain of volcanic origin, more than 100 m high, that does not reach to the surface of the ocean.
c. A mountain of volcanic origin, more than 1 m high, that does not reach to the surface of the ocean.
d. A mountain of volcanic origin, less than 1 km high,
that does not reach to the surface of the ocean.
e. A mountain of volcanic origin, less than 1 m high, that does not reach to the surface of the ocean.
23. What is the origin of the New England Seamounts? When did this process start and when did it
end? (You will need to check out the links on the left side of the webpage to answer this question.)
a. Hot spot volcanism; the New England seamounts formed between 125 and 10-20 million years ago.
b. Hot spot volcanism; the New England seamounts formed between 10-20 million years ago.
c. Hot spot volcanism; the New England seamounts fo
rmed between 100-80 million years ago, but the hot spot
itself was active for a longer time (between 125 and 10-20 million years ago.)
d. Volcanic activity along the Mid-Atlantic Ridge (similar to the process that formed Iceland) between 125 and
10-20 million years ago.
24. What is the difference between deep sea and shallow water corals?
a. Deep sea corals are found at water depths below the photic zone, shallow water corals only live in shallow
water.
b. Deep sea corals tolerate low temperatures, shallow water corals do not.
c. Shallow water corals have algae symbionts which require light for photosynthesis, deep sea corals do not.
d. All of the above are correct
ESSC 320-Lab3 Blake Plateau (km) 40 60 B0 120 100-300 140-400 120-400 180-400 320-330 410-420 410-420 400-500 420-550 450-550 450-550 b. 40 40 C. d. 40 140 TABLE4 Where in your profile Shelf edge Blake Plateau Blake Escarpment Ocean Floor Buke Escarpment Main features of the Atlantic continental margin offshore FloridaExplanation / Answer
14. D
15.1. Rifting of Pangaea
2. Development of narrow elongated depression
3.Continued growth of Atlantic ocean
4. Periodic flooding
5. Northward movement
6. Scouring of current
16. Florida current origin gulf of Mexico and warm
17. Blake spur, erosion is the reason
18.Great Abaco canyon, linked to vertical motion along the Great Abaco fracture zone from Cretaceous to Eocene
19. B . Erosion at the base by deep ocean currents
20 Most probably it's B according to me
21.B
22.A
23.C
24.D
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