EKSAMEN
i
GEO-3121, Marin geologi
Tirsdag 13. desember, 2005, klokka 09.00 - 13.00
Asg5rdveien 9
Du kan bruke linjal, kalkulator og ordbok!
You are allowed to use a ruler, a calculator, and a dictionary!
f-'
Du har fire oppgaver & lsse og for hver oppgave kan du f& 20 poeng, totalt 80
poeng.
You have four major tasks and for each task you can reach 20 points, and a total
of 80 points.
Ved eventuelle sporsmil ringer varamann Stefan Buenz
tel. 7764-($5266
Lykke ti]!
Juergen Mienert
Task 1 : Sea floor spreading
Sea floor spreading is one component of the theory of plate tectonics. According to
this concept an ocean basin can develop.
Procedures: A map of Iceland and a portion of the Norwegian-Greenland sea region
are provided (Fig.1). On either side of the ocean ridge are stripes of oceanic crust
labelled from chron 0 (ridge) to chron 24 (margin). The distance between Point A and
Point B, which has approx. the width of Iceland is ca. 400 kilometres (km).
A: Determine the ages (polarity boundary from black to white) in millions of
years using the geomagnetic polarity time scale (Fig. 2)
Chron 5: AgeChron6: AgeChron 24: Age-
Ma
Ma
Ma
B. Calculate the half-rate of sea floor spreading, the velocity a t which one strip of
this rock has spread away from the ocean ridge for Chron 6. (Note: Rate of
spreading = distance of chron from ocean ridge crest divided by time of polarity
change)
Chron 6 (Ma):
half spreading rate =
krn/Ma and
cmlyear
C. Calculate the total rate of seafloor spreading, and answer whether this is a
fast o r a slow spreading ridge.
Chron 6 (Ma):
total spreading rate = -k m M a and
,
cmlyear
D. What are the geological periods and the age during which (i) the NonvegianGreenland Sea and (ii) Iceland began to form? Use the geomagnetic polarity time
scale (Fig. 2) and Fig. 1.
Figure 1: TOP figure - Age of spreading shown along line A-B indicated by magnetic
isochrones. 'Ihe approximate distance between point A and B is 400 km. BOTTOM
figure - Sketch of the mid-ocean ridge showing Iceland an the direction of the NWh
American and Eurasian Plate movement.
The magnetic reversal timescale
*8
Ml
MI
81,
Yn
ilii
Uf9
M11
MI,
MU
MI*
ma0
111
YII
Mi3
U14
l t l
Yt7
)te the long
riod of
irmal
polarity in the
Cretaceous:
from -83 to
135 Ma you
have no
reversals to
work with
!:
a:
Figure 2: Geomagnetic polarity timescale. Note: the age of chron 5 is -1 1 Ma.
Task 2: Ocean basins, mid-ocean ridges and sealevel
You will deduce that if sea floor is created at mid-ocean ridges, it must be destroyed
elsewhere, or the Earth would be expanding. A digital map showing isochrones of
ocean basins (Figure 3) allows you to identify areas of subduction and creation of sea
floor.
A: Does the Atlantic or the Pacific Ocean show major sea floor subduction along
its plate boundaries? Mark the subduction zones on the map in Figure 3.
B: Would the sea level rise or fall if all ocean ridges today would become fast
spreading ridges? Explain your answer.
C: Is the seafloor spreading rate increasing or decreasing towards the pole of
rotation? Where is the pole of rotation for the Nansen basin in the Arctic Ocean
(Figure 4). Mark it on the map in Fig. 4.
D: Which of the ocean ridges in Figure 5 are fast and which are slow spreading
ridges? Explain your answer.
I
Figure 5: Ocean ridges showing various spreading rates
Task 3: Ocean water mass circulation
A: What drives the global circulation of surface and deep-water masses? How
much water moves the Gulfstram poleward on a daily scale if you assume a flux
of 50 Sv, and how much water exchange has a fjord on a daily scale if you
assume 0.2Sv inflow? Note that 1Sv = 106 m3s-1
B: How can the density of surface water and thus water mass sinking processes
in the oceans to be increased in (a) the Greenland Sea and (h) the Mediterranean
Seas?
C: Draw a schematic diagram for a fjord circulation and the Mediterranean
circulation and explain the major differences.
D: Explain the effect of cyclonic and anticyclonic winds in the northern and
southern hemisphere on a) the shape of the sea-surface and the depth of the
thermocline, and h) ocean biogenic productivity.
Figure 6: Surface ocean circulation showing current directions and major gyres.
Figure 7: Siliceous and calcareous zooplankton and phytoplankton.
Task 4: Sediments in ocean basins
A. What controls the location of high biogenic productivity along the
ocean margins? Make a sketch of wind systems and water mass
movements for the direction of the Ekman transport off NW and SW
Africa. Indicate areas of high siliceous concentrations in Figure 6 and
identify the siliceous phytoplankton and zooplankton in figure 7.
B. What controls the sedimentation rate and distribution of terrigenous
and biogenic sediments in the Norwegian-Greenland Sea during glacial
and interglacial times? Indicate the areas with increased silica and
carbonate concentrations for the Norwegian-Greenland Sea during
interglacial times in Figure 6.
C. Explain - using a sketch -the solubility of carbonate and silica changes
with depth and temperature? Do you expect to find higher carbonate
concentrations in water depth shallower or deeper than 4000 m? Use
Figure 8 to explain and to determine the depth of the carbonate
compensation depth (CCD) !
D. A sedimentary sequence drilled in the eastern Mediterranean basin
shows fkom bottom to top: carbonates, anhydrite, gypsum, halite,
terrigenous sediments, carbonate, anhydrite, gypsum, and halite. Explain
the conditions of basin water mass inflow and climate using the
sedimentary sequence.
carbonate ion concefltration
0
0
-
[GO:-] (mat m-3}
0.04 0.08 0.12 0.16 0.20 0.24 0.28
1
1 * I
I
1
1 000 -
-
-
2 000
C
E
5
n
w
3000
-
Atlantic
t8" S, 3 i 0 W
-
carbonate ion concentration
[co~;](lo6 moi T')
Figure 8: Laboratory derived saturation curves of ~ 0 3concentration
~versus depth
for calcite and aragonite (solid lines). Dots present a profile of measured and
calculated values for a station in the Atlantic.