til
til
0
......
0
....
u
:E
Open Tasks and Queslions
37
Paleomagnetic Ages
CRETACEOUS
JURASSIC
LOWER
UPPER
TERT IARY
PALAEOGENE NEOG.
Million .
(j I .
>-0
0::: W ,.
< { Z
I- W
,.
Z ·
a:: W
W <.9 ' "
1- 0
Lf)
~
0
W
U
<{
lW
a::
u
W
<{
-.J
rt. ••
a::
W
a l, !
Q..
Q..
••
~
""
a::
w
~
0
...J
U
i7)
Lf)
<{
a::
~
-,
'60
' \ 0
140
1]0
110
no
100
t o
' "
lCr
H I
.... 0
.. 0
) 0
M 20
15
10 M 1 Magn Anomal,E'S
30 25
20 15 10
•
•
10
o IN io
'9
14.
~ l Eo
depth '.,.'~ "" "" ~ ~
distance"""' "
• Mognetlc oge
I Mlcropoleon to -
IOgicOl07
,/I
i. ;; L Sites
I\.OlIll lEIS,...,
:!CO
fm all.""
Fig. 1.18. Comparison of magnetic anomaly ages ("basement age s") and biostratigraphic ages for
oldest sediment. Glomar Challenger Sites I ~417 (l968 ~ 1976). Compiled by M. Sarnthein, Kiel.
Note that most of the sediment ages are slightly younger than the pal eomagnetic basement ages as
is expected. Insert Age-distance plot of DSDP Leg 3 data, on a profile across the Mid-Atlantic
Ridge off Brazil at 30° S. These data (published by A. E. Maxwell et aI., 1970, Science 168: 1047)
first demonstrated the agreement between paleomagnetic dating based on the hypothesis of sea floor
spreading, and the dates deri ved from biostratigraphy
Both the physics of motion and the chemistI)' of the fractionation of materials
constitute the focus of such studies. How exactly are sulfide deposits formed near the
Ridge crest? What is their fate in the subduction zones? Do they contribute to the
formation of ore bodies there? What is the role of hydrothermal fluids in both environments? More fundamentally, how do these processes bear on the composition of
seawater and the atmosphere? We shall return to some of these questions, especially
in Chapter 10.