Download Introduction

GEO 3121: Marine Geology
Juergen Mienert
Høst 2008
1
Literature
• The ocean basins: Their structure and evolution. The open
•
•
•
university 2nd edition. p. 185.
Ocean chemistry and deep-sea sediments. p.134
Seawater: Its composition, properties and behaviour. The
open university 2nd edition. p. 168.
Ocean circulation: The open university 2nd edition. p. 286.
• Kennett J.P., 1982. Marine Geology.
• Emery, D. and Myers, K.J., 1996, Sequence Stratigraphy
2
Introduction
• What is the goal of this course?
• What is marine geology and why is it important?
• Sediments of the Oceans: Touring today’s sea bed from
microscopic to macroscopic features
3
What is the goal of this course?
• Understanding the oceans and its geology: To introduce the fundamental
oceanographic and geological processes active in marine environments.
• Understanding the marine environment: To provide a solid background for
the characteristics of marine geology in various parts of the world's oceans
focussing on polar regions.
4
What is marine geology?
• Marine geology is a discipline of geological
sciences in oceans. (sea floor spreading & plate tectonic, ocean
crust, sediments above ocean crusts, stratigraphy, chronostratigraphy, sea
floor morphology)
• Investigations concentrate on ocean conditions
relevant for sediment accumulation or
transportation. Data acquisition (CTD, sediment traps, benthic sledges,
current meters etc.) carried out from ships.
• Investigations concentrate on the sea floor and
sub-sea floor geology. Data acquisition (seismic profiling, sediment
coring) carried out from ships, submersibles or remotely operated vehicles.
5
6
Oceans: 1338 x 106 km3
Total: 1386 x 106 km3
7
Properties of water
8
The ocean planet- OCEANUS
1. How did the earth acquire such a large amount of water in the first place?
2. Once acquired, how was it retained?
First question has to do how the earth was formed, and the second involves the
evolution of the earth and its atmosphere!
1. Earth created by a gravitational collapse, where heavier elements migrate to
the centre and lighter elements (H,O,..) are still in the orbit.
2. Sun stabilized and the Earth went through a process of degassing from its interior
and it developed a lithosphere, atmosphere (CH4, CO2 but no oxygen) and
hydrosphere. The tempertaure of the Earth dropped and water condensed into
the oceans.
The mass of water present in the ocean is about the same as the mass of water
that was contained in the crust when the degassing process started.
Note: First known rock evidence for water comes from zircons (E-Greenland= 3,8
billion yrs, Australia= 4,3 billion yrs)
9
Why is it important?
• The ocean is covering approx. 71 % of our planet; it is the very
source of life on Earth. Over 90 percent of our planet’s living
and non-living resources are found within ocean margins a few
hundred kilometres of the coasts, where two-thirds of the
world’s population is living.
• Even if we are improving our understanding of how the ocean
system is functioning today, we are a very long way from
being able to predict natural changes and man induced changes
that may be expected in the next century due to global climate
impacts.
10
• Improved and more systematic observations of the ocean
surrounding our continents allow a better understanding of our
planet’s dynamics (Storegga film).
• There are drastic environmental changes natural and man
made and research knowledge may help to forecast or even
prevent otherwise unforeseen events.
11
• The majority of rocks exposed at the Earth's surface have
their origin in the oceans, either as sediments or as
igneous rocks. An igneous rock has solidified from
magma (lava flows, ocean crust).
• Therefore, to understand earth science processes it is
necessary to know what is happening in ocean basins.
• If you do understand the action of endogen forces than
you can answer why 70% of the earth is covered by the
ocean, why 2/3 of the land masses is on the northern
hemisphere, why the average water depth of the ocean is
3700 meters, why marine resources such as for example
oil and gas occur in ocean margins?
12
The planet earth “Oceanus”
• The ocean contains about
1.360.000 km3 of liquid water.
Since there have been about 26
ice ages during the last 2,6 Mio
years, water mass volume and
sealevel changed as well.
• How much ice exists on earth today
and how much sea-level change
could be caused by these ice masses?
- 32.000.000 km3of ice equivalent to
- 70 m sea level rise
13
Sediments of the oceans
Touring today’s sea bed from microscopic to macroscopic features
Ocean chemistry and deep sea
sediments
14
Biogenous sediments
Calcareous ooze (calcitic or aragonitic): 48%
Silicious ooze (zooplankton and phytoplankton): 14%
Terrigenous sediments
fluvial
aeolian
ice rafted debris (IRD)
Ocean chemistry and deep sea
sediments
15
Carbonate sediments - foraminifera
• calcitic zooplankton
• quite large (scale bar 50
micron)
Ocean chemistry and deep sea
sediments
16
Carbonate sediments - pteropods
• aragonitic zooplankton
• size variable
Ocean chemistry and deep sea
sediments
17
Carbonate sediments - coccoliths
• phytoplankton (algae)
• small (typically 10 micron)
Ocean chemistry and deep sea
sediments
18
Calcareous ooze
Photograph H. Edmonds
19
Siliceous sediments - radiolarians
• siliceous zooplankton
• 50 - 300 microns (scale bar
50 microns)
Ocean chemistry and deep sea
sediments
20
Siliceous sediments - diatoms
• siliceous phytoplankton
• 10-200 microns in diameter
(scale bar 20 micron)
Ocean chemistry and deep sea
sediments
21
Red clay sediments
• cosmic dust particles /
•
spherules of Ni-Fe with
oxidisation layer
aeolian sediments
Ocean chemistry and deep sea
sediments
22
Red clay of the deep ocean
Heezen and Hollister, 1971
23
Pillow basalts of the mid-ocean
ridges (MOR)
Heezen and Hollister, 1971
24
Manganese nodules of the seabed
More on web site
Heezen and Hollister, 1971
25
Photograph of the Sea Bed
• pelagic
•
sedimentation
bioturbation
Heezen and Hollister, 1971
26
Evidence for life in the abyss
Heezen and Hollister, 1971
27
Evidence for deep ocean currents –
sediment ripples
Heezen and Hollister, 1971
28
Terrigeneous sediments
• Debris from erosion processes or ice melting (IRD)
• Grain size varies from very coarse in littoral to very fine
grained in distal ocean regions depending on the transport
energy
29
Summary
• The sea floor of the deep ocean is often flat due to reduced
gravitational forces and minor submarine erosion.
• There are terrigenous and biogenous sediments that lie upon
igneous rocks. (There are also sediments due to chemical
processes but we will hear about them later).
30