Records of Change

"OBSERVATIONS"  OF  THE   GEOLOGIC   RECORD

Timescale Methods
*SOLAR SYSTEM, EARTH  FORMATION
 109 Y (Billion Years)
     -Optical and Radio Telescopes
     -Land Rocks

*TECTONIC PROCESSES
108-106 Y (100 Million-Million Years)
     -Ocean Sediment Cores
     -Land Rocks
     -Fossils

*CLIMATE CHANGE
102-105 Y (100 - 100,000 Years)
     -Tree Rings
     -Ice cores, annual snow layers
     -Trapped gas (air)
     -Particles
     -Marine corals (growth bands)
     -Sediment cores (Up to 200 million years)
     -Written history (5000 Years)

The Atmosphere

1. Life formed ~   3.1 billion years ago
2. Photosynthesis began ~ 3 billion years ago
3. Oxygen increases through time:

     2 Billion years ago: 1% of today

About this time, RED rocks appear in the geologic record. This occurred through oxidation of iron from Fe (II) to Fe (III).
     700 Million years ago:  10% of today

4.  An OZONE (O3)   Layer was produced in the upper atmosphere by the interaction of O2 with ultraviolet (UV) light.   This shields the earth from Ultraviolet  (UV) radiation.  This allowed life to proliferate on land.

     350 Million Years ago: 100 % of today
Ozone

         UV light
 1)    O2     ------------->    2O
        diatomic ------------->   atomic
         oxygen                        oxygen

  2)    O    +    O2 ---------->  O3
    atomic     diatomic------> ozone

                                                                           oxygen     oxygen

     UV Light
          O3      ------------->  O2   +   O

Ozone is mostly in a band 10 to 25 miles above sea level. This protective layer is being damaged by the release of chloroflurocarbons, and certain nitrogen compounds (NO, NO2).

Climate Indicators in the Ice

1. The Oxygen Isotope Record - indicates amount of glacial ice

     There are two isotopes of oxygen......O16 and O18  ---  H2O16   and   H2O18

      *When ice forms, the O16 stays in the ice, the O18 stays in the water.
      *So during glacials, there is more O18  in the ocean, and more O16 in the
        ice.

2. The CO2 Record

      *The ice record the atmospheric CO2 content.

3. The Dust Record

      *The ice records the dust in the air.
      *Drier, windier


Marine Sediments

Marine Sediments - Loose particulate material that has been deposited on the ocean floor
Why are sediments of interest to scientists?

1. Great economic importance:

2. Record Book - Earth of History-

IN GENERAL - Sediments
  1. ubiquitous -
  2. accumulate constantly over time,
  3. variable in character
HOW DO SCIENTISTS STUDY SEDIMENTS-

DIRECTLY -

INDIRECTLY -

Sedimentary Sources and Processes: Where do the sediments come from?

Primary Source: Weathering - water, wind and ice erodes continental rocks, soils

  1. Rivers - carry most terrigenous sediments to the coast
  2. Currents - move sediments in suspension, depositing them far from where they entered the oceans,
  3. Winds - transport fine grain, silts and clays in suspension over vast regions of the ocean
  4. Icebergs - deposit assorted debris in high latitudes oceans up to 1000 km from their source.

Distribution of Sediments:

neritic sediments -
continental shelves, current or wave deposited, coarse grained, accumulate very rapidly >10 cm/1000 yr.
pelagic sediments -
deep sea, material that is deposited from suspension fine grained, accumulate slowly 0.1 to 1 cm /1000 yr.

Source of Sediments -

1. Terrigenous (lithogenous) Sediments - sediments formed by the weathering of rocks on the continents, delivered by wind, rivers, and ice-bergs.
Glacial marine sediments - high latitudes - ice rafted sediments
Rivers - carry terrigeneous. sediments to the cont. margin
Eolian - winds transport fine dust particles 1000's of kilometers
2. Hydrogenous (Chemical precipitates)
- minerals precipitated directly from seawater -
Sources of dissolved ions for precipitates include rock, seawater, sediment,
evaporites - form in isolated seas in areas of high evaporation
salt (NaCl)
-hydrothermal systems- sulfide deposits rich in zinc, iron, copper, and silver, along the mid-ocean ridges
Precipitate from hot hydrothermal solutions
manganese nodules
3. Cosmogenic and Volcanogenic Sediments (minor)
Cosmogenic - tektites - extraterrestrial origin -enter at the top of the atmosphere as dust and meteorites

Volcanic - ash - glassy - large and small fragments (pumice) -explosive volcanoes - deposit distinct ash layers over large areas of the world

4. Biogenic    - comprised of the fossil shells of microscopic organisms
Shell Construction -
Organisms extract ions out of the seawater, Ca, HCO3, Si, to secrete organic tissue and skeletons (or shells)
3 Categories of Biogenic Sediments
carbonate - CaCO3 (calcite)
siliceous - SiO2 - silica
organic matter
PRIMARY SEDIMENT PRODUCING ORGANISMS:

PLANKTON

-suspended organisms carried from place to place by currents
most are microscopic almost too small to be seen by the naked eye
1. Phytoplankton - unicellular algae (photosynthetic)
produce most of the ocean biomass - base of the marine food chain (grasses of the sea)
2 groups:
COCCOLITHS - carbonate plates (shields). common in warm waters
DIATOMS - siliceous - silica shell, common in cold waters , upwelling waters

2. Zooplankton - grazers, feed on detritus and other organisms.

Most abundant zooplankton are the smallest: single cell organisms:
2 groups:
FORAMINIFERA - carbonate shell
RADIOLARIA - siliceous shell

Factors controlling the distribution of sediments

Sediments are generally a mixture of the above sediments (biogenic, terrigeneous)
Several factors control the relative % of each component
Distance from land -
Nearshore - continental margin
dominated by terrigeneous sediments
accumulate more rapidly, thickest (10-100 cm/kyrs)
Deep ocean regions - oozes/clays
biogenic rich sediments
relatively thin/slow accumulation (1-5 cm/kyrs)
Ocean Ecology - Productivity (nutrients) - where the organisms grow
nutrient distribution - high nutrient content- favors silica shelled organisms
Climate -
Warm waters (low to mid-latitudes) - mostly calcareous microfossils

Economic value of marine sediments -

reservoirs tend to form in areas of relatively high sedimentation and productivity.

California - Santa Barbara, Santa Monica
Elsewhere - Gulf of Mexico, Persian Gulf, North Sea, and north coast of Australia, north slope of Alaska.