Week 11 Flashcards
Evidence for more massive glaciers catalogued by Jean de Charpentier
GLACIAL ERRATICS
STRIATIONS/GROOVES
ROCHES MOUTONNEES
MORAINES
4 ice ages
Günz
Mindel
Riss
Würm
Possible reasons for ice ages in 1860s
Pole shift
Earth moving through space
Sun = variable star
Land distribution change
James Croll
Astronomical theory of ice ages
1875
Milankovich cycles
Eccentricity
- 100,000
- shape
Obliquity
- 41,000
- tilt
Precession
- 21,000
- wobble
What affects northern hemisphere timing
Precession
1/2 = N pole points to vega not North Star
What controls the timing of the solstice I.e. seasons?
Eccentricity and precession
- n hemisphere winter solstice currently when earth closest to the sun
- I’m 10,500 yrs will be when furthest
What kind of glaciation pattern does Croll develop?
Alternating glaciations
When pointing away and furthest
Problems with Croll
Actually simultaneous G
Max ice age acc. 80ka B.P. but Niagara Falls erodes 1m/yr = 10-20ka B.P.
Milankovich theory
Colder summer T and warmer winter T
=…
Obliquity is key - most land is in the N hemisphere therefore 65’N important
Simultaneous G
Matched geomorphology
Problems with milankovich
Geomorphology proven wrong
Orbital variations not enough
First ocean sediment core
Swedish deep sea expedition on albatross ship 1947-1949
What can foraminifera tell us (and what are they)
= amoboid protists with calcite shell
ISOTOPIC COMPOSITION
WATER T
SALINITY
DEGREE OF DISSOLUTION
DEGREE OF BIOTURBATION
What is the 18O signature of forams during G?
High 18O as 16O is locked in continental ice sheets
G-IG cycles are controlled by… and modulated by…
Eccentricity
Precession
N.B. Mid-Pleistocene transition ~1ma cycles increased
