cenozoic- 65ma to present

8/13/2019 Cenozoic- 65Ma to Present

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• Greenland and Scandinavia separated during the early Cenozoic about 55

million years ago and the Norwegian-Greenland Sea emerged, linking the North

Atlantic and Arctic oceans.

• The Atlantic continued to expand while the Pacific experienced a net reduction

in size as a result of continued seafloor spreading. The equatorially situated

east– west Tethyan seaway linking the Atlantic and Pacific oceans was modified

significantly in the east during the middle Eocene—about 45 million years ago—

by the junction of India with Eurasia, and it was severed into two parts by the

confluence of Africa, Arabia, and Eurasia during the early Mioceneapproximately 18 million years ago.

• The western part of the Tethys evolved into the Mediterranean Sea not long

after it had been cut off from the global ocean system about 6 to 5 million years

ago and had formed evaporite deposits which reach up to several kilometers inthickness in a land-locked basin that may have resembled Death Valley in

present-day California.

• Antarctica remained centered on the South Pole throughout the Cenozoic, but

the northern continents converged in a northward direction.



• Several of the world’s great mountain ranges were built during the Cenozoic. The

main Alpine orogeny, which produced the Alps and Carpathians in southern

Europe and the Atlas Mountains in northwestern Africa, began roughly between

37 and 24 million years ago. The Himalayas were formed some time after

the Indian Plate collided with the Eurasian Plate.

• From about five million years ago, the RocKy Mountains and adjoining areas

were elevated by rapid uplift of the entire region without faulting.



• Lithospheric Plate motion

• Vertical Tectonism

• Weathering Reactions

• Fluctuation of Atmospheric CO2 content

• Volcanism

• Changes in oceanic circulation

• Biologic evolution

• Cyclic variation in earths orbit around the sun

Potential Factors



Introduction How to Interpret stable Oxygen & Carbon isotope

data



• Earth's climate has undergone a significant and complex evolution

• This (Cenozoic) evolution includes:-

1. gradual trends of warming and cooling driven by tectonic

processes on time scales of 105 to 107 years

2. rhythmic or periodic cycles driven by orbital processes with 104 -

to 106 -year cyclicity

3. rare rapid aberrant shifts and extreme climate transients with

durations of 103 to 105 years



More consequential changes in boundary conditions over the last 65My include

1. North Atlantic rift volcanism,

2. opening and widening of the two Antarctic gateways, Tasmanian

and Drake Passages

3. collision of India with Asia and sub-sequent uplift of the Himalayas

and Tibetan Plateau

4. uplift of Panama and closure of the Central American Seaway, and

5. a sharp decline in pCO



Role of Deep-Sea Stable

Isotope RecordC13 & O18



• High-resolution deep-sea oxygen (δ18O) and carbon (δ13C) isotope ->

records progress in resolving the rates and scales of Cenozoic climate

change

• Importance - latest generation of Cenozoic deep-sea isotope records:-

1. detailing both the rate and magnitude of past environmental

perturbations

2. Opened windows into a climatically dynamic period in Earth

history

3. has proven invaluable for developing and testing new theories onmechanisms of past climate change

4. providing the frame-work to assess the influence of climate on

the environment



Oxygen Isotope Record • Importance/Uses:-

1. principal means - reconstructing global and regional climate change on a variety of

geologic time-scales - millennial to tectonic

2. multidimensional - both climatic and stratigraphic information

3. quickly generated with automated mass spectrometers

4. discovery of geologically abrupt shifts in climate, as well as 'transient' events

5. facilitated efforts to extend the 'astronomically calibrated' geological time scale back into

the early

6. constraints on the evolution of deep-sea temperature and continental ice volume

7. deep-sea temperature data also double as a time-averaged record of high-latitude sea-

surface temperatures (SST)

• Examples:-

1. First marine isotope records were relatively coarse, but still provided valuable insight into

the general structure of the Pleistocene glacial and interglacial cycles

2. Records delineating the long-term patterns of Cenozoic climate change

3. First global compilation of records for the Cenozoic (resolution of 105 to 106 years)



Carbon Isotope Record

• Importance/Uses:-

1. Stratigraphic correlation

2. Insight into the nature & operation of the global carbon cycle &

its perturbations

3. First-order changes in deep-sea circulation patterns



Oxygen and Carbon isotope data for bottom-dwelling, deep-sea foraminifera from over 40 DSDP and ODP sites representing various intervals of the Cenozoic were culled from the literature and compiled into a single global deep-sea isotope record



Cenozoic Climate: From

Greenhouse to Icehouse



• climate evolution (depicted by this record)- under three categories

1. long-term (~ 106 to 107 years),

2. short-term or orbital-scale (~ 104 to 105 years), and

3. aberrations or event-scale (~ 103 to 104 years).



Long-term trends

1. mid-Paleocene (59 Ma) to early Eocene (52 Ma)

• most pronounced warming trend,

• 1.5ppm decrease in δ18O

• peaked with the Early Eocene Climatic Optimum (EECO;

52 to 50 Ma)

th l iddl ( t 8 M ) d l t E ( t 6 M )



2. over the early-middle (50 to 48 Ma) and late Eocene (40 to 36 Ma)

• 17 My long trend toward cooler conditions

• a 3.0 ppm rise in δ18O

entire increase in δ18O prior to the late Eocene (~1.8 ppm) can

be attributed to a 7.0°C decline in deep-sea temperature

(from ~12° to ~4.5°C)

All subsequent δ18O change reflects a combined effect of ice-

volume and temperature. Eg, rapid >1.0 ppm step in δ18O at

34 Ma - roughly half this signal (~0.6 ppm) must reflect

increased ice volume

• This long-term pattern of deep-sea warming and cooling is

consistent with reconstructions - early Cenozoic subpolar climates

based on both marine and terrestrial - geochemical and fossil

evidence



3. earliest Oligocene

• cooling and rapid expansion of Antarctic continental ice-sheets

• deep-sea δ18O values remained relatively high (>2.5 ppm) -

indicating a permanent ice sheet(s)

temperate in character

mass as great as 50% of that of the present-day ice sheet and

bottom temperatures of ~4°C



4. latter part of the Oligocene (26 to 27 Ma)

• warming trend reduced the extent of Antarctic ice

• until the middle Miocene (~15 Ma)

global ice volume remained low

bottom water temperatures trended slightly higher

with the exception of several brief periods of glaciation (e.g.,

Mi-events!)



5. middle Miocene (15 Ma)

• warm phase peaked in the late middle Miocene climatic optimum

(17 to 15 Ma)

• followed by

gradual cooling and

re-establishment of a major ice-sheet on Antarctica by 10 Ma

• Mean δ18O values then - continued to rise gently through the late

Miocene until the early Pliocene (6 Ma), indicating

additional cooling and

small-scale ice-sheet expansion on west-Antarctica and in the

Arctic



6. early Pliocene

• marked by a subtle warming trend until ~3.2 Ma

• when δ18O again increased reflecting the onset of Northern

Hemisphere Glaciation (NHG)



Rhythms Milankovich Cycle

• Frequency and amplitude - orbital scale climate variability evolved

through the Cenozoic

• benthic δ18O time-series demonstrate -

climate varies in a quasi-periodic fashion during all intervals

characterized by glaciation - regardless of the location and

extent of ice-sheets

In terms of frequency - much of the power in the climatespectrum since the early Oligocene appears to be

concentrated in the obliquity band (~40 Ky). Additional

power resides in the eccentricity bands.



Fig: Primary orbitalcomponents are displayedon the left, and Cenozoic

paleogeography on theright.

The gravitational forcesexerted by other celestial bodies affect Earth's orbit. As

a result, the amount and,more importantly, thedistribution of incoming solarradiation oscillate with time.There are three orbitalperturbations with fiveperiods: eccentricity (at 400and 100 Ky), obliquity (41Ky), and precession (23 and19 Ky)



High-resolution time-series spanningfour intervals: 0.0 to 4.0, 12.5 to 16.5,20.5 to 24.5, and 31.0 to 35.0 Ma,

each representing an interval ofmajor continental ice-sheet growth ordecay



Aberrations• Definition:-

brief (~103 to 105 y) anomalies

stand out well above 'normal' background variability in terms

A. rate, and/or

B. amplitude

usually accompanied by - a major perturbation in the global carbon cycle

• three largest occurred at :- LPTM (55 Ma), Oi-1 (34 Ma), and Mi-1 (23 Ma)

• all near or at epoch boundaries <=> widespread and long-lasting impacts on the

biosphere

1. Late Paleocene Thermal Maximum (LPTM, 55 Ma)



( , 55 )

1. 5° to 6°C rise in deep-sea temperature (>1.0 ppm negative isotope excursion) in

less than 10 Ky

2. Sea surface temperatures increased (constrained by planktonic isotope records)1. 8°C at high latitudes, and

2. lesser amounts toward the equator

3. Recovery was gradual - taking ~200 Ky from the onset of the event

4. higher humidity & precipitation - globally; evidenced by - changes in the

character and patterns of continental weathering 5. negative carbon isotope excursion (~3.o ppm) - marine, atmospheric, and

terrestrial carbon reservoirs and organic carbon deposition

6. widespread dissolution of seafloor carbonate

7. mass extinction of benthic foraminifera

8. wide-spread proliferation of exotic planktic foraminifera taxa and thedinoflagellate Apectodinium genus

9. the dispersal and subsequent radiation of Northern Hemisphere land plants and

mammals

10. The recovery interval is marked by a possible rise in marine and terrestrial

productivity



2. Oi-1 (34 Ma)

• lies just above the Eocene/Oligocene boundary (34 Ma)

• 400-Ky-long glacial - initiated with the sudden appearance of large continental

ice sheets on Antarctica (-transition, referred to as Oi-1)

• reorganization of the climate/ocean system as evidenced by

global wide shifts in the distribution of marine biogenic sediments and

an overall increase in ocean fertility

major drop in the calcium carbonate compensation depth



3. Mi-1 (~23 Ma)

• coincided with - Oligocene/Miocene boundary (~23 Ma)

• brief but deep (~200 Ky) glacial maximum

• followed by a series of intermittent but smaller glaciations



Salient Characteristics - Oi-1 & Mi-1

A. Positive oxygen isotope excursions

B. Accelerated rates of turnover & speciation in certain groups of biota

C. Rise of modern whales (i.e., baleen)

D. Change in habitat

• shift in continental floral communities at the E/O boundary and

• the extinction of Caribbean corals at the O/M boundary

E. Small but sharp positive carbon isotope excursions (~0.8 ppm)

• suggestive of perturbations to the global carbon cycle



Implications for Climate

Forcing Mechanisms Has the greater temporal resolution of Cenozoic

climate, afforded by the latest isotope

reconstructions, altered our understanding of thenature of long- and short-term climate change?



Yes & NoMost important developments:-

• the glacial history of Antarctica

evident - ice sheets' presence on Antarctica for the last 40 My

over much of that time - extremely dynamic

implying a high degree of instability and/or sensitivity to forcing.

• the scale and timing of climatic aberrations

mere existence points - the potential for highly nonlinear

responses in climate to forcing



Gateways or pCO2?

• Cenozoic climate - warm and ice-free in the beginning to cold and

glaciated at present

• Earlier - attribute the unidirectional trend, Cenozoic cooling, to asingle factor - Gateways

• Now - becoming clear that more than one factor was responsible

• But - so many variables, some still not well constrained



Transition into and out of the long-term Oligocene glaciation:-

•Thermal isolation of Antarctica by widening oceanic passages

Explains - the initial appearance of Antarctic ice-sheets

Fails to explain - the subsequent termination

•Reconstructions of Cenozoic pCO2

Explains - termination occurred at a time - greenhouse gas levels

were declining or already relatively low

moisture supply was the critical element - maintaining large

polar ice-sheets (at least during the middle Cenozoic)



Last 25 My :-

• tectonic events - a dominant role in triggering large -scale shifts in

climate

•subtle changes in pCO2 (at least within the error of the proxyestimates) may be important in triggering ice-volume changes

through influences on radiative forcing

atmospheric circulation patterns and humidity .



Orbital pacing

• proven successful - periodic climate variability relation to forcingthrough the Cenozoic

• primary beat of the glaciated Cenozoic is in the obliquity band

regardless of the state of other boundary conditions or

the location of ice sheets

• But- the overall influence of obliquity on global climate during ice-free periods, with-out an ice-sheet amplifier, is weaker or less

apparent

• strong pre-Pleistocene climate response to eccentricity oscillations

Thresholds methane



Thresholds, methane

eruptions, and orbitalanomalies

• LPTM

the abrupt negative ~3.0 ppm global carbon isotope excursion

(CIE)

implicates - rise in greenhouse gas concentrations,

Reason - 'marine clathrates' - dissociation and subsequent

oxidation of 2000 to 2600 Gt of isotopically light (~-60ppm)

methane

Oi d i



• Oi-1 and Mi-1 events

greenhouse gas forcing was probably not the primary causal

mechanism

may have served as a positive or amplifying feedback

tectonic forcing - the primary triggering mechanism

Such feedbacks would be short-lived, because other coupled

biogeochemical processes would eventually restore equilibrium

to the system



Conclusion



• Correlation does not necessarily prove causation

• Extreme aberrations in global climate can arise through a number of

mechanisms

• Importance of aberrations

the short time scales involved significantly reduces the number

of potential variables

rendering the task of identifying and testing mechanisms a moretractable proposition



References

• Zachos et al, Science, 2001:Vol. 292 no. 5517 pp.

686-693 - "Trends, Rhythms, and Aberrations in

Global Climate 65 Ma to Present“

• Bloom, A.L., 1998. Geomorphology: A

Systematic Analysis of Late Cenozoic Landforms,

Pearson Education.

• http://en.wikipedia.org

• http://eprints.soton.ac.uk/343314/

http://en.wikipedia.org/

http://eprints.soton.ac.uk/343314/



















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