The past 66 million years, known as the Cenozoic Era, is particularly relevant to climate change because the world's climate changed from the greenhouse world of the dinosaurs to our modern icehouse world. But Cenozoic sediments in the Arctic are notoriously difficult to date using fossils (‘biostratigraphy’). The talk describes the methodology, based on 40 years work by Dr Jonathan Bujak, for establishing a biostratigraphic framework for the Cenozoic of the Arctic. This enables the history of the entire region to be correlated within the Arctic and with events in lower latitudes.
2. The talk is split into three parts
• Arctic paleoceanography and climate
• historical review of the problems
• solutions leading to an regional biozonation
3. we first need a climatic and oceanographic
perspective going back into the Mesozoic
4. MESOZOIC OCEANOGRAPHY AND CLIMATE
• Glaciation was absent from both poles during the Mesozoic
due to open marine connection, warming by oceanic currents
and higher CO2 levels
• the Arctic comprised a warm highly productive ocean
that had open marine connection to the Pacific
5. ….during the Triassic…..
source: L.A. Lawver, A. Grantz, L.M.
Gahagan & D.A. Campbell,
University of Texas Institute for
Geophysics
9. the warm highly productive ocean was also fringed by abundant vegetation
so that the rich and diverse marine and nonmarine fossils
provide a high-resolution zonal scheme for the Arctic…..
10. …..that has been applied by
Jonathan Bujak across the Alaskan
and Canadian Arctic from the
Chukchi Sea to the Sverdrup Basin
11. including the 2004 Arctic
Coring Expedition which drilled
the Lomonosov Ridge
13. CENOZOIC BIOSTRATIGRAPHY:
REGIONAL SETTING AND CLIMATE
the Arctic Basin occupied a high-latitude position during
the Cenozoic
the climate shifted dramatically after the Early Eocene
from warm-temperate to today’s Arctic environments….
…..so the assemblages became progressively impoverished
and this affected both marine and nonmarine taxa
14. from the Mesozoic - early Eocene greenhouse world
the Cenozoic cooling had
a massive effect on the
Arctic Basin
19. p
source: L.A. Lawver, A. Grantz,
L.M. Gahagan & D.A. Campbell,
University of Texas Institute for
Geophysics
Arctic Basin
centred on the North Pole through
the Cenozoic
and the Late Cretaceous
20. Arctic Basin
the entire Arctic region therefore
underwent the same temperature
changes during the Cenozoic -
but several problems need
to be solved in order to erect
a reliable Arctic-wide scheme
22. AGE RANGES AND FACIES
most marine and nonmarine palynomorphs died out early
in the Arctic due to decreased water and air temperature
so that the age ranges differ from those to the south
how can we develop a chronostratigraphy tied to the lower latitudes?
23. AGE RANGES AND FACIES
.....and there is also the problem of reworking
in the Canadian Beaufort Mackenzie Delta
24. reworked Mesozoic assemblages strongly dilute
the impoverished in situ Cenozoic populations
the reworked taxa are large and conspicuous, whereas the
in situ populations are small, pale and easily overlooked…..
…..and this has resulted in many erroneous ages, such as Early
Cretaceous age assigned to Eocene and Oligocene sections
25. CENOZOIC BIOSTRATIGRAPHY
PERCEPTION
….. so that there is a widespread view that
1. Arctic Cenozoic biostratigraphy is unreliable
2. the Cenozoic can only be subdivided into a few zones
3. and the zones must be based mostly on non-marine pollen
26. LACK OF PUBLISHED ZONAL SCHEMES
like the Mesozoic, a comprehensive
palynological zonation has not been published
the only published Cenozoic scheme is that of
Geoff Norris (1989) at the University of Toronto
27. NORRIS’ PUBLISHED SCHEME
but this has few zones
and low resolution
there is little or no
chronostratigraphic control
the three Oligocene ‘zones’ are
actually diachronous biofacies…..
…..and the scheme is based
on a single well – Nuktak C-22
which TD ‘d in the Middle Eocene
28. CENOZOIC BIOSTRATIGRAPHY
STRATEGY
…..so we need to go beyond traditional biostratigraphic techniques, using
FLUORESCENCE MICROSCOPY
to locate and identify rare and inconspicuous in situ species
to distinguish different populations and provenance of reworking
PALEOCLIMATIC CORRELATIONS
to tie into chronostratigraphy established in lower latitudes
29. FLUORESCENCE
short wavelength fluorescence
is progressively lost by
dinocyst and angiosperm walls
as they become older
Bujak and Davies
(GSC 1982, 1983)
called this ‘biochemical
fluorescence’
30. as seen in the Canadian Beaufort Kopanoar M-13 well under normal light
35. NEW OBSERVATIONS
Fluorescence also shows common Neogene dinoflagellates
that migrated into the Arctic during the Miocene warm phase
most of these have not been recorded before in the Arctic
but they are known from the North Atlantic and Pacific…..
….. so the dinocysts and pollen together provide
a high-resolution Cenozoic zonation
36. Bujak and Davies (GSC 1982, 1983) also examined
other Arctic wells and the Hibernia P-15 discovery well
in the NE Newfoundland Basin
They observed a regeneration of fluorescence coincident
with the onset of the oil window which they termed ‘thermochemical
fluorescence’
39. STRATEGY
Cenozoic temperatures changed as a series of steps
as marine gateways opened and closed and CO2 levels changed
the steps are global chronostratigraphic datums
and have a stronger expression towards the poles
each step caused temperature-sensitive species to die out and
the number of affected species increased towards the poles
CHRONOSTRATIGRAPHY
40. CORRELATION FROM LOW TO MID LATITUDES
so let’s look at the effect of the cooling steps
on dinoflagellates species at different latitudes by
first constructing a latitudinal transect from the Tethys
through the North Atlantic into the North Sea
43. ONSET OF COOLING
(AZOLLA EVENT)
we can then overlay the middle and late
Eocene cooling steps based on palynology
beginning with the Azolla event which
marked the onset of cooling
44. this shows that a cooling step
occurs in the North Sea region
coincident with the Azolla Event
ONSET OF COOLING
(AZOLLA EVENT)
45. and that cooling did not
significantly affect the Tethys until
the Terminal Eocene Event (TEE)
TEE
46. it also shows that the extinction of temperature-
sensitive dinoflagellates was diachronous
with latitude (e.g. T. delicata)
47. indicating that the North Sea System
had a cooler water regime than the
North Atlantic System
48. due to separation of two oceanographic
systems along the Wyville Thompson Ridge
and Artois Dome……
53. for example - the diachronous range of T. delicata which is older
in the North Sea System than in the North Atlantic System -
reflecting a progressive SST fall to below the temperature
tolerance of T. delicata (e.g., to below 14oC)
54. so we can use the dinoflagellate record
to reconstruct SST for the entire region
55. the succession of cooling steps
is reflected by dinoflagellates,
non-marine pollen and
the isotope record
56. showing that the controlling mechanism
was temperature change rather than local facies
57. most of the cooling steps correspond to Stage boundaries
because the boundaries were originally defined by major biotic,
tectonic, sedimentary and oceanographic changes
58. so we can correlate the events and stages across the entire region
using Bujak’s North Atlantic palynological zones
59. this gives us a robust framework with strong
magnetostratigraphic, chronostratigraphic,
biostratigraphic and isotope control
61. the climatic cooling had a massive effect on high-latitudes
because the middle and late Eocene cooling steps
progressively eliminated most dinocyst
and angiosperms species from the Arctic
62. we can document the changes on both sides of Greenland even though
these has restricted marine connection to the Arctic.
Let’s look at the western transect through the Labrador Sea
66. so the cooling events and our Arctic zones can be
correlated chronostratigraphically to the south and
hence with absolute time and lower latitude stages
67. giving us a chronostratigraphic framework
for the Arctic Cenozoic succession
68. ARCTIC CENOZOIC ZONATION
SUMMARY
[1] fluorescence microscopy provides a high-resolution zonal scheme
by helping us to see the in situ palynomorphs
[2] the cooling steps provide a chronostratigraphic framework tied to the south
[3] the scheme can be applied to the entire Arctic region because the Arctic
was centered on the North Pole through the Cenozoic
70. BUJAK’S ARCTIC CENOZOIC
PALYNOLOGICAL ZONATION
[1] has good resolution
though most of the section
[2] avoids local biofacies
[3] can be tied to
lower-latitudes and
hence absolute time
71. giving us an integrated
climatic–biostratigraphic
scheme that can be
correlated with
paleotemperature …..
72. …..using a succession of
chronostratigraphically
defined climatic datums,
which help us reconstruct
the climatic history
of the Arctic
73. we first see a Paleocene-Early Eocene
greenhouse world with warm
temperatures…..
74. …..with the Azolla and
Apectodinium (PETM/EETM)
events being
chronostratigraphic datums
tied to lower latitudes
75. and the Azolla event
triggering the initial shift
from greenhouse
towards icehouse
76. the Azolla Event
was followed by
a succession of
Middle and Late Eocene
cooling steps
83. and finally
because the Arctic Ocean
was centred on the North
Pole through the Cenozoic
we can predict that the
scheme should be valid for
the entire Arctic Basin…..