Bujak Arctic Cenozoic talk

TOWARDS A BASIN-WIDE SCHEME
ARCTIC CENOZOIC BIOSTRATIGRAPHY
DR JONATHAN BUJAK

The talk is split into three parts
• Arctic paleoceanography and climate
• historical review of the problems
• solutions leading to an regional biozonation

we first need a climatic and oceanographic
perspective going back into the Mesozoic

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

….during the Triassic…..
source: L.A. Lawver, A. Grantz, L.M.
Gahagan & D.A. Campbell,
University of Texas Institute for
Geophysics

….. continuing through
the Middle and Late Jurassic….

…..into the Early Cretaceous

this was reflected by the marine biotas

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…..

…..that has been applied by
Jonathan Bujak across the Alaskan
and Canadian Arctic from the
Chukchi Sea to the Sverdrup Basin

including the 2004 Arctic
Coring Expedition which drilled
the Lomonosov Ridge

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

from the Mesozoic - early Eocene greenhouse world
the Cenozoic cooling had
a massive effect on the
Arctic Basin

and this temperature fall was the
most important control on the
Cenozoic palynological
succession

p
Arctic Basin location
the Arctic Basin was centred on the
North Pole through the Cenozoic
from the present…..

p
Arctic Basin
centred on the North Pole
through the Cenozoic
…..back to the Paleocene

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

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

CENOZOIC ARCTIC BIOSTRATIGRAPHY
PROBLEMS

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?

AGE RANGES AND FACIES
.....and there is also the problem of reworking
in the Canadian Beaufort Mackenzie Delta

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

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

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

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

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

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’

as seen in the Canadian Beaufort Kopanoar M-13 well under normal light

normal light
yellow-green
fluorescence emission
yellow-green biochemical fluorescence
highlights the in situ population

normal light
yellow-green
and blue
and blue fluorescence does this even more

normal light
yellow-green
blue
this lets us see and identify the rare in situ palynomorphs

normal light
yellow-green
blue
which are very difficult to observe under normal light

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

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’

normal lightbiochemical fluorescence
thermochemical fluorescence
and the combination of biochemical and thermochemical fluorescence
helps to distinguish different populations and provenance of reworking

CHRONOSTRATIGRAPHY
PROBLEM
it is difficult to correlate Arctic Cenozoic sections with lower latitudes because
stratigraphic ranges are truncated in the Arctic

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

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

the Tethyan to North Sea transect

oxygen isotope stratigraphy
magnetostratigraphy
standard NP & P zones
Stages and absolute time
provides us with a robust chronostratigraphy

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

this shows that a cooling step
occurs in the North Sea region
coincident with the Azolla Event
ONSET OF COOLING
(AZOLLA EVENT)

and that cooling did not
significantly affect the Tethys until
the Terminal Eocene Event (TEE)
TEE

it also shows that the extinction of temperature-
sensitive dinoflagellates was diachronous
with latitude (e.g. T. delicata)

indicating that the North Sea System
had a cooler water regime than the
North Atlantic System

due to separation of two oceanographic
systems along the Wyville Thompson Ridge
and Artois Dome……

the entire region had
full marine connection
in the Danian

…but late Paleocene
uplift of the Greenland
mantle plume

NORTH
SEA
SYSTEM
NORTH ATLANTIC
SYSTEM
BAFFIN
SYSTEM
separated the region
into three distinct
oceanic/biotic
systems/provinces

NORTH
SEA
SYSTEM
NORTH ATLANTIC
SYSTEM
BAFFIN
SYSTEM
dinoflagellates clearly
show the differences in
sea-surface temperature
(SST) between
these systems

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)

so we can use the dinoflagellate record
to reconstruct SST for the entire region

the succession of cooling steps
is reflected by dinoflagellates,
non-marine pollen and
the isotope record

showing that the controlling mechanism
was temperature change rather than local facies

most of the cooling steps correspond to Stage boundaries
because the boundaries were originally defined by major biotic,
tectonic, sedimentary and oceanographic changes

so we can correlate the events and stages across the entire region
using Bujak’s North Atlantic palynological zones

this gives us a robust framework with strong
magnetostratigraphic, chronostratigraphic,
biostratigraphic and isotope control

STEP 2:
CORRELATE FROM MID TO HIGH LATITUDES

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

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

western transect into the Arctic

we see that the cooling events caused major extinctions in the Arctic
that affected the marine dinocysts and terrestrial angiosperms

…..both of which define our Arctic palynological zones

so the cooling events and our Arctic zones can be
correlated chronostratigraphically to the south and
hence with absolute time and lower latitude stages

giving us a chronostratigraphic framework
for the Arctic Cenozoic succession

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

ARCTIC CENOZOIC ZONATION
AND PALEOTEMPERATURE

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

giving us an integrated
climatic–biostratigraphic
scheme that can be
correlated with
paleotemperature …..

…..using a succession of
chronostratigraphically
defined climatic datums,
which help us reconstruct
the climatic history
of the Arctic

we first see a Paleocene-Early Eocene
greenhouse world with warm
temperatures…..

…..with the Azolla and
Apectodinium (PETM/EETM)
events being
chronostratigraphic datums
tied to lower latitudes

and the Azolla event
triggering the initial shift
from greenhouse
towards icehouse

the Azolla Event
was followed by
a succession of
Middle and Late Eocene
cooling steps

…..which are zonal and
subzonal boundaries

ending with the
Terminal Eocene
Cooling Event

leading to the impoverished
Oligocene cold phase
which is difficult
to subdivide due to
the scarcity of markers

….except in the early
Oligocene of the Barents Sea
due to inflow of the
proto Gulf Stream

this was followed by the
Miocene warm period
characterised by the
migration of temperate
dinocysts and
angiosperms
into the Arctic

with strong
Plio-Pleistocene cooling leading
to the
modern Arctic marine
and terrestrial regime

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…..

giving us
our Arctic-wide
biostratigraphic
scheme

Please contact Dr Jonathan Bujak for
more information
or for a free copy of this talk
Email: info@azollabiosystems.co.uk.

Bujak Arctic Cenozoic talk

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