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

into the Cenozoic

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

to the modern icehouse world

and this temperature fall was the

most important control on the

Cenozoic palynological

succession

p

Arctic Basin location

the Arctic Basin was centred on theNorth 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 lightyellow-green

fluorescence emission

yellow-green biochemical fluorescence highlights the in situ population

normal lightyellow-green

fluorescence emissionand blue

fluorescence emission

and blue fluorescence does this even more

normal lightyellow-green

fluorescence emissionblue

fluorescence emission

this lets us see and identify the rare in situ palynomorphs

normal lightyellow-green

fluorescence emissionblue

fluorescence emission

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

NORTHSEA

SYSTEM

NORTH ATLANTIC SYSTEM

BAFFINSYSTEM

separated the region

into three distinct

oceanic/biotic

systems/provinces

NORTHSEA

SYSTEM

NORTH ATLANTIC SYSTEM

BAFFINSYSTEM

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.