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On Fri, 21 Jul 2006, Martin J. Head wrote:
> Date: Fri, 21 Jul 2006 12:47:06 -0400
> From: Martin J. Head <mhead@brocku.ca>
> Reply-To: paleonet@nhm.ac.uk
> To: paleonet@nhm.ac.uk
> Subject: Re: paleonet Pliocene time
>
> Dear David,
>
> Others including myself would be interested in the answer to your question,
> so perhaps replies could indeed be posted to the list. As an aside, the ICS
> time scale is certainly authoritative, but it does not as I understand become
> "official" until sanctioned by the IUGS in Oslo, 2008.
>
> Martin
Dear Martin,
following your suggestion to post the reply on the list, I do so
with a modified off-list reply I made some days ago.
(...)
To: David Goodwin <goodwind@denison.edu>
Subject: Re: paleonet Pliocene time
> To: paleonet@nhm.ac.uk
> Subject: paleonet Pliocene time
( ... )
> Dear Paleonet,
>
> I am looking for some clarification about the official Pliocene time scale.
> Gradstein et al., 2004 seems to define the Piacenzian as Middle Pliocene
> (Page 416 and Figure 21.1) But the color plates in the front part of the
> volume does not include the Middle Pliocene - the Piacenzian and Gelasian are
> lumped together in the Late Pliocene. Is there officially Middle Pliocene
> time?
Dear Prof. Goodwin,
Dear Martin,
the question addresses two -one of them ongoing- items:
Synopsis:
1) Is there a "Mid-Pliocene"
2) Environmental differentiation within the Pliocene.
3) Aspects on the definition of the Quarternary (relevant to
the Upper Pliocene, e.g. with/without the Gelasian).
4) Is it in some regions possible to see a Mid-Pliocene boundary?
5) To avoid misunderstandings (for those interested in Pliocene
environments):
6) Stratigraphy
End of Synopsis.
1) Is there an official Mid-Pliocene?
The strict answer to this is "no".
This is one reason why some authors working on Neogene Climates
(such as the PRISM and PRISM2 (ff) - reconstructions) use the term
"Mid-Pliocene" in quotation marks.
2) Environmental differentiation within the Pliocene.
Thus, independent of using strtaigraphic terms as age boundaries,
e.g. describing isochrons, one might think about dividing/grouping
Pliocene intervals - such as introducing a Mid-Pliocene.
On the other hand
the more we know about Pliocene and Miocene environmental
variability the more the variability of Pliocene climates/environments
approaches to the variability that is known from post 2.6 Ma times
(Gelasian, Pleistocene and Holocene).
Thus introducing a Mid-Pliocene, such as with a boundary at about 4 Ma
(s.b.) may be overolled by advancing knowledge.
So: In case it comes to giving classes I would stress that a
Mid-Pliocene is not a stratigraphic term but an overall description of
an interval that is different from the "glacial Pliocene" (see below)
and the (see how cautious I formulate) "not so glacial Pliocene".
As for example ice-rafted debris (e.g. ice floes in the ocean above)
are observed in the Norwegian Sea (ODP Site 642A, off Norway) from
about 5.1x Ma on (= in the Pliocene the Norwegian Sea was colder
than today as today there is ice-rafting observed) there is
from environmental reason no strong evidence that suggestst
grouping some existing Pliocene intervals to a "Mid-Pliocene".
Comparably cold conditions (ice rafting) existied by the way
in the Pliocene North Pacific (Leg 145, contribution of Krissek
to IRD, see by the way also the IRD in Pleistocene warm times,
e.g. in times with 3 deg C above preindustrial temperatures ...., see
below, contribution of the IGC in Florence).
That is: The pre 2.6 Ma time can well be distinguished from the
post 2.6 Ma time (massive ice rafting). Subgrouping intervals to
a "Mid-Pliocene" is not possible worldwide or almost worldwide.
In addition some Miocene intervals (around the Messinian) are in
the Northern Mid Latitudes and Northern Higher Latitudes also
"quite cold" (more on that, also regarding the Mid-Pliocene, below).
3) With above question you pointed to ongoing issues, namely the
definition of the Quaternary.
Above-sketched environmental conditions lead to long discussions
on Neogene stratigraphic subdivisions. They lead to ballots on occasion
of IGCs and discussions within the SNS (collecting of preferences
among "SNS-people").
There is, based on discussions and opinion-polls (see below), a formal
vote within the next INQUA congress in Cairns to accept the base of the
Quaternary as about 2.6 Ma (instead of 1.8 Ma) and (overall) leave
the other subdivisions (Gelasian, Pleistocene, Holocene) as they
are.
That is: The environmental change (incursion of species) that lead to
a definition of the "old" base of the Pleistocene to 1.8 Ma (= top
Gelasian) is left as it is.
The worldwide, marine and continental, observable environmental change
at about 2.6 Ma is "awarded" a respective stratigraphic importance.
(e.g. base Quaternary will be = base Gelasian).
The Tertiary will go up to 2.6 Ma. The Tertiary as unit is retained.
Below follows an excerpt of a summary from Prof. Hilgen on these issues.
This summary is based on a preceding discussion, questionaires,
workshops and other that follow a vivid discussion, sometimes referred
to as "upheaval" focusing on the Tertiary/Quaterany definition.
For those being unfamiliar with some details: There was a publication
that overall "eliminated" Quaternary and Tertiary as overall
"not longer necessary". This proposal created what some called
"upheaval". With the term "upheaval" I refer to the vivid discussion,
in a friendly sense (= no subpositive connotation implied).
In the following excerpt (in quotation marks) the term "I" refers
thus to Prof. Hilgen in his capacity of coordinator of the Subcommision
on Neogene Stratigraphy (SNS).
( summary of results from questionaire and dicussions)
Acronyms: Q: Quaternary
N: Neogene
T: Tertiary
"In Leuven I" (e.g. Prof. Hilgen) "presented the point of view of the
SNS. I stated that the
problem does not only concern the definition of the Q but also that of the
N and pointed at the imbalance in this respect in the composition of the
Task Force that was installed last year to come up with recommendations for
solving the Q issue before the Leuven meeting. I further presented the
outcome of the SNS 3rd questionnaire and stated that SNS was willing to
accept the compromise solution as formulated in the Aubry et al. paper.
That is also my personal point of view because this option seems the only
solution that might be acceptable for both communities as well as for a
wider stratigraphic community.
The Task Force installed last year came up with the following
recommendations before the Leuven meeting:
1) That the Quaternary is to be recognized as a formal chronostratigraphic/
geochronological unit.
2) That the lower boundary of the Quaternary will coincide with the base of
the Gelasian Stage and thus be defined by the Gelasian GSSP.
3) That the Quaternary will have the rank of either
a. System/Period and will be at the top of the Neogene System/Period, with
its lower boundary marking the top of a shortened Neogene, or
b. Sub-erathem/Sub-era and will be correlative with the upper part of the
Neogene System/Period
The different options under 3 were voted upon by the ICS voting membership
(ICS board and chairs of the subcommissions) and the only option that
received a (clear) majority of votes was the option with a subdivision of
the Cenozoic in Paleogene and Neogene Periods and the Quaternary maintained
as Subera with its base at 2.6 Ma (i.e. the "compromise" solution presented
in Aubry et al., 2005). This option clearly leaves open the possibility for
a revival of the Tertiary as a Subera preceeding the Q.
This decision of course is not final yet. The outcome of the voting is now
forwarded to the IUGS and INQUA. I will keep you informed about the
continuing story of the Q definition.
Best wishes,
Frits Hilgen "
The last paragraph answers indirectly also an aspect Martin addressed
(IUGS issues).
Your question (Pliocene definitions) touches through the base
of the Quarternary also above.
With a massive environmental change, almost worldwide, both
terrestrial and marine, observable at around 2.6 Ma I (Peter Smolka)
am quite happy with above new developments.
4) Is it in some regions possible to see a Mid-Pliocene boundary?
There is of course another major environmental change quite close to
4 Ma. This shows up in paleotemperature records off the North American
East Coast, in several ODP sites off the North American West coast
and in several DSDP and ODP sites off East Australia (parts of the
results of IGCP341, the data on the CD in the respective book,
selected diagrams also printed in that book (contr. of Smolka 2000) and
overall summarized in a contribution to the "Greatest Hits" brochure of
the Ocean Drilling Program (search function from the IODP website).
It is possible to think about a major reorganization of important
ocean currents, including the deep ocean circulation (see effects around
the closing of the Straits of Panama). This would explain their
occurrence not only at the East coast of North America but also at
the West coast of Australia.
In this context thinking about a boundary at about 4 Ma is possible
as the large ocean currents are an (almost) globally coupled system -
a pronounced effect at one important point might impact large parts.
Thus your question regarding the possible establishment of a
Mid-Pliocene is, in addition to for example the PRISM reonstructions,
justified.
5) To avoid misunderstandings (for those interested in Pliocene
environments):
I referred at several times to ice-rafted debris, e.g. hard data,
in the Pliocene Norwegian Sea and the North Pacific (Krissek 1989,
1995). The PRISM recconstructions favor quite warm Pliocene conditions,
e.g. also a subsequent possibly reduced ice-extent.
The reconstructions within the IGCP341 (Smolka 2000) show quite
warm tropical SSTs in some Pliocene times, in fact a permanent
Pliocene (time interval 4-5 Ma) El Nino. The El-Nino issues are
with different methods (Alkenone SSTs) also shown by Wara, Wara and
Ravelo. They (W, W and R) published recently in Science (around 2005 or
2006).
My contribution to the IGC in Florence ("Warm Climates - Origin
of the Ice Ages") showed the results of above reconstructions
(high El-Nino-type SSTs in the _tropical_ Pacific in
coexistence with observed IRD at 642B and in the North Pacific).
That is: Based on the IRD the ice-cover in the time interval 4-5 Ma
was at least as large as today, possibly larger. This lead to
pronounced N-S temperature gradients and - as result of a GCM
driven by the SSTs, to quite cold winter conditions on the NH
continents and "normal" ones for summer).
There are differences to PRISM. The IRD and the Alkenone SSTs are
independently of me (e.g. similar high SSTs in the tropical Pacific).
I have no intention to be in any subpolite communication with the
PRISM authors (= if some sentences might be understood so, I apologize
in advance). In fact: If the strong sides of both projects, IGCP341
and PRISM are linked up, PRISM authors are welcome.
CO2 approximations for Pliocene times must of course allow for
ice rafting in the Norwegian Sea and the North Pacific....
I hope it gets printed soon ("Warm Climates - Origin of the Ice Ages",
possibly with a slightly modified title to avoid misunderstandings).
The title of course referres to one _additional_ mechanism for the
generation of glacials - of course not to the only one (to avoid
other communicative misunderstandings).
6) Stratigraphy
(things that might become relevant if a "Mid Pliocene" might be
introduced).
During IGCP341 we needed for the generation of worldwide SST maps
(from DSDP and ODP faunal census) a worldwide uniform stratigraphy
that enabled, at that time fossil based, maps with an interval-distance
of 1 Ma (4-5, 5-6, 6-7 Ma and so forth - at the start of IGCP341
quite a challenge).
We searched for the available fossils for the earliest and latest
observation worldwide (considering the world ocean in a similar
way as one would do with a basin). The resulting earliest and latest
observations (evolutionary FAD and LAD, eFAD and eLAD) stretched
often compared to known intervals (Smolka 2000, the stratigraphy
contribution, data on the CD of the IGCP341 book).
The large number of fossils of the DSDP and ODP database
(see the G. mitra question a few days ago) made then quite precise
(at that time) age assignements possible.
That is: After the eFAD and eLAD of each species had been approximated
these dates are regarded as worldwide usable (earlier than the eFAD
a species cannot occur, except by new data the boundary is pushed
downward; it might of course occur later within the eFAD-eLAD interval).
That is: With above the GSSPs remain as they are. They are _that_
age at which at the respective site respective fossils have been
observed. Some kilometers away the same fossils may indicate a later
sometimes also an earlier age.
For hemisphere and global applications, in case of dating with
fossils, eFADs and eLADs can be used.
The publication of Berggren (around 1996) where he used a term like
"transferring ages" addresses this problem, if and how to apply GSSPs
worldwide for practical questions, dating with fossils, in a different
way.
Recently, and this should be done extensively before a Mid-Pliocene
is introduced, fluctuations of the Earth Magnetic field
(paleointensities) have been used to establish time-series that
are comparable to time-series based on stable isotopes
(a recent IODP Leg, see also a recent PAGES contribution).
This method has the great advabtage that it can be employed both
in the marine and the terrestrial realm (as suggested early this year
orally as hint:
if for ICDP drillsites in the Quaidam Basin dating-problems might
be inferred this might be an opportunity to apply paleonitensity
approaches also in terrestrial environments).
To be applied worldwide the existing DSDP (where possible) and ODP
cores should be measured. In case of success, the depth of the
In case of success, the depth of the
observed fossils exist, quite easily an enhanced database of eFADs
and eLADs can be established with a different method and
quite a high resolution.
That is: paleointensity-based eFADs and eLADS might be compared with
the IGCP341 eFADs and eLADs (resulting fine-tuning).
After this is done and the fossil record justifies this, one
might think of a Mid-Pliocene as stratigraphic unit.
Right now we have environmental changes at about 4 Ma in various
oceans. Compared to earlier evidence that was regarded justified
for the introduction of a subdivision this might also be the case here.
Considering however the data-quality we have today, we should wait
until by a worldwide set of fine-tuned eFADs and eLADS, e.g. using
fossils, a "Mid-Pliocene" might be separated out a additional unit.
In the higher mid and high latitudes (NH) I regard this as difficult
as we have pronounced climatic variabiliy, also IRD since about 5.1
(or 4.9x) Ma. We might see many (more than today) environmental
fluctuations comparable to the Quaternary environmental
record.
In the lower and low latitudes at least those areas that have been
affected by faunal/floral changes around 4 Ma (currently interpreted
as result of a change of large, including deep, ocean currents,
resulting from the gradually shallowing of the Panama Straits,
the Mid-Pliocene question might be addressed much easier.
Paleointensity-time-series (worldwide, also based on core
repositories) should be awaited until enough data to consider
a boundary exist.
I referred above at several places to NH-data. This does not
imply that I disregard SH data (= I greatly appreciate to
have them). It is however absolutely needed to have the same
density of IODP drillsites for (not only) paleotemperature time series
in the SH as we have in the NH (of course, fossils identified,
estimated or counted (or, if this will be a problem, "electronically"
in the futute), paleointensities and much more.
Formulated with a polite smile: The SH oceans are quite large and
also logistically things are not absolutely easy (= refferring to
the NH is thus not ignorance).
I hope no typos that change the intended meaning crept in.
If there are any: Please apologize.
>
The reply got longer than intended. I hope the prepended synopsis
spared the time of those who regard the Neogene as "something
just before yesterday" (polite smile of course).
Best regards
Peter
>
> ------------------------------------------------------------------------
> Martin J. Head
> Professor
> Department of Earth Sciences
> BROCK UNIVERSITY
> 500 Glenridge Avenue
> St. Catharines, Ontario L2S 3A1
> CANADA
> Tel 905-688-5550 ext. 5216
> Fax 905-682-9020
> Email mjhead@brocku.ca
>
>
**********************************************************************
Dr. Peter P. Smolka
University Muenster
Geological Institute
Corrensstr. 24
D-48149 Muenster
Tel.: +49/251/833-3989 +49/2533/4401
Fax: +49/251/833-3989 +49/2533/4401
E-Mail: smolka@uni-muenster.de
E-Mail: PSmolka@T-Online.de
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