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On Fri, 23 Aug 2002, Van Heck, Shirley SIEP-EPT-DE wrote:
> Date: Fri, 23 Aug 2002 09:28:47 -0500
> From: "Van Heck, Shirley SIEP-EPT-DE" <Shirley.vanHeck@Shell.Com>
> Reply-To: paleonet@nhm.ac.uk
> To: PaleoNet@nhm.ac.uk, "Nannolist (E-mail)" <COCCOLITHS@MORGAN.UCS.MUN.CA>
> Subject: paleonet biostratigraphy: the relation between NN9, N13 and N14
>
> I am currently involved in a dispute about the sequence of the following biostratigraphic events: 1) the FAD of D. hamatus (defining base NN9), 2) the LAD of G. subquadratus (top N13) and 3) the LAD of G. mayeri / siakensis (top N14). In literature (e.g. Bolli et al, 1985, Plankton stratigraphy) the base of NN9 is placed near the top of N14.
>
> In the South China Sea, off NW Borneo, I have regularly observed an overlap of D. hamatus with G. mayeri / siakensis, and even, in a few cases, of D. hamatus with G. subquadratus (one sample only). These observations were made in oil wells, based on sidewall samples. Hence in my opinion, base NN9 is at about the same level as top N13.
>
> My question is: has anyone else observed this, and if so, where?
Dear Shirley,
the answer comes in two sections (a) general and (b) specific.
I am aware that I formulate extreme compact.
So:
Zones (such as N9) are defined at (in a wide sense) GSSPs.
During the application step two approaches are possible:
1) When the FAD of a species is found (such as in a well) the respective
age might be assigned. This applies also to related approaches such
as markers, asssamblage zones and related.
In / near the region of definition this generally works well. Further
away often problems occur.
This is shown by Kennet et al. 1978:14: They show a diagram of the extension
of various zones along an N-S transect off Australia. The base of
N22 (G. truncatulinoides) varies between about 3.5 m.y. (off Antarctica)
to about 1.8 m.y. (site 586). The same applies more pronounced to
the range of O. suturalis.
(could also be Kennett 1987:14, the transect east of Australia).
This problem of applying zones over wider distances was also seen
by Berggren (around 1995) who then concluded that after definition of
a zone (formulated very compact) the "age needs to be transferred"
respectively.
That is: Ages defined by zones, expressed in m.y. can have those meanings
as they have at the respective GSSP.
Extremely compact: At OTHER places, further away, see below, problems
might occurr.
The problem is however with that: Worldwide dating does not become easier.
2) Thus another approach, also in your company, is possible:
2a) The GSSPs are left as they are.
2b) Each species has however an evolutionary first appearance (worldwide)
whereever it is and (mostly) also an evolutionary last appearance
wherever it is.
Referring to above example from Kennet: G. truncatulinoides starts
along E Austraila at about 3.5 m.y. (in that diagram evolutionary oldest
age based on 5 sites), O. suturalis (in that diagram) has an evolutionary
first appearance (eFAD)
at about 25 m.y. and an evolutionary last appearance (eLAD)
in that diagram) at about 15 m.y.
If MORE wells are included (for example worldwide) the evolutionary
life-spans of the species increase.
During the APPLICATION step these extended age-ranges are used, NOT
as markers, BUT as indicators saying: AT LEAST nnnn m.y. old or younger
(from the eFAD) and NOT OLDER than mmmm m.y. or older (from the eLAD).
Each fossil gets thus an index fossil. The great number of species
(all DSDP/ODP wells or all wells from within your company, much more)
and thus the considerable number of species that are included in each
analysis narrows the age-span in many cases considerably.
Conceptually there is no difference between a small basin and the
world ocean that is: All stratigraphic principles remain as they are.
With the help of computers (your company is a pioneer in that field)
a worldwide giant range chart (eFAD, eLAD for each
species, follwoing the rules that are applied to a limited set
of wells in a small basin) is established.
Calibrating this relative range-table (where possible) with good
age-depth plots (magnetic and other) results in a set of ages
(eFADs, eLADs) on a worldwide scale.
The recent isotope-calibration curve (Sr stable isotopes) at high-quality
wells is another way to transform relative ages in m.y. (not common
at the start of below-mentioned project).
The results (specific):
Within IGCP-341 we had the problem of creating worldwide maps of Neogene
sea surface temperatures (also as part of a forthcoming special
issue, of GPC as discussed in Strasbourg 2001). We thus created worldwide
age ranges from all processible DSDP/ODP holes (Smolka 2000).
Each new well might of course improve (extend) the age-ranges.
I looked your species up in the respective table:
Globorotalia mayeri: FGLOA0288 (DSDP code): Site 140, 210.36 m
eFAD: 41.9 m.y., eLAD n.a.
(e.g. this species was found at its oldest position at site 140,
at 210.36 m depth; the inferred corresponding age is 41.9 m.y..
(eFAD).
For the calibration steps the ages of magnetic boundaries have been changed
to those available at 1995. That is: The age of the Gauss Chron, even though
the site is quite old, such as 140, is that from 1995.
G. subquadratus: FGLOD0530 (DSDP-code): 41.9, also from site 140,
210.36 m depth.
D. hamatus: NDIS0200: Site 527, 110.44, eFAD: 26.93 m.y. eLAD 2.066 m.y.
(that is: in the respective DSDP volume there should for site
527 at 110.44 m a core/sample which could overall have an age of
26.93 m.y. (calculated age). If the "old" burial graph (age-depth plot)
is 26 or 25.5 m.y. it is ok (other method, also progress).
Side aspect: D. hamatus should have evolved at that age in that area (or
there is an unknown well where it occurres earlier).
I hope I did not mix up the code (in this e-mail) of G. mayeri and
subquadratus.
Site 527 is quite a young one with much better coring etc. available.
This does NOT mean that the zone-definition of D. hamatus is
proposed to be changed. By no means not. The definition, which is
bound to the PLACE of definition, remains as it is.
It is only meant to say: If a D. hamatus is found it can be inferred;
26.93 m.y. OR YOUNGER and 2.06 m.y. OR OLDER. Not more, but also
not less (the value of fossils).
Within IGCP-341 we focused on Neogene and Paleogene fossils.
Within your company you can focus on the whole phanerozoic.
Thus after tremendous work was done to establish all GSSPs,the next
step of stratigraphy is to establish worldwide, ever extending
age ranges of all species, so in the future, stratigraphy is
a matter of linking findings with age-ranges (software) and
(interest to permit us using respective equipment by us exists)
to determine microfossils automatically (core into CT, work is needed
but the goal is now realistical) (plus above age-determination step).
(two micropaleontologists, one from Forams one from Coccolithes expressed
interest to cooperate, high yield, but also high risk (of success)
clearly expressed).
To link to your question: When D. hamatus, G. subquadratus etc are regarded
as indicator of what EVOLUTION provides us, the maximum and minimum
age (not less but also not more),the problem that appeared might
REDUCE.
For the application step the GSSPs are that (politely meant) "random"
place where an FAD/LAD was observed. The species might have evolved
earlier (at some other place and migrated various million years later
to the site of the GSSP) and it might have (quite old principles of
the field) died out much later than at the GSSP somewhere else.
If establishment of GSSPs, evolutive maximum and minimum ages (eFADs,
eLADs) and the application step (bringing all fossils together, each
fossil is an index fossil, no one is undiagnostic, each one can
be used for dating) are considered as different (independent) steps,
questions of the mentioned type reduce.
Thus I propose that we (you especially as your company has an
enormous database of wordwide wells) focus in the future in
stratigraphy on worldwide age-ranges for all fossils available,
for reasons of practicability PForams, Diatoms, Coccolithes, Radiolaria
and maybe Conodonts first (all sentences meant politely although they
are sometimes formulated compact).
References:
Berggren WA, Hilgen FJ, Lagenreis CG, Kent DV, Obradovich JD, Raffi I,
Raymo ME, Shackleton NJ (1995) Late Neogene chronology: New perspectives
in high-resolution stratigraphy. Geol. Soc. Am. Bull., 107: 1272:1287.
(I referred to them extremely compact and their view is one of
several points to be considered).
KennettKM, von der Borch CC (1978 (or 87)): Init. Repts, DSDP, 90,
Washington. (a transect east of Australia).
Smolka PP (2000): A Worldwide Uniform High-Resolution Stratigraphic
Standard with Data for the Neogene and Paleogene. In: Smolka PP,
Volkheimer W (Eds): Southern Hemisphere Paleo- and Neoclimates.
Key Sites, Methods, Data and Models, p. 299-316 (with CD ROM).
The data are on the CD (also the age ranges mentioned here).
Each new well extends them, so there is work left to do.
The diagram from Kennet and one from Berggren et al. (showing the
problems of the APPLICATION step of zones, especially worldwide,
Borneo is quite far away from many Tertiary zone definition places)
is also in above contribution.
This e-mail is not proofread, so please apologize for any typing
errors.
I hope that helps for your question and encourages future age ranges
(worldwide, eFAD, eLAD) for other fossil classes and especially the
"remained of the phanerozoic" (Meszoic, Paleozoic, bacteria and virus
from ODP drillsites and other).
Best regards, Peter
>
> Shirley E. van Heck
> Stratigrapher
> Shell International Exploration and Production Inc.
> Deepwater Services / BEAST
> 200 North Dairy Ashford, room 2230
> Houston, Texas 77079, USA
>
> Phone: +1 281 544 2638
> Email: shirley.vanheck@shell.com
>
P.S.: Lets see whether this e-mail goes directly to you or to the list.
>
>
**********************************************************************
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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