The Chalk of the Northern Province: its regional context
Symposium
a joint meeting of the Hull Geological Society
with the Yorkshire Geological Society and Hull University
10th to 13th September 2015
"Chalk
macrofossil biostratigraphy – can we get it right please?
By Mike Horne FGS
September 2015
Abstract –
We all use the macrofossil biozones when we write
or talk about the Chalk – but do we really know what they are? Some of them are
just vague, for example one of the zones in Yorkshire is named after a
misidentified fossil that occurs in only a small part of the sequence. None of
the zones have been defined using the modern criteria, as far as I know. How can
we compare the biostratigraphy of different provinces if the researchers are not
using a commonly agreed scientific standard?
Is it not time to define the macrofossil biozones
to give them scientific credibility? Could we abandon the existing zones in
favour of ones based on different fossil groups that could give us better
resolution? Are they still relevant now that we have more accurate
lithostratigraphy, chemostratigraphy and event stratigraphy?
Introduction.
“By far the most satisfactory method of dividing
the Chalk is by the use of the fossil remains as zonal indicators.”
Ellis Owen in the
introduction of
Fossils of the Chalk
in 1987
We have been using macrofossil biozones for a long
time in the study of the stratigraphy of the Yorkshire Chalk.
As we all know biostratigraphy is based on the
presence or absence of zonal fossils. A good zonal fossils is a species that has
a limited time span (evolved suddenly and became extinct after a short period of
geological time) and that has a wide distribution (it is not confined to a
single facies). Ammonites make perfect zonal fossils because there is a turnover
of species and they are free swimming so can been found in a wide variety of
rock types over vast areas. Benthic fossils that have a planktonic larval stage
would also be quite good.
Lingula
would be useless as a zonal fossil because it is has hardly changed since the
Cambrian and is only found in some facies.
For the fossils to be useful for biostratigraphy I
would also suggest that they should ideally be common throughout the zone and
easy to identify to species level in the field. To aid that identification
descriptions and pictures should be widely available (for example published in
British Mesozoic Fossils or
Fossils of the Chalk). Small fossils
would be better than large ones because they are more likely to be intact and
not crushed. Very small fossils require the use of specialist techniques.
When we read the rules of stratigraphy we learn
that there are different types of zones (e.g. total range zones, partial range
zones &c.) and that they should be defined by a palaeontological event at the
base (e.g. the first appearance of a species, the last appearance of a species,
&c.). I would add that the definitions of the zones should be published and
readily available to all.
Background
Members of the Hull Geological Society started a
project in 1984 to log the geology of the Yorkshire Chalk (Horne 1988). The
results were displayed in poster form at the Society’s Centenary Meeting. It
became obvious during the research that there were problems with the
biostratigraphy and in December 1989 I gave a talk to the Society highlighting
some of the issues. Unfortunately these were never resolved and I returned to
the theme at the Society’s 125th Anniversary Meeting. Enquiries to
other stratigraphers revealed that the macrofossil biozones had no agreed
definitions. I therefore asked the Yorkshire Geological Society to help convene a
meeting of Chalk stratigraphers to debate the issues.
Yorkshire Chalk zonal fossils.
Because the aragonite shells of ammonites are not
preserved in the Chalk and the fossilised internal casts are rarely found
stratigraphers have used a variety of other groups as zonal indicators in the
Chalk.
There should not be a problem caused by different
facies because we are looking at the Chalk – a white rock deposited over a large
area for about 35 million years.
Some of
the fossils used in the Southern Province are rare in the Northern Province so
some local equivalents have been used.
It should be noted that the data for the
Flamborough Formation is mostly collected from the cliffs of Flamborough Head;
whilst that is quite detailed, correlation with inland quarries is not perfect.
Let us have a look at the zones we use in
Yorkshire & Lincolnshire at present (starting at the lowest one) to see if they
are good zonal fossils and how their base is defined:-
Holaster subglobosus. This zone fossil is
described in Fossils of the Chalk
(Smith 1987) as being common in Chalk of Middle and Late Cenomanian age in all
areas. [Note - all the fossils below are described in
Fossils of the Chalk
unless indicated.] Felix Whitham
(1991) places the base of the zone at the erosion surface at the top of the Red
Chalk Formation. This confused me when I started to research the Chalk because
in the Northern Province it is used as the zonal fossil for the Lower Cenomanian
yet in the Southern Province the zone covers the last four of seven ammonite
zones!
Sternotaxis trecensis. The fossil is not described
in Fossils of the Chalk or
British Mesozoic Fossils. Felix
Whitham (1991) places the base of the zone at the top of the
Pycnodonte Band and the top of the zone at the base of the Black
Band Member.
Sciponiceras gracile. I have never seen one of
these fossils; Whitham 1991 does not record finding it.
Mytiloides labiatus. In
British Mesozoic Fossils its range is
listed as being Cenomanian to Coniacian. In
Fossils of the Chalk its age is listed
as being the Rhynchonella cuvieria zone of the Turonian and we are told that the
nomenclature of the M.labiatus lineage
has frequently been misconstrued.
Felix Whitham (1991) places the base of the zone at the flood of the zonal
fossil.
Trerebratulina lata. This is quite a small fossil
so we have a better chance of finding whole specimens, but there are other small
brachiopods that looks quite similar. It is noted in
Fossils of the Chalk that the species identified as
T. lata in Yorkshire and Lincolnshire
may not be the same as the one described from the Southern Province. Felix
Whitham (1991) places the base of the zone 30cm above the First Main Flint. He
does not show the range of the fossil in figure 3 or show it in any of the
detailed graphic logs; in the text he says it is not common but it does occur “at
specific horizons” as ferruginous pseudomorphs.
Sternotaxis plana. In
Fossils of the Chalk the fossils is
described as being common and widespread in the labiatus to cortestudinarium
zones. Felix Whitham (1991) places the base of the zone lithostratigraphically at the base of the
Burnham Formation.
Micraster cotestudinarium. The fossil is described
in Fossils of the Chalk as being rare
in Yorkshire. Felix Whitham (1991) proposes that the base of the zone should
lithostratigraphically be
at the Base of the Middle Kiplingcotes Marl because there is “a major change in
lithology from harder to very much softer chalks”. He does not show the range of
the fossil in figure 3 of the paper and does not record any definite
identifications in the text or other figures.
Hagenowia rostrata. This zone was proposed by Ted
& Willy Wright as a Yorkshire alternative to Micraster coranguinum zone. The
fossils is described in Fossils of the
Chalk as being very rare in being very rare in Yorkshire. However the small
echinoid Hagenowia anterior is quite
common in some beds exposed in the cliffs near South Landing – so is this a zone
named after a mistaken identity? This zone was split into a Flinty Hagenowia
rostrata Zone and Flintless Hagenowia rostrata Zone by Neale 1974 based on
lithostratigraphic changes. Horne 1988 and Whitham 1991 renamed these the Lower
Hagenowia rostrata Zone and Upper Hagenowia rostrata Zone. Whitham 1991 records
that the base of the Lower rostrata zone was seen in Little Weighton Quarry and
states that large involute inoceramids first appear just about the base of the
zone.
Uintacrinus socialis. I have never seen a complete
specimen of this fossil The disarticulated plates of this crinoid are small: can they be identified accurately to species level in the field? Felix Whitham
1993 defines the base of the zone lithostratigraphically and states that the
zonal fossil first appears in that bed. Horne 1988 [poster] and Mitchell 1994
both record that Hagenowia anterior
and Uintacrinus occur together in part
of the sequence. Horne 2013 proposed that the base of the zone should be defined
as the first appearance of Uintacrinus
socialis.
Marsupites testudinarius. The plates of this
crinoid are quite distinctive and are not uncommon in the cliff exposures near
Danes Dyke, though complete specimens are rare. Whitham 1993 places the base of
the zone at the Maidlands Upper Marl and notes that isolated plates of
Marsupites are to be found in the overlying chalk. Mitchell 1995 and
Horne 2013 proposed that the base of the zone be defined as the first appearance
of Marsupites testudinarius.
Uintacrinus anglicus. This fossil is not
illustrated in British Mesozoic Fossils
nor described in Fossils of the Chalk.
Mitchell 1995 introduces this zone for the first time in Yorkshire and defines
the base as the last appearance of
Marsupites testudinarius and the top as the last appearance of Uintacrinus anglicus; he notes that the small plates are swamped by
the abundance of Sphenocermus lingua
fragments.
Sphenocermus
lingua. This fossil is not illustrated in
British Mesozoic Fossils nor described in
Fossils of the Chalk. Whitham 1993
places the base of the zone at the last appearance of
Marsupites testudinarius. Mitchell
1995 and Hampton et al. 2007 take the
base of the Campanian Stage to be the extinction level of Marsupites. Horne 2013
proposed that the base of the partial range zone be defined as the first
appearance of Sphenocermus lingua.
Discoscaphites binodosus. Whitham 1991 places the
base of the subzone at the Sewerby Steps Marl because specimens of
Discoscaphites binodosus
had been found at Sewerby Steps in fallen blocks by G W Lamplugh, A Rowe and
Martin Whyte. Horne 1988 [poster] suggested the base of the zone occurred in the
chalk above the highest coastal exposure but has subsequently seen the zonal
fossil in situ on the wave cut
platform near Sewerby Steps. Horne 2013 proposed that the base of the partial
range zone be defined as the first appearance of
Discoscaphites binodosus.
Is there a problem?
As seen above, the base of most of the Chalk biozones
in Yorkshire has been defined using lithostratigraphy or sometimes even the
position of local landmarks. Could we just forget about the local
biostratigraphy rely on the now well established lithostratigraphy (if there
were consistency of lithostratigraphic methods)? However nearly every publication
apart from Wood & Smith 1978 shows the biostratigraphy in graphic logs and it is
used to make comparisons. For example: Whitham 1993 and Mitchell 1994 compare
their measurements of the thickness of the Chalk in the Upper Hagenowia rostrata
zone with those of Rowe 1904 and Jackie Burnett (Burnett & Whitham 1999)
compares the nanofossil zones with the macrofossil zones.
Alternative zonal fossils.
Are there other macrofossils that have been
recorded stratigraphically that can be used to create better biozones?
Inoceramids – there does seem to be quite a
variety of species which when found complete are easy to identify; mostly though
we find broken or crushed fragments.
Belemnites – belemnites are reasonably common in
the Chalk but in Yorkshire are not easy to identify to species level. Whitham
(1993) and Mitchell (1995) have shown that the depth of the alveolus in relation
to the total length of the guard (the Reidel Quotient) increases as we work our
way up the sequence. This can be used stratigraphically but not in the field.
Mitchell 1994 notes that Yorkshire coast specimens are “philologically
retrograde compared with coeval populations in Germany”.
Echinocorys
– the shape of the test of this irregular echinoid shows condiderable
variation. Some shapes are quite distinctive and further research could find
that they are useful stratigraphically.
Microfossils
Ostracods – these are generally rare
Planktonic foraminifera – the really distinctive keeled planktonic forams tend
not to be common in marl band samples.
Benthic foraminifera – they are there in good
numbers but most are not so easy to identify to species level.
Nanofossil – coccoliths have been used
successfully but are a really specialised field of research.
References –
Burnett J & F Whitham 1999. Correlation between
the nannofossil and macrofossil biostratigraphies and the lithostratigraphy of
the Upper Cretaceous of N E England.
Proceedings of the Yorkshire Geological Society
52, 371-381.
Hampton M, H W.
Bailey, L T. Gallagher, R N. Mortimore &
C J. Wood 2007.
The
biostratigraphy of Seaford Head, Sussex, southern England; an international
reference section for the basal boundaries for the Santonian and Campanian
Stages in chalk facies. Cretaceous
Research 28 46-60
Horne M
1988. The Centenary Chalk Project of the Hull Geological Society. Humberside
Geologist 6,19-20.
- 1988, The
Stratigraphy of the Yorkshire Chalk [Conference Poster – Hull Geological Society
Centenary Meeting]
- 2013
Proposal to define some of the biozones of the Yorkshire Chalk. Hull
Geological Society 125th Anniversary Meetings Abstracts handbook.
(available online
http://www.hullgeolsoc.co.uk/hg125.htm)
Mitchell S
M 1994.New data on the biostratigraphy of the Flamborough Chalk Formation
(Santonian, Upper Cretaceous) between South Landing and Danes Dyke, North
Yorkshire.
Proceedings of the Yorkshire
Geological Society 50, 113-118.
- 1995 -
Uintacrinus anglicus Rasmussen from the Upper Cretaceous Flamborough
Chalk Formation of Yorkshire: implications for the position of the
Santonian-Campanian boundary.
Cretaceous
Research. 16, 745-756.
Natural
History Museum - British Mesozoic Fossils
Owen E and
Smith AB (eds) 1987. Fossils of the Chalk. Palaeontological Association - field
guide to fossils no. 2, 306pp.
Neale J W
1974. Cretaceous. Chapter 8,pp225-243 of Raynor D H & Hemmingway J E (eds) Geology
and Mineral Resources of Yorkshire, Yorkshire Geological Society, 405 pp.
Rowe A W
1904. The zones of the White Chalk of the English Coast. IV Yorkshire. Proceedings
of the Geologists' Association 18,
193-296.
Whitham F
1991. The stratigraphy of the Upper Cretaceous Ferriby, Welton and Burnham
Formations north of the Humber, north east England. Proceedings
of the Yorkshire Geological Society 48,
227-254.
Whitham F
1993. The stratigraphy of the Upper Cretaceous Flamborough Chalk Formation north
of the Humber, north east England. Proceedings
of the Yorkshire Geological Society 49,
235-258.
Wood C J &
Smith E G 1978. Lithostratigraphical classification of the Chalk in North
Yorkshire, Humberside and Lincolnshire. Proceedings
of the Yorkshire Geological Society 42,
263-287.
Wood C J
1980. Upper Cretaceous. p 92 105 of Kent P British
Regional Geology. Geology of Eastern England from the Tees to the Wash.
H.M.S.O. 155pp.
Wright C W & Wright E V 1942. The Chalk
of the Yorkshire Wolds. Proceedings
of the Geologists' Association 53,
112-127.
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