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 zoned 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 hep 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 (staring 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.

Sciponicerus 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 Coniacion. 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 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 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 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 rostrate 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.

Unitacrinus socialis. I have never seen a complete specimen of this fossil The disarticulated plates of this crinoid are small but 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 Unitacrinus 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 Miadlands Upper Marl and notes that isolated plates of Marspites 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 las 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 zones in Yorkshire has been defined using lithostratigraphy or sometimes even the position of local landmarks. We could just forget about the local biostratigraphy rely on the now well established lithostratigraphy (if there were consistency of lithostratgraphic 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 nannofossil 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) has 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 echinoid shows condiderable variation. Some shapes are quite distinctive and further research could find that they are useful stratigraphically.

Microfossils

The Yorkshire Chalk is hard so we have to use thin sections or process the marl bands

Ostracods – these are generally rare

Planktonic foraminifera – the really distinctive keeled planktonic forams tend not to be common in the marl band samples.

Benthic foraminifera – they are there in good numbers but most are not so easy to identify to species level.

Nannofossil – 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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