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

Abstracts

A Finlay, J Griffiths & D Wray - "An integrated elemental Chemostratigraphic and stable isotope study of chalk cuttings from the Central North Sea: iplications for petroleum exploration".

Within the Central North Sea (CNS), chalk horizons are a major challenging, petroleum play and are primarily found in the Late Cretaceous to Early Palaeocene Ekofisk, Tor and Hod Formations.The chalk forms both seal for underlying clastic reservoirs, as well as being a reservoir in higher porosity areas, with the Late Jurassic Kimmeridge and Oxford clays the source. Therefore, a thorough understanding of the stratigraphy and petrological properties of the chalk is key to future successful exploration.

Traditional techniques used for providing a stratigraphic framework in chalks include biostratigraphy, petrophysics and seismic surveying. However; these techniques often lead to stratigraphic records that have poor resolution and miss out key features. For example, seismic interpretation of chalk reservoirs in the Kraka Field, Danish North Sea is at best ~ 12m vertical resolution, decreasing to ~25m in the gas bearing crestal area of the field, due to a lowered frequency band width1, In addition, below the Top Maastrichtian there is limited variation in velocity and densities of the chalk1, meaning that reflection coefficients are very small, further limiting the viability of seismic in the area.

This paper demonstrates the applicability of using an integrated elemental and stable isotope chemostratigraphy to provide a detailed stratigraphy of two wells from the CNS. In comparison to biostratigraphy and petrophysical analysis, these techniques are both quicker and more economical, key advantages in today's challenging economic environment. By combining stable isotopes and elemental Chemostratigraphy it is possible to not only gain a high resolution stratigraphy but also gain an understanding of the petrology of the chalk, e.g. biogenic/detrital silica, the presence of hardgrounds, clay and organic input and porosity. The other advantage of integrating elemental data into this study is that it enables a suite of petrophysical logs to be calculated from the elemental data which can then be used to provide better porosity data for the successions as well as ground truth and quality control down-hole petrophysics. Importantly, all of this information is produced from cutting samples, negating the need for hugely expensive coring to be undertaken.


A Newell, M Woods, A Farrant, R Haslam & H Smith - "Using geophysical logs and geological models to understand the stratigraphy, structure and physical properties of the Chalk Group".

The once "homogenous" Chalk Group has, over recent years, been revised as the internal variations have become more important to our understanding of this geological unit. This has been greatly helped by the redefining of the Chalk stratigraphy in the southern province which relies more on the physical properties of the Chalk and the depositional origin rather than the age. However the spatial variation and controls on facies variation is still poorly understood especially between the Southern, Transitional and Northern Chalk Provinces.

Using a combination of cored boreholes, geophysical logs and outcrop sections BGS has built a spatial database of chalk stratigraphy marker beds and lithofacies across the Chalk Group of southern Britain as far north as The Wash, at the southern limit of the Northern Province. The stratigraphic markers and mapped outcrop lines were used to construct a 3D geological grid through which property and facies simulations can be interpolated. A total of 8 chalk facies were identified; Chalk, Marl, Marly Chalk, Hardgrounds, Hard Chalk, Fractured Chalk (including Fractured, Faulted and Channelised Chalk), Sandy Silty Chalk, Stylolitic Marl, Nodular Chalk. These were interpolated through the volume using kriging with a nominal range of 100 km, reflecting the typically high lateral continuity of lithofacies within the Chalk. In addition to the stratigraphic model, a revised structural model was developed based on the large scale features and published interpretations. The structural model has been incorporated in order to resolve if there is any structural control on the distribution of facies.
The broad scale modelling allows us to identify trends within the chalk facies and the relationship this has with the large scale structures. Additionally the model gives a framework in which further; more detailed studies may be framed.

Anastasios Sravrou, James Lawernce, Bedros Awakian & William Murphy - "3D Discontinuity characterisation of Chalk sea cliffs using terrestrial laser scanning systems".

The 3D characterization of discontinuities constitutes one of the most crucial steps in any geo-engineering project that requires detailed rock mass characterisation. Conventional methods such as scanline surveys or window sampling have proven to be time consuming and subject to sampling bias, inconsistent approaches, accessibility and safety issues. On the other hand, the characterization of blocky rock masses using 3D laser scanning data is a safe and cost effective technique that allows consistent unbiased and rapid collection of high quality rock surface data, The objective of this study is to present a comparison between data that obtained by traditional scanline surveys and 3D laser scanners and to prove that there is a strong correlation between them.

The field investigations were undertaken along the coastal section between Brighton Marina and Newhaven, in the south of the United Kingdom, which is dominated by 15-40 m high Chalk sea cliffs. The results however; provide a transferable knowledge that can be used in any coastal section that composed of highly fractured Chalk Cliffs like those along the Yorkshire coast. The laser scanning data were collected using both vehicle and boat based scanning systems and verified that the technique is highly flexible in studying rock faces whose access is not possible or poses hazardous working environment. In general, the comparison shows a very good fit between both methods and provides a robust initial validation of the performance of laser scanners in flat, planar; low relief, chalk cliffs. Laser scanners are therefore considered to have the potential of replacing traditional discontinuity characterization methods but with the lack of any official standards and guidelines, its use cannot be recommended as a stand-alone technique for discontinuity characterization.

Christopher Jeans  - The Upper Cretaceous Chalk of eastern England and its diagenetic significance

The understanding of the processes involved in the hardening of the originally uncemented Chalk in eastern England has been a long established problem that has never been satisfactorily solved. Results from an on-going investigation - using classical and novel methods - of the lithofacial, geochemical and physical conditions of diagenesis are providing evidence of the natural patterns of modifications responsible for the hardening. These patterns could form a basis for the development of more sensitive and successful predictive models for the exploration of Chalk reservoirs in the North Sea and elsewhere.

Felix Gradstein - On The Cretaceous - Global And Local Aspects

Global greenhouse conditions, like during Cretaceous time from 145 to 66 Ma, have occurred during 75% of the Phanerozoic. Cretaceous itself experienced low global relief causing sluggish river run-off, much higher C02 levels than today with oceans at least I3C warmer on average than present, extremely high-stands of sea level, and localized ocean circulation patterns without polar overflow water exchange. Dinosaurs waded in swamps, rather than trampling on land.

The Upper Cretaceous of NW Europe starved of terrigenous elastics and became blanketed with immense nannofossil carbonates. Oceans were more susceptible to development of oxygen deficits, expressed in various ways. Not only were dark shales more widespread, but half a dozen 'anoxic events' were recorded by condensed shale sequences in widely separated parts of the world, linked by global isotope anomalies.

Although Cretaceous land ice is controversial, major and minor sea-level changes are well documented, like the Late Aptian long-lived glacio-eustatic low stand on the Arabian Plate (Maurer et al., 2012). Gale et al. (2002) interpreted twelve sea-level sequences in the Cenomanian as being driven by 405-kyr long-eccentricity cycles; with high-resolution ammonite correlation of marine successions in southeast India and northwest Europe the authors demonstrated that these sea- level changes are globally synchronous.

Despite the magnificent compilation of Rawson, Dhondt et al. (1996) defining Cretaceous stages is a painfully slow process, with only 4 of 12 stages having GSSP's. Albian and Campanian may be next, assisted by splendid Corg correlation bypassing fossil endemism, Milankowitch-cycle numbered bed by bed correlation on a supra-regional scale, as achieved already for Danian and Neogene, is the new challenge for formal Cretaceous chronostratigraphy.

Stratigraphic revision and update is finally nearing completion of the Cromer Knoll, Shetland and Chalk Groups in the North Sea, and of the Cromer Knoll and Shetland Groups in the Norwegian Sea. The lithostratigraphy of the North Sea, now unified for the UK and Norwegian sectors, describes 3 groups, 30 formations and one (sand) member. The Cretaceous lithostratigraphy for the Norwegian Sea describes 2 groups, 17 formations and 14 new (sand) members. A majority of sands are gravity flow deposits in open marine settings.

The Cretaceous offshore biostratigraphy calculated for the microfossil record in 37 Norwegian wells integrates over 100 foraminifer, dinoflagellate cyst, diatom and miscellaneous events in nineteen zones, numbered from NCFI through NCFI9 (North Sea Cretaceous Micro Fossil Zones I - 19). A literature based Dinoflagellate Cyst Zonation (DCZ), linked to the NCF zones, is also presented, with eleven zones and thirty-nine subzones. Both zonations are optimized for industrial applications with ditch cuttings samples.

This (long overdue) stratigraphic update alleviates misnaming and incidental use of unique names for reservoir units, without documentation and lack of biostratigraphic and correlative insight. The internet site www.nhm2.uio.no/norlex provides core archives for the lithostratigraphic units.

Gale, A. et al., 2002. Global correlation of Cenomanian sequences. Evidence for Milankowitch control on sea level. Geology 30(4), 291-294.

Maurer, F. et al., 2012. Late Aptlan long-lived glacio-eustastic low stand recorded on the Arabian Plate. Terra Nova.

Rawson, P.F., Dhondt, A.V., Hancock, J.M., and Kennedy, W.J. (editors), 1996. Proceedings 'Second International Symposium on Cretaceous Stage Boundaries' Brussels 8-16 September 1995. Bulletin van het Koninklijk Belgisch Instituut voor Natuurwetenschappen, Aardwetenschappen, 66 - Supplement, 117 pp

Haydon Bailey -  Controls On Late Cretaceous Chalk Deposition In The North Sea Basin

We tend to assume that the white chalk of the English coast was deposited in fully open marine, clean, clear, well oxygenated epicontinental seas, which stretched from the Atlantic to the Caucasus and beyond. Whilst some of this may be true, there are subtle indications which point to a different story. There is evidence to suggest that the sea floor during chalk deposition in both the North Sea and the Anglo-Paris basins wasn't such a pleasant environment to live in.

Evidence from the planktonic foraminifera from the Chalk succession of southern England has always been regarded as anomalous, but perhaps it's giving us an indication of the true state of affairs. This is a preliminary attempt to re-assess the micropalaeontological data available in order to start to build a more accurate picture of what the water column and the sea-floor were like during the Late Cretaceous.

A picture emerges of semi-restricted to restricted basins on the margins of an expanding oceanic realm, within which the water masses were generally oxygen deficient and the impoverished sea floor fauna indicating background dysaerobic conditions at times disrupted by rapid, mass flow and turbidite sedimentation. The chalk seas of the North Sea basin was also punctuated by sporadic influxes of more open marine warm water masses carrying with them plankton originating in better oxygenated and generally much more pleasant regions of the AtlanticWe tend to assume that the white chalk of the English coast was deposited in fully open marine, clean, clear, well oxygenated epicontinental seas, which stretched from the Atlantic to the Caucasus and beyond. Whilst some of this may be true, there are subtle indications which point to a different story. There is evidence to suggest that the sea floor during chalk deposition in both the North Sea and the Anglo-Paris basins wasn't such a pleasant environment to live in.

Evidence from the planktonic foraminifera from the Chalk succession of southern England has always been regarded as anomalous, but perhaps it's giving us an indication of the true state of affairs. This is a preliminary attempt to re-assess the micropalaeontological data available in order to start to build a more accurate picture of what the water column and the sea-floor were like during the Late Cretaceous.

A picture emerges of semi-restricted to restricted basins on the margins of an expanding oceanic realm, within which the water masses were generally oxygen deficient and the impoverished sea floor fauna indicating background dysaerobic conditions at times disrupted by rapid, mass flow and turbidite sedimentation. The chalk seas of the North Sea basin was also punctuated by sporadic influxes of more open marine warm water masses carrying with them plankton originating in better oxygenated and generally much more pleasant regions of the Atlantic

John Green -  Fossils from the Welton and Burnham Chalk Formations of Lincolnshire'' [display]

John Green - ''The benthic palaeocommunity of the Burnham Chalk Formation of Lincolnshire ( Upper Turonian, Plesiocorys ( sternotaxis ) plana biozone )"

John Green Ammonite

The Burnham Chalk Formation in Lincolnshire is particuarly well exposed at the North Ormsby quarry ( TF 2893 ) and, in North Lincolnshire, at the Ulceby Vale quarry ( TA 104133 ). Both of these exposures represent important sections of the Plesiocorys ( sternotaxis ) plana biozone of the Upper Turonian stage. Biostratigraphical bed by bed collecting by the author, over more than twenty years, mainly from the North Ormsby quarry, has resulted in the recovery of a large and varied macrofauna.

These are depicted by the author within the context of a palaeoenvironmental reconstruction, depicting the Upper Turonian sea floor and its associated faunal groups, such as Inoceramid bivalves, echinoderms and brachiopods, in addition to rarer nektonic forms, such as ammonites and fish remains. This talk will discuss the afformentioned fauna  in addition to a brief discussion of the ecological environment.

 

Malcolm Hart - "The 'Black Band': local expression of a global event."

 

The 'Black Band' of the Northern Province is a well-known feature of the chalk succession in Yorkshire, Humberside and Lincolnshire, although in the latter county it is black, red and green in a series of colour zones extending from north to south. It is recorded extensively in the North Sea Basin and can be correlated widely using geophysical logs. Though highly variable in detail, it is part of a global event in the latest Cenomanian. The biostratigraphy and chemostratigraphy show this to be a globally synchronous event, with regional variations caused by local situations. Though exceptionally well-studied there are still debates as to its formation. In this case the uniformitarianism approach does not work as, if one studies the interaction of the modern oxygen minumum zone (OMZ) and present-day continental shelves, there are no black, organic-rich sediments with unusual assemblages of benthic foraminifera to be found. Despite this, the OMZ is widely invoked in many interpretations of these latest Cenomanian events. Why, therefore, are oil source rocks in Brazil, Angola, Texas, Tunisia, etc., found from this geological interval and does the formation of the 'Black Band' still help in our interpretations? Silled-basins, high productivity, slow sedimentation, dinocyst 'blooms' and a fragmented Cretaceous ocean system all figure in the on-going debate.

Mike Horne - "Chalk Biostratigraphy – can we get it right, please?"

[click here for the full text]

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?

Hagenowia

Mike Horne - Field Excursion for Flamborough, East Yorkshire.

Danes Dyke or South Landing – To examine the Flamborough Formation –

Selwicks Bay –

To examine the top of the flinty Burnham Formation and the base of the flintless Flamborough Formation.

Safety, ethics & logistics–

Hard hats and non-slip footwear must be worn. We will be walking on chalk wave cut platform which will be slippery if wet, sandy beach, rocky-pebbly beach and perhaps seaweed. Walking distance will be about 2km but will involve steep paths and steps.

The sites are SSSIs so please restrict you collecting from in-situ material. There is a Marine No Take Zone at one of the sites which means that material with living plants or animals attached must not be removed.

Refreshments will not be provided – please bring your own food and drink. For delegates using their own transport – there are pay & display parking fees to be paid at the sites. The field meeting will end about 3pm. We aim to return to the University of Hull by 4-30pm and if requested the coach will take delegates to the Transport Interchange..

Selwick's Bay

Mike Horne - Welcome on behalf of the Hull Geological Society

click here for the full text

Paul Hildreth - The Distribution Of Flint with Particular Reference to the Chalk Group Of The Northern Province

Flints are a well-known and easily identifiable feature of Upper Cretaceous rocks belonging to the Chalk Group. The formation of flint remains open to discussion though Clayton (1986) has produced a convincing argument for its deposition triggered by geochemical activity at a redox boundary at shal­low depth below the sea bed, Lithostratigraphic logging of the Chalk identifies flint at certain levels on a regional scale and many have characteristic features which make them useful for the purposes of correlation. In the Northern Province, flint is found in only two of the four formations exposed on land. The Ferriby Chalk Formation is flint-free as are the lowest beds of the overlying Welton Chalk Formation. Nodular and burrow flints appear in most of the Welton Chalk but the Burnham Chalk Formation is characterised by the appearance of tabular; paramoudra and carious, or imperfect, flints. The Flamborough Chalk Formation is flint-free. Little documented work has been published on the distribution or variation of form of flints. It is probable that flint distribution, and likewise flint form, is determined by a variety of factors. It is hoped that this overview might prompt discussion and further interest in the quest for an acceptable model.

Rory Mortimore - "Offshore Northern Province Chalks in the North Sea".

Chalk has been encountered in the foundation areas for offshore windfarms and is increasingly of interest as a seal-rock or fractured reservoir in the petroleum industry. It would be a great advantage if an onshore analogue for the offshore geology could be identified to aid construction of the offshore geological model. Onshore field sections are needed for determining the general geology including likely stratigraphy, range of lithology and tectonic structure and for determining the style and depth of weathering. Most of the offshore wind farms to be founded on Chalk in the UK sector are in the Southern North Sea from north Norfolk to offshore East Yorkshire.

Stratigraphically, the offshore wind farm areas span all the onshore Chalk formations especially the Northern Province formations present in the Lincolnshire and Yorkshire Wolds. Cored-boreholes illustrate that the detailed Iithostratigraphy can be extrapolated offshore supported by key fossil marker beds. There are, however; some differences offshore especially off Norfolk where there are variations in lithology not represented onshore and where there is a mixture of both Northern and Southern Province lithologies. Seismic sections also illustrate the lateral variations in thicknesses of units with respect to tectonic structure. The offshore successions have added to our knowledge and understanding of the onshore Northern Province Chalk.

Russell Yoemans - "Observations On Pot Stones."

A chance discovery of trace markings and fossils of sponges inside the upper rims of Paramoudra on the North Norfolk coast which led on to the examination of in-situ flints shows that silica gel was beginning to lithify on the Chalk Sea floor around and in conjunction with the sponges.The sea bed in this area was between a series of basins and sponges were making their own protection from the effects of currents in the form of Paramoudra and Silica Bioherms.Further investigation has revealed the migration of elements within Flint and the photovoltaic action of sunlight are producing banding, secondary silica and stones that grow in the topsoil.

Simon Mitchell - "Lithostratigraphy and Biostratigraphy of the Chalk of the Northern Province".

The Chalk of the Northern Province has its own lithological character that differs significantly from the soft chalks of the Southern Province. This has led to the development of separate lithostratigraphic schemes for the two provinces. In the Northern Province, Chalk sedimentation began in the Middle Albian, and onshore sections extend up into the Campanian. The fauna of the Northern Province also contrasts with that of the Southern Province, and there are more belemnites and inoceramids and fewer ammonites; there are also differences in the ranges of the microfossils, particularly foraminifers. In the Albian, correlation of the Hunstanton (Red Chalk) Formation can be achieved using belemnites and inoceramids, and rare ammonite records.

The Cenomanian has a distinctive stratigraphy that can be traced across the Northern Province and thickens towards Speeton where bed-for-bed correlations are possible with the chalk-marl couplets in the Lower Chalk of the Southern Province, using faunal and chemostratigraphic marker events such as pulse faunas, inoceramids and carbon stable isotope peaks. Faunal studies for the Turonian to early Campanian can be tied to a detailed marker stratigraphy defined by flint layers and bentonites, allowing a detailed correlation across the province. Inoceramids provide the most suitable biostratigraphic markers, with belemnites and crinoids (Marsupites and Uintacrinus) being valuable in the Santonian and Campanian. The crinoid zones in the Upper Santonian show a particularly thick, development on the Flamborough coast, and represent amongst the thickest development of these zones in chalk facies. Stage boundaries can be established by use of biostratigraphic and chemostratigraphic indicators.


For further information 'phone 01482 346784.

 

e-mail - m.j.horne @ hull.ac.uk

updated 14th August 2015

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