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Photomicrographs of cellulose peels from the Mesozoic rocks of Dorset
Photomicrographs of cellulose peels from the Mesozoic rocks of Dorset K. W. Abineri ABINERI , K. W. 19R9. Photomi crograph s of cellulose peels from the Mesozoic rocks of Do rset. Proc. Geol. A ss. 100(2), 161-74. Cellulo se lacquer peels have been developed, as a simpler, cheaper and quicker alternative to thin section s, for the preparation of microscope slides. The slides have been used to make photomicrographs showing nannofossils, microfossils and other fine detail in so me sedimentary rocks. By including staining of the rock surfaces, the composition of carbo nate mater ial and calcareous microfossils can be deduced. Wher e appropriate, the method allows many microscope slides to be prepared from single small samples of rock . Furthermore the amount of detail record ed can warrant numbers of photomicrographs being made from each slide. The technique is employed for exploratory work at some Dorset Mesozoic coastal sites. A selection of photomicrographs is presented and the characteristic featur es are discussed. Gordon House, 42 West Borough, wimborne. Dorset, BH21 INQ
I. INTRODUCTION
Using a proprietary rapid drying cellulose lacquer, formulat ed to produce a tough smooth film with good flexibility and adhesion , a very simple technique has been developed to make microscope slides based on rock peels (Abineri , 1986). These show minute nannofossil and microfossil detail as well as giving a general picture of the fine structure of rock surfaces. The procedure involves the application of lacquer to a small prepared area of rock surface, using a self-adhe sive paper label , cut in the form of a small frame , and a clean small nylon artists' paint brush. The " flow" characteristics of the cellulose lacquer are crucial. The frame is used to remove the lacquer film after dry ing for about 1 hour at a temperature of 35-40°C. The peels are only about 1 em" in area and are easily mounted on to microscope slides under standard glass cover slips (No. 1 18 x 18 mm, BSS 3836-17). To facilitate the use of an oil-immersion objective for the examination and photography of fine detail, th e microscope slides are sealed carefully with shellac. More recently stained peels have been prepared by combining this basic method with the well-known simple staining procedure for carbonate rocks. (Adams, MacKenzie & Guilford, 1984). This method can distinguish between carbonate rocks with regard to composition and texture , and produce individual differential sta ining of microfossils and nannofossils, helping in their detection . Many Dorset coastal sedimentary rock formations have been sampled and characteristic photomicrographs have been made from the peels. Variat ions in the surface treatment of samples have been used to suit different types of rock . Sometimes problems occur with interpretation , but the investigation of these can involve quite interesting microscopy ,
including critical visual examination and the use of various modes of ilIumination (brightfield, with or without polarizing plates, darkfield or pha se contrast). Clearly the method has its limitations, especially with hard consolidated rock . However with many sedimentary rocks, above alI with those showing a finely layered structure or relatively weak cohesive properties, very detailed pictures have been obtained by means of this essentially simple technique , because the tough lacquer film removes a thin bound layer of rock material when peeled from the rock surface . The basic procedure has been applied also to a few igneous and metamorphic rock samples with some success, although here generally " prints" or " moulds" of the surface are obtained. The use of powerful etching reagents may help in some cases. Peels prepared from the Dorset Kimmeridge Clay upper stone bands present much variable material, consisting of numerous minute marine nannofossils (coccoliths and coccolithophores), a variety of microfossils , plant microspores, microscopic grains of pyrites and organic residues with plant fragments including fossil wood fragments (fusain). The detection of these microscopic features is of interest because it tends to confirm the variable influx of land swamp debris to the sea at the time of deposition of the Kimmeridgian marine microplankton (Ioannides, Stavrinos & Downie, 1976). Furthermore close examination of some microscopic fusain wood fragments on peels from many horizons in the Dorset Kimmeridge Clay show "bordered pit" tracheid structures very similar to those known from later times in the Lower Purbeck Dirt Beds and which have been related to conifer trees (Francis, 1983). In a similar manner to the above , other exploratory investigations, especialIy by amateurs or students, might well make use of this simple rock peel technique.
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2.PHOTONDCROGRAPHY In view of the amount of detail recorded on some of the prepared microscope slides, the photomicrography completed so far has had to be very selective. For example a photograph taken with the oil-immersion objective covers a field of only about 135 11m x 90 usn, In order to record the whole 1 em' area of the peel mounted on the microscope slide, using the same objective, over 8000 similar photographs would be required! Therefore in practice visual examination is completed using the mechanical stage and an intermediate power objective, before selective high power pictures are taken. In spite of adopting this procedure, much material inevitably remains unexplored on the present collection of microscope slides (c. 3(0). The following equipment has been used for visual and photographic work on the peels: i) Nikon "Labophot" microscope fitted with Trinocular eyepiece tube type F. This allows 100% of the light to be diverted from the binocular eyepiece to the camera. ii) Nikon FE camera body with connecting tube and mounting, fitted with a projection lens. iii) Phase contrast turret condenser with additional positions for brightfield and darkfield microscopy. Facilities for the use of an analyzer and a polarizer plate. iv) Illumination brightness control, field diaphragm control, condenser aperture diaphragm control and a mechanical stage. v) A range of filters for visual and photographic observations. Objectives N.A. 0.1, 0.25, 0.65 and 1.25 (oil-immersion) giving visual magnifications of x60, X150, x600 and x1500 respectively with the binocular eyepiece. The main film used so far has been Fujichrome DX ASA 100, to produce 35 mm colour slides. The approximate fields covered by these slides with the various objectives are as follows: N.A.0.1 3370 p.m x 2250 lim N.A. 0.25 1350 11m x 900 lim N.A. 0.65 337 11m x 225 11m N.A. 1.25 135 11m x 90 ~m (oil-immersion). A correcting filter is used for the light with the illumination brightness control at maximum. The Nikon camera employs automatic exposure. Methods of illumination have been varied to improve contrast or to emphasize certain features and are determined by visual inspection. The following methods have been used with some success: i) Brightfield with an extra blue filter or with one polarizing plate above the objective; alternatively with analyzer and polarizer plates parallel or crossed. ii) Darkfield with, or without crossed polarizing
plates. Foraminifera sections in the Upper Chalk on unstained peels have given interesting pictures using dark field illumination with crossed polarizing plates. iii) Phase Contrast. This tends to be effective when the peels are mainly "prints" of hard consolidated rock surafaces. With those peels which have removed a definite layer of rock material, objects which are slightly "out of focus", due to the finite thickness of the layer, tend to form conspicuous "haloes" which may interfere with the foreground objects especially in a crowded field. It is intended to experiment in the future with alternative films and filters to improve the photomicrography of the stained peels. From personal experience, a relatively simple, good-quality, students' microscope used with these peels will give visual images comparable to the following selected photomicrographs. It is therefore strongly suggested that students or amateurs who wish to extend their interest in sedimentary rocks to include some micropalaeontology or related topics, will find cellulose lacquer peels of some value. Again it should be emphasized that the use of an intermediate power objective, giving a combined magnification of about x600, is satisfactory for the close visual inspection of the slides. Of course there are many well-established methods for isolating and studying microfossils apart from the use of peels or thin sections. These involve separation techniques which include pulverization of rock samples, the use of various chemicals, washing, sieving or decanting (Brasier, 1980). For the complete morphological examination of individual microfossils these separation procedures may be essential. However the peel technique discussed here can produce overall pictures of the rock in terms of its microscopic contents. As these features are often shown in considerable detail using a basically simple, quick and cheap method, this approach is recommended. Furthermore very little damage need occur to hand samples collected by the student for more general use and, if sufficiently interesting, one small rock sample can produce many microscope slides. 3. SELECTED PHOTOMICROGRAPHS FROM DORSET COASTAL FORMATIONS These include pictures from both unstained and stained lacquer peels. Before etching or staining, a small area of each rock surface was finally polished or flatted with 1200 grade "wet or dry" abrasive paper to give a light sheen. Any earlier grinding with coarser abrasive paper was reduced to a minimum. For the preparation of unstained peels, etching with dilute acid or dilute alkali was used depending on the type of rock. With all the stained peels the following solution
PHOTOMICROGRAPHS OF C E L L U LO SE PEELS
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was used:
b) OsmiDg1on Oolite, Corallian, Oxfordian (SY742814)
10crrr' 0.5 molar hydrochloric acid Solution (A) 20 ern" distilled water { 3.6 x 10- 2 grams alizarin red S
This Upper Jurassic oolite is well exposed at Bran Point on the Dorset coast east of Osmington Mills. Fig. 2 was prepared from a stained peel off a sample containing numerous ooliths . The low power photomicrograph was made with brightfield illumination and one polarizing plate above the objective. It shows the finely layered structure of the oolith sections. The staining is interesting and indicates the presence of calcite, ferro an calcite, grains of silica but perhaps also some dolomite. The microscope slide shows considerable detail under high power, including foraminifera sections and other microfossils. The blue ferroan calcite background exhibits a finely structured surface and much unidentified material. Also the use of crossed polarizing plates gives complex birefringence patterns. Further peels will be made from this rock sample .
Just before stauung 4.0 x 10- 2 g of potassium ferricyanide (potassium hexacyanoferrateflflj) were dissolved in 5 ern' of solution (A) with two drops of methylated spirit or ethanol. This mixture stained many samples but was used as soon as possible. Each sample required only a few drops on the surface for a period of up to 2 minutes (depending on the rock type). The staining stage was completed by a thorough rinse with distilled water and then acetone (propanone) to dry the surface before the application of the cellulose lacquer in the usual manner. In the absence of an accurate chemical balance the quantities of alizarin red S and potassium ferricyanide were carefully estimated using a small spatula only and the following approximate pack densities : alizarin red S 0.5 grams cm" potassium ferricyanide 1.5 grams cm" Although very small quantities of the above chemicals are needed with this simple staining procedure great care must be taken to avoid contact with skin or eyes. This applies equally to the cellulose lacquer, solvents and all other etching reagents. Furthermore the cel1ulose lacquer, cel1ulose solvent and acetone are all very flammable. They should be stored and handled with due care. a) Belemnite Marls, Channouthian, Lower Lias (SY 380927) This Lower Jurassic grey marl is well exposed at lower cliff level on the shore east of Charmouth. It is well known for small pyritised ammonites . Fig. 1 was prepared from a stained peel derived from a rock sample containing numerous minute crinoid stems. This low power photomicrograph was made with darkfield illumination and shows the complex structure of the crinoid stem transverse section which contains an infilling of deep blue stained ferroan calcite, whereas the main pale pink structure is probably pure calcite. The deep blue general background on this peel is fine ferroan calcite. The brown mottled area to the left of the picture and elsewhere is microcrystalline pyrites . The co-existence of large amounts of ferroan calcite and pyrites in this rock are indicative of strongly anaerobic conditions. The whole microscope slide is filled with fine detail which is an incentive for much further work on the Lower Lias.
c) Kimmeridge Clay, Kimmeridgian, from Washing Ledge Stone Band (SY 906791) to Fresbwater Steps Stone Band (SY 943772) A number of bands and zones in this complex section of the Upper Jurassic have been sampled and peels have been prepared to a varying extent. A total of almost 100 microscope slides have been made from the section , including both stained and unstained types. The complexity of Kimmeridge Clay sediments appears very great indeed, perhaps in part due to their biogenic nature. Here only two aspects will be shown , firstly the occurrence of minute fossil wood fragments in the marine sediments and secondly the results of staining microfossils and nannofossils in the Freshwater Steps Stone Band . (i) Fossil wood fragments These are shown on Figs. 3 & 4. Microscopic fossil wood fusain has been found so far on lacquer peels from the following horizons in the Kimmeridge Clay: Washing Ledge S.B. Aulacostephanus autissiodorensis zone. Maple Ledge S.B . (uppermost level). Blakes Bed 42. Pectinatites elegans zone . Pectinatites scitulus zone . Pectinatites wheatleyensis zone . Rope Lake Head S.B . White S.B. (especially in a dark centre layer) . Middle White S.B. Freshwater Steps S.B. The amount found at different horizons appears to vary considerably. For example in the dark shale at
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Fig. 1. Crinoid stem transverse section showing calcite, ferroan calcite and microcrystals of pyrites. Belemnite Marls, Lower Lias, Jurassic. (SY 380927). Field: 1350 I'm x 900 I'm. Visual magnification x 150. Darkfield illumination. Objective N.A. 0.25. Stained lacquer peel.
Fig. 2. Oolith Sections showing calcite, ferroan calcite, silica grains and suspected dolomite. Osmmgton Oolite, Corallian, Jurassic. (SY 742814). Field: 3370 I'm x 2250 pm. Visual magnification x60. Brigbtfield illumination with one polarizing plate above objective N.A. 0.1. Stained lacquer peel.
PHOTOMICROGRAPHS OF CELLULOSE PEELS
the uppermost level of the Maple Ledge S.B. some peels have shown 50-100 fragments on 1 em" area, whereas for most of the White S.B. very few are found, with the exception of the 1 em thick dark centre layer. The Middle White S.B. contains many wood fragments but the finely layered Freshwater Steps S.B. shows very variable numbers. Earlier studies have reported the presence of wood fragments in the Kimmeridge Clay (Downie , 1957). Close inspection of fusain fossil wood fragments on the above Kimmeridge Clay peels has shown the presence of bordered pit tracheid structures from conifer trees similar to Protocupressinoxylon purbeckensis found in the Lower Purbeck (Francis , 1983). Many of these objects have been identified. Bordered pits are shown on Fig. 3 from the upper Maple Ledge S.B. (SY 908790). This picture was taken at high magnification but the tracheid structure can be seen easily with an intermediate power objective. Examples have been recorded at all the above horizons. .Dr J. E . Francis has examined some of the pictures of these objects from the lacquer peels and confirms the close similarity to material from the Lower Purbeck studied by her . The salient features appear on Fig. 3 and are concerned with a single line of contiguous bordered pits, each with an oblique aperture and a thickened rim. The outer diameters average about 15 J1.m and agree reasonably well with the figure of 14.3lJm from the Lower Purbeck data (Francis, 1983). Some pits from the upper Maple Ledge S.B. are smaller, as is shown on Fig. 3. The upper Maple Ledge site is easily located and very accessible at the base of the cliff in the centre of Kimmeridge Bay, just above the hard stone band which is directed into the bay south-east of Gaulter Gap. The dark shale splits easily and cleanly, parallel to the bedding , giving flat smooth surfaces ideal for lacquer peels. If a drop of water is placed on the exposed surface numerous minute black specks can be seen with a hand lens. Many of these are fossil wood fragments. The peels exhibit also many fine grains of pyrites, yellow to brown transparent organic material, numerous coccoliths, some coccolithophores and microfossils which stain blue (ferroan calcite) and other microfossils which remain unstained (silica). Numbers of bordered pits have been identified, including some completely isolated pits i.e, individual fusain rings. More recently similar damaged fossil wood fusain has been identified on peels from some of the Middle Purbeck beds in Durlston Bay, including numbers of isolated pits. (see (d) below). Fig. 4 is a highly magnified picture of a fossil wood fragment embedded in a relatively pure coccolith layer. This and several other similar objects were detected on an unstained peel from the Freshwater Steps S.B. (SY 943772). Part of this fragment is probably a print or mould. Peels from all the above mentioned Kimmeridge
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Clay horizons contain numerous coccoliths and the upper stone bands exhibit also many coccolithophores (coccospheres) . The existence of conifer wood fusain in association with marine microplankton gives rise to a number of interesting aspects. Firstly it must reinforce the assumption of the variable input of terrigenous swamp generated material to the sea in Kimmeridgian times. (Ioannides et al., 1976.) Furthermore the shedding of gymnosperm wood fragments into the Kimmeridgian sea, and perhaps much later into Middle Purbeck lakes or pools (see (d) below), seems to reflect the dominant position of the Jurassic conifer forests, before the rise of the angiosperms in the early Cretaceous. It is also interesting to note that studies of the climatic environment of Protocupressinoxylon purbeckensis in the Lower Purbeck indicate very dry seasons but also periods of higher rainfall (Francis, 1984). This agrees with the presence of evaporites and other related phenomena in the Basal Purbeck areas (West , 1975). Did these trees evolve under similar climatic conditions in the earlier Kimmeridgian times? This might explain the variable movement of organic debris into the sea from the periodic flooding of low lying forest land. How does this agree with more modem concepts of Upper Jurassic palaeogeography (Wills, 1952)? Another point of interest which arises from the occurrence of conifer wood fusain in the Kimmeridge Clay relates to off-shore petroleum. These late Jurassic shales, matured in the Viking Graben in the North Sea, are believed to be the source of the Brae and Brent oil (Brown, 1987). In recent years some geologists have linked prospective petroleum and natural gas sources to fossil amber resin from conifer forests. For example this applies to Tertiary fossil forests in the Canadian Arctic (Francis & McMillan, 1987). Where is the fossil amber from the dominant Mesozoic conifer forests? With a density of only 1.08 g em - 3 , is some of this resin an ingredient of the allochthonous organic material in the Kimmeridge Clay? Input of large amounts of decaying organic matter to the sea would promote anaerobic conditions and the activity of anaerobic bacteria, giving rise to grains of pyrites and calcareous microfossils showing ferroan calcite composition. These objects occur on the stained cellulose lacquer peels, often associated with fossil wood fusain and yellow-brown transparent organic residues. Is this latter material derived from fossil amber? It has been found on all peels prepared from all the above mentioned Kimmeridge Clay bands and zones. Clearly much further work is needed on the detection, distribution and examination of these conifer fossil wood tracheids and the related quantity and distribution of the transparent organic material , in a determined search for the missing amber.
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Fig. 3. Bordered pit tracheid structure from Mesozoic conifer wood on a background of organic material containing coccoliths, grains of pyrites and fusain. The embedded coccoliths are unstained . Dark shale at upper-most level of the Maple Ledge S.B., Kimmeridge Bay, Kimmeridge Clay, Upper Jurassic . (SY 908790). Field : 135 J.lm x 90 um. Visual magnification x 1500. Brightfield illumination . Objective N.A . 1.25 oil-immersion . Stained lacquer peel.
Fig. 4. Microscopic fossil wood fragment embedded in a coccolith layer. Part of this fragment is probably an external mould. Freshwater Steps S.B. , Kimmeridge Clay, Upper Jurassic . (SY 943772) . Field: 135 J.lm x 9OJ.lm. Visual magnification x 1500. Brighttield illumination with orie polarizing plate above objective N.A . 1.25 oil-immersion . Unstained lacquer peel.
PHOTOMICROGRAPHS OF CELLULOSE PEELS
(ii) Freshwater Steps Stone Band (SY 943772) The three upper conspicuous stone bands in the Kimmeridge Clay (Pectinatites pectinatus zone) each have their special features. The lowest, the White S.B., shows the purest white coccolithic limestone generally with the least organic residues, but there is nevertheless a dark centre layer of about 1 em thickness as mentioned above . The Middle White S.B. is more complex and contains much organic material with fine grains of pyrites and fossil wood fusain, as well as numerous coccoliths and larger microfossils. It contains also microcrystals of ferroan calcite , which have not been detected in the other two stone bands . Few blue stained coccolithophores are found . The most complex however is the uppermost, the Freshwater Steps S.B. This has been sampled close to Freshwater Steps at the base of the cliff. The rock shows a very finely layered structure which includes white and grey components well seen with a hand lens. Some of these very thin layers are quite dark but others are almost pure white. Coccoliths and coccolithophores occur in vast numbers, but the greyer layers contain also yellow-brown organic material, pyrites, calcispheres, various plant microspores and microfossils of diameters 15-50 jlm , and varying amounts of wood fragments. The coccoliths are generally from 3 to 6 jlm in diameter and appear much more uniform and well preserved than those in the Dorset Upper Chalk. Although not classified so far they show agreement with descriptions given in previous studies . (Downie, 1957). The coccoliths can be examined alone very easily by applying a nylon brush, dampened with distilled water, to the clean rock surface and making a "smear" on a microscope slide. If a standard glass cover slip is placed over the smear, good high power images will be obtained; alternatively by using crossed polarizing plates the characteristic optical figures are seen. The rock is ideal for the preparation of cellulose lacquer peels due to its layered structure. When polished or lightly flatted with 1200 grade abrasive paper, inevitably a smooth surface is formed which includes white and grey patches. The resulting peels present the white areas as showing mainly coccoliths and coccolithophores, whereas the grey areas include layers of organic material lying over, or embedding, these minute nannofossils . The organic layers are often transparent with a fairly pale yellow-brown colour, but sometimes they are much darker due to embedded fine black particles, which include grains of pyrites and some fusain. When the layer is transparent, coccoliths can be seen clearly below it, or sometines embedded in it. Careful visual work with the microscope helps here, especially with practiced use of the fine focus control. No distortion of the images appears to occur. These covered coccoliths are usually well preserved and unaffected
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by the etching or staining reagents. The underlying coccoliths appear golden coloured, but those embedded often have a grey appearance. When crossed polarized plates are used many of these coccoliths produce the characteristic optical figures, proving that they are not moulds or prints, but the real nannofossils peeled from the rock surface. There are other brown and orange particles in these organic layers which may be partially oxidized grains of pyrites or unidentified nannofossils . Using the simple staining procedure with dilute hydrochloric acid, alizarin red S and potassium ferricyanide, quite surprising results are obtained, showing individual differential staining of microfossils and nannofossils, whilst leaving the covered coccoliths golden coloured. The occurrence of deep blue staining, indicating ferro an calcite, with some coccolithophores, microfossils or parts of microfossils, seems very interesting when similar neighbouring objects are stained pink, indicating pure calcite. If this truly represents difference in composition on such a microscopic scale, then it seems to the writer that microbiological processes might explain its cause. Recently small areas of unstained microcrystals of dolomite have been detected on some peels. Where external moulds of coccoliths and coccolithophores exist on the peel due to the removal of these nannofossils by the polishing, etching or staining procedures, or where moulds occur on the lower side of the lacquer film, the resulting images show no optical figures with crossed polarizing plates. Comparisons between stained and unstained peels from the same rock surfaces using crossed polarizing plates , indicate fewer external moulds on the unstained peels; also these peels seem to show better detailed images, due to far less drastic etching conditions, i.e. 12 to 15 seconds with 2% dilute acid instead of the period up to 2 minutes used with staining . This would not apply generally to those nannofossils covered by transparent organic material. Some results with the staining of Freshwater Steps S.B. material are shown on Figs. 5,6 & 7. Fig. 5 is an intermediate power picture from the Freshwater Steps S.B., with a field area of about 337 jlm x 225 utt», using brightfield illumination with one polarizing plate above the objective. It illustrates complex individual differential staining of nannofossils. The visual appearance through the microscope shows greater brightness and contrast than is shown on this photomicrograph. The deep blue coccolithosphores are richer in colour and readily distinguished from black grains of pyrites and fusain . The organic layer in the top left corner region covers unstained coccoliths with the consequent golden colour . There are pink coccoliths and coccolithophores, which are assumed to be of pure calcite composition, in close association with the deep blue coccolithophores, believed to be made of ferroan calcite. Unstained minute areas or
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Fig. 5. Complex individual staining of nannofossils. The top left field shows a yellow-brown organic layer with unstained covered coccoliths, grains of pyrites and fusain. Freshwater Steps S.B., Kimmeridge Clay, Upper Jurassic. (SY 943772). Field: 337/-1m x 225/-1m. Visual magnification x 600. Brightfield illumination with one polarizing plate above objective N.A. 0.65. Stained lacquer peel.
Fig. 6. Differential staining of coccoliths and coccolithophores with unstained covered "golden" coccoliths. Freshwater Steps S.B., Kimmeridge Clay, Upper Jurassic. (SY 943772). Field: 135 /-1m X 90/-lm. Visual magnification x 1500. Brightfield illumination. Objective N.A. 1.25 oil-immersion. Stained lacquer peel.
PHOTOMI CROGRAPHS OF C ELLULOSE PEELS
objects may be external moulds, siliceous nannofossils or small patches of dolomite . Fig. 6 is a high power picture from the same stained peel covering an area of about 135 Jlm x 90 Jlm. This was prepared with the oil-immersion objective using brightfield illumination and shows aspects discussed above in greater detail. Since we are examining a layer of finite thickness, not all objects are accurately in focus, especially with high power. Careful visual observations have an advantage here by employing the fine focus control. Some photomicrographs made from the Freshwater Steps S.B. stained peels show clusters of deep blue coccolithophores, which cover relatively large areas. Better individual images of coccolithophores tend to occur on the unstained peels from the upper stone bands. These nannofossils average from 9 to 12 Jlm in diameter and many exhibit coccoliths on their surfaces. It is difficult to estimate the number of coccoliths on each of the coccolithophores but a figure of 10 to 12 seems likely. Fig. 7 shows unicellular plant microfossils partly embedded in an organic layer, photographed under high magnification. Many covered coccoliths are also shown. A large variety of plant microfossils occur in the Freshwater Steps S.B., usually in association with organic material. They exhibit differing size, structure and staining patterns; some showing wall staining different from interior staining. There is a tendency for similar types to cluster. The object at the top of the picture , right of centre, is covered with coccoliths and some exterior moulds of coccoliths . This effect and the microfossil feature in the lower right corner of the picture occur frequently in the Freshwater Steps S.B. They have been described in earlier studies of the Kimmeridge Clay. (Down ie, 1957). Detailed classification of related microfossils and many others from lower Kimmeridge Clay horizons have been published in past papers (Ioannides et al.• 1976). With these microfossils close visual inspection will identify external moulds on the peels. The Dorset Kimmeridge Clay formation has in some ways been a challenge on the use of optical microscopy. However the lower sides of these cellulose lacquer peels can be spattered with metal and examined in far greater detail with the scanning electron microscope . SEM photographs were very kindly prepared for the writer by staff in the Laser Division, Rutherford Laboratory, SERC, from the lower side of a very detailed peel derived from the Rope Lake Head S.B . These pictures, with their great depth of field, show " solid" coccoliths at magnifications up to c. x 5000. However there are equally clear coccolith external moulds, where the corresponding coccolith was left on the rock sample surface , when the thin layer was removed (Abineri, 1986). These interesting pictures have given some insight into the
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effects of polishing, etching and staining discussed above. Clearly there are still very considerable opportunities for further exploratory work on the Kimmeridgian shales, clays and carbonate stone bands, using the optical microscope. Furthermore the rock materials seem ideal for the use of cellulose lacquer peels. Any problem which may arise with interpretation can present the observer with an additional interesting challenge .
d) Middle Purbeck, Lulworth Beds, Durlston Bay (SZ 036784) A number of these beds just below the Cinder Beds have been sampled recently. This location is south west of Peveril Point in Durlston Bay, close to the place where the Cinder Beds are exposed at shore level. Fig. 8 is from Bed 102, designated "Shales with thin sandy biosparites at base" (Cope et al., 1969). It is a low power picture of a stained Cypridea ostracod carapace section . The approximate field is 1350 Jlm x 900 Jlm with brightfield illumination, using one polarizing plate above objective N.A. 0.25. The whole microscope slide shows other detail of interest, including more ostracod sections and fragments , very damaged fusain fossil wood fragments , brown organic residues and minute unidentified nannofossils which are embedded in this organic material. A number of other peels have been prepared from Bed 102, which show damaged fusain bordered pit tracheids and some isolated fusain rings, indicating Mesozoic conifer wood. Ostracods and conifer wood fragments have been found in most of the Middle Purbeck beds examined so far. These sediments are believed to have formed in partly saline lakes or pools. More peels will be prepared from the Durlston Bay location, but it is hoped to compare these with corresponding beds at Worbarrow Tout and Bacon Hole. e) Lower Cretaceous, Wealden Lignite, Worbarrow Bay (SY 868801) Fig. 9 is an intermediate power photomicrograph, with a field area of about 337 Jlm x 225 um. It was prepared from a preliminary unstained peel derived from lignite, which was flatted with fine abrasive paper and then treated with a fairly concentrated solution of sodium silicate (water-glass), which reacts as an alkali. A brown solution was produced on the surface , assumed to be partly lignin, and then after rinsing with distilled water and drying, the cellulose lacquer peel was prepared in the usual manner. It is fairly certa in that the cellulose cell walls were exposed
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Fig. 7. UniceUular plant microfossils and coccoliths embedded in organic material. Freshwater Steps S.B., Kimmeridge Clay, Upper Jurassic. (SY 943772). Field: 135 /-lm X 90 11m. Visual magnification x 1500. Brightfield illumination. Objective N.A. 1.25 oil-immersion. Stained lacquer peel.
Fig. 8. Stained Cypridea ostracod section. Bed 102, Lulworth Beds, Durlston Bay, Middle Purbeck, Upper Jurassic. (SZ 036784). Field: 1350 um x 900 11m. Visual magnification x 150. Brightfield illumination with one polarizing plate above objective N.A. 0.25. Stained lacquer peel.
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Fig. 9. Cellulose plant cell walls in lignite. Wealden lignite, Worbarrow Bay, Lower Cretaceous. (SY 868801). Field: x 2251lffi. Visual magnification x 600. Brightfield illumination with one polarizing plate above objective N.A. 0.65. Unstained lacquer peel.
3371lm
Fig. 10. Axial section of Heterohelix, a biserial foraminifera. Actinocamax quadratus zone, Upper Chalk, Upper Cretaceous, Cliff west of Arish Mell. (SY 851802). Field: 135 /-1m x 90 Jlm. Visual magnification x 1500. Brightfield illumination with parallel polarizing plates (PPL). Objective N.A. 1.25 oil-immersion. Unstained lacquer peel.
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Fig. 11. Complex staining of Chalk nannofossils and microfossils. A section of a Globigerinid foraminfera is in the left of the field. Actinocamax quadratus zone, Upper Chalk, Upper Cretaceous, Cliff west of Arish Mel!. (SY 851802). Field: 337 Jlm x 225 Jlm. Visual magnification x 600. Brightfield illumination with parallel polarizing plates (PPL). Objective N.A. 0.65. Stained lacquer pee!.
Fig. 12. A typical Upper Chalk Calcisphere on a background of stained coccoliths and other calcareous nannofossils. Actinocamax quadratus zone, Upper Chalk, Upper Cretaceous, Cliff west of Arish Mell. (SY 851802). Field: 135 um x 90 Jlm. Visual magnification )(1500. Brightfield illumination. Objective N.A. 1.25. oil-immersion. Stained lacquer peel.
PHOTOMICROGRAPHS OF CELLULOSE PEELS
and removed from the surface. Examination of the peel shows a complex microscopic network with other details which have yet to be explored. These might include plant microspores or pollens. Alternative reagents, such as stronger alkalis, may be tried. f) Upper Cretaceous, Upper Chalk, Actinocamax quadratus zone, Cliff west of Arish MeU (SY 851802)
Small samples of chalk, collected from a shallow fault close to the coastal path at the above location, were the first rocks to be examined using unstained lacquer peels. Numbers of microscope slides were prepared which were crowded with detail, including numerous foraminifera sections, macrofossil fragments, calcispheres and coccoliths. More recently the samples have been re-examined with stained peels. As with the Kimmeridge Clay, etching was less drastic with the unstained chalk than with the stained chalk and this may have shown some advantages. Fig. 10 is a high power photomicrograph taken from an unstained chalk peel. It was prepared with the oil-immersion objective using parallel polarizing plates to give a field area of about 1351lm x 90 urn, The picture shows an axial section of Heterohelix, a biserial foraminifera. The focus was adjusted to give clear images of the chambers at the right apex of the test, which show complex surface structure. The use of plane polarized light with brightfield illumination increases contrast. Heterohelix has been found also in the Actinocamax quadratus zone of the Upper Chalk on the cliffs west of Bats Head (SY 792805). Since the sections of foraminifera in the peels can vary greatly with identical microfossils, depending on their orientation, problems can occur with identification. In view of the numbers of these objects in an average chalk peel and their variations in structure and size, there is ample scope for the enthusiast, especially with very small species which would be difficult to isolate by other methods. By using darkfield illumination with crossed polarizing plates interesting pictures can be obtained of foraminifera from unstained chalk peels. These show the delicate structure of the chamber walls. Photographs with 100ASA film require from 6 to 7 seconds exposure. The visual image is very effective when the eye is completely dark-adapted after some time. Figs. 11 & 12 were prepared from the same stained chalk peel derived from the Actinocamax quadratus zone at SY 851802. The 1 em" area peel on the microscope slide is crowded with differentially stained microfossils, nannofossils and macrofossil fragments. Although the usual staining reagents were used there is no apparent indication of blue objects or areas, i.e. no ferroan calcite. This may seem obvious in the case
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of the Upper Chalk, but it does tend to confirm the reliability of the staining procedure. Fig. 11 is a picture with intermediate magnification showing a field of area about 337 /lm x 225 /lm. It gives a general impression of the fine structure of the stained chalk surface. Brightfield illumination was used with parallel polarizing plates. The differential staining of the nannofossils, due to the alizarin red S dye only, is interesting and seems to confirm how the intensity of staining may depend on the fineness of the physical grain boundaries as well as on composition (Adams et al., 1984). Close inspection suggests that dye is concentrated on edges in the nannofossils, probably by adsorption, thus enhancing visibility and contrast. The prominent object on the left of the field is a partial section of. a globigerinid foraminifera. Similar damaged strucures appear elsewhere. High magnification pictures of this peel with the oil-immersion objective confirm the staining effects mentioned above. Coccoliths show a greater variety in structure and size than those in the Freshwater Steps S.B. The coccoliths have diameters from 1 /lm to lO/lm approximately. Many are partly buried in the surface or damaged. Fig. 12 is a high power view of a typical chalk calcisphere from a stained peel. Very large numbers of these microfossils are found in the Upper Chalk and by far the majority show a circular wall, which tends to confirm that the objects must be spherical. However, since every section must be circular, the actual diameter of an individual calcisphere cannot be estimated unless it is a small embedded object; nevertheless a range of values from 15 Ilm to over 100 /lm seems reasonable. Oval sections have been found though these seem more common in the Middle and Lower Chalk. As with many other microfossils, the systematic classification of these widely distributed objects remains very uncertain and could be a subject for detailed research. Some pyriform sections, similar in other respects to calcispheres, have been found on chalk peels. Visual inspection of calcispheres on lacquer peels indicate that most are external moulds.
4. CONCLUSION The preparation of cellulose lacquer peels and photomicrographs is continuing on samples from selected Dorset coastal formations and from other geological sites. The programme includes experiments with alternative etching and staining procedures as well as attempts to improve the colour photography of the stained peels. A low power stereomicroscope is now being used for the initial examination of rock samples, to select areas on the rock surfaces of special interest for peels and for general use during the preparation of the microscope slides.
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ACKNOWLEDGEMENTS Very special thanks are due to Dr. Ian West, Department of Geology, University of Southampton for his kind advice and encouragement on possible projects where lacquer peels might be used for exploratory purposes. The information from Dr. Jane E. Francis, Department of Geology and Geophysics, University of Adelaide, on Mesozoic conifers and her confirmation of the nature of the fossil wood fragments from the Kimmeridge Clay was of very special interest to me. I wish to express my appreciation for this generous help. My thanks are
due also to Paul Ensorn, Dorset County Museum, Dorchester, for his general encouragement and the time spent examining and discussing 35 mm slides from various Dorset sites. I wish to acknowledge also the very helpful co-operation and encouragement received from the Quekett Microscopical Club. Finally I wish to express my appreciation to Lieutenant Colonel C. P. G. Turner, Gunnery School, RAC centre, Lulworth Camp, for permission to publish pictures from samples collected in the Army Range area, and for his co-operation on the future sampling of Purbeck sites at Worbarrow Tout and Bacon Hole.
References ABINERI, K. W. 1986. The preparation of cellulose lacquer rock peels. Microscopy. (The Journal of the Quekett Microscopical Club). 35, 451-59. - - 1988. Notes on methods of staining lacquer rock peels. Microscopy Bulletin. (The Quekett Microscopical Club). 11, July 1988, 3-5. ADAMS, A. E., W. S. MACKENZIE & C. GUILFORD. 1984. Atlas of sedimentary rocks under the microscope. Longman. BIGNOT, G. 1985. Elements of micropalaeontology. Microfossils-their geological and palaeobiological applications. Graham & Trotman Ltd. BRASIER, M. D. 1980. Microfossils. Appendixreconnaissance methods. Bibliography. George Allen & Unwin. BROWN, S. 1987. Jurassic depositional systems in the North Sea basins and associated hydrocarbon plays. J. Open Univ. Geol. Soc., 8 (2), 1-5. COPE, J. C. W., A. HALLAM, H. S. TORRENS, R. G. CLEMENTS, M. R. HOUSE, C. F. PARSONS, J. SENIOR, R. T. SMITII & I. M. WEST. 1969. International Field Symposium on the British Jurassic. Guide for Dorset and South Somerset. Annotated cumulative section of the Purbeck Beds, Durlston Bay, Fig. A35b. Geology Department, Keele University. DAVIES, G. M. 1956. The Dorset Coast. A geological guide.
Adam & Charles Black. DOWNIE, C. 1957. Microplankton from the Kimmeridge Clay. Q. fl. Geol. Soc. Lond., 1U, 413-33:~ FRANCIS, J. E. 1983. The dominant conifer of the Jurassic Purbeck Formation, England. Palaeontology, 26,277-94. - - 1984. The seasonal environment of the Purbeck (Upper Jurassic) Fossil Forests. Palaeogeogr., Palaeoclimatol., Palaeoecol., 48,285-307. - - & N. J. McMILLAN. 1987. Fossil Forests in the Far North. Geos., 16(1), 6-9. HOUSE, M. R. 1969. The Dorset Coast [rom Poole to the Chesil Beach. Geologists' Association Guide, No. 22. IOANNIDES, N.S., G. N. STAVRINOS & C. DOWNIE. 1976. Kimmeridgian microplankton from C1avell's Hard, Dorset, England. Micropalaeontology, 22,443-78. MELVILLE, R. V. & E. C. FRESHNEY. 1982. The Hampshire Basin and adjoining areas. British Regional Geology, H.M.S.O. PERKINS, J. W. 1977. Geology explained in Dorset. David & Charles. WEST, I. M. 1975. Evaporites and associated sediments of the basal Purbeck Formation (Upper Jurassic) of Dorset. Proc. Geol. Ass., 86,205-25. WILLS, L. J. 1952. Palaeogeographical Atlas of the British Isles and adjacent parts of Europe. Plate XVIlA, Upper Jurassic (Kimmeridgian). Blackie & Son Ltd.
I. INTRODUCTION
Using a proprietary rapid drying cellulose lacquer, formulat ed to produce a tough smooth film with good flexibility and adhesion , a very simple technique has been developed to make microscope slides based on rock peels (Abineri , 1986). These show minute nannofossil and microfossil detail as well as giving a general picture of the fine structure of rock surfaces. The procedure involves the application of lacquer to a small prepared area of rock surface, using a self-adhe sive paper label , cut in the form of a small frame , and a clean small nylon artists' paint brush. The " flow" characteristics of the cellulose lacquer are crucial. The frame is used to remove the lacquer film after dry ing for about 1 hour at a temperature of 35-40°C. The peels are only about 1 em" in area and are easily mounted on to microscope slides under standard glass cover slips (No. 1 18 x 18 mm, BSS 3836-17). To facilitate the use of an oil-immersion objective for the examination and photography of fine detail, th e microscope slides are sealed carefully with shellac. More recently stained peels have been prepared by combining this basic method with the well-known simple staining procedure for carbonate rocks. (Adams, MacKenzie & Guilford, 1984). This method can distinguish between carbonate rocks with regard to composition and texture , and produce individual differential sta ining of microfossils and nannofossils, helping in their detection . Many Dorset coastal sedimentary rock formations have been sampled and characteristic photomicrographs have been made from the peels. Variat ions in the surface treatment of samples have been used to suit different types of rock . Sometimes problems occur with interpretation , but the investigation of these can involve quite interesting microscopy ,
including critical visual examination and the use of various modes of ilIumination (brightfield, with or without polarizing plates, darkfield or pha se contrast). Clearly the method has its limitations, especially with hard consolidated rock . However with many sedimentary rocks, above alI with those showing a finely layered structure or relatively weak cohesive properties, very detailed pictures have been obtained by means of this essentially simple technique , because the tough lacquer film removes a thin bound layer of rock material when peeled from the rock surface . The basic procedure has been applied also to a few igneous and metamorphic rock samples with some success, although here generally " prints" or " moulds" of the surface are obtained. The use of powerful etching reagents may help in some cases. Peels prepared from the Dorset Kimmeridge Clay upper stone bands present much variable material, consisting of numerous minute marine nannofossils (coccoliths and coccolithophores), a variety of microfossils , plant microspores, microscopic grains of pyrites and organic residues with plant fragments including fossil wood fragments (fusain). The detection of these microscopic features is of interest because it tends to confirm the variable influx of land swamp debris to the sea at the time of deposition of the Kimmeridgian marine microplankton (Ioannides, Stavrinos & Downie, 1976). Furthermore close examination of some microscopic fusain wood fragments on peels from many horizons in the Dorset Kimmeridge Clay show "bordered pit" tracheid structures very similar to those known from later times in the Lower Purbeck Dirt Beds and which have been related to conifer trees (Francis, 1983). In a similar manner to the above , other exploratory investigations, especialIy by amateurs or students, might well make use of this simple rock peel technique.
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2.PHOTONDCROGRAPHY In view of the amount of detail recorded on some of the prepared microscope slides, the photomicrography completed so far has had to be very selective. For example a photograph taken with the oil-immersion objective covers a field of only about 135 11m x 90 usn, In order to record the whole 1 em' area of the peel mounted on the microscope slide, using the same objective, over 8000 similar photographs would be required! Therefore in practice visual examination is completed using the mechanical stage and an intermediate power objective, before selective high power pictures are taken. In spite of adopting this procedure, much material inevitably remains unexplored on the present collection of microscope slides (c. 3(0). The following equipment has been used for visual and photographic work on the peels: i) Nikon "Labophot" microscope fitted with Trinocular eyepiece tube type F. This allows 100% of the light to be diverted from the binocular eyepiece to the camera. ii) Nikon FE camera body with connecting tube and mounting, fitted with a projection lens. iii) Phase contrast turret condenser with additional positions for brightfield and darkfield microscopy. Facilities for the use of an analyzer and a polarizer plate. iv) Illumination brightness control, field diaphragm control, condenser aperture diaphragm control and a mechanical stage. v) A range of filters for visual and photographic observations. Objectives N.A. 0.1, 0.25, 0.65 and 1.25 (oil-immersion) giving visual magnifications of x60, X150, x600 and x1500 respectively with the binocular eyepiece. The main film used so far has been Fujichrome DX ASA 100, to produce 35 mm colour slides. The approximate fields covered by these slides with the various objectives are as follows: N.A.0.1 3370 p.m x 2250 lim N.A. 0.25 1350 11m x 900 lim N.A. 0.65 337 11m x 225 11m N.A. 1.25 135 11m x 90 ~m (oil-immersion). A correcting filter is used for the light with the illumination brightness control at maximum. The Nikon camera employs automatic exposure. Methods of illumination have been varied to improve contrast or to emphasize certain features and are determined by visual inspection. The following methods have been used with some success: i) Brightfield with an extra blue filter or with one polarizing plate above the objective; alternatively with analyzer and polarizer plates parallel or crossed. ii) Darkfield with, or without crossed polarizing
plates. Foraminifera sections in the Upper Chalk on unstained peels have given interesting pictures using dark field illumination with crossed polarizing plates. iii) Phase Contrast. This tends to be effective when the peels are mainly "prints" of hard consolidated rock surafaces. With those peels which have removed a definite layer of rock material, objects which are slightly "out of focus", due to the finite thickness of the layer, tend to form conspicuous "haloes" which may interfere with the foreground objects especially in a crowded field. It is intended to experiment in the future with alternative films and filters to improve the photomicrography of the stained peels. From personal experience, a relatively simple, good-quality, students' microscope used with these peels will give visual images comparable to the following selected photomicrographs. It is therefore strongly suggested that students or amateurs who wish to extend their interest in sedimentary rocks to include some micropalaeontology or related topics, will find cellulose lacquer peels of some value. Again it should be emphasized that the use of an intermediate power objective, giving a combined magnification of about x600, is satisfactory for the close visual inspection of the slides. Of course there are many well-established methods for isolating and studying microfossils apart from the use of peels or thin sections. These involve separation techniques which include pulverization of rock samples, the use of various chemicals, washing, sieving or decanting (Brasier, 1980). For the complete morphological examination of individual microfossils these separation procedures may be essential. However the peel technique discussed here can produce overall pictures of the rock in terms of its microscopic contents. As these features are often shown in considerable detail using a basically simple, quick and cheap method, this approach is recommended. Furthermore very little damage need occur to hand samples collected by the student for more general use and, if sufficiently interesting, one small rock sample can produce many microscope slides. 3. SELECTED PHOTOMICROGRAPHS FROM DORSET COASTAL FORMATIONS These include pictures from both unstained and stained lacquer peels. Before etching or staining, a small area of each rock surface was finally polished or flatted with 1200 grade "wet or dry" abrasive paper to give a light sheen. Any earlier grinding with coarser abrasive paper was reduced to a minimum. For the preparation of unstained peels, etching with dilute acid or dilute alkali was used depending on the type of rock. With all the stained peels the following solution
PHOTOMICROGRAPHS OF C E L L U LO SE PEELS
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was used:
b) OsmiDg1on Oolite, Corallian, Oxfordian (SY742814)
10crrr' 0.5 molar hydrochloric acid Solution (A) 20 ern" distilled water { 3.6 x 10- 2 grams alizarin red S
This Upper Jurassic oolite is well exposed at Bran Point on the Dorset coast east of Osmington Mills. Fig. 2 was prepared from a stained peel off a sample containing numerous ooliths . The low power photomicrograph was made with brightfield illumination and one polarizing plate above the objective. It shows the finely layered structure of the oolith sections. The staining is interesting and indicates the presence of calcite, ferro an calcite, grains of silica but perhaps also some dolomite. The microscope slide shows considerable detail under high power, including foraminifera sections and other microfossils. The blue ferroan calcite background exhibits a finely structured surface and much unidentified material. Also the use of crossed polarizing plates gives complex birefringence patterns. Further peels will be made from this rock sample .
Just before stauung 4.0 x 10- 2 g of potassium ferricyanide (potassium hexacyanoferrateflflj) were dissolved in 5 ern' of solution (A) with two drops of methylated spirit or ethanol. This mixture stained many samples but was used as soon as possible. Each sample required only a few drops on the surface for a period of up to 2 minutes (depending on the rock type). The staining stage was completed by a thorough rinse with distilled water and then acetone (propanone) to dry the surface before the application of the cellulose lacquer in the usual manner. In the absence of an accurate chemical balance the quantities of alizarin red S and potassium ferricyanide were carefully estimated using a small spatula only and the following approximate pack densities : alizarin red S 0.5 grams cm" potassium ferricyanide 1.5 grams cm" Although very small quantities of the above chemicals are needed with this simple staining procedure great care must be taken to avoid contact with skin or eyes. This applies equally to the cellulose lacquer, solvents and all other etching reagents. Furthermore the cel1ulose lacquer, cel1ulose solvent and acetone are all very flammable. They should be stored and handled with due care. a) Belemnite Marls, Channouthian, Lower Lias (SY 380927) This Lower Jurassic grey marl is well exposed at lower cliff level on the shore east of Charmouth. It is well known for small pyritised ammonites . Fig. 1 was prepared from a stained peel derived from a rock sample containing numerous minute crinoid stems. This low power photomicrograph was made with darkfield illumination and shows the complex structure of the crinoid stem transverse section which contains an infilling of deep blue stained ferroan calcite, whereas the main pale pink structure is probably pure calcite. The deep blue general background on this peel is fine ferroan calcite. The brown mottled area to the left of the picture and elsewhere is microcrystalline pyrites . The co-existence of large amounts of ferroan calcite and pyrites in this rock are indicative of strongly anaerobic conditions. The whole microscope slide is filled with fine detail which is an incentive for much further work on the Lower Lias.
c) Kimmeridge Clay, Kimmeridgian, from Washing Ledge Stone Band (SY 906791) to Fresbwater Steps Stone Band (SY 943772) A number of bands and zones in this complex section of the Upper Jurassic have been sampled and peels have been prepared to a varying extent. A total of almost 100 microscope slides have been made from the section , including both stained and unstained types. The complexity of Kimmeridge Clay sediments appears very great indeed, perhaps in part due to their biogenic nature. Here only two aspects will be shown , firstly the occurrence of minute fossil wood fragments in the marine sediments and secondly the results of staining microfossils and nannofossils in the Freshwater Steps Stone Band . (i) Fossil wood fragments These are shown on Figs. 3 & 4. Microscopic fossil wood fusain has been found so far on lacquer peels from the following horizons in the Kimmeridge Clay: Washing Ledge S.B. Aulacostephanus autissiodorensis zone. Maple Ledge S.B . (uppermost level). Blakes Bed 42. Pectinatites elegans zone . Pectinatites scitulus zone . Pectinatites wheatleyensis zone . Rope Lake Head S.B . White S.B. (especially in a dark centre layer) . Middle White S.B. Freshwater Steps S.B. The amount found at different horizons appears to vary considerably. For example in the dark shale at
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Fig. 1. Crinoid stem transverse section showing calcite, ferroan calcite and microcrystals of pyrites. Belemnite Marls, Lower Lias, Jurassic. (SY 380927). Field: 1350 I'm x 900 I'm. Visual magnification x 150. Darkfield illumination. Objective N.A. 0.25. Stained lacquer peel.
Fig. 2. Oolith Sections showing calcite, ferroan calcite, silica grains and suspected dolomite. Osmmgton Oolite, Corallian, Jurassic. (SY 742814). Field: 3370 I'm x 2250 pm. Visual magnification x60. Brigbtfield illumination with one polarizing plate above objective N.A. 0.1. Stained lacquer peel.
PHOTOMICROGRAPHS OF CELLULOSE PEELS
the uppermost level of the Maple Ledge S.B. some peels have shown 50-100 fragments on 1 em" area, whereas for most of the White S.B. very few are found, with the exception of the 1 em thick dark centre layer. The Middle White S.B. contains many wood fragments but the finely layered Freshwater Steps S.B. shows very variable numbers. Earlier studies have reported the presence of wood fragments in the Kimmeridge Clay (Downie , 1957). Close inspection of fusain fossil wood fragments on the above Kimmeridge Clay peels has shown the presence of bordered pit tracheid structures from conifer trees similar to Protocupressinoxylon purbeckensis found in the Lower Purbeck (Francis , 1983). Many of these objects have been identified. Bordered pits are shown on Fig. 3 from the upper Maple Ledge S.B. (SY 908790). This picture was taken at high magnification but the tracheid structure can be seen easily with an intermediate power objective. Examples have been recorded at all the above horizons. .Dr J. E . Francis has examined some of the pictures of these objects from the lacquer peels and confirms the close similarity to material from the Lower Purbeck studied by her . The salient features appear on Fig. 3 and are concerned with a single line of contiguous bordered pits, each with an oblique aperture and a thickened rim. The outer diameters average about 15 J1.m and agree reasonably well with the figure of 14.3lJm from the Lower Purbeck data (Francis, 1983). Some pits from the upper Maple Ledge S.B. are smaller, as is shown on Fig. 3. The upper Maple Ledge site is easily located and very accessible at the base of the cliff in the centre of Kimmeridge Bay, just above the hard stone band which is directed into the bay south-east of Gaulter Gap. The dark shale splits easily and cleanly, parallel to the bedding , giving flat smooth surfaces ideal for lacquer peels. If a drop of water is placed on the exposed surface numerous minute black specks can be seen with a hand lens. Many of these are fossil wood fragments. The peels exhibit also many fine grains of pyrites, yellow to brown transparent organic material, numerous coccoliths, some coccolithophores and microfossils which stain blue (ferroan calcite) and other microfossils which remain unstained (silica). Numbers of bordered pits have been identified, including some completely isolated pits i.e, individual fusain rings. More recently similar damaged fossil wood fusain has been identified on peels from some of the Middle Purbeck beds in Durlston Bay, including numbers of isolated pits. (see (d) below). Fig. 4 is a highly magnified picture of a fossil wood fragment embedded in a relatively pure coccolith layer. This and several other similar objects were detected on an unstained peel from the Freshwater Steps S.B. (SY 943772). Part of this fragment is probably a print or mould. Peels from all the above mentioned Kimmeridge
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Clay horizons contain numerous coccoliths and the upper stone bands exhibit also many coccolithophores (coccospheres) . The existence of conifer wood fusain in association with marine microplankton gives rise to a number of interesting aspects. Firstly it must reinforce the assumption of the variable input of terrigenous swamp generated material to the sea in Kimmeridgian times. (Ioannides et al., 1976.) Furthermore the shedding of gymnosperm wood fragments into the Kimmeridgian sea, and perhaps much later into Middle Purbeck lakes or pools (see (d) below), seems to reflect the dominant position of the Jurassic conifer forests, before the rise of the angiosperms in the early Cretaceous. It is also interesting to note that studies of the climatic environment of Protocupressinoxylon purbeckensis in the Lower Purbeck indicate very dry seasons but also periods of higher rainfall (Francis, 1984). This agrees with the presence of evaporites and other related phenomena in the Basal Purbeck areas (West , 1975). Did these trees evolve under similar climatic conditions in the earlier Kimmeridgian times? This might explain the variable movement of organic debris into the sea from the periodic flooding of low lying forest land. How does this agree with more modem concepts of Upper Jurassic palaeogeography (Wills, 1952)? Another point of interest which arises from the occurrence of conifer wood fusain in the Kimmeridge Clay relates to off-shore petroleum. These late Jurassic shales, matured in the Viking Graben in the North Sea, are believed to be the source of the Brae and Brent oil (Brown, 1987). In recent years some geologists have linked prospective petroleum and natural gas sources to fossil amber resin from conifer forests. For example this applies to Tertiary fossil forests in the Canadian Arctic (Francis & McMillan, 1987). Where is the fossil amber from the dominant Mesozoic conifer forests? With a density of only 1.08 g em - 3 , is some of this resin an ingredient of the allochthonous organic material in the Kimmeridge Clay? Input of large amounts of decaying organic matter to the sea would promote anaerobic conditions and the activity of anaerobic bacteria, giving rise to grains of pyrites and calcareous microfossils showing ferroan calcite composition. These objects occur on the stained cellulose lacquer peels, often associated with fossil wood fusain and yellow-brown transparent organic residues. Is this latter material derived from fossil amber? It has been found on all peels prepared from all the above mentioned Kimmeridge Clay bands and zones. Clearly much further work is needed on the detection, distribution and examination of these conifer fossil wood tracheids and the related quantity and distribution of the transparent organic material , in a determined search for the missing amber.
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Fig. 3. Bordered pit tracheid structure from Mesozoic conifer wood on a background of organic material containing coccoliths, grains of pyrites and fusain. The embedded coccoliths are unstained . Dark shale at upper-most level of the Maple Ledge S.B., Kimmeridge Bay, Kimmeridge Clay, Upper Jurassic . (SY 908790). Field : 135 J.lm x 90 um. Visual magnification x 1500. Brightfield illumination . Objective N.A . 1.25 oil-immersion . Stained lacquer peel.
Fig. 4. Microscopic fossil wood fragment embedded in a coccolith layer. Part of this fragment is probably an external mould. Freshwater Steps S.B. , Kimmeridge Clay, Upper Jurassic . (SY 943772) . Field: 135 J.lm x 9OJ.lm. Visual magnification x 1500. Brighttield illumination with orie polarizing plate above objective N.A . 1.25 oil-immersion . Unstained lacquer peel.
PHOTOMICROGRAPHS OF CELLULOSE PEELS
(ii) Freshwater Steps Stone Band (SY 943772) The three upper conspicuous stone bands in the Kimmeridge Clay (Pectinatites pectinatus zone) each have their special features. The lowest, the White S.B., shows the purest white coccolithic limestone generally with the least organic residues, but there is nevertheless a dark centre layer of about 1 em thickness as mentioned above . The Middle White S.B. is more complex and contains much organic material with fine grains of pyrites and fossil wood fusain, as well as numerous coccoliths and larger microfossils. It contains also microcrystals of ferroan calcite , which have not been detected in the other two stone bands . Few blue stained coccolithophores are found . The most complex however is the uppermost, the Freshwater Steps S.B. This has been sampled close to Freshwater Steps at the base of the cliff. The rock shows a very finely layered structure which includes white and grey components well seen with a hand lens. Some of these very thin layers are quite dark but others are almost pure white. Coccoliths and coccolithophores occur in vast numbers, but the greyer layers contain also yellow-brown organic material, pyrites, calcispheres, various plant microspores and microfossils of diameters 15-50 jlm , and varying amounts of wood fragments. The coccoliths are generally from 3 to 6 jlm in diameter and appear much more uniform and well preserved than those in the Dorset Upper Chalk. Although not classified so far they show agreement with descriptions given in previous studies . (Downie, 1957). The coccoliths can be examined alone very easily by applying a nylon brush, dampened with distilled water, to the clean rock surface and making a "smear" on a microscope slide. If a standard glass cover slip is placed over the smear, good high power images will be obtained; alternatively by using crossed polarizing plates the characteristic optical figures are seen. The rock is ideal for the preparation of cellulose lacquer peels due to its layered structure. When polished or lightly flatted with 1200 grade abrasive paper, inevitably a smooth surface is formed which includes white and grey patches. The resulting peels present the white areas as showing mainly coccoliths and coccolithophores, whereas the grey areas include layers of organic material lying over, or embedding, these minute nannofossils . The organic layers are often transparent with a fairly pale yellow-brown colour, but sometimes they are much darker due to embedded fine black particles, which include grains of pyrites and some fusain. When the layer is transparent, coccoliths can be seen clearly below it, or sometines embedded in it. Careful visual work with the microscope helps here, especially with practiced use of the fine focus control. No distortion of the images appears to occur. These covered coccoliths are usually well preserved and unaffected
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by the etching or staining reagents. The underlying coccoliths appear golden coloured, but those embedded often have a grey appearance. When crossed polarized plates are used many of these coccoliths produce the characteristic optical figures, proving that they are not moulds or prints, but the real nannofossils peeled from the rock surface. There are other brown and orange particles in these organic layers which may be partially oxidized grains of pyrites or unidentified nannofossils . Using the simple staining procedure with dilute hydrochloric acid, alizarin red S and potassium ferricyanide, quite surprising results are obtained, showing individual differential staining of microfossils and nannofossils, whilst leaving the covered coccoliths golden coloured. The occurrence of deep blue staining, indicating ferro an calcite, with some coccolithophores, microfossils or parts of microfossils, seems very interesting when similar neighbouring objects are stained pink, indicating pure calcite. If this truly represents difference in composition on such a microscopic scale, then it seems to the writer that microbiological processes might explain its cause. Recently small areas of unstained microcrystals of dolomite have been detected on some peels. Where external moulds of coccoliths and coccolithophores exist on the peel due to the removal of these nannofossils by the polishing, etching or staining procedures, or where moulds occur on the lower side of the lacquer film, the resulting images show no optical figures with crossed polarizing plates. Comparisons between stained and unstained peels from the same rock surfaces using crossed polarizing plates , indicate fewer external moulds on the unstained peels; also these peels seem to show better detailed images, due to far less drastic etching conditions, i.e. 12 to 15 seconds with 2% dilute acid instead of the period up to 2 minutes used with staining . This would not apply generally to those nannofossils covered by transparent organic material. Some results with the staining of Freshwater Steps S.B. material are shown on Figs. 5,6 & 7. Fig. 5 is an intermediate power picture from the Freshwater Steps S.B., with a field area of about 337 jlm x 225 utt», using brightfield illumination with one polarizing plate above the objective. It illustrates complex individual differential staining of nannofossils. The visual appearance through the microscope shows greater brightness and contrast than is shown on this photomicrograph. The deep blue coccolithosphores are richer in colour and readily distinguished from black grains of pyrites and fusain . The organic layer in the top left corner region covers unstained coccoliths with the consequent golden colour . There are pink coccoliths and coccolithophores, which are assumed to be of pure calcite composition, in close association with the deep blue coccolithophores, believed to be made of ferroan calcite. Unstained minute areas or
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Fig. 5. Complex individual staining of nannofossils. The top left field shows a yellow-brown organic layer with unstained covered coccoliths, grains of pyrites and fusain. Freshwater Steps S.B., Kimmeridge Clay, Upper Jurassic. (SY 943772). Field: 337/-1m x 225/-1m. Visual magnification x 600. Brightfield illumination with one polarizing plate above objective N.A. 0.65. Stained lacquer peel.
Fig. 6. Differential staining of coccoliths and coccolithophores with unstained covered "golden" coccoliths. Freshwater Steps S.B., Kimmeridge Clay, Upper Jurassic. (SY 943772). Field: 135 /-1m X 90/-lm. Visual magnification x 1500. Brightfield illumination. Objective N.A. 1.25 oil-immersion. Stained lacquer peel.
PHOTOMI CROGRAPHS OF C ELLULOSE PEELS
objects may be external moulds, siliceous nannofossils or small patches of dolomite . Fig. 6 is a high power picture from the same stained peel covering an area of about 135 Jlm x 90 Jlm. This was prepared with the oil-immersion objective using brightfield illumination and shows aspects discussed above in greater detail. Since we are examining a layer of finite thickness, not all objects are accurately in focus, especially with high power. Careful visual observations have an advantage here by employing the fine focus control. Some photomicrographs made from the Freshwater Steps S.B. stained peels show clusters of deep blue coccolithophores, which cover relatively large areas. Better individual images of coccolithophores tend to occur on the unstained peels from the upper stone bands. These nannofossils average from 9 to 12 Jlm in diameter and many exhibit coccoliths on their surfaces. It is difficult to estimate the number of coccoliths on each of the coccolithophores but a figure of 10 to 12 seems likely. Fig. 7 shows unicellular plant microfossils partly embedded in an organic layer, photographed under high magnification. Many covered coccoliths are also shown. A large variety of plant microfossils occur in the Freshwater Steps S.B., usually in association with organic material. They exhibit differing size, structure and staining patterns; some showing wall staining different from interior staining. There is a tendency for similar types to cluster. The object at the top of the picture , right of centre, is covered with coccoliths and some exterior moulds of coccoliths . This effect and the microfossil feature in the lower right corner of the picture occur frequently in the Freshwater Steps S.B. They have been described in earlier studies of the Kimmeridge Clay. (Down ie, 1957). Detailed classification of related microfossils and many others from lower Kimmeridge Clay horizons have been published in past papers (Ioannides et al.• 1976). With these microfossils close visual inspection will identify external moulds on the peels. The Dorset Kimmeridge Clay formation has in some ways been a challenge on the use of optical microscopy. However the lower sides of these cellulose lacquer peels can be spattered with metal and examined in far greater detail with the scanning electron microscope . SEM photographs were very kindly prepared for the writer by staff in the Laser Division, Rutherford Laboratory, SERC, from the lower side of a very detailed peel derived from the Rope Lake Head S.B . These pictures, with their great depth of field, show " solid" coccoliths at magnifications up to c. x 5000. However there are equally clear coccolith external moulds, where the corresponding coccolith was left on the rock sample surface , when the thin layer was removed (Abineri, 1986). These interesting pictures have given some insight into the
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effects of polishing, etching and staining discussed above. Clearly there are still very considerable opportunities for further exploratory work on the Kimmeridgian shales, clays and carbonate stone bands, using the optical microscope. Furthermore the rock materials seem ideal for the use of cellulose lacquer peels. Any problem which may arise with interpretation can present the observer with an additional interesting challenge .
d) Middle Purbeck, Lulworth Beds, Durlston Bay (SZ 036784) A number of these beds just below the Cinder Beds have been sampled recently. This location is south west of Peveril Point in Durlston Bay, close to the place where the Cinder Beds are exposed at shore level. Fig. 8 is from Bed 102, designated "Shales with thin sandy biosparites at base" (Cope et al., 1969). It is a low power picture of a stained Cypridea ostracod carapace section . The approximate field is 1350 Jlm x 900 Jlm with brightfield illumination, using one polarizing plate above objective N.A. 0.25. The whole microscope slide shows other detail of interest, including more ostracod sections and fragments , very damaged fusain fossil wood fragments , brown organic residues and minute unidentified nannofossils which are embedded in this organic material. A number of other peels have been prepared from Bed 102, which show damaged fusain bordered pit tracheids and some isolated fusain rings, indicating Mesozoic conifer wood. Ostracods and conifer wood fragments have been found in most of the Middle Purbeck beds examined so far. These sediments are believed to have formed in partly saline lakes or pools. More peels will be prepared from the Durlston Bay location, but it is hoped to compare these with corresponding beds at Worbarrow Tout and Bacon Hole. e) Lower Cretaceous, Wealden Lignite, Worbarrow Bay (SY 868801) Fig. 9 is an intermediate power photomicrograph, with a field area of about 337 Jlm x 225 um. It was prepared from a preliminary unstained peel derived from lignite, which was flatted with fine abrasive paper and then treated with a fairly concentrated solution of sodium silicate (water-glass), which reacts as an alkali. A brown solution was produced on the surface , assumed to be partly lignin, and then after rinsing with distilled water and drying, the cellulose lacquer peel was prepared in the usual manner. It is fairly certa in that the cellulose cell walls were exposed
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Fig. 7. UniceUular plant microfossils and coccoliths embedded in organic material. Freshwater Steps S.B., Kimmeridge Clay, Upper Jurassic. (SY 943772). Field: 135 /-lm X 90 11m. Visual magnification x 1500. Brightfield illumination. Objective N.A. 1.25 oil-immersion. Stained lacquer peel.
Fig. 8. Stained Cypridea ostracod section. Bed 102, Lulworth Beds, Durlston Bay, Middle Purbeck, Upper Jurassic. (SZ 036784). Field: 1350 um x 900 11m. Visual magnification x 150. Brightfield illumination with one polarizing plate above objective N.A. 0.25. Stained lacquer peel.
PHOTOMICROGRAPHS OF CELLULOSE PEELS
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Fig. 9. Cellulose plant cell walls in lignite. Wealden lignite, Worbarrow Bay, Lower Cretaceous. (SY 868801). Field: x 2251lffi. Visual magnification x 600. Brightfield illumination with one polarizing plate above objective N.A. 0.65. Unstained lacquer peel.
3371lm
Fig. 10. Axial section of Heterohelix, a biserial foraminifera. Actinocamax quadratus zone, Upper Chalk, Upper Cretaceous, Cliff west of Arish Mell. (SY 851802). Field: 135 /-1m x 90 Jlm. Visual magnification x 1500. Brightfield illumination with parallel polarizing plates (PPL). Objective N.A. 1.25 oil-immersion. Unstained lacquer peel.
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Fig. 11. Complex staining of Chalk nannofossils and microfossils. A section of a Globigerinid foraminfera is in the left of the field. Actinocamax quadratus zone, Upper Chalk, Upper Cretaceous, Cliff west of Arish Mel!. (SY 851802). Field: 337 Jlm x 225 Jlm. Visual magnification x 600. Brightfield illumination with parallel polarizing plates (PPL). Objective N.A. 0.65. Stained lacquer pee!.
Fig. 12. A typical Upper Chalk Calcisphere on a background of stained coccoliths and other calcareous nannofossils. Actinocamax quadratus zone, Upper Chalk, Upper Cretaceous, Cliff west of Arish Mell. (SY 851802). Field: 135 um x 90 Jlm. Visual magnification )(1500. Brightfield illumination. Objective N.A. 1.25. oil-immersion. Stained lacquer peel.
PHOTOMICROGRAPHS OF CELLULOSE PEELS
and removed from the surface. Examination of the peel shows a complex microscopic network with other details which have yet to be explored. These might include plant microspores or pollens. Alternative reagents, such as stronger alkalis, may be tried. f) Upper Cretaceous, Upper Chalk, Actinocamax quadratus zone, Cliff west of Arish MeU (SY 851802)
Small samples of chalk, collected from a shallow fault close to the coastal path at the above location, were the first rocks to be examined using unstained lacquer peels. Numbers of microscope slides were prepared which were crowded with detail, including numerous foraminifera sections, macrofossil fragments, calcispheres and coccoliths. More recently the samples have been re-examined with stained peels. As with the Kimmeridge Clay, etching was less drastic with the unstained chalk than with the stained chalk and this may have shown some advantages. Fig. 10 is a high power photomicrograph taken from an unstained chalk peel. It was prepared with the oil-immersion objective using parallel polarizing plates to give a field area of about 1351lm x 90 urn, The picture shows an axial section of Heterohelix, a biserial foraminifera. The focus was adjusted to give clear images of the chambers at the right apex of the test, which show complex surface structure. The use of plane polarized light with brightfield illumination increases contrast. Heterohelix has been found also in the Actinocamax quadratus zone of the Upper Chalk on the cliffs west of Bats Head (SY 792805). Since the sections of foraminifera in the peels can vary greatly with identical microfossils, depending on their orientation, problems can occur with identification. In view of the numbers of these objects in an average chalk peel and their variations in structure and size, there is ample scope for the enthusiast, especially with very small species which would be difficult to isolate by other methods. By using darkfield illumination with crossed polarizing plates interesting pictures can be obtained of foraminifera from unstained chalk peels. These show the delicate structure of the chamber walls. Photographs with 100ASA film require from 6 to 7 seconds exposure. The visual image is very effective when the eye is completely dark-adapted after some time. Figs. 11 & 12 were prepared from the same stained chalk peel derived from the Actinocamax quadratus zone at SY 851802. The 1 em" area peel on the microscope slide is crowded with differentially stained microfossils, nannofossils and macrofossil fragments. Although the usual staining reagents were used there is no apparent indication of blue objects or areas, i.e. no ferroan calcite. This may seem obvious in the case
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of the Upper Chalk, but it does tend to confirm the reliability of the staining procedure. Fig. 11 is a picture with intermediate magnification showing a field of area about 337 /lm x 225 /lm. It gives a general impression of the fine structure of the stained chalk surface. Brightfield illumination was used with parallel polarizing plates. The differential staining of the nannofossils, due to the alizarin red S dye only, is interesting and seems to confirm how the intensity of staining may depend on the fineness of the physical grain boundaries as well as on composition (Adams et al., 1984). Close inspection suggests that dye is concentrated on edges in the nannofossils, probably by adsorption, thus enhancing visibility and contrast. The prominent object on the left of the field is a partial section of. a globigerinid foraminifera. Similar damaged strucures appear elsewhere. High magnification pictures of this peel with the oil-immersion objective confirm the staining effects mentioned above. Coccoliths show a greater variety in structure and size than those in the Freshwater Steps S.B. The coccoliths have diameters from 1 /lm to lO/lm approximately. Many are partly buried in the surface or damaged. Fig. 12 is a high power view of a typical chalk calcisphere from a stained peel. Very large numbers of these microfossils are found in the Upper Chalk and by far the majority show a circular wall, which tends to confirm that the objects must be spherical. However, since every section must be circular, the actual diameter of an individual calcisphere cannot be estimated unless it is a small embedded object; nevertheless a range of values from 15 Ilm to over 100 /lm seems reasonable. Oval sections have been found though these seem more common in the Middle and Lower Chalk. As with many other microfossils, the systematic classification of these widely distributed objects remains very uncertain and could be a subject for detailed research. Some pyriform sections, similar in other respects to calcispheres, have been found on chalk peels. Visual inspection of calcispheres on lacquer peels indicate that most are external moulds.
4. CONCLUSION The preparation of cellulose lacquer peels and photomicrographs is continuing on samples from selected Dorset coastal formations and from other geological sites. The programme includes experiments with alternative etching and staining procedures as well as attempts to improve the colour photography of the stained peels. A low power stereomicroscope is now being used for the initial examination of rock samples, to select areas on the rock surfaces of special interest for peels and for general use during the preparation of the microscope slides.
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ACKNOWLEDGEMENTS Very special thanks are due to Dr. Ian West, Department of Geology, University of Southampton for his kind advice and encouragement on possible projects where lacquer peels might be used for exploratory purposes. The information from Dr. Jane E. Francis, Department of Geology and Geophysics, University of Adelaide, on Mesozoic conifers and her confirmation of the nature of the fossil wood fragments from the Kimmeridge Clay was of very special interest to me. I wish to express my appreciation for this generous help. My thanks are
due also to Paul Ensorn, Dorset County Museum, Dorchester, for his general encouragement and the time spent examining and discussing 35 mm slides from various Dorset sites. I wish to acknowledge also the very helpful co-operation and encouragement received from the Quekett Microscopical Club. Finally I wish to express my appreciation to Lieutenant Colonel C. P. G. Turner, Gunnery School, RAC centre, Lulworth Camp, for permission to publish pictures from samples collected in the Army Range area, and for his co-operation on the future sampling of Purbeck sites at Worbarrow Tout and Bacon Hole.
References ABINERI, K. W. 1986. The preparation of cellulose lacquer rock peels. Microscopy. (The Journal of the Quekett Microscopical Club). 35, 451-59. - - 1988. Notes on methods of staining lacquer rock peels. Microscopy Bulletin. (The Quekett Microscopical Club). 11, July 1988, 3-5. ADAMS, A. E., W. S. MACKENZIE & C. GUILFORD. 1984. Atlas of sedimentary rocks under the microscope. Longman. BIGNOT, G. 1985. Elements of micropalaeontology. Microfossils-their geological and palaeobiological applications. Graham & Trotman Ltd. BRASIER, M. D. 1980. Microfossils. Appendixreconnaissance methods. Bibliography. George Allen & Unwin. BROWN, S. 1987. Jurassic depositional systems in the North Sea basins and associated hydrocarbon plays. J. Open Univ. Geol. Soc., 8 (2), 1-5. COPE, J. C. W., A. HALLAM, H. S. TORRENS, R. G. CLEMENTS, M. R. HOUSE, C. F. PARSONS, J. SENIOR, R. T. SMITII & I. M. WEST. 1969. International Field Symposium on the British Jurassic. Guide for Dorset and South Somerset. Annotated cumulative section of the Purbeck Beds, Durlston Bay, Fig. A35b. Geology Department, Keele University. DAVIES, G. M. 1956. The Dorset Coast. A geological guide.
Adam & Charles Black. DOWNIE, C. 1957. Microplankton from the Kimmeridge Clay. Q. fl. Geol. Soc. Lond., 1U, 413-33:~ FRANCIS, J. E. 1983. The dominant conifer of the Jurassic Purbeck Formation, England. Palaeontology, 26,277-94. - - 1984. The seasonal environment of the Purbeck (Upper Jurassic) Fossil Forests. Palaeogeogr., Palaeoclimatol., Palaeoecol., 48,285-307. - - & N. J. McMILLAN. 1987. Fossil Forests in the Far North. Geos., 16(1), 6-9. HOUSE, M. R. 1969. The Dorset Coast [rom Poole to the Chesil Beach. Geologists' Association Guide, No. 22. IOANNIDES, N.S., G. N. STAVRINOS & C. DOWNIE. 1976. Kimmeridgian microplankton from C1avell's Hard, Dorset, England. Micropalaeontology, 22,443-78. MELVILLE, R. V. & E. C. FRESHNEY. 1982. The Hampshire Basin and adjoining areas. British Regional Geology, H.M.S.O. PERKINS, J. W. 1977. Geology explained in Dorset. David & Charles. WEST, I. M. 1975. Evaporites and associated sediments of the basal Purbeck Formation (Upper Jurassic) of Dorset. Proc. Geol. Ass., 86,205-25. WILLS, L. J. 1952. Palaeogeographical Atlas of the British Isles and adjacent parts of Europe. Plate XVIlA, Upper Jurassic (Kimmeridgian). Blackie & Son Ltd.