Revision of the Gault foraminifera from the Hollis and Neaverson Collection (1921)

In 1921, Hollis and Neaverson listed 135 species and varieties of foraminifera from the Gault Phosphatic Nodule Bed at Ford, Buckinghamshire, England. The material has been re-examined, the list is brought up to date and the species are figured. The Collection has yielded a diverse and well preserved foraminiferal fauna of 90 species. Nodosariacea are the dominant group, though Ataxophragmiacea, Hedbergellacea and Miliolacea are abundant. The recorded assemblages allow us to date the Phosphatic Nodule Bed at Ford as belonging to the uppermost Euhoplites lautus Zone to lower part of Mortoniceras inflatum Zone within the Albian standard ammonite zonation.


INTRODUCTION
published a short paper on the Gault foraminifera from the workings for phosphatic nodules at Ford, four miles southwest of Aylesbury, Buckinghamshire (England). They listed 135 species and varieties of foraminifera but neither descriptions nor illustrations were given by the authors. After their paper no other workers have given additional infomiation about the foraminifera of the Gault at Ford. In fact, no references to the paper of Hollis and Neaverson (1921) have been found in the Early Cretaceous literature of Great Britain except for one by Crittenden (1988: p. 19, Unpublished Ph.D. Thesis, Plymouth Polytechnic).
The location of the site in which the Gault was worked at Ford for phosphatic nodules is not known exactly. In their paper, Hollis and Neaverson (1921) commented that the workings from which Hollis had collected his material in 1919 were abandoned and nothing remained but the spoil-heap which was by then (1921) completely grassed over. The available information, about the fields where the workings are said to have been (Fig. 1), was provided by the locals or elderly relatives of the locals to the Buckinghamshire County Museum (pers. comm. Ms K. M. Hawkins, Keeper of Biology and Geology of that Museum). The only description of the nodules beds is that of Keeping, who saw earlier workings near Ford in 1876. According to Jukes-Brown, who incorporated his observations into his memoir (1900), the nodules were worked on this occasion between the years 1875 and 1884. Keeping's remarks include the following: The coprolite seam is 3 to 4 inches thick and is constant throughout the pit, though the bed is irregular in position. The irregularity is of two kinds, the commonest being slips of a few inches (4 to lo), cutting off the seam with a clear face marked by slickensides; in other cases the bed is bent downwards to a similar extent, and this bending is due, I am inclined to think, to subsequent folding and not to irregularity of deposition.
The matrix of the seam is a stiff calcareous clay crowded with phosphatised shells and lumps of 'coprolite' which in my cursory search, I could not prove to have suffered from erosion previous to being embedded in the Gault, while some of them, such as Hamites were in such a condition that they could not have sustained much knocking about on a shore.
Above the [nodule] bed comes a hard clay with iron-stained joint planes, which is covered by a true clay, somewhat lighter in colour than ordinary Gault, and containing a second irregular coprolite zone in a series of lenticular patches. Its nodules are smaller than in the regular seam below.
It should be noted that the emphasis on structural relationships in this account may be explained by the fact that Keeping was teaching geology at Aberystwyth at this time and attempting to work out the structure of Plynlimmon! Jukes-Brown visited the workings in 1885 after they had been abandoned but was able to collect fossils. Collections were also made by a local schoolmaster (Mr Hayter of Monks Risborough) which put together with those of Keeping presented a 'curious assemblage for the Lower Gault', including 'Ammonites' auritus, cristatus and lautus.
Hollis and Neaverson in their remarks on the ammonites said, Judging by specimens of ammonites in the Bucks. County Museum, Aylesbury, the deposit worked belonged to the zones of Hoplites auritus and H . luutus. At the typical locality of Folkestone, these zones occupy 17 feet out of a total of 99 feet for the whole of the Gault; but at Ford only three or four feet seem to have been worked. Critical zonal study is, of course, impossible; . . .
We were pleasantly surprised to discover that there were three different sets of slides of the Hollis and Neaverson Collection of the Gault at Ford. One set is located in the Buckinghamshire County Museum (Aylesbury, England), the other one in the Natural History Museum (London, England) and the last one in the Micropalaeontological Museum of the University of Wales (Aberystwyth, Wales). The first two sets in the Museums were donated by E. Hollis while the third one was eventually deposited at Aberystwyth when acquired by Prof. A. Wood from Neaverson who had been his research supervisor at Liverpool University.
The aim of this work is to bring up to date the list of foraminifera of the Hollis and Neaverson paper, document the three scattered collections of slides and their contents and illustrate all the species, which are mostly represented by very well preserved specimens. On this basis we will attempt to relate the fauna to the modern, foraminiferal biostratigraphy of the Gault, foraminiferal ranges now being regarded as somewhat more 'critical' than in the time of Hollis and Neaverson who were under the heavy influence of Chapman and the 'English School'.

MATERIAL
The state and characteristics of the collections are described below.

Buckinghamshire County Museum (Aylesbury)
The set consists of slides made of cedar-wood, originally without cover-glasses (covered in the course of this study). The accession register, number 38, dates from 29 January 1920, and to quote from it, describes the collection as consisting of '108 microscope slides, foraminifera from Gault, Ford, Bucks., collected by Hollis 1919'. They are well set out and labelled but the information on them is limited. The labels are arranged in horizontal orientation and comprise on the left side the generic and/or specific identification and the locality and unit (Gault, Ford, Bucks.) and on the right side the specific classification, or

Natural History Museum (London)
As in the Aylesbury collection the slides are made of cedar-wood and without cover-glasses. The labels are arranged in the same way. The only difference is that there are no labels on the back of the slides. The accession register indicates that the material was deposited by E. Hollis in 1926 and the register numbers are from P23018 to P23232 (Tray 494). All the slides have specific identification and of those, 56 are included in the published list of Hollis and Neaverson, 10 are not in it and 79 species and varieties of the list were not found in the slides (see Tables 1 &  2).

RESULTS
In bringing up-to-date the list of species names used by Hollis and Neaverson for the Foraminifera. of the Gault (see Table l), it has been necessary to change most of the generic names and a number of specific names as well. In part this simply reflects progress in taxonomic discrimination but also the tendency of the members of the 'English School', such as Chapman, to apply Recent names to fossil species. However, in his work on the Gault, Chapman ( I 891-1898) recognized many new species and accepted many set up by Continental authors. Interestingly, this preceded the disastrous 'discovery' of the supposed Cambrian foraminifera of the Malverns in 19010 which seemed to confirm all the prejudices of the 'English School'.
In Table 3, the updated names used in this work are in the left column and are arranged following the foraminifera1 classification of Haynes (1981). The right column includes the equivalencies of the list of Hollis and Neaverson (1921). The species with an asterisk are those that are not included in the published list but were found in the slides. The 'p.p.' for some species is explained at the end of the table.
The agglutinated foraminifera are represented by two species of the Order Astrorhizida and 14 of the Order Lituolida. Of them, two species, Thurammina sp. and Reophax sp., have been left in open nomenclature and another, Bigerina? asperula (Chapman), with doubtful generic identification due to the bad preservation of the initial portion of the test in all the examined specimens. In addition, Sagrina calcarata (Berthelin) although on the list could not be identified because it is represented in the slide by two indeterminate fragments of agglutinated foraminifera only. The species Ammodiscus millettianus Chapman was misindentified by Hollis and Neaverson (1921) Owen's (1971Owen's ( , 1973Owen's ( ,1975 Standard ammonite zonation (columns 1 and 2) and Hart's (1973) foraminifera1 zonation (column 3) at the Middle-Upper Albian boundary. Note that Hart includes the crisfuturn Subzone in the luutus rather than the injratum Zone.
and Tritaxia pyramidata Reuss are the best represented among the agglutinated foraminifera and Quinqueloculinu antiqua (Franke) and Spiroloculina cretacea Reuss are the commonest species of the porcelaneous group.

DISCUSSION: AGE OF THE ASSEMBLAGES
Many of the species recorded in the Phosphatic Nodule Bed of the Gault at Ford are also present in the Chapman Collection of the Gault of Folkestone (England) which has been examined in the Natural History Museum during the course of the present work (see Chapman, 1891Chapman, -1898. Hollis and Neaverson (1921) pointed out that the relative abundances of the different groups were not the same for these two geographical areas. However, Walters (1958, Unpublished Ph.D. Thesis, U.C.W. Aberystwyth) studying the foraminifera from several outcrops in Southeast England, including Folkstone, shows similar relative abundances to those at Ford. These apparently contradictory results could be due to different approaches in the procedures used to pick and count the specimens. The recorded assemblages at Ford, which are dominated by the superfamily Nodosariacea, do not seem to be typical of the Middle Albian because in that interval the dominant group is the Superfamily Robertinacea (e.g. Hart & Carter, 1975;Hart et al., 1981Hart et al., , 1989. At the same time they are not quite the same as the typical assemblages of the Upper Albian because in the upper part of the Gault Clay Formation, the fauna totally changes and becomes dominated by agglutinated taxa although nodosarids and gavelinellids are quite numerous (Hart, 1990;Talwar, 1990 However, looking at the stratigraphical distribution of foraminifera as seen in several key sections of southern and eastern England, Northern Ireland, northwestern Scotland and the North Sea Basin (Carter & Hart, 1977;Hart, 1973Hart, , 1990Hart et al., 1981Hart et al., , 1989Hart et al., , 1990 it is apparent that some of the species recorded in the Gault at Ford, such as Haplostiche? sherborni Chapman, Eggerellina mariae Ten Dam, Tritaxiu pyramidata Reuss, Textularia chapmani Lalicker, Quinqueloculina antiqua (Franke), Frondicularia pinnaeformis Chapman and Vuginulina mediocarinata Ten Dam, are indicative of the Upper Albian.
The presence of Frondicularia pinnaeformis Chapman, an important zonal indicator in the Upper Albian (Carter & Hart, 1977), in association with the typical Upper Albian Arenobulimina chapmani Cushman, Nodobacularia nodulosa (Chapman) and poorly developed specimens of Epistomina spinulifera (Reuss), characteristic of the lower Gault Clay (Hart & Carter, 1975;Carter & Hart, 1977;Price, 1977), points to the possibility of the Phosphatic Nodule Bed being in the Epistomina spinuliYeralFrondicularia pinnaeforrnis Concurrent Range Zone (Zone 4a) of the benthonic zonal scheme of Carter & Hart (1977). However, the presence of Eggerellina mariae Ten Dam could indicate at least the Frondicularia pinnaeformis Assemblage Zone (Zone 5) of the same authors.
So, according to the benthonic zonal scheme proposed by Hart (1973) and Carter & Hart (1977) it is most probable that the foraminifera of Ford were recovered from the uppermost lower Gault Clay-lower part of the upper Gault Clay, Zones 4a-5 (from the uppermost Middle Albian to the lower part of the Upper Albian), equivalent to the uppermost Euhoplites luutus Zone (cristatum Subzone) to lower part of Mortoniceras inflaturn Zone (orbignyi-varicosum-lowermost auritus? Subzones) of the Albian ammonite zonation (see Fig. 2).
It must be noted that Hart's treatment of the ammonite zones differs slightly from that of Owen (1971Owen ( , 1973Owen ( , 1975 in that the cristatum Subzone is placed in the lautus Zone, i.e. the Middle Albian rather than the Upper Albian. Hart (1973, p. 272) comments, in relation to the Copt Point section at Folkstone, 'The cristatum Subzone contains a distintive bed of rounded nodules . . . which represents a non-sequence marking the Lower-Upper Gault boundary (although the top of the cristatum Subzone is some 30 cms above this level)'. The Ford section is therefore quite similar both lithologically and faunally to the Folkstone section.
Although Hart (1973) states that his faunal scheme, 'can, unfortunately, only be described as being of local application,' the type Albian at L'Aube, again shows a similar, major faunal change over the Middle-Upper Albian boundary (lower-upper Gault boundary). Here, as at Folkstone, the passage to the Upper Albian is marked by the appearance of Arenobulimina chapmani Cushman and Frondicularia pinnaeformis Chapman and their overlap with Epistomina spinulifera (Reuss) (see table 3 of Magniez-Jannin, 1975).