Rotaliine Foraminiferida from the type section of the Atherfield “Group” (Lower Aptian), Isle of Wight, U.K.

A preliminary study has been made of the Foraminiferida fauna of the type section of the Atherfield “Group” on the Isle of Wight. The fauna is sparse but diagnostic of the Lower Aptian as defined by faunas worldwide. This paper describes and illustrates the rotaliine Foraminiferida fauna and complements a previous publication describing and illustrating the textulariine fauna.

microfauna. Casey (1961) described the Atherfield section and proposed an ammonite biostratigraphy which provides a documented macrofossil zonation with which to calibrate the Foraminiferida fauna (Fig. 1). The fauna is the earliest fully marine Foraminiferida fauna describcd and published from the Cretaceous of S.E. England and is similar to, but smaller in number and less diverse than, the Aptian faunas recorded by Damotte & Magniez-Jannin (1973) and Damotte et al. (1978) from the Paris Basin, by Colin et a / . (1981) from the north Celtic Sea Basin, by Jaworski (pers. comm., 1981) from S.E. England and by Dupeuble from the Bay of Biscay (1979).
The complete fauna from the Atherfield "Group" is reminiscent of the Ammobaculites Association of Haig (1979) where a low diversity association is characterised by abundant arenaceous Foraminiferida, with the accompanying rotaliine species being mainly very small and unornamented. This association, according to Haig, is extensively developed in shallow, partially enclosed, epicontinental seas in the northern and southern cool temperature belts of the late Early Cretaceous. However, the fauna from the Atherfield "Group" docs suggest a Tethyan "warm" water influence (the Trinidad Lower Cretaceous fauna is also a transitional TethyanITemperate type according to Bartenstein & Bolli, 1977).

THE ROTALIINE FORAMINIFERIDA FAUNA
The fauna described herein was not well preserved; indeed it shows signs of etching, breakage, wear and replacement by pyrite. These phenomena of preservation are probably due to a combination of decalcification of the strata by percolating ground water, distortion of the fauna by compression and post-mortem transport of the fauna. The section at Atherfield is a S.W.-facing (dominant wind direction) sea cliff which is highly weathered, fractured and slumped and is partially obscured by downwash. The rotaliine fauna recorded from the Atherfield "Group" is low in numbers of individuals and of species. This is a reflection of the preservation phenomena mentioned above and perhaps also subtle differences in ecology between the Isle of Wight and other areas where the faunas are much more diverse. That recorded by Jaworski (pers. comm.) from S.E. England, for example, is diverse and abundant and includes species neither previously recorded from the Aptian of the U.K., e.g. Lenticulina schreiteri (Eichenberg), L . spinosa (Eichenberg) and L . crepidularis (Roemer) (recorded as L . tricarinella (Reuss 1863) by Magniez-Jannin, 1973), nor by the present author from the Isle of Wight. Jaworski's faunas are, however, from subsurface sections. All those rotaliine species recorded from the Isle of Wight are present also in S.E. England (pers. comm.  (Colin et al., 1981) consists of the following species: Hoeglundina chapmani (ten Dam), Valvulineria grucillima (ten Dam), Lenticulina ex.gr. nodosu (Reuss), Lenticulina cf. L. gaultina (Berthelin) and L . Waginulina) humilis (Reuss) Crittenden). No planktonics were observed. The fauna recorded from D.S.D.P. Leg 48 in the Bay of Biscay (Dupeuble, 1979) is very similar and provides a faunal link to the Tethys area to the south during early Aptian times. Other remarkably similar faunas include those from the Scotian shelf, offshore eastern Canada (Ascoli, 1976) and from Trinidad (Bartenstein & Bolli, 1977).
Examination of the total Foraminiferida fauna is important in providing an overall picture comparable to the pattern of Lower Aptian deposits worldwide (Bartenstein, 1976(Bartenstein, a, b, c, 1977(Bartenstein, , 1978(Bartenstein, , 1979. The biostratigraphical, palaeogeographical and palaeoecological implications of the total fauna recorded from the Atherfield "Group" are further discussed by Crittenden (in press). In that paper, a number of planktonic species were recorded on the range chart for the Atherfield clay S.S. These species, apart from the ones described herein are now placed in "undifferentiated planktonics".

Systematic descriptions
The classification follows that of Loeblich & Tappan (1964.For brevity, the synonymy consists of the first citation of the species in the literature plus one or two other references where appropriate. The figured material is deposited in the collections of the British Museum (Natural History).

Remarks
The study of the Nodosariidae is notorious for the problems posed for classification both generically (as Lenticulinu, Astacolus, Marginulina, Dentalina, Nodosuria, etc.) and subgenerically. Magniez-Jannin (1973, 1975 has discussed this taxonomic problem in some detail with reference to whether the great morphological variation seen in the Nodosariidae should be placed at a generic or sub-generic level. In this study the material available was not sufficient to enable a full appreciation of the generic problems. Remarks. This specics differs from L . rotulata (Lamarck) by the tendency of the last chambers to become higher, to unroll and become uniserial. Juveniles of the two species are particularly difficult to separate. Stratigraphical range. This species is not very common at Atherfield but it is extant throughout the Albian in north-west Europe. Bartenstein (1 976a, 1977)  Remarks. Bartenstein (1974) and Aubert & Bartenstein (1976) have discussed fully the taxonomy, and stratigraphical and worldwide distribution of the L . ( L . ) nodosa group. The material from the Atherfield "Group" is too sparse to enable a "splitting" of the specimens into the various subspecies noted by the above mentioned authors. To place it into the new species Lenticulina ( L . ) Kemperi Aubert & Bartenstein created for Aptian "forms" of the Boreal province would be incorrect. Stratigraphical range. This species is important stratigraphically in N.W. Germany. Ascoli (1976) uses its first occurrence downholc to denote the Aptian on the Scotian shelf. However, Michael (1967) states that the L. ( L . ) nodosa group represents an iterative evolutionary modification of a smooth "lenticuline" rootstock (c.g. L . L . muensteri). Therefore, at successive geological times and in different geographical locations (worldwide) in the Lower Cretaceous "forms" (? homeomorphs) attributable to the L . ( L . ) nodosa group have developed in response to similar ecological conditions. Ideally, each lineage arising from iterative evolution should be given a species name but in practice this is very difficult especially when dealing with borehole cuttings or when the age of the fauna of which the "form" is a member is not precisely known. Therefore these "forms" are of limited use to a stratigrapher but are useful in palaeoecological reconstruction. Remarks. This species has a closed spire which is regular and a circular periphery which places it distinctively within the morphology of "Lenticulina". It portrays a remarkable variation in a number of characters which have been discussed by Magniez-Jannin (1 973). The specimens from the Atherfield "Group" section display the same variation and could conceivably by "split" into a number of morphotypes (species ?) e.g. Lentic d i n a subangulata (Reuss, 1863, p. 74, pl. 8, fig. 7) and L . macrodisca (Reuss. 1863, p. 78, pl. 9, fig. 5). Magniez-Jannin ( 1973) recognises these forms plus others not seen at Atherfield e.g. L . roemeri (Reuss, :1863, p. 75, pl. 8, fig. 9) and L . secans (Reuss, 1863, p. 214, pl. 9, fig. 7). L . rotulata is similar toL. heiermanni I3 e t tenstae d t , 1 9 5 2. Stratigraphical range. This species has been recorded from the Albian and Lower Aptian of Francc (Magniez-Jannin, 1973, 1975. It has no stratigraphical importance as an index species but does illustrate the wide range of variation exhibited by a single species which previous authors have "split" into separate species. Lenticulina (Astacolus) atherfieldensis Crittenden, 1982 (Reuss); C ri t t e n d e n , sensu Mag n i ez -J a n n i n , 1 9 7 3, in press . 1982 Lenticulina (A .) atherfieldensis Crittenden, in press.

Remarks.
Crittenden (1 982) has discussed the taxonomy, morphology, stratigraphical range and geographical distribution of this species. Its presence in the Aptian of the Isle of Wight and France (Magniez-Jannin 1973) demonstrates the iterative evolution of the "form" from a smooth "Lenticuline" rootstock in the Lower Cretaceous.
L,enticulina (Marginulina) aff. Parallela (Reuss, 1863) (PI. 1, figs. 14, 1.5) Remarks. An elongate "lenticuline" species which is compressed, has 2-6 chambers in the enrolled stage, with 3-5 in the uniserial stage, has an angular dorsal periphery, a compressed oval cross-section, and depressed slightly curved sutures. Stratigraphical range. Although very rare in the section studied, this species appears very similar to that described by Magniez-Jannin (1973)  Remarks. This species is similar to Lenticulina (Astucolus) pachynota (ten Dam) but differs in lacking thc limbatc, elcvated sutures and is not so laterally depressed. Ten Dam's species has been renamed L . (A) neopachynota Bartenstein & Kaever ( 1973). Stratigraphical range. Although occurring very rarely in the Atherfield section its presence is important as it has been previously recorded only from the Upper Ryazanian to the Lower Barremian of Speeton.

Explanation of Plate 1
The dimensions given are for maximum diameter, except where otherwise stated.     Remarks. Only one crushed specimen, very similar to the species recorded by Bartenstein & Bolli (1977) from the Lower Aptian Cuche Formation of Trinidad as G . prisca (Reuss), was found in the Atherfield section. Magniez-Jannin (1973) records G . aff. lacrimu (Reuss) from the Aptian of the Paris Basin.

1-4.
Remarks. This small planktonic species is easily recognised by its quadrate shape and umbilical aperture. It is very variable in the size of the last four chambers and in the height of the apertural arch. Masters (1977) & Gradstein (1978 discuss the taxonomy of this species. It is known from the Jurassic (Mid-Bathonian) to Mid-Aptian. Van Hinte (1976) restricts it to the Upper Hauterivian. In the Atherfield "Group" this species is rare but quite distinctive.
Remarks. Masters (1977, p. 454) places this species in the synonymy of H . delrioensis (Carsey) but both Price (1977) and Carter & Hart (1977) have upheld their separate identity while recognising that the two "species" are end members of a complete range of variability (see also Harris, C.S., 1980, unpubl. Ph.D. thesis, Plymouth Polytechnic, C.N.A.A.). Bartenstein ( 1962) originally named Globigerina D l 1 of Hecht (1938) as Hedbergella infracretacea but later (1965) changed this to H . delrioensis. Globigerina D9 (Hecht, 1938) has been named by Bartenstein ( I 965) as H . aptiana but really could be placed within the range o f variability of the H . infracretucea-delrioensis group. The paucity of material from the Isle o f Wight favours this approach and Magnicz-Jannin's (1973) illustrations (pl. 4, figs. 31-34) show a typical H . infracretucea (her "forme convexe" o f H . infracretacea) and also (pl. 4, figs. 26-30) show a typical H.. aptiana (her "forme plate" of H . infracretacea). H . aptiana is stratigraphically important as an index fossil in the Lower Aptian of N.W. Germany (Bartenstcin. 1965;Hecht, 1938) and the present author re'cognises its importance as an index fossil in the Lower Aptian of the southern North Sea Basin (from boreholes supplied by Shell U K Exploration & Production). For this stratigraphical reason in the southern North Sea both H . infiacretuceu and H . uptiana are separated from H . delrioensis. This "species" is rare in the Isle of Wight material and is also rare in the Atherfield Clay material of S.E. England (Jaworski, pers. comm. Remarks: This species seems t o be the ancestral form of G. intermedia and is similar to G. cf. barremiana Bcttenstaedt sensu Bartenstein & Bettenstaedt 1962. Stratigraphical range. In the U.K. this species is found in the Lower Aptian Atherfield Clay of Kent. It has not been recorded from the north of England, although the present author has seen specimens attributable to G. brielensis from the Lower Aptian of the southern North Sea Basin. Gavelinella ex. gr. intermedia (Berthelin, 1880) (PI. 2, fig. 8) 1977 Gavelinella intermedia (Berthelin); Price: 5 16, pl. 60, figs. 7, 8. 1981 Gavelinella intermedia (Berthelin); Hart et al.: 194,pl. 7.11, Remarks. This species has had a chequered history in the literature but Price (1977) adequately sums up the main points of controversy. Specimens attributable to this group are extremely rare in the Atherfield section on the Isle of Wight. Stratigraphical range. Essentially an Albian-Cenomanian species although ancestral species are present in the Aptian. The whole Gavelinella group in the Lower Cretaceous is in need of further study and revision.

Explanation of Plate 2
The dimensions given are for maximum diameter, except where otherwise stated.

CONCLUSION
The rotaliine Foraminiferida fauna from the Atherfield "Group" of the type section on thc Isle of Wight is sparse and not at all diverse. The fauna is, however, an aid to the identification of the Aptian Stage offshore in the commercially explored areas of the North Sea and the Western Approaches. This paper will, hopefully, stimulate further research on thc neglected Aptian Foraminiferida faunas o f the United Kingdom.