All nannofossil taxa encountered during this study of the Oxford Clay are listed below, and discussed where necessary. Figure numbers refer to this thesis.
Anfractus harrisoniiMedd 1979
Axopodorhabdus atavus(Griin et al. 1974) Bow n 1987
A. cylindratus(N oël 1965) Wind & W ise inW ise & Wind 1977
Biscutum constans(Gorka 1957) Black inBlack & Barnes 1959 (Fig. 5.6)
B. dorsetensis(Varol & Girgis 1994) Bow n & Cooper 1998
Bussonius p rin sii(N oël 1973) G oy 1979
Calyculus ^o'è\ 1973
Calyculussp.
Carinolithus magharensis(M oshkovitz & Ehrlich 1976) Bown 1987
Crepidolithus crassus (Deüsindre 1954) N oël 1965 C granulatusB ow n 1987
C. perforata (M edd 1979) Griin & Zw eili 1980
Crucirhabdus prim ulus Rood et al. 1973
Cyclagelosphaera^o'èX 1965
Morphotypes previously assigned to C. tubulata(Griin & Z w eili 1980) C ooper 1987 are thought to be Cyclagelosphaeraprotococcoliths (Fig. 5.6; Lees Burnett et al. in prep.). The specim ens observed m ost likely represent C. margerelii,as no other species in this genus w as observed in the Oxford Clay. These protococcoliths are easily distinguished from their fully-form ed counterparts on the basis o f the central area, which is open in the former and closed in the latter.
Cyclagelosphaera m argerelii ^ o ë \1965 (Fig. 5.6)
Som e Cyclagelosphaeraspecim ens observed here are larger and thicker than ‘cla ssic’ C.
margerelii(this large morphotype is the Cyclagelosphaerasp. 1 o f B ow n inMartill et al.
(1994); Bown pers. comm. (1999)). However, given an apparent spectrum o f size variability in these and other members o f the Watznaueriaceae, together with a lack o f other m orphological differences, these were included under C. margereliiin the present study.
Discorhabdus striatusM oshkovitz & Ehrlich 1976
Ethmorhabdus gallicus'Ho'èX 1965
O xford C la y taxonom y
M itrolithus elegansDeflandre inDeflandre & Fert 1954
M. ja n sa e(W iegand 1984b) Bown inY oung et al. 1986
Octopodorhabdus decussatus(M anivit 1961) Rood et al. 1971
ParhabdoUthus liasicus distinctusB ow n 1987
P. m arthaeDeflandre inDeflandre & Fert 1954
Podorhabdus grassei'Ho'éX1965
Polypodorhabdus escaigii^o'èX 1965
Pseudoconus enigm aBow n & Cooper 1989b
Retecapsa incomptaBow n 1987
Schizosphaerella punctulata Deflandre & Dangeard 1938 (Fig. 5.6)
Staurolithites leptostaurus(Cooper 1987a) Bow n & Cooper 1998 (Fig. 5.6)
S. quadriarculla(N oël 1965) W ilcoxon 1972
Stephanolithion bigotii bigotiiDeflandre 1939 (Fig. 5.6)
S. bigotii m axim um Deflandre 1939 (Fig. 5.6)
S. hexumRood & Barnard 1972 (Fig. 5.6)
TriscutumDockerill 1987
"I Triscutumsp.
A single specim en o f ITriscutumbearing an axial cross in its central area was
observed. An axial cross is not known to be characteristic o f any species in this genus.
T. beaminsterensisDockerill 1987
T. expansus(M edd 1979) Dockerill 1987
Tubirhabdus patulus Rood et al. 1973
The large, thick coccolith rim and enlarged spine girth o f specim ens observed here are characteristic o f the m odified morphotype o f this species that appeared in the M iddle Jurassic (B ow n & Cooper 1998; Bow n pers. comm. 2000).
WatznaueriaReinhardt 1964
A lthough it is possible to recognise Watznaueriacoccospheres in the LM (Fig. 5.6), species identification is often problematic due to the difficulty o f resolving sm all-scale m orphological features on the surface o f such thick particles. Watznaueriacoccospheres were thus excluded fi’om routine population counts (this also prevented over
representation o f Watznaueriacoccolith abundances, as this genus is fi’equently
represented by intact coccospheres (Appendix 8), each o f w hich contain numerous liths).
Watznaueriaprotococcoliths have been identified as such by Y oung & B ow n (1991) and Lees Burnett et al.(in prep.). M ost lack developed m orphological features and cannot be assigned to species. Exceptional are those with an incom plete bar in the central area, which must belong to W. britannica(Fig. 5.6).
Watznaueria barnesae(Black inBlack & Barnes 1959) Perch-Nielsen 1968 (Fig. 5.6)
W. britannica(Stradner 1963) Reinhardt 1964 (Fig. 5.6)
This species is very variable in size and central area m orphology in the Oxford Clay, ranging fi-om very small (several m icrons) with a small central area filled by the bar, to
m edium/large (e.g. 7 or Sjini) with a large central area spanned by the bar. It has been suggested that such large specim ens (as observed in Kimmeridgian sedim ents) represent a distinct population (Lees Burnett et al. in prep.); however, the apparently continuous spectrum o f variability in size observed in this study may be the result o f intra-species variation. Rarely, specim ens possess a bar which bifurcates at both ends. These are thought to represent a late stage o f W. britannica coccolithogenesis (Lees Burnett et al. in prep.).
W. fo ssa c in c ta (Black 1971) Bow n in Bow n & Cooper 1989 (Fig. 5.6)
Late growth stages o f W. fo ssa cin c ta are not easily discerned from fully formed coccoliths, on account o f the variable size o f the central area in relation to the coccolith rim w hich characterises this species. Count data may thus include som e protococcoliths and marginally over-represent the abundance o f this taxon.
W. m a n ivitia e Bukry 1973
Z e u g rh a b d o tu s erectu s (Deflandre in Deflandre & Fert 1954) Reinhardt 1965
Z. erectus show s unusual variability in size in the Oxford Clay. The rim o f this species show s an inconsistently bicyclic appearance in XPL, and the transverse bar varies substantially in brightness; these observations may be a factor o f coccolith size and/or preservation.
Z. cf. Z fis s u s (Fig. 5.6)
The transverse bar o f som e Oxford Clay zeugrhabdotids exhibits a light m icroscope im age w hich splits along its long axis when rotated in XPL; this is not characteristic o f Z.
erectus. These specim ens are labelled with reference to Z. fissu s Grün & Z w eili 1980, albeit the bar o f Z. fissu s does not exhibit the brightness in XPL shown by these
specim ens (Bow n pers. com m . 2000), and the interval studied here pre-dates the range o f this species (middle Oxfordian-?upper Valanginian; Bow n & Cooper 1998).
Sp. 1 (Fig. 5.6)
These are large {ca. 10 x 12pm), broadly elliptical placoliths o f uncertain taxonom ic affinity. The central area is o f normal width to wide. Little further m orphological detail could be ascertained as only several, badly-preserved specim ens were observed.
O xford C lay data