Arkell.1956.Jurassic..

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THE BRITISH ISLES
1935-48; for the stratigraphy in the south, various papers by Arkell,
and for the north, various papers by Wilson.)
LOWER OXFORDIAN (Lower Corallian Beds and Upper Oxford Clay)
Zone of Cardioceras cordatum (Sowerby). The thickest development
of this zone is in Yorkshire, where it comprises the Ball Beds, Passage
Beds and (probably) Lower Limestone (Hambleton Oolite). In all
other parts of England the lower part of the zone is in Oxford Clay facies,
while the upper part consists of sands (often current-bedded) with bands
and doggers of calcareous sandstone—the Lower Calcareous Grit. Three
ammonite subzones are recognizable: the true C. cordatum occurs only
in the highest, and the three faunas are in reality just as worthy of promotion
to true zones as some of the zones of the Kimeridgian, and have
sometimes been so used (Arkell, 1941c; 1945, p. 346).
Subzone of Cardioceras cordatum (Sow.), with C. persecans (Buckman),
Euaspidoceras acuticostatum (Y. & B.), E. nikitini (Borissjak), etc. Nothe
Grits of Dorset (9-10 m.); Lower Calcareous Grit of Wiltshire and
Berkshire (up to 20 m.), especially Seend and Calne; Lower Elsworth
Series of Cambridge (pars); Hambleton Oolite of Yorkshire?
Subzone of Cardioceras costicardia Buckman, with C. costellatum
Buckman, Peltoceratoides williamsoni (Phillips), etc. Red Nodule Beds
at top of Oxford Clay in Dorset and Wiltshire, Oxford Clay of Oxford
(pars); Lower Elsworth Series of Cambridge (pars); Passage Beds of
Yorkshire.
Subzone of Cardioceras bukowskii Maire, with many other species of
Scarburgiceras, Goliathiceras anacantkum, etc. Oxford Clay (pars) of
Dorset and Wiltshire; Ball Beds of Yorkshire.
There is a considerable development of late-Lower and early-Upper
Oxfordian in Scotland, but the ammonites require redetermination in
the light of work done in England during the last twenty years; in
particular there is confusion due to ambiguity in the use of the name
Cardioceras cordatum, by which was often meant Card. (Subvertebriceras)
densiplicatum Boden (figured Arkell, 1933, pi. xxxviii, fig. 5), characteristic
of the Plicatilis Zone. The type specimen of C. cordatum is shown on
pi. 38, fig. 1.
Zone of Quenstedtoceras mariae (d'Orb.). This zone comprises the
whole Oxford Clay in Yorkshire, and also the Lower Calcareous Grit;
in Scotland it is represented by at least part of the Brora arenaceous series.
The Oxford Clay of this zone in the south contains a rich fauna of
pyritized ammonites of many families, best known from Woodham brickpit,
Buckinghamshire. Commonest are Cardioceras (Scarburgiceras)
praecordatum R. Douville (upper and middle parts of zone), C. (S.)
scarburgense (Y. & B.) (middle and lower parts), Quenstedtoceras (Pavloviceras)
mariae (d'Orb. sp.), Euaspidoceras babeanum (d'Orb.), Creniceras
renggeri (Oppel), Taramelliceras (Proscaphites) richei (de Loriol), and
many small Hecticoceras, Perisphinctes, etc. Between this assemblage
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