Arkell.1956.Jurassic..

2 38 THE IBERIAN PENINSULA
comprises thick dolomites with intercalations and lenses of coral limestones,
Nerinea limestones and Diceras limestones, and beds of quartzite pebbles
at two levels, the upper one becoming in western Algarve a limestone
conglomerate with quartzite and lydite pebbles, resting on Upper
Callovian. A Lower Kimeridgian ammonite fauna with Ataxioceras
effrenatum (Fontannes), Sowerbyceras loryi (Munier-Chalmas), Simoceras
herbichi (Hauer), 5. aff. explanatum Neumayr, etc., first makes its appearance
about 5 m. above the Callovian. There appears to be in some places
a condensed representative of the Bimammatum Zone also, for Epipeltoceras
bimammatum and Ochetoceras marantianum are recorded from the same
beds (Choffat, 1887, pp. 258-61).
North of the Tagus the Kimeridgian is well developed in the Montejunto
Range (Torres Vedras country) between the Tagus basin and the sea.
Here the succession is:
'Pterocerian'. Argillaceous sandstones and marls with local intercalations
of limestone, and locally beds of well-preserved Trigonia
lusitanica, etc. (Choffat, 1885, pis. vii, viii). North of the Montejunto
Range marine fossils disappear and all passes into sandstones with plant
remains and Unios (Choffat, 1885, 1894). No ammonites are known,
but there are corals, from which and the gastropods and pelecypods a
'Pterocerian', i.e. Lower Kimeridgian, age is inferred (Koby & Choffat,
1904-5, p. 160). Underneath are similarly undatable beds with Lima
pseudo-alternicosta and corals, said to form a passage down into the
Lusitanian.
Upper Lusitanian (Abadia Marls), 800 m. Mainly marls or clays, with
intercalated sandstones, conglomerates and pebble beds, the pebbles
largely derived from the pre-Cambrian: one such lenticle is 50 m. thick.
In the marls are sometimes fossiliferous nodules with many pelecypods
and gastropods and some corals. In the middle is an ammonite horizon
containing a rich Lower Kimeridgian assemblage (Choffat, 1893, pis.
xvii-xix), mainly Progeronia spp. (pi. xviii), with Aspidoceras cf acanthicum,
A. cf. longispinum and others, Simoceras spp. (pi. xvii, 6-10, xix, 4),
Taramelliceras nimbatum (Oppel), T. trachynotum (Oppel), Idoceras ?
guimaraesi Choffat sp. (pi. xvii, n), /. planula (Hehl), Prorasenia cf.
stephanoides (Oppel), etc. The exact age of this fauna is difficult to
assess, but it is probably somewhat earlier than the Ataxioceras effrenatum
asemblage of Algarve and may belong to the lower part of the Tenuilobatus
Zone.
Middle Lusitanian pro parte (Upper Montejunto Beds). The Montejunto
Beds, 200-350 m. thick, comprise coralline limestones with here and
there beds of different facies, in which Choffat recognized four ammonite
horizons. The lowest (1) is certainly Upper Oxfordian and the highest
(4) certainly Lower Kimeridgian, but the age of the two middle horizons
is debatable. The fauna is listed by Choffat (1893, p. 77, beds 1-4
separated) and any specialist may form his own judgment. Definite
Lower Kimeridgian ammonites in the highest horizon (4) are Enosphinctes
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