Arkell.1956.Jurassic..

588 THE ANDES OF SOUTH AMERICA
Arietitid beds (Tilmann, 1917, pi. xxi, figs. 1, 2). In Argentina the
Hettangian is probably represented by coral limestones and sandstones
(Jaworski, 1914, p. 323).
The Lias in some places rests on plant-bearing sandstones believed to
be Rhaetian, in which Estheria, Unto and fish occur (Gerth, 1935, pp.
225-9).
e a s t
1° Equador there is a lithological passage up from marine
Trias (Tschopp, 1945). In many other places, from Venezuela in the
north (Oppenheim, 1940) to Patagonia in the south (Feruglio, 1949,
p. 109), the Lias or its supposed equivalents transgress on to Palaeozoic
and pre-Cambrian rocks.
THE SOUTH AMERICAN SHIELD
The description and correlation of the continental deposits and eruptive
rocks of the shield lie outside the scope of this book. The dating of
these rocks, as of their counterparts in the south of the African shield, is a
specialized enquiry which will demand more field-work and perhaps will
be solved only by introduction of new techniques. Sedimentary petrology
and micropalaeontology have as yet been little employed.
The upper part of the great 'Santa Catarina System', the lower parts of
which are Palaeozoic, consists of unfossiliferous aeolian sandstone
(Botucatu Sandstone, 0-300 m.) overlain by the Sera Geral fissureeruptives
of the Parana basin, which are the largest known mass of volcanic
rocks in the world. These two formations correspond with the Cave
Sandstone and Stormberg Lavas of South Africa, and it is customary to
regard them as Rhaetian (Gerth, 1935, table VI, p. 251).
It is sometimes argued that some if not all of the Sera Geral lavas may
be Jurassic (Gordon, 1947, p. 17), but this depends at present on personal
evaluation of the time-significance of the Botucatu Sandstone and two
unconformities which separate the lavas from the highest fossil-bearing
beds of basal Upper Triassic age.
In either case, whether these lavas are Rhaetic or Liassic, the shield
during the whole Jurassic period was a land-area, about which at present
next to nothing is known.
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