Arkell.1956.Jurassic..

VOLCANICITY 629
Nevadan orogeny, thousands of metres of varied volcanics in the Franciscan
and Knoxville formations, largely of Tithonian age.
In Mexico no volcanic activity seems to have occurred until the
Oxfordian, when there was an outpouring of andesitic lavas during a
brief continental episode. Tuffs and bentonite occur also in the Tithonian.
For South America the picture is less clear; much more work needs to
Tithonian and
Portlandian
TABLE 26.—VOLCANIC ROCKS OF JURASSIC AGE IN AMERICA,
AND THEIR DATES
SOUTH
AMERICA
Lavas and
tuffs,
Patagonia
Kimeridgian Volcanics
1000 m.
Argentina
(?)
Oxfordian
(?)
Callovian Lavas in
Peru and
Chile
Bathonian
Bajocian
Toarcian Volcanic
Volcanic
Volcanic
series
series
series
Pliensbachian 900 m.,
in Peru
Sinemurian
Hettangian
MEXICO
Tuffs and
bentonite
Lavas
150-300 m.
OREGON AND
CALIFORNIA
Interbedded
volcanics
several
1000 m.
Some lavas
and tuffs
Lavas and
tuffs
870 m.
BRITISH
COLUMBIA
(HARRISON
LAKE)
Tuffs
540 m.
ALASKA
Some
tuffs
Volcanic
series
2700 m. Volcanic
series
300 m.
be done. A volcanic island festoon probably existed off-shore along much
•of the Andes in Lower and Middle Jurassic times. In Peru volcanic
rocks 900 m. thick of probably Liassic age rest directly on ancient gneiss,
and in both Peru and Chile further eruptions of submarine lava occurred
in the Callovian. The climax of activity was reached in west-central
Argentina at the end of the Oxfordian, with the building up of 1000 m.
of basic lavas and pyroclastics. This episode may correspond to any or all
of the Kimeridgian. Finally, in Patagonia the Tithonian shales are underlain,
overlain and interfingered with porphyritic lavas and contain thick
beds of tuff.
For NE. Asia information is too sketchy for dating the extensive volcanics
that occur supposedly at the top of the Jurassic of NE. Siberia and in
http://jurassic.ru/