Arkell.1956.Jurassic..

CHAPTER 17
INDO-CHINA, HONG KONG, AND
INDONESIA
This area measures about 2500 miles across and contains some of the most
difficult and complicated geology in the world. By far the greater part of
the area is covered by sea, and the land surface is decayed by deep tropical
weathering and mantled in dense vegetation. Jurassic sediments of widely
varied facies occur at numerous scattered points, but the outcrops are
separated on different islands and there are virtually no sections. Splendid
collections of ammonites and other fossils, from Hettangian to Tithonian
in age, have been made at many places in the Indonesian islands, from
loose nodules in stream-beds or among the ejectamenta of mud-volcanoes.
To the student of the Jurassic, therefore, the area is full of possibilities
and tantalising uncertainties. Instead of its almost complete suite of
Jurassic faunas helping to check the universality or otherwise of the standard
sequence elsewhere, the isolated elements have to be pieced together
solely from a knowledge of the succession in other parts of the world.
Thanks chiefly to sixty years of enterprising work by Dutch geologists,
some limited generalizations are possible. It appears that there was
continuous sedimentation throughout the Mesozoic in a sinuous trough
or geosyncline, which may have originated in the Permian, from eastern
Celebes through Buru, Ceram, Jamdena and Timor, and recent discoveries
in NW. Australia suggest that it continued southward into the
Broome and Derby districts. In this trough all the stages of the Lower
and Upper (but not the Middle) Lias are represented by prolific ammonite
faunas of European genera and in some cases even species. Neritic
Lower Lias sea also spread at least over NW. Borneo, Indo-China and the
fringe of southern China (Hong Kong). It may also have overspread
Sumatra and Java, but the Mesozoic rocks there have been converted by
dynamo-metamorphism into phyllites and schists. Eastwards in New
Guinea, so far as known, the first Jurassic transgression was in the Toarcian,
after which there was more or less continuous deposition in a wide belt
stretching through central New Guinea and probably connected by sea
with New Caledonia and New Zealand. The Toarcian transgression is
also recorded in Cochin China.
In an area that has been affected by such intense disturbance both
(locally) before the Cretaceous transgressions of various ages and during
the Tertiary, where nummulitic Eocene limestone can be converted into
schist and Pleistocene coral reefs may be elevated (as in central Timor)
to over 1200 m. and Pliocene sediments (as in Ceram) to at least 3000 m.
above the sea, it is of doubtful value to attempt detailed reconstructions
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