Page 274 - Carbonate Facies in Geologic History

Miogeosynclinal Basins 261

Oolite

Figures. IX-l and IX-2 indicate important areas of oolite accumulation in north-
western Europe which are interpreted as patchy areas of irregular migrating
shoals on shelves surrounding the shallow basins. In northwestern Europe these
oolitic shelf deposits, like the earliest Maim patch reefs, are chiefly of Oxfordian
age. As the southeastward regression of pure carbonate sedimentation developed
during Late Jurassic time, oolite beds become younger in the section until they
occur in Kimmeridgian strata in the Jura Mountains, partly behind the Tithonian
reef tract. In the Middle East the famous oolite and shoal water grainstone of the
Arabian Shield is essentially all Kimmeridgian and lies on a shelf east of the
Arabian Shield.

Reefs

Lying in patches around shallow basins (Paris, English and North German ba-
sins) are coral reefs, mostly of Oxfordian age. At the edge of the European shelf-
island-basin area, facing south into the Tethys, almost the total Maim (Upper
Oxfordian-Tithonian) developed massive sponge and coralline limestone. This is
particularly widespread around the northern edge of the Tethyan geosyncline in
Latest Jurassic (Tithonian) time. The Jurassic section is capped by Tithonian reef
facies overlying deep water sediments of early Maim age, especially in the eastern
and south-central Mediterranean as far west as Sardinia and Sicily. Reefs devel-
oped on platforms within the geosyncline. None are known in the Jurassic sec-
tions of the Middle East.

Deep Lagoonal Carbonate

Immediately behind the reef rim in Franconia and Schwabia (southern Germany)
and in Spain (Montsech) lay basins filled with quiet-water sediments, now pre-
served as interbeds of platy limestone and marl and including thin turbidites.
These small, reef-surrounded basins have preserved remarkable faunas of nek-
tonic marine, flying, and land animals in an environment completely inhospitable
to normal benthonic creatures. These beds constitute a most remarkable facies of
the Jurassic, the Solnhofen.

Miogeosynclinal Basins

An area of thick carbonate sedimentation (miogeosyncline) in southeastern Eu-
rope separated the interior (Tethyan) geosyncline of the Mediterranean area from
the Russian platform and Scandinavian shield. Massive shallow water limestones,
mainly of Tithonian age, reach almost 1000 m in this trough whose sediments are
exposed in the Caucasus Mountains and the Elburz range of Iran. Similar shallow
shelf deposits up to 600 m thick are represented in the Late Jurassic section in the