Page 275 - Carbonate Facies in Geologic History

262 Reef Trends and Basin Deposits in Late Jurassic Facies

North African ranges of Algeria and Tunisia. At this time the North African-
Arabian shield was mainly land. A prong of the continent extends north through
Israel, Jordan, and Syria to the Mosul block in North Iraq. The Mesopotamian
and northern Persian Gulf area is underlain by a Late Jurassic euxinic basin with
salt, whose southern end is bordered by another wide carbonate shelf connecting
the Arabian shield to an Iranian positive block, the Surmeh shelf. Within the
Zagros geosyncline, 400-600 m of shoal-water cyclic carbonate sand and muds
are present across this mildly positive area. The Rub Al Kali basin of southern
Saudi Arabia contains euxinic, dark argillaceous limestone and salt. Other similar
basins occur in Iran and Saudi Arabia. The Zagros geosyncline facies thus differs
from the Mediterranean-Alpine Ammonitico Rosso and radiolarite facies.

Northern Tethyan and Continental Margin Facies

Bernoulli (1972) has subdivided the Late Jurassic Alpine and Appenine facies into
several provinces. The interior or oceanic part consists of ophiolites, radiolarites,
and pelagic shales with some volcanic sandstones and graywackes. The continen-
tal margin to the north is subdivided into two parts: the Helvetic black Quintner-
kalk belt (Standard Facies belt 3) which grade into a deep trough and swell facies
of the southern continental margin and slope. The latter facies occur in the
external zones of the Appenines and Dinarids, and in the Southern Alps, and
Austroalpine nappes. The paleotopography was complex with carbonate plat-
forms, submerged sea mounts with abbreviated sections and adjacent deep
troughs with continuous pelagic sediments. On the swells, thin pelagic limestones
contain condensed faunal successions, early lithified red nodular limestone, hard
grounds, and filled tectonic fissures. On the slopes of the swells peloidal limestone
and encrinite pass to bioclastic debris limestone with pelagic bivalves and cocco-
lith lime mudstones. The basins contain some clay but are mainly of pelagic
limestone with radiolarite and redeposited and slumped sediment derived from
up the slopes.

Basic Microfacies

Extensive petrographic work has been accomplished on Jurassic microfacies.
Best references include the volumes of the International Petrographical Series
edited by Cuvillier and Schiirmann (1951-1969) and Carozzi et aI., (1972) for the
Aquitaine basin, France. Some of the most important of the microfacies are
described and illustrated here, numbered J 1 to J 17 to distinguish them from the
standard ones (SMF-).

Shelf and Shelf Margin in Europe

J 1. Light-colored lime mudstone with fenestral-peloid fabric, commonly laminated; pelle-
toids partly deformed-squashed together but retaining identifiable form. Fenestrules
formed originally as holes caused by entrapped air or by gases from organic decay in the