Page 301 - Carbonate Facies in Geologic History

288 Shoaling upward Shelf Cycles and Shelf Dolomitization

25 km
YONNE R.
+

c::::::::J C0 5 t.l.D
c::::::J MUOOY PELLETOIO SAND
ONCOIDAL GRAVEL
~ PELLETOIDAL SAND
CORAL BIOSTROME
DlIIIIIll MIXED OOLITE -BIOCLAST. SAND
_ PURE OOLITIC SAND
c::::::::J CRINOID-CORAL - BRYOZOA SAND
CALLOVIAN ~ -SILT
CALCI
CYCLE IlmlmI ARGILLACEOUS c05 Ml.()
E2i:5l DOLOMITE
--.r-v- HARD GROUND
Fig.X-7. Detailed facies model of Callovian cycle across low relief carbonate bank. Section
trends down outcrop belt on southeast side of Paris basin. The black zigzag belt merely
outlines the vertical line pattern of oolitic-bioclastic sand. The pure oolite beds which occur
as intervals within the former facies and are also marked in black. Fig.X-7 and X-8 show
respectively the south and north sides of the bank and fit together, overlapping at the Seine
River. The original relief was low (far less than 1/2 degree slope) but sufficient to create a facies
differentiation across the broad bank interior which progressively became more restricted
during Callovian time. Vertical exaggeration 2500 X. Courtesy of B. Purser (1972)

Although the Callovian facies outlined by Purser circumscribe a somewhat
local bank, the well-formed oolite of the cycles is much more regional and is
widely exposed in the Dogger of the Jura Mountains of Switzerland and France
as well as far north in England. No major reef belts are known to be equivalent to
this extensive oolite, although coral patches and biostromes occur within it in
places.

Late Jurassic Arab Zone Lime Sands of Arabia

Regional setting: Late Jurassic grainstone beds contain important oil reservoirs in
the Middle East and currently produce annually at least one-quarter of the vast
petroleum supply from that part of the world-principally from Saudi Arabia.
The Arab zones (Kimmeridgian strata) form a remarkable cyclic series containing
coarse lime sand and gravel spread across part of the Arabian shield.
This area lies across a tectonically neutral shelf between the eastern side of the
Arabian Shield and a positive area, the Qatar-Surmeh high, which lay farther east,
out in the Zagros miogeosyncline. Late Jurassic basins were situated north and
south of this shelf. The Basrah basin in the northern Persian Gulf area was the site