Page 322 - Carbonate Facies in Geologic History

Summary-Comparison with Permian Reef Complex 309

Table X-3. Summary diagram of three cycle types
Cycle type Lithic sequence Environmental Paleogeography
interpretations,
climatic and
hydrographic
factors
Shelf oolite a. Lagoonal laminated Tropical or arid Wide shallow
mudstone or hardground climate, moderate shelves around
over major oolite circulation. basin and wide, low,
development High tidal range flat banks on such
b. Oolite bars, good cross- (at least 1 meter) shelves
bedding
c. Normal marine marl or
wackestone at base with
rare reefs
Shelf lime a. Sabkha evaporites Evaporitic-arid Wide shallow
mud b. Laminated tidal-flat or tropical climate, shelves around
mudstones. very poor marine basins and terminal
Restricted marine circulation. fillings of shall ow
lagoonal mudstones and Low tidal range basins
wackestones
c. Normal marine marl or
wackestone
Platform with a. Soil zones with caliche Strongly seasonable Open-sea major
intense or sabkha-restricted evaporitic climate, banks or exposed
diagenesis, marine-lagoonal to intermittent good platforms or ramps
Loferites intertidal mudstones circulation and very with considerable
b. Coarse lime sand, gravel, restricted circulation bathymetric relief.
lumps, and onkoids. in lagoons; con- Good drainage
Little oolite or cross- siderable sea-level during low sea-level
bedded bioclastic sands fluctuation, abrupt stands and strongly
c. Large heavy-shelled subaerial exposure fluctuating water
organisms in calcirudites tables
d. Sand banks in wide
marginal belts grading
to bank interior muds

The environment reconstructed for Loferite cycles is one of large, steep-sided
well-drained porous carbonate platforms or major offshore banks standing high
above sea level at repeated periods during their early history. Dunham's (1972)
indication of large-scale sea-level fluctuations in the Permian Reef Complex be-
comes highly significant in terms of backreef diagenetic history.
The use of Fischer's term Loferite for such characteristic strata is to expand its
meaning beyond purely shrinkage pore or fenestral fabric, but this is a convenient
and recommended term for such cycles. Similar strong diagenetic imprint on
restricted marine sediment has been observed in Early Mississippian beds in the
Williston basin and in some Cretaceous bank deposits in Mexico, but neither of
these examples shows the degree of extreme diagenesis of the Permo-Triassic
strata. Table X-3 and Fig. X-20 contrast certain lithologic characteristics of the
platform Loferite cycles with those composed largely of shelf oolite or tidal flat
muds.