Page 45 - Carbonate Facies in Geologic History

32 The Stratigraphy of Carbonate Deposits

NORTH TEXAS
,
, BASIN

,
·,'G
,
I

;
----~ /
" 'SAN MARCOS
IlIis!s ARCH
·SA
Stith,. "tcrl, ~
MAVERICK BASIN
1--.---<
1- II ••

Fig. II-9. Fredericksburg facies over central Texas-San Marcos arch after Fisher and Rodda
(1969). The central Texas (Llano uplift) area was a gentle dome on the larger Comanche
platform but sufficiently positive to influence the carbonate facies. For additional diagrams
and discussion see Chapter XI. This illustration from original with permission of American
Association of Petroleum Geologists

within basins and in most cases clearly defined organic buildups are lacking. An example is
the Mississippian of the Williston Basin (Fig. II-8). The original facies model of Edie (1958),
Shaw (1964), and Irwin (1965), was drawn from these strata. Shoaling upward shelf cycles
following the standard carbonate facies patterns are characteristic. No pronounced rim of
organic buildups occurs in these strata, but scattered shelf mounds or patch reefs are com-
mon. Chapter IV (Middle Paleozoic Buildups) and the summary in Chapter XII describe
several types of these shelf buildups. Shallow intracratonic basins within the subtropical belts
which produce carbonate sediments are essentially absent on the present surface of the earth.

4. Buildouts from Low Positive Areas on Platforms -
Areas of Moderate Subsidence

Because of reduced subsidence at margins of these low structural highs, low depositional
relief develops and irregular patterns and wide facies belts exist. Nevertheless, the familiar
pattern may be discerned. For example, Mississippian facies across and around the Central