Page 344 - Carbonate Facies in Geologic History

The Great Middle Cretaceous Carbonate Banks of Central Mexico 331

W E
I 2
9

~mj PeUetoidal facies D Skeletal siltite
facies
D Birdseye and stromatolitic ~ Skeletal sand facies
mud facies ~L
10
I=-=--~ Aphanitic mud focies m Organic reef facies
o 600m
!·\t¥iJ Porosity

Fig.XI-6. Facies distribution of El Abra limestone as determined by factor analysis. From
Griffith et al. (1969, Fig. 8) in a traverse across the Cuesta de El Abra, 15 km east of Valles,
San Luis Potosi, Mexico. Compare with Fig.XI-10. Illustration courtesy of Society of Eco-
nomic Paleontologists and Mineralogists

of these Cuesta El Abra exposures and are available from Bonet (1952), Griffith et
al. (1969), and from the Corpus Christi, Texas, Geological Society Guidebook of
1963. Unfortunately, as is usual, the foreslope deposits are incompletely repre-
sented along this scarp, having been downfaulted into the coastal plain. A well
15 km east of the El Abra scarp (Coco no. 22) penetrated a basinal section of
Tamaulipas limestone (Facies belt 3).
A particular problem in foreslope interpretation relates to the important re-
servoir trend of Poza Rica lying in the subsurface not far to the south of the
Cuesta El Abra outcrops (Fig. XI-7). The Poza Rica trend parallels the western
border of the Golden Lane, curving in an arc for 150 km and lies as much as
1000m structurally lower than the latter. Is this great difference in relief structural
or depositional? The interpretations are (1) that either the Poza Rica trend con-
sists of downwarped (faulted) outer margin (reef knoll) sediments of the Golden
Lane bank whose present hummocky configuration results merely from karst
erosion and faulting or (2) that the Poza Rica trend is formed merely from great
piles of forereef breccia in basinal lime mud. The problems connected with these
interpretations and their significance are discussed by Coogan et al. (1972) who
ascribed to the first view.
The following facts and ideas represent a general consensus despite some
disagreement as to the Poza Rica trend:
1. The Golden Lane platform is an elongate bank of shallow water limestone
(El Abra Formation) tilted gulfward. It is 145 by 65 km in size and its total post-
Jurassic thickness may be about 1500 m. It is Albian and Cenomanian? in age. If
true stratigraphic thickness is accepted for the Jardin 35 well in the Golden Lane,
the El Abra Formation must be 3000 m thick ; if not the thickness could be half
that.