Geology Reference
In-Depth Information
Fig. 16.11. South view of the
Hamar Lakhdad Ridge southeast of
Erfoud, southern Morocco, show-
ing the Early Devonian Kess-Kess
mounds exhumed from the overly-
ing Emsian to Famennian shales
and limestones. The height of the
mounds ranges between 35 and
60 m. The flanks are asymmetrical,
exhibiting a steep slope (about 50°)
and a shallower slope. Most
mounds have similar shapes. Cour-
tesy of W. Buggisch (Erlangen).
Plate 144 Mud Mounds: Early Carboniferous (Lower Mississippian) Muleshoe Mound, Sacramento
Mountains, New Mexico, U.S.A.
The dome-shaped Muleshoe buildup, 12 km SSE of Alamagordo in New Mexico, formed on the outer and
deeper part of a ramp (Ahr 1989), comprises two, superimposed knoll-form 'cores' with a total thickness of
more than 100 m and a width of several hundreds of meters across. The mound consists of a syndepositional
wackestone core facies (100 m thick) flanked by steeply dipping crinoidal beds (Bolton et al. 1982). The lower
slopes of the core facies and the proximal flanks were probably the major growth sites of crinoids at the mound.
Much crinoidal sediment may be essentially in place. The lower part of the central core facies is mud-rich,
lacking porosity and permeability and consisting of skeletal wackestones and lime mudstones with bryozoans
and crinoids, micrite and void-filling cements (-> 8, 9). The upper part of the mound differs in the abundance of
fenestrate bryozoans and sparry calcite (-> 3). The flanking beds (-> 1, 4, 5) are characterized by encrinites
(crinoid packstones) exhibiting abundant solutional grain contacts. The intermound facies consists of skeletal
wackestones (-> 2).
1 Proximal flank facies. Thin-bedded crinoid-bryozoan limestone. Eastern slope, lower part.
2 Mound base. Sediment below the mud mound. Interbedding of thin-bedded crinoid-bryozoan limestone beds and marls.
Grains are bryozoan fragments and crinoids.
3 Upper mound facies. Clast of a megabreccia deposited as debris flow along the flanks of the mound. The clast was
derived from the upper core facies, as indicated by bryozoans embedded in micrite and the void-filling cement.
4 Flank facies. Thick-bedded crinoid limestone. Flank facies, interfingering with massive micritic core facies. Note com-
paction and stylolitic boundaries (arrows) between crinoid fragments. The biofabric of the sample is characterized by
dense packing of abundant crinoidal elements. Proximal facies of the eastern slope, higher part.
5 Flank Facies. Bedded crinoid limestone. The flank facies interfingers with the massive upper core facies. Moderately
sorted crinoid packstone. The arrows point to syntaxial echinoderm rim cement. Western slope.
6 Upper mound facies. Massive limestone of the central part of the upper mound facies. Poorly sorted crinoid packstone. In
contrast to -> 5, syntaxial cement is absent, indicating differences in primary intergranular porosities.
7 Upper mound facies. Massive limestone. Central part of the upper mound core facies. Bryozoan-crinoid wackestone.
Fistuliporid bryozoans (FB) are parautochthonous.
8 Lower mound facies. Hard, massive limestone. Mound facies. Some of the core facies are mudstones and wackestones
poor in fossils. Common fossils are bryozoans and in places brachiopods.
9 Lower mound facies. Hard massive limestone. Mound facies. Burrowed bioclastic wackestone. Skeletal grains are echi-
noderms (E), bryozoans (B), ostracods (O) and sponge spicules. The micritic matrix is inhomogeneous and contains a
high proportion of fine-bioclastic and peloidal particles.
10 Mound facies. Dark massive limestones with open-space structures (not shown). Interfingering of the upper mound
facies with crinoid-rich grainstones and wackestones of the flank facies. Burrowed wackestone with crinoids and
cryptostome bryozoans ( Rhombopora , R).
Search WWH ::




Custom Search