Geology Reference
In-Depth Information
Flügel, E., Kraus, S. (1988): The Lower Permian Sexten Brec-
cia (Sexten Dolomites) and the Tarvis breccia (Carnic
Alps): microfacies, depositional environment and paleo-
tectonic implications. - Memoria della Società Geologica
Italiana,
34
, 67-90
Herbig, H.-G. (1984): Rekonstruktion eines nicht mehr
existierenden Sedimentationsraums - Die Kalkgerölle im
Karbon-Flysch der Malagiden (Betische Kordillere). -
Facies,
11
, 1-108
Pohler, S.M.L., James, N.P. (1989): Reconstruction of a
Lower/Middle Ordovician shelf margin: Cow Head Group,
Western Newfoundland. - Facies,
21
, 189-262
Further reading
: K072, K190
Plate 146 Fingerprinting a Lost Carbonate Platform: Early Carboniferous of the Betic Cordillera, Southern
Spain
The plate displays microfacies types observed in thin sections of limestone boulders of the Late Viséan Marbella
Conglomerate deposited in a deep-water basin. The microfacies of the boulders reflect the microfacies types of
a carbonate shelf adjacent to the Paleozoic Alboran Block (comprising the Betic Cordillera, the internal zones of
the Rif, Menorca, the Chenoua Massif and the Kabylies). Microfacies criteria and the composition and diversity
of biota allow the facies differentiation of an attached platform to be reconstructed (Fig. 16.14).
1
Ooid grainstone.
Microfacies b1. The well-sorted sediment consists of tangential ooids. Most ooid cores are crinoid
debris. Interpretation: Crinoid material has been transported from shallow, moderate energy environments to areas of high
energy forming ooid sand bars. The interpretation is supported by the dominance of tangentially structured ooids and the
occurrence of other stenohaline skeletal grains acting as cores for the ooids.
2
Oolitic dasyclad grainstone.
Microfacies b2. The well-sorted sediment consists predominantly of dasyclads (predomi-
nantly
Eovelebitella
; see Pl. 59/1) with tangential oolitic coatings and some aggregate grains. Interpretation: Dasyclad
material was transported from open shelf lagoon areas to high energy areas forming sand bars.
3
Coated crinoid packstone.
Microfacies b3. Most grains are variously sized, poorly sorted cortoids. The matrix is pelsparite.
Interpretation: Formed in areas of continuous water energy, at the periphery of lime sand bars. Continuous turbulence is
indicated by winnowing, dominance of only a few organism groups that were adapted to shifting substrate, and the
disintegration of crinoid elements.
4
Oncoid rudstone.
Microfacies c1. The large grain is an oncoid formed by cyanobacteria encrusting a shell. Smaller com-
ponents are aggregate grains. Interpretation: Protected and deeper parts of sand areas, formed behind ooid bars. This
interpretation is supported by the occurrence of large cyanoids with sessile foraminifera, the association of oncoids with
aggregate grains and ooids, and the scarcity of biota that are not incorporated within oncoids.
5
Fine-grained foraminiferal grainstone.
Microfacies c2. The sediment consists of bioclasts and peloids. Skeletal grains are
benthic foraminifera and a few calcareous algae and gastropods. Interpretation: Very shallow, moderately energetic sand
areas. The interpretation is based on the composition of the highly diverse foraminiferal fauna comprising more than
50 taxa in some samples of this microfacies.
6
Bioclastic wackestone.
Microfacies e6. The sediment is characterized by an inhomogeneous, micritic and siltitic matrix
and various broken skeletal grains including bryozoans (top and left), shells and some echinoderms. Interpretation: Cen-
tral part of the open shelf lagoon. Below storm wave base. A relatively deep environment is deduced from the occurrence
of open-marine biota (fish remains, conodonts, juvenile ammonites) and the lack of bioturbation.
7
Laminated fenestral mudstone/bindstone.
Microfacies g3. Characteristic features are laterally extended spar-filled fenes-
trae and densely spaced peloids forming irregular layers. Interpretation: Formed in supra- to intertidal restricted bays,
indicated by the fenestral mudstone/bindstone fabrics and the almost total absence of skeletal grains both in thin sections
and in acid residues.
8
Microfacies boundary.
Erosional contact between a grainstone with aggregate grains, amalgamated peloids and skeletal
grains (bottom; microfacies f2) and a fine-grained peloidal grainstone with densely packed peloids (top: microfacies g2).
Interpretation: The microfacies indicates fluctuations of open and restricted circulation. Microfacies g2 is characterized
by biota pointing to higher salinities. Shelf lagoon. Open circulation and well-lighted conditions (microfacies f2) are
deduced from common burrowing and the abundance of algae. Restricted conditions (microfacies g2) are indicated by
low-diversity biota dominated by a few taxa adapted to salinity fluctuations (e.g.
Fasciella,
see Pl. 56/4; calcispheres).
Micrite laminae point to microbial binding of the sediment.
9
Quartz-bearing poorly-sorted ooid grainstone
with radially structured ooids. Microfacies g6a. The irregularly shaped
radial ooids are broken and regenerated. The cores of the ooids are terrigenous quartz grains. Interpretation: The abun-
dance of regenerated radial ooids as well as the scarceness of biota point to a protected, hypersaline environment. The
quartz grains indicate relatively near-coast areas.
