IANIGLA   20881
INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Coral facies of the La Manga Formation at Portada Covunco, Neuquén Basin, Argentina.
Autor/es:
BERESI M.S., CABALERI N.G. AND ARMELLA C.,
Lugar:
Buenos Aires
Reunión:
Congreso; XII Reunión Argentina de Sedimentología; 2008
Institución organizadora:
Asociación Sedimentológica Argentina
Resumen:
Coral facies of the La Manga Formation at Portada Covunco, Neuquén Basin,
Argentina
Matilde S. Beresi1, Nora G. Cabaleri2 and Claudia Armella21, Nora G. Cabaleri2 and Claudia Armella2
1- CCT-CONICET Mendoza,A.Ruiz Leal s/n Parque Gral. San Martín, 5500 Mendoza.
mberesi@lab.cricyt.edu.,ar
2- CONICET-UBA. Pabellón Ingeis. Ciudad Universitaria. C1428EHA, C. A. de
Buenos Aires. cabaleri@ingeis.uba.ar
During the Late Oxfordian, the Neuquén epicontinental shelf was the site of major coralline
evolution and reef building (Legarreta, 1991). The colonial scleractinid corals contributed with their
skeletons to an extensive and impressive reef development in high latitudinal position suggesting an
equilibrated climate. Shallow, warm and relatively clear water enabled the growth and spread of reef
corals (Matheos and Morsh, 1990). They extend along the southernmost part of the Sierra de la Vaca
Muerta, about 400 m long, reaching a thickness of 8 m. The reef coral facies of the La Manga Fm. at
Portada Covunco, were studied. The bioherms are basically composed of massive, platy, branching, and
phaceloid scleractinian over solitary corals that built the framework, accompanied by a variety of
microencrusting and boring metazoans (algae, lithophagus bivalves, Tubiphytes and serpulids). The vertical
successions of coral morphotypes represent a shallowing upward trend evidenced by a gradual transition
from finger-like colonies to laminar, platy coral. In the associated microfacies a general coarsening
upward trend from peloid mudstones to bioclastic wacke/pack/floastones and finally grain/rudstones is
also detectable. The result of microfacies analysis shows that about 40 % can be considered as coral
framestones whereas about 60 % consist of peloid-bioclast-lithoclast-ooid wackestones-packstones to
grainstones. The microfacies model suggests an oolithic sand shoal area (packstone ooidal - MF1-) in the
highest energy zone and five small coral patch reefs (lens shaped) with similar constructional and
compositional reef types that intercalate in a succession of limestones and marls, developed on a
carbonate ramp. The first stage of coral patch reef growth is characterized by the almost exclusive thin
laminoid, platy (microsolenids) coral framestones (MF3) in a peloidal mudstone matrix (MF2). Boring
metazoans affected the upper part of the colonies. The middle part consists of bioclastic coral-sponge
wackestones/packstones (MF4) and a layer of calcareous marls with small siliceous sponges and scarce
solitary corals accumulated in depressions. Platy corals and bioclastic dasycladacean-packstones (MF5)
occur at the top of the bioherm. The second stage is characterized by a framestone of flabellatemeandriforme
and platy coral colonies with microbial crusts growing on the top of the colonies (MF6) in
bioclastic wackestones. Intersticial material is a floastone with coral debris, bioclasts and siliciclastic
grains (MF 7). Microbial-crusts point to low energy conditions for the top part of this coral patch reef. In
the third stage there are bafflestones of phaceloid colonies of dense, tall finger-like coral in calcareous
marls (MF8); mudstones/fine bioclastic wackestones. Reefal debris are represented by platy coral
rudstones with 5 % of siliciclastic grains. The fourth stage is characterized by a small algal-patch reef of
phylloid algal boundstone (MF 9) in microbial-bioclastic wackestones with aligned bioclasts and dark
algal laminae. Reefal boundstone shows a fine-grained fabric with interwoven filaments forming crust up
to several millimeters thick within a micritic matrix with differences in colorations. This alga points to
very shallow conditions for the top-most part of this patch reef. Irregular channels are infilled with
bioclastic-serpulids-wackestone with oriented small fragments. The fifth stage is the more fully
preserved coral reef within the area, characterized by low diversity of corals with dominance of tabularplaty
coral which is replaced upwards by tall, dense, phaceloid colonies. Such succession is repeated
several times. In the middle part of the reef grey calcareous marls with ramose corals, echinoids and small
siliceous sponges occur. The intersticial material between corals is a bioclastic-pelecypods-wackestone
matrix with serpulids. Towards the top of the reef, tabular-platy corals, bioclastic-packstones and
lithoclastic-grainstones point to shallower depositional conditions.
Legarreta, L. 1991. Evolution of a Callovian-Oxfordian carbonate margin in the Neuquén Basin of westcentral
Argentina: facies, architecture, depositional sequences and global sea-level changes. Sedimentary
Geology, 70: 209-240Tubiphytes and serpulids). The vertical
successions of coral morphotypes represent a shallowing upward trend evidenced by a gradual transition
from finger-like colonies to laminar, platy coral. In the associated microfacies a general coarsening
upward trend from peloid mudstones to bioclastic wacke/pack/floastones and finally grain/rudstones is
also detectable. The result of microfacies analysis shows that about 40 % can be considered as coral
framestones whereas about 60 % consist of peloid-bioclast-lithoclast-ooid wackestones-packstones to
grainstones. The microfacies model suggests an oolithic sand shoal area (packstone ooidal - MF1-) in the
highest energy zone and five small coral patch reefs (lens shaped) with similar constructional and
compositional reef types that intercalate in a succession of limestones and marls, developed on a
carbonate ramp. The first stage of coral patch reef growth is characterized by the almost exclusive thin
laminoid, platy (microsolenids) coral framestones (MF3) in a peloidal mudstone matrix (MF2). Boring
metazoans affected the upper part of the colonies. The middle part consists of bioclastic coral-sponge
wackestones/packstones (MF4) and a layer of calcareous marls with small siliceous sponges and scarce
solitary corals accumulated in depressions. Platy corals and bioclastic dasycladacean-packstones (MF5)
occur at the top of the bioherm. The second stage is characterized by a framestone of flabellatemeandriforme
and platy coral colonies with microbial crusts growing on the top of the colonies (MF6) in
bioclastic wackestones. Intersticial material is a floastone with coral debris, bioclasts and siliciclastic
grains (MF 7). Microbial-crusts point to low energy conditions for the top part of this coral patch reef. In
the third stage there are bafflestones of phaceloid colonies of dense, tall finger-like coral in calcareous
marls (MF8); mudstones/fine bioclastic wackestones. Reefal debris are represented by platy coral
rudstones with 5 % of siliciclastic grains. The fourth stage is characterized by a small algal-patch reef of
phylloid algal boundstone (MF 9) in microbial-bioclastic wackestones with aligned bioclasts and dark
algal laminae. Reefal boundstone shows a fine-grained fabric with interwoven filaments forming crust up
to several millimeters thick within a micritic matrix with differences in colorations. This alga points to
very shallow conditions for the top-most part of this patch reef. Irregular channels are infilled with
bioclastic-serpulids-wackestone with oriented small fragments. The fifth stage is the more fully
preserved coral reef within the area, characterized by low diversity of corals with dominance of tabularplaty
coral which is replaced upwards by tall, dense, phaceloid colonies. Such succession is repeated
several times. In the middle part of the reef grey calcareous marls with ramose corals, echinoids and small
siliceous sponges occur. The intersticial material between corals is a bioclastic-pelecypods-wackestone
matrix with serpulids. Towards the top of the reef, tabular-platy corals, bioclastic-packstones and
lithoclastic-grainstones point to shallower depositional conditions.
Legarreta, L. 1991. Evolution of a Callovian-Oxfordian carbonate margin in the Neuquén Basin of westcentral
Argentina: facies, architecture, depositional sequences and global sea-level changes. Sedimentary
Geology, 70: 209-240. The microfacies model suggests an oolithic sand shoal area (packstone ooidal - MF1-) in the
highest energy zone and five small coral patch reefs (lens shaped) with similar constructional and
compositional reef types that intercalate in a succession of limestones and marls, developed on a
carbonate ramp. The first stage of coral patch reef growth is characterized by the almost exclusive thin
laminoid, platy (microsolenids) coral framestones (MF3) in a peloidal mudstone matrix (MF2). Boring
metazoans affected the upper part of the colonies. The middle part consists of bioclastic coral-sponge
wackestones/packstones (MF4) and a layer of calcareous marls with small siliceous sponges and scarce
solitary corals accumulated in depressions. Platy corals and bioclastic dasycladacean-packstones (MF5)
occur at the top of the bioherm. The second stage is characterized by a framestone of flabellatemeandriforme
and platy coral colonies with microbial crusts growing on the top of the colonies (MF6) in
bioclastic wackestones. Intersticial material is a floastone with coral debris, bioclasts and siliciclastic
grains (MF 7). Microbial-crusts point to low energy conditions for the top part of this coral patch reef. In
the third stage there are bafflestones of phaceloid colonies of dense, tall finger-like coral in calcareous
marls (MF8); mudstones/fine bioclastic wackestones. Reefal debris are represented by platy coral
rudstones with 5 % of siliciclastic grains. The fourth stage is characterized by a small algal-patch reef of
phylloid algal boundstone (MF 9) in microbial-bioclastic wackestones with aligned bioclasts and dark
algal laminae. Reefal boundstone shows a fine-grained fabric with interwoven filaments forming crust up
to several millimeters thick within a micritic matrix with differences in colorations. This alga points to
very shallow conditions for the top-most part of this patch reef. Irregular channels are infilled with
bioclastic-serpulids-wackestone with oriented small fragments. The fifth stage is the more fully
preserved coral reef within the area, characterized by low diversity of corals with dominance of tabularplaty
coral which is replaced upwards by tall, dense, phaceloid colonies. Such succession is repeated
several times. In the middle part of the reef grey calcareous marls with ramose corals, echinoids and small
siliceous sponges occur. The intersticial material between corals is a bioclastic-pelecypods-wackestone
matrix with serpulids. Towards the top of the reef, tabular-platy corals, bioclastic-packstones and
lithoclastic-grainstones point to shallower depositional conditions.
Legarreta, L. 1991. Evolution of a Callovian-Oxfordian carbonate margin in the Neuquén Basin of westcentral
Argentina: facies, architecture, depositional sequences and global sea-level changes. Sedimentary
Geology, 70: 209-240first stage of coral patch reef growth is characterized by the almost exclusive thin
laminoid, platy (microsolenids) coral framestones (MF3) in a peloidal mudstone matrix (MF2). Boring
metazoans affected the upper part of the colonies. The middle part consists of bioclastic coral-sponge
wackestones/packstones (MF4) and a layer of calcareous marls with small siliceous sponges and scarce
solitary corals accumulated in depressions. Platy corals and bioclastic dasycladacean-packstones (MF5)
occur at the top of the bioherm. The second stage is characterized by a framestone of flabellatemeandriforme
and platy coral colonies with microbial crusts growing on the top of the colonies (MF6) in
bioclastic wackestones. Intersticial material is a floastone with coral debris, bioclasts and siliciclastic
grains (MF 7). Microbial-crusts point to low energy conditions for the top part of this coral patch reef. In
the third stage there are bafflestones of phaceloid colonies of dense, tall finger-like coral in calcareous
marls (MF8); mudstones/fine bioclastic wackestones. Reefal debris are represented by platy coral
rudstones with 5 % of siliciclastic grains. The fourth stage is characterized by a small algal-patch reef of
phylloid algal boundstone (MF 9) in microbial-bioclastic wackestones with aligned bioclasts and dark
algal laminae. Reefal boundstone shows a fine-grained fabric with interwoven filaments forming crust up
to several millimeters thick within a micritic matrix with differences in colorations. This alga points to
very shallow conditions for the top-most part of this patch reef. Irregular channels are infilled with
bioclastic-serpulids-wackestone with oriented small fragments. The fifth stage is the more fully
preserved coral reef within the area, characterized by low diversity of corals with dominance of tabularplaty
coral which is replaced upwards by tall, dense, phaceloid colonies. Such succession is repeated
several times. In the middle part of the reef grey calcareous marls with ramose corals, echinoids and small
siliceous sponges occur. The intersticial material between corals is a bioclastic-pelecypods-wackestone
matrix with serpulids. Towards the top of the reef, tabular-platy corals, bioclastic-packstones and
lithoclastic-grainstones point to shallower depositional conditions.
Legarreta, L. 1991. Evolution of a Callovian-Oxfordian carbonate margin in the Neuquén Basin of westcentral
Argentina: facies, architecture, depositional sequences and global sea-level changes. Sedimentary
Geology, 70: 209-240second stage is characterized by a framestone of flabellatemeandriforme
and platy coral colonies with microbial crusts growing on the top of the colonies (MF6) in
bioclastic wackestones. Intersticial material is a floastone with coral debris, bioclasts and siliciclastic
grains (MF 7). Microbial-crusts point to low energy conditions for the top part of this coral patch reef. In
the third stage there are bafflestones of phaceloid colonies of dense, tall finger-like coral in calcareous
marls (MF8); mudstones/fine bioclastic wackestones. Reefal debris are represented by platy coral
rudstones with 5 % of siliciclastic grains. The fourth stage is characterized by a small algal-patch reef of
phylloid algal boundstone (MF 9) in microbial-bioclastic wackestones with aligned bioclasts and dark
algal laminae. Reefal boundstone shows a fine-grained fabric with interwoven filaments forming crust up
to several millimeters thick within a micritic matrix with differences in colorations. This alga points to
very shallow conditions for the top-most part of this patch reef. Irregular channels are infilled with
bioclastic-serpulids-wackestone with oriented small fragments. The fifth stage is the more fully
preserved coral reef within the area, characterized by low diversity of corals with dominance of tabularplaty
coral which is replaced upwards by tall, dense, phaceloid colonies. Such succession is repeated
several times. In the middle part of the reef grey calcareous marls with ramose corals, echinoids and small
siliceous sponges occur. The intersticial material between corals is a bioclastic-pelecypods-wackestone
matrix with serpulids. Towards the top of the reef, tabular-platy corals, bioclastic-packstones and
lithoclastic-grainstones point to shallower depositional conditions.
Legarreta, L. 1991. Evolution of a Callovian-Oxfordian carbonate margin in the Neuquén Basin of westcentral
Argentina: facies, architecture, depositional sequences and global sea-level changes. Sedimentary
Geology, 70: 209-240third stage there are bafflestones of phaceloid colonies of dense, tall finger-like coral in calcareous
marls (MF8); mudstones/fine bioclastic wackestones. Reefal debris are represented by platy coral
rudstones with 5 % of siliciclastic grains. The fourth stage is characterized by a small algal-patch reef of
phylloid algal boundstone (MF 9) in microbial-bioclastic wackestones with aligned bioclasts and dark
algal laminae. Reefal boundstone shows a fine-grained fabric with interwoven filaments forming crust up
to several millimeters thick within a micritic matrix with differences in colorations. This alga points to
very shallow conditions for the top-most part of this patch reef. Irregular channels are infilled with
bioclastic-serpulids-wackestone with oriented small fragments. The fifth stage is the more fully
preserved coral reef within the area, characterized by low diversity of corals with dominance of tabularplaty
coral which is replaced upwards by tall, dense, phaceloid colonies. Such succession is repeated
several times. In the middle part of the reef grey calcareous marls with ramose corals, echinoids and small
siliceous sponges occur. The intersticial material between corals is a bioclastic-pelecypods-wackestone
matrix with serpulids. Towards the top of the reef, tabular-platy corals, bioclastic-packstones and
lithoclastic-grainstones point to shallower depositional conditions.
Legarreta, L. 1991. Evolution of a Callovian-Oxfordian carbonate margin in the Neuquén Basin of westcentral
Argentina: facies, architecture, depositional sequences and global sea-level changes. Sedimentary
Geology, 70: 209-240fourth stage is characterized by a small algal-patch reef of
phylloid algal boundstone (MF 9) in microbial-bioclastic wackestones with aligned bioclasts and dark
algal laminae. Reefal boundstone shows a fine-grained fabric with interwoven filaments forming crust up
to several millimeters thick within a micritic matrix with differences in colorations. This alga points to
very shallow conditions for the top-most part of this patch reef. Irregular channels are infilled with
bioclastic-serpulids-wackestone with oriented small fragments. The fifth stage is the more fully
preserved coral reef within the area, characterized by low diversity of corals with dominance of tabularplaty
coral which is replaced upwards by tall, dense, phaceloid colonies. Such succession is repeated
several times. In the middle part of the reef grey calcareous marls with ramose corals, echinoids and small
siliceous sponges occur. The intersticial material between corals is a bioclastic-pelecypods-wackestone
matrix with serpulids. Towards the top of the reef, tabular-platy corals, bioclastic-packstones and
lithoclastic-grainstones point to shallower depositional conditions.
Legarreta, L. 1991. Evolution of a Callovian-Oxfordian carbonate margin in the Neuquén Basin of westcentral
Argentina: facies, architecture, depositional sequences and global sea-level changes. Sedimentary
Geology, 70: 209-240fifth stage is the more fully
preserved coral reef within the area, characterized by low diversity of corals with dominance of tabularplaty
coral which is replaced upwards by tall, dense, phaceloid colonies. Such succession is repeated
several times. In the middle part of the reef grey calcareous marls with ramose corals, echinoids and small
siliceous sponges occur. The intersticial material between corals is a bioclastic-pelecypods-wackestone
matrix with serpulids. Towards the top of the reef, tabular-platy corals, bioclastic-packstones and
lithoclastic-grainstones point to shallower depositional conditions.
Legarreta, L. 1991. Evolution of a Callovian-Oxfordian carbonate margin in the Neuquén Basin of westcentral
Argentina: facies, architecture, depositional sequences and global sea-level changes. Sedimentary
Geology, 70: 209-240