INVESTIGADORES
ALIOTTA Salvador
artículos
Título:
Origen de una roca de playa en la región costera de Bahía Blanca, Argentina.
Autor/es:
SALVADOR ALIOTTA; JORGE O. SPAGNUOLO; ESTER A. FARINATI
Revista:
PESQUISAS EM GEOCIENCIAS
Editorial:
Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brasil
Referencias:
Año: 2009 p. 107 - 116
ISSN:
1518-2398
Resumen:
Abstract - ORIGIN OF A BEACHROCK IN THE COASTAL REGION OF BAHÍA BLANCA, ARGENTINA.
Sedimentological and stratigraphical analysis were carried out in order to determine the
paleoenvironmental conditions that originated a large beachrock outcrop in the northern coast of
the Bahía Blanca estuary, Buenos Aires province, Argentina. This beachrock outcrops along a 2.5-
km-long intertidal, muddy plain with a slight inclination towards the sea (SE). Its calcitecemented
matrix is composed of coarse to very coarse sand and gravel with scarce fragments of
molluscs. Acoustic data reveal a submarine continuity of the sandy sediment forming this
beachrock outcrop. A progradational seismic stratigraphic configuration can be observed at the
subbottom, on Pleistocene materials. The quartzitic gravel of this beachrock evidences the
contribution of the Napostá Chico River, which retracted its base level and reduced its volume
and competency during the Holocene transgression. Littoral drift subsequently redistributed the
material incorporating biogenic remains. This sediment had been buried during transgression,
reached sediment stability. Its porosity favoured the phreatic circulation of saturated solutions
coming from Pleistocene carbonatic sediments. The mixture of continental and marine
groundwaters consolidated the material. Subsequent shallowing of the lithified platform, wave
action and low sedimentation rate left the rock exposed as a result of erosion. The presence of
mud on the intertidal flat, partially covering this beachrock, is indicative of current low-energy
sedimentary conditions.
Sedimentological and stratigraphical analysis were carried out in order to determine the
paleoenvironmental conditions that originated a large beachrock outcrop in the northern coast of
the Bahía Blanca estuary, Buenos Aires province, Argentina. This beachrock outcrops along a 2.5-
km-long intertidal, muddy plain with a slight inclination towards the sea (SE). Its calcitecemented
matrix is composed of coarse to very coarse sand and gravel with scarce fragments of
molluscs. Acoustic data reveal a submarine continuity of the sandy sediment forming this
beachrock outcrop. A progradational seismic stratigraphic configuration can be observed at the
subbottom, on Pleistocene materials. The quartzitic gravel of this beachrock evidences the
contribution of the Napostá Chico River, which retracted its base level and reduced its volume
and competency during the Holocene transgression. Littoral drift subsequently redistributed the
material incorporating biogenic remains. This sediment had been buried during transgression,
reached sediment stability. Its porosity favoured the phreatic circulation of saturated solutions
coming from Pleistocene carbonatic sediments. The mixture of continental and marine
groundwaters consolidated the material. Subsequent shallowing of the lithified platform, wave
action and low sedimentation rate left the rock exposed as a result of erosion. The presence of
mud on the intertidal flat, partially covering this beachrock, is indicative of current low-energy
sedimentary conditions.