CHAPTER 7 . Hydrography and Sediment Transport Characteristics of the Rio de la Plata
139
Canal Oriental: A long depression extending, with E-W direction, from the East of the
Canal Norte (from which it is separated by the Umbral de Cufn!) up to the vicinity of
Punta del Este where its direction changes to the NE and it deepens abruptly. Here it
is known as "Mud Wells" ("Pozos de Fango").
Barra del Indio: A gentle and wide plain extending to the NE from the Argentinean
coast between Punta Indio and Punta Piedras. Morphologically it corresponds to a
gentle convex and subhorizontal surface with depths ranging from 6.5-7 m. It is a recent and clayey aggradation form.
Franja Costera Sur: The Argentinean coastal area located between the Lujan River and
Cabo San Antonio, representing an inclined plane extending from the coast up to the
6-9 m isobath.
Alto Maritimo: The outer Rio de la Plata region containing the Ingles, Arquimedes and
Rouen banks; the first two represents stable areas.
Umbral de Samboromb6n: A triangular surface determined by a slope change interposed between the center of Samborombon Bay and the Canal Maritimo.
Canal Maritimo: A widespread and gentle depression, with asymmetrical profile, extending between Barra del Indio, Franja Costera Sur, Umbral de Samborombon and
Alto Maritimo.
7.3.2
Surficial Bottom Sediments
The Rio de la Plata surficial bottom sediments (Urien 1966; 1967; 1972; Parker et al.
1985; Lopez Laborde 1987a,b; Parker and Lopez Laborde 1989) exhibit a graded distribution with sands in the river watersheds, silts in the middle river and clayey silts
in the mouth, where they overlap relict Holocene sands (Urien 1967). The facies distribution is longitudinal, following the main flow directions: parallel to the coast in
the upper and middle river, whilst in the outer river they form a parabolic arch (Parker
et al. 1985).
According to Parker et al. (1985), in the upper and middle river it is possible to distinguish, along the coasts, two facies associations that are texturally interconnected
and formed by sediments with mean diameter decreasing to the SE:
1. along the northern coast the Uruguay and Parana Guazu Rivers discharge towards
Playa Honda there is an association of sands and silty sands, grading to silty sands
and silts in the Banco Grande de Ortiz, and then to silts, clayey silts and even silty
clays in the outer region, and
2. along the southern coast from the mouth of Lujan and Parana de las Palm as Rivers, finer textured sediments are observed, with greater organic carbon content
(Hallcrow 1965), sediments spreads over the coast, forming an unique unit of sandy
silts and silts grading to silty clays.
139
Canal Oriental: A long depression extending, with E-W direction, from the East of the
Canal Norte (from which it is separated by the Umbral de Cufn!) up to the vicinity of
Punta del Este where its direction changes to the NE and it deepens abruptly. Here it
is known as "Mud Wells" ("Pozos de Fango").
Barra del Indio: A gentle and wide plain extending to the NE from the Argentinean
coast between Punta Indio and Punta Piedras. Morphologically it corresponds to a
gentle convex and subhorizontal surface with depths ranging from 6.5-7 m. It is a recent and clayey aggradation form.
Franja Costera Sur: The Argentinean coastal area located between the Lujan River and
Cabo San Antonio, representing an inclined plane extending from the coast up to the
6-9 m isobath.
Alto Maritimo: The outer Rio de la Plata region containing the Ingles, Arquimedes and
Rouen banks; the first two represents stable areas.
Umbral de Samboromb6n: A triangular surface determined by a slope change interposed between the center of Samborombon Bay and the Canal Maritimo.
Canal Maritimo: A widespread and gentle depression, with asymmetrical profile, extending between Barra del Indio, Franja Costera Sur, Umbral de Samborombon and
Alto Maritimo.
7.3.2
Surficial Bottom Sediments
The Rio de la Plata surficial bottom sediments (Urien 1966; 1967; 1972; Parker et al.
1985; Lopez Laborde 1987a,b; Parker and Lopez Laborde 1989) exhibit a graded distribution with sands in the river watersheds, silts in the middle river and clayey silts
in the mouth, where they overlap relict Holocene sands (Urien 1967). The facies distribution is longitudinal, following the main flow directions: parallel to the coast in
the upper and middle river, whilst in the outer river they form a parabolic arch (Parker
et al. 1985).
According to Parker et al. (1985), in the upper and middle river it is possible to distinguish, along the coasts, two facies associations that are texturally interconnected
and formed by sediments with mean diameter decreasing to the SE:
1. along the northern coast the Uruguay and Parana Guazu Rivers discharge towards
Playa Honda there is an association of sands and silty sands, grading to silty sands
and silts in the Banco Grande de Ortiz, and then to silts, clayey silts and even silty
clays in the outer region, and
2. along the southern coast from the mouth of Lujan and Parana de las Palm as Rivers, finer textured sediments are observed, with greater organic carbon content
(Hallcrow 1965), sediments spreads over the coast, forming an unique unit of sandy
silts and silts grading to silty clays.