10
J.N. Kellogg and W.U. Mohriak
Subsequent subduction erosion or strike-slip faulting eliminated large
pieces of the Paleozoic forearc assemblages. The central and southern
Andean region experienced severe deformation during the Middle to Late
Cretaceous, including arc-continent collision and over 100 km of convergence (Vicente 1989). In pre-Miocene time, the western half of the present
Amazon watershed is inferred to have had at least one large, westernflowing river called "Sanozama"- Amazonas spelled backward (de Almeida 1974). Some of these sediments were deposited in sedimentary basins
up to 5,000 m thick on the subsiding Pacific continental shelf near the
Guayaquil Gap.
Uplift in the region of the Altiplano began around 25 Ma, coincident
with an increased plate convergence rate (Allmendinger et al. 1997).
Shortening slowed in the Altiplano and shifted eastward beginning
between 12 and 6 Ma. The base of the upper slope off northern Peru subsided to lower bathyal water depths by middle Miocene time. Thus, the seaward edge of the continent subsided at least 2 km during the early stages of
the uplift of the modern Andes. This subsidence suggests a subduction
zone dominated by subcrustal tectonic erosion rather than accretion. Sedimentation in the forearc basins of Peru records the detailed oceanographic
history of one of the best-developed coastal upwelling regimes. Tectonic
subsidence of the Lima Basin since late Miocene has resulted in a 100-kmeastward movement of coastal upwelling.
4 The North Andean and Caribbean Margins
4.1 Geomorphology and Active Tectonics
The Cordillera Occidental (Western Cordillera) and coastal range (Serrania de Baudo) of Colombia are part of the Basic Igneous Complex, which is
one of the world's largest ophiolitic complexes, extending from Costa Rica
through Panama and Colombia to Ecuador.
The Caribbean margins of Panama, Colombia, and Venezuela consist of
extensive fold belts (Case 1974; Bowin 1976) which are part of a deformed
zone extending from Costa Rica to eastern Venezuela. Up to 10 km of Tertiary turbidites, carbonates, and fluvial and lacustrine sediments have been
preserved in the deformed belt in northern Colombia (Duque-Caro 1979).
The North Panama and North Colombia fold belts are characterized by
numerous volcanoes that are formed by overpressured Miocene muds and
occasionally capped with reefs.
J.N. Kellogg and W.U. Mohriak
Subsequent subduction erosion or strike-slip faulting eliminated large
pieces of the Paleozoic forearc assemblages. The central and southern
Andean region experienced severe deformation during the Middle to Late
Cretaceous, including arc-continent collision and over 100 km of convergence (Vicente 1989). In pre-Miocene time, the western half of the present
Amazon watershed is inferred to have had at least one large, westernflowing river called "Sanozama"- Amazonas spelled backward (de Almeida 1974). Some of these sediments were deposited in sedimentary basins
up to 5,000 m thick on the subsiding Pacific continental shelf near the
Guayaquil Gap.
Uplift in the region of the Altiplano began around 25 Ma, coincident
with an increased plate convergence rate (Allmendinger et al. 1997).
Shortening slowed in the Altiplano and shifted eastward beginning
between 12 and 6 Ma. The base of the upper slope off northern Peru subsided to lower bathyal water depths by middle Miocene time. Thus, the seaward edge of the continent subsided at least 2 km during the early stages of
the uplift of the modern Andes. This subsidence suggests a subduction
zone dominated by subcrustal tectonic erosion rather than accretion. Sedimentation in the forearc basins of Peru records the detailed oceanographic
history of one of the best-developed coastal upwelling regimes. Tectonic
subsidence of the Lima Basin since late Miocene has resulted in a 100-kmeastward movement of coastal upwelling.
4 The North Andean and Caribbean Margins
4.1 Geomorphology and Active Tectonics
The Cordillera Occidental (Western Cordillera) and coastal range (Serrania de Baudo) of Colombia are part of the Basic Igneous Complex, which is
one of the world's largest ophiolitic complexes, extending from Costa Rica
through Panama and Colombia to Ecuador.
The Caribbean margins of Panama, Colombia, and Venezuela consist of
extensive fold belts (Case 1974; Bowin 1976) which are part of a deformed
zone extending from Costa Rica to eastern Venezuela. Up to 10 km of Tertiary turbidites, carbonates, and fluvial and lacustrine sediments have been
preserved in the deformed belt in northern Colombia (Duque-Caro 1979).
The North Panama and North Colombia fold belts are characterized by
numerous volcanoes that are formed by overpressured Miocene muds and
occasionally capped with reefs.