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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 888

Last Page: 889

Title: Early Cretaceous Sedimentation in Peruvian Andes: ABSTRACT

Author(s): Antenor M. Aleman

Article Type: Meeting abstract


Continuous Early Cretaceous marine sedimentation is recorded in the Lima basin prior to the development of a Late Cretaceous volcanic arc. An abrupt change in source and tectonic

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style of sedimentation occurred in the middle Berriasian from arc-derived to basement-derived sediment. These changes are ascribed to a decrease in the angle of subduction, which caused a cessation of volcanism and widespread uplift of basement rocks. Sedimentation and subsidence continued only along the frontal-arc and rear-arc due to thermally induced subsidence. Away from the arc, sedimentation was initiated diachronously after regional unconformity, and subsidence was mainly controlled by the rate of sedimentation.

Two subparallel metamorphic belts were the main source terranes for the Morro Solar Group, which was deposited in a tectonically quiescent basin. The Brazilian shield furnished sediment only to the foreland basin. A complex distribution of source terranes gave rise to nonsystematic distribution of environments along and across the Andes. Fluviodeltaic and shallow-marine peritidal sedimentation characterizes most of the lowermost Cretaceous strata in the Peruvian Andes.

In the Lima basin, the Morro Solar Group consists of quartz-rich sandstone, shale, and minor micritic limestone beds. Sandstones are highly mature and exhibit cross-bedding that suggests paleosediment transport to the southeast. Shale units are thinly laminated and contain minor interbedded siltstone. Vertical facies variation suggests progradation of a braided system toward a broad intertidal zone prior to encroachment of the late Valanginian sea.

Lower Neocomian siliciclastic sedimentation in the Peruvian Andes is consistent with earlier facies developed in the initial stages of fore-arc evolution prior to the emplacement and localization of the volcanic arc. Continuous Mesozoic continental erosion not only accounts for the lack of an accretionary wedge, but also for the landward migration of the trench and uplifting of metamorphic cores. These processes resulted in a shortening of the fore-arc basin.

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