[an error occurred while processing this directive]

Geological evolution of the Subandean foothills basins and the inter-relation of facies development and tectonics in South America

South America comprises a large part of the Mesozoic Gondwana craton, consolidated during the Precambrian. Three main types of Phanerozoic sedimentary basin are associated with it.

·         Its eastern margin is formed by a string of Mesozoic to Tertiary passive margin basins which were formed as a result continental rifting and the subsequent separation from Africa with the formation of the Atlantic Ocean.

·         Within the South American continent a number of interior sag basins, mainly of Palaeozoic age, are developed.

·         Its western flank is defined by the Tertiary fold mountains if the Andes, which overlie an active zone of compressional deformation where Pacific crust is being subducted below the continent margin. The Andes are bounded to the east by a string of foreland-foredeep basins known as the Subandean basins, which have a complex Phanerozoic tecto-stratigraphic history.

In this lecture we shall make a broad regional review of the sedimentary evolution of the Subandean basins and, with the help of a series of palaeogeographic maps, trace the complex interrelationship between facies and tectonics from the Cambrian to the present-day. During this history we shall see the gradual evolution from extensional basins through passive continent margin basins into today’s foreland basins, separated from the open ocean by a massive mountain chain. The complex, often confusing and controversial impact on the geology of processes like variable speeds of ocean-floor spreading, widespread translational movements, hot-spot trails and climatic changes will be discussed. Since the Subandean basins host some of the most prolific hydrocarbon accumulations in the World, we shall also examine how the tecto-stratigraphic development has had an impact on oil and gas prospectivity.

The western edges of the Subandean basins are incorporated on the Andean fold and thrust belt, and we shall examine the various structural styles that characterize the basins from Venezuela in the north to Chile in the south. Significant differences are observed between those in which basement is involved in the thrusting (thick-skinned) and those in which the thrusting is detached from basement (thin-skinned). Especially in the areas where basement is involved, the influence of Andean tectonics can be traced far across the South American continent. Thus, in the Palaeozoic Amazon basins, we can see widespread evidence for Mesozoic inversion and crustal stretching.

An open question that can be posed is whether early Andean movements had any structural impact on Atlantic margin rift development. Certainly the uplift of the mountain chain led to a fundamental reversal of drainage in the Subandean basins. Prior to the end of the Cretaceous, most drainage was directed westwards, but during the early Tertiary uplift phases it switched to the east. This led to the formation of the huge Amazonian catchment and river system, which today carries vast quantities of clastic sediments from the rising Andes into the Atlantic Ocean, more than 3000km from its source.

back
[an error occurred while processing this directive]