PRELIMINARY SEDIMENTOLOGICAL, PALEONTOLOGICAL, AND GEOCHEMICAL ANALYSES OF THE CENOZOIC SUB-ANDEAN ZONE, MADRE DE DIOS, PERU

Sediments of the Andean foreland that are presently exposed in the Peruvian Sub-andean zone record the history of the Amazon throughout much of the Cenozoic. These deposits record changes in sedimentary environment influenced by the uplift of the Andes, changes in biotic composition due to the evolution of the Neotropical rainforest, and changes in the regional climate that were influenced by Andean uplift, biotic evolution, and global climate evolution. However, these sediments are generally difficult to access and most of their scarce outcrops are covered and deeply weathered. Thus, we still know very little about the nature of these sediments, their ages, their depositional and paleoenvironmental settings, and their significance in addressing long-standing questions such as the Pebas mega-wetland or the marine incursions hypotheses.

We have undertaken preliminary field studies on a series of outcrops exposed along the Alto Madre de Dios River, the Manu River, and the Pantiacolla River, and in road cuts along the Transamazon Highway between the towns of Quincemil and Mazuko. These outcrops were described in detail for sediment composition, sedimentary structures, paleo-environment determination, and fossil content. Samples were taken for zircon provenance analysis, petrographic analysis, and for stable isotope composition of paleosol carbonates and organic matter. Samples were also collected for pollen analysis to provide palynostratigraphic age determination and to aid in paleoenvironmental reconstruction. Vertebrate fossils were collected and screen washed in the field. Vertebrate fossils will be identified and should allow refinement of biostratigraphic age control and paleoenvironmental reconstruction. Preliminary results from the fossil fauna indicate an age range of Early Miocene to Pliocene and deposition in a fluvial (not marine or tidal) environment.