The nature of aquatic landscapes in the Miocene of western Amazonia: An integrated palaeontological and geochemical approach

The Miocene Pebas Formation from the section Santa Rosa de Pichana (Loreto, Peru) was investigated using a combination of analyses of sedimentary facies, molluscan communities and taphonomy, and stable isotopes of both entire shells and growth bands in bivalves. Three sequences, comprising a succession of transgressive, maximum flooding and regressive/prograding intervals, are documented. Molluscs are most common in the transgressive/highstand intervals and are almost absent in regressive/prograding intervals. The fauna is dominated by endemic Pebasian species, such as Pachydon and Dyris spp. The nature of the deposits as well as the availability of oxygen varied in a predictable way within each of the sequences and determined the nature of the assemblages. Highest diversity was reached in the late transgressive phase before the development of dysoxia that was widespread during the late highstand and early regressive/prograding phase. The mollusc and isotope data show no indications of elevated salinities, in contrast to ichnofossils found in the section. This discrepancy is interpreted to result either from temporal separation of the ichnofossils and the mollusc fossils or from evolution beyond usual ecological tolerances of taxa that produced these ichnofossils into freshwater settings

Lines of Time : Seasonality, climate and environments of the Miocene Pebas Formation in western Amazonia derived from chemical records in molluscan growth-bands

Hinte, J.E. [Promotor]van Kroon, D. [Promotor]Ganssen, G.M. [Copromotor]Vonhof, H.B. [Copromotor

Ecological implications from geochemical records of Miocene western Amazonian bivalves

Stable-isotope profiles through successive growth increments of Miocene bivalves from Western Amazonia reveal paleobiological characteristics, such as biotope preferences, longevity, and ontogenetic development. Two groups of bivalves, a fluvial and a lacustrine group, are recognized. The fluvial group is composed of pearly freshwater mussels whose isotope profiles are characterized by clearly recognizable cyclicity of considerable amplitude, similar to those from pearly freshwater mussels studied from the modern Amazon region. The lacustrine group, dominated by pachydontine bivalves, is characterized by very low amplitude and irregular isotope signals. Additional trace element analyses show seasonal variation in phase with stable isotope cycles. Seasonal stable isotope cycles show growth rates and longevity in bivalves from the fluvial group but are not clearly expressed in the lacustrine group. The Miocene Pebas ecosystem of Western Amazonia can be characterized as a wetland system of connected shallow lakes, swamps, and tributaries. The stable isotope signatures of fluvial bivalves are good recorders of prior seasonal climate changes, in contrast with those of lacustrine bivalves. © 2005 Elsevier Ltd. All rights reserved

Intra-tooth study of modern rhinoceros enamel δ18O: Is the difference between phosphate and carbonate δ18O a sound diagenetic test?

The carbonate and phosphate oxygen isotopic difference (

The nature of aquatic landscapes in the Miocene of western Amazonia: an integrated palaeontological and geochemical approach

The Miocene Pebas Formation from the section Santa Rosa de Pichana (Loreto, Peru) was investigated using a combination of analyses of sedimentary facies, mollusca