D. Rossetti, P. Mann de Toledo, A.-M. Góes, New geological framework for Western Amazonia (Brazil) and implications for biogeography and evolution, Quaternary Research 63 (2005) 78–89

OSL age determinations of Pleistocene fluvial deposits in Central Amazonia

“…Furthermore, the validity of previous age measurements for these deposits is now questioned, as well as the resolution of the 14 C method being insufficient for accurately dating such older deposits. Also, if collections were taken from areas close to the surface, these deposits could become contaminated by organicrich soil material (Irion et al 2005). Considering these limitation, dating by crystal luminescence has become one of the most promising tools for determining absolute age of diverse Quaternary sedimentary deposits (Suguio et al 2003, Gianinni et al 2003, Barreto et al 2004, D. Bentz, unpublished data, Tatumi et al 2006, including those from fluvial systems (Page et al 1996, Fuller et al 1998, Mozzi et al 2000, Nanson et al 2005, Sylvia and Galloway 2006.…”

New Geological Framework for Western Amazonia (Brazil) and Implications for Biogeography and Evolution

“…In their discussion of our paper on the Miocene to Quaternary geological history of Western Amazonia (Rossetti et al, 2005), Irion et al (2005) raised some interesting points, especially concerning carbon rejuvenation and resulting potential inaccuracies in our age determinations. However, our geologic interpretation did not rely on 14 C dating alone, but on its integration with sedimentologic, geomorphologic and stratigraphic information.…”

“…This model is supported by the main northeastward orientation of faults of Late Pleistocene age, as well as by subsequent drainage capture by northwest/ southeast faults, as mentioned in our paper. We note that formation of the Rio Negro proposed by Irion et al (2005) by deep erosion during glacial lowstands is one model, but an alternative interpretation is that the Rio Negro installed on a major NW-SE fault zone formed in association with W-E strike-slip motion that culminated with a rhombic basin located between this river and the Rio Solimões (Bezerra, 2003). A tectonic origin for the Rio Negro has been confirmed in a recent work (Almeida Filho et al, 1995).…”

“…We are thankful for the timely comments of Irion et al (2005) that have allowed us to clarify certain aspects regarding to the new geological framework proposed for Western Amazonia. Their criticism alerted all to potential pitfalls and the need for further studies, which must be carried out on an integrative scientific basis.…”