Abstract
We present a new 52 m composite record (COL17c) composed of five sedimentary sequences retrieved from the Colônia basin (Southeastern Brazil). The COL17c record is composed of two main sub-units deposited under different regimes: a peatland above ∼14 m and lacustrine sediments below. Sedimentary description and core scanning (MSCL and XRF) are first used to align individual cores in order to produce a nearly continuous composite record. We then established an original chronological framework based on radiocarbon, paleomagnetic, optically stimulated luminescence (OSL), post-infrared infrared stimulated luminescence at elevated temperature (pIRIR290°C) and authigenic 10Be/9Be dating. We describe the protocols used for each technique and discuss the positive and negative results, as well as their implications for proxy interpretation. In spite of negative results of some techniques, mainly due to the absence of adequate sample material, the multi-proxy approach used is essential to maximize the chances of obtaining a satisfactory age model for this unique continental sedimentary sequence. All valid chronological proxies, comprising three AMS 14C ages, one pIRIR290°C age, two paleomagnetic constraints and eight authigenic 10Be/9Be datum, are integrated within a Bayesian age-depth modeling to produce a 1.5 ± 0.1 Ma chronology for the whole COL17c sequence. This age model represents the first long-term chronological estimate of sediments deposition in the Colônia basin. The record allows to refine the age of the Colônia basin formation between 5.3 and 11.2 Ma, much older than previously estimated from short sedimentary cores.