Reconstructing Miocene Paleoclimate through Paleosol Analysis in the Acre Basin

• Grant number: 25/01906-0
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• Start date: January 01, 2026
• End date: March 31, 2030
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: André Marconato
• Grantee: Rafaela Maciel Lopes de Paula
• Host Institution: Instituto de Geociências (IGC). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

The Acre Basin contains a Miocene sedimentary record characterized by silty-sandy deposits with red and greenish bands, containing nodules and concretions. These deposits, associated with the Solimões Formation, which extends across several basins in Brazil and related units in eastern Peru, preserve one of the most important records of the transition from an extensive wetland area to a transcontinental river system. This transition, crucial for the reorganization of the Amazonian landscape and biodiversity, is documented in these deposits, which also contain abundant vertebrate, invertebrate, and palynomorph fossils. Although various paleoclimatic indicators have been used for environmental reconstructions, paleosols stand out as particularly powerful tools in continental contexts because they continuously integrate and record the climatic and environmental conditions prevailing during their formation. However, the origin and evolution of paleosols in the Solimões Formation remain poorly studied, representing a significant gap in understanding the paleoclimate of the western Amazon. The objective of this doctoral project is to conduct a detailed and quantitative investigation of the paleoclimate and paleoenvironment at the end of the Miocene in the Acre Basin. To this end, paleosols from the Solimões Formation will be analyzed using samples obtained from the Trans-Amazon Drilling Project (TADP-1A) and outcrops along the Juruá River. The analysis will adopt a multidisciplinary approach, beginning with macro- and micromorphological characterization. Based on these observations, complementary analytical techniques will be applied, including geochemical analyses, clay mineralogy, isotopic analyses, and magnetic property measurements. From these analyses, climate indicators will be identified and subsequently used in paleoclimatic functions. These functions allow estimation of the Average Annual Temperature (AAT) and Average Annual Precipitation (AAP), enabling inference of paleoclimatic variations throughout the late Miocene. This integrated approach offers a new perspective on the environmental dynamics of the ancient Amazon, contributing to a better understanding of climate change and its implications for the region's biodiversity. (AU)