Trans-Amazon Drilling Project (TADP): origins and evolution of the forests, climate, and hydrology of the South American tropics

Startdate: 18 March, 2015
Enddate: 20 March, 2015

Workshop Report: Baker, P.A., Fritz, S.C., Silva, C.G., Rigsby, C.A., Absy, M.L., Almeida, R.P., Caputo, M., Chiessi, C.M., Cruz, F.W., Dick, C.W., Feakins, S.J., Figueiredo, J., Freeman, K.H., Hoorn, C., Jaramillo, C., Kern, A.K., Latrubesse, E.M., Ledru, M.P., Marzoli, A., Myrbo, A., Noren, A., Piller, W.E., Ramos, M.I.F., Ribas, C.C., Trnadade, R., West, A.J., Wahnfried, I., Willard, D.A., 2015. Trans-Amazon Drilling Project (TADP): origins and evolution of the forests, climate, and hydrology of the South American tropics. Sci. Dril. 20, 41-49.

The origin of the great biodiversity observed in tropical South America has spurred debate for well over a hundred years (Darwin, 1859; Agassiz and Agassiz, 1868; Wallace, 1878) and remains one of the foundational problems in modern science. Wallace (1878) suggested that low tropical extinction rates, resulting from a relatively equitable and stable tropical climate, enabled the progressive accumulation of species throughout the Cenozoic, a hypothesis that has been termed the “museum” model. In contrast, the “cradle” model (Stebbins, 1974) posits that most tropical diversity arose from episodic pulses of speciation associated with climatic and geological drivers (Richardson et al., 2001). Some propose that the majority of present-day species originated prior to the Pleistocene (Hoorn et al., 2010) and that species origination rates were shaped primarily by geological agents of vicariance, such as Andean uplift, tectonic arches, marine incursions, fluvial barriers, and the expansion of mega wetlands. Others argue for significant Quaternary diversification, influenced by the temporal and spatial dynamism of regional climate (Rull, 2011). These different interpretations of the patterns and drivers of tropical biodiversity can best be resolved by recovering the entire Cenozoic record of plant diversity in the Amazon region itself and by placing these biotic data into a well-resolved geologic, climatic, phylogenetic, and biogeographic framework. We propose an ambitious ICDP drilling project that will continuously sample Upper Cretaceous to modern sediment to 1–2km depth at five sites in four different ancient sedimentary basins that transect the equatorial Amazon region of Brazil, from the Andean foreland to the Atlantic Ocean margin (Fig. 1). The overarching goals of this project are (1) to document the assembly of Amazon plant diversity across the entire basin throughout the entire history of the angiospermdominated mega thermal forests, and (2) to determine how the evolution of the physical environment, including climate, tectonism, and landscape change, has shaped the generation and distribution of neotropical plant diversity and the origins of its species and higher-level taxa. These goals require long sedimentary records distributed across the continent, which, in most of the Amazon region, can only be obtained by drilling. The Cenozoic geology of the westernmost (proximal Andean) and easternmost (offshore Foz do Amazonas basin) parts of the Amazon region is better known than that of the central Brazilian Amazon, where we propose to drill. In the far western Peruvian, Ecuadorean, and Colombian Amazon, ongoing uplift of Andean foreland basin sequences provides outcrops of Cenozoic sediments that are relatively easily accessed. Yet even here, complete and continuous sections are non-existent. Beyond the eastern limit of the Amazon region, on the Ceará Rise far offshore of the mouth of the Amazon, drilling during ODP Leg 154 recovered long sequences of sediment with some Amazonian provenance (Dobson et al., 2001; Harris and Mix, 2002). Even longer stratigraphic records were recovered in industry exploration wells on the Amazon slope and shelf, which were dated using marine microfossils. But these sections are poor records of continental history, because they are distal to the Amazon basin itself and because continental indicators of climate and biotic history are greatly diluted by marine influences. In the heart of the central Brazilian Amazon, Cenozoic outcrops are scarce, vegetation-covered, and deeply weathered – the critical sedimentary sequences are only available in the subsurface. And, despite extensive hydrocarbon exploration undertaken in this region, including many deep drill cores and thousands of kilometers of seismic lines, little is known about the nonpetroleum-bearing shallow (Cenozoic age) part of the sedimentary record, which holds key information about the evolution of the modern rainforest and the establishment of the Amazon river drainage system. Most of the samples that are still available are decades old, composed only of cuttings, undated, in poor condition, and sometimes contaminated, and also relatively difficult to access even by Brazilian scientists. Thus, collecting continuous, fresh drill cores from the central Amazon region is critical. In March 2015, we held a 3-day ICDP-sponsored workshop at the Instituto Nacional de Pesquisas da Amazônia in Manaus, Brazil, to discuss the scientific framework for the TADP, to identify and begin to resolve technical and logistical issues, and to further develop the international team needed for carrying out the drilling and associated science. Thirty scientists from eight nations in the Americas and Europe attended. The first day included overview presentations on the history of the Amazon forest and its biodiversity and on the geologic history of the Amazon and Andes, as well as presentations on recent research results on more specific topics. The second day was devoted to small group discussions of methodological and logistical issues, followed by discussions on how to develop the drilling plans and effectively interface with ICDP, IODP, various Brazilian organizations, and other related international efforts. The final day featured a field trip led by Edgardo Latrubesse, visiting the flooded Igapó forests and white sand beaches along the Rio Negro, as well as the “Meeting of the Waters” at the confluence of the black-water Rio Negro and the white-water Rio Solimões.


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