Reconstructing the Eocene-oligocene tropical rainforests from the Southeastern Brazil (Fonseca and Gandarela Basins, Minas Gerais) with leaves of fabacea, myrtaceae and other angiosperms : the Mata Atlantica origins

Author(s)

Jean Carlo Mari Fanton

• Document type: Doctoral Thesis
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Geociências
• Defense date: 2013-03-27

Examining board members

Giorgio Basilici; Luiza Sumiko Kinoshita; André Jasper; Rosemarie Rohn Davies

• Advisor: Fresia Soledad Ricardi Tores Branco

Abstract

Isolated fossil angiosperm leaves preserved in fluvial-lacustrine deposits from the Fonseca and Gandarela basins were analyzed to reconstruct the paleoenvironment. Angiosperms are good climatic indicators since the species distribution in space/time is influenced by the climate. Located in central-southern part of the State of Minas Gerais, the Fonseca and Gandarela basins are grabens embedded in the Precambrian basement, deposited during the Late Eocene-Early Oligocene interval, according to palynological data. As methods, informative architecture characteristics allowed taxonomic identifications solely on the basis of leaves. To estimate paleotemperatures, the Leaf Margin Analysis (LMA) was applied, based on the relationship between the proportion of untoothed woody "dicot" species (pE) and mean annual temperature (MAT). Before, the ability of South American models was tested on modern sites of Atlantic forests from southeastern Brazil. Because of high pEs (0,78-0,87), temperatures of the low-elevation sites (MAT ? 23°C) were predicted accurately, but the error was greater in the high-elevation ones (MAT ? 22°C, 610-890 m). Although obligate untoothed lineages were richly represented in low and high-temperature sites (in average 38% of the species per site), the development of highlands in southeastern Brazil since the Late Cretaceous and Cenozoic invalidate hypotheses about an insufficient time to evolve teeth in angiosperms adapted to high-elevations. Both fossil floras Fonseca (40 morphotypes) and Gandarela (20) showed pEs (0,90 and 0,95) so high as observed in Amazonian equatorial rainforests. MATs ? 24,7°C were yielded for the majority of the models (in average ?27-28°C), isotherm today registered mainly in lowlands from northern Brazil. Over half of the morphotypes described were identified in families essentially tropical, such as Lauraceae (FS06, GR03 and GR09), Fabaceae (FS01-03, FS05, FS09 and GR08), Combretaceae (FS08) and Myrtaceae (FS11-13 and GR02). All these lineages have a long evolutionary history (since at least the Paleocene- Eocene) in the north (Fabaceae and Lauraceae) and south (Myrtaceae) of South America, revealing an antique legacy of tropicality and mixed floristic influence from boreal-laurasian and austral-Antarctic regions. Today, such families have controlled a major portion of the ecological resources in the Atlantic forests from southeastern Brazil probably retaining dominance since the Paleogene. Similar composition and some environmental aspects suggest that the rainforests from the southern Atlantic block (including Araucaria rainforest) are the closest living analogues to the Fonseca and Gandarela extinct vegetation: high temperatures and heavy rainfall sustaining an evergreen and multilayered canopy dominated by angiosperms (Myrtaceae, Lauraceae and Fabaceae) and austral conifers (Podocarpaceae and Araucariaceae). Additional evidence supporting the tropical rainforest hypothesis is: (1) the Fonseca Formation leaf physiognomy (40-65% of the morphotypes evaluated have drip tips, 80-90% untoothed margins and 50% are notophyll-mesophyll), and (2) the presence of water-demanding and coldintolerant lineages, such as dacrydioid podocarps (Dacrydiumites) and the Myrtaceae morphotype FS13 (identified as Curitiba), which bears an acuminate leaf 2× longer than the extant C. prismatica. The paleoenvironment reconstructed agree with the higher atmospheric CO2 levels, the wider Tropical zone and the relatively mild winters during the Late Paleogene (AU)

• FAPESP's process: 07/04489-3 - Angiosperms from paleogene paleofloras Fonseca and Gandarela: taxonomic and paleoclimate implications
• Grantee: Jean Carlo Mari Fanton
• Support Opportunities: Scholarships in Brazil - Doctorate