Late Holocene mangrove dynamics dominated by autogenic processes |
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| Authors: | Caio A. Moraes Neuza A. Fontes Marcelo C.L. Cohen Marlon Carlos França Luiz C.R. Pessenda Dilce F. Rossetti Mariah I. Francisquini José A. Bendassolli Kita Macario |
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| Affiliation: | 1. Graduate Program of Geology and Geochemistry, Federal University of Pará, Belém, Brazil;2. Federal Institute of Pará, Belém, Brazil;3. CENA/14C Laboratory, University of S?o Paulo, S?o Paulo, Brazil;4. National Space Research Institute (INPE), S?o José dos Campos, Brazil;5. CENA/Stable Isotopes Laboratory, University of S?o Paulo, S?o Paulo;6. Physics Department, LAC‐UFF AMS Laboratory‐Fluminense Federal University, Rio de Janeiro, Brazil |
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| Abstract: | Generally, palaeoenvironmental interpretations consider only allogenic processes, when autogenic factors may have a strong influence on proxies of stratigraphic sequences. For instance, the Holocene history of the vegetation along the southern littoral of the State of Bahia in north‐eastern Brazil is characterized by mangrove dynamics controlled by allogenic processes. However, over smaller timescales (~700 years), autogenic processes may have controlled vegetation dynamics and hence observed pollen distribution. This work proposes tidal channel dynamics as one of the main cause for changes in pollen assemblage along the studied stratigraphic profiles during the last centuries, based on sedimentology, pollen and elemental analysis (δ13C, δ15N and C/N) and radiocarbon dating of sedimentary organic matter from two cores sampled from an abandoned meander and a tidal flat at the mouth of the Jucuruçu River. One core was sampled from a mangrove formed during the past ~550 cal yr bp . Another core recorded sediments in a várzea forest (swamp seasonally and permanently inundated by freshwater) located ~2.7 km from the current shoreline, which displayed a maximum age of ~680 cal yr bp . Two facies associations were identified: tidal channel (A) and tidal flat/oxbow lake (B). This work proposes allogenic processes as the main driving forces controlling the wetlands dynamics at the studied site during the Holocene. However, our data also reveal that part of the changes in vegetation over the last ~700 years reflect tidal channels and tidal flats development, which represent autogenic processes. The change in timescale analysis from the Holocene to recent centuries may have weakened the influence of allogenic factors. However, this needs interpretation with reference to the spatial scale of the depositional environment as the larger the depositional system analyzed, the stronger the influence of autogenic processes on stratigraphic sequences over longer timescales. Copyright © 2017 John Wiley & Sons, Ltd. |
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| Keywords: | C and N isotopes climate Holocene palynology, relative sea level |
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