Age of the Serra do Martins Formation, Borborema Plateau, northeastern Brazil : constraints from apatite and zircon fission track analysis.
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2008
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Resumo
Results of apatite and zircon fission track analysis
of samples from the Serra de Santana mesa provide
quantitative constraints on the depositional age of the
nonfossiliferous Serra do Martins Formation. This unit
consists of sedimentary remnants preserved at high
elevations on the Borborema Plateau and its distribution
and age are considered important in understanding the
geomorphological evolution and denudation history of
northeastern Brazil following the early Cretaceous
breakup. We also report apatite fission track results from
post-rift units of the Potiguar Basin (Açu and Tibau
formations). Apatite fission track analysis (AFTA) of
samples from the Serra do Martins Formation suggests
that they reached maximum paleotemperatures around
60°C, from which they began to cool some time
between 30 and 0 Ma. Due to the high thermal
gradients related to the prolonged Cenozoic volcanism
in the study area, we hypothesize that the
paleotemperatures modeled for those samples may be
related dominantly to an anomalous heat flow, rather
than to significant burial. Zircon fission track analysis
(ZFTA) in two samples of the Serra do Martins Formation
yields ages of 135±18 Ma and 165±40 Ma, but both
samples show a significant spread in the data, and the
youngest population of grains in these samples are
characterized by ages of 83±5 Ma and 64±5 Ma,
respectively. As the AFTA data show that these ages
have not been reset after deposition, the zircon fission
track ages must represent inherited provenance ages,
demonstrating that those sediments can be no older
than Paleocene. Independent lithological observations
provide additional support to reject a stratigraphic
correlation between the Serra do Martins and Açu
formations. Combining the AFTA and ZFTA results, and
integrating available geological evidence, we suggest
that the Serra do Martins Formation was deposited some
time between 64 and 25 Ma (Paleocene-Oligocene).
Modeled thermal history solutions from AFTA in the
Serra do Martins Formation samples suggest a cooling
event during late Cretaceous/early Paleogene,
interpreted as reflecting exhumation of sediment
provenance terrain. The resulting erosional products form
the clastics for the Serra do Martins Formation, which
were deposited on an extensive regional planation
surface – the Borborema Surface.
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Serra do Martins Formation, Apatite and zircon fission track analysis, Paleotemperature, Potiguar Basin
Citação
MORAIS NETO, J. M. de et al. Age of the Serra do Martins Formation, Borborema Plateau, northeastern Brazil: constraints from apatite and zircon fission track analysis. Boletim de Geociências da Petrobras, v. 16, p. 23-52, 2008. Disponível em: <http://vdpf.petrobras.com.br/vdpf/PDFHighlightServlet.svlt?acao=pdf&codigoArtigo=861#xml=http://vdpf.petrobras.com.br/vdpf/PDFHighlightServlet.svlt?acao=xml&codigoArtigo=861>. Acesso em: 20 jun. 2017.