Arquitetura sísmica do sistema de canais de maré Galinhos-Guamaré (NE do Brasil) como evidência às variações do nível do mar Holocênico
This study aims to reconstruct the seismic stratigraphy of a Holocene tropical tidal channel system through the interpretation of shallow seismic data associated with vibracores analyses. Therefore, it was necessary to recognize the chronostratigraphic limits, the termination patterns of the seism...
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| Formato: | Dissertação |
| Idioma: | pt_BR |
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Universidade Federal do Rio Grande do Norte
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| Endereço do item: | https://repositorio.ufrn.br/handle/123456789/32637 |
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| Resumo: | This study aims to reconstruct the seismic stratigraphy of a Holocene tropical tidal channel system
through the interpretation of shallow seismic data associated with vibracores analyses. Therefore,
it was necessary to recognize the chronostratigraphic limits, the termination patterns of the seismic
reflectors, the analysis of the facies seismic and the external geometry of the packages. This shallow
system, with a maximum depths around 10 m, is located on the north coast of the state of Rio
Grande do Norte - Brazil, having developed from a system of spit-barrier islands (~ 5900 BP) on a
coast dominated by tide, with semidiurnal mesotidal regime. 42km of high-resolution seismic data
were collected, with an average spacing of 30m, using a Chirp seismic (0.5kHz-7kHz). The data
were processed using the softwares ReflexWin and Petrel. The seismic analysis allowed the
identification of five Holocene seismic facies (U01-U05) and five boundaries or strata surfaces
(SF01-SF05). The basal unit (U01) was formed in an environment of moderate energy with
thickness ranging from ~ 1.4 to 3.5 m. The U02 unit indicates a high energy environment, with an
average thickness between ~ 1.4m to 3.5m. The U03 unit represents a moderate energy
environment with an average thickness between ~ 0.35m to 2.45m. The shallower surface (SF05)
is ~ 7 m below the current sea level. Unit U04 (1227 Cal year AP) and U05 are formed by tidal flat
muds facies. The geometry of the units and their respective surfaces were examined in detail in this
work using a series of isopach maps, designed to understand their development in time and pace.
These results and interpretation indicate new insights: (1) the formation of paleochannels located
in the current spit may have started before the middle Holocene; (2) there was a network of preexisting channels with a different configuration from the current ones formed by units U02 and
U03, constituting the transgressive and highstand systems tracts (7500 – 5000 Cal yrs BP); (3) the
closure of the paleochannels and the formation of the spit occurred during deposition; (4) the SF04
surface marks the transition from transgressive to regressive system tract (within the past 5000 Cal
yrs BP); (5) the current configuration of the system has been active since the formation of the U03
unit, that is, since the closure of the paleochannels; and (6) the Galinhos region shows the
progressive sedimentary infilling of a lagoon behind a coastal barrier via sediment accumulation
from marine sources and its ultimate transformation into a coastal swamp with tidal channels. |
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