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Authors
Advisor(s)
Abstract(s)
Geochemical analysis of sedimentary deposits is a fundamental tool for
paleo environmental reconstructions. In this study, samples from the Lower
Cretaceous sequences of the Praia do Areia do Mastro (PAM) and Boca do Chapim
(BC) (northern coast of the Espichel Cape , Portugal) were analyzed. Macroscopic and
microscopic observations were carried out, associated with calcimetric determinations,
L.O.I. measurements, EA IRMS analysis for the determination of total C and δ 13 C
content, and ICP MS analysis for the definition of REE element concentrations to
reconstruct their paleo environme ntal conditions.
The samples from the PAM site all belong to the Papo
Seco formations, and are
mainly composed of sandstones, limestones and mudstones in which organic matter
mainly of plant nature is present in varying percentages. The negative δ 13 C value s of
the PAM samples, in agreement with the other data obtained, suggest that these
samples formed an estuarine paleo environment with intertidal lagoon zones. With
respect to all the analysis results of this work, three phases of probable
paleo environmen tal development of the area are confirmed: 1. Open intertidal and
lagoon region from low to high and then low temperature. 2. Open lagoon like region
developed into an estuary. 3. Open estuary transformed into closed lagoon.
The BC site
s samples that wer e studied belong to the Areia do Mastro and Papo Seco
ii
formations. Samples from the Areia do Mastro formation of the BC site show fairly
formations. Samples from the Areia do Mastro formation of the BC site show fairly similar characteristics among them, including an almost completely carbonate similar characteristics among them, including an almost completely carbonate composition and a micritic texture, while tcomposition and a micritic texture, while those belonging to the Papohose belonging to the Papo--Seco formation Seco formation were found to be sandy limestones, mudstones, sandstones and lignite with gypsum. were found to be sandy limestones, mudstones, sandstones and lignite with gypsum. The negative δThe negative δ1313C values recorded in the samples from this BC site and the lignite C values recorded in the samples from this BC site and the lignite sediments with gypsum are also consistent with a sediments with gypsum are also consistent with a lagoon and estuarine lagoon and estuarine paleopaleo--environment. In this case, the data that emerged from this work for the BC site environment. In this case, the data that emerged from this work for the BC site samples allowed us to confirm a probable estuarine to closed lagoon samples allowed us to confirm a probable estuarine to closed lagoon paleopaleo--environmental development with reducing anoxic conditions under climatic environmental development with reducing anoxic conditions under climatic coconditions varying from low temperature to high temperature.nditions varying from low temperature to high temperature.
In conclusion, the microscopic and geochemical characterization of sediments from
In conclusion, the microscopic and geochemical characterization of sediments from the Boca do Chapim and Praia do Areia do Mastro sequences has allowed us to the Boca do Chapim and Praia do Areia do Mastro sequences has allowed us to investigate the paleoinvestigate the paleo--environmental conenvironmental conditions that characterized this particularly ditions that characterized this particularly paleontologically important environment during the Barremian (Lower Cretaceous) paleontologically important environment during the Barremian (Lower Cretaceous) period.period.