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Facies and sequence analysis of Miocene open-shelf warm-temperate carbonates in Portimão (Lagos-Portimão Formation, Portugal)

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Armenteros Armenteros, Ildefonso and Dabrio, Cristino J. and Legoinha, P. and González-Delgado, J. A. and Martínez-Graña, Antonio Miguel and Alonso-Gavilán, Gaspar and Civis Llovera, Jorge and Pais, Joao (2019) Facies and sequence analysis of Miocene open-shelf warm-temperate carbonates in Portimão (Lagos-Portimão Formation, Portugal). Facies, 64 (3). ISSN 0172-9179, ESSN: 1612-4820

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Official URL: https://link.springer.com/article/10.1007%2Fs10347-019-0575-2


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Abstract

The Lower–Middle Miocene Lagos-Portimão Formation at Portimão, southern Portugal, consists of three main heterozoan carbonate facies: mollusc-rich rudstone in a matrix of skeletal packstone/grainstone (MR), fine-to-medium skeletal packstone/grainstone (SPG), and quartz-rich skeletal packstone (QSP). These facies occur in different arrangements and indicate deposition on a wave-dominated open shelf with a well-established heterozoan fauna, most likely related to increased trophic resources where continent supply and upwelling contributed nutrients. These facies form belts inferred to have lain roughly parallel to the strike lines of the shelf, with the MR occupying the more landward, shallower areas and the SPG and QSP extending progressively offshore on the open shelf. Bryozoan abundance in the QSP facies indicates a deep setting on the middle/outer shelf, whereas the absence of rhodalgal components is attributed to a combination of temperature decrease and seafloor eutrophication during the late Langhian and Serravallian, coeval with the “Middle Miocene climatic cooling”. The large photosymbiont-bearing foraminifers and the absence of calcareous algae and zooxanthellate corals point to deposition under warm-temperate conditions. Two main orders of cyclicity are present. Small-scale sequences, 40–60 cm thick, may represent minor sea-level changes related to fifth-order sequences modulated by (~ 100-kyr) eccentricity forcing. Six large-scale sequences, 3–9 m in thickness, are recognized. Based on LAD and FAD of planktic foraminifers and the occurrence of two erosive surfaces related to major sea-level falls (Lang2/Ser1 and Ser4/Tor1), five Miocene sequences (Bu, L1, S1, S2, and S3) are correlated with third-order eustatic cycles.


Item Type:Article
Uncontrolled Keywords:Heterozoan carbonates, Warm-temperate waters,Open shelf ,Cyclicity, Burdigalian, Langhian, Serravallian, Lagos-Portimão Formation
Subjects:Sciences > Geology > Stratigraphic geology
ID Code:55886
Deposited On:19 Jun 2019 17:26
Last Modified:20 Jun 2019 11:03

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