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Ammonites from lumpy limestones (Lower Pliensbachian, Portugal). Taphonomic analysis and palaeoenvironmental implications.



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Fernández López, Sixto Rafael and Duarte, Luís Vitor and Henriques, María Helena Paiva (2000) Ammonites from lumpy limestones (Lower Pliensbachian, Portugal). Taphonomic analysis and palaeoenvironmental implications. Revista de la Sociedad Geológica de España, 13 (1). pp. 3-15. ISSN 0214-2708

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Official URL: http://www.sociedadgeologica.es/publicaciones_revista.html‎


Preservational features of ammonites recorded in the Lower Pliensbachian lumpy limestones
of the Lusitanian Basin confirm the deep marine origin previously established for this facies. These
deposits can be subdivided into three main taphofacies which are distinguished by preservational
ammonite features: 1) lumpy limestones and marly intervals with reelaborated ammonites, 2) laminated
marls and bituminous shales with accumulated ammonites, and 3) homogeneous limestones with
resedimented ammonites. The background sedimentation of suboxic (dysaerobic, bioturbated lumpy
muds; taphofacies 1) to anoxic conditions (anaerobic, laminated muds; taphofacies 2) on deep zone
was interrupted by depositional events related to distal gravity flows (taphofacies 3). Lumpy limestones
containing reelaborated ammonites, and showing gradational boundaries and inverse grading developed
in deep environments due to sedimentary starving. The stratigraphic intervals of taphofacies 1 represent
the lowest values of sedimentation and accumulation rates. Taphofacies of type 1 alternate with
taphofacies of type 2 composing stratigraphic cycles of metric order. Such cycles resulted from cyclical
environmental changes of hundreds of thousands of years. Deepening episodes of 4th-order led to the
development of dysaerobic to anaerobic environments, whilst subsequent shallowing episodes increased
the levels of bottom oxygenation.

Item Type:Article
Uncontrolled Keywords:Tafonomía aplicada, Estratigrafía secuencial, Ammonites, Tafofacies, Plataformas carbonáticas, Ciclos ambientales, Paleobatimetría, Jurásico Inferior, Cuenca Lusitánica, Iberia
Subjects:Sciences > Geology > Paleontology
ID Code:22685
Deposited On:29 Aug 2013 11:14
Last Modified:11 Dec 2018 08:42

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