Recent data on the ostracod fauna from the Lower and Middle Toarcian of Peniche, Portugal

• Autorzy: Pinto S. , Cabral M. , Duarte L.
• Konferencja: International Congress on the Jurassic System (7 ; 06-18.09.2006 ; Kraków, Poland]
• Języki publikacji: EN

Abstrakty

EN

At Peniche region, western Portugal, a rather continuous marly limestone succession ranging in age from the Sinemurian to the earliest Aalenian crops out. The ostracod fauna from a 74 m thick packet within this succession has been studied, encompassing deposits that range from the topmost Pliensbachian (topmost Spinatum Biozone) to the Middle Toarcian (Polymorphum, Levisoni, Bifrons and basal Gradata biozones). The studied levels belong to Lemede (2 m) and Cabo Carvoeiro Formations. From the 47 samples collected in the marly layers, a single one is azoic. Sample numbers and bed subdivision are according to biozonation in Duarte (1995), which considers 5 packets: topmost Spinatum, Polymorphum, Levisoni, Levisoni+Bifrons, Bifrons+basal Gradata. The systematic study of the ostracods has been undertaken, and some palaeoecological aspects have also been addressed, namely hydrodynamics (carapace/valve ratio), bathymetry and oxygenation, based on marker genera/groups. Around 8000 individuals were obtained (1 individual =1 carapace or 1 valve), which are commonly badly preserved. At least 58 species belonging to 22 genera have been identified until now. The top of Spinatum Biozone displays both high diversity (8-15 species/sample) and abundance (222-402 individuals/sample) of ostracods. The dominant species are from the genus Ogmoconcha, Ogmoconchella and Liasina, associated with Polycope, Paracypris, Ledahia, among others. The Polymorphum Biozone shows high diversity (3-22 species/sample) and variable abundance (1-150 individuals/sample). The genera Ogmoconcha, Ogmoconchella and Liasina still dominate and, from the first levels of the biozone, heavily ornamented species of Kinkelinella are present; the genus Isobythocypris occurs for the first time. In Levisoni Biozone, the ostracod diversity (1-4 species/sample) and abundance (1-150 individuals/ sample) are low, in contrast with previous biozones. Ogmoconcha and Ogmoconchella disappear, and the genus Cytherella appears for the first time, becoming dominant together with Liasina in the first levels of the biozone. In the upper part, Kinkelinella dominates and at the top Bairdiacypris and Cytheroptheron occur for the first time. Levisoni+Bifrons shows that ostracod diversity is moderate (5-11 species/sample) and abundance is high (60-310 individuals/sample). Species from the genera Bairdiacypris and Kinkelinella dominate, Cytherella and Patellacythere are common. Bifrons+basal Gradata shows higher diversity (3-18 species/sample) than previous unit and variable abundance (16-468 individuals/sample). Bairdiacypris, Cytherella and Kinkelinella dominate, and Macrocypris and Trachycythere(?) occur for the first time. All of the recognized species have been found in formations of a similar age in Western Europe, and are benthic marine species, except the genus Polycope (pelagic). Most of the species indicates a deep marine setting, with variable oxygenation levels, from normal to low (predominance of Metacopina and Cytherella), for the all section. The water energy was also variable, being stronger at the topmost Spinatum and Polymorphum biozones, within which ostracod valves are dominant, and lower at the Levisoni and Levisoni+Bifrons biozones, within which ostracod carapaces clearly dominate.

Słowa kluczowe

EN

ostracods; biostratigraphy; palaeoecology; Toarcian; Peniche; Portugal

• Wydawca: Państwowy Instytut Geologiczny - Państwowy Instytut Badawczy
• Czasopismo: Volumina Jurassica
• Rocznik: 2006
• Tom: Vol. 4, no. 1
• Strony: 204--205
• Opis fizyczny: Bibliogr. 1 poz.

Twórcy

autor

Pinto S.

autor

Cabral M.

autor

Duarte L.

• Departamento de Geologia e Centro de Geologia, Faculdade de Ci.ncias, Universidade de Lisboa, Campo Grande, C6, 4o, 1749-016 Lisboa, Portugal,

Bibliografia

• Duarte L. V. 1995. O Toarciano da Bacia Lusitaniana: estratigrafia e evolucao sedimentogenetica. Unpublished PhD thesis, Faculdade de Ci˘ncias e Tecnologia da Universidade de Coimbra, Portugal. 1-349.