22 research outputs found
FaciÚs du Cambrien inférieur et moyen de la mer Morte (Jordanie); signification paléoenvironmentale
Les microfossiles extraits des calcaires de la formation cambrienne de Valdemiedes (Chaßnes ibériques, NE
Espagne) mettent en Ă©vidence lâessor dâune microfaune Ă©pibenthique Ă caractĂšre encroĂ»tant (composĂ©e de foraminifĂšres
et de serpulidés), qui a infesté les substrats durs fournis par des coquilles en milieu non-récifal. Elle semble avoir exploité
les niches écologiques liées auparasitisme et/oucommensalisme sous des conditions environnementales
dâĂ©nergie basse Ă modĂ©rĂ©e. MalgrĂ© le caractĂšre grĂ©gaire de lâĂ©pifaune, la prĂ©sence de recouvrements squelettiques est
rare, ce qui traduit un taux faible de compétition spatiale. Les foraminifÚres à paroi agglutinée, de type psammosphaeridé,
Ă©taient capables de dissoudre partiellement les coquilles carbonatĂ©es quâils encroĂ»taient : malgrĂ© lâabsence de perforations,
des cicatrices de cet encroûtement sont visibles sur la face interne des coquilles. Ces deux taxons opportunistes
ont rĂ©agi de façon diffĂ©rente au remplacement des communautĂ©s benthiques reprĂ©sentĂ© par lâĂ©vĂ©nement Valdemiedes :
les psammosphaeridĂ©s ont traversĂ© cet Ă©vĂ©nement avec un pic dâabondance dans le niveau stratigraphique de reconquĂȘte
de lâĂ©cosystĂšme, tandis que les serpulidĂ©s, dominants Ă ce niveau, sont absents ou extrĂȘmement rares en conditions normales
Cambrian microfauna and palecology of the Campo Pisano Formation at Gutturu Pala (Iglesiente, SW Sardinia, Italy)
The microfossil content of nodular limestones of the late Early to Middle Cambrian Campo Pisano Formation from the Gutturu Pala section of southwestern Sardinia is described and discussed with respect to palaeoecological conditions. Based on detailed facies investigations, the vertical succession of the sedimentary evolution and fossil distribution is interpreted as an environmental change from shallow-subtidal conditions at the beginning of the Campo Pisano Formation to at least deep-subtidal conditions at its end.
Due to the faunal characteristics, an interim shallowing during that process is likely.
A dramatic facies replacement with the onset of the Campo Pisano Formation indicates a strong reorganisation of the environment, explained by tectonic instability of the platform, accompanied by moderate sea-level rise and palaeogeographical and maybe climate changes. During most of the time, the persistence of only one palaeoecological assemblage indicates a more or less stable, open marine, deeper subtidal environment for most of the Campo Pisano time.
Among the taxa represented in the highly fossiliferous sediments, trilobites, echinoderms, brachiopods, and poriferids predominates; further elements are chancellorids, hyolithids, pelagiellids, hyolitheminthids, and bradoriids arthropods. This occurrence in the Campo Pisano Formation is published here for the first time. The following bradoriid and trilobite species are newly introduced: Hipponicharion ichnusum n. sp., Condylopyge antiqua n. sp., and â described in open nomenclature â Clavigellus? n. sp