5 research outputs found
Lithostratigraphic, paleoenvironmental and sequential evolution of the Cenomanian-Lower Turonian in the Guir area (western Algeria)
La lithostratigraphie, les palĂ©oenvironnements et la stratigraphie sĂ©quentielle des terrains crĂ©tacĂ©s affleurant au pied mĂ©ridional de l'Atlas saharien (Sud-Ouest de l'AlgĂ©rie), sont discutĂ©s dans le prĂ©sent article. Les Ă©tudes s'appuient sur l'analyse de quinze coupes rĂ©parties le long des limites mĂ©ridionale et septentrionale du bassin du Guir, entre Ben-Zireg, Ă l'Est et l'axe Meridja-Boukais Ă l'Ouest. Dans cette rĂ©gion, trois formations ont Ă©tĂ© identifiĂ©es et interprĂ©tĂ©es sur le plan environnemental et sĂ©quentiel : 1- La Formation des "GrĂšs rouges", attribuĂ©e au CĂ©nomanien infĂ©rieur, est dominĂ©e par des dĂ©pĂŽts grĂ©seux fins, fluviatiles ou littoraux ; 2- La Formation des "Marnes Ă gypse infĂ©rieures", rapportĂ©e au CĂ©nomanien infĂ©rieur-moyen, est caractĂ©risĂ©e par des assises Ă caractĂšres littoraux, soumises Ă l'influence des tempĂȘtes, notamment vers la base ; 3- La Formation des "Calcaires de Sidi Mohamed Ben Bouziane", d'Ăąge CĂ©nomanien supĂ©rieur-Turonien infĂ©rieur, correspond Ă une sĂ©dimentation carbonatĂ©e franchement marine de plate-forme peu profonde trĂšs gĂ©nĂ©ralisĂ©e. Les dĂ©pĂŽts de ces entitĂ©s lithostratigraphiques s'agencent en mĂ©gasĂ©quence d'ouverture, composĂ©e de mĂ©so-sĂ©quences "transgression-rĂ©gression". L'ouverture des milieux de dĂ©pĂŽts en direction du Nord est confirmĂ©e par l'organisation des unitĂ©s lithostratigraphiques et par l'affinitĂ© palĂ©obiogĂ©ographique nettement tĂ©thysienne de l'Ă©chinofaune, des bivalves et en particulier de l'ammonite Neolobites vibrayeanus.The lithostratigraphy, paleoenvironment and sequence stratigraphy of the Cretaceous succession outcropping at the southern foot of the Saharan Atlas (south-western Algeria) are discussed in this work. Our current study focuses on the analysis of fifteen sections distributed along to the northern and southern limits of the Guir Basin, between the Ben-Zireg to the East and the Meridja-Boukais axis to the West. In this area, three lithostratigraphic formations were identified and interpreted from an environmental and a sequential points of view: 1 - The lower "GrĂšs rouges" Formation attributed to the Lower Cenomanian, is dominated by fluvial or coastal detrital deposits; 2 - The middle "Marnes Ă gypse infĂ©rieures" Formation assigned to the Lower-Middle Cenomanian is characterized by littoral setting with some storm influences, especially towards the base; 3 - The upper "Calcaires de Sidi Mohamed Ben Bouziane" Formation of upper Cenomanian-early Turonian in age, is represents a laterally extensive, shallow carbonate platform environment. The three formations constitute an overall transgressive megasequence built of a number of transgressive-regressive minor sequences. The opening of the deposits towards the North is confirmed by the organization of the lithostratigraphic units and by the Tethyan paleobiogeographic affinity of the echinoids and bivalves, and especially the occurrence of Neolobites vibrayeanus ammonite
Lower Palaeozoic acritarchs from the Traras Mountains â First evidence of Ordovician sediments in northwestern Algeria
Litho- and biostratigraphy, facies patterns and depositional sequences of the Cenomanian-Turonian deposits in the Ksour Mountains (Saharan Atlas, Algeria)
International audienc
Roveacrinids (Crinoidea, Roveacrinida) from the Cenomanian-Turonian of southwest Algeria (Saharan Atlas and Guir Basin)
International audienceIn the southwestern part of Algeria, the Cenomanian-Turonian marine deposits build up a prominent ledge in a perched syncline (Ksour Mountains, western Saharan Atlas) or at high radius of curvature (Guir Basin). The petrographical analysis of the Cenomanian-Turonian deposits of the Ksour Mountains and of the Guir Basin reveals unexpected assemblages of roveacrinoidal ossicles comparable with those formerly reported from the Tinrhert area. For the first time, isolated ossicles of genuine and undisputable Roveacrinidae are illustrated. Three sections, Djebel Rhoundjaia (western Saharan Atlas), Berridel and Kenadsa (Guir Basin), were scrutinized to recognize the microcrinoidal sections within the carbonate microfacies and to compile the successive occurrence of respective roveacrinid taxa (besides the classical search for standard index microfossils) in an attempt to pinpoint more precisely the position of the Cenomanian-Turonian boundary (C/T B). These assemblages are particularly morphologically and taxonomically diverse with three species of genus Roveacrinus and one of genus Orthogonocrinus. The presence of Saccocomidae (Applinocrinus) is especially unusual in such stratigraphic levels. The relative abundance and diversity of Roveacrinidae evidence a peak when approaching the C/T B. Such an event is recurring in the latest Cenomanian in various Tethyan and Atlantic areas. These fluctuations are consistent with a high surface-water productivity just before the C/T B. (C) 2017 Elsevier Masson SAS. All rights reserved