The present work,based on lithostratigraphy and biostratigraphy,is focused on ammonites,microfacies,and chemostratigraphic study(δ^(13)C and δ^(18)O)of the late Cenomanian-early Turonian sequence in the El Bayadh ar...The present work,based on lithostratigraphy and biostratigraphy,is focused on ammonites,microfacies,and chemostratigraphic study(δ^(13)C and δ^(18)O)of the late Cenomanian-early Turonian sequence in the El Bayadh area(Saharan Atlas,Algeria).Five informal stratigraphic units(units 1 to 5)have been defined within the Rhoundjaia Formation,which is subdivided into four ammonite biozones:the Neolobites vibrayeanus,the Metoicoceras geslinianum,the Vascoceras cauvini,and the Choffaticeras sinaiticum zones.The Cenomanian-Turonian boundary(CTB)is located at the limit between units 2 and 3.Field data and microscopic analysis have resulted in the recognition of fourteen microfacies types(MT 1 to MT 14)that are described in terms of depositional environments,and grouped into six main limestone and limestone-marl facies associations(FA 1-6),representing two different palaeosettings:(i)open shelf/ramp-type carbonate platform and(ii)isolated carbonate platform.The sequence stratigraphic analysis revealed two third-order depositional sequences(DS1 and DS2)covering a period of about 2.8 million years.The depositional model for the uppermost Cenomanian shows the presence of a rudist-and microbial-rich isolated carbonate platform,away from terrigenous influence,and surrounded by deep-water open shelf facies.The comparison of the isotopic fluctuation profile with those of various marine sites in the Tethyan Ocean shows synchronous global events.展开更多
基金financed by the‘Rezerwa Dyrektora INoZ,University of Silesia in Katowice’for 2023by AGH-UST Grant no.16.16.140.315(MK)。
文摘The present work,based on lithostratigraphy and biostratigraphy,is focused on ammonites,microfacies,and chemostratigraphic study(δ^(13)C and δ^(18)O)of the late Cenomanian-early Turonian sequence in the El Bayadh area(Saharan Atlas,Algeria).Five informal stratigraphic units(units 1 to 5)have been defined within the Rhoundjaia Formation,which is subdivided into four ammonite biozones:the Neolobites vibrayeanus,the Metoicoceras geslinianum,the Vascoceras cauvini,and the Choffaticeras sinaiticum zones.The Cenomanian-Turonian boundary(CTB)is located at the limit between units 2 and 3.Field data and microscopic analysis have resulted in the recognition of fourteen microfacies types(MT 1 to MT 14)that are described in terms of depositional environments,and grouped into six main limestone and limestone-marl facies associations(FA 1-6),representing two different palaeosettings:(i)open shelf/ramp-type carbonate platform and(ii)isolated carbonate platform.The sequence stratigraphic analysis revealed two third-order depositional sequences(DS1 and DS2)covering a period of about 2.8 million years.The depositional model for the uppermost Cenomanian shows the presence of a rudist-and microbial-rich isolated carbonate platform,away from terrigenous influence,and surrounded by deep-water open shelf facies.The comparison of the isotopic fluctuation profile with those of various marine sites in the Tethyan Ocean shows synchronous global events.
