The upper Aeronian to lower Telychian (Llandovery Series, lower Silurian) strata at the east end of El Pintado reservoir, Seville Province, Spain are documented in terms of their lithologies, graptolite biostratigraphy and δ 13 C org record. This is the first time that a continuously graptolitic section throught the Aeronian/Telychian boundary has been studied in detail. The upper Aeronian part of the section is assigned to the Stimulograptus halli Biozone which is divisible into three, the middle part being referred to the Lituigraptus rastrum Subzone. The Telychian strata are assigned to the Spirograptus guerichi Biozone and lower Sp. turriculatus Biozone. Unusually, two specimens of Sp. turriculatus were found at a level low in the guerichi Biozone. 118 graptolite species are recorded, 18 of which are new and described here together with other species for which the El Pintado material provides new information. Diversity increases considerably in some genera (Glyptograptus, Parapetalolithus, Rastrites, Streptograptus) in the upper halli Biozone and/or lower to middle guerichi Biozone only to decline again (except for Streptograptus) in the upper part of the guerichi Biozone as part of the "utilis Event". This diversity decline coincides with an interval of elevated δ 13 C org values. There are no major δ 13 C org excursions present in the El Pintado sections. The δ 13 C org record through the guerichi Biozone is very similar to that in Arctic Canada. Portsmouth, Burnaby Road, Portsmouth PO1 3QL, UK; david.loydell@port.ac.uk • Jiří Frýda, Faculty of Environmental Sciences, Czech University of Life Sciences Prague, Kamýcká 129, 165 21, Praha 6 and Czech Geological Survey, Klárov 3, 118 21 Praha 1, Czech Republic;, Facultad de Ciencias Geológicas, E-28040 Madrid, Spain; jcgrapto@ucm.es Our knowledge of the geological column is remarkably patchy. For some stratigraphical intervals numerous papers exist documenting sections, their contained fossils and chemostratigraphical record. Other intervals -unfortunately these are often around chronostratigraphical boundaries -are remarkably bereft of useful published stratigraphical data. This is usually because of the paucity or even absence of sections without major facies changes that are continuously fossiliferous. One such "unknown" interval has been the uppermost Aeronian to lowermost Telychian (middle to upper Llandovery Series). Recognition that the GSSP for the base of the Telychian Stage is unsatisfactory from a number of viewpoints (Temple 1988;Loydell 1993a;Davies et al. 2011Davies et al. , 2013 has heightened recent interest in the search for more informative sections. The aim of this paper is to document the upper Aeronian and lower Telychian graptolitic strata through sections on the shores of El Pintado reservoir in Seville Province, Spain and to discuss the bio-, chrono-and chemostratigraphy of this part of the Silurian System. The paper commences with a review of published sections, to indicate why the El Pintado sections are so important. It contin...