Paleoecología y cronoestratigrafía de las diatomeas del Miembro Los Indios en la Mesa La Misión, del Mioceno de Baja California, México.

The aim of the present study is to identify and analyze the paleoenvironmental and biostratigraphic aspects of the diatoms, in the sediments of the Mesa La Misión outcrop. The Mesa La Misión in Baja California is an outcrop of the Member Los Indios, part of the Rosarito Beach Formation. This formation consists of a volcanoclastic sequence with abundant and diverse vertebrate fauna named “La Misión Local Fauna”. The presence of 15 different diatom species were found in samples taken from four stratigraphic levels of the Mesa La Misión outcrop. Deposition of the Los Indios Member occurred in a marine progradational platform. Benthic diatoms are abundant in the lower part of the sequence and become less abundant at higher stratigraphic levels. Most of the diatom species found indicate temperate waters. However, mixing of water may have been present due to some tropical and cold water specimens that were found. An increase of the deposition depth towards the top of the section was found. This was due to the occurrence of diatoms from different temperature gradients, combined with the reduction of benthic diatoms towards the top of the section. This sea level can be associated with the Middle Miocene Climatic Optimum. It may correspond to the global cycle TM 2.2. In addition, the presence of Actynocyclus ingens var. nodus, a biostratigraphical taxon, places the deposition of the sediments during the middle Miocene. More specifically, between 15.6 and 13.0 million years (middle Langhian). This age correlates with the radiometric dating of the underlaying and overlaying basalts dated 16.1 ± 2.1 and 14.3 ± 2.6, respectively. [ABSTRACT FROM AUTHOR]