Lake Chalco is one of the few lakes in Mexico that has a long, continuous sedimentary sequence covering the Upper Pleistocene (> 150 000 yrs). The diatom content of its lacustrine sediments includes a variety of centric species. In particular, the sediments dating to Marine Isotope Stage 5 (MIS5) were alternately dominated by four Cyclotella spp: C. meneghiniana Kützing, C. quillensis Bailey, and two new species which are described here: C. poyeka and C. tlalocii. These two new Cyclotella spp. resemble C. stylorum Brightwell, because of the presence of marginal chambers. Nevertheless, the new species from Lake Chalco have a different structure of the marginal chambers and marginal fultoportulae with three satellite pores. Cyclotella poyeka and C. tlalocii differ from each other by the relative proportion of the central area to valve face diameter, the central fultoportula arrangement, and the striation pattern. Ecological affinities of the four Cyclotella species in the MIS5 sediments from Lake Chalco are discussed based on their modern distribution (for C. meneghiniana and C. quillensis) and their fossil assemblages (for C. quillensis, C. tlalocii and C. poyeka), leading to the conclusion that C. tlalocii was a freshwater species while C. meneghiniana, C. quillensis, and C. poyeka thrived in saline conditions.
Bibliographical noteFunding Information:
This research was funded by the National University of Mexico (UNAM), projects PAPIIT IN100820 ‘Registros Interglaciares del Centro de México’ and DGAPA-PAPIIT-IN103819 ‘Variabilidad climática y paleoambientes durante la terminación II (130 ka): El paso del penúltimo glacial (MIS 6) al penúltimo interglaciar (MIS 5)’. Diana Avendaño thanks the Posgrado de Ciencias de la Tierra, UNAM and CONACyT (Consejo Nacional de Ciencia y Tecnología) [CVU 854736] for financial support. Laura Gómez Lizárraga gave technical assistance for sample preparation and observation with the scanning electron microscopy. Dr. Nienow provided advice on the taxonomy of Cyclotella stylorum. Dr. Socorro Lozano and Dr. Beatriz Ortega have been lead collaborators in the Chalco drilling projects and their support has been fundamental for the recovery, description and dating of the sediment sequence. We also thank two anonymous reviewers, Dr. Eileen J. Cox and Dr. Jeffery Stone for their valuable comments that greatly improved our manuscript.
© 2022 The International Society for Diatom Research.
- centric diatoms
- complex alveoli
- diatom ecology
- diatom taxonomy
- marginal chambers
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