Palynomorphs in southern Western Australian lake sediments: evidence of climate change and hypersalinity during the Cenozoic

Abstract

This study focuses on five cores in and around three of the hundreds of shallow ephemeral hypersaline lakes distributed in chains along traces of ancient drainages that dominate the southern Western Australian landscape. Cores within and on the shore of Lake Aerodrome (LA1-09, LA2-09), Prado Lake (PL1-09, PL2-09), and Gastropod Lake (GLE1-09) in the Cowan Paleodrainage were drilled as part of a multidisciplinary study to understand the evolution of the lakes. Lithological and palynomorph data provide insights into the region’s the depositional history, and floristic and climate evolution of the region. The nearly 60 m deep LA2-09 core provides the most comprehensive data. The basal ∼15 m interval of this core comprises two distinct lignite units with a clay interbed that preserve a rich palynomorph assemblage of the Werillup Formation. This assemblage is characterized by the first appearance datum (FAD) and last appearance datum (LAD) of key late Eocene taxa that correlate with the Middle Nothofagidies asperus Zone, and is indicative of freshwater swamp surrounded by subtropical to temperate rainforest. Above the upper lignite (except the topmost sample), evaporitic-siliciclastic units preserve a depauperate palynomorph assemblage comprising mostly long-ranging sclerophyllic-xerophilous-halophilic taxa. The pollen Myrtaceidites lipsis constrains the age of the upper ∼23 m interval as Pliocene to Recent. This younger assemblage also preserves reworked palynomorphs from the Werillup Formation and older units, and is identified in the other four cores. The presence of the halophilic green alga Dunaliella in the younger assemblage is used as a proxy for aridity and hypersaline conditions during post-Eocene deposition in southern Western Australia. Its absence in the neutral-alkaline lake water and uppermost core samples of GLE1-09 is either due to predation by the acidophobic gastropod Coxiella residing in the lake, or the fact that the type of Dunaliella preserved in the core samples is acidophilic.

Keywords:

• Dunaliella
• acidic-saline lakes
• Werillup Formation
• late Eocene
• Pliocene
• evaporite
• Western Australia

Acknowledgements

We thank Kathleen Benison, Brenda Beitler Bowen, and Stacy Story for their collaboration on this Western Australian study and are grateful for their immense contributions during field work, and the stratigraphic, mineralogical and geochemical data. We also thank Wayne Hitchcock, the core librarian at the Geological Survey of Western Australia for providing the facilities at the Joe Core Library in Kalgoorlie and logistics with field work, and Mike Macphail for his suggestions on pollen identification.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was funded by a National Science Foundation grant (NSF EAR-0719838) to Francisca Oboh-Ikuenobe.

Notes on contributors

Carlos A. Sanchez Botero

CARLOS A. SANCHEZ BOTERO is a consultant palynologist at the Biostratigraphy laboratory of the Colombian Petroleum Institute of ECOPETROL, the Colombian oil company. He received his B.Sc. in Geology at the Universidad de Caldas, Manizales, Colombia in 2003, and his Ph.D. from the Missouri University of Science and Technology in 2013. His experience focuses on Cenozoic climate change in Australia and palynostratigraphy of Cretaceous and Cenozoic of northern South America.

Francisca E. Oboh-Ikuenobe

FRANCISCA OBOH-IKUENOBE is a professor of geology and geophysics at the Missouri University of Science and Technology where she serves as Interim Associate Dean for Academic Affairs in the College of Engineering and Computing. She received geology degrees from the University of Cambridge (PhD) and University of Ife, Nigeria (now Obafemi Awolowo University, MSc, BSc). Her research interests focus mainly on the palynofacies and palynostratigraphy of Cretaceous and Cenozoic sediments. She is a former president of AASP-TPS.

Lutfia Grabel

LUTFIA GRABEL is an assistant lecturer in the Department of Geology at Zawia University, Libya. Her research interest is palynology. A native of Zawia City, she received her MS degree in Geology and Geophysics from Missouri University of Science and Technology. Her Master’s thesis explored the palynomorph and palynofacies assemblages of hypersaline lakes in southern Western Australia. At Zawia University, she teaches macropaleontology and micropaleontology, as well as general geology courses since being hired in 2013. Lutfia has been a nominee for a PhD scholarship by Libyan Ministry of Higher Education.

Onema C. Adojoh

ONEMA C. ADOJOH received a PhD in geology and environmental sciences from the University of Liverpool, an MSc in petroleum geology from the University of Benin, Nigeria, a PGD in higher educational teaching and learning from the University of Plymouth, and a BTech in applied geology from Abubakar Tafawa Balewa University, Nigeria. A former post-doctoral fellow at the Missouri University of Science and Technology, he is currently on a courtesy appointment with the university. His research and teaching interests focus on sedimentology, paleontology, stratigraphy, climatology, palynology, geochemistry, micropaleontology, and environmental change. He is currently the North America regional representative for the PAGES-ECN.