Preliminary analysis of detrital zircon U–Pb ages from the fossil-rich Tabbowa beds, Sri Lanka

Abstract

The Jurassic Tabbowa beds of northwestern Sri Lanka contain various plant fossils, including conifer, cycad, and fern. Well-preserved plant fossils have been discovered in mudstone and brownish siltstone horizons of the sandstone units since the early 20th century. Recent investigations for example have identified Otozamites latiphyllus and Otozamites tabbowensis fossils within these sediments. These species belong to an extinct seed plant of the Bennettitales order, which occurred throughout Gondwana during the Jurassic. Additionally, diverse assemblages of insect trace fossils have been found from the leaves of plant fossils. These insect trace fossils and plant fossils provide a unique window into Mesozoic plant–insect relationships and Jurassic terrestrial ecosystems. However, a majority of the Tabbowa fossils have not been systematically investigated or described in international journals. The Tabbowa beds also lack definitive stratigraphic correlation and sedimentary interpretation. This study describes the geologic context of the Tabbowa beds, summarizes previous studies of the Tabbowa Basin, and interprets chronostratigraphic constraints using detrital zircon U–Pb geochronology. Furthermore, our work demonstrates some of the limitations of detrital zircon geochronology and suggests the need for alternative methods in order to establish chronostratigraphic constraints on the Tabbowa beds.