Surface texture, mineralogy and stable isotope studies of nodular calcretes preserved in the YTT ash of Padang Terap river basin and lenggong valley, peninsular Malaysia: Implications in its origin and paleoclimatic reconstruction
Document Type
Article
Publication Date
9-1-2021
Abstract
Rounded to sub-rounded calcrete nodules, preserved in Youngest Toba Tuff (YTT, similar to 75 ka) ash, exposed at the Padang Terap river basin and Lenggong valley of Malaysia, have been investigated for their micromorphology, mineralogy and stable isotope compositions (delta O-18 and delta C-13) with the aim to interpret their origin, climatic conditions and vegetational scenario in the studied areas. These nodules are associated with cylindrical, pipe -like, root calcretes and highly calcretized ant traces. The FESEM study shows dominance of sparry calcite and microsparite as groundmasses and presence of bacteria microfossils and microbial features. The microfossils are represented mainly by microcodium, calcified pedostructures and organic filaments, whereas, the microbial features as extracellular polymers substances (EPS) and bacillus type bacteria. Mineralogical compositions as reflected by X-ray diffractograms show dominant peaks of calcite followed by quartz, chlorite, illite and paly-gorskite. The delta O-18 and delta C-13 values suggest that the precipitation of calcium carbonate might have happened in in-situ manner that leached under the influence of meteoric water in presence of C-4 dominated vegetation during the formations of the nodules. Presence of C-4 vegetation in the area suggests that the same had revived after the YTT event. The study suggests that the CaCO3 would have been supplied to the host sediments by dust, rainwater and local geological set-ups during arid, semi-arid and humid climatic conditions.
Keywords
Nodular calcrete, Ant traces, Biogenic structures, Bacteria microfossils, C-4 vegetation, Stable isotope, Toba volcanism
Divisions
GEOLOGY
Funders
Universiti Malaya (RU013-2019)
Publication Title
Rhizosphere
Volume
19
Publisher
Elsevier
Publisher Location
RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS