Rounded to sub-rounded calcrete nodules, preserved in Youngest Toba Tuff (YTT, ~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 (δ¹⁸O and δ¹³C) 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 palygorskite. The δ¹⁸O and δ¹³C 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 C₄ dominated vegetation during the formations of the nodules. Presence of C₄ 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.

四舍五入到分圆滑钙质结砾岩结节，保存在最年轻的鸟羽凝灰岩（YTT，〜75万年）灰，在巴东Terap流域和马来西亚的冷宫山谷暴露，已经研究了它们的微观形态，矿物学和稳定同位素组成（δ ¹⁸ O和δ ¹³C）旨在解释研究区域的起源，气候条件和植被状况。这些小结节与圆柱形，管状，根状小结和高度钙化的蚂蚁痕迹有关。FESEM研究表明，以方解石为主要成分的方解石和微碎石以及细菌微化石和微生物特征的存在。微化石的主要代表是微柱，钙化的细微结构和有机细丝，而微生物则具有细胞外聚合物（EPS）和芽孢杆菌型细菌的特征。通过X射线衍射图反映的矿物学组成显示方解石的主要峰，随后是石英，绿泥石，伊利石和坡缕石。的δ ¹⁸ O和δ ¹³C值表明，在结节形成过程中，在C ₄为主的植被存在下，碳酸钙的沉淀可能是在流水的影响下原位沉淀的。该地区C ₄植被的存在表明，YTT事件发生后，C ₄植被已经恢复。研究表明，在干旱，半干旱和潮湿的气候条件下，可能通过灰尘，雨水和当地地质构造将CaCO ₃提供给宿主沉积物。