Deep to shallow-marine sedimentology and impact of volcanism within the Middle Triassic Palaeo-Tethyan Semantan Basin, Singapore

•The Pulau Ayer Chawan Formation is a key sedimentary rock unit of south-western Singapore.•It was deposited in the deep to shallow marine volcanic environment of the Semantan Basin.•Sedimentary deposits include turbidite fans, debris cones, hyaloclastites, interbedded with hemi-pelagite.•The active Sukhothai Arc greatly influenced sedimentation in the Singapore area.•The formation records sedimentation and volcanism during the Triassic closure of Palaeo-Tethys Ocean.