Several impact structures have been recently discovered in pre-Tertiary Peninsular Malaysia. In the Langkawi islands three of four arcuate ridges are associated with cleaved quartz that crops out as a sill and dyke complex. Other shock-metamorphic features include ribbon quartz and mosaicism. The two major craters, named Mahsuri Rings, partially overlap and each is about 2.4 km across. In 280° - 100° direction their centres are 600 metres apart. Bouguer gravity cross sections prove their crater form, one being 45 m deep, the other attaining 107 m depth into the target rocks of Carbo-Permian Singa Formation. Both depressions are filled, the top surface consisting of Quaternary alluvium. The partially encircling hills of Singa Formation crest at less than 150 m elevation and are open to the west. Towards SW are two other circular/arcuate topographic features: Temoyong Ring and horseshoe-shaped Tepor Island. The diameters decrease in the same direction: approximately 800 m and 500 m, respectively. These four ring-like structures have been interpreted as products of serial impacts by a flight of extraterrestrial projectiles arriving from the Southwest. The impact age is not yet determined and field relations only indicate a post-granite (Triassic-Jurassic) event. In the case that the morphologically young Mahsuri Rings are not exhumed features, impact could have occurred within the last 10 million years.
Another proven impact structure is the Paloh Ring that straddles the state boundary between Terengganu and Pahang. The proof consists of planar deformation features (PDFs) and mosaicism in vein quartz intruded into undivided Carboniferous metasedimentary strata that compose the lower eastern slope of the 623m high Paloh peak. PDFs are also seen in thin sections of quartz phenoclasts of polymict-breccia boulders in Sungai Mengkuang that drains the east side of the hill. Bukit Paloh is the peak on the high, circular topography surrounding a deep depression, now referred to as Paloh Ring-1. This ring-like topography is 3.5 km across and has local relief of the order of 150 to 200 metres. A small -about 0.5 km across-circular depression is located on the Paloh Ring-1. The south half of the larger ring consists of felsic igneous rock whose K/Ar age is 243 Ma, while the north half is composed of Carboniferous metasedimentary rocks. The youthful morphology of Paloh Ring-1 points to a geologically young impact event, estimated to be not later than Late Miocene. More than a decade earlier, PDFs in quartz were discovered in partly weathered granite underlying the Quaternary basalt at Gebeng, some 40 km SE of Bukit Paloh. The granite at Bukit Ubi quarry, located in the same area but nearer to Kuantan town, also contains quartz with PDFs. These two findings are the initial proofs for impact products in the whole of Malaysia. It is unresolved if the Gebeng-Bukit Ubi impact products and those at Bukit Paloh originated from the same event.
