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The transitional sequence from the Setul Limestone to the Kubang Pasu Formation is well exposed at Ouar Sanai, Kampung Ouar Jentik, Beseri District, northwest Perlis, Malaysia. The rocks of the study area are divided into three major units: Upper Setul Limestone, Jentik Formation, and Kubang Pasu Formation. The Upper Setul Limestone exposed in Ouar Sanai contains Scyphocrinites, which gives it a late Silurian age. The name Jentik Formation is proposed for the roughly 300 m thick sequence between the Setul Limestone and Kubang Pasu Formation. The Jentik Formation can be further divided into six informal units: (a) Unit 1; (b) Unit 2; (c) Unit 3; (d) Unit 4; (e) Unit 5; (f) Unit 6. Unit I consists mainly of black shales containing a Dacryoconarid-Monograptus-Plagiolaria faunal assemblage, which gives an early Devonian age. Unit 2 consists of light coloured, unfossiliferous sandstones and shales. Unit 3 is mainly thick red mudstone, interbedded with sandstone, sometimes showing graded bedding. A brachiopod-Diacoryphe-Posidonomya faunal assemblage gives it a late Devonian age. Unit 4 consists of well bedded, dark limestone, containing straight coned nautiloid fossils. Unit 5 is composed mainly of black mudstone interbedded with cherts, with slump structures. The base of the unit contains a brachiopod-gastropod fossil assemblage. Unit 6 consists mainly of thick beds of brownish red mudstone, interbedded with sandstone. The red mudstones contain a Macrobole-crinoid fossil assemblage, which is earliest Carboniferous in age. The Kubang Pasu Formation is suspected to be unconformably overlying the Jentik Formation. The epicontinental sea that covered present day northwest Peninsular Malaysia during the Palaeozoic was probably density stratified. Transition from shelf carbonate, to black shale and redbed deposition could be due to shifting of the boundary between the oxygen minimum layer and the deeper oxic layer of the sea, triggered by sea level changes.

Scyphocrinoid loboliths, the bulbous floats attached to the roots of a group of large Late Silurian to Early Devonian crinoids, were found within the top part of the Upper Setul limestone at two localities, in a band of limestone at Memplam Bay and in limestone blocks from a soil quarry at Guar Jentik, in northwest Peninsular Malaysia. The loboliths belong to the plate type, characterized by having plated chamber walls, few internal chambers and the presence of chamber openings near the axil of each primary root. Plate loboliths belong to species of Marhoumacrinus and Camarocrinus of the uppermost Pȓídolían to lowermost Lochkovian, and occur generally above cirrus loboliths, which are Pȓídolían only. Armoured floats are believed to have provided better protection against predators and the physical elements. These loboliths are important for correlation with other occurrences worldwide and especially within the Shan-Thai or SIBUMASU (SinoBurMalayaSumatra) terrane of southeast Asia.

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