Pa Kae Fm

Named after Pa Kae village where type section located, to the north of Langu district, Satun province by Wongwanich et al. (1990),

[Figure: Sketch geological map (from various sources) of the southern part of Peninsular Thailand and Langkawi Island of Malaysia. Note that Thai stratigraphic nomenclature has been extended to Langkawi Island (Ridd. 2011)]

Synonym: หมวดหินป่าแก

The lower part, 34 m thick, limestone, red, poorly laminated to very thin bedded; with darker red argillaceous partings, and abundant crinoids debris, stromatolitic polygons. The upper part, 32 m thick, dominated by nodular limestone.
Parent unit: Top-most unit of the Thung Song Gr (Wongwanich and others, 1990), but Ridd (2011) also assigned it to the Satun Gr.
Thickness: 66 m at the type section, 126 m thick at Petra National Park

[Figure1: Upper Ordovician Pa Kae Formation; pale pink to grey limestone dipping gently to the right, with characteristic network of non-calcareous mineral, possibly caused by clay-filled pressure-solution cracks. East of Langu-Thung Wa road at about 6858 0 34 00 N, 99846 0 28 00 E (Ridd, 2011).]

[Figure2: Composite stratigraphic section of the Upper Ordovician to Carboniferous near Ban Thung Samet, between Km 10 and Km 11 on the Langu to Thung Wa road in Satun Province. From Ridd (2011), which is modified after Wongwanich et al. 2002).]

The Pa Kae Fm has an abundant trilobite fauna which was the subject of an important study by Fortey (1997). He described 39 species and found very close similarities to the Pagoda Formation of southern China, stating ‘. . . the extraordinary similarity of the Thai fauna to those of the Yangtze Platform is beyond question, and might favor geographical proximity over the distributive effects of ocean currents.’ It is an outer-shelf assemblage dominated by nileids, Ovalocephalus and remopleuridids.

On the basis of its trilobites, orthoconic nautiloids, gastropods, crinoids, brachiopods and ostracods, the Pa Kae Fm was considered by Cocks et al. (2005) to be of latest Caradoc to early Ashgill age. Conodonts studied by Agematsu et al. (2007) indicated a Darriwilian (mid-Ordovician) to Late Ordovician age (Ridd, 2011, p.8-9; used here).

Low-energy continental slope or deeper water (Agematsu et al., 2007)