Comments on the Definition of the Ordovician-Silurian Boundary

Latest Ordovician to earliest Silurian graptolites of northwest Peninsular Malaysia

“…A . lata (Elles and Wood, 1906), Korenograptus elegantulus (Mu and Ni, 1983), Metabolograptus extraordinarius (Sobolevskaya, 1974), Metabolograptus ojsuensis (Koren’ and Mikhaylova in Koren et al, 1980), Neodiplograptus shanchogensis (Li, 1984) (Li, 1984b), Normalograptus ajjeri (Legrand, 1977), Normalograptus aff. N. mirnyensis (Obut and Sobolevskaya in Obut et al, 1967), and Normalograptus temalaensis (Jones, 1973) (Figs.…”

“…This finding seems to match well with biostratigraphy schemes in the nearby regions such as in the Mandalay Region in Myanmar (Chen et al, 2020) and South China (Chen et al, 2004), suggesting a close paleogeographical tie, but it seems to differ from that reported in southern Thailand (Wongwanich et al, 1990). In the Mandalay region, graptolites that can be found from the extraordinarius Biozone include Korenograptus acanthus (Lin in Mu et al, 1993), Korenograptus selectus Chen et al, 2020, Neodiplograptus incommodus Legrand, 2009, Normalograptus ajjeri (Legrand, 1977), Normalograptus angustus (Perner, 1895), Normalograptus pseudovenustus (Legrand, 1986), Metabolograptus ojsuensis (Koren’ and Mikhaylova in Koren et al, 1980), and Metabolograptus extraordinarius (Sobolevskaya, 1974) (Chen et al, 2020). The Global Boundary Stratotype Section and Point (GSSP) for the base of the Hirnantian Stage itself was proposed at a point below the base of the Kuanyinchiao Bed in the Wangjiawan North section (Chen et al, 2006) and coincided with the first appearance of Metabolograptus extraordinarius (Sobolevskaya, 1974) and a slightly earlier appearance of Metabolograptus ojsuensis (Koren’ and Mikhaylova in Koren et al, 1980).…”

“…In the Mandalay region, graptolites that can be found from the extraordinarius Biozone include Korenograptus acanthus (Lin in Mu et al, 1993), Korenograptus selectus Chen et al, 2020, Neodiplograptus incommodus Legrand, 2009, Normalograptus ajjeri (Legrand, 1977), Normalograptus angustus (Perner, 1895), Normalograptus pseudovenustus (Legrand, 1986), Metabolograptus ojsuensis (Koren’ and Mikhaylova in Koren et al, 1980), and Metabolograptus extraordinarius (Sobolevskaya, 1974) (Chen et al, 2020). The Global Boundary Stratotype Section and Point (GSSP) for the base of the Hirnantian Stage itself was proposed at a point below the base of the Kuanyinchiao Bed in the Wangjiawan North section (Chen et al, 2006) and coincided with the first appearance of Metabolograptus extraordinarius (Sobolevskaya, 1974) and a slightly earlier appearance of Metabolograptus ojsuensis (Koren’ and Mikhaylova in Koren et al, 1980). In the Satun province of southern Thailand, however, the index fossil Metabolograptus persculptus (Elles and Wood, 1907) instead was reported from the lower member of Wang Tong Formation, below the Hirnantia fauna bed (Rickards in Wongwanich et al, 1990).…”

“…However, without any graptolite illustrations to confirm this, it is perhaps more appropriate to restudy the Satun material. At the Vinini Creek section in north central Nevada, the interval defined by the extraordinarius Biozone possesses a moderate species diversity that includes the index species Metabolograptus extraordinarius (Sobolevskaya, 1974) and Metabolograptus ojsuensis (Koren’ and Mikhaylova in Koren et al, 1980), which are abundant throughout, while normalograptids such as Normalograptus ajjeri (Legrand, 1977), Normalograptus mirnyensis (Obut and Sobolevskaya in Obut et al, 1967), and rare Normalograptus angustus (Perner, 1895) also make their first appearance in the interval (Štorch et al, 2011). Diplograptina such as A. lata (Elles and Wood, 1906) do occur but made their last appearance within the extraordinarius Biozone, which coincides with the first appearance of the normalograptids in the Vinini Creek section (Mitchell et al, 2007; Štorch et al, 2011); the same pattern can also be seen in South China (Chen et al, 2005a, b).…”

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Figure 3.The stratigraphy and occurrence of the graptolites of the uppermost Ordovician to the lowermost Silurian of Tanjung Dendang Formation in Pulau Langgun, Langkawi.

Figure 4.Graptolites of the Metabolograptus extraordinarius Biozone in Pulau Langgun, Langkawi. ( 1–7 ) Metabolograptus ojsuensis (Koren’ and Mikhaylova in Koren’ et al, 1980): ( 1 ) 191F-1_1; ( 2 ) 179F_1; ( 3 ) 175F_3; ( 4 ) 188F_1; ( 5 ) 176F_2; ( 6 ) 173F_1; ( 7 ) 176F_4. ( 8, 9 ) Anticostia aff.

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