Lower Permian (Late Kungurian) conodonts from the Sibumasu Terrane, Malaysia: paleoecological, paleobiogeographical and tectonic implications

Abstract Late Kungurian (Lower Permian) conodonts are described from the Kanthan Limestone, Perak, Peninsular Malaysia and for the first time from the Sibumasu Terrane of the Malay Peninsula. The co-occurrence of Gullodus duani, Gullodus hemicircularis, Gullodus sicilianus, Mesogondolella lamberti and Mesogondolella siciliensis represent the Mesogondolella lamberti International Conodont Zone and the broadly equivalent Mesogondolella siciliensis Regional Conodont Zone. A small fault-bounded basal Pennsylvanian (basal Bashkirian) conodont fauna including Gnathodus girtyi simplex and Declinognathodus inaequalis is also reported. The late Kungurian conodonts from the Kanthan Limestone were deposited in a relatively deep-water environment on the northern passive margin of the Sibumasu Terrane of the eastern Cimmerian Continent located at c. 35oS latitude. Biogeographically, the fauna represents the southern peri-Gondwana Cool Water Province which is consistent with its palaeogeographic location. A new scheme, utilizing characteristics of P1 elements, including position of the 1st denticle, location of 2nd and 3rd denticles, platform shape, platform cross-section, denticle shape in cross-section, and lateral denticle development is proposed for distinguishing between species of the hindeodid genera Gullodus, Hindeodus and Isarcicella. The late Kungurian fauna from the Kanthan Limestone represents the southern peri-Gondwana Cool Water Province supporting palaeogeographic reconstructions placing the Sibumasu Terrane in moderate southern palaeolatitudes in the Kungurian.


Introduction
Carbonate complexes are extensively developed on the Sibumasu Terrane (Metcalfe, 1984(Metcalfe, , 2017a in the western part of the Malay Peninsula (west of the Palaeo-Tethyan Bentong-Raub Suture Zone) ranging in age from Ordovician to Triassic. Extensive Palaeozoic limestones and dolostones in the Kinta Valley region of Perak in the Malay Peninsula form part of these carbonate complexes, and these have been subject to karstification and are now exposed in mogote limestone hills and in the valley floor beneath alluvial deposits and have been historically exposed in alluvial tin mines. These limestones have been subjected to regional tectonic metamorphism and to thermal metamorphism by Triassic granites. Limestones in the Kinta Valley, Perak, have been variably referred to in the historical literature as the 'Kinta Limestone' or the 'Chemor/Kanthan Limestone' and 'Kampar Limestone' in the Chemor and Kampar areas, respectively, and range in age from Silurian to Early Permian (Metcalfe, 2017b). Limestone, dolostones and marbles exposed in the Chemor area of the Kinta Valley were referred to as the Kanthan Limestone (after Gunong Kanthan) by Metcalfe (2002), and this term is used in this paper for the carbonate sequences in the Kanthan area. Other Kinta Valley limestones form part of the Palaeozoic sequences to the west of Kampar which were formerly exposed in open cast tin mines (Suntharalingam, 1968;Metcalfe, 2017a). Devonian, Carboniferous and Permian conodonts have been recovered from surface outcrops of the Kanthan Limestone (Alexander & Müller, 1963;Lane et al. 1979;Metcalfe, 1979Metcalfe, , 1981aMetcalfe, , 1983Metcalfe, , 2002Metcalfe, , 2017b) and more recently from limestones in boreholes near Sungai Siput north of Kanthan and at Malim Nawar a few kilometres north-west of Kampar (Tsegab et al. 2017). The first Permian conodonts in Malaysia were reported from a single sample from the Kanthan Limestone at Gunong Kanthan by Metcalfe (1981a). This poorly preserved fauna included 'Neogondolella' bisselli (Clark and Behnken) and 'Anchignathodus' (Hindeodus) minutus (ElIison) and was interpreted as lateWolfcampian (= Artinskian) in age. Extensive sampling of limestones and dolostones in the Palaeozoic sequence west of Kampar (Suntharalingam, 1968) did not yield any conodonts (Metcalfe, 2017b). Based on the small Permian conodont fauna recovered from Gunong Kanthan by Metcalfe (1981a), additional sampling was undertaken in 2002 at Gunong Kanthan aimed at obtaining additional Permian conodont material, and this paper reports the results of that subsequent study.

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unconformably overlain by continental redbeds, the Saiong Beds, of late Jurassic-Cretaceous age.

2.b.3. Structural geology
The sampled sequence forms part of the eastern limb of a large N-S trending anticline (Fig. 4). The core of the anticline is formed by Devonian limestones, and the eastern flank includes faulted packages of Carboniferous and Permian strata. Deformation includes syn-sedimentary faults and slump folds on which have been superimposed Indosinian tectonic folding and faulting and ductile hightemperature folding and shearing related to Late Triassic-Early Jurassic granite emplacement (Choong et al. 2016); see Fig. 6 for some examples. Major faults are represented by thick breccia zones (Fig. 6).

2.b.4. Sample locations
Twenty samples were collected from a sequence of limestones and breccias measured in 2002 located on the eastern flank of the anticline at Gunong Kanthan (Fig. 4). The sampled sequence comprises 160 m of strata which generally dips steeply (70-75 degrees east but in places vertical). There are two major fault zones represented by thick breccia horizons that separate an out of  Metcalfe, 1979Metcalfe, , 1981aMetcalfe, , 2002Metcalfe, , 2017b and 2002 (results presented in this paper). After Metcalfe (2002).
Lower Permian (Late Kungurian) conodonts from the Sibumasu Terrane, Malaysia sequence sliver of Carboniferous limestones from the otherwise Lower Permian limestones (Fig. 6). The sampled limestones also exhibit some minor folds and faults, some of which may represent slumps and soft-sediment deformation (Fig. 6). The sampled limestones include dark-grey thin-bedded shaley limestones, dark grey to black bedded laminated limestones, paler grey bedded and more massive limestones. The limestones are dolomitized to variable degrees and exhibit multiple phases of dolomitization from early diagenetic through various stages of replacement dolostones related to fracture systems and hydrothermal fluids (Hui et al. 2022). Limestone breccias recorded in the sampled section are highly sheared and contain angular clasts and some discontinuous limestone beds and are interpreted here as major fault zones. The discontinuous limestone beds in the breccia zones only yielded a few fragmentary conodont elements and could not be specifically dated.

3.a. Faunas and ages
Fourteen of the 20 samples collected yielded conodonts. Preservation is variable with all conodonts showing both metamorphic colour and textural alteration due to both regional tectonism and thermal heating as previously reported at Gunong Kanthan by Metcalfe (2002Metcalfe ( , 2003. Recovered faunas are mainly of P1 elements and of low diversity. Conodont abundances are variable but generally low from less than 1 element per kilogram up to 26 per kilogram (Table 1).

3.a.2. Permian conodonts
Permian conodonts have been recovered from limestones to the west (0-60 m) and east (98-160 m) of the out of sequence Carboniferous block bounded by major fault breccia zones (Figs. 4,6). Limestones within the 0-60 m limestone package yielded moderately abundant conodonts, whereas the limestones from 98 to 160 m yielded very few conodonts (Table 1).
The co-occurrence of Gullodus duani, Gullodus hemicircularis, Gullodus sicilianus, Mesogondolella lamberti and Mesogondolella siciliensis in samples GK01 to GK07 indicate a late Kungurian age for the package of limestones represented by these samples (Fig. 6) and represent the Mesogondolella lamberti International Conodont Zone and the broadly equivalent Mesogondolella siciliensis Regional Conodont Zone (Henderson, 2018;Lambert et al. 2007;Yuan et al. 2022); see Fig. 9. Similar Late Kungurian Limestones from 98 to 160 m yielded only three conodont elements. The occurrence of Mesogondolella siciliensis together with Hindeodus sp. indicates a probable Late Kungurian age representative of the Mesogondolella siciliensis Regional Conodont Zone.
Genus Gullodus Kozur (1993) Original Diagnosis (Kozur, 1993): Spathognathodiform element with short to moderately long anterior blade that bears 3-6 broad denticles. In the anterior part of the anterior blade, one to two small denticles are present. The following two denticles are large, and the third or fourth denticle is the largest one. After the largest denticle two smaller, but also broad denticles may be present.
The posterior blade is somewhat to very much longer than the anterior one. It consists mostly of numerous (more than 10, mostly 13-15) small triangular denticles of nearly equal size. Only in the stratigraphically oldest form the posterior blade has 7, rather long subtriangular denticles. Under the entire posterior blade, a large cup is present. Basal cavity strongly expanded. Under the posterior blade, a broad basal furrow is present that becomes narrower against the anterior end of the blade.
Emended Diagnosis (Sun et al. 2017): Spathognathodiform elements with a medium to long anterior blade and a posteriorly positioned, strongly expanded basal cavity. Denticles occur on the blade and above the basal cavity and are in most cases without ornamentations. Denticles are generally 10-18 in number, and those above the basal cavity can be expanded and form a carinalike structure or narrow transverse ridges. Small coalesced denticles are sometimes developed on the anterior edge forming an 'anterior blade'. Length/height ratio is between 1.5 and 3. Basal Lower Permian (Late Kungurian) conodonts from the Sibumasu Terrane, Malaysia cavities are expanded and non-ornamented and occupy 1/3 to 2/3 of the full body.
Emended Diagnosis (This paper): Spathognathodiform elements with a medium to long anterior blade and a posteriorly positioned, strongly expanded basal cavity. Denticles occur on the blade and above the basal cavity and are in most cases without ornamentation. Denticles are generally 10-18 in number, and those above the basal cavity can be expanded and form a carinalike structure or narrow transverse ridges. The cusp and subsequent few denticles have a pear-shaped cross-section. Other denticles are round to sub-rectangular in cross-section and not laterally compressed. Small coalesced denticles are sometimes developed on the anterior edge forming an 'anterior blade'. Length/height ratio is between 1.5 and 3. Basal cavities are expanded and lobed, non-ornamented and occupy 1/3 to 2/3 of the full body.
Remarks: The genus Gullodus was first established by Kozur (1993) who designated Gnathodus sicilianus Bender and Stoppel (1965) as the type species. Kozur (1993) also described a new species, Gullodus hemicircularis and designated the specimen figured as Hindeodus? sp. by Van Den Boogaard (1987, p. 25, Fig . 10e) as the holotype specimen. The hindeodid genera Gullodus, Hindeodus, Pseudohindeodus and Isarcicella are all similar, and some species have been assigned to different hindeodid genera by different authors using different criteria. Sun et al. (2017) proposed a new amended diagnosis for the genus Gullodus as they regarded the original Kozur diagnosis as inadequate in recognizing the difference between Hindeodus and Gullodus. In the amended diagnosis, the main features considered diagnostic of Gullodus are a medium to long anterior blade, a posteriorly positioned, strongly expanded basal cavity, a length/height ratio of between 1.5 and 3 and expanded non-ornamented basal cavities that occupy 1/3 to 2/3 of the full P1 element. The cross-sectional shape of denticles, used by Metcalfe and Crowley (2020) to distinguish between Hindeodus (laterally compressed denticles) and Isarcicella (round peg-like denticles), was not considered as a criteria by Sun et al. (2017) in distinguishing hindeodid genera. The denticles of Gullodus are round to sub-rectangular in cross-section and not laterally compressed (Fig. 10), and this characteristic is here considered important following Metcalfe and Crowley (2020). This has been taken into account in the amended diagnosis presented in this paper to help distinguish the genus from Hindeodus. It is here Fig. 10. Proposed criteria to distinguish between the genera Hindeodus, Gullodus and Isarcicella (Partly after Metcalfe & Crowley, 2020). Note: 1st denticles of some P1 elements may have one or more small anterior accessory denticles and are not necessarily the cusp of the element.
Stratigraphic range: Kungurian to Capitanian Remarks: This species was re-interpreted to belong to Hindeodus by Sun et al. (2017) but is here retained in the genus Gullodus because it does not have laterally compressed denticles on the P1 element that are diagnostic of species of Hindeodus (Fig. 10). Some elements identified as Hindeodus gulloides (Kozur & Mostler, 1995) by Burrett et al. (2015, Fig. 6, j-m) are here regarded as probable Gullodus hemicircularis, but unfortunately no oral views were provided. Burrett et al. (2015) commented on the transitional nature of these forms between Gullodus and Hindeodus.
Occurrence: Sicily, South China, Malay Peninsula, Timor. Stratigraphic range: Kungurian to Wordian. Remarks: Gullodus sicilianus (Bender & Stoppel, 1965) is a rare taxon known mainly from the Wordian (Roadian) of the Tethys realm (Kozur, 1993(Kozur, , 1995. Its occurrence in the Late Kungurian of Malaysia extends the known range of this species. The species differs from Gullodus duani in that the carina extends to the end of the cup, and it has a higher blade and larger size  Mesogondolella lamberti   (Fig. 12; 1-8) Diagnosis (from : Pa element of young and adult specimens has a small cusp that is only slightly bigger than the posterior denticles, an anterior blade with largely fused denticles, and a platform with the middle and posterior parts usually parallel-sided and anterior part tapering evenly towards anterior and thus straight-sided. The apparatus is as the same as that constructed by Orchard and Rieber (1999) for Neogondolella and has a bifurcate Sc 1 element in which one of the bifurcate processes consists of only one denticle.
Diagnosis (from Lambert et al. 2007): A species of Mesogondolella characterized by a P1 element with a moderate cusp of circular to elongate circular cross-section, a moderateheight to low blade, roughly parallel posterior lateral margins, and a thin brim on larger specimens.

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Stratigraphic range: Kungurian to Wordian. Remarks: Designation of this taxon as a species of Mesogondolella (Lambert et al. 2007) rather than a sub-species of Mesogondolella idahoensis ) is here supported.
Mesogondolella siciliensis (Kozur, 1975) ( Fig. 13; 1-20; Fig. 14; 1-16; Fig. 15; 1-20) Synonomy: See Kozur (1975) and . Emended Diagnosis (from : A species of Mesogondolella in which the Pa element of young and adult specimens has a small cusp that is equal to or only slightly bigger than the posterior denticles, an anterior blade with high and largely fused denticles, and a platform that is usually widest around the middle part. The posterior denticles are more discrete than the anterior ones. The apparatus is the same as that constructed by Orchard and Rieber (1999) for Neogondolella, but the Sc1 element does not have a bifurcate anterior process.
Stratigraphic range: Late Kungurian. Remarks: Carinal denticles of M. siciliensis are discrete unlike those in Mesogondolella lamberti and M. idahoensis which are fused at their bases.
Streptognathodus sp. ? (Fig. 12, Figs 9, 10) Remarks: Two poorly preserved P1 elements tentatively assignable to Streptognathodus were recovered, one from sample GK5 and one from sample GK15. The element from sample GK15 is too poorly preserved to warrant illustration or discussion. The specimen from sample GK5 (specimen GK5/2), is a poorly preserved, broken P1 element and poor preservation precludes unequivocal specific assignment. The presence of Streptognathodus in sample GK5 together with late Kungurian conodonts is anomalous. The genus Streptognathodus does not extend above the Sakmarian (Henderson, 2018), and this specimen must therefore be re-worked from older upper Carboniferous or Asselian/Sakmarian sediments. Re-worked conodonts are already well documented in the slopedeposited Carboniferous limestones of the Kanthan Limestone (Metcalfe, 2002(Metcalfe, , 2017b, so re-working of older conodonts in the Permian is plausible and not unexpected.

4.a. Carboniferous conodonts
The small Carboniferous fauna reported here includes Gnathodus girtyi simplex, Gnathodus girtyi? and Declinognathodus inaequalis which are regarded as representing a deep-water (basinal) biofacies and are cosmopolitan species (Hu et al. 2019a(Hu et al. , 2019b. The occurrence of these conodonts in the Kanthan Limestone interpreted to have formed on the continental margin/slope of the Sibumasu Terrane located along the Australian Gondwana margin is consistent with the inferred depositional setting (Fig. 3).

4.b.1. Biofacies
Gullodus was interpreted as a shallow-water conodont genus and restricted to the upper part of reef slopes but absent on Permian carbonate platforms or in intraplatform shallow basins by Kozur (1993Kozur ( , 1995. It is interesting to note that species of Gullodus occur in the Kanthan Limestone with Mesogondolella siciliensis, regarded as a pelagic, open-sea conodont by Kozur (1993) who also noted its co-occurrence with shallow-water conodonts in the platformslope-derived Socio Limestone blocks of Sicily (Di Stefano & Gullo, 1997). Mesogondolella lamberti, also common in the Kanthan Limestone fauna, is also regarded as a pelagic, opensea conodont.
Water, Equatorial Warm Water and southern peri-Gondwana Cool Water provinces recognized (Mei & Henderson, 2001). The North Cool Water Province is characterized by abundant Neostreptognathodus and a general absence or rare occurrence of Sweetognathus. The Equatorial Warm Water Province is characterized by abundant Sweetognathus and a general absence or rare occurrence of Neostreptognathodus. Pseudosweetognathus appears to be restricted to the eastern Palaeo-Tethys of this province. The southern peri-Gondwana Cool Water Province is characterized by the distinctive cold-water genus Vjalovognathus (Metcalfe & Nicoll, 1995;Nicoll & Metcalfe, 1998) which is restricted to this southern hemisphere province. Mesogondolella idahoensis exhibits an antitropical distribution, occurring in both the North Cool Water and peri-Gondwana Cool Water provinces but not in the Tethyan Equatorial Warm Water Province. Occurrences in West Texas are in a location that appears, based on palaeogeograhic reconstructions, to be in a low-latitude warm climate location which seem anomalous (Fig. 16). Further taxonomic studies on the West Texas faunas or the tectonic setting of that location might resolve this issue. The antitropical distribution of Mesogondolella idahoensis is mirrored by the cool-water foraminifera genus Monodiexodina. Mesogondolella lamberti also shows an antitropical distribution. Mesogondolella siciliensis is commonly found in the southern peri-Gondwana Cool Water Province and in the Equatorial Warm Water Province but has not been recorded in the North Cool Water Province, suggesting that other factors in addition to temperature may be controlling its distribution. The occurrence of Mesogondolella siciliensis cannot be used as an unequivocal indication of warm or tropical ecological conditions. The co-occurrence of 'warmwater' and 'cool-water' conodont faunas in the same samples from deep-water carbonates in Guangxi, South China (Zhang et al. 2010) demonstrates this. The genus Gullodus occurs in both the Equatorial Warm Water and southern peri-Gondwana Cool Water provinces (Fig. 16) but has so far not been reported from the North Cool Water Province. The late Kungurian conodont fauna reported here from the Kanthan Limestone of the Sibumasu Terrane does not contain any Sweetognathus nor any associated fusulinids and represents the southern peri-Gondwana Cool Water Province which is consistent with the palaeogeographic position of the fauna on the Sibumasu Terrane located at about 35 degrees South latitude based on multidisciplinary data. The occurrence of Mesogondolella lamberti in the fauna demonstrates the antitropical distribution of this biostratigraphically important species (Fig. 16). The late Kungurian fauna with M. siciliensis and co-occurring Sweetognathus subsymmetricus and Sweetognathus guizhouensis together with fusulinids on the South Qiangtang Block (Yuan et al. 2022) indicates a warmer water setting within the Equatorial Warm Water Province reflecting a lower latitudinal position for South Qiangtang. The eastern Cimmerian continental strip therefore straddles the boundary between the Equatorial Warm Water and peri-Gondwana Cool Water provinces (Fig. 16).

Conclusions
(1) Late Kungurian (Lower Permian) conodonts are described for the first time from the Sibumasu Terrane of Malaysia.