Carnets Geol. 22 (14)  

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[1. Introduction] [2. Material and depository] [3. geological settings]
[4. Systematic micropalaeontology] [5. Biostratigraphy]
[6. Discussion] [7. Conclusions] and ... [Bibliographic references]

The Lower Cretaceous Tuburan Limestone of Cebu Island, Philippines:
Microfacies, micropalaeontology, biostratigraphy,
and palaeogeographic perspectives

Jerali Rodrigo

Degree Programs in Life and Earth Sciences, Graduate School of Science and Technology, University of Tsukuba, Tsukuba City, Ibaraki (Japan)

Felix Schlagintweit

Corresponding author;
Lerchenauerstr. 167, 80935 Munich (Germany)

Published online in final form (pdf) on August 10, 2022
DOI 10.2110/carnets.2022.2214

[Editor: Bruno R.C. Granier; language editor: Simon F. Mitchell]

Click here to download the PDF version!


The occurrence of orbitolinid-bearing shallow water limestone blocks (Tuburan Limestone) incorporated into the volcanic series from Cebu Island, Central Philippines, has been known since the 1950's. Taxonomic studies including solid biostratigraphic data however are lacking or not substantiated. Herein we report the occurrence of Mesorbitolina texana (Roemer), transitional forms between M. texana and M. subconcava (Leymerie), Mesorbitolina birmanica (Sahni), Palaeodictyoconus actinostoma Arnaud-Vanneau & Schroeder, Neorbitolinopsis conica (Matsumaru), Paracoskinolina sp. and other benthic foraminifera (Akcaya, Praechrysalidina, Vercorsella) indicating a latest Aptian age. The previously accepted Late Albian age for the Tuburan Limestone based on Neorbitolinopsis conulus (Douvillé) is rejected herein and suggested as a misidentification with the recently revised Aptian - Lower Albian Neorbitolinopsis conica (Matsumaru). The general poverty of Lower Cretaceous dictyoconids in the Tuburan Limestone is interpreted as being caused by the lack of suitable extensive lagoonal facies that is generally typical for carbonate platforms of passive continental margins. The observed microfacies types instead refer to external platform margin settings with corals, stromatoporoids, sclerosponges (e.g., Acanthochaetetes), and planktic foraminifera. The recovered (micro) fauna from Cebu Island shows striking similarities to assemblages reported from Western and Mid-Pacific guyots but with indicated younger ages (up to the late Albian) based on data that - in our opinion - do not stand up to close scrutiny. Finally, a model is proposed interpreting the Tuburan Limestone from Cebu Island as remnants of a former carbonate cover of a guyot that originated as a volcanic island in the Western-Central Pacific, and later became incorporated into an accretionary wedge/mélange zone due to subduction-collisional processes.


• larger benthic foraminifera;
• orbitolinidae;
• calcareous algae;
• taxonomy;
• biostratigraphy;
• palaeobiogeography


Rodrigo J. & Schlagintweit F. (2022).- The Lower Cretaceous Tuburan Limestone of Cebu Island, Philippines: Microfacies, micropalaeontology, biostratigraphy, and palaeogeographic perspectives.- Carnets Geol., Madrid, vol. 22, no. 14, p. 661-679.


Le Calcaire de Tuburan (Crétacé inférieur) de l'île de Cebu, Philippines : Microfaciès, micropaléontologie, biostratigraphie et perspectives paléogéographiques.- La présence de blocs de calcaires d'eaux peu profondes, recelant des orbitolinidés (Calcaire de Tuburan), incorporés dans la succession volcanique de l'île de Cebu, au centre des Philippines, est connue depuis les années 1950. Toutefois, nous manquions d'études taxonomiques comprenant des données biostratigraphiques robustes, ou alors ces dernières étaient peu ou mal étayées. Nous signalons ici la présence de plusieurs taxons : Mesorbitolina texana (Roemer), des formes de transition entre M. texana et M. subconcava (Leymerie), Mesorbitolina birmanica (Sahni), Palaeodictyoconus actinostoma Arnaud-Vanneau & Schroeder, Neorbitolinopsis conica (Matsumaru), Paracoskinolina sp., ainsi que de quelques autres foraminifères benthiques (genres Akcaya, Praechrysalidina, Vercorsella), qui attestent d'un âge Aptien supérieur. L'âge Albien supérieur antérieurement retenu pour le Calcaire de Tuburan, basé sur Neorbitolinopsis conulus (Douvillé), est donc rejeté. Cela pourrait provenir d'une erreur d'identification avec Neorbitolinopsis conica (Matsumaru), un orbitolinidé de  l'Aptien - Albien inférieur récemment révisé. La rareté des dictyoconidés du Crétacé inférieur dans le Calcaire de Tuburan est attribuée à l'absence d'environnements favorables, i.e., à l'absence de faciès  lagunaires étendus, une caractéristique des plates-formes carbonatées des marges continentales passives. Les microfaciès identifiés ici correspondent  plutôt à ceux de bordures de plate-forme externe avec coraux, stromatoporoïdes, sclérosponges (par exemple, Acanthochaetetes) et foraminifères planctoniques. La (micro-) faune de l'île de Cebu que nous avons pu étudier présente des similitudes frappantes avec celle d'associations signalées dans les guyots de l'ouest et du centre du Pacifique. Les âges supposés de ces dernières sont plus jeunes (jusqu'à la fin de l'Albien) mais établis sur des données qui ne devraient pas résister à une nouvelle expertise. En conclusion, nous proposons un modèle dans lequel le Calcaire de Tuburan de l'île de Cebu est interprété comme représentant les vestiges de la couverture calcaire d'un ancien guyot qui aurait pris naissance à partir d'une île volcanique dans le Pacifique centre-ouest avant d'être incorporé dans un prisme d'accrétion (ou zone de mélange) lié aux processus régionaux de subduction et de collision.


• grands foraminifères benthiques ;
• orbitolinidae ;
• algues calcaires ;
• taxinomie ;
• biostratigraphie ;
• paléobiogéographie

1. Introduction

Orbitolinidae are a group of agglutinated conical larger benthic foraminifera with biostratigraphic importance especially for Lower and "Middle" Cretaceous shallow-water, mainly carbonatic strata (e.g., Schroeder & Neumann, 1985). They are particularly widespread in carbonate platforms of the western (e.g., Arnaud-Vanneau, 1980), central-eastern Neotethys (e.g., Henson, 1948) and America-Caribbean (e.g., Douglass, 1960) realms. Occurrences from the western Pacific active margin are more patchily distributed often referring to shallow-water limestone clasts and megablocks in hemipelagic accretionary wedge sediments. They have been recorded from Japan (e.g., Yabe & Hanzawa, 1926; Iba & Sano, 2006, 2007; Iba et al., 2011; Matsumaru et al., 2005; Matsumaru & Furusawa, 2007), Malaysia (Hashimoto & Matsumaru, 1977), the Philippines (Amiscaray & Nilayan, 1984; Fernandez et al., 1994, Masse et al., 1996), and Indonesia (Martin, 1889; Hofker, 1963; Hashimoto & Matsumaru, 1974; Bassi et al., 2009; BouDagher-Fadel & Price, 2019). In the Central Pacific area, between the Marshall Islands and Hawai respectively, Lower Cretaceous orbitolinids have been recorded from drillings on West- and Mid-Pacific seamounts (guyots) (Konishi, 1989; Arnaud-Vanneau & Sliter, 1995; Arnaud-Vanneau & Premoli Silva, 1995). The occurrences from the Philippines refer to the islands of Cebu, Catanduanes and the Caramoan Peninsula respectively (Amiscaray & Nilayan, 1984; Fernandez et al., 1994; Militante-Matias, 1995; Takizawa et al., 1996; David et al., 1997). At Cebu Island, the orbitolinid bearing strata (blocks, olistoliths) are known as the Tuburan Limestone (Fig. 1 ). Amiscaray & Nilayan (1984) reported the occurrence of Orbitolina texana and O. kurdica but none of the illustrated specimens shows the embryo needed for determination. From Cebu Island, Masse et al. (1996) reported (without illustrations) the occurrence of Mesorbitolina texana (Roemer) and Neorbitolinopsis conulus (Douvillé) concluding a late Albian age. New sampling from Tuburan Limestone blocks from Cebu Island yielded orbitolinids and other benthic foraminifera as well as calcareous algae (e.g., Dasycladales) that are taxonomically treated herein. The new data contribute to sound biostratigraphic data, and a refined distribution of these taxa enabling a discussion on their palaeobiogeographic relevance (Tethys vs. Pacific).

Fig. 1
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Figure 1: Geological map of Central Cebu, Cebu Island modified from the 1:50.000 scale Geologic Quadrangle maps published by BMG (1983) superimposed on IFSAR DEM. Green boxes: investigated locations of Tuburan Limestone outcrops (1) Tuburan area, (2) Barangay Lanao, Asturias, (3) Manipis Road, (4) Barangay Lutak, Naga. Red star: outcrop location of the polyconitid rudistid bivalve Magallanesia canaliculata Sano et al. (2014).

2. Material and depository

The thin-sections of the studied carbonate rock samples with illustrations provided in the taxonomic part are stored at the Geology and Paleontology Division of the National Museum of the Philippines, Manila (see Table 1). In the entire manuscript the original sample and thin-section numbers are used.

Table 1: Field sample numbers, localities, and thin-section depository numbers at the Geology and Paleontology Division of the National Museum of the Philippines, Manila.

Sample number Depository number Locality
KENMT12201 NMP-2225 Tuburan area
KENTM12202 NMP-2226a, NMP-2226b Tuburan area
TUBI62035 NMP-2227a to -2227f (six thin-sections) Tuburan area
TUBI62036 NMP-2228a to -2228c (three thin-sections) Tuburan area
ASH232015B NMP-2229 Barangay, Lanao, Asturias
LTH212021 NMP-2230 Barangay, Lutak, Naga
LTH212016 NMP-2231 Barangay, Lutak Naga
TUBI62027 NMP-2232 Tuburan area
TUBI62034 NMP-2233a to NMP-2233c Tuburan area
MNH222025 NMP-2234 Manipis Road

3. Geological settings

3.1 Geological overview

The Philippines represent an island arc system within a complex system of subduction and collision zones as well as marginal seas in the Western Pacific area (e.g., Yumul et al., 2003). This active region is bounded by oppositely dipping subduction zones where the bounding plates, namely the Philippine Sea Plate and Eurasian/Sunda Plate, are being consumed (Rangin et al., 1999; Yumul et al., 2003). Cebu Island belongs to the eastern portion of the Central Philippines being part of the Philippine Mobile Belt, a region of complex deformation consisting of amalgamated allochthonous blocks of volcanic and plutonic rocks and their derived sediments, as well as ophiolithic and ophiolite complexes and their metamorphosed equivalents (McCabe et al., 1985; Yumul et al., 2005; Dimalanta et al., 2006). Cebu represents a SSW-NNE trending, rather long (~196 km) and narrow (~32 km) island (Fig. 1 ). It is underlain by a Mesozoic basement consisting of ultramafic, metamorphic, plutonic and volcanic rocks overlain by sedimentary rocks, and is exposed in the northern and central parts of the island (Corby et al., 1951; Santos-Yñigo, 1951, Bureau of Energy Development (BED), 1986a, 1986b; Porth et al., 1989; Rangin et al., 1999; Diegor et al., 1996; Dimalanta et al., 2006; Deng et al., 2015, 2017, 2019; Rodrigo et al., 2020; Gong et al., 2021). The Lower Cretaceous Tuburan Limestone occurs as small, isolated ridge-top remnants in the highland areas of Central Cebu (Santos-Yñigo, 1951). In some areas, this unit overlies either the Tunlob Schist or the Cansi Volcanics, while in several places it is incorporated in the Pandan Formation. The samples from the Tuburan Limestone studied herein are from four localities: the Tuburan area, Barangay Lanao (Asturias), Manipis Road, and Barangay Lutak (Naga) (Figs. 1 - 2 ).

Fig. 2
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Figure 2: Field views of outcrops of the Tuburan Limestone of Cebu Island, Philippines. (A) Massive outcrop of bedded limestone exposed in Marmol Gorge (canyon walls of Languyon River) (sample location KENMT12201 and KENMT12202). (B) Olistolith admixed with volcanics, siliceous mudstones, sandstones and limestones exposed along the road in the Tuburan Area (sample location TUBI62035 and TUBI62036). (C) Limestone ridge linking the Marmol Gorge and the basal section observed along the road at higher elevation which is characterized by olistolith blocks. (D) Upper conglomeratic unit of the Baye Formation exposed along the road in Barangay Lanao, Asturias (sample location ASH232015). (E) Clast-supported polymictic conglomerate bed consisting of basalt, andesite, siliceous mudstones, sandstones and limestone clasts with orbitolinids (sample location MNH222022). (F) Limestone boulders exposed along the road cut at station 4 along the Manipis Road (sample location MNH222026). (G) Massive limestone boulder exposed along the upper benches of the FDR Mine Quarry in Barangay Lutak in Naga City (sample location LTH212021).

3.2 Outcrop localities

3.2.1 Tuburan area (samples KENMT12201, KENMT12202, TUBI62026, TUBI62027, TUBI62034, TUBI62036, TUBI62035)

At the type locality of the Tuburan Limestone along Marmol Gorge (10°41'26.5"N 123°51'55.9"E), the limestone unit occurs as a thickly bedded outcrop exposed along the canyon walls of the Languyon River (Fig. 2.A ). Samples collected from this locality are white to beige, dense, and brecciated with iron oxide stains along fractures. Biogenic grains are sub-angular to sub-rounded which tend to be visible to the naked eye with sizes ranging from 1 to 7 millimeters.

Along a newly constructed road South of Marmol Gorge, cobble to mega-blocks of the Tuburan Limestone are exposed (10°41'16.3"N 123°51'18.5"E) (Fig. 2.B-C ). These exposures are part of the southern extension of the massive limestone found along the Marmol Gorge. The only difference is that the basal section is exposed and admixed with volcaniclastic materials identified as debris flow deposits and considered as part of the lower unit of the Pandan Formation. Adjacent to the outcrop, a slump-folded turbiditic sandstone-mudstone sequence caps the debris flow deposits. The paraconglomeratic outcrop in this area is moderately weathered and composed predominantly of admixtures of sub-angular to sub-rounded cobble- to boulder-sized volcanics (basalt, andesite, and siliceous mudstones) and pebble- to mega-block sized limestones.

3.2.2 Barangay Lanao, Asturias (sample ASH232015)

The orbitolinid-bearing limestones in this locality occur as cobble clasts in the upper part of the Baye Formation (10°36'01.0"N 123°50'11.0"E) (Fig. 2.D ). The Baye Formation exposed in its type locality is characterized by a lower unit consisting of moderately to highly weathered paraconglomerate that in turn is composed of sub-angular to sub-rounded basalts, andesite, siliceous mudstones and limestone clasts in a sandy to silty matrix, interbedded within a reddish hematite rich claystone. The upper unit consists of moderately thick limestone-rich sandstone/pebbly sandstone (0.3-0.5 meters) overlain by a massive bed of thick, poorly indurated conglomerate predominantly composed of sub-angular to sub-rounded limestones that in turn are capped by a massive calcareous sandstone.

3.2.3 Manipis Road (samples MNH222022, MNH222024, MNH222025, MNH222026)

Several limestone blocks intercalated within the clastic units of the Pandan Formation are exposed from Camp 4 all the way to Camp 7 (Tabunoc-Toldedo Road). Exposures of the limestone units are observable along the Mananga Canyon or along the stretch of the Manipis Road. In this study, four outcrop locations were sampled and analyzed for petrographic analyses. At outcrop station 1 (10°19'38.1"N 123°48'29.7"E), the polymictic and clast-supported conglomerate unit consists of sub-angular to sub-rounded, gravel to cobble sized basalts, andesite, red and green sandstones and siltstone clasts (Fig. 2.E ). Associated volcanic clasts are characterized by amygdaloidal textures containing chlorite-calcite amygdales and porphyritic texture characterized by lath shape plagioclases, clinopyroxene (augite) in a pilotaxitic groundmass of feldspar microlites. This unit occurs adjacent to a volcaniclastic-pillow lava unit which is interbedded or in thrust fault contact with the lower unit of the Pandan Formation. Further inward along the Manipis Road, three stations of massive limestones interbedded with sedimentary breccias were sampled: station one (10°19'30.4"N 123°47'44.7"E), station two (10°19'27.4"N 123°47'17.0"E) and station three exposing limestone boulders exposed along the walls of the road cut (10°19'19.1"N 123°46'46.1"E).

3.2.4 Barangay Lutak, Naga (samples LTH212016, LTH212021 )

Boulders of limestones are exposed on the upper benches of FDR Mine Quarry in Barangay Lutak in Naga City (10°15'31.5"N 123°43'07.2"E) (Fig. 2.G ). These carbonate boulders are buff, dense and highly recrystallized and are underlain by volcaniclastic materials belonging to the lower member of the Pandan Formation. Some of these carbonate rocks are characterized by embossed conical orbitolinids due to weathering and others are grainy to sandy in texture

3.3 Microfacies of the Tuburan Limestone

The microfacies of the studied thin-sections from the Tuburan Limestone are summarized in Table 2, illustrated exemplarily in Figures 3 - 4 . The microfacies types and the identified macro- and microfossil assemblages including planktic foraminifera (Fig. 4.B-C ) can be ascribed to external platform-partly upper slope depositional settings (see generalities in Flügel, 2004). Boundstones with diverse types of framebuilding organisms (corals, stromatoporoids, diverse sponge types) and microbial crusts suggest a rimmed platform type with patch-reefs of unknown dimensions (Figs. 3.D , 4.G-H ). Orbitolinids are present in almost all investigated samples with varying abundances. Many specimens display agglutination of needle- and kidney-shaped (rhaxes = "calcite eyes", see Schroeder, 1965) sponge spicules within the central zone (Fig. 4.D, F ). Some samples can be referred to well-agitated back-reef or open lagoonal facies with miliolids, vercorsellids, rivulariacean-type cyanobacteria, and dasycladalean green algae along with taxa also characteristic for external platform deposits (see details in the Taxonomic part; Fig. 5 ). The lack of internal platform (lagoonal) facies is worth mentioning, obviously caused by the original platform morphology, dimensions, and other abiotic factors.

Table 2: Microfacies, macrofossils, and observed micropalaeontological associations of the Tuburan Limestone of Cebu Island.

samples locality microfacies macrofossils microfossils depositional environment (interpretation)
KENMT12201 KENTM12202 Tuburan area Bioclastic packstone Corals, rudists, bryozoans Polystrata alba (Pfender), elianellaceans, Mesorbitolina texana (Roemer) External platform
TUBI62026 TUBI62027 Packstone Echinoids, bryozoans, sclerosponges (Neuropora), fine rudist debris Lenticulinids, planktic foraminifera, Neorbitolinopsis conica (Matsumaru & Furusawa), P. alba, corallinaceans, Neomeris sp. External platform-upper slope
TUBI62034 TUBI62036 Orbitolinid floatstone Sponge spicules (incl. rhaxes), debris of echinoids Palaeodictyoconus actinostoma Arnaud-Vanneau & Schroeder, Mesorbitolina birmanica (Sahni), M. texana, N. conica, transitional form M. texana-M. subconcava (Leymerie) External platform-upper slope
TUBI62035 Grain-packstone Debris of rudists and corals Vercorsella ssp., miliolids, Praechrysalidina infracretacea Luperto Sinni, Paracoskinolina aff. sunnilandensis Maync Outer lagoonal-back-reefal facies
ASH232015 Barangay Lanao, Asturias Packstone Rudist debris Miliolids, bacinellid fabrics, P. aff. sunnilandensis, N. conica, M. texana Outer lagoonal-back-reefal facies
MNH222024 Manipis Road Boundstone Phareotronis sponges, stromatoporoids Encrusting foraminifera, rare orbitolinids, corallinaceans Platform margin reefal facies
MNH22025 Boundstone Corals, stromatoporoids, sclerosponges (e.g., Acanthochaetetes), pharetronid sponges, microbial crusts, serpulids, echinoids Encrusting foraminifera, rare orbitolinids, P. alba Platform margin reefal facies
MNH22026 Boundstone, p.p. bioclastic packstone Corals, bryozoans, echinoids Rare orbitolinids (among N. conica) Platform margin reefal facies
LTH212016 Barangay Lutak, Naga Packstone Rudist debris, small gastropods P. aff. sunnilandensis, rivularicean-type cyanobacteria, Vercoresella ssp., Dasycladale gen. et sp. indet. 1, Morelletpora turgida (Radoičić) Outer lagoonal-back-reefal facies
LTH212020 Internal brecciated packstone echinoids Encrusting and planktic foraminifera, debris of elianellaceans External platform-upper slope
LTH212021 Packstone Vercorsella ssp., Akcaya minuta (Hofker), P. actinostoma, rivulariacean-type cyanobacteria, Salpingoporella pygmaea (Gümbel) Outer lagoonal-back-reefal facies

Fig. 3
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Figure 3: Microfacies of the upper Aptian (lowermost Albian?) Tuburan Limestone of Cebu Island, Philippines. (A) Packstone with Mesorbitolina texana (Roemer), sample KENTM12202. (B) Orbitolinid wackestone yielding Mesorbitolina texana (Roemer), Mesorbitolina birmanica (Sahni), and Neorbitolinopsis conica (Matsumaru) (not all visible in the image section), sample TUBI62036. (C) Subaxial to tangential section section of Neorbitolinopsis conica (Matsumaru), sample TUBI62034. (D) Near-reefal facies with large bioclast formed by an unknown stromatoporoid (left) and the coralline sclerosponge Acanthochaetetes Fischer (right), sample MNH222025. (E-F) Subaxial section of Palaeodictyoconus actinostoma Arnaud-Vanneau & Schroeder with detail of initial spire (not sectioning the embryo) in (F), sample TUBI62036. (G) Rudstone with corals, rudists (see Fig. 4E), and orbitolinids, sample KENTM12201.

Fig. 4
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Figure 4: Microfacies of the upper Aptian (lowermost Albian?) Tuburan Limestone of Cebu Island, Philippines. (A) Bioclastic packstone with debris of pelecypods, orbitolinids, and planktic foraminifera (hedbergellids or favusellids (B-C). (D) Transverse section of an orbitolinid displaying needle-shaped sponge spicules in the central part of the test; note the absence of spicules in the radial zone, sample ASH232015. (E) Rudist shells, sample KENTM12201. (F) Subaxial section of an orbitolinid with sponge rhaxes ("calcite eyes") agglutinated in the central zone, sample TUBI62034. (G) Stromatoporoid-coral boundstone, sample MNH222025. (H) Corals and stromatoporoids (left) with microbialitic crust (middle, right), sample MNH222025.

4. Systematic micropalaeontology

The treatment of calcareous algae refers to dasycladalean green algae that are generally rare, observed only in samples from the locality Barangay Lutak, Naga (Fig. 5 ). Among the red algae, debris of indeterminable corallinaceans and the bright-yellowish thalli of the peyssonelliacean alga Polystrata alba (Pfender) Denizot (Fig. 5.I ) is worth mentioning. The systematic section of the foraminifera refers exclusively to the Orbitolinidae due to their biostratigraphic importance (Fig. 5.A-Q ) (see Chapter 5). In addition the occurrence of Praechrysalidina infracretacea Luperto Sinni (Fig. 5.R ), Vercorsella sp. cf. V. arenata Arnaud-Vanneau (Fig. 5.S-T ), and Akcaya minuta (Hofker) (Fig. 5.U ), a typical assemblage from Lower Cretaceous carbonates observed from Central Pacific Guyots (Arnaud-Vanneau & Sliter, 1995; Arnaud-Vanneau & Premoli Silva, 1995), is demonstrated (see Chapter 6).

4.1 Calcareous algae (Dasycladales)

Phylum Chlorophyta

Class Ulvophyceae Stewart & Mattox, 1978

Order Dasycladales Pascher, 1931

Family Triploporellaceae (Pia, 1920)

Gen. et sp. indet. 1

(Fig. 5.A )

Remarks: Nothing is known about the thallus morphology and structure of this comparably large sized form. Our specimen resembles Griphoporella cretacea (Dragastan, 1967) a species recorded from Barremian-Aptian external platform environments (e.g., Bucur et al., 2008; Bucur & Schlagintweit, 2009).

Gen. et sp. indet. 2

(Fig. 5.C, G )

Remarks: Medium-sized alga with comparably high d/D (inner-outer diameter) ratio and presumably single-order laterals. Our sections resemble to some extent Piriferella somalica (Conrad et al., 1983) (= Similiclypeina somalica, see discussion in Bucur et al., 2021), that has been recorded by Masse and Arnaud-Vanneau (1995) from Lower Cretaceous carbonates of Northwest Pacific guyots (for Recent taxonomy see Conrad et al., 2009).

Genus Salpingoporella Pia in Trauth, 1918

Type-species: Diplopora muehlbergii Lorenz, 1902.

Salpingoporella pygmaea (Gümbel, 1891)

(Fig. 5.B )

1891 Gyroporella pygmaea n. sp. - Gümbel, Figs. 6-7.

2006 Salpingoporella pygmaea (Gümbel) - Carras et al., p. 484, Pl. 9, figs. 1-9.

Remarks: Our oblique section can be assigned to S. pygmaea that represents a long-lasting taxon (Bathonian-Aptian) characterizing "open marine, reefal platform margin and environs, high to moderate energy" (Carras et al., 2006, Table 1, p. 488). It is worth mentioning that the species has a wide distribution (see the comprehensive synonymy list in Carras et al., 2006), lacking any record from strata younger than Aptian.

Genus Morelletpora Varma, 1950

Type-species: Morelletpora nammalensis Varma, 1950.

Morelletpora turgida (Radoičić, 1975, non 1965)

(Fig. 5.D-E )

1965 Pianella turgida n. sp. - Radoičić, p. 195, Pl. 1, figs. 1-2; Pl. 2, figs. 1-4; Pl. 3, figs. 1-3; Pl. 4, figs. 1-4. Nomen nudum.

1975 Salpingoporella turgida (Radoičić) - Radoičić (designation of a lectotype, Pl. 1, fig. 2A in Radoičić, 1965).

2016 Morelletpora turgida (Radoičić) - Bucur et al., p. 171, Figs. 4-10.

Remarks: Our material includes one oblique and one tangential section of individual articles. M. turgida is widely reported from the western and central Neotethys including occurrences from both margins but more from the southern one (Bucur et al., 2016: Dinarides, Italy, Turkey, Lebanon, Iran, Somalia, Oman, Central Iran, Tibet). The known stratigraphic range is Aptian to lower Cenomanian. The Barremian record from one locality in Central Iran has to be corrected to lower Aptian (Schlagintweit & Rashidi, 2022).

Genus Triploporella Steinmann, 1880

Type-species: Triploporella fraasi Steinmann, 1880.

Triploporella? sp.

(Fig. 5.F )

Remarks: One fragment (oblique section); a similar section has been recorded by Masse and Arnaud-Vanneau (1995, Pl. 2, fig. 3) as Triploporella aff. steinmanni from the Lower Cretaceous of the MIT Guyot, northwest Pacific.

Family Dasycladaceae Kützing, 1843

Genus Neomeris Lamouroux, 1816

Neomeris sp.

(Fig. 5.H )

Remarks: One oblique section; no specific determination possible. Neomeris cretacea Steinmann has been recorded by Masse and Arnaud-Vanneau (1995) from the Takuyo-Daisan Guyot, Japan.

Fig. 5
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Figure 5: Calcareous algae from the upper Aptian (lowermost Albian?) Tuburan Limestone of Cebu Island, Philippines. A) Gen. et sp. indet. 1, sample LTH212016. B) Salpingoporella cf. pygmaea (Gümbel), sample LTH212021. C, G) Gen. et sp. indet. 2, sample LTH212021. D-E) Morelletpora cf. turgida (Radoičić) Barattolo, samples LTH212016, LTH212021. F) Triploporella? sp., sample LTH212021. H) Neomeris sp., sample TUBI62028. I) Polystrata alba (Pfender) Denizot, sample TUBI62026. J) Rivulariacean-type cyanobacteria, sample TUBI212016.

4.2 Larger benthic foraminifera

Phylum Foraminifera (Orbigny, 1826) Pawlowski et al., 2013

Class Globothalamea Pawlowski et al., 2013

Order Loftusiida Kaminski & Mikhalevich in Kaminski, 2004

Suborder Orbitolinina Kaminski, 2004

Superfamily Orbitolinoidea Martin, 1890

Family Orbitolinidae Martin, 1890

Subfamily Diytorbitolininae Schroeder in Schroeder et al., 1990

Genus Paracoskinolina (Moullade, 1965) Arnaud-Vanneau, 1980

Type-species: Coskinolina sunnilandensis Maync, 1955.

Paracoskinolina sp.

(Fig. 6.A-I )

1982 Paracoskinolina sp. 1 - Peybernès, Pl. 3, figs. 1-3.

1995 Paracoskinolina sp. cf. P. sunnilandensis - Arnaud-Vanneau & Sliter, p. 555, Pl. 4, figs. 14-16.

1995 Paracoskinolina sp. cf. P. sunnilandensis - Arnaud-Vanneau & Premoli Silva, p. 208, Pl. 5, figs. 5-6.

Remarks: Small-sized, medium-conical representative of the genus with eccentrically positioned, trochospirally coiled initial part, pillars in the central zone, and a marginal zone that lacks rafters. The typical alignment of pillars and main partitions is poorly constrained due to the lack of adequate axial section. The oblique and subaxial sections available do not permit accurate measurements of the test dimensions to be made. It appears, however, that the specimens from Cebu Island, the guyots of the west and central Pacific (Arnaud-Vanneau & Premoli Silva, 1995; Arnaud-Vanneau & Sliter, 1995) as well as those from Senegal (Peybernès, 1982) are smaller than the type specimens from the Lower Albian type-locality of Florida, U.S.A. (Maync, 1955). The stratigraphic range of Paracoskinolina sunnilandensis in the Gulf Coast Area, Texas respectively, is latest Aptian-earliest Albian (Scott, 2002, Fig. 2). The relationship of the Philippine taxon to forms reported as Paracoskinolina aff. sunnilandensis from the Hauterivian and Barremian of Spain (Becker, 1999) and southern France (Clavel et al., 2014) on the one hand and to the American type-species on the other hand need further clarification; however, that is beyond the scope of the present contribution.

Subfamily Dictyoconinae Schubert, 1912

Genus Palaeodictyoconus Moullade, 1965

Type-species: Dictyoconus cuvilieri Foury, 1963.

Palaeodictyoconus actinostoma Arnaud-Vanneau & Schroeder, 1976

(Figs. 3.E-F , 6.Q )

1976 Palaeodictyoconus actinostoma n. sp. - Arnaud-Vanneau & Schroeder, Pl. 1, figs. 1-6, Pl. 2, figs. 1-6.

1980 Palaeodictyoconus actinostoma Arnaud-Vanneau & Schroeder - Arnaud-Vanneau, p. 661, Pl. 62, figs. 6-10, Pl. 107, figs. 4-5 (cum synonymy).

1999 Palaeodictyoconus actinostoma Arnaud-Vanneau & Schroeder - Becker, p. 407, Pl. 8, Figs. 1-7.

Remarks: The large-sized (several mm), low- to medium-conical tests, displaying an early trochospire and a central test depression due to sigmoseptal or also annular chambers in the adult test part, are common constituents in the studied samples. This is the first record of this species from the Pacific area. The type-locality of P. actinostoma is situated in southern France (Arnaud-Vanneau & Schroeder, 1976; Arnaud-Vanneau, 1980; Clavel et al., 2014); other records are from Spain (Becker, 1999), Iraq, Iran, and Tibet (Schlagintweit, 2020, 2021).

Genus Neorbitolinopsis Schroeder, 1965

Type-species: Orbitolina conulus Douvillé, 1912.

Neorbitolinopsis conica (Matsumaru in Matsumaru & Furusawa, 2007)

(Fig. 3.C )

1984 Orbitolina spp. - Amiscaray & Nilayan, Pl. 8, fig. 17 (specimen in the middle above).

1995 Orbitolina (Mesorbitolina) sp. cf. O. (M.) pervia - Arnaud-Vanneau & Premoli Silva, p. 208, Pl. 4, fig. 10.

2007 Paleodictyoconus conica (rect. conicus) n. sp. - Matsumaru in Matsumaru & Furusawa, p. 82, Pl. 2, Figs. 1-3.

2022 Neorbitolinopsis conica (Matsumaru) - Schlagintweit & Rashidi, Figs. 6.1-6.5, 6.9-6.16, 7-8 (cum synonymy).

Remarks: This rather large-sized high-conical orbitolinid was originally described by Matsumaru in Matsumaru & Furusawa (2007) as the new species Paleodictyoconus conica (rect. conicus) from the Aptian of the Takisato Orbitolina limestone, Lower Yezo Group, of Hokkaido Island, Japan. In a recent taxonomic revision, the species has been transferred to the genus Neorbitolinopsis Schroeder with the new combination N. conica (Matsumaru) (see Schlagintweit & Rashidi, 2022).

Subfamily Orbitolininae Martin, 1890

Genus Mesorbitolina Schroeder, 1962

Synonym Columnorbitolina Zhang, 1982.

Type-species: Orbitulites texanus Roemer, 1849.

Mesorbitolina texana (Roemer, 1849)

(Figs. 3.A , 6.J-M )

1849 Orbitulites texanus n. sp. - Roemer, p. 392.

1852 Orbitulites texanus - Roemer, p. 86, Pl. 10, Figs. 7a-d.

1985 Orbitolina (Mesorbitolina) texana (Roemer) - Schroeder, p. 77-80, Pl. 36.

1995 Orbitolina (Mesorbitolina) texana oculata - Arnaud-Vanneau and Premoli Silva, p. 208, Pl. 5, figs. 3-4.

Remarks: Mesorbitolina texana (Roemer) represents a cosmopolitan species (e.g., type-locality in Texas) that has also been recorded from the Pacific area (e.g., Arnaud-Vanneau & Premoli Silva, 1995). For a detailed description and illustrations see Schroeder (1985). The specimens from Cebu Island have diameters of the megalospheric embryo from 0.32 mm to 0.36 mm, and 0.15 mm to 0.17 mm for the hemispherical protoconch.

Mesorbitolina birmanica (Sahni, 1937)

(Fig. 6.N, P )

1937 Orbitolina birmanica n. sp. - Sahni, p. 365-369, Pl. 29, figs. 1-7, Pl. 30, figs. 1-19.

1957 Orbitolina birmanica Sahni - Sahni & Sastri, p. 30-32, Fig. 13 (?Pl. 6, figs. 1-3?), Pl. 4, figs. 12-19, Pl. 5, figs. 1-11.

1986 Orbitolina (Mesorbitolina) birmanica (Sahni) - Zhang, p. 112, Pl. 5, figs. 2-5, 9.

1995 Orbitolina (Conicorbitolina) sp. cf. O. (C.) aliensis - Arnaud-Vanneau & Premoli Silva, p. 208, Pl. 5, figs. 1-2.

2014 Mesorbitolina birmanica (Sahni) - Schlagintweit & Wilmsen, p. 127, Figs. 3D-G, J-L, 4A-D.

Remarks: This species, originally described from the Lower Cretaceous of Tibet, is characterized above all by its embryonic apparatus, respectively its planoconvex protoconch (Sahni & Sastri, 1957, p. 31 "distinctly flattened lower and convex upper side").

Fig. 6
Click on thumbnail to enlarge the image.

Figure 6: Orbitolinidae (A-Q) and other benthic foraminifera (R-U) from the upper Aptian (lowermost Albian?) Tuburan Limestone of Cebu Island, Philippines. A-I) Paracoskinolina sp.; oblique sections (A-B), tangential sections (C-D), passing the initial spire (H), slightly oblique sections of juvenile (F) and adult parts (I), subaxial section (E). J-M) Mesorbitolina texana (Roemer) oblique and axial sections of megalospheric specimens. N, P) Mesorbitolina birmanica (Sahni), axial sections of megalospheric specimens. O) Possible transitional form between Mesorbitolina texana (Roemer) and Mesorbitolina subconcava (Leymerie). Q) Oblique section of Palaeodictyoconus actinostoma Arnaud-Vanneau & Schroeder (for subaxial section see Fig. 3.E-F ). R) Praechrysalidina infracretacea Luperto Sinni. S-T) Vercorsella sp. cf. V. arenata Arnaud-Vanneau, subaxial and oblique transverse sections. U) Akcaya minuta (Hofker), axial, section. Samples: TUBI62035 (A-G, H-I); ASH232015 (J); KENTM21202 (K, M); TUBI62036 (L, N-P); LTH212021 (Q, R, T); TUBI62035 (S).

5. Biostratigraphy

Orbitolinid larger foraminifera are the most useful taxa for age constraints of the Tuburan Limestone. There are numerous records of Orbitolinidae from the "Pacific realm" many referring to papers published in the 1970's that have to be critically assessed. For example, Hashimoto & Matsumaru (1974) reported the species Palorbitolina lenticularis (Blumenbach) from West Kalimantan, Indonesia, that would account for a late early Barremian to early Aptian age (Schroeder, 1965; Schroeder et al., 2010; Clavel et al., 2014). The two specimens shown in Plate 11, figs. 31-32 therein, however, correspond to Mesorbitolina subconcava (Leymerie) that has a younger range, latest Aptian-early Late Albian respectively (Schroeder, 1985). Another specimen assigned to P. lenticularis (Hashimoto & Matsumaru, 1974, Pl. 12, fig. 28, represents a transverse section of Mesorbitolina parva Douglass resulting in an early late Aptian age (Schroeder et al., 2010). True P. lenticularis, however, has also been illustrated (Hashimoto & Matsumaru, 1974, Pl. 12, fig. 35). A thorough analysis of the illustrated specimens (many undiagnostic sections not showing the megalospheric embryo; e.g., Fernandez et al., 1994, Pl. 1, or Konishi, 1989, Fig. 11) in the literature, however, is beyond the scope of the present contribution. Coming back to Cebu Island, also little is known on the biostratigraphy of the Tuburan Limestone. Hashimoto et al. (1978) reported the occurrence of Orbitolina lenticularis (Blumenbach) from Central Cebu. The study "Orbitolina from Tuburan, Cebu" by Amiscaray & Nilayan (1984) includes the presence of Orbitolina texana (Roemer), Orbitolina kurdica Henson, and Orbitolina ssp. The authors just confirm a Lower Cretaceous age, without further refinements. It is worth mention that among the specimens illustrated in seven plates none show the megalospheric embryo that would allow determination. The last and most recent work dealing with the biostratigraphy of the Tuburan Limestone is the one by Masse et al. (1996). They mention (without illustration) Orbitolina (Mesorbitolina) gr. texana (Roemer), Neorbitolinopsis conulus (Douvillé) along with an assemblage of taxa that we also identified in our samples (Vercorsella, nezzazatids, valvulinids, globigerinelloids). N. conulus is a taxon reported from Spain where it is in fact a good Late Albian marker (Schroeder & Neumann, 1985) leading Masse et al. (1996) to assign the Tuburan Limestone to this age. It is worth mentioning that according to Schroeder & Neumann (1985, Fig. 1), the presence of M. texana however would exclude a Late Albian age. We suspect that Masse et al. (1996) was referring in fact to Neorbitolinopsis conica (Matsumaru), a different species from the Aptian of Japan that has recently taxonomically been revised by Schlagintweit & Rashidi (2022). N. conica is more primitive (= smaller embryo) than N. conulus, and reported from upper lower Aptian - Lower Albian. Our data indicate a latest Aptian (?earliest Albian) age for the Tuburan Limestone of Cebu Island contrasting the inferred Late Albian age by Masse et al. (1996) (Table 3). This age indication is furthermore supported by specimens interpreted as transitional forms between Mesorbitolina texana (Roemer) and M. subconcava (Leymerie) (Fig. 6.O ). It is worth mentioning that the (in our opinion incorrect) Late Albian age was also the stratigraphic base for the description of the new genus and species of the polyconitid rudist Magallanesia canaliculata from Cebu Island by Sano et al. (2014). In this context, the Late Albian age for the youngest sediments from Mid- and West-Pacific guyots obtained from benthic foraminifera (Arnaud-Vanneau & Sliter, 1995; Arnaud-Vanneau & Premoli Silva, 1995) that in turn has been used as "reference age" for the rudist assemblages of these localties (Swinburne & Masse, 1995), also should be reconsidered in details. A compilation of the taxa that were considered as evidence for a Late Albian age (Neoiraqia, Orbitolina, Conicorbitolina) is provided in Table 4. Therefore, the discussions in the diverse following papers on phylogeny, palaeogeographic comparisons, endemism and bioprovinces of Pacific rudists deriving from ophiolitic mélanges and guyots (Skelton et al., 2013, Table 1) need a re-evaluation in our opinion as they are based in parts on ambiguous age data.

Table 3: Biostratigraphy of the studied samples of the Tuburan Limestone from Cebu Island.

species stratigraphy references
Mesorbitolina birmanica (Sahni) lower upper Aptian-?Lower-?Middle Albian Schlagintweit and Wilmsen (2014)
Mesorbitolina texana (Roemer) upper Aptian-Middle Albian Schroeder (1985)
Transitional types between
M. texana and M. subconcava (Leymerie)
uppermost Aptian Schroeder (1985),
Schroeder et al. (2010)
Neorbitolinopsis conica
(Matsumaru & Furusawa)
upper lower Aptian-uppermost Aptian (? lowermost Albian) Schlagintweit and Rashidi (2022)
Palaeodictyoconus actinostoma Arnaud-Vanneau & Schroeder Upper Hauterivian-Aptian Arnaud-Vanneau and Schroeder (1976), Clavel et al. (2014)

Table 4: Critical reconsideration for Late Albian stratigraphic implications based on benthic foraminifera for the top parts of some Central- and West-Pacific guyots.

taxon stratigraphy (according to
Schroeder & Neumann, 1985*)
Arnaud-Vanneau & Sliter (1985)*, Arnaud-Vanneau & Premoli Silva (1985)** current interpretation
Neoiraqia Danilova Upper Albian-middle Cenomanian* Neoiraqia(?) sp. (** Pl. 4, fig. 10) not diagnostic
Orbitolina Orbigny Upper Albian-early Cenomanian* Orbitolina (Orbitolina) sp. (* Pl. 5, fig. 4) Mesorbitolina sp.
Conicorbitolina Schroeder uppermost Albian-middle Cenomanian* Orbitolina (Conicorbitolina) sp.
cf. O. (C.) aliensis (* Pl. 5, figs. 1-2)
Mesorbitolina cf. birmanica (Sahni)
Hensonipapillus lenticularis (Henson) Lower - p.p. Middle Cenomanian (Rosales & Schlagintweit, 2015) Trocholina sp. cf. T. lenticularis
(** Pl. 5, fig. 1)
Coscinoconinae indet.

6. Discussion

Cebu Island is located in the central part of the Philippine Mobile Belt with complex plate boundaries and terranes (e.g., Gong et al., 2021). The geological history of the Philippines includes various events of subduction, collision and accretion (e.g., Yumul et al., 2003). The blocks and clasts of the Lower Cretaceous Tuburan Limestone from Cebu Island, the associated volcanic rocks and radiolarian-bearing siliceous shales occur in series typical for ophiolitic mélanges-accretionary prism. As already previously noted the microfauna and partly also microflora of the Tuburan Limestone show affinities to shallow-water carbonates of Central Pacific Guyots (Arnaud-Vanneau & Premoli Silva, 1995; Arnaud-Vanneau & Sliter, 1995; Masse & Arnaud-Vanneau, 1995, 1999). In this context, we want to highlight the presence of a small taxon designated as Paracoskinolina sp. and reported from Cebu Island (this work), west and central Pacific Guyots (Arnaud-Vanneau & Sliter, 1995; Arnaud-Vanneau & Premoli Silva, 1995) and Senegal, western Africa (Peybernès, 1982). It is worth mentioning that Paracoskinolina sp. 1 sensu Peybernès (1982, Fig. 4) has been reported from upper Aptian (upper Gargasian - lower Clansayesian) strata of Senegal. The late Aptian (?earliest Albian) age of the Tuburan Limestone as referred herein is in the range indicated for the carbonates of the mentioned guyots. Taking into account these data and the overall tectono-sedimentary situation, it is put for discussion herein that the Tuburan Limestone represents parts of a former seamount (guyot) coverage that became accreted to the Philippine Mobile Belt (Fig. 7 ). It is worth mentioning that such an interpretation would also explain the lack of an inner platform sheltered lagoonal facies. The classical model of formation and evolution of a guyot refers to an active volcanic island, for instance within a mid-plate setting that becomes inactive, being carried along through plate motions and eventually subducted or accreted (e.g., Flood, 1999; Staudigel & Clague, 2010; Watts et al., 2010; Clarke et al., 2018). Guyots or flat-topped seamounts like oceanic plateaus and submarine ridges were formed through excessive magmatism breaching the oceanic plates (Tetreault & Buiter, 2014). Subduction of the paleo-Pacific plate along the oceanic leading edge of the Australian margin or Eastern Indochina margin (still under scrutiny) have caused successive eruptive events leading to the emergence of Cebu Island in the Early Cretaceous (e.g., Deng et al., 2015; Gong et al., 2021). Continued subduction of the paleo-Pacific plate resulted to the eventual accretion of radiolarian-bearing siliceous shales and limestones (Tuburan Limestone) perceived to be on top of a Central- or a Mid-Pacific guyot into the emergent Cebu Island arc.

Fig. 7
Click on thumbnail to enlarge the image.

Figure 7: Schematic conceptual model of the origin of the Tuburan Limestone (inspired from Konishi, 1989, Fig. 14).

7. Conclusions

Resedimented Lower Cretaceous shallow-water carbonates of Cebu Island, Philippines, the Tuburan Limestone respectively, have been investigated with respect to microfacies, micropalaeontology, and biostratigraphy. Among the samples coming from four localities, no age differences have been evidenced. Instead, the available data, based on Orbitolinidae, indicate a latest Aptian-?earliest Albian age. The samples of the Tuburan Limestone mainly refer to external platform (including back-reefal, peri-reefal areas, bioconstructions with corals, stromatoporoids and sclerosponges), and slope depositional settings with mixed assemblages. The obvious lack of internal platform (lagoonal) microfacies accounts for the reduced number of Dictyoconinae (Palaeodictyoconus actinostoma), while the majority of the taxa belong to the Orbitolininae (Mesorbitolina, Neorbitolinopsis). The indicated Late Albian age for these orbitolinid-bearing limestones from Cebu Island as indicated in the literature, is rejected herein. This previous age assignment was based on Neorbitolinopsis conulus, that represents a Late Albian marker, while the specimens from Cebu Island refer to the recently revised species Neorbitolinopsis conica that has a late early Aptian-?earliest Albian stratigraphic range. The observed assemblage of Mesorbitolina texana, M. birmanica, Palaeodictyoconus actinostoma, and N. conica indicate a latest Aptian-?earliest Albian age for the Tuburan Limestone. Endemic species or a typical assemblage that would allow to define a geographically limited distribution (e.g., Western Pacific province, including a Northwest subprovince) are lacking. The comparably low number of recorded species may be simply explained by the reduced available niches (e.g., lack of lagoonal facies with distinct assemblages) and the reduced stratigraphic interval obtained from Cebu Island compared for example with southern France (Upper Hauterivian - lower Aptian). Also among the rare dasycladaleans, any species displaying a geographic restriction is lacking. Instead, the species Morelletpora turgida displays a wide Neotethyan distribution. The great resemblance of the foraminiferal and partly also algal assemblages from Cebu Island with those from time-equivalent shallow-water carbonates drilled from Western and Central Pacific guyots is worth mentioning. The collision and accretion/subduction of a former guyot including associated Lower Cretaceous carbonates as source for the Tuburan Limestone blocks is herein put for discussion. Such a scenario would also fit the lack (or reduced occurrence) of lagoonal facies as observed from drilled cores of Western and Central Pacific guyots.


Jerali Rodrigo would like to thank former DENR USec. Jeremiahs Dolino and Ms. Annie Dee, President of the Quarry Ventures Philippines Incorporated/Teresa Marble Corporation for the logistical support. QVPI field staff (Messrs. Rex Lachica, Mike Angelo Castro, Eli Macanas, Roland Ringor, Rey Cariliman, and Engr. Manny Gabriel) are gratefully acknowledged for their assistance during fieldwork. In addition, thanks to former Regional Director Loreto Alburo and Chief Geologist Al Emil Berador of the Mines and Geosciences Bureau Region VII for their support during his stint at the agency. The MEXT scholarship through the University of Tsukuba under the Special Course on "Trans-world Professional Human Resources Development Program on Food Security and Natural Resources Management (TPHRD)" under the guidance of Professor Kazuo Watanabe is highly appreciated. Associate Professor Kohtaro Ujiie of the Life and Environmental Sciences, University of Tsukuba, is thanked for giving access to the use of facilities in the Geodynamics laboratory. Associate Professor Sachiko Agematsu-Watanabe for her guidance in the doctoral program for Jerali Rodrigo and Dr. Takuma Haga, Division of Geology and Paleontology of the National Museum of Nature and Science, Japan, for the funding granted for this work (NMNS grant #3225). The two reviewers Ioan Bucur (Cluj-Napoca) and Michel Septfontaine (Froideville) are thanked for their comments.

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