◄ Carnets Geol. 22 (14) ►
Outline:
[1. Introduction]
[2. Material and depository]
[3. geological settings]
[4. Systematic micropalaeontology]
[5. Biostratigraphy]
[6. Discussion]
[7. Conclusions] and ... [Bibliographic references]
Degree Programs in Life and Earth Sciences, Graduate School of Science and Technology, University of Tsukuba, Tsukuba City, Ibaraki (Japan)
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]
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
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).
|
|
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). |
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 |
3.1 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 ).
|
|
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 |
|
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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. |
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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. |
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.
|
|
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)
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").
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|
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 |
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. |
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.
|
|
Figure 7: Schematic conceptual model of the origin of the Tuburan Limestone
(inspired from Konishi, 1989, Fig. 14). |
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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