Central Palawan Research Articles

Evolution of Arc‐Continent Collision in the Southeastern Margin of the South China Sea: Insight From the Isugod Basin in Central‐Southern Palawan

AbstractThe evolution of arc‐continent collision between the Palawan microcontinental block and the Cagayan Ridge in the southeastern margin of the South China Sea (SCS) is vital to understand how this collision correlated with seafloor spreading of the SCS. To address the evolution of arc‐continent collision, we studied the biostratigraphy and provenance of syn‐collisional sediments in the Isugod Basin in central‐southern Palawan. Microfossil analysis indicates a Late Miocene age (11.5–5.6 Ma) for the Isugod and Alfonso XIII Formations and rapid subsidence during initiation of the basin which may have been triggered by local extensional collapse of the wedge in response to forearc uplift. Multidisciplinary provenance analysis reveals that the Isugod and Alfonso XIII Formations were derived from the Middle Eocene–lower Oligocene Panas‐Pandian Formation on the Palawan wedge and the Late Eocene Central Palawan Ophiolite. These results suggest the emergence of both the orogenic wedge and obducted forearc ophiolite at ∼11.5 Ma, implying collision onset before ∼11.5 Ma. The collision initiation in Palawan could be better constrained to ∼18 Ma, based on the drowning of the Nido carbonate platform in the foreland. Therefore, the gravitational collapse of the Palawan wedge and the subsidence/formation of the Isugod Basin might reflect a significant uplift pulse in the hinterland of the wedge beginning within 13.4–11.5 Ma in the late stage of collision. It indicates that although compression originated from spreading of the SCS had ceased at 16–15 Ma, arc‐continent collision in Palawan did not stop and was sustained by compression from the upper plate afterward.

From rifting to emplacement: Variable mantle melting preserved in the central Palawan Ophiolite peridotites, Philippines

ABSTRACT The mantle section of the central Palawan Ophiolite (CPO) in western Philippines is dominantly composed of dunites and harzburgites. Basal lherzolites and harzburgites juxtaposed with the metamorphic sole of the CPO are also exposed within the vicinity of Ulugan Bay, Puerto Princesa. These basal peridotites provide novel information regarding the processes transpiring in the upper mantle during the evolution of this preserved oceanic lithosphere. The Nasuduan lherzolite is characterized by low Cr# of spinel and high concentrations of REEs in clinopyroxenes. The Oyster Bay lherzolite displays similar fertile characteristics and occurs with harzburgites. Both contain fine-grained and interstitial clinopyroxenes derived from interstitial melts. Tremolite and talc in the Oyster Bay lherzolite and harzburgite and in other CPO harzburgites are attributed to slab-fluid metasomatism. Harzburgites and dunites from Bentoan Beach and other CPO harzburgites have high spinel Cr# and low clinopyroxene REE concentrations. These indicate that these peridotites have undergone extensive degrees of melting facilitated by fluids. The petrological and geochemical signatures of the CPO peridotites record the transition of a supra-subduction zone from back-arc spreading, incipient subduction, to the obduction of an ancient oceanic lithosphere.

Mixing, fluid infiltration, leaching, and deformation (MILD) processes on the slab-mantle wedge interface at high T and P conditions: Records from the Dalrymple Amphibolite, Philippines

The whole rock compositions of the blocks and the surrounding matrix of the Dalrymple Amphibolite are investigated in this study to determine the protolith of the blocks and the effect of mechanical mixing and fluid infiltration in the matrix of this fossil slab-mantle wedge interface. The major and trace element contents of the metamafic blocks indicate their mid-oceanic ridge basalt origin similar to the mafic lavas of the crustal section of central Palawan Ophiolite. Similarities in their rare earth and trace element patterns indicate the genetic relationship between the mafic lavas of the Palawan Ophiolite and the metamafic blocks of the Dalrymple Amphibolite. This confirms that the metamafic blocks represent the basalt to gabbro section of the oceanic lithosphere of the subducting slab.The matrix surrounding the blocks exhibit highly variable phase assemblages. In order to determine its petrogenesis, we distinguished groups of components/elements which behave similarly (Group 1 TiO2, Al2O3, Zr, Th and the light rare earth elements; Group 2 Cr, Ni and MgO) based on statistical (correlation coefficient) analyses. These groups indicate mixing of metasedimentary (Group 1) and metamafic (Group 2) end-members to form the matrix. The mixing proportions of the end-members were estimated by employing regression analysis wherein the measured concentration of fluid immobile elements (Cr, Ni, Zr, TiO2 and Al2O3) in the matrix samples were fitted against a modelled concentration by changing the end-member and their relative proportions. The end-members and mixing ratio with the highest regression value (r2) was selected to obtain the modelled composition of the matrix. The modelled and the measured matrix compositions were then used as the original (unmetasomatized) rock and the altered rock respectively in the isocon analysis, assuming that TiO2, Al2O3, Cr, Nd, Zr, and Hf are immobile. This assumption is supported by the prevalence of kyanite, ilmenite and zircon in the matrix mineral assemblage.This procedural workflow helped distinguish end-member components, estimate their mixing ratios, and determine the effects of infiltrating fluids. In particular, the whole rock composition of the matrix was controlled by mixing of a subordinate amount of metamafic blocks in a metasedimentary-dominated shear zone. This is supported by the Cr-Nb content of rutile grains included in the matrix samples which indicate mixed metamafic and metapelitic signatures. The metamafic-metasedimentary dominated matrix in the Dalrymple Amphibolite contrasts with other high-pressure/temperature (P/T) type metamorphic terranes which are dominated by low T minerals (serpentine, Mg-chlorite, and talc) derived from an ultramafic end-member, and could be reflective of conditions in warmer subduction zones. Mass balance calculations further revealed that an early fluid infiltration event likely occurred following the mixing process. This preferentially leached out elements which are either fluid-mobile (e.g. CaO and SiO2) or are not incorporated into the growing minerals in the matrix. The strong control of mineral assemblage of the matrix in its chemistry is exhibited by a number of samples which showed variable degrees of losses and gains in elements traditionally interpreted to be fluid immobile (e.g. heavy rare earth elements and Y). A later hydration event linked to retrograde metamorphic stage imprinted gains of K2O, Rb, and Ba in the matrix samples with the growth of replacement minerals (e.g. muscovite on kyanite). This later fluid infiltration event possibly masked the original loss of these fluid-mobile elements in the matrix samples during the earlier fluid-rock interaction.

Corybas kaiganganianus (Orchidaceae), a new, rare helmet orchid from Samar Island, Philippines

Corybas Salisbury (1807: t. 83) comprises approximately 120 highly distinctive and diminutive terrestrial and lithophytic species widely distributed from India to the western Pacific (Pridgeon et al. 2001, Aldrich & Haggins 2008, Chung & Hsu 2008, Chantanaorrapint & Chantanaorrapint 2016, Govaerts et al. 2019). The Philippines has six Corybas species (Pelser et al., 2011): C. boholensis Tandang, Bustamante, Reyes & Lyon (2020a: 261), Bohol, Visayas;, C. circinatus Tandang & Bustamante (2020b: 135), central Palawan; C. geminigibbus Smith (1927: 13), Mt. Victoria, Palawan; C. laceratus Williams (1937: 54), Rizal Prov., Luzon; C. merrillii (Ames) Ames (1908: 42), Mt. Mariveles, Luzon; and C. ramosianus Dransfield in Dransfield et al. (1986: 611), Ilocos Norte Prov., Luzon. Corybas is often overlooked and understudied owing to its diminutive size and ephemeral flowers (Tandang et al. 2020a), and ongoing explorations of the Philippine Archipelago have demonstrated the merit of this observation, with several species having been newly documented and described in recent years from areas that are known to have been botanized in the past.

1008. STIGMATODACTYLUS DALAGANGPALAWANICUM: Orchidaceae

SummaryStigmatodactylus dalagangpalawanicum A.S. Rob. is a miniature orchid endemic to the highest reaches of the ultramafic Mount Victoria massif in central Palawan, the Philippines. Its habitat and ecology are described and additional background to this relatively poorly documented genus provided.

Juxtaposition of Cenozoic and Mesozoic ophiolites in Palawan island, Philippines: New insights on the evolution of the Proto-South China Sea

The proto-South China Sea (proto-SCS) is a fully consumed Mesozoic plate that once existed between the South China-Eurasian margin and Borneo. Remnants of this oceanic domain are believed to be emplaced as ophiolitic lithologies in Palawan and Zambales, Philippines and Borneo. Cretaceous and Eocene ophiolitic lithologies are exposed in the central and southern portions of Palawan island. The Eocene central Palawan Ophiolite (CPO) is composed of mantle peridotites, isotropic and layered gabbros, and massive and pillow lavas. In lieu of a sheeted dike complex, mafic dikes with distinct bake-and-chill margins cut the CPO, from the metamorphic sole to the crustal section. The Cretaceous southern Palawan Ophiolite (SPO) comprises of peridotite and pillow basalt exposures. Isotropic olivine gabbros are mainly preserved as floats. Troctolite and olivine gabbro dikes also cut the peridotites in the SPO.The CPO crustal rocks and mafic dikes have dominantly back-arc basin basalt affinities. The SPO lithologies exhibit ocean island basalt-like signatures with a mafic dike showing island arc basalt-like compositions. A plagiogranite sample from Puerto Princesa indicates an Eocene age (40.01 ± 0.54 Ma) for the CPO. U-Pb dating of olivine gabbro and syenite floats yielded a minimum age of Early Cretaceous (100.73 ± 1.07 and 102.97 ± 1.07 Ma, respectively) for the SPO. This is the first reported radiometric age for the now completely subducted Mesozoic proto-SCS exposed in southern Palawan, which complements existing paleontological dates. Geochemical and geochronological characteristics of the SPO and CPO are similar to those of the Darvel Bay and Telupid Ophiolites in Borneo, which are interpreted to originate from the proto-SCS. The CPO and SPO are thus construed to represent fragments of the proto-SCS emplaced in Palawan. Complex tectonic processes in the region during the Cretaceous to Eocene led to the inception of multiple subduction and rifting events involving the proto-SCS.

Cenozoic Evolution of the Sulu Sea Arc‐Basin System: An Overview

AbstractThe Cenozoic Sulu Sea arc‐basin system is situated in the tectonic junction between the South China Sea (SCS), northern Borneo, Palawan Continental Terrane, Philippine Mobile Belt, and Celebes Sea. We compare new/published geochronological and geochemical data from across the circum‐Sulu Sea region, and summarize seven major magmatic phases from the Middle Eocene to Pleistocene. The Middle Eocene (42.65 Ma) Sabah ophiolite and Eocene‐Oligocene (34‐33 Ma) Central Palawan ophiolite have MORB‐IAT‐transitional features, representing an intraoceanic subduction setting in the Paleogene northern Borneo and central‐southern Palawan. After the SCS opening (∼32 Ma) and ridge jump (∼25 Ma), late‐stage Proto‐SCS subduction (24‐21 Ma) may have formed the Panay arc andesite and the BABB magmatism in SW Zamboanga peninsula. Starting of final convergence between the Palawan Continental Terrane and northern Borneo‐SW Philippines (∼21 Ma) likely caused regional uplift/thrusting, forming the Top Crocker Unconformity and triggering the NW‐dipping Celebes Sea subduction. The subduction may have formed arc magmatism (21‐18 Ma) in the Cagayan ridge and its continuation in Panay and NE Sabah, and opened the NW Sulu Sea back‐arc basin through continental crust attenuation. Subduction rollback likely occurred in 17‐14 Ma and 13‐9 Ma, shifting arc magmatism southeast to the Sulu ridge and opening the SE Sulu Sea back‐arc basin. NW‐dipping Celebes Sea subduction largely ceased after ∼9 Ma, followed by extension‐related uplift/exhumation and 4‐0.2 Ma intraplate volcanism in northern Borneo. SE‐dipping Sulu Sea subduction likely occurred along the Negros‐Sulu trenches, and produced arc volcanism from ∼4 Ma.

Volcanic rocks from the Central and Southern Palawan Ophiolites, Philippines: Tectonic and mantle heterogeneity constraints

Recent studies suggest the existence of two ophiolites in Palawan Island: the Central Palawan Ophiolite (CPO) and the Southern Palawan Ophiolite (SPO). New geochemical data in this study from the volcanic rocks of the Palawan ophiolites further support this interpretation. The CPO lavas have back-arc basin basalt (BABB) affinities with LILE enrichment and depleted LREE. In contrast, volcanic rocks of the SPO are geochemically diverse, including low-TiO2 boninitic andesites, MORB-like lavas, and high TiO2, high Nb lavas. Sr, Nd and Pb isotopic ratios of the CPO and SPO samples suggests that a mantle source was enriched due to the interaction of depleted MORB mantle with EMI component and ancient Mariana Trench-like sediment. Utilizing available paleomagnetic data and regional plate reconstruction models, we propose that the CPO represents the Late Eocene back-arc basin fragments formed within the proto-South China Sea. The SPO has a subduction initiation origin and formed in the Sundaland-Eurasian margin in Early Cretaceous. Both ophiolites were emplaced on the Palawan Continental Terrane (PCT) due to the collision of the PCT with Borneo and Cagayan Ridge.

Comparison of Agathis philippinensis resin tapping and collection practices in three selected sites in the Philippines

Abstract. Daracan VC, Mendoza RC, Torres AM, Jara AA, Manalo RD, Batallones CHR, Razal RA. 2020. Comparison of Agathis philippinensis resin tapping and collection practices in three selected sites in the Philippines. Biodiversitas 21: 5595-5604. This study documented and compared almaciga (Agathis philippinensis Warb.) resin tapping and collection practices in three sites namely Mt. Hamiguitan, Governor Generoso, Davao Oriental; Mt. Mantalingahan, Brooke’s Point, southern Palawan; and Puerto Princesa Subterranean River National Park, Marufinas, central Palawan. Resin tappers, mostly male belonging to a local organization, were interviewed, and tapping sites were visited. Tapping and collecting A. philippinensis resin is one of the supplemental income sources of the respondents from the three sites. Market influences, and how tappers learned the trade could partly explain the similarities and differences in tapping practices. Discrepancies in selecting trees to be tapped, tools used, type of incisions made on the bark, and how resin was harvested were noted. Differences in resin appearance across sites were observed, and the existence of uncollected and wasted resins clinging to trees or sprawling at its base was found in all sites. Removing dirt from the portion of the stem to be tapped, covering the bark incision with plastic for protection, and contriving handmade resin baskets from plant parts available in the site were some practices found to be worth replicating. On the other hand, there were damaged or dying trees due to the intensity of tapping, the lack of tapping skills, and limited attention given to the health of trees. There is a need for strengthening tappers’ organizations for increased bargaining power to secure better resin price and policy support to prioritize indigenous peoples in tapping into their ancestral domain. Tappers can benefit from cross-visits and other learning opportunities for sharing lessons and experiences to improve tapping practices for better resin quality and higher prices.

<p class="ZootaxaTitle"><strong>Diversity of Trichoptera emergence and their longitudinal distribution along streams in central Palawan, the Philippines</strong></p>

Trichoptera emergences were cumulatively collected from two rivers in central Palawan over 11 months by use of specially modified emergence traps. The quantitative samples were identified at species level. Fifty morphospecies, of which fifteen have been recently newly described, are recognized. The highest species diversity was found in pristine headwater streams. Leptoceridae were most speciose with eleven Oecetis spp., four Leptocerus spp., two Adicella spp., and one species each of Tagalopsyche, Triaenodes, and Triplectides. Highest abundances were observed for Ecnomus cabayugani (Ecnomidae), Dipseudopsis digitata, and Hyalopsyche winkleri (Dipseudopsidae) which contributed alone 34% of the annual emergence. A mid-stream site where mayflies were mainly absent had the highest Trichoptera emergence, brackish water sites the lowest. Many species in Palawan (44% of the taxa) were recorded at a single locality, suggesting that they are stenoecious and that the real number of species on the island might be distinctly higher. This is the first study ever covering quantitative and species-level Trichoptera emergence data for a longitudinal river course.

Slab-controlled elemental–isotopic enrichments during subduction initiation magmatism and variations in forearc chemostratigraphy

Supra-subduction zone (SSZ) ophiolites formed in forearc settings and the Izu–Bonin–Mariana (IBM) in-situ forearc show conversions from normal mid-ocean ridge basalt (MORB) to boninitic affinities, which are widely interpreted as rules for the evolving chemical geodynamics of subduction initiation magmatism (SIM). Nevertheless, forearc sequence generated by subduction initiation need not always include boninitic rocks. Here we reconstruct a forearc chemostratigraphy without boninitic affinity based on the Central Palawan and Amnay (CPA) ophiolites of the west Philippines to show diversity in melt evolution of SIM. Zircon U–Pb dating on the MORB-type Amnay gabbros reveal a 10 m.y. of seafloor spreading from 33 to 23 Ma. These ages together with the progressively enriched zircon in-situ oxygen isotopes (δ18O= 1.62–10.1‰) and whole rock elemental and Nd–Hf isotopic signatures ([La/Yb]N= 0.19–3.45; Nb/Yb= 0.07–5.24; εNd= 2.1–10.2; εHf= 11.2–24.1) indicate that the depleted MORB mantle (DMM)-type source of the Amnay ophiolite was getting enriched by fluxing of aqueous slab fluid in the early stage followed by addition of adakitic and Nb-enriched slab melts in the later stage. This distinct mantle evolution together with higher εHf at a given εNd of the Amnay mafic samples than the contemporaneous South China Sea (SCS) oceanic samples do not support previous interpretation that the Amnay ophiolite was a fragment of the SCS. However, the 33–23 Ma Amnay ophiolite can be the younger part of the 34 Ma forearc-type Central Palawan ophiolite, and both (i.e. the CPA ophiolites) represent on-land fragments of the NW Sulu Sea. We propose that the 34–23 Ma CPA ophiolites and the NW Sulu Sea constitute forearc basin of the late Oligocene–middle Miocene island arc–backarc basin duo of the Cagayan Ridge and SE Sulu Sea, associated with subduction of the Cretaceous to Eocene Proto-SCS since 34 Ma. The CPA ophiolites lack boninite but show geochemical progression from normal to enriched MORB affinities, whose melt evolution differs from that of the IBM SIM. We attribute the differences in SIM and variations in forearc chemostratigraphy to the subduction of a younger slab with thick terrigenous sediment cover of the Proto-SCS versus an older slab with thin pelagic sediment cover of the Pacific Plate.

Recalibrating burdens of blame: Anti-swidden politics and green governance in the Philippine Uplands

In Southeast Asia, the presence of cleared and burned forests has long evoked deep emotions, symbolism and representations that powerfully inform the governance of forests and upland peoples. In particular, the palpable visibility of shifting (swidden) agriculturalists ‘slashing and burning’ forests has fuelled centuries-old political agendas to criminalise swidden farmers for supposedly destroying swaths of forests valued for timber, biodiversity and now ecosystem services. Swidden farmers who regularly clear and burn forests, have endured a disproportionate burden of blame for investing in and maintaining an old livelihood practice into the 21st Century. Drawing on Hall’s politics of representation, we examine the contrasting political frames, management and practices of clearing and burning forests among upland farmers, state and non-state actors who govern forests on Palawan Island, the Philippines. We describe the social, economic, and biophysical character of swidden clearing and burning among the indigenous Tagbanua of central Palawan, whose livelihoods and landscapes are impacted by green governance and enclosures. Informed by several years of ethnographic fieldwork, we explore how and why Tagbanua farmers continue to clear and burn forest despite state and non-state actors criminalising these practices for decades. We argue that, despite sustained vilification and reduced fallows arising from governance policies and enclosures, Tagbanua farmers continue to clear and burn knowing well that, despite the practices being illegal, levels of tolerance and leniency toward swidden is the local norm, rather than exception—highlighting the importance of what we call ‘atmospheres of consent’. Ethnoecological understandings of clearing and burning in the uplands, we argue, are crucial to recalibrating the burden of blame placed on poor farmers whose agriculture is deemed destructive by the region’s burgeoning sustainability discourse.

New species of caddisflies (Insecta: Trichoptera) from emergence traps at streams in central Palawan, Philippines

New species of Trichoptera were identified in samples collected from emergence traps along two streams (Cabayugan River and Panaguman River) at Puerto Princesa Subterranean River National Park, Palawan, Philippines in 2000–2001. The species are described as: Orthotrichia ligula sp. n., Chrysotrichia minutula sp. n., Chimarra ligula sp. n., Pahamunaya panagumani sp. n., Tinodes sanctipauli sp. n., Ecnomus cabayugani sp. n., E. tagbanwae sp. n., Hyalopsyche palawanensis sp. n., Pseudoneureclipsis extensata sp. n., Helicopsyche forcipula sp. n., Anisocentropus palawanensis sp. n., Leptocerus palaservius sp. n., Leptocerus membranellus sp. n., Tagalopsyche brunneoides sp. n. and Oecetis ausani sp. n. All male genitalia are illustrated, supplemented by the female genitalia for some species. The illustrations of the male genitalia of an unnamed species of Triplectides Kolenati, 1859 (Leptoceridae) are provided. The relationship of the new species to congeners is briefly discussed. The subfamilies Hyalopsychinae (Dipseudopsidae), represented by two species, and Pseudoneureclipsinae (Dipseudopsidae), represented by one species, are recorded from Palawan for the first time. The genus Pahamunyana Schmid, 1958 (Poycentropodidae) is a new country record.urn:lsid:zoobank.org:pub:9718C49C-29A0-42EF-9CC3-6D1C942B1B19

3D seismic investigation of the structural and stratigraphic characteristics of the Pagasa Wedge, Southwest Palawan Basin, Philippines, and their tectonic implications

The Pagasa Wedge is a poorly imaged deepwater orogenic wedge that has been variously interpreted as representing an accretionary prism, a former accretionary prism modified by thrusting onto a thinned continental margin, and a gravity-driven fold-thrust belt. This study, using 2D and 3D seismic data, together with well information indicates that at least the external part of the wedge is dominantly composed of mass transport complexes, capped by syn-kinematic sediments that have thrusts and normal faults superimposed upon them. Drilling shows that despite stratigraphic repetition of Eocene Middle Miocene units, there is stratigraphic omission of Oligocene and Early Miocene units. This absence suggests that mass transport processes have introduced the Eocene section into the wedge rather than tectonic thrusting. The accretionary prism stage (Oligocene) of the Central Palawan Ophiolite history appears to be marked by predominantly north-vergent deformation. The Deep Regional Unconformity (∼17 Ma) likely indicates the approximate time when obduction ceased in Palawan. The Pagasa Wedge is a late-stage product of the convergence history that was active in its final phase sometime above the top of the Nido Limestone (∼16 Ma) and the base of the Tabon Limestone in the Aboabo-A1X well (∼9 Ma). The top of the wedge is traditionally associated with the Middle Miocene Unconformity (MMU), However the presence of multiple unconformities, diachronous formation tops, local tectonic unconformities and regional diachronous events (e.g. migrating forebulges) all suggest simply giving a single age (or assigning a single unconformity, such as the MMU as defining the top of the Pagasa Wedge is inappropriate. The overall NE-SW trend of the wedge, and the dominant NW transport of structures within the wedge diverge from the more northerly transport direction determined from outcrops in Palawan, and also from the Nido Limestone in the SW part of the Pagasa Wedge. Possibly this NW transport direction is more related to gravity-driven structures responding to uplift of NE-SW Dangerous Grounds margin during the Middle Miocene (related to slab breakoff?) than it is to thrusting rooted in a plate boundary. The final modification of the wedge occurred when the effects of compression deformation on the wedge had largely ended, but gravity processes (in particular mass transport and normal faulting) still operated.

A new narrow-leaved species of Capparis (Capparaceae) from central Palawan, Philippines

A new species of Capparis, C. tagbanuorum, is described and illustrated from Palawan Island in the Philippines. It is known from a single locality in Mount Victoria, in forest habitats at medium elevation. The new species is characterized by a peculiar leaf morphology, with blade up to 9 times as long as wide, by the racemose inflorescence and by the size of the petals and the number and length of the stamens. The diagnostic characters are discussed and a key is given for the species of Capparis known from the Philippines.

Robinson, A.S., Gironella, E.P. & Cervancia, J.M. (2016) New orchid species of Sigmatodactylus (Orchidoideae; Diurideae) and a new record of Cryptostylis carinata from central Palawan, Philippines. Phytotaxa 252 (2): 99–113.

Two new species of Stigmatodactylus from Palawan Island in the Philippines are described and illustrated. The taxa, which represent the first records for the genus Stigmatodactylus in the Philippines, are restricted to the ultramafic peaks of central Palawan. Cryptostylis carinata, originally described from New Guinea, is also documented, representing a first record for this species in Palawan.

New orchid species of Stigmatodactylus (Orchidoideae; Diurideae) and a new record of Cryptostylis carinata from central Palawan, Philippines

Two new species of Stigmatodactylus from Palawan Island in the Philippines are described and illustrated. The taxa, which represent the first records for the genus Stigmatodactylus in the Philippines, are restricted to the ultramafic peaks of central Palawan. Cryptostylis carinata, originally described from New Guinea, is also documented, representing a first record for this species in Palawan.

A new species of the genus Stiphodon from Palawan, Philippines (Gobiidae: Sicydiinae).

Palawan is an island in the western Philippines, and the freshwater fish fauna of this island has received limited research attention. In the present study, a new goby species, Stiphodon palawanensis, is described on the basis of 57 specimens collected from freshwater streams on the island. This species can be distinguished from its congeners by having nine segmented rays in the second dorsal fin, 15 rays in the pectoral fin, a pointed first dorsal fin in males, premaxilla with 45-71 tricuspid teeth, the nape and posterior half of the occipital region covered by cycloid scales, 9-11 dusky transverse bars laterally on the trunk and tail, a line of black blotches (in male) or a black band (in female) on the distal part of the second dorsal fin, and the first dorsal and pectoral fins lacking distinctive markings. The new species has been found only on the Sulu Sea side of central Palawan. Three congeners, S. percnopterygionus, S. atropurpureus, and S. pulchellus have also been recorded from Palawan.

Middle to Late Cenozoic tectonic events in south and central Palawan (Philippines) and their implications to the evolution of the south-eastern margin of South China Sea: Evidence from onshore structural and offshore seismic data

Using recently gathered onland structural and 2D/3D offshore seismic data in south and central Palawan (Philippines), this paper presents a new perspective in unraveling the Cenozoic tectonic history of the southeastern margin of the South China Sea. South and central Palawan are dominated by Mesozoic ophiolites (Palawan Ophiolite), distinct from the primarily continental composition of the north. These ophiolites are emplaced over syn-rift Eocene turbidites (Panas Formation) along thrust structures best preserved in the ophiolite–turbidite contact as well as within the ophiolites. Thrusting is sealed by Early Miocene (∼20 Ma) sediments of the Pagasa Formation (Isugod Formation onland), constraining the younger limit of ophiolite emplacement at end Late Oligocene (∼23 Ma). The onset of ophiolite emplacement at end Eocene is constrained by thrust-related metamorphism of the Eocene turbidites, and post-emplacement underthrusting of Late Oligocene – Early Miocene Nido Limestone. This carbonate underthrusting at end Early Miocene (∼16 Ma) is marked by the deformation of a seismic unit corresponding to the earliest members of the Early – Middle Miocene Pagasa Formation. Within this formation, a tectonic wedge was built within Middle Miocene (from ∼16 Ma to ∼12 Ma), forming a thrust-fold belt called the Pagasa Wedge. Wedge deformation is truncated by the regionally-observed Middle Miocene Unconformity (MMU ∼12 Ma). A localized, post-kinematic extension affects thrust-fold structures, the MMU, and Late Miocene to Early Pliocene carbonates (e.g. Tabon Limestone). This structural set-up suggests a continuous convergent regime affecting the southeastern margin of the South China Sea between end Eocene to end Middle Miocene. The ensuing structures including juxtaposed carbonates, turbidites and shallow marine clastics within thrust-fold belts have become ideal environments for hydrocarbon generation and accumulation. Best developed in the Northwest Borneo Trough area, the intensity of thrust-fold deformation decreases towards the northeast into offshore southwest Palawan.

South China continental margin signature for sandstones and granites from Palawan, Philippines

We report results of heavy mineral analysis and U–Pb dating of detrital zircons from metasediments and Cenozoic sandstones, and U–Pb dating of zircons from Cenozoic granites of the North Palawan Continental Terrane (NPCT) and the South Palawan Terrane (SPT). The NPCT metasediments are derived mainly from granitic and metamorphic rocks of continental character. They contain zircons that indicate a maximum depositional age of Late Cretaceous and other age populations indicating a South China origin. The sediments were deposited on the South China margin before rifting of the continental margin during opening of the South China Sea. Miocene SPT sandstones contain similar heavy mineral assemblages suggesting sources that included NPCT metasediments, metamorphic basement rocks at the contact between the SPT and the NPCT, South China Sea rift volcanic and/or minor intrusive rocks, and the Palawan ophiolite complex. The SPT sandstones are very similar to Lower Miocene Kudat Formation sandstones of northern Borneo suggesting a short-lived episode of sediment transport from Palawan to Borneo in the Early Miocene following arc-continent collision. U–Pb dating of zircons shows that the Central Palawan granite is Eocene (42±0.5Ma). The Capoas granite was intruded during a single pulse, or as two separate pulses, between 13.8±0.2Ma and 13.5±0.2Ma. Inherited zircon ages from the Capoas granite imply melting of continental crust derived from the South China margin with a contribution from Cenozoic rift-related and arc material.