The age and origin of the Pacific islands: a geological overview

The Pacific Ocean evolved from the Panthalassic Ocean that was first formed ca 750 Ma with the rifting apart of Rodinia. By 160 Ma, the first ocean floor ascribed to the current Pacific plate was produced to the west of a spreading centre in the central Pacific, ultimately growing to become the largest oceanic plate on the Earth. The current Nazca, Cocos and Juan de Fuca (Gorda) plates were initially one plate, produced to the east of the original spreading centre before becoming split into three. The islands of the Pacific have originated as: linear chains of volcanic islands on the above plates either by mantle plume or propagating fracture origin, atolls, uplifted coralline reefs, fragments of continental crust, obducted portions of adjoining lithospheric plates and islands resulting from subduction along convergent plate margins. Out of the 11 linear volcanic chains identified, each is briefly described and its history summarized. The geology of 10 exemplar archipelagos (Japan, Izu-Bonin, Palau, Solomons, Fiji, New Caledonia, New Zealand, Society, Galápagos and Hawaii) is then discussed in detail.     

Isolation by distance and vicariance drive genetic structure of a coral reef fish in the Pacific Ocean

We studied the genetic diversity of a coral reef fish species to investigate the origin of the differentiation. A total of 727 Acanthurus triostegus collected from 15 locations throughout the Pacific were analyzed for 20 polymorphic loci. The genetic structure showed limited internal disequilibrium within each population; 3.7% of the loci showed significant Hardy-Weinberg disequilibrium, mostly associated with Adh*, and we subsequently removed this locus from further analysis of geographic pattern. The genetic structure of A. triostegus throughout the tropical Pacific Ocean revealed a strong geographic pattern. Overall, there was significant population differentiation (multilocus F(ST) = 0.199), which was geographically structured according to bootstraps of neighbor-joining analysis on Nei's unbiased genetic distances and AMOVA analysis. The genetic structure revealed five geographic groups in the Pacific Ocean: western Pacific (Guam, Philippines, Palau, and Great Barrier Reef); central Pacific (Solomons, New Caledonia, and Fiji); and three groups made up of the eastern populations, namely Hawaiian Archipelago (north), Marquesas (equatorial), and southern French Polynesia (south) that incorporates Clipperton Island located in the northeastern Pacific. In addition, heterozygosity values were found to be geographically structured with higher values grouped within Polynesian and Clipperton populations, which exhibited lower population size. Finally, the genetic differentiation (F(ST)) was significantly correlated with geographic distance when populations from the Hawaiian and Marquesas archipelagos were separated from all the other locations. These results show that patterns of differentiation vary within the same species according to the spatial scale, with one group probably issued from vicariance, whereas the other followed a pattern of isolation by distance. The geographic pattern for A. triostegus emphasizes the diversity of the evolutionary processes that lead to the present genetic structure with some being more influential in certain areas or according to a particular spatial scale.     

A palaeospinacid shark from the Upper Triassic of south-west England

The fin spines of a new neoselachian shark are described from die Upper Triassic of Aust Cliff, Avon and Holwell, near Frome in Somerset. The spines are assigned to Palaeospinax rhaeticus sp. nov. This record adds to the known diversity of Upper Triassic marine vertebrates from Britain and extends the range of the palaeospinacid sharks into the Rhaetian.     

Divergence time of the two regional medaka populations in Japan as a new time scale for comparative genomics of vertebrates

The southern and northern Japanese populations of the medaka fish provide useful tools to gain insights into the comparative genomics and speciation of vertebrates, because they can breed to produce healthy and fertile offspring despite their highly divergent genetic backgrounds compared with those of human–chimpanzee. Comparative genomics analysis has suggested that such large genetic differences between the two populations are caused by higher molecular evolutionary rates among the medakas than those of the hominids. The argument, however, was based on the assumption that the two Japanese populations diverged approximately at the same time (4.0–4.7 Myr ago) as the human–chimpanzee lineage (5.0–6.0 Myr ago). This can be misleading, because the divergence time of the two populations was calculated based on estimated, extremely higher molecular evolutionary rates of other fishes with an implicit assumption of a global molecular clock. Here we show that our estimate, based on a Bayesian relaxed molecular-clock analysis of whole mitogenome sequences from 72 ray-finned fishes (including 14 medakas), is about four times older than that of the previous study (18 Myr). This remarkably older estimate can be reconciled with the vicariant events of the Japanese archipelago, and the resulting rates of molecular evolution are almost identical between the medaka and hominid lineages. Our results further highlight the fact that reproductive isolation may not evolve despite a long period of geographical isolation.     

A new species of Leptocycas(Zamiaceae)from the Upper Triassic sediments of Liaoning Province,China

A new cycad,Leptocycas yangcaogouensis sp.nov.,was found in sediments from the Late Triassic in western Liaoning,China.The pinnately compound leaves(Pseudoctenis type)are screwed in a crown on the stem top.The leaflets are linear,with parallel veins and decurrent bases on the rachis.The leaf bases are persistent.The cataphylls intermix with the leaves.The female cone is ovoid in shape.The characteristics of the new plant are more similar to those of Leptocycas gracilis,a Triassic cycad from North America,but the new species differs from L.gracilis in the size of its stem(7-8 vs.3-5 cm in diameter,respectively),leaves(length × width 100 × 16 vs.30 × 7 cm,respectively)and leaf density along the stem(4-6 vs.1-2 bases/1 cm length,respectively).Both L.gracilis and L.yangcaogouensis,having leaves of the Pseudoctenis type,show a closer relationship to the extant Dioon of Zamiaceae.The present study provides evidence for the origin of the genus Dioon,which may have come from Leptocycas plants of the Triassic.It would be assumed that the extent cycads in Zamiaceae originate from the pteridosperms in the Late Paleozoic and have evolved through the stage of L.gracilis and L.yangcaogouensis in Late Triassic,and reaching the extant Dioon.     

Facies patterns of a tectonically-controlled Upper Triassic platform-slope carbonate depositional system (Carnian Prealps, Northeastern Italy)

Summary Upper Triassic (Middle-Upper Norian) shallow-water carbonates of the Dolomia Principale and its deep-water counterparts (Forni Dolomite) have been studied in the Carnian Prealps (northeastern Italy). The Dolomia Principale was a storm-dominated carbonate platform; in the Mt. Pramaggiore area, along a well-preserved 3.5 km-long platform-to-basin transition, the inner platform facies of the Dolomia Principale, characterized by m-scale shallowing upward cycles, give way seaward to open marine storm-dominated shallow subtidal lagoon deposits with frequent hardgrounds and evidence of microbial stabilization of the bottom sediment. The margin of the Dolomia Principale platform was colonized by meter-scale stromatolites and serpulid-microbial mounds that thrived due to the local highly stressed environment, characterized by drastic salinity fluctuations and turbid waters, that excluded the Upper Triassic coral-sponge communities. The Forni Dolomite slope-basin complex was characterized by an upper slope facies with debris flows, megabreccias, turbidites and serpulid-microbial mounds. The lower slope and basinal facies show thinning and fining trends. After restoring the original geometry of the slope, the depositional angles of the clinoforms range between 11 and 36 degrees, reflecting closely the coarse-grained character of the Forni Dolomite slope complex, which can be interpreted as a slope apron that, as a model, can be extended to steeply inclined carbonate slopes. The onset of synsedimentary extensional tectonics at the Middle-Late Norian boundary affected the platform-slope depositional system via: 1) localized inner platform collapses and the formation of an intraplatform anoxic depression at Mt. Valmenone, 2) a switch from platform lateral progradation during the Middle Norian to vertical aggradation in the Late Norian, reflected in an increase in platform relief, steeper foreslope angles and coarser-grained slope facies, and 3) controlling the spatial orientation of the margin of the Dolomia Principale.     

A comparison between the Upper Triassic floras of China and the Rhaeto-Liassic floras of Europe and East Greenland

A survey is given of the geological and geographical distribution of the Upper Triassic floras of China, based chiefly on many articles published in Chinese during the last ten years. This is followed by a comparison between the Upper Triassic flora of China and the Rhaeto-Liassic floras of Europe (Sweden, Germany) and East Greenland. It is pointed out that important floral assemblages (for example that of the Liassic Thaumatopteris schenkii Assemblage-zone) occur considerably earlier in China (especially in S.W. China) than in Europe and East Greenland.     

Dasycladalean green algae from the Upper Triassic of Mt. Rotonda (Verbicaro Unit, Calabria-Lucania Border, Southern Italy)

Summary A rich and diverse dasycladalean algae association is described from the Upper Triassic succession of Mt. Rotonda (Calabria-Lucania border, Southern Italy). This association consists of:Neoteutloporella rajkae n.sp.,Griphoporella bechst?dti n.sp.,Physoporella zamparelliae n.sp.,Spinaporella andalusica Flügel & Flügel-Kahler, 1984,S.? granadaensis Flügel & Flügel-Kahler, 1984,Chinianella? sp.,Gyroporella sp.,Griphoporella? sp. andPhysoporella aff.leptotheca. Neoteutloporella rajkae n.sp. is characterised by an undulated calcareous skeleton with short acrophore primary laterals bearing a tuft of 4–6 elongate, segmented, trichophore secondary laterals. This species allows to extend back to the Upper Triassic the stratigraphic range of the genusNeoteutloporella, previously known only from Upper Jurassic levels. Griphoporella bechst?dti n.sp. has a cylindrical calcareous skeleton and primary laterals only, consisting of a thin proximal part followed by a swollen portion that pinches out distally and finally opens outward with a cup-like swelling. Physoporella zamparelliae n.sp. is characterised by a calcareous skeleton made by partly welded thin individual sheaths enclosing the laterals. The laterals are piriferous, vertically compressed, roughly triangular both in vertical and in verticillar section. In some specimens they end with a spine-like thin apophysis. This species confirms that the typical Middle Triassic genusPhysoporella survived up into the Norian. The dasycladalean algal association of the Norian of Mt. Rotonda shows some similarities with the algal association found in the Upper Triassic of the Betic Cordillera whereas it is markedly different from the rich association occurring in the Upper Triassic of Sicily and of the Northern Calcareous Alps. This pattern is coupled with a different composition of the platform margin communities: microbial/serpulids bioconstructions in the Upper Triassic of the Calabria-Lucania border and of Alpujarridevs. Dachstein-type reefs in Sicily and the Northern Calcareous Alps. This indicates that the palaeoceanographic and palaeogeographic conditions controlled both the development of the different platform margin and of the different algal assemblages.     

Mitochondrial DNA variation suggests river capture as a source of vicariance in Gadopsis bispinosus (Pisces: Gadopsidae)

Gadopsis bispinosus from the Australian Capital Territory (ACT) were genetically similar to a population in north-east Victoria, but highly divergent from another population in central Victoria. Upper tributary populations from the Murray and Murrumbidgee Rivers were similar probably due to river capture.     

Microfacies and depositional environment of an Upper Triassic intra-platform carbonate basin: the Fatric Unit of the West Carpathians (Slovakia)

Facies associations of the Rhaetian Fatra Formation from the Veká Fatra Mts. (West Carpathians) were deposited in a storm-dominated, shallow, intra-platform basin with dominant carbonate deposition and variable onshore peritidal and subtidal deposits, with 21 microfacies types supported by a cluster analysis. The deposits are formed by bivalves, gastropods, brachiopods, echinoderms, corals, foraminifers and red algae, ooids, intraclasts and peloids. A typical feature is the considerable variation in horizontal direction. The relative abundance and state of preservation of components as well as the fabric and geometric criteria of deposits can be correlated with depth/water energy-related environmental gradients. Four facies associations corresponding to four types of depositional settings were distinguished: a) peritidal, b) shoreface, above fair-weather wave base (FWWB), c) shallow subtidal, above normal storm wave base and d) above maximum storm wave base. The depositional environment can be characterized as a mosaic of low-relief peritidal flats and islands, shoreface banks and bars, and shallow subtidal depressions. The distribution and preservation of components were mainly controlled by the position of base level (FWWB), storm activity and differences in carbonate production between settings. Poorly or moderately diverse level-bottom macrobenthic assemblages are dominated by molluscs and brachiopods. The main site of patch-reef/biostrome carbonate production was located below the fair-weather wave base. Patch-reef/biostrome assemblages are poorly diverse and dominated by the branched scleractinian coral Retiophyllia, forming locally dm-scale autochthonous aggregations or more commonly parautochthonous assemblages with evidence of storm-reworking and substantial bioerosion by microborings and boring bivalves.Facies types and assemblages are comparable in some aspects to those known from the Upper Triassic of the Eastern and Southern Alps (Hochalm member of the Kössen Formation or Calcare di Zu Formation), pointing to similar intra-platform depositional conditions. The absence of large-scale patch-reefs and poor diversity of level-bottom and patch-reef/biostrome assemblages with abundance of eurytopic taxa indicate high-stress/unstable ecological conditions and more restricted position of the Fatric intra-platform setting from the open ocean than the intra-platform habitats in the Eastern or Southern Alps.     

New dasycladalean algae from the Middle Norian (Upper Triassic) of northern Italy (Mt. Pramaggiore, Carnic Prealps)

In the Eastern Southern Alps of northern Italy (Carnic Prealps, Friuli region), the shallow-water carbonate platform deposits of the Dolomia Principale Fm. (Norian–Rhaetian, Upper Triassic) show best-preserved platform to basin facies transition. The palaeontological study of an algal-rich level recovered from the platform margin facies (Mt. Pramaggiore) has displayed a very interesting association of Dasycladales. Two new genera (Bystrickyella and Elliottporella) and four new species (Bystrickyella ottii, Elliottporella morelloae, Palaeodasycladus lorigae and Holosporella conradii) have been described. These new data suggest that the Norian represents a period of turnover in the evolutionary history of the green algae community. This stage, placed between two extinctions, end-Ladinian and end-Norian, is here interpreted as a re-organization period of the evolutionary schemes of Dasycladales. The new lineages originated in the Norian developed further and characterized the Early Jurassic scenery. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A biogeographic review of Parahebe (Scrophulariaceae)

Distribution maps and notes are given for the 41 species of Parahebe sensu lata. The genus occurs in New Zealand, south-east Australia and New Guinea, with greatest diversity in New Zealand, especially in the Spenser Mountains region of South Island. A group of species with ciliate floral discs is found in north-east South Island, and also in eastern Papua New Guinea. This outer Australasian arc distribution is attributed to the group having originated before the break-up of Gondwana. Within New Zealand the P. catarraclae complex shows disjunction along the Alpine Fault, a plate boundary of the transform type. The disjunction is attributed to massive lateral displacement on the Fault during Tertiary time pulling apart plant populations. Parahebe sect. Paniculatae is newly described. The following new combinations are made: Parahebe brevistylis, P. macrantha, P. macrantha var. brachyphylla, P. raoulii, P. r. subsp. maccaskillii, P. r. subsp. pentasepala, P. lavaudiana, P. hulkeana, P. nivea, P. arenaria, P. velutina, P. blakelyi, P. arcuata, P. derwentiana subsp. maideniana, P. d. subsp. homalodonta, P. d. subsp. anisodonta and P. d. subsp. subglauca.     

High-resolution sequence stratigraphy of a mixed carbonate-siliciclastic, cratonic ramp (Upper Ordovician; Kentucky–Ohio, USA): insights into the relative influence of eustasy and tectonics through analysis of facies gradients

Detailed facies analysis and event stratigraphy of an Upper Ordovician (Rocklandian–Edenian) cratonic ramp succession in eastern North America yields insights into eustatically driven sequence architecture and localized tectonic instability. Seven, predominantly subtidal, mixed carbonate-siliciclastic depositional sequences (3rd order) are identified and correlated across the length of a 275-km ramp–to–basin profile. Within the larger depositional sequences (3rd order) at least two smaller orders (4th and 5th) of cyclicity are recognizable. Three systems tracts occur within each sequence (transgressive, TST; highstand, HST; regressive, RST) and are considered in terms of their component parasequences (5th order). Generally, TSTs are composed of skeletal grainstone–rudstone facies, HSTs are dominated by shaly nodular wacke-packstone facies, and RSTs are mostly calcarenite facies. Systems tracts, sequence boundaries and their correlative conformities, maximum flooding surfaces, and forced regression surfaces were traced from shallow shelf to basinal settings. This high-resolution framework also provides insight into the timing of tectonic fluctuations on this cratonic ramp during the Taconic Orogeny and documents the relative influence of tectonism on lateral facies distributions and eustatically derived cyclicity.     

Flux and grain size variation of eolian dust as a proxy tool for the paleo-position of the Intertropical Convergence Zone in the northeast Pacific

A 328 cm-long piston core (KODOS 02-01-02) collected from the northeast equatorial Pacific at 16°12′N, 125°59′W was investigated for eolian mass fluxes and grain sizes to test these proxies as a tool for the paleo-position of the Intertropical Convergence Zone (ITCZ). The eolian mass fluxes of the lower interval below 250 cm (15.5-7.6 Ma) are very uniform at 5 ± 1 mg/cm²/10³ yr, while those of the upper interval above 250 cm (from 7.6 Ma) are over 2 times higher than the lower interval at 12 ± 1 mg/cm²/10³ yr. The median grain size of the eolian dusts in the lower interval increases from 8.4? to 8.0? downward, while that of the upper interval varies in a narrow range from 8.8? to 8.6?. The determined values compare well in magnitude to those of central Pacific sediments for the upper interval and equatorial and southeast Pacific sediments for the lower interval. This result suggests a possibility that the study site had been under the influence of southeast trade winds at its earlier depositional period due to the northerly position of the ITCZ, and subsequently of the northeast trade winds for a later period when the upper sediments were deposited. This interpretation is consistent with a mineralogical and geochemical study published elsewhere that assigned the provenance of the study core dust to Central/South America for the lower interval and to Asia for the upper interval. This study suggests that the distinct differences in eolian mass flux and grain size observed across the ITCZ can be used to trace the paleo-latitude of the ITCZ.