Trace Elements in the Standard Carbonate Samples by PIXE Analysis

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A new species of the larger porcelaneous foraminifer Borelis provides novel insights into Neogene to Recent western Pacific palaeobiogeographical dispersal patterns

Only three species of alveolinoidean larger foraminifera occur in present-day tropical shallow-water marine settings. Alveolinella quoyi thrives in the Central Indo-Pacific and Eastern Indo-Pacific, Borelis pulchra in the Central and Eastern Indo-Pacific and in the central Atlantic, whereas Borelis schlumbergeri inhabits the Indo-Pacific Ocean. The northernmost record is that of Alveolinella quoyi from the shallow-water settings in Okinawa (central Ryukyu Islands, Japan). A new porcelaneous larger foraminiferal species, Borelis matsudai sp. nov. (Alveolinoidea, Borelinae), is established herein, based on specimens discovered in present-day shallow-water sediments from Sekisei Lagoon, southern Ryukyu Islands (Japan). This is the northernmost record of the genus in the western Indo-Pacific Warm Pool. The architectural characters of this species suggest its phylogenetic relationship with the Borelis pulchra group. A comprehensive literature survey of fossil and modern records of Borelis pulchra over the past 30 million years shows that the Middle Miocene constriction of the Indonesian Seaway and the Late Miocene–Early Pliocene restriction of the Indonesian Throughflow impacted the species-level dispersal of this species in the Indo-Australian Archipelago. Driven by the Kuroshio dispersal route Borelis matsudai sp. nov. likely appeared in the southern and central Ryukyu Islands at least from the Chibanian (Middle Pleistocene). This species represents a marginal part of a population in significant contact with its ancestor (B. pulchra), which is widespread southward since the Oligocene (Philippines). With ongoing global warming possible occurrences of Borelis matsudai sp. nov. in northern Ryukyu Islands, where it has not yet been found, are expected. The Sekisei Lagoon represents, therefore, a biogeographical stepping stone relay station in northward migration of the shallow-water benthic organisms along the Kuroshio dispersal route

Reef response to sea-level and environmental changes during the last deglaciation: Integrated Ocean Drilling Program Expedition 310, Tahiti Sea Level

The last deglaciation is characterized by a rapid sea-level rise and coeval abrupt environmental changes. The Barbados coral reef record suggests that this period has been punctuated by two brief intervals of accelerated melting (meltwater pulses, MWP), occurring at 14.08-13.61 ka and 11.4-11.1 ka (calendar years before present), that are superimposed on a smooth and continuous rise of sea level. Although their timing, magnitude, and even existence have been debated, those catastrophic sea-level rises are thought to have induced distinct reef drowning events. The reef response to sea-level and environmental changes during the last deglacial sea-level rise at Tahiti is reconstructed based on a chronological, sedimentological, and paleobiological study of cores drilled through the relict reef features on the modern forereef slopes during the Integrated Ocean Drilling Program Expedition 310, complemented by results on previous cores drilled through the Papeete reef. Reefs accreted continuously between 16 and 10 ka, mostly through aggradational processes, at growth rates averaging 10 mm yr-1. No cessation of reef growth, even temporary, has been evidenced during this period at Tahiti. Changes in the composition of coralgal assemblages coincide with abrupt variations in reef growth rates and characterize the response of the upward-growing reef pile to nonmonotonous sea-level rise and coeval environmental changes. The sea-level jump during MWP 1A, 16 ± 2 m of magnitude in ~350 yr, induced the retrogradation of shallow-water coral assemblages, gradual deepening, and incipient reef drowning. The Tahiti reef record does not support the occurrence of an abrupt reef drowning event coinciding with a sea-level pulse of ~15 m, and implies an apparent rise of 40 mm yr-1 during the time interval corresponding to MWP 1B at Barbados. © 2012 Geological Society of America

High-resolution upper Pliocene to Pleistocene calcareous nannofossil biostratigraphy in Ocean Drilling Program Hole 1146A in the South China Sea

We established a high-resolution calcareous nannofossil biostratigraphy for the late Pliocene–Pleistocene by analyzing a 242 m-thick, continuous sedimentary succession from Ocean Drilling Program Site 1146, Hole A, in the South China Sea (SCS). A total of 14 calcareous nannofossil datums were detected in the SCS succession. They are, in descending order: first occurrence (FO) of Emiliania huxleyi, last occurrence (LO) of Pseudoemiliania lacunosa, LO of Reticulofenestra asanoi, FO of Gephyrocapsa parallela, FO of R. asanoi, LO of large Gephyrocapsa spp., FO of large G. spp., FO of Gephyrocapsa oceanica, FO of Gephyrocapsa caribbeanica, LO of Calcidiscus macintyrei, LO of Discoaster brouweri, LO of Discoaster pentaradiatus, LO of Discoaster surculus, and LO of Discoaster tamalis. The FO of E. huxleyi was not precisely detected due to poor preservation and dissolution of nannofossils in the underlying strata. We refined the previous calcareous nannofossil biostratigraphy in the SCS by identifying Gephyrocapsa species and four evolutionary extinction events of the genus Discoaster. The proposed calcareous nannofossil biostratigraphy correlates with those reported in other terrestrial and marine areas/sites and global benthic foraminiferal δ18O records. The age–depth curves based on nannofossil biostratigraphy indicate a significant increase in the sedimentation rates at the LO of R. asanoi (0.91–0.85 Ma). The timing of this increase corresponds to reef expansion in the Ryukyu Islands linked to a stepwise increase in Kuroshio Current intensity. This timing is broadly coeval with a sea surface temperature increase of ∼2°C in the northwestern Pacific due to expansion of the Western Pacific Warm Pool towards the north and south subtropical regions. This can be explained by increased weathering and erosion of terrestrial areas in glacial periods and increased rainfall causing higher sediment transport in interglacial periods, which were both linked to Middle Pleistocene Transition-related climatic changes

Response of the Great Barrier Reef to sea level and environmental changes over the past 30,000 years

Previous drilling through submerged fossil coral reefs has greatly improved our understanding of the general pattern of sea-level change since the Last Glacial Maximum, however, how reefs responded to these changes remains uncertain. Here we document the evolution of the Great Barrier Reef (GBR), the world\u27s largest reef system, to major, abrupt environmental changes over the past 30 thousand years based on comprehensive sedimentological, biological and geochronological records from fossil reef cores. We show that reefs migrated seaward as sea level fell to its lowest level during the most recent glaciation (~20.5-20.7 thousand years ago (ka)), then landward as the shelf flooded and ocean temperatures increased during the subsequent deglacial period (~20-10 ka). Growth was interrupted by five reef-death events caused by subaerial exposure or sea-level rise outpacing reef growth. Around 10 ka, the reef drowned as the sea level continued to rise, flooding more of the shelf and causing a higher sediment flux. The GBR\u27s capacity for rapid lateral migration at rates of 0.2-1.5 m yr−1 (and the ability to recruit locally) suggest that, as an ecosystem, the GBR has been more resilient to past sea-level and temperature fluctuations than previously thought, but it has been highly sensitive to increased sediment input over centennial-millennial timescales

Rapid glaciation and a two-step sea-level plunge into The Last Glacial Maximum

The approximately 10,000-year-long Last Glacial Maximum, before the termination of the last ice age, was the coldest period in Earth’s recent climate history1. Relative to the Holocene epoch, atmospheric carbon dioxide was about 100 parts per million lower and tropical sea surface temperatures were about 3 to 5 degrees Celsius lower2,3. The Last Glacial Maximum began when global mean sea level (GMSL) abruptly dropped by about 40 metres around 31,000 years ago4 and was followed by about 10,000 years of rapid deglaciation into the Holocene1. The masses of the melting polar ice sheets and the change in ocean volume, and hence in GMSL, are primary constraints for climate models constructed to describe the transition between the Last Glacial Maximum and the Holocene, and future changes; but the rate, timing and magnitude of this transition remain uncertain. Here we show that sea level at the shelf edge of the Great Barrier Reef dropped by around 20 metres between 21,900 and 20,500 years ago, to −118 metres relative to the modern level. Our findings are based on recovered and radiometrically dated fossil corals and coralline algae assemblages, and represent relative sea level at the Great Barrier Reef, rather than GMSL. Subsequently, relative sea level rose at a rate of about 3.5 millimetres per year for around 4,000 years. The rise is consistent with the warming previously observed at 19,000 years ago1,5, but we now show that it occurred just after the 20-metre drop in relative sea level and the related increase in global ice volumes. The detailed structure of our record is robust because the Great Barrier Reef is remote from former ice sheets and tectonic activity. Relative sea level can be influenced by Earth’s response to regional changes in ice and water loadings and may differ greatly from GMSL. Consequently, we used glacio-isostatic models to derive GMSL, and find that the Last Glacial Maximum culminated 20,500 years ago in a GMSL low of about −125 to −130 metres.Financial support of this research was provided by the JSPS KAKENHI (grant numbers JP26247085, JP15KK0151, JP16H06309 and JP17H01168), the Australian Research Council (grant number DP1094001), ANZIC, NERC grant NE/H014136/1 and Institut Polytechnique de Bordeaux

Cyjanobakteryjna geneza mikrytowych cementow z plejstocenskich rodolitow i naskorupien krasnorostowych Okierabu-shimy, Japonia

Microcrystalline (micritic) Mg-calcite cements generated by in vivo calcified coccoid cyanobacteria have been identified in rhodoliths and coralline algal crusts from the Pleistocene Ryukyu Group of Okierabu-jima (Ryukyu Islands, Japan). The cements occur as: (i) fringes and festoons on ventral surfaces of Neogoniolithon fosliei, (ii) coatings on dorsal and ventral surfaces of Mastophora pacifica, and (iii) encrustations on tubular thalli of epiphytic and/or chasmolithic green algae. The calcification of the cyanobacteria colonizing spaces within the coralline algal framework was presumably enhanced by a local increase in calcium carbonate saturation due to CO₂ uptake by the living red and green algae strengthened by increased alkalinity resulting from decay processes in the framework. Many microcrystalline (micritic) cements described from other modern and ancient reefal limestones may, by analogy, be products of similar in vivo calcified cyanobacteria.Geneza mikrytowych (synonimy: mikrokrystalicznych, kryptokrystalicznych, pelitowych, drobnoziarnistych) cementów w dzisiejszych i kopalnych strukturach rafowych jest jednym z bardziej kontrowersyjnych zagadnień współczesnej sedymentologii węglanowej. Sporna jest zarówno kwestia organicznego czy nieorganicznego pochodzenie takich cementów, jak i problem syngenetycznego bądź wczesnodiagenetycznego charakteru ich genezy. Praca przedstawia wyniki badań nad mikrytowymi cementami wypełniającymi w różnym stopniu pory w rodolitach i naskorupieniach krasnorostowych z powierzchniowych odsłonięć plejstoceńskich utworów rafowych na wyspie Okierabu-shima (Wyspy Riukiu, Japonia). Zespół krasnorostów i towarzyszących im organizmów szkieletowych występujący w tych utworach wskazuje, że powstały one w głębszej strefie skłonu rafy, na głębokości 50-150 m. Analiza cementów wykazała, że zostały one utworzone w wyniku wytrącenia bardzo drobnych, bo liczących zaledwie 2-3 µm średnicy, ziaren magnezowego kalcytu przez maty kokkoidalnych cyjanobakterii (sinic) rosnących w porach i kawernach rodolitów i naskorupień krasnorostowych. Cementy te występują w postaci guzowatych narośli na brzusznych powierzchniach Neogoniolithon fosliei oraz jako powłoki na brzusznych i grzbietowych powierzchniach Mastophora pacifica i nitkowatych plechach epifitycznych i chasmolitycznych zielenic (Ostreobium, Gomontia). In situ - i najprawdopodobniej in vivo - kalcyfikacja mat cyjanobakteryjnych zasiedlających przestrzenie wewnątrz rafowych struktur krasnorostowych była przypuszczalnie wywołana lokalnie podwyższonym, w porównaniu ze średnią wodą morską, poziomem przesycenia środowiska węglanem wapnia w stosunku do teoretycznego iloczynu rozpuszczalności kalcytu. Spowodowane było to intensywnym pobieraniem z wody CO₂, zarówno przez same cyjanobakterie, jak i fotoasymilujące krasnorosty i zielenice, a także podwyższonym poziomem alkaliczności związanym z procesami rozkładu wewnątrz rafowych struktur krasnorostowych. Uzyskane wyniki dają podstawę do przypuszczeń, że wiele mikrytowych cementów opisanych z innych dzisiejszych i kopalnych struktur rafowych jest również wytworem mat kokkoidalnych cyjanobakterii

Recent progress in study on calcareous algae and algal sediments

The International Fossil Algae Association (IFAA), an international group of scientists who are interested in any aspect of fossil and living algae, organizes an international symposium every 4 years. Okinawa was selected to host the 11th International Symposium on Fossil Algae (Figure 1) because of great contributions to the study of calcareous algae by Japanese scientists such as Ryuji Endo, Wataru Ishijima, and Kenji Konishi (Iryu, 2004) and easy accessibility to modern and Pleistocene coral reefs for which many sedimentological and paleontological studies have been performed for more than 100 years (e.g. Iryu et al., 2006). The Symposium was held on September 14–18, 2015 with the support of the Geological Society of Japan and the Palaeontological Society of Japan. A total of 13 scientists from five countries attended the symposium. Pre-symposium field excursions (September 14–15) visited modern dasycladacean meadows (Figure 2) and Pleistocene carbonate deposits on Okinawa-jima, Central Ryukyus and coral reefs off Kerama Islands. The next 2 days (September 16–17) were devoted for the scientific sessions at the University of the Ryukyus. A special session was organized to discuss “Morphology versus molecular evidence in determining algal taxonomy and phylogeny.” A post-symposium excursion was conducted on September 18. We visited the Shuri Castle and then observed Pleistocene carbonate successions on southern Okinawa-jima. Although the number of participants was limited, there were prolonged discussions for every presentation. This thematic section collects recent studies on calcareous algae and algal sediments by IFAA members. Five papers are assembled here, covering Devonian to modern materials from Europe, Africa, and Japan