Many Atolls may be Uninhabitable by Mid Century

Sea-level rise and wave-driven flooding will negatively impact freshwater resources on many low-lying atoll islands in such a way that many could be uninhabitable in just a few decades. According to a new study published in Science Advances, scientists found that such flooding not only will impact terrestrial infrastructure and habitats, but, more importantly, it will also make the limited freshwater resources non-potable and, therefore, directly threaten the sustainability of human populations.

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New Campanian/Maastrichtian Cretaceous Island Vertebrate Site From Romania

Petreşti-Arini – An important but ephemeral Upper Cretaceous continental vertebrate site in the southwestern Transylvanian Basin, Romania

Authors:

Vremir et al


Abstract:

The Transylvanian region of Romania preserves some of the most unusual and iconic dinosaurs in the global fossil record, including dwarfed herbivores and aberrant carnivores that lived during the very latest Cretaceous (Maastrichtian) in an ancient island ecosystem (the Haţeg Island). A series of artificial outcrops recently exposed during a hydroelectric project, the Petreşti-Arini section near Sebeş in the Transylvanian Basin, records a 400+ meter sequence documenting the transition from fully marine to terrestrial environments during the Campanian–Maastrichtian. Calcareous nannofossil biostratigraphy indicates that the lower marine beds in this section, part of the uppermost Bozeş Formation, can be assigned to the CC22 biozone, corresponding to the lower–mid upper Campanian. These beds smoothly transition, via a brackish-water unit, into the fully continental Maastrichtian Sebeş Formation. Dinosaur and pterosaur fossils from the uppermost Bozeş Formation can be assigned a late Campanian age making them the oldest well-dated terrestrial fossils from the Haţeg Island, and indicating that the classic Haţeg dinosaur fauna was becoming established by this time, coincident with the first emergence of widespread land areas. Vertebrate fossils occur throughout the overlying Sebeş Formation at the site and are dominated by the small-bodied herbivorous dinosaur Zalmoxes. The dominance of Zalmoxes, and the absence of many taxa commonly seen elsewhere in Maastrichtian sites in Romania, suggests the possibility that either the Petreşti-Arini section preserves a somewhat unusual near-shore environment, or the earliest Haţeg Island dinosaur communities were structured differently from the more diverse communities later in the Maastrichtian. Alternatively, due to the limited sample size available from the studied succession, it is also conceivable that sampling biases give an incomplete portrayal of the Petreşti-Arini local fauna. Support for any one of these alternative hypotheses requires further data from Petreşti-Arini as well as from the larger Transylvania area.

Japan's Newest Island Grows Larger

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Evidence for Island Arc–Continent Collision in Neoproterozoic Brazil

Electromagnetic constraints for subduction zones beneath the northwest Borborema province: Evidence for Neoproterozoic island arc–continent collision in northeast Brazil

Authors:

Padilha et al

Abstract:

The Borborema province in northeast Brazil occupies a crucial position in the complex Neoproterozoic West Gondwana reconstruction puzzle. However, correlation attempts between northeast Brazil and West Africa have been hampered because key links in the internal structure of the Borborema province have yet to be identified. To aid such an correlation, a magnetotelluric study was undertaken along two subparallel profiles to image the deep electrical structure in the northwestern part of the province. Despite the occurrence of recurrent tectonothermal episodes that affected the region in the past, two-dimensional models show that a large-scale signature of the assembled terrane during the Neoproterozoic accretion and collision is plausibly preserved in the area. Two resistive features dipping from the upper crust into the upper mantle in downward convergence (opposite directions) are defined beneath one of the profiles that are interpreted to be related to remnants of former subduction slabs, since the observed high-resistivity zone is consistent with a dehydrated oceanic lithosphere depleted of sediments. On the basis of geological and geochemical information, a model of collision of an intraoceanic magmatic arc coalesced into an earlier passive margin is proposed for the Neoproterozoic tectonic evolution of the province, involving processes of reversal of subduction polarity and oceanic slab breakoff.

Evidence of a Cambrian-Ordovician Paleozoic Island Arc in NorthWest China

Heishan mafic-ultramafic rocks in the Qimantag area of Eastern Kunlun, NW China: Remnants of an early Paleozoic incipient island arc

Authors:

Fancong Meng, Meihui Cui, Xiangke Wu and Yufeng Ren

Abstract:

The Heishan mafic-ultramafic complex in the Qimantag Mountains of the Eastern Kunlun Orogen, consist of olivine pyroxenites, pyroxenites, gabbros, and massive basalts. Zircons from the gabbros have magmatic sector zoning, with Th/U ratios of 0.5 - 2.3, and yield a SHRIMP age of 486 ± 6 Ma (MSWD = 0.31), which is taken as the time of magma crystallization. Spinel, pyroxene, and plagioclase mineral compositions indicate that the rocks formed in an island arc environment. The cumulates have low (La /Yb) N ratios (0.6-0.8) and depleted LREE patterns, high abundances of Cr (3031-1185 ppm), Co (119 - 50 ppm), and Ni (953 - 291ppm), and εNd (t) values of about + 8.0. The massive basalts have somewhat higher contents of TiO2 (1.0%-1.3%), Na2O (2.6%-2.8%), total REE and Mg#s (55-63) than those of the cumulates. The (La /Yb) N ratios of the basalts range from 0.8 to 1.2 and the chondrite-normalized REE patterns are flat. εNd(t) values of the basalts range from + 7.7 to + 9.4. The compositions of the cumulates and volcanic rocks, especially their similar Nd isotopes, suggest that the rocks were derived from similar depleted mantle sources. The primary magmas were probably generated in an initial arc environment. We conclude that the Heishan mafic-ultramafic complex in the Qimantag area preserves a record of Proto-Tethyan oceanic lithosphere formed in the early Paleozoic. It possibly marks a suture between the Qaidam and North Kunlun terranes in the western segment of the Eastern Kunlun Orogen.

Evidence of at Least Three Proterozoic Islands Arcs in the Northern Arabian–Nubian Shield

Three successive Proterozoic island arcs in the Northern Arabian–Nubian Shield: Evidence from SIMS U–Pb dating of zircon

Authors:

Eyal et al.

Abstract:

Four isolated metamorphic complexes located within post-collisional granitoids occupying up to 70% of the total area, were distinguished in Sinai (Egypt) and Elat area (southern Israel), the northernmost part of the Arabian–Nubian Shield. The metamorphic rocks include metasediments, felsic and mafic metavolcanic rocks intruded by granitic, dioritic, and gabbroic plutons, all subjected to penetrative deformation.

We present new SIMS U–Pb dating of zircons from 13 rock units comprising metasediments, volcanic rocks, gneisses and plutons from three metamorphic complexes (Sa'al, Feiran–Solaf, and Kid). In addition we present a SIMS U–Pb titanite age of a granitic gneiss previously dated using zircon. On the basis of the new and published U–Pb data, three successive Meso- to Neoproterozoic island arcs formed during a period of ca. 500 My are recognized. The Sa'al arc (represented by the oldest arc rocks in the ANS) evolved from 1.03 to 0.93 Ga (100 My); the Feiran–Elat arc developed from ca. 870 to 740 Ma (130 My), and the Kid arc formed from ca. 640 to 620 Ma (20 My). Evidence for an older, ca. 1.1 Ga, pre-Sa'al island arc was established from the zircon xenocryst population, though no exposures of rocks of this age were found. In the Sa'al and Kid arcs both volcanic and sedimentary rocks are preserved, whereas in the Elat–Feiran arc volcanic rocks are missing. We suggest that at ~ 700 Ma the Elat−Feiran arc was subjected to rifting that resulted in separating of the Qenaia block and its movement to the SE.

Evidence of NeoArchean Volcanic Islands Arcs in India

Zircon U-Pb geochronology and Hf isotope of felsic volcanics from Attappadi, southern India: Implications for Neoarchean convergent margin tectonics

Authors:

1. M.N. Praveen (a)
2. M. Santosh (b)
3. Q.Y. Yang (b)
4. Z.C. Zhang (b)
5. H. Huang (b)
6. S. Singanenjam (c)
7. K.S. Sajinkumar (d)

Affiliations:

a. Geological Survey of India, Dharani Bhawan, Manikanteshwaram PO, Thiruvananthapuram 695 013, India

b. School of Earth Sciences and Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, China

c. Geological Survey of India, Rajaji Bhavan, Besant Nagar, Chennai 600 090, India

d. Department of Geology, University of Kerala, Thiruvananthapuram 695 581

Abstract:

The Attappadi area on the south-western flanks of the Archean Dharwar Craton in southern India is located along the E-W trending Bhavani Shear Zone which marks the trace of a Neoarchean suture zone. The dominant rock types in the area include meta-ultramafics, amphibolites, TTG (tonalite-trondhjemite-granodiorite) gneisses, metapelites, and sulphidic banded iron formation (BIF). Here we report the occurrence of felsic volcanic rocks preserving primary textures from the Anaikatti area in eastern Attappadi. The felsic volcanics are interbanded with the BIF, amphibolite, metapelite, metapyroxenite and hornblende gneisses. The felsic volcanics are divided into two types based on their textures. The Type-1 rock is medium grained with gneissic texture and lack unequivocal primary volcanic textures. Type-2 felsic volcanics are thinly laminated, fine grained and at places preserve relict soft-sediment deformation structures. They also contain relict volcanic clasts or lapilli and are interpreted as felsic tuff. Geochemically, the Attappadi felsic volcanics are rhyolitic in composition and have arc-related trace element signatures. They also possess a calc-alkaline volcanic affinity.

We report LA-ICPMS U-Pb ages from zircons in four samples of the felsic tuffs which show weighted mean ages of 2567 ± 18 Ma and (MSWD = 1.4), 2499 ± 19 Ma (MSWD = 0.57), 2555 ± 24 Ma (MSWD = 1.7) and 2576 ± 64 Ma (MSWD = 5.8). The late Neoarchean – early Paleoproterozoic ages obtained in our study correlate well with the zircon U-Pb ages reported in recent studies from ophiolites and other suprasubduction suites from Attappadi and surrounding regions. The zircon εHf values range from -11.1 to 7.6 suggesting heterogeneous source material involving both juvenile and older reworked components. We build a tectonic model for the SW margin of the Dharwar Craton with an oceanic realm characterized by island arcs and widespread submarine tholeiitic as well as komatiitic ultramafic and mafic volcanism during the Neoarchean. This predominantly mafic volcanism on the ocean floor is represented by primitive komatiitic lavas, oxide and sulphide facies BIF. The birth of volcanic arc at the convergent margin is marked by felsic volcanism and the deposition of felsic volcanics and volcano-sedimentary successions. In the final stage of ocean closure, the ocean-plate and continental arc assemblages were brought in juxtaposition including the accretion of the ophiolitic fragments. Our study confirms the recent models of arc-arc and arc-continental accretion to the southern margin of the Dharwar Craton and major continental growth at the end of the Archean.

Evidence of Sea Faring NorAms Over 11,000 Years Ago?

Evidence for a diversified sea-based economy among North American inhabitants dating from 12,200 to 11,400 years ago is emerging from three sites on California's Channel Islands.

Reporting in the March 4 issue of Science, a 15-member team led by University of Oregon and Smithsonian Institution scholars describes the discovery of scores of stemmed projectile points and crescents dating to that time period. The artifacts are associated with the remains of shellfish, seals, geese, cormorants and fish.

Funded primarily by grants from the National Science Foundation, the team also found thousands of artifacts made from chert, a flint-like rock used to make projectile points and other stone tools.

Some of the intact projectiles are so delicate that their only practical use would have been for hunting on the water, said Jon Erlandson, professor of anthropology and director of the Museum of Natural and Cultural History at the University of Oregon. He has been conducting research on the islands for more than 30 years.

"This is among the earliest evidence of seafaring and maritime adaptations in the Americas, and another extension of the diversity of Paleoindian economies," Erlandson said. "The points we are finding are extraordinary, the workmanship amazing. They are ultra thin, serrated and have incredible barbs on them. It's a very sophisticated chipped-stone technology." He also noted that the stemmed points are much different than the iconic fluted points left throughout North America by Clovis and Folsom peoples who hunted big game on land.

The artifacts were recovered from three sites that date to the end of the Pleistocene epoch on Santa Rosa and San Miguel islands, which in those days were connected as one island off the California coast. Sea levels then were 50 to 60 meters (about 160-200 feet) below modern levels. Rising seas have since flooded the shorelines and coastal lowlands where early populations would have spent most of their time.

Erlandson and his colleagues have focused their search on upland features such as springs, caves, and chert outcrops that would have drawn early maritime peoples into the interior. Rising seas also may have submerged evidence of even older human habitation of the islands.

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