Kim, SeongyeongHwang, In GulGhim, Yong SikKim, Noe-Heon...
16页
查看更多>>摘要：Dinosaur egg-bearing deposits of the Upper Cretaceous (Coniacian-Santonian) Wido Volcanics at Wi Island, South Korea, were studied from a taphonomic perspective to improve understanding of nesting behavior. Based on facies, bedset geometry, and other sedimentological characteristics, the section can be classified into three facies associations: (1) ephemeral fluvial channels (FA I), (2) crevasse splay lobes (FA II), and (3) floodplains (FA III). FA I is characterized by single- and multi-storey channel fills enclosed within FA III, while FA II consists of horizontally-stratified sandstone and calcareous mudstone reflecting weakly developed paleosol profiles. The ephemeral fluvial channels are locally developed at 160 m distance from the main egg locality, suggesting that the nesting site was relatively protected from levee failure and favorable for fossil preservation. Isolated eggs and reworked eggshell fragments of three different types (Propagoolithus widoensis, Reticuloolithus acicularis, and Aenigmaoolithus vesicularis) are frequently found together. The most common type, P. widoensis is preserved as clutches and characterized by numerous closely-spaced pore canals, indicating that the eggs were buried during oviposition, increasing preservation potential. Such in situ clutches occur in at least nine horizons and some occur closely spaced (<1 m apart), lateral to crevasse splay lobe successions (FA II). It suggests that the egg-layers of P. widoensis preferred this facies as a nesting ground for extended periods. FA II was deposited at a higher paleoelevation than FA III, which may have benefited nesting dinosaurs, allowing them to easily detect predators (FA III) while being less frequently exposed to flood hazards.
Matysik, MichalStachacz, MichalKnaust, DirkWhitehouse, Martin J....
22页
查看更多>>摘要：Sedimentology and paleoecology of omission or discontinuity surfaces in carbonate strata is well documented, but the geochemistry of such surfaces is poorly recognized. This work describes morphology, fabrics, geochemistry, and biota succession in omission levels from Middle Triassic (Muschelkalk) platformal carbonates in Upper Silesia, southern Poland. Three types of omission levels are distinguished: firmgrounds, hardgrounds, and intraformational conglomerates. (1) Firmgrounds are characterized by burrows of Balanoglossites triadicus. Some burrows are enclosed by a dark and/or (minor) bright diagenetic halo. The prevailing dark color, lower delta C-13 and delta O-18 ratios, and increased concentration of redox-sensitive elements (U, As, Mo, Cu, Zn, Pb, Ni) in the halos compared to the host micrite indicate a significant enrichment in organic matter, which most likely resulted from impregnation of the burrow walls with organic mucus from the burrowing organism, a process observed in modern burrows. The burrow walls were in contact with stagnant saline water (recorded by elevated Sr-87/Sr-86), but were locally bleached by oxygenated fresh seawater pumped by the burrow producer. (2) Hardgrounds show encrustations of the bivalve Placunopsis ostracina and borings Trypanites weisei. In many hardgrounds, the uppermost 5-mm-thick layer has a different color and higher delta O-18 values than the underlying micrite. This heavier delta O-18 signal reflects a higher content of O-18-enriched early-marine microcrystalline cement precipitated from colder bottom seawater. (3) Intraformational conglomerates consist of flat pebbles derived from reworked firmgrounds and hardgrounds. Many pebbles contain the same encrustations and borings as observed in the hardgrounds, which occur on both sides of the clasts and mimic their shape, indicating that they were developed after pebble formation. All studied types of omission level are laterally discontinuous at some scale and are thus unsuitable for regional correlation.
Maksic, J.Venancio, I. M.Shimizu, M. H.Chiessi, C. M....
12页
查看更多>>摘要：The Last Glacial Maximum (LGM, 26.5-19 ka) was marked by atmospheric cooling, in contrast to the current warming climate, which will probably continue in the coming decades, according to climate models projections. The LGM to pre-industrial transition provides an opportunity to test the vegetation response to a very large temperature change that can then be applied to project pre-industrial to end-of-century changes. In order to explore the changes in Brazilian biomes due to temperature change, we projected potential vegetation for both past and future scenarios. We compared biome projections with a compilation of 149 published LGM reconstructions of climate and vegetation within Brazil and adjacent areas. In addition, we evaluated the particular effects that changes in precipitation, temperature and CO2 had on vegetation by performing sensitivity experiments. Our results suggest that biomes in the western and central portions of the Amazon forest remained largely unchanged during the LGM mainly due to negative temperature anomalies, while a decrease in past precipitation was responsible for the shift from tropical evergreen forest to tropical seasonal forest in the eastern portion of the Amazon. These results are consistent with proxy reconstructions. LGM model projections and proxy reconstructions suggest expansion of grassland in the southern Brazilian highlands. Under future warming scenarios, biome changes are mostly forced by decreasing precipitation and increasing temperatures, which counteract potential biomass gain from the positive CO2 fertilization effect. Under future warming, our simulations show an expansion of Savanna/Cerrado and a reduction of tropical seasonal forest and Caatinga, with potential large impacts over biodiversity and regional climate.
Takata, HiroyukiCho, Jin HyungKang, JeongwonAsahi, Hirofumi...
12页
查看更多>>摘要：We investigated Quaternary benthic foraminifera in core GPC1803 in the eastern equatorial Indian Ocean since-740 ka to examine the relationship between benthic foraminiferal fauna and ballasting of particulate organic matter (POM) by calcareous plankton skeletons. Because plankton skeletons affect POM sinking in the water column as ballasts, ballasting of POM by biominerals may play an important role to linkage between the surface and deep-sea paleoceanography. We consider this scheme, based on faunal analysis of benthic foraminifera. From multidimensional scaling (MDS) of fossil benthic foraminifera, we recognized two MDS axes. Based on the scores of MDS axis 1, we subdivided our study period into five intervals and identified two major faunal transitions at-370 ka and -210 ka. After-210 ka, the food supply to the seafloor increased with an increase in the past flux of calcareous plankton skeletons. A positive correlation between the benthic foraminifera accumulation rate and the carbonate mass accumulation rate existed during-600-370 ka and after-210 ka. It is reasonable to suppose that the increase in calcareous plankton skeletons stimulated more efficient vertical transport of POM through the water column due to the positive ballasting effect on POM. The-370-210 ka period seemed to represent a transitional phase in food supply. Prior to-370 ka, alternations among three seasonal food supply-related species were generally observed along with glacial-interglacial variations probably under lower food supply, compared with the after-210 ka period; however, alternations among these three species became obscure and intermittent after-370 ka. The nearly continuous common occurrences of these seasonal food supply-related species before-370 ka might have been enhanced by a lower past flux of calcareous plankton skeletons. Scenario of ballasting of POM by biomineral might explain long-term changes of carbonate corrosivity in the Indian Ocean, similarly in the Atlantic and eastern equatorial Pacific Oceans, during the mid-Brunhes dissolution interval.
查看更多>>摘要：The Permian-Triassic transition witnessed the extinction of some 90% in the marine realm and 70% taxa on land. Paleoclimate seems to have played a key role in this largest Phanerozoic biodiversity crisis. However, to understand past climatic conditions on land, which display significant spatial variability (e.g., in terms of local temperature and humidity), regional sedimentary records need to be investigated in detail to reconstruct local paleoclimate and inform larger scale models. Here we present a paleosols study of the Permian-Triassic Shichuanhe section in the Shaanxi Province of the central North China Basin. Based on field observation and microscopic study, six types of paleosols have been identified as calcic Inceptisol, vertic Aridisol, gleyed Vertisol, gleyed Inceptisol, calcic Vertisol, and gleyed Aridisol. Fe quasi-coating and calcite hypo-coating disappear in the Early Triassic, taking Fe depleted nodules as major morphological pedofeature. Mean annual precipitation was calculated as 320 +/- 147 mm/yr in the latest Permian and 520-680 +/- 147 mm/yr in the late Early Triassic. The results suggest local aridity in the latest Permian, and intensified precipitation in the late Early Triassic, contributing to the mass extinction and recovery in its aftermath on land.
Zapalski, Mikolaj K.Krol, Jan J.Halamski, Adam T.Wrzolek, Tomasz...
11页
查看更多>>摘要：Tabulates, an extinct Palaeozoic group of corals, developed diverse colony morphologies during the Silurian to Devonian peak of reef development. Coralliths, or circumrotatory colonies, are passively motile coral colonies constantly overturned by wave action or currents. Such overturning allows tissue growth on all sides of the colony. They are among the most rarely reported growth forms. Recent corallith-forming scleractinian corals mostly inhabit the shallowest reef environments, but coralliths can also develop at greater depths in areas of low topographic relief, unconsolidated substratum, low coral cover and high water movement. Here, we report on Devonian (Givetian Favosites goldfussi and Frasnian Alveolites? tenuissimus) coralla from the Holy Cross Mountains, Poland. Our analysis suggests these colonies are coralliths, although less mature than usually reported. These corals, unlike previously described growth forms of this kind, lived in relatively deep environments: probably the upper mesophotic (Givetian, Milosz ' ow), or deep reef fore-slope (Frasnian, Jaz ' wica and Kowala). Microfacies analysis of the Jaz ' wica site suggests unconsolidated substratum and high hydrodynamic energy. We conclude that these corals lived in deeper environments where bottom currents caused their autorotation. A good modern analogue for such a corallith-forming environment is the Wistari Channel (Southern Great Barrier Reef), where bottom tidal currents at nearly 30 m of depth are strong enough to overturn colonies of Stylocoeniella cf. guentheri reaching 15 cm in diameter. Our discovery shows that the spectrum of coral growth forms during the Devonian peak of reef development was broader than previously assumed, and that tabulate corals displayed numerous adaptive strategies to various environments.
查看更多>>摘要：The Bohai Strait connects the Bohai Sea with the Yellow Sea, allowing material and energy exchange between the seas. The sedimentary record in this region is important for reconstructing the Quaternary sea-level changes and environmental evolution in the Bohai Sea area; however, long sedimentary sequences with a reliable chronological framework from this area are scarce. We assessed the sedimentary characteristics, grain size, microfossils, accelerator mass spectrometry 14C ages and optically stimulated luminescence ages of core BHS01 from the Bohai Strait. From these and previous paleomagnetic results, new insights into regional sea-level changes and environmental evolution in the Bohai Strait over the last 2.25 Myr are obtained. The sedimentology and environmental proxies (benthic foraminifera and marine ostracods) indicate that the sedimentary environment of the area around core BHS01 was mainly dominated by fluvial-lacustrine deposits from 2.25 to 0.89 Ma, and subsequently by alternating marine and fluvial deposits. Comparative analyses of the chronological and sedimentary results of core BHS01 with previous drilling records in the eastern marginal seas of China revealed that the Quaternary initial marine transgression of the Bohai Sea occurred no later than 0.89 Ma (latest early Pleistocene) since Quaternary. The initial transgression presumably resulted from the partial subsidence and disintegration of the Miaodao Islands Uplift with sea-level rise during this period or slightly earlier. This result is generally consistent with the timing of the Quaternary regional marine transgressive processes of the Yellow and Bohai seas; thus, we propose a conceptual model in which the first marine transgression of the Yellow Sea and the Bohai Sea during the Quaternary occurred no later than 1.66 Ma and 0.89 Ma, respectively. This study provides new evidence for understanding the Quaternary sea-level changes and regional environmental evolution in the Bohai Sea.
NSTL
Elsevier