Pliocene Research Articles

Indian monsoon variability in response to orbital forcing during the late Pliocene

Abstract The Asian monsoon is a major component of the global climate system and can be divided into two subsystems, the Indian monsoon and the East Asian monsoon. Insights into monsoon behaviour and dynamics can be gained through studying past warm intervals in Earth's history. One such interval is the Pliocene epoch, specifically the mid-Piacenzian Warm Period (mPWP; 3.264–3.025 Ma). This time is characterised as a period of sustained warmth, with annual mean temperatures 2–3 °C higher than the pre-industrial era. Studies have examined the East Asian monsoon during the mPWP from both a geological data and climate modelling perspective. However, there has been little investigation into the behaviour of the Indian monsoon. Using a coupled atmosphere-ocean global climate model (HadCM3), the Indian summer monsoon response to orbital forcing during the mPWP is studied. Of the simulated interglacial events (Marine Isotope Stages KM5c, KM3, K1 and G17), MIS KM5c is the only one with a near-modern orbital forcing. This experiment is compared to a pre-industrial simulation to determine the nature of the mPWP Indian summer monsoon in the absence of a different pattern if insolation forcing. The monsoon at MIS KM5c, is simulated to be stronger than pre-industrial, with higher surface air temperatures and precipitation over land due to higher levels of CO2. MIS G17, K1, and KM3 represent interglacial events of similar magnitude with different insolation forcing than MIS KM5c. The Indian summer monsoon is simulated to be significantly stronger for the interglacials K1 and KM3, compared to KM5c. This is due to stronger precession forcing causing an increase in summer surface air temperature and precipitation. When combined with Pliocene geological boundary conditions, these results highlight the significant effect of orbital forcing on the strength of the Indian summer monsoon. The sensitivity of the Indian monsoon to orbital forcing has important implications for any parallels drawn between Pliocene and future monsoon behaviour.

Accumulations of Fossils of the Whale Barnacle Coronula bifida Bronn, 1831 (Thoracica: Coronulidae) Provides Evidence of a Late Pliocene Cetacean Migration Route through the Straits of Taiwan.

John Stewart Buckeridge, Benny K.K. Chan, and Shih-Wei Lee (2018) This paper describes a remarkably prolific accumulation of the whale barnacle Coronula bifida Bronn, 1831 in sediments of late Pliocene to earliest Pleistocene age from central Taiwan. Extant Coronula is host-specific to baleen whales; as such, this accumulation of Coronula fossils represents a site where cetaceans congregated during the Plio-Pleistocene - perhaps for breeding. Although whale bones are found at the site, they are rare and fragmentary; the relatively robust shells of Coronula are thus a useful proxy for establishing ancient cetacean migration routes.

Nuclear and chloroplast DNA phylogeography suggests an Early Miocene southward expansion of Lithocarpus (Fagaceae) on the Asian continent and islands

BackgroundMost genera of Fagaceae are thought to have originated in the temperate regions except for the genus Lithocarpus, the stone oaks. Lithocarpus is distributed in subtropical and tropical Asia, and its ancestral population is hypothesized to be distributed in tropical regions in Borneo and Indochina. Borneo and the nearby islands (the Greater Sunda Islands) were connected to the Malay Peninsula and Indochina prior to the Pliocene epoch and formed the former Sundaland continent. The Southeast Asian Lithocarpus, is thought to have dispersed between continental Asia and the present Sundaland. The drastic climate changes during the Pliocene and Pleistocene epochs which caused periodic sea-level changes is often used to explain the cause of its diversity. The aim of this study was to establish phylogenetic relationships by analyzing nuclear (nrDNA) and chloroplast (cpDNA) DNA in order to describe and analyze the origin, causes of diversification and historical biogeography of Lithocarpus.ResultsPhylogeny reconstructed through the multiple-species coalescent method with nrDNA and cpDNA revealed that the continental-Asian taxa were clustered at the basal lineages. The derived lineages of tropical Lithocarpus, with the inference of a subtropical ancestral state, imply a southward migration in the Early Miocene period with subsequent in situ diversification in the Greater Sunda Islands. The gradual decrease in temperature since the Middle Miocene period is proposed as a cause of the increase in the net diversification rate.ConclusionsThe historical ancestral origin of Lithocarpus has been suggested to be mainland Asia. Southward migration in the Early Miocene period with subsequent in situ diversification could explain the current diversity of stone oaks in Southeast Asia. This study also considered the multiple origins of stone oaks currently indigenous to the subtropical islands offshore and near mainland China. Our results provide phylogenetic evidence for a subtropical origin of Asian stone oaks and reveal the process of diversification and how it fits into the timeline of major geologic and climatic events rather than local, episodic, rate-shifting events.

Stratigraphic distribution and biostratigraphic utility of the fossil diatom Lancineis rectilatus in the central Kanto Plain, central Japan

The stratigraphic range of extinct shallow-marine diatom species Lancineis rectilatus Naya was investigated in upper Pliocene to Holocene marine strata from five sediment cores drilled on the central Kanto Plain, central Japan. The lowest occurrence of L. rectilatus in the five cores was in the marine strata between the Kd25 and Kd12-Type tephra layers, and was dated at ca 1.45 Ma. The uppermost occurrence of L. rectilatus was in marine strata deposited during marine isotope stage 17, which has an estimated age of ca 0.7 Ma. Occurrences of L. rectilatus can thus provide a useful biostratigraphic index for sediments deposited during ca 1.45–0.7 Ma in the Kanto Plain. This is the first report showing that diatom fossil is applicable as a biostratigraphic indicator for the Quaternary shallow marine strata.

A late surviving Pliocene seal from high latitudes of the North Atlantic realm: the latest monachine seal on the southern margin of the North Sea.

BackgroundThe family of true seals, the Phocidae, is subdivided into two subfamilies: the southern Monachinae, and the northern Phocinae, following the subfamilies’ current distribution: extant Monachinae are largely restricted to the (sub-)Antarctic and the eastern Pacific, with historical distributions of the monk seals of the genus Monachus in the Caribbean, the Mediterranean and around Hawaii; and Phocinae to the northern temperate and Arctic zones. However, the fossil record shows that Monachinae were common in the North Atlantic realm during the late Miocene and early Pliocene. Until now, only one late Pliocene record is known from the Mediterranean, Pliophoca etrusca from Tuscany, Italy, but none from farther north in the North Atlantic.MethodsWe present the description of one partial phocid humerus collected in the early 20th century from the Antwerp area (Belgium), with an assessment of its stratigraphic origin using data from the literature.ResultsThe studied humerus was recovered during construction works at the former Lefèvre dock in the Antwerp harbour (currently part of the America dock). Combining the information associated to the specimen with data from the literature and from local boreholes, the upper Pliocene Lillo Formation is ascertained as the lithological unit from which the specimen originates. Morphologically, among other features the shape of the deltopectoral crest and the poor development of the supinator crest indicates a monachine attribution for this specimen. The development of the deltopectoral crest is closer to the condition in extant Monachinae than in extinct Monachinae.DiscussionThe presented specimen most likely represents a monachine seal and a literature study clearly shows that it came from the latest early to late Pliocene Lillo Formation. This would be the first known monachine specimen from the latest early to late Pliocene of the North Sea, and more broadly from the northern part of the North Atlantic realm. This humerus differs from the humerus of P. etrusca and suggests a higher diversity of Monachinae in the latest early to late Pliocene than previously assumed.

Grain-size analysis of Upper Pliocene red clay deposits from Linxia Basin: Implications for Asian monsoon evolution on the NE margin of the Tibetan Plateau

Little is known about the evolution of the East Asian winter monsoon (EAWM) on the NE margin of the Tibetan Plateau (TP) during the late Pliocene-early Pleistocene, due to the poor exposure of pre-Quaternary eolian deposits and ambiguities in the interpretation of paleoclimatic proxies. In this study, we performed detailed grain-size analyses of eolian sequences (spanning 3.7–2.4 Ma) from two new boreholes in Linxia Basin, in the NE TP. We compared our results with contemporaneous loess-red clay sequences across the Chinese Loess Plateau (CLP) and identified a substantial decrease in the thickness and grain size of upper Pliocene-lower Pleistocene loess and red clay sediments from the western to central parts of the CLP. This observation supports the view that the grain size of upper Pliocene eolian sequences from Linxia Basin can be used to reconstruct the evolution of the EAWM. In addition, it demonstrates that the modern spatial pattern of the EAWM regime in the western CLP has been maintained since at least the late Pliocene. Records of both median grain-size (Md) and sand content from the boreholes exhibit an overall upward-increasing trend during the interval from ~3.7–2.4 Ma, indicating a long-term stepwise intensification of the EAWM and aridity on the NE margin of the TP. In addition, a dramatic coarsening of the grain size in loess unit L34 documents a large climatic shift at ~2.75 Ma, which may be closely linked with the major intensification of Northern Hemisphere glaciation during the late Pliocene.

Upper Pliocene to Lower Pleistocene Plant Microfossils from The Basal Part of the Lukundol Formation (Southern Kathmandu Valley) and Their Climatic Implications

The Late Pliocene to Lower Pleistocene fluvio-lacustrine sediments of the Lukundol Formation distributed in the southern part of the Kathmandu Basin, consists of various fossils of flora and fauna which are very useful proxies to reconstruct the past climate. Twenty seven samples were collected for palynological study from different beds of the Lukundol Formation exposed in the Pharsidol area due to recent road cut. The exposure is about 100 m thick. The study revealed the dominance of gymnosperms over angiosperm plants. On the basis of the pollen assemblage, the Lukundol Formation could be divided into three different pollen zones namely PD-I, PD-II and PD-III. The variation in the climate observed in these three zones indicates that the climate of the Kathmandu valley during the deposition of the Lukundol Formation was not uniform. The climate had been warmer in the lower and upper zones while colder in the middle zone than today. Bulletin of Department of Geology, vol. 20-21, 2018, pp: 71-81

A new species of Hyloxalus Jiménez De La Espada, 1871 ''1870'' (Anura: Dendrobatidae: Hyloxalinae) from a cloud forest near Bogotá, Colombia, with comments on the subpunctatus clade

A new species of frog of the genus Hyloxalus from a high Andean forest of the central parts of the Cordillera Oriental, Colombia is recognized and described using integrative taxonomy. Using phylogenetic analyses of 2590 base pairs (bp) of mitochondrial DNA, Hyloxalus felixcoperari sp. nov. was shown to belong to a lineage of the subpunctatus clade, part of a subgroup that comprises high altitude-occurring lineages (subgroup I) and sister taxa of H. subpunctatus sensu stricto from the Bogotá plateau region. The genetic distance between both taxa is 2.1% and 5.1% for the 16S and cytochrome b gene fragments respectively. Hyloxalus felixcoperari sp. nov. is a medium-sized frog, which can be distinguished morphologically from H. subpunctatus by having dark throat and chest and unwebbed toes, and bioacoustically by emitting an advertisement call consisting of trill-like calls repeated at a rate of 50 – 104 repititions/min, with a dominant frequency ranging from 3028.9 – 3861.2 Hz. Molecular dating analysis revealed that the already known lineages of the subpunctatus clade subgroup I from the middle Cordillera Oriental of Colombia, recently diverged during the lower Pleistocene – Upper Pliocene, most probably due to environmental fluctuations. Threats and main aspects of the natural history of this new species including breeding and habitat are reported in this article.

Decoding a post-collisional multistage magma system: The Quaternary ignimbrites of Aragats stratovolcano, western Armenia

Quaternary eruptions from an intraplate multistage magma reservoir of the Aragats stratovolcano in western Armenia formed pyroclastic density currents and fallouts deposited in an area around 2,000 km2, comprising six ignimbrite units and three fallout deposits. Published K/Ar and Ar/Ar age data allow for a distinction between older (Calabrian, 1.8–0.90 Ma) and younger (Middle Pleistocene, 0.75–0.65 Ma) ignimbrites. The detailed characterization of the crystal-poor to crystal-rich, trachyandesitic to rhyolitic ignimbrite sequence deciphers the pre-eruptive magmatic conditions. It also contributes to the understanding of Plinian eruptions of the largest volcanic complex in the Lesser Caucasus.The chemical variation of pumice fragments reveals the conditions of both, homogeneous and mingled heterogeneous magma systems. The phenocryst assemblage of the older crystal-poor units (Ab-rich plagioclase + amphibole ± pyroxene) indicates growth in a cooler hydrous magma chamber, whereas the partially resorbed phenocrysts of the younger crystal-rich units (An- to Ab-rich plagioclase + pyroxene) suggest growth in a superheated magma chamber fueled by mafic, mantle-derived melts. In the younger units, external (e.g. sieve fabrics) and internal phenocryst textures have been generated by decompression and convection during ascent. With the older units, the chemical variation in amphibole from core to the narrow break-down rim reveals magma ascent from a deep (13 km depth) to a shallow (up to 8 km) level.Tracking the p-T paths of cumulate fragments (pyroxene, plagioclase) in the younger units, we estimate the depth of the anhydrous crystal-rich magmatic chamber at around 25 km. Based on the composition of clinopyroxene cumulates, we propose a multi-stage evolution of melts from subalkaline and tholeiitic to calc-alkaline composition. The pronounced high Zr content and Zr/Hf ratios of the entire Upper Pliocene to Quaternary post-collisional magmatism could be attributed to partial melting of an enriched mantle source in the Lesser Caucasus.

NEW DATA ON THE STRATIGRAPHY OF STROFADES ISLANDS (IONIAN SEA, W. GREECE)

This study focuses on the fauna collected from the sediments, which outcrops on Strofades islands, with the view to defining their age, which so far has been ascribed to the Pleistocene (Tyrhennian). The studied material was sampled from the two islets of Stamfani and Arpya. Between these two, there are several reefs, collectively known as "Soumari reefs". Our studies resulted in the following. 1. Lower Pliocene, L - Middle Pliocene, Uppermost - Middle Pliocene, and Upper Pliocene strata were identified on Stamfani islet. 2. On Arpya islet the determined ages of the outcropping strata are Lower Pliocene, Upper Pliocene and Tortonian - Pleistocene

RADIOCHRONOLOGICAL DATA WITH U/TH METHOD IN LAGUNAL /MARINE DEPOSITS OF THE NW PELOPONNESE, GREECE.

Pleistocene lagoonal sediments exposed in northwestern Peloponneses were dated by U/Th methods in Cladocora coespitosa and in Area sp. samples, were collected from the southern part of the Rion - Antirrion and western end of the Corinth grabens, which were both formed in the upper Pliocene. Our dating results, indicate a Tyrrhenian age, Upper Pleistocene, and not Lower Pleistocene ages which were reported for these sediments up until now. In particular, the absolute ages from the collected samples from Ano Kastrisi are 203.6 ±11 kyr.s, from Arachovitika 164 ± 5.8 kyr.s and from Agios George Drepanou 88.1 ± 2.3 kyr.s. The above ages belong in isotopie stages 7, 6, 5 respectively. Based on the U/Th reported ages the calculated relatives rates of uplift are, 2.8 mnvyr"1 and 4.8 mnryr"1 for the areas of Ano Kastrisi and Agios George Drepanou respectively (south-eastern margin of the Rion - Antirrion graben) and 0.4 mnryr"1 Arachovitika samples (western end of Corinth graben). The calculated different relatives rates of uplift demonstrate probably that the two grabens had a different neotectonic and paleogeographic evolution.

Integration of geological and geophysical data for re-evaluation of local seismic hazard and geological structure: the case study of Rometta, Sicily (Italy)

The village of Rometta, northern-eastern Sicily (Southern Italy), experienced severe damage during the most energetic earthquakes that occurred in eastern Sicily and southern Calabria in the last centuries. Geological maps indicate that Rometta primarily lies on a stiff plate of Upper Pliocene – Lower Pleistocene calcarenites and only to minor extent on Middle Pleistocene overlying clays. Rometta represents an interesting case study for site response investigation because of the apparent mismatch between the currently available geological knowledge and the level of damage caused by historical seismic events. The local seismic response has been investigated through a grid of 64 single-station measurements of ambient seismic noise by the Horizontal to Vertical Noise Spectral Ratio technique (H/V). Also, phase velocity dispersion curves from seismic array through the Extended Spatial Auto-Correlation method were analyzed. The H/V curves obtained show a ubiquitous frequency peak between 0.5 Hz and 0.9 Hz due to the deep interface between the metamorphic substrate and sedimentary sequence, and a secondary peak in the 2.5–15 Hz interval in most of the measurement points that may be related to a larger extent of the clay outcrops with respect to what is already known from geological investigations. Joint inversion of dispersion and H/V curves was also performed in order to obtain the velocity profile. Results acquired through the combined use of geophysical methods furnished useful information for seismic hazard evaluation where surface geology is not clearly visible because of urbanization and vegetation cover, thus suggesting that a wide extent of clays may reasonably be the cause of past earthquake damage distribution.

Diapiric activity affecting Late Pliocene to Pleistocene sediments under a tectonic compressive regime: an example from the Western Iberian Margin (Srª da Vitória beach, central Portugal)

The structural evolution of a folded and faulted Upper Pliocene to Lower Pleistocene sedimentary unit exposed at the coastal cliffs of Sra da Vitoria beach was studied. This sequence is wedged between the S. Pedro de Moel diapir, to the north, and the Pombal–Leiria–Nazare fault zone, to the south, providing striking evidence of neotectonic activity in the Western Iberian Margin and of its role in the triggering of halokinesis. Several deformational events were recognised, related to a regional NW–SE compression that activated halokinesis of underlying Triassic to Lower Jurassic (Hettangian) silty clays and gypsiferous marls. The combined effects of the compression and of the triggered halokinesis generated a NW-verging asymmetric syncline affecting the studied sedimentary unit, where strain was partially accommodated by faulting and crenulation in micaceous horizons of the sandy deposits. This deformation represents the local accommodation on the sedimentary cover of transpression along the S. Pedro de Moel fault, which was intruded by the Triassic to Hettangian evaporitic marls and silty clays, and reactivated with left-lateral reverse movement. This regional fault prolongs offshore, being parallel to other NE–SW trending faults that are located near the upper reach of the Nazare submarine canyon, reinforcing the evidence for neotectonic activity on this major fault system of the Portuguese Atlantic margin.

PLIOCENE BRACHIOPODS FROM RHODES ISLAND (CAPE VAGIA SECTION)

Six brachiopod species (5 terebratulids and 1 craniid) from the upper Pliocene sandy and calcareous deposits of the Cape Vagia (Rhodes Island) are described: Gryphus sp., Terebratulina refusa, Megerlia truncata, Megerlia truncata var. monstruosa, Argyrotheca cordata, Megathiris detruncata and Novocrania anomala. This is the first record of Megerlia truncata var. monstruosa from the Pliocene of Greece and of Megerlia truncata from the Pliocene of Rhodes. Megathiris detruncata, Terebratulina retusa and Argyrotheca cordata are described for the first time from the Pliocene of Rhodes. This brachiopod association displays close affinity with those from the Mediterranean province, where assemblages of similar composition are associated with shallow-water, high energy environments. However, the association of Gryphus sp., Terebratulina retusa and Novocrania anomala corresponds to deeper water moderate environments.

Minimal East Antarctic Ice Sheet retreat onto land during the past eight million years.

The East Antarctic Ice Sheet (EAIS) is the largest potential contributor to sea-level rise. However, efforts to predict the future evolution of the EAIS are hindered by uncertainty in how it responded to past warm periods, for example, during the Pliocene epoch (5.3 to 2.6 million years ago), when atmospheric carbon dioxide concentrations were last higher than 400 parts per million. Geological evidence indicates that some marine-based portions of the EAIS and the West Antarctic Ice Sheet retreated during parts of the Pliocene1,2, but it remains unclear whether ice grounded above sea level also experienced retreat. This uncertainty persists because global sea-level estimates for the Pliocene have large uncertainties and cannot be used to rule out substantial terrestrial ice loss 3 , and also because direct geological evidence bearing on past ice retreat on land is lacking. Here we show that land-based sectors of the EAIS that drain into the Ross Sea have been stable throughout the past eight million years. We base this conclusion on the extremely low concentrations of cosmogenic 10Be and 26Al isotopes found in quartz sand extracted from a land-proximal marine sediment core. This sediment had been eroded from the continent, and its low levels of cosmogenic nuclides indicate that it experienced only minimal exposure to cosmic radiation, suggesting that the sediment source regions were covered in ice. These findings indicate that atmospheric warming during the past eight million years was insufficient to cause widespread or long-lasting meltback of the EAIS margin onto land. We suggest that variations in Antarctic ice volume in response to the range of global temperatures experienced over this period-up to 2-3 degrees Celsius above preindustrial temperatures 4 , corresponding to future scenarios involving carbon dioxide concentrations of between 400 and 500 parts per million-were instead driven mostly by the retreat of marine ice margins, in agreement with the latest models5,6.

Revised and refined age model for the upper Pliocene of IODP Site U1389 (IODP Expedition 339, Gulf of Cádiz)

Revised and refined age model for the upper Pliocene of IODP Site U1389 (IODP Expedition 339, Gulf of Cádiz)

The active submarine NW termination of the South Aegean Active Volcanic Arc: The Submarine Pausanias Volcanic Field

Methana peninsula shows the longest recorded volcanic history at the western end of the South Aegean Active Volcanic Arc, including volcanic products from the Upper Pliocene to recent times. The volcanic rocks comprise widespread dacite domes and andesite lava flows from several small volcanic centers and are only imprecisely dated. In this paper, the integrated analysis of swath bathymetry, side scan sonar data, and high resolution seismic reflection profiles correlated with core samples, has allowed detailed mapping, characterization and precise chronological identification of the Pausanias submarine volcanic field activity offshore northern Methana. Six volcanic cones or domes are recognized, typically 1–3 km in diameter, some elongated NE–SW and some with a small central crater. On their flanks, the acoustically reflective volcanic rocks pass laterally into incoherent transparent seismic facies interpreted as volcaniclastic deposits, possibly including hyaloclastites, that interfinger with the regional basin sediments. A sea-bottom hummocky field, is interpreted as volcanic avalanche and appears to be the submarine continuation of the volcaniclastic apron of northern Methana peninsula. A robust chronostratigraphic framework has been established, based on the recognition of shoreline progradational units and their connection with Quaternary eustatic sea level cycles. Relative dating of the different phases of submarine volcanic activity during the Upper Quaternary has been achieved by correlating the imaged volcaniclastic flows, interlayered within the chronostratigraphically dated sediments. Dating by stratigraphic position, relative to 2D imaged eustatic sea level clinoform wedges appears to be more precise than radiometric methods on land. Three main submarine Volcanic Events (VE) are recognized: VE3 at ~450 ka, a less precisely dated interval at 200–130 ka (VE2), and VE1 at ~14 ka. Based on chronostratigraphic constraints, subsidence rates of 0.16 (±0.008) m/ka in-between Marine Isotopic Stages 6 and 12 and 0.19 (±0.009) m/ka in-between Marine Isotopic Stages 12 and 16 were estimated for the marine basin north of Methana. The morphological similarity to the onshore volcanoes of Methana Peninsula implies that magmatic constructive processes were dominant, regardless of whether in air or in water. The Upper Quaternary submarine volcanic rocks of Methana differ from those known from stratovolcanoes elsewhere in the Mediterranean, (e.g. Kos-Nisyros, Stromboli) and in other volcanic arcs (e.g., Montserrat, St Vincent), in the submarine development of domes or small cones, the paucity of volcano flank failure deposits and the lack of explosive events. Pausanias volcanic products date the onset of NE–SW faulting as well as the following tectonic phase of E-W striking faults, possibly related to basin inversion, caused by a major rifting phase that also affected most of the South Aegean Arc and the adjacent Gulfs of Corinth and Argolikos.

Soil-landscape relationship as indicated by pedogenesis data on selected soils from Southwestern, Iran

Soils of semiarid regions of Dehdasht and Choram in Southwestern Iran have formed on alluvium derived from mixed calcareous-gypsiferous materials from Lower Miocene to Upper Pliocene. In order to characterize and classify the soils and to determine the soil-landscape relationship in the area, nine pedons located on different physiographic positions including plateau, river alluvial plain, piedmont plain, alluvial plain and alluvial fan have been described, sampled and analyzed. Physicochemical analyses, clay mineralogy and micromorphological studies were performed. The results showed that topography and parent material were two important soil forming factors affecting soil formation in the area. The soils were dominated by carbonate, gypsum, and clay illuviation and accumulation. More developed soils were found on the stable plateau and piedmont plain. Clay illuviation and argillic horizon development in soils of the more stable alluvial plain were assumed to be relict features from presumably more humid climates. Palygorskite, illite, chlorite, smectite, kaolinite, and quartz clay minerals were identified in almost all physiographic surfaces, but more palygorskite and less smectite were found in the soils with gypsiferous parent materials. Observations by SEM revealed the occurrence of neoformed palygorskite as thread-like faces and coating of gypsum crystals and marly matrix. Coating and infilling of gypsum and calcite crystals in voids and channels were common pedofeatures observed in the soils studied. Two different distribution patterns of Fe-Mn oxides were identified in aquic and non-aquic soils.

Formation and chemistry of the groundwater resource in the Mekong river delta, South Vietnam

The origin and chemistry of the groundwater in the middle Pleistocene (qp23), lower Pleistocene (qp1), upper Pliocene (n22), lower Pliocene (n21), and the Miocene (n13) in the Mekong river delta (MKRD) were investigated by using isotopic and geochemical techniques. The origin of the groundwater was evaluated based on the composition of the water stable isotopes (d2H and d18O) in the local precipitation, in water from the rivers system, and in the groundwater samples. The hydraulic interaction between the surface water and the groundwater as well as between the aquifers was assessed by a statistical treatment for the mean and standard deviation of the d18O signature and based on the 14C-ages of the water samples taken from different aquifers. The salinization of groundwater in the deep aquifers was investigated using the d18O signature combined with the geochemical composition of the water samples. It was revealed that the groundwater in the deep aquifers in the MKRD could be divided into two groups. The first group is fresh and represents the regional precipitation with the long traveling time ranging from older than 100 years to older than 40 ka BP (kilo years Before Present). The second group is the regional precipitation that is recharged from the remote areas mixed with the seawater. Statistical treatment with the mean d18O using the Mann-Whitney test showed that the water from the Mekong river system did not or very weakly recharged the deep aquifers. The groundwater in the deep aquifers in that region was likely to be connate, so that fresh groundwater resource in the region seemed to be limited. The chemistry of the groundwater in the study region is controlled by the incongruent dissolution of the Mg-calcite as well as sulfate and iron oxy-hydroxide reductions by organic matters presented in the aquifer sediment. The groundwater in the deep aquifers in the MKRD from some locations was saline, but the salinity in most aquifers was thought to result from the migration of saline water entrapped in the marine sediment pores to the fresh water in the aquifers. Meanwhile, in other locations, the salinity was suggested to result from the salt intrusion due to the over-abstraction rate, as it was evident from the d18O vs. [Cl-] relationship, or due to the up conning of saline water from the deeper aquifers to the upper ones. Particular measures must be developed for the better management of groundwater in the MKRD to ensure a sustainable resource of freshwater being supplied to the local population in future.

Genomics of the origin and evolution of Citrus

The genus Citrus, comprising some of the most widely cultivated fruit crops worldwide, includes an uncertain number of species. Here we describe ten natural citrus species, using genomic, phylogenetic and biogeographic analyses of 60 accessions representing diverse citrus germ plasms, and propose that citrus diversified during the late Miocene epoch through a rapid southeast Asian radiation that correlates with a marked weakening of the monsoons. A second radiation enabled by migration across the Wallace line gave rise to the Australian limes in the early Pliocene epoch. Further identification and analyses of hybrids and admixed genomes provides insights into the genealogy of major commercial cultivars of citrus. Among mandarins and sweet orange, we find an extensive network of relatedness that illuminates the domestication of these groups. Widespread pummelo admixture among these mandarins and its correlation with fruit size and acidity suggests a plausible role of pummelo introgression in the selection of palatable mandarins. This work provides a new evolutionary framework for the genus Citrus.