Pleistocene foraminifera from Botany Bay,New South Wales

Unconsolidated sediments from a borehole in Botany Bay have been analyzed for their foraminiferal content. Faunas from between 41 and 54 m below sea level are interpreted as Pleistocene in age. The foraminiferal assemblage from 54 m indicates marine conditions of moderately deep water (25–30 m), and a climate warmer than at present. The higher assemblages indicate a more brackish environment

The foraminifera, belonging to 123 species in 67 genera, are tabulated and 24 are discussed and illustrated. Three species, Oolina bifidocostata, Fissurina alatoquadrata and Elphidium botaniensis and one subpecies, Quinqueloculina affinis atrata, are described as new.     

A rare,late Paleocene molluscan faunule from the Kings Park Formation,Perth Basin,Western Australia

A shallow marine faunule of eight taxa from the Kings Park Formation of the Perth Basin is the first described Paleocene molluscan assemblage from Western Australia. These species are part of a depauperate suite of macroinvertebrates (molluscs, echinoids and corals) derived from deep, onshore caissons in Perth and are inferred to be late Paleocene in age, based on planktonic foraminiferal biostratigraphy and associated age ranges of the molluscan fauna. Bivalves are Sarepta austranaxa sp. nov. (Sareptidae), Solemya kingsparki sp. nov. (Solemyidae), Periploma vivarirex sp. nov. (Periplomatidae), Parvamussium sp. nov.? (Propeamussiidae), Serripecten? sp. (Pectinidae) and Venericardia (Rotundicardia) petraea Darragh (Carditidae). Gastropods are Levifusus? sp. cf. L.? quadrifunifer Darragh (Buccinidae), and Columbarium rumatoides Darragh (Turbinellidae). Bivalves dominate the fauna in dark, glauconitic siltstone and sandstone facies; gastropods are of relatively poor preservation and low diversity.     

Relict Anthropogenic Ecosystem from the Middle Ages: History of a Salt Marsh from Transylvania (Sic,N Romania)

ABSTRACT

A paleoecological study was performed on a sediment core recovered from a former artificial lake – the Reedbed of Sic near Cluj-Napoca, Romania – in order to explore the history of water management and nearby salt mining, and its impact on the environment. From the Roman period, the area served as a recipient of salty wastewaters. The most significant shift in the sediment composition and macrofossil assemblages took place after 1000 AD, suggesting a significant upturn in salt mining. The impact of mining-related activities was further increased in the Middle Ages when, according to documentary sources, fishponds and watermills were constructed in the area. They led to the stabilisation of the water level in the lakebed, and enhanced the appearance of reed beds and the spread of secondary salt marsh vegetation. This biotop was later invaded by the Entzia macrescens, an agglutinated foraminiferal taxon, known mostly from the high intertidal marshes worldwide. In the investigated marshland, the dominance of halophytic species reached their acme in the seventeenth century, which coincides with the acme of mining activities. This medieval – early Modern Age industrial ecosystem survived the abandonment of salt mines and fishponds, being preserved until today.     

Wombats (Vombatidae: Marsupialia) from the Pliocene Chinchilla Sand,southeast Queensland,Australia

Louys, J., 23.3.2015. Wombats (Vombatidae: Marsupialia) from the Pliocene Chinchilla Sand, southeast Queensland, Australia. Alcheringa 39, XXX–XXX. ISSN 0311-5518

The Chinchilla Local Fauna is one of the richest Pliocene vertebrate fossil assemblages in Australia. However, Vombatidae material preserved in the Chinchilla Sand is very poorly known, and no systematic examination of the wombats from Chinchilla has been conducted. Here I review the cranio-dental and mandibular wombat remains derived from Chinchilla. This material includes both adults and pouch-young specimens. At least five species of wombats are preserved in the fluviatile Chinchilla deposits, although a lack of stratigraphically controlled excavations makes it impossible to determine whether all five species were sympatric. Several wombat taxa are revised: Sedophascolomys gen. nov. is formally erected to replace the invalid ‘Phascolomys’; Vombatus mitchelli (Owen) is recognized as a species distinct from Vombatus ursinus (Shaw), and is recorded for the first time from Chinchilla. In addition to Vombatus mitchelli, the Chinchilla Sand also preserves evidence of Phascolonus gigas, Ramsayia magna, Ramsayia lemleyi and Sedophascolomys medius.

Julien Louys [julien.louys@anu.edu.au], Department of Archaeology and Natural History, School of Culture, History, and Languages, ANU College of Asia and the Pacific, The Australian National University, Canberra, ACT 2601, Australia.     

Early Miocene bivalves from the Cape Melville Formation,King George Island,West Antarctica

Seven species of marine bivalves, including six new taxa, are described from the Cape early Miocene Melville Formation which crops out on the Melville Peninsula, King George Island, West Antarctica. The bivalve assemblage includes representatives of the families Nuculidae, Ennucula frigida sp. nov., E. musculosa sp. nov.; Malletidae, Neilo (Neilo) rongelii sp. nov.; Sareptidae, Yoldia peninsularis sp. nov.; Limopsidae, Limopsis psimolis sp. nov.; Hiatellidae, Panopea (Panopea) sp. cf. P. regularis; and Pholadomyoida (Periploma acuta sp. nov.). Species studied come from four sedimentary sections measured in the upper part of the unit. Detailed morphologic features of nucloid and arcoid species are exceptionally well preserved and allow for the first time reconstruction of muscle insertions as well as dentition patterns of Cenozoic taxa. Known geological distribution of the species is in agreement with the early Miocene age assigned to the Cape Melville Formation. The bivalve fauna from Cape Melville Formation is the best known from Antarctic Miocene rocks, a time of complex geologic, paleogeographic and paleoclimatic changes in the continent. The new fauna introduces new taxonomic and palaeogeographic data that bear on the question of opening of sea gateways and distribution of Cenozoic biota around Antarctica.     

Trilobite faunas and palaeoenvironmental setting of the Silurian (early Ludlow) Melbourne Formation,central Victoria

Trilobites are common faunal elements in the Melbourne Formation, a unit of early Ludlow (upper nilssoni Biozone) age, which crops out extensively in the Darraweit Guim Province of the Melbourne Zone, central Victoria. New diagnoses are given for species previously described, including Maurotarion euryceps (McCoy, 1876; = Cyphaspis spryi Gregory, 1901), Raphiophorus jikaensis (Chapman, 1912; = Ampyx yarraensis Chapman, 1912), Cromus simpliciculus (Talent, 1964), Cromus spryi (Chapman, 1912), Sthenarocalymene kilmorensis (Gill, 1945; = Gravicalymene hetera Gill, 1945) and Trimerus harrisoni (McCoy, 1876). A new phacopid genus, Orygmatos is described, represented by the species O. yanyeani gen. et sp. nov. Other species newly described include Cromus melbournensis sp. nov., Arcticalymene australis sp. nov., “Ananaspis” woiwurrungi sp. nov. and Kettneraspis hollowayi sp. nov.

Species composition of the trilobite fauna varies spatially, and a number of distinct assemblages can be defined. Abundant trilobite moult configurations are conclusive for interpretation of the benthic fauna as autochthonous, inferring depth estimations based on benthic community distribution to be valid. A depth-related succession of communities is recognised and indicate the Melbourne Formation was deposited at relatively shallow depths on a broad, eastwardly deepening shelf, with deposition dominated by storm processes. The palaeoenvironment comprised a BA-1 community including the Arcticalymene australis trilobite assemblage, restricted to very shallow depths (～20 m) on the SW coastal margin of the shelf and preserved in proximal tempestite lithologies; and a BA-5 community group containing three distinct trilobite assemblages dominated by species of Cromus and a deeper water fauna, preserved in distal tempestite lithologies and ranging widely over the shelf at depths in the range of maximum storm wave base (～50 – 80 m).     

Insight into lingulid evolution from the Late Devonian

Well preserved lingulids from near the base of the Mandagery Sandstone in the Late Devonian Hervey Group, N.S.W. are described as Apsilingula parkesensis gen. et sp. nov. The internal structures are better preserved than those of any previously described Palaeozoic lingulid and it has been possible to reconstruct the muscle system and to demonstrate a close similarity to living species of Lingula.     

The application of microfossils in assessing the provenance of chalk used in the manufacture of Roman mosaics at Silchester

Microfossils recovered from chalk tesserae in mosaics from the Roman town of Calleva Atrebatum, modern Silchester, southern England, are used to suggest a provenance for the source-rock. The microfossils include foraminifera characteristic of late Cretaceous (Campanian) foraminiferal biozone BGS20 (quadrata macrofaunal biozone) and foraminiferal subzone BGS21i (basal mucronata macrofaunal biozone). Calcareous nannofossil assemblages from the same tesserae are poorly preserved, preventing precise age determination, but confirm an age of Santonian to Campanian. As indurated chalk beds of this age are not normally present in the stratigraphically higher chalks of southern England, it is probable that calcretised chalk, formed by secondary calcification beneath Palaeogene rock cover, was used to manufacture the tesserae. This suggestion is supported by a comparative analysis of chalk tesserae from the Norden Roman site in Dorset. Although the provenance of the chalk in some of the Silchester tesserae can be placed only within a broad geographical area of downland in southern England, others may have originated in the Dorchester–Swanage area, some 100 km to the southwest of Silchester, or the Portsdown area of southern Hampshire. None of the tesserae have been constructed from chalk found near Silchester.     

New data on the structure of the Early Devonian lungfish,Dipnorhynchus

A skull of a young specimen of Dipnorhynchus sussmilchi (Etheridge Jr), from the base of the Bloomfield Limestone Member (mid-Emsian, probably perbonus Zone) at Taemas, has both sides of the skull roof preserved, but the cheeks are missing. The posterior end of the endocranium, up to its dorsal extremity, provides new data on the endolymphatic sacs, and the attachment of the epaxial muscles. The endolymphatic region is compared with that of Chirodipterus australis. The palate is not fully formed and the marginal ridges are not fully developed. The fine structures around the dermopalatines and the pterygoids are preserved, indicating the manner in which the plates grew. The position of the parasphenoid is clearly outlined against the pterygoids, and confirms the view that this primitive genus of dipnoans did not have the pterygoids divided by the parasphenoid. All these features provide new information and comparison with Dipterus valenciennesi, the next oldest genus on which the same regions are preserved. In addition, a new mandible from a horizon low in the Cavan Bluff Formation is well preserved and provides information on the external bones of Dipnorhynchus.     

Fossil wood of the Mimosoideae from the early Paleocene of Patagonia,Argentina

Brea, M., Zamuner, A.B., Matheos, S.D., Iglesias, A. & Zucol, A.F., December, 2008. Fossil wood of the Mimosoideae from the early Paleocene of Patagonia, Argentina. Alcheringa 32, 427–441. ISSN 0311-5518.

An anatomically preserved mature stem from the Salamanca Formation (early Paleocene) at Palacio de Los Loros, central Patagonia, Argentina, is described and assigned to Paracacioxylon frenguellii sp. nov. The material was preserved by siliceous permineralization and shows features of the secondary xylem typical of subfamily Mimosoideae. This species represents the oldest record of the genus and of the Leguminosae along the western border of Gondwana, and is the world's second oldest record of Leguminosae wood. The species is characterized by ring-porous to semi-ring-porous vessels that are solitary, in multiples of 2–4 and clustered, simple perforation plates, alternate and vestured inter-vessel pitting, homocellular 1–6 seriate rays, tyloses, crystals and diffuse apotracheal, vasicentric paratracheal and confluent axial parenchyma. Paracacioxylon frenguellii has anatomical similarities to Acacia Miller. The presence of Paracacioxylon frenguellii associated with pulvinate leaves suggests that the legumes might have been a component of mesothermal forests developed along the western margin of the Golfo San Jorge Basin during the early Paleocene.     

Vertebrate microremains from the presumed earliest Carboniferous of the Mansfield Basin,Victoria

The Agnostida are the most important part of the fauna of the Abbey Shales, which is the best-known middle St David's (Middle Cambrian) sequence in Britain. Revision of Illing's (1916) collections allows a correlation of the Paradoxides hicksii fauna with Westergaard's (1946) Ptychagnostus atavus-Tomagnostus fissus Zone, and the Paradoxides davidis fauna with Westergaard's Hypagnostus parvifrons Zone and Ptychagnostus punctuosus Zone (based on the Swedish sequence). A Metadiscus sp. is described. Six species of Condylopygidae are discussed, of which three show a pygidial ‘fringe’. Eleven species of Quadragnostinae, three of Ptychagnostinae (one showing a hypostome), and four of Tomagnostinae (including young growth-stages) are illustrated or discussed. Two species of Diplagnostidae, one species of Phalacroma and two of Phalagnostus are illustrated.     

South polar greenhouse insects (Arthropoda: Insecta: Coleoptera) from the mid-Cretaceous Tupuangi Formation,Chatham Islands,eastern Zealandia

Stilwell, J.D., Vitacca, J. & Mays, C., April 2016. South polar greenhouse insects (Arthropoda: Insecta: Coleoptera) from the mid-Cretaceous Tupuangi Formation, Chatham Islands, eastern Zealandia. Alcheringa 40, xxx–xxx. ISSN 0311-5518

Rare insect body fossils have been discovered for the first time after 175 years of research on the Chatham Islands, eastern ‘Zealandia’. The coleopteran (beetle) insects, dated to ca 95 Ma and extracted from fine-grained, upper delta plain facies in the lower Upper Cretaceous (Cenomanian–lowermost Turonian) Tupuangi Formation at Waihere Bay on the remote Pitt Island, represent the most southern, polar-latitude (ca 70–80°S) faunal assemblage from the Cretaceous recorded to date. Three species are represented in the insect fauna: a portion of a segmented abdomen of a probable carabid? ground beetle and two distinct coleopteran elytra, one preserved with a brilliantly iridescent carapace upon discovery, comparable with Cretaceous taxa within the Buprestidae (metallic wood borers), but identification with the Chrysomelidae (leaf beetles) or Tenebrionidae (darkling beetles) can not be discounted entirely. Another specimen has more weakly preserved greenish iridescence and has a morphology consistent with Carabidae; given the preservational deficiencies and rarity of material, the specimens are attributed to Buprestidae? genus et species indeterminate and Carabidae? genus et species indeterminate A and B, respectively. These coleopteran fossils represent the only recorded iridescence in Mesozoic invertebrates from Zealandia. Importantly, these mid-Cretaceous insects existed in South Polar forests near the height of the ‘hothouse’ phase of relatively warm, alternating intervals of full daylight in the summer months and total darkness during the winter, before eastern Zealandia diverged at ca 83 Ma from the Marie Byrd Land region of West Antarctica, as part of the final break-up of Gondwana.

Jeffrey D. Stilwell* [jeffrey.stilwell@monash.edu], Jesse V. Vitacca [jesse.vitacca@gmail.com] & Chris Mays [chris.mays@monash.edu], School of Earth, Atmosphere and Environment, Monash University, Clayton VIC 3800, Australia. *Also affiliated with the Australian Museum, 6 College Street, Sydney NSW 2000, Australia.     

Tertiary gymnosperms from Tasmania: Araucariaceae

Three new species of the Araucariaceae are described from leaf remains, Araucaria readiae from the Early Eocene Regatta Point flora, A. hastiensis from the Middle-Late Eocene Hasties flora, and Agathis tasmanica from the Early Oligocene-Early Miocene Little Rapid River flora. Additionally, emended diagnoses are presented for Araucarioides linearis and A. annulata. A. readiae is the first organically preserved species in the section Eutacta described from Tasmania, A. hastiensis is the first record of a species not in section Eutacta in Tasmania, and A. tasmanica is the first record of Agathis in Tasmania. These species, along with other records from south-eastern Australia indicate the presence of a high diversity of araucarian species in the region in the Early-Middle Tertiary, although no species survive there today. Climatic change and competition from angiosperms may have led to their demise in that region.     

Permian brachiopods from the Tupe Formation,San Juan Province,Precordillera, Argentina

The brachiopod fauna from the Tupe Formation at La Herradura Creek, located on the west flank of Perico Hill, San Juan Province, Argentina, palaeogeographically belongs to the western sector of the Paganzo basin (‘Guandacol embayment’). The stratigraphical section of the Tupe Formation at La Herradura Creek is the stratotype of the Tivertonia jachalensis-Streptorhynchus inaequiornatus biozone, was previously regarded as being of Late Carboniferous age but here is assigned to the earliest Permian (Asselian). We describe and review the biozone assemblage, which consists of Streptorhynchus inaequiornatus, Tivertonia jachalensis, Kochiproductus sp., Costatumulus sp., Coronalosia argentinensis, Tupelosia paganzoensis, Trigonotreta pericoensis, Septosyringothyris sp. aff. Septosyringothyris jaguelensis and Crurithyris? sp. This brachiopod assemblage is related to Indian and Australian Early Permian faunas and its presence in the La Herradura Creek section provides new evidence in support of an Asselian (Early Permian) age for the Tivertonia jachalensis-Streptorhynchus inaequiornatus biozone. This assemblage is also important for intra- and inter-basinal correlation because several of its characteristic species have been identified from other sections of the Paganzo basin and the Río Blanco basin. The proposed age for this biozone is consistent with the age of palynological data from slightly above the marine faunas from the stratotype locality.     

A new Early Permian bivalve fauna from the Río Genoa Formation,Patagonia, Chubut Province,Argentina

Fourteen Bivalvia species are described from the Lower Permian Río Genoa Formation, exposed in the southern Tepuel-Genoa Basin (Chubut Province, Argentina), of which one, Fletcheripecten genoensis, is new. The studied specimens are well preserved, retaining fine details of the ornament and shell morphology. Palaeotaxodonta is represented by two species of Nuculopsis and four species of Phestia; Pteriomorphia by five species in five genera; and Heteroconchia by three informal species. Most of the species recorded also occur in the northern part of Tepuel-Genoa Basin and allow demarcation of new and distinct marine intervals in the Río Genoa Formation, which was classically interpreted to represent continental deposits. The bivalve fauna confirms a Cisuralian (Early Permian) age for the Río Genoa Formation and offers potential for improved regional and global correlations.     

Subsistence continuity,change, and environmental adaptation at the site of Nugljanska,Istria, Croatia

This paper investigates changes in subsistence strategies at the upland cave site of Nugljanska (Croatia) at the end of the last ice age, during a time of rapid sea level rise and changing environment. We analysed the faunal assemblage from archaeological levels spanning the Pleistocene–Holocene transition (15,000–8000 years BP) and evaluated changes in relative abundance of species, measured species diversity, and compared the representation of terrestrial mammal and marine resources. We found a significant shift in the most abundant prey species exploited (from red deer, Cervus, to wild boar, Sus). There was some correlation between dietary diversification and periods of increased moisture availability and the spread of deciduous forest in the area. Our results suggest that there was a continuing reliance on terrestrial resources throughout time and that changes in dietary patterns were likely due to local environmental change and potentially, changing seasonal mobility strategies, at the Pleistocene–Holocene transition.     

The Palaeoenvironmental Implications of the Distribution of Intertidal Foraminifera in a Tropical Australian Estuary: a Reconnaissance Study

Modern intertidal foraminifera were investigated in a mangrove‐lined microtidal distributary channel of the Barron River Delta (Cairns, Queensland, Australia). A monospecific assemblage of Trochammina inflata characterises saltmarsh environments (Biozone 1), whilst the more regularly inundated tidal flat is dominated (≥55%) by Ammonia beccarii (Biozone 2). Within the tidal flat environment, two foraminiferal subdivisions can be recognised; a high tidal flat assemblage (Biozone 2a) characterised by ≥70% Ammonia beccarii and low diversity, and a low tidal flat assemblage (Biozone 2b) with 55–65% Ammonia beccarii and high diversity (due to the settling out of small allochthonous species transported into the estuary from shelf environments). Foraminiferal distributions are also compared with tide levels estimated in the field. It appears approximately that Biozone 1 occurs between High Water and Mean High Water (MHW), Biozone 2a between MHW and Mean Tide Level (MTL), and Biozone 2b between MTL and Low Water. From this preliminary study, it is concluded that foraminifera possess significant potential in palaeoenvironmental studies of tropical Australian estuaries as indicators of intertidal environments, and also tidal levels.     

Late Silurian trace fossils from the Melbourne Formation,Studley Park,Victoria, southeastern Australia

An ichnoassemblage of 10 ichnospecies is described for the first time from the Late Silurian Melbourne Formation at Studley Park, Victoria, southeastern Australia. The ichnofauna is preserved in a typical deep-water turbidite succession of alternating thin- to thick-bedded sandstone and thin- to medium-bedded mudrocks. Trace fossils observed within the study site have been assigned to three main ichnofacies. Ichnofacies 1 is best developed on the linguoid-rippled upper surface of thin sandstone beds and includes Laevicyclus, Aulichnites, Nereites, Helminthoidichnites, small Chondrites and possible Zoophycos. Ichnofacies 2 is very similar to Ichnofacies 1 in ichnospecies composition but instead contains large forms of Chondrites together with other thin burrow types usually poorly preserved and in very low abundance compared with Ichnofacies 1. Ichnofacies 3 is preserved mainly as casts on the underside of medium- to thick-bedded turbiditic sandstones, and has a very low diversity, with Planolites being the most common trace. A detailed analysis of the ichnofabrics and tiering structures of these ichnofacies suggest that Ichnofacies 1 and 3 represent ‘simple tiering’, in contrast to Ichnofacies 2, which is more characteristic of ‘complex tiering’. Despite the differences in ichnospecies composition and ichnofabrics between the three recognized ichnofacies, the collective ichnoassemblage from the study site can be assigned confidently to the Nereites ichnofacies and is, therefore, interpreted to have formed in a distal submarine fan environment of lower bathyal to abyssal depth. Further, it is possible to recognize two main subenvironments within this deep-sea setting to account for the differences between the ichnofacies. Ichnofacies 1 and 2 are interpreted to represent a typical Nereites ichnofacies located on a level basin floor subenvironment of relatively low energy conditions at the distal end of a submarine fan deposit. In comparison, Ichnofacies 3 is dominated by Planolites with rare other facies-crossing trace fossil forms, and lacks Nereites. It is, therefore, best interpreted as representing a relatively high-energy environment, possibly a distributary channel near the distal end of the submarine fan system.     

Conodont fauna and biostratigraphy of the Honghuayuan Formation (Early Ordovician) of Guizhou,South China

Serratognathus diversus An, Cornuodus longibasis (Lindström), Drepanodus arcuatus Pander, and eleven other less common conodonts, including Cornuodus? sp., Oistodus lanceolatus, Protopanderodus gradatus, Protoprioniodus simplicissimus, Juanognathus variabilis, Nasusgnathus dolonus, Paltodus? sp., Scolopodus houlianzhaiensis, Semiacontiodus apterus, Semiacontiodus sp. cf. S. cornuformis and Serratognathoides? sp., are described and illustrated from the Honghuayuan Formation in Guizhou, South China, concluding revision of the conodont fauna from this unit, which comprises 24 species in total. The most distinctive species in the fauna, S. diversus, consists of a trimembrate apparatus, including symmetrical Sa, asymmetrical Sb and strongly asymmetrical Sc elements. This species concept is supported by the absence of any other element types in a large collection represented by nearly 500 specimens of this species. The fauna indicates a late Tremadocian to mid-Floian age (Early Ordovician) for the Honghuayuan Formation, which was widely distributed on the Yangtze Platform in shallow water environments. Previously published biostratigraphic zonations for the Honghuayuan Formation are reviewed, and revised on the basis of our knowledge of the entire conodont fauna, supporting the establishment of three biozones, Triangulodus bifidus, Serratognathus diversus, and Prioniodus honghuayanensis biozones in ascending order. Species of Serratognathus enable correlation between Ordovician successions of South China, North China (North China Platform and Ordos Basin), Tarim Basin, and further afield into Malaysia and northwestern Australia.     

New Late Permian rugose corals from Pahang,peninsular Malaysia

Aye Ko Aung, Ng Tham Fatt, Kyaw Kyaw Nyein & Myo Htut Zin, 2013. New Late Permian rugose corals from Pahang, peninsular Malaysia. Alcheringa 37, 422–434. ISSN 0311-5518.

Late Permian rugose corals are described from a limestone unit of the Gua Musang Formation at Selborne Estate, Padang Tengku area, Pahang, peninsular Malaysia. These include one genus, Iranophyllum, which is reported for the first time from Malaysia, with two new species Iranophyllum aequabilis and I. pahangense belonging to Waagenophyllidae. A Late Permian age is confirmed by a Paleofusulina–Colaniella–Reichelina foraminiferal fauna co-preserved with the corals.

Aye Ko Aung [akaung.mm@gmail.com], Ng Tham Fatt [thamfatt@gmail.com], Kyaw Kyaw Nyein [konyein@gmail.com], Department of Geology, University of Malaya, 50603, Kuala Lumpur, Malaysia and Myo Htut Zin [myohtutgreat@googlemail.com], Lab. Services, Pte. Co. Ltd., Singapore. Received 16.10.2012; revised 5.1.2013; accepted 17.1.2012.