Ambiguous biogeographical patterns mask a more complete understanding of the Ordovician to Devonian evolution of Japan     

Mark Williams  Simon Wallis  Tatsuo Oji  Philip D. Lane 《Island Arc》2014,23(2):76-101

Fossil assemblages of the Ordovician to Devonian successions of Japan suggest complex temporal, environmental and geographical controls on their biogeographical signature. Thus, limited similarity at the species‐level between the trilobite, brachiopod and ostracod faunas of the South Kitakami, Hida‐Gaien and Kurosegawa terranes in part reflects the sporadic stratigraphic distribution of shelly fauna within these terranes. As a result, and with the exception of corals and pan‐tropical radiolarians, species‐level similarities are greater with other regions of East Asia and Australia than amongst the Japanese terranes. The Silurian faunas of the South Kitakami Terrane have affinities with North America, Europe, Central Asia and Australia, but there is no overriding signature to support proximity either to South China or Gondwana. Notably, brachiopod and trilobite faunas of the Middle Devonian suggest strong connections with North China. Trilobite, coral and ostracod faunas of the Hida‐Gaien Terrane show affinity, including at species level, with Siluro‐Devonian faunas from westerly‐situated palaeocontinents, especially those of Central Asian and European affinity, suggesting a continuation of the Central Asian Orogenic Belt, or of its associated lithofacies. Greater diversity of groups such as ostracods and trilobites in this terrane may signal closer links with continental shelf faunas of East Asia. The dominant biogeographical signature of the Kurosegawa Terrane is from corals and trilobites, suggesting links with the Siluro‐Devonian of Central Asia, Australia and South China. The variable biogeographic signal of the Japanese faunas may reflect the lifestyles of organisms with different physiologies and larval dispersal mechanisms, as well as the relative incompleteness of the Japanese fossil record. The present state of knowledge of the faunas cautions against placing Japan in relative proximity to the North or South China plates, or of presenting the Japanese terranes as a unified island arc to the north of the South China Plate during the Early Palaeozoic.  相似文献   

A late Holocene palaeolimnological record from central Mexico, based on faunal and stable-isotope analysis of ostracod shells     

N.D. Bridgwater  T.H.E. Heaton  S.L. O'Hara 《Journal of Paleolimnology》1999,22(4):383-397

A late Holocene palaeolimnological record for central Mexico has been obtained from Lake Pátzcuaro, using recent and fossil ostracods. Lake Pátzcuaro, Michoacán, is a closed-basin lake which responds rapidly to changes in the ratio of precipitation/evaporation in the region. The record from a single lake-sediment core, dated by AMS radiocarbon method, covers the last ~3,530 yrs, and is based on ostracod faunal palaeoecology coupled with analysis of the stable-isotope (¹⁸O/¹⁶O and ¹³C/¹²C) composition of ostracod valves. The faunal distribution is determined by the presence or absence of aquatic vegetation and, to a lesser extent, salinity. The ¹⁸O/¹⁶O and ¹³C/¹²C ratios in ostracod calcite show good agreement with palaeolimnological inferences from the faunal assemblages, principally recording changing precipitation/evaporation and primary-productivity levels, respectively. Wetter conditions existed in central Mexico between approximately ~3,600 and ~2,390 yr BP, between ~1,330 to ~1,120 yr BP, and from ~220 yr BP to present, characterised by fluctuating lake levels. A dilution of the sediment load in the lake reduced turbidity levels allowing for a marked increase in productivity. During these phases, the combination of a deeper lake and increased macrophyte cover reduced the degree of mixing of the waterbody. In the earliest of these phases there was sufficient stratification of the waterbody for methanogenesis to occur in the sediment interstices. The wet phases were separated by prolonged dry periods, during which time the climatic conditions were relatively stable. Good agreement was found between the findings of this study and others from the central Mexican/Caribbean region suggesting that abrupt climate changes occurred at least at a regional scale.  相似文献   

Lake evolution in a semi-arid montane environment: response to catchment change and hydroclimatic variation     

Henry Lamb  Neil Roberts  Melanie Leng  Philip Barker  Abdelfattah Benkaddour  Sander van der Kaars 《Journal of Paleolimnology》1999,21(3):325-343

Pollen, geochemical and sedimentological data from Sidi Ali, a montane Moroccan lake, provide a 7000 yr record of changes in climate, catchment vegetation and soil erosion intensity. Diatoms, non-silicious algae, macrophyte fossils and ostracods from the same core record the dynamics of the lake ecosystem. Oxygen isotope and trace-element ratios of benthic ostracods appear to be relatively insensitive to climatic variation in this open lake with low water-residence time, but diatom plankton / periphyton (P/L) ratios show lake-level variations that are probably climate controlled. At least two superimposed processes are recorded, but at different timescales: catchment vegetation and soils show long-term changes due to climate and human impact, whereas P/L ratios suggest century-scale oscillations in lake depth. The timing of changes in algal and macrophyte productivity and carbon cycling within the lake broadly corresponds to changes in terrestrial vegetation, suggesting either that lake nutrient status is linked to catchment vegetation and soils, or that both were influenced by climate. The lack of a sensitive and independent (non-biological) climate proxy makes it more difficult to assess the lake's ecological response to short-term climate variation. Overall, the lake's evolution has been influenced both by catchment-mediated nutrient flux and by changes in water balance, thus having characteristics in common with both temperate and arid zone lakes.  相似文献   

Fish and ostracod remains from the Santos Basin (Cretaceous to Recent), Brazil     

C. Giles Miller  Martha Richter  Dermeval A. Do Carmo 《Geological Journal》2002,37(4):297-316

For the first time, ichthyoliths are described from the Santos sedimentary basin, offshore southern Brazil. Isolated teeth, dermal scales and the first documented otoliths from Cretaceous (Albian) to Recent cuttings from five wells are described. The following groups are represented: Chondrichthyans: Triakidae, Carcharhinidae; Ginglymostomatidae: ?Ginglymostoma sp., Lamnidae indet., Scyliorhinidae; Osteichthyans: Teleostei; Myctophiidae: Diaphus aff. splendidus sp. complex, Diaphus spp., Diaphus cf. garmani, Ceratoscopelus aff. warmingii; Sternoptychidae: Valenciennellus tripunctulatus, teeth of indeterminate Teleostei. The majority of these ichthyofossils represent extant forms, known to occur in the Atlantic Ocean, and are of potential value for stratigraphical correlations between oil‐yielding basins in the region. Ostracods are not well preserved but can be identified to generic level indicating marine environments. The ostracod faunas offer potential for intrabasinal correlation in the Eocene and Oligocene. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Japan's earliest ostracods     

David J. Siveter  Gengo Tanaka  Mark Williams  Peep Mnnik 《Island Arc》2019,28(1)

Mesozoic, Cenozoic and especially Holocene ostracod faunas have been documented from Japan. Not surprisingly, considering the plate tectonic factors at play, very few ostracod faunas are known from its early Paleozoic successions. Our pilot studies have recovered new ostracod assemblages from early Paleozoic terranes of Japan. Acid preparation of carbonates has yielded low diversity, poorly preserved yet significant palaeocopid and podocopid ostracod faunas from Wenlock/Ludlow Series Silurian rocks at Gionyama in the Kurosegawa Terrane, Miyazaki Prefecture, Kyushu, and Hitoegane in the Hida‐Gaien Terrane, Gifu Prefecture, Honshu. The ostracod faunas include new eurychilinoid (Pauproles supparata gen. et sp. nov.), hollinoid (Hollinella orienta sp. nov.) and beyrichioid (Clintiella antifrigga sp. nov.) palaeocopid taxa. Conodonts recovered from the same sample as the ostracods from Gionyama confirm a mid‐Silurian age for the part of the Gionyama Formation in question. The ostracod faunas recovered from Gionyama and Hitoegane are the first confirmed, well‐documented record of the group from the Silurian of Japan and are therefore the earliest known ostracods from that country (a previous record of purported Ordovician ostracods from Japan is incorrect). The ostracod taxa display links with the paleocontinents of particularly Laurentia and Baltica and demonstrate a pan‐tropical signature; it appears that climate control was stronger than geographical control in shaping this pattern of ostracod distribution. The material recovered includes adult dimorphic (assumed sexual) pairs of three palaeocopid species, which represent Japan's oldest (423–433 million years) known ‘couples’.  相似文献   

Stratigraphic evidence for a high marine shore-line during the late Weichselian deglaciation on the Kullen Peninsula,southern Sweden     

Per Sandgren  Ian F. Snowball  Dan Hammarlund  Jan Risberg 《第四纪科学杂志》1999,14(3):223-237

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Late Silurian (Ludlow–Přídolí) microfossils and sedimentation in the Welsh Basin near Clun,Shropshire     

C. Giles Miller  Stuart J. E. Sutherland  Ken J. Dorning 《Geological Journal》1997,32(1):69-83

The base of the Clun Forest Formation at Clun, Shropshire, has previously been taken to correlate with the base of the Downton Castle Sandstone Formation (Přídolí Series, upper Silurian) on the basis of brachiopod, bivalve, gastropod and ostracod faunas. The detailed distribution of microfossils (acritarchs, chitinozoans, conodonts and ostracods) is documented at Nantyrhynau Quarry, Clun, Shropshire, to test this correlation. Three new species of chitinozoans, Eisenackitina clunensis, Eisenackitina kerria and Angochitina paucispinosa, are described from the quarry. Macrofossil and ostracod distributions suggest that the correlation is correct. However, a typical Ludlow acritarch flora is present throughout the section and suggests that the basal part of the Clun Forest Formation is Ludlow in age. The mixture of characteristic Ludlow and Přídolí microfossils at Nantyrhynau Quarry may be the result of differing environmental conditions between the Ludlow (shelf) and Clun (basinal) areas at this time. Alternatively, the strata exposed at Nantyrhynau Quarry may represent a period towards the end of the Ludlow Series when there are no strata represented in corresponding shelf sections due to non-deposition or erosion. © 1997 John Wiley & Sons, Ltd.  相似文献   

Cenomanian events in the deep western Basque Basin: the Leioa section     

Julio Rodriguez-Lázaro  Ana Pascual  Javier Elorza 《Cretaceous Research》1998,19(6):673-700

Analysis of the microfaunas (foraminifera, ostracods) and the stable isotope values (δ¹³C, δ¹⁸O) of the Leioa section, as representative of the deep Basque Basin, has allowed us to propose a detailed palaeoenvironmental reconstruction of this region during the Cenomanian, as well as to register global chronostratigraphic reference levels to facilitate interregional correlations. During the Cenomanian, part of the basin, the Plentzia Trough, was occupied by intermediate water masses, as deduced by the relative percentages of planktonic (Rotalipora) and benthonic foraminifera. A noticeable change is observed at the middle-late Cenomanian transition: the replacement of the dominance of keeled (rota-liporids) by incipiently-keeled (dicarinellids, praeglobotruncanids) planktonic foraminifera, indicative of the new influence of the upper intermediate waters. The temporary effect of shallow waters is deduced in one interval of the latest early Cenomanian and two more of the middle Cenomanian, as indicated by the dominance of globular planktonic foraminifera (hedbergellids). These water masses were moderately to strongly hypoxic (<4 to <2 ml/l of disolved oxygen) after the ostracod platycopid signal and benthonic foraminiferal hypoxic indicators. The dysaerobia may have been particulary strong (almost anoxia?) during part of the middle Cenomanian. Micronutrient availability was also restricted during several intervals of the middle Cenomanian, as indicated by the sudden decrease in the species diversity of the calcitic benthonics during the period when increased trends of the δ¹³C isotopic signals are observed. The combination of both hypoxia and nutrient depletion produced drastic changes in the microfaunal assemblages, with emigrations and local extinctions, showing benthonic perturbations from the time indicated by the base of theRotalipora reicheliZone onwards. From the beginning until the end of the middle Cenomanian, eleven of these perturbations are recorded as regional bioevents, using as bioevent-markers, intervals where microfauna was absent (including benthic-free intervals, B-FI; benthonic calcitic-free intervals, BC-FI; and ostracod-free intervals, O-FI). These changes led to the renewal of the microfaunas; benthonic foraminifera renewed their specific stocks during the early to early middle Cenomanian, with planktonic foraminifera and ostracods undergoing renewal at the end of the middle Cenomanian. Isotope values of δ¹⁸O and δ¹³C are consistent with the palaeoenvironmental changes detected by the microfaunas; their maximum and minimum shifts coincide with the bioevents. The double-peaked positive shift of δ¹³C for the mid-Cenomanian of northwest Europe (Jenkynset al., 1994; Paulet al., 1994a) has been recognized in this series of the Basque Basin. The palaeoenvironmental perturbations deduced in the Cenomanian of the Leioa section are attributed essentially to palaeoceanographic changes, where intermediate water masses profoundly influenced the planktonic and benthonic ecosystems. The influence of other local causes, such as volcanic activity at that time, or tectonics between the Iberian and European plates, are more difficult to prove. Several of the bioevents defined in the middle Cenomanian of this basin could probably be global in nature, and thus may be useful for establishing interregional correlations.  相似文献   

Response of deep-sea ostracod assemblages to Late Cretaceous palaeoceanographical changes: ODP Site 689 in the Southern Ocean     

Stefan Majoran  Joen G.V. Widmark 《Cretaceous Research》1998,19(6):843-872

Twenty-six deep-sea ostracod species are described from the late Campanian to late Maastrichtian of ODP Site 689 in the Southern Ocean. Three are described as new:Cytherelloidea megaspirocostata,Agulhasina sudoceanicaandPennyella foveolata. Correspondence analysis identified three faunal sample groups. The first is mainly characterised byA. sudoceanica,Kirthesp. andCytherellasp. This is replaced, first temporarily (betweenc. 71 and 69 Ma) by a group mainly characterised byArgilloeciaspp. andC. megaspirocostata, possibly a consequence of a short-lived global palaeoceanographic event marked by increased ventilation and cooling of intermediate waters at site 689. It then reappears before finally being replaced by a third group largely characterised byEucytherecf.circumcostata,P. foveolataandDutoitella mimicaDingle. This final change is coeval with a marked increase in the faunal density of ostracods, probably owing to an increase in food supply. However, the oxygen isotopic records of benthonic foraminifera suggests that the replacement of the first ostracod group by the third is a result of the long term Maastrichtian cooling of intermediate waters at high latitudes. This replacement is also coeval with a gradual change in benthonic foraminiferal assemblages at site 689. It is suggested, therefore, thatPennyellaandDutoitellahad a greater potential of adapting to successively colder palaeoceanographical conditions thanAgulhasina. The former genera have a cosmopolitan deep-sea distribution today.  相似文献   

内蒙古巴林右旗三叠纪化石的新发现   总被引：1，自引：0，他引：1  

和政军  王瑜 《地层学杂志》1998,22(4):293-294

巴林右旗位于内蒙古东部,地处大兴安岭南段。自１９７２年内蒙古区调二队＊＊提出相邻的陶海营子等地存在着三叠纪地层以来,大兴安岭南段三叠系的存在与否就一直有着不同的认识。在内蒙古区调二队（１９８８）进行１／５万地质填图之后,朱儒峰等（１９９２）根据发现的...  相似文献