Response of Late Ordovician paleoceanography to changes in sea level, continental drift, and atmospheric pCO2: potential causes for long-term cooling and glaciation

We performed sensitivity experiments using an ocean general circulation model at two stages of the Late Ordovician (Caradoc, 454 Ma; Ashgill, 446 Ma) under a range of atmospheric pCO₂ values (8–18× PAL; pre-industrial atmospheric level) at high and low sea level.

The model results indicate that the long-term cooling trend during the Late Ordovician can be explained by progressive cooling of the global ocean in response to falling levels of atmospheric pCO₂, sea level change, and paleogeographic change. These results also explain the occurrence of low latitude cool-water carbonates in North America.

In all simulations, a drop in sea level led to a reduction in poleward ocean heat transport. This indicates a possible positive feedback that could have enhanced global cooling in response to sea level drop during the Late Ordovician. Alterations in poleward ocean heat transport linked to changes of atmospheric pCO₂ also indicate that there is a threshold of 10× PAL, above which ocean current change cannot be responsible for glaciation in the Late Ordovician. Continental drift could explain the observed global cooling trend in the Late Ordovician through a combined poleward ocean heat transport feedback and increased ice-albedo effect if atmospheric pCO₂ was low during the entire Late Ordovician.

The model results further indicate that the response of meridional overturning to changes in paleogeography, atmospheric pCO₂, and sea level is stronger than the response of surface circulation to these perturbations. Because the overturning circulation is so strong, meridional overturning was the dominant mechanism for described changes in heat transport in the Late Ordovician.     

A new species of Golunda (Rodentia, Muridae) from the Late Pleistocene of Indian Himalaya

The youngest fossil Golunda (Rodentia, Muridae) is described from the Late Pleistocene fluvio-lacustrine deposits, exposed at Dulam (Bageshwar), Kumaun Lesser Himalaya, India. The age of fossiliferrous horizon is estimated as 31,000 yr BP. A new species, Golunda dulamensis nov. sp. has highly derived characters, e.g., antero-posteriorly stretched molars, upper molars with more length and less width, stephanodonty, cusps in M₃ strongly inclined backward giving the molars a very stretched aspect, and metaconid and entoconid in M₃ forming almost straight lingual row of the cusps. G. dulamensis nov. sp. is most similar to present day G. ellioti but differs from the later slightly by larger size, a thin connection between t₄ and t₅ in M¹, and comparatively larger entoconid and very weakly developed antero-labial cusp in M₃. We suggest that highly specialized molars of G. dulamensis nov. sp. and present day G. ellioti are derivable through G. kelleri. We also propose that Golunda migrated from Asia to Africa, not from Africa to Asia as was thought by earlier workers.     

内蒙古西部雅布赖盆地中侏罗世晚期植物群

首次报道产于内蒙古自治区西部阿拉善右旗雅布赖盆地红柳沟剖面中侏罗统新河组的 7属 1 2种植物化石 ,主要由真蕨纲和苏铁纲组成。真蕨纲有Gleichenites,Coniopteris和Cladophlebis等 ,苏铁纲有丰富的Otoza mites和Nilssonia ,Nilssoniopteris等。地质时代为中侏罗世中晚期 ,大致为巴通期到卡洛维期。     

新疆三塘湖盆地塘参1井晚侏罗世齐古组孢粉组合

研究的孢粉化石发现于新疆三塘湖盆地塘参 1井齐古组 (井深 95 5— 1 2 38m) ,共计 5 3属 1 30种 (包括1新属 :Santanghusporitesgen .nov .和 6新种 ) ,其中蕨类植物孢子 2 4属 4 0种 ,裸子植物花粉 2 9属 90种。组合以高含量的Classopollis、丰富的松柏类花粉及含少量早白垩世的分子为特征。根据孢粉组合特征 。     

西藏申扎地区晚奥陶世-志留纪牙形刺

本文描述的牙形刺采自西藏申扎地区晚奥陶世-志留纪刚木桑组、德悟卡下组和扎弄俄玛组。根据牙形刺首次提出该区志留系四分方案和确定了奥陶系与志留系的界线位置,为西藏自治区的志留系的研究与划分,提供了重要的依据。     

Granulocyte‐Macrophage Colony‐Stimulating Factor (GM‐CSF) Controls the Proliferation and Differentiation of Mouse Epidermal Melanocytes from Pigmented Spots Induced by Ultraviolet Radiation B

Repeated exposure of ultraviolet radiation B (UVB) on the dorsal skin of hairless mice induces the development of pigmented spots long after its cessation. The proliferation and differentiation of epidermal melanocytes in UVB‐induced pigmented spots are greatly increased, and those effects are regulated by keratinocytes rather than by melanocytes. However, it remains to be resolved what factor(s) derived from keratinocytes are involved in regulating the proliferation and differentiation of epidermal melanocytes. In this study, primary melanoblasts (c. 80%) and melanocytes (c. 20%) derived from epidermal cell suspensions of mouse skin were cultured in a basic fibroblast growth factor‐free medium supplemented with granulocyte‐macrophage colony‐stimulating factor (GM‐CSF). GM‐CSF induced the proliferation and differentiation of melanocytes in those keratinocyte‐depleted cultures. Moreover, an antibody to GM‐CSF inhibited the proliferation of melanoblasts and melanocytes from epidermal cell suspensions derived from the pigmented spots of UV‐irradiated mice, but not from control mice. Further, the GM‐CSF antibody inhibited the proliferation and differentiation of melanocytes co‐cultured with keratinocytes derived from UV‐irradiated mice, but not from control mice. The quantity of GM‐CSF secreted from keratinocytes derived from the pigmented spots of UV‐irradiated mice was much greater than that secreted from keratinocytes derived from control mice. Moreover, immunohistochemistry revealed the expression of GM‐CSF in keratinocytes derived from the pigmented spots of skin in UV‐irradiated mice, but not from normal skin in control mice. These results suggest that GM‐CSF is one of the keratinocyte‐derived factors involved in regulating the proliferation and differentiation of mouse epidermal melanocytes from UVB‐induced pigmented spots.     

Middle Jurassic trace fossils from the Ridang Formation in Sajia County,South Tibet,and their palaeoenvironmental significance

An ichnofauna consisting of 18 ichnospecies (one of them new) in 14 ichnogenera are described for the first time from the Middle Jurassic Ridang Formation in Sajia County, South Tibet. The ichnofauna can be subdivided into two ichnoassemblages in ascending stratigraphic order: the Palaeophycus–Megagrapton ichnoassemblage in the lower and middle parts of the Ridang Formation, followed by the Cosmorhaphe–Nereites–Paleodictyon ichnoassemblage in the upper Ridang Formation. Overall, the trace fossils occur in a middle–distal turbidite fan sequence, as evidenced by both sedimentological analysis and the composition of the trace fossils. Several subenvironments of the middle–distal fan system have been recognized on the basis of the spatial distribution of the trace fossils. Typically, the channel-fill deposits in the middle part of the turbidite fan lack trace fossils, the interchannel and upper channel-fill (levee) subenvironments of the middle turbidite fan contain abundant facies-crossing trace fossils, in contrast to the distal part of the turbidite fan where deep-water trace fossils are dominant. The ichnofauna is similar to typical flysch ichnofaunas from Europe and North America in characteristics, and is interpreted to represent a typical deep-sea Nereites ichnofacies. The presence of these deep-sea trace fossils therefore would suggest that a continental slope environment existed in southern Tibet during the Middle Jurassic and the study area was located in a slope-abyssal plain setting.     

深海钻探计划(DSDP)31航次296站晚新生代介形类

本文研究了深海钻探(DSDP)31航次296站晚新生代介形类动物群的性质及其古海洋学意义.此站钻孔上部上新统至全新统以超微浮游生物软泥和粘土为主的16块岩芯中,共分析获得介形类化石8属11种,计有:Poseidonamicus major Benson, P. anteropunctatus Whatley et al., P. punctatus Whatley et al., Pennyella dorsoserrata (Brady), Henryhowella sp., Pterygocythere mucronalatum (Brady), Abyssocythere sp., Abyssocythereis sulcatoperforata (Brady), Pelecocythere sp., Krithe sp. 1和Krithe sp.2.这些介形类属种均为冷海域深海区介形类分子.由此表明,西北太平洋边缘地区在晚新生代曾为一深海区.在第四纪,其深度可能和现今296站的深度大致相当;在上新世,其深度可能更深一些.研究结果证实,深海底栖介形类属种的分布具全球性;在相当长的地质时期内,介形类属种的形态和壳饰都非常稳定,无明显变化.同时,进一步证实,介形类个体大小变化与深度相关,同一种介形类壳体随水域深度加深而增大.     

HYBODONT SHARKS OF THE ENGLISH BATHONIAN AND CALLOVIAN (MIDDLE JURASSIC)

Abstract:  Recent bulk sampling and study of museum collections has revealed a high diversity of hybodont sharks from the English Bathonian, with 15 species being recognised. In addition, study of dental and skeletal material from the English Callovian has allowed the diagnosis of a new genus and species, Planohybodus peterboroughensis gen. et sp. nov., allowing the Bathonian species Hybodus grossiconus Agassiz to be referred to Planohybodus . Two additional new genera, Secarodus and Frangerodus , are erected for the Bathonian taxa Hybodus polyprion Agassiz and Strophodus lingualis Woodward, respectively. Egertonodus duffini sp. nov. is described and the diagnosis of Egertonodus based on dental material is discussed. The previously unrecorded Hybodus sp., Parvodus sp., and Lonchidion sp. are recognised but left in open nomenclature. Asteracanthus medius (Owen) is recorded in the British Bathonian for the first time, and the status of Bathonian nominal species of Asteracanthus are assessed. Bathonian hybodonts showed great diversity in trophic ecology and many of the species are specific to particular palaeoenvironments.     

Ants of the tribe Formicini (Hymenoptera,Formicidae) from Late Eocene amber of Europe

The tribe Formicini (Formicinae) from the Late Eocene Baltic, Bitterfeld, Rovno, and Scandinavian ambers is revised. Ants are recorded for the first time from the Bitterfeld and Scandinavian ambers. Two new genera (Cataglyphoides gen. nov. and Conoformica gen. nov.) and six new species (Cataglyphoides intermedius sp. nov., Conoformica bitterfeldiana sp. nov., Formica kutscheri sp. nov., F. palaeopolonica sp. nov., F. radchenkoi sp. nov., F. zherikhini sp. nov.) are described. A new combination, Cataglyphoides constrictus (Mayr, 1868), comb. nov., is established. A lectotype of Camponotus constrictus Mayr, 1868 and a neotype of Formica phaethusa Wheeler, 1915 are designated. Formica clymene Wheeler, 1915 is recognized as a new synonym of F. phaethusa Wheeler, 1915. An identification key for workers of Formicini species from Late Eocene European ambers is provided.