重庆老龙洞二叠系-三叠系界线地层微生物岩研究

The largest mass extinction in the Phanerozoic happened at the end of the Permian. The microbialites formed in the extreme environments after the mass extinction has become a hotspot for geologists and paleontologists throughout the world. The dendroid microbialites that were described for the first time in 1999 from the Permian-Triassic boundary section at Laolongdong, Chongqing, have been studied by many geologists from China and overseas. Two important viewpoints about their origin have been proposed. Some researchers believed that they resemble Quaternary travertine shrubs in form, and may belong to microbialites. Some other researchers proposed that the dendroid structure is composed of clots formed by coccoidal cynaobacteria, and is microbialite. Our detailed survey on the section reveals that: (1) there is an interval of speckled “microbialite” in the section, and it underlies the dendroid “microbialite”, (2) the dendroid “microbialite” does not always have dendroid appearance; they are dendroid only in very local places; they are not dendroid in most places; for this reason, they are not comparable to recent tufa; (3) the volume of the dendroid structure greatly increases toward the top of the dendroid microbialite interval: accounting to 70% of the whole rock in the top part. This distribution pattern implies that the formation of this structure may be related to downward migration of the diagenetic fluid. Examination of thin sections reveals that the dendroid structure or point-like structure in the “microbialite” look as lighter areas in the thin sections and are composed of large blocky clear calcites containing scattered yellow dirty small calcite rhombi and irregular “points” of relict lime mudstone or wackestone or packstone. Their formation is by any one of the following two processes: (1) dissolution → filling of large blocky calcite; (2) dolomitization → dedolomitization → dissolution by meteoric fresh water → filling by large blocky calcites. It has been found that there are at least two sea-level falls during the P-T transition. As the sea level fall, the carbonate deposits came into supratidal environment, and suffered dolomitization caused by evaporative fluid or mixing water of sea water and meteoric water. Since the fluid migrated downward from the top of the deposits and in random pathway, the dolomitization formed dendroid or speckled dolomitic areas. As the deposits came into subaerial environments, the meteoric fresh water migrated along the dendroid or speckled dolomitic area with higher porosity, and dissolution happened, which caused the rock became spongy or alveolate. In later time, after the strata came into phreatic zone, large clear blocky calcites grew in and filled the pores in the spongy areas. The dendroid and speckled structure were formed in this way, rather than composed of clots formed by coccoid cyanobecteria. The microbial fossils in Laolongdong section include two types. The first is the tube-like cyanobecteria in middle Bed 3, which are generally less than 1 mm in length, taper toward one end, and are internally filled by microspars. They are straight or sinuous, with micritic wall 0.005~0.01 mm thick. Since this kind of microbial fossils are abundant in middle Bed 3, this rock belongs to microbialite. The second type occurs in Bed 5 and lower and middle Bed 6. They are irregular globular in shape, generally 0.2 ~ 0.5 mm in size, with several outward progresses, and internally filled by one layer of needle-like calcite cements on the wall and the large blocky calcite in the inner space. According to their shape and preservation way, it is inferred that this kind of fossils were formed from some kind of bacterial colony. The bacterial colony may be cuticle in composition, since it has some hardness as it is indicated by its resistance to deposit loading. These organisms discomposed during diagenetic time, and formed good porosity. In later diagenetic time, these pores were firstly cemented by needle-like calcites and later filled by large blocky calcites. So, the bacterial colony promoted the formation of dendroid and speckled structures. However, they did not always form such structures. On the other hand, even though no bacterial colony or other microbes or any kind of fossils were present, dendroid or speckled structures can form. Bed 4 of Laolongdong section contains abundant gastropods but no microbial fossils, and is not microbialite, even though it is speckled. The top of Bed 6 is dendroid, but contain no microbial fossils, and is not micrbialite.

Dietary inference from upper and lower molar morphology in platyrrhine primates.

The correlation between diet and dental topography is of importance to paleontologists seeking to diagnose ecological adaptations in extinct taxa. Although the subject is well represented in the literature, few studies directly compare methods or evaluate dietary signals conveyed by both upper and lower molars. Here, we address this gap in our knowledge by comparing the efficacy of three measures of functional morphology for classifying an ecologically diverse sample of thirteen medium- to large-bodied platyrrhines by diet category (e.g., folivore, frugivore, hard object feeder). We used Shearing Quotient (SQ), an index derived from linear measurements of molar cutting edges and two indices of crown surface topography, Occlusal Relief (OR) and Relief Index (RFI). Using SQ, OR, and RFI, individuals were then classified by dietary category using Discriminate Function Analysis. Both upper and lower molar variables produce high classification rates in assigning individuals to diet categories, but lower molars are consistently more successful. SQs yield the highest classification rates. RFI and OR generally perform above chance. Upper molar RFI has a success rate below the level of chance. Adding molar length enhances the discriminatory power for all variables. We conclude that upper molar SQs are useful for dietary reconstruction, especially when combined with body size information. Additionally, we find that among our sample of platyrrhines, SQ remains the strongest predictor of diet, while RFI is less useful at signaling dietary differences in absence of body size information. The study demonstrates new ways for inferring the diets of extinct platyrrhine primates when both upper and lower molars are available, or, for taxa known only from upper molars. The techniques are useful in reconstructing diet in stem representatives of anthropoid clade, who share key aspects of molar morphology with extant platyrrhines.

Radiolaria: Major exporters of organic carbon to the deep ocean

Very large pulses of particulate organic matter intermittently sink to the deep waters of the open ocean in the Northeast Atlantic. These pulses, measured by moored sediment traps since 1989, can contribute up to 60% of the organic flux to 3000 m in a particular year and are thus a major cause of the variability in carbon sequestration from the atmosphere in the region. Pulses occur in the late summer and are characterized by material that is very rich in organic carbon but with low concentrations of the biominerals opal and calcite. A number of independent lines of evidence have been examined to determine the causes of these pulses: (1) Data from the Continuous Plankton Recorder (CPR) survey show that in this region, radiolarian protozoans intermittently reach high abundances in the late summer just preceding organic pulses to depth. (2) CPR data also show that the interannual variability in radiolarian abundance since 1997 mirrors very closely the variability of deep ocean organic deposition. (3) The settling material collected in the traps displays a strong correlation between fecal pellets produced by radiolaria and the measured organic carbon flux. These all suggest that the pulses are mediated by radiolarians, a group of protozoans found throughout the world’s oceans and which are widely used by paleontologists to determine past climate conditions. Changes in the upper ocean community structure (between years and on longer timescales) may have profound effects on the ability of the oceans to sequester carbon dioxide from the atmosphere.

A Lopingian (Late Permian) brachiopod fauna from the Qubuerga formation at Shengmi in the Mount Qomolangma region of Southern Xizang (Tibet), China

A small fauna of 11 species belonging to 10 genera of Permian Brachiopoda from the lower part of the Qubuerga Formation outcropping near Shengmi village in the Qomolangma region of southern Xizang (Tibet) is figured and new taxa are described. New taxa are Quinquenella semiglobosa and Costatumulus shengmiensis. The fauna is most likely of Wuchiapingian (Djhulfian) age as indicated by the majority of the brachiopod species.

Early carboniferous athyridid brachiopods from the Qaidam Basin, Northwest China

Four new Early Carboniferous athyridid species in three genera, including one new genus, Bruntonathyris, are described from the Qaidam Basin, northwest China: Lamellosathyris qaidamensis, Bruntonathyris amunikeensis, Bruntonathyris? heijianshanensis, and Lochengia qinghaiensis. Based on the new material and also on published information, we also reviewed the taxonomic composition and the stratigraphic and paleogeographic distributions of the three genera. As a result, Lamellosathyris is considered to be indicative of late Famennian to Viséan age, originating in late Famennian in central North America and Armenia of Russia, respectively. Later, the genus appears to have two migratory directions: one branch rapidly dispersed over Mississippi Valley, Oklahoma, Texas and New Mexico of central North America in Tournaisian; alternatively, another branch from Armenia migrated westerly to Belgium, France, Spain, Britain, Ireland, via the Moscow Basin and Ural seaway, eastward to the Tienshan Mountains and Qaidam Basin of northwest China during the Tournaisian to Viséan, and easterly along the southern shelves of the Paleo-Tethys to Iran and western Yunnan of southwestern China in Tournaisian. Both Bruntonathyris and Lochengia are restrictedly Tournaisian to Viséan in age, and probably originated in the Qaidam Basin. Later, Bruntonathyris migrated easterly to South China and Japan, and westerly to Urals, Moscow Basin, Donetsk Basin and Britain; Lochengia migrated easterly to South China and westerly to the Urals seaway and the adjoined Russian Platform (i.e., both the Moscow and Donetsk Basins).

A Guadalupian-Lopingian (Middle to Late Permian) brachiopod fauna from the Juripu formation in the Yarlung-Zangbo suture zone, Southern Tibet, China

A brachiopod fauna of 16 species belonging to 11 genera and three genera and species indeterminate from the middle and upper parts of the Juripu Formation in the Yarlung-Zangbo (Indus-Tsangbo) Suture zone (=Yarlung-Zangbo River zone), southern Tibet, is described and figured for the first time. A new species, Taeniothaerus zhongbaensis, is described. The fauna is comparable with that in the Kalabagh Member of the Wargal Formation of the Salt Range, Pakistan, and is considered to be most likely Capitanian (late Guadalupian/Middle Permian) to Wuchiapingian (early Lopingian/early Late Permian) in age, as indicated by the majority of the brachiopod species and by being constrained by an underlying fusulinacean fauna (Parafusulina Zone) and an overlying ammonite fauna (Cyclolobus fauna).

Adventures of punctuated equilibria : a struggle for authority in the evolutionary sciences

The theory of ‘punctuated equilibria’ was formulated by two paleontologists, Niles Eldredge and Stephen Gould, in 1972 and has been the focus of considerable controversy within the evolutionary sciences ever since. The primary intentions of this thesis are to relate the history of punctuated equilibria and to examine how it has affected evolutionary science. Several modes of analysis have been used to illuminate the history: The sociological perspectives of Pierre Bourdieu and Bruno Latour (who see scientific debate as a ‘struggle for authority’); Rhetorical analysis of some of the key documents; Communication with practising scientists via questionnaires and correspondence; Citation Analysis. Chapter 1 gives a short summary of the history and introduces the methods and socio-philosophical perspectives used to illuminate the history. Chapters 3 and 4 examine the rhetorical process by which Eldredge and Gould constructed the ‘punctuationist revolution’. Chapters 2, 3, 5 and 6 relate the history of punctuated equilibria.

The briefing in paleodesign: selection and arrangement of data for the reconstruction of Paleovertebrates

Representing visually the external appearance of an extinct animal requires, for a reasonably reliable and expressive reconstitution, a good compilation and arrangement of the scientific conclusions on the fossil findings. It is proposed in this work an initial model of a briefing to be applied in a paleodesign process of a paleovertebrate. Briefing can be understood as a gathering of all necessary data to perform a project. We point out what must be known about the relevant structures in order to access all the data and the importance of such information. It is expected that the present briefing suggested might be faced with flexibility, serving as a facilitating interface of the relation between paleoartists and paleontologists.

BOOK REVIEW of Oceans of Kansas: A Natural History of the Western Interior Sea by Michael J. Everhart

Just as there are seashells on Mt. Everest, there is an exceptional wealth of fossil remains of marine organisms preserved in the chalk of western Kansas. This Cretaceous-aged rock, and the fossils therein, were deposited at a time when a great sea cut northward across the interior of the continent around 85 million years ago, inspiring the provocative title of Everhart's book. The title is true to its subject: documentation of the Cretaceous fossils of western Kansas, their geographic and stratigraphic occurrences, and the inferences that paleontologists can make about how the organisms represented by these fossils may have once lived and interacted with one another.