Fluorescence intensity studies of Triassic acritarchs from the Yanchang Formation in Ordos basin, northwestern China

Fluorescence properties of Early Cambrian acritarchs were investigated using Leica das Mikroskop (DM) microscopy with a mercury lamp. Well-preserved autoflurescence properties show a correlation between acritarchs morphology and the intensity of emitted fluorescence. In accordance with the fluorescence intensity of organic cell walls, two groups of microfossils were distinguished. Results of observation in this study, which are consistent with those of the previous foreign studies, are in good agreement with regular difference in autofluorescence intensity among palynomorphs reported by McPhilemy (1998). Spores and algae, including Botryococcus, have very bright fluorescence while acritarchs often show less intense fluorescence. Dark brown microfossils have been reworked, and have little or no fluorescence. __________ Translated from Acta Micropalaeontologica Sinica, 2006, 23(3): 309–312 [译自: 微体古生物学报]     

Diverse small spinose acritarchs from the Ediacaran Doushantuo Formation, South China

The Ediacaran Doushantuo Formation in South China is underlain by the Cryogenian Nantuo Formation (glacial rocks) and overlain by the late Ediacaran Dengying Formation. It is characterized by well-preserved, large (normally >100 μm in size) spinose acritarchs (LSAs), which have been shown to be probably the only useful biostratigraphic tool for the global correlation of the early- and middle-Ediacaran. Acritarchs are organic microfossils normally known as single-celled eukaryotic organisms (protists). Although recent research suggests that some large spinose acritarchs may represent diapause egg cysts of metazoans, the biological affinities of the Ediacaran spinose acritarchs, especially for those displaying remarkable size ranges, are still debatable.Recently, smaller specimens of the Ediacaran spinose acritarchs have been found in cherts and phosphorites of the Doushantuo Formation in South China. Many described Ediacaran spinose acritarch taxa display large size variation (from tens to hundreds of microns in vesicle diameter), but some taxa only have smaller (<70 μm) specimens. The morphological comparison with Paleozoic counterparts indicates that some Ediacaran spinose acritarchs may have phylogenetic affinity to eukaryotic algae. More evidence, including wall ultra-structure, geochemical analysis and comparison with modern analogs, is needed to understand the biological affinity of the Ediacaran spinose acritarchs. The remarkable radiation of planktonic protists, characterized by abundant, diverse spinose acritarchs, occurred as early as in the late Neoproterozoic, i.e., 40–60 million years earlier than previously thought.     

Habitats and probable nature of acritarchs from the Upper Riphean Chencha Formation

Morphology and taphonomy of acritarchs from the Upper Riphean deposits of the Baikal Folded Region (eastern Siberia) are analyzed. The morphotypes of acritarchs are compared to various stages in the life cycle of modern green algae of the order Chlorococcales. The acritarchs Dictyotidium minor Stan. and the modern coenobial taxon Pediastrum boryanum (Turp). Menegh. showed the greatest similarity of structure.     

陕西鄂尔多斯盆地中三叠统一离片椎类牙齿化石

陕西省鄂尔多斯盆地渭北油田中三叠统铜川组发现一枚牙齿化石。该枚牙齿具有如下特征:牙齿细长,外形呈圆锥形,齿冠基部横截面为圆形,齿冠整体较直,沿长轴稍微向后缘弯曲,齿冠表面无齿脊和锯齿分布,发育纵向延伸的沟槽状纹饰。通过与鳄型类、蛇颈龙类和离片椎类的牙齿比较,该标本可以归入离片椎类。这枚牙齿化石为这一类群在中三叠统铜川组的首次发现,代表了离片椎类在华北板块最晚的化石记录。     

鄂尔多斯盆地三叠系延长组疑源类的荧光特征

在鄂尔多斯盆地三叠纪湖相沉积的延长组中,发现保存很好的藻类化石,荧光显微镜下显示很好的荧光;我们发现同层位产出的不同藻类化石具有不同的荧光强度,对这些藻类荧光强度的观察,符合以往国外学者提出的化石荧光与化石类别相关的结论。这也是我国首次用化石藻类荧光与生物属性关系进行研究的尝试,为今后利用荧光进行化石藻类分选和超微结构研究作了有益的探索。     

Recovery dynamics of benthic marine communities from the Lower Triassic Werfen Formation,northern Italy

The Lower Triassic Werfen Formation of northern Italy represents an important archive for Early Triassic ecosystems. Based on quantitative community analysis using species level identifications, we reconstruct the recovery of benthic ecosystems after the end‐Permian mass extinction throughout this unit. The analysis of benthic macrofossil communities shows that incipient recovery has taken place during the Griesbachian and the Griesbachian–Dienerian transition. A probable deterioration in environmental conditions is observed towards the end of the Dienerian. The Smithian part of the Werfen Formation is characterized by high siliciclastic input, which ceases around the Smithian‐Spathian boundary. The Spathian marks the definitive phase of recovery in the Werfen Formation. The comparison of this pattern with other palaoegeographical regions suggests that both the Griesbachian recovery and the Dienerian decline were of inter‐regional if not global extent, whereas the Smithian diversity low in the Werfen Formation is a local signal. In contrast to the recovery dynamics of ammonoids and conodonts, the Smithian–Spathian boundary interval was no caesura for benthic ecosystems. The Spathian recovery pulse is possibly also an inter‐regional event, at least in the palaeotropics. These results are in contrast with the previously proposed scenario of persistent hostile conditions during the Griesbachian time interval and highlight an initial recovery phase restricted to Griesbachian times. Instead, the apparently sluggish recovery of benthic ecosystems was at least partly shaped by set‐backs due to short‐term environmental perturbations during the Dienerian.     

Formation Conditions and Sedimentary Characteristics of a Triassic Shallow Water Braided Delta in the Yanchang Formation,Southwest Ordos Basin,China

A large, shallow braided river delta sedimentary system developed in the Yanchang Formation during the Triassic in the southwest of the Ordos basin. In this braided delta system, abundant oil and gas resources have been observed, and the area is a hotspot for oil and gas resource exploration. Through extensive field work on outcrops and cores and analyses of geophysical data, it was determined that developments in the Late Triassic produced favorable geological conditions for the development of shallow water braided river deltas. Such conditions included a large basin, flat terrain, and wide and shallow water areas; wet and dry cyclical climate changes; ancient water turbulence; dramatic depth cycle changes; ancient uplift development; strong weathering of parent rock; and abundant supply. The shallow water braided river delta showed grain sediment granularity, plastic debris, and sediment with mature composition and structure that reflected the strong hydrodynamic environment of large tabular cross-bedding, wedge cross-bedding, and multiple positive rhythms superimposed to form a thick sand body layer. The branch river bifurcation developed underwater, and the thickness of the sand body increased further, indicating that the slope was slow and located in shallow water. The seismic responses of the braided river delta reflected strong shallow water performance, indicated by a progradation seismic reflection phase axis that was relatively flat; in addition, the seismic reflection amplitude was strong and continuous with a low angle and extended over considerable distances (up to 50 km). The sedimentary center was close to the provenance, the width of the river was large, and a shallow sedimentary structure and a sedimentary rhythm were developed. The development of the delta was primarily controlled by tectonic activity and changes in the lake level; as a result, the river delta sedimentary system eventually presented a “small plain, big front” character.     

The Ichnofossils of the Triassic Hope Bay Formation,Trinity Peninsula Group,Antarctic Peninsula

The Triassic Hope Bay Formation (Trinity Peninsula Group) includes a diverse ichnocoenosis in the Puerto Moro succession (Hope Bay, Antarctic Peninsula). The Hope Bay Formation is a thick turbidite succession with a minimum vertical exposure of 533 meters along the Hope Bay coast. The rocks are locally affected by contact metamorphism related to later arc magmatism. The ichnofossils are found mainly in thick- and thin-bedded sandstone-mudstone facies composed of a monotonous repetition of sandstone-mudstone cycles. The sandstones are usually medium grained, massive or parallel laminated; the mudstones are massive and rarely laminated. In the fine-grained rocks, mainly the mudstones, there are distinct densities of bioturbation, and at least six patterns were observed. The following ichnogenera were recognized: Arenicolites Salter 1857, Lophoctenium Richter 1850, Taenidium Heer 1877, Palaeophycus Hall 1847, Phycosiphon von Fischer-Ooster 1858 and Rhizocorallium Zenker 1836. All appear to be feeding-traces. The trace fossil assemblages occur mainly in black mudstones rich in organic material that suggest a low oxygen environment. The stratigraphic interval in which they occur is interpreted as progradational supra-fan lobes with channel fill and levee deposits. The thin-bedded turbidite and mudstone lithofacies, where the ichnofossils are abundant, is interpreted as a distal fan turbidite or levee deposit related to a long-term channel fill. This study is the first significant report of trace fossils in the Hope Bay Formation.     

Early Triassic bivalves from the Feixianguan Formation in Xingyi,Guizhou and the Ximatang Formation in Qiubei,Yunnan (southern China)

Based on newly collected materials from the Lower Triassic Feixianguan Formation of Xiongwu section in Xingyi, Guizhou and the Ximatang Formation of Ximatang section in Qiubei, Yunnan, southern China, nine species belonging to seven genera are described. Two bivalve assemblages are recognized and regionally correlated in South China. The bivalve assemblage from the Feixianguan Formation of Xiongwu exhibits a higher diversity including seven species belonging to seven genera: Claraia griesbachi, Leptochondria virgalensis, Entolium (Entolium) microtis, Towapteria scythicum, Bakevillia exporrecta, Bositra sp., and Unionites? fassaensis. In contrast, the bivalve assemblage from the Ximatang Formation of Ximatang has a much lower diversity, consisting of only two species, i.e., Claraia griesbachi and Claraia radialis. Additionally, C. griesbachi and C. radialis, as the most common species of Claraia in the Early Triassic, are revised.     

Multina from the Late Triassic Luning Formation,Nevada

The discovery of the network trace fossil Multina isp. in the Luning Formation of central Nevada provides new insight into the depositional setting of the Shaly Limestone Member of the Luning Formation. The ichnofossils occur in tabular mudstone beds deposited on a shelf environment or open carbonate platform. Although Multina resembles Paleodictyon, as both share polygonal burrow nets and both frequently occur in deep-water habitats, Multina is less regular and has other morphological traits such as crossing burrow branches not seen in Paleodictyon or Protopaleodictyon.     

Chirothere Footprint Sites from the Otter Sandstone Formation (Middle Triassic,late Anisian) of Devon,United Kingdom

Three chirothere footprint sites are documented from the Middle Triassic (Anisian) fluvial Otter Sandstone Formation of Sidmouth, Devon, UK. One site, on the foreshore below Peak Hill, has revealed numerous tracks, including a probable manus imprint, which are recorded here. Another site, also beneath Peak Hill, has produced a single probable manus track from a higher horizon. The third site, on the foreshore below Salcombe Hill Cliff, has yielded a small number of pes tracks similar to those from Peak Hill. The footprints at all sites are interpreted as belonging to a large Chirotherium ichnospecies, perhaps C. barthii Kaup. Unusually, the tracks are preserved in mudstone, often in convex epirelief, and are inferred to have been generated subaqueously. The apparent restriction of the footprints to the higher part of the Otter Sandstone Formation supports other evidence, such as a greater abundance of vertebrate skeletal material, subhorizontal rather than vertical rhizocretions, and a greater frequency of lacustrine facies, for a less arid climate and higher water table than lower in the sequence.     

Plants of Leptostrobus Heer （Czekanowskiales） from the Early Cretaceous and Late Triassic of China, with Discussion of the Genus

Investigation of the Mesozoic seed plant Leptostrobus Heer from the Yangcaogou Formation of the Late Triassic and the Yixian Formation of the Early Cretaceous, Liaoning Province, China, provides new Insight Into Its general morphology and geographical distribution. The materials of L. cancer from the Yixian Formation described herein are later than all the past findings of this species and add to the record of L. cancer during the Early Cretaceous. Based on well-preserved specimens, the specific diagnosis Is slightly emended and the reconstructlon of L. cancer Is perfected. The materials from the Yangcaogou Formation of the Late Triassic are placed in L. spheericus, in addition, we review the history of investigation of the genus Leptostrobus since its establishment in 1876 and discuss the main characteristics of each species.     

Triassic temnospondyl biostratigraphy, biochronology and correlation of the German Buntsandstein and North American Moenkopi Formation

Based on temnospondyl distributions, we propose a correlation of the non-marine Lower and Middle Triassic strata of Germany and the western United States. This correlation relies principally on the presence of two genera, Nonesian (late Early Triassic) Parotosuchus and Perovkan (early Middle Triassic) Eocyclotosaurus . The distribution of Parotosuchus helgolandicus indicates that the Torrey Member of the Moenkopi Formation in Utah, USA is equivalent to the Volpriehausen Formation of the German Buntsandstein of Nonesian age. Magnetostratigraphy and the distribution of Eocyclotosaurus indicate that the Perovkan Holbrook Member of the Moenkopi Formation in Arizona corresponds to a short interval of Anisian time, as does the German Upper Buntsandstein. The Buntsandstein and Moenkopi biostratigraphic schemes agree with a recently proposed biochronology of Triassic terrestrial tetrapods.     

云南罗平中三叠世意外裸鱼的再研究

意外裸鱼(Gymnoichthys inopinatus)于2010年由Tintori等首次记述并归入基干新鳍鱼类。依据在云南省曲靖地区罗平县大凹子村中三叠世关岭组二段发现的新材料,对意外裸鱼进行了补充描述,并重新讨论了其系统发育关系。在意外裸鱼的新标本上,可见其续骨前端很可能与关节骨相关节,并有确切无疑的单一辅上颌骨,表明意外裸鱼应为鲱亚部(Halecomorphi)鱼类。此外,意外裸鱼的体表无鳞、椎体未骨化、髓棘和髓弓的结构和排列方式以及牙齿和尾脉棘的形状都与金尾鱼超科鱼类(caturoids)一致。系统发育分析结果表明意外裸鱼属于金尾鱼超科的基干类群。之前金尾鱼类主要见于欧洲和北美的侏罗系,现在公认的金尾鱼超科鱼类主要包括Liodesmidae中的Liodesmus属和金尾鱼科(Caturidae)中的Caturus和Amblysemius两属。意外裸鱼的发现不仅使金尾鱼类的出现提前了40Ma,而且填补了我国相关材料的空缺。     

A new species of the enigmatic archosauromorph Doswellia from the Upper Triassic Bluewater Creek Formation,New Mexico,USA

Abstract: Doswellia sixmilensis is a new species of the doswelliid archosauromorph genus Doswellia named for an incomplete skeleton from the Upper Triassic Bluewater Creek Formation of the Chinle Group in west‐central New Mexico, USA. D. sixmilensis differs from D. kaltenbachi Weems, the type and only other known species of Doswellia, in its larger size, higher tooth count and greater heterodonty, possession of keels on the cervical centra and the presence of discrete knobs or spikes on some osteoderms. The holotype of D. sixmilensis is the fourth occurrence of Doswellia and only the second occurrence of a Doswellia skull, which includes the previously unknown premaxilla and maxilla (and therefore the best dentition) and has the best‐preserved cervical vertebrae. Although it adds to our knowledge of the anatomy of Doswellia, this new information does not alter previous concepts of the phylogenetic relationships of the doswelliid genera, largely because they are so poorly known anatomically. The genus Doswellia is known from the Newark Supergroup in Virginia, and the Chinle Group in Texas, New Mexico and Utah, in strata of Otischalkian–Adamanian age. The type locality of D. sixmilensis is c. 43 m stratigraphically below a bed from which U‐Pb dating of detrital zircons yields a maximum depositional age of c. 220 Ma, so this is a reasonable approximate numerical age for D. sixmilensis.     

Diversity and palaeoecology of a highly diverse Late Triassic marine biota from the Cassian Formation of north Italy

A sample of marine invertebrates from the Late Triassic Cassian Formation (north Italy) yielded one of the most diverse Early Mesozoic fossil assemblages ever reported (c. 170 species). The assemblage was found in basin clays, but was transported from nearby carbonate platforms as indicated by fragmentation, microbial encrustation and the presence of coated grains and ooids. Most of the specimens are small (< 1 cm) reflecting both, small adult sizes and size sorting during transport. Rarefaction analysis suggests that diversity of surface collection and bulk sampling is the same. However, rank abundance, species richness and taxonomic composition differ strongly according to sampling method. Low‐grade lithification of the sediments is the main reason that high diversity can be recognized, because it facilitates disaggregation and finding of small molluscs. Sample standardization shows that the studied assemblage is much more diverse than known Early Triassic assemblages. However, its diversity is similar to that of Anisian assemblages. This suggests that recovery from the end‐Permian mass‐extinction was quite advanced in the Middle Triassic and alpha‐diversity remained high until the Late Triassic. According to current models, Early Triassic and Anisian faunas match the niche overlap phase of recovery during which diversity is built up by increasing alpha‐diversity, whereas beta‐diversity rises slowly. Subsequently, habitat width of species contracts because of increasing competition, making beta‐diversity the principal drive of overall diversity increase. The diversity pattern of various Late Triassic Cassian associations meets the predictions for the transition from the niche overlap to the habitat contraction phase.: Triassic, Cassian Formation, palaeoecology, diversity, mollusc dominance.     

Triassic trace fossils from lacustrine shoreline deposits of the Passaic formation,douglassville, pennsylvania

Lake‐margin deposits of the Late Triassic Passaic Formation, Douglassville, Pennsylvania, have yielded a moderate variety of trace fossils. The greatest diversity and abundance of trace fossils occurs on the sole of a thin gray claystone overlain and underlain by gray siltstones. Specimens of Cochlichnus anguineus, Helminthoidichnites tenuis, Helminthopsis hieroglyphica, Treptichnus pollardi, and paired trails reflect simple, unspecialized, horizontal grazing as well as feeding traces under very shallow water lacustrine conditions. The lack of commonly associated Scoyenia burrows in these deposits may possibly be related to the degree of maturation of the organic debris available. The traces, as well as a lack of meniscate burrows, compare favorably to the Mermia ichnofacies, except Passaic deposits exhibit evidence of subaerial exposure. This unit most likely records a lacustrine expansion whereby grazing trails were emplaced under fully subaqueous conditions. Subsequent shallowing and desiccation, followed by sediment influx during rainstorms, favored preservation of these traces.

In contrast, the Scoyenia ichnofacies consists of feeding burrows of Scoyenia gracilis and Spongeliomorpha milfordensis within reddish brown siltstones and mud‐stones (redbed sequence). The Scoyenia ichnofacies records limited exploitation, by opportunistic infaunal deposit feeders, of lake‐margin nutrients carried in during occasional rainstorms that punctuated otherwise extended periods of aridity.     

Additional thylacocephalans (Arthropoda) from the Lower Triassic (upper Olenekian) Osawa Formation of the South Kitakami Belt,Northeast Japan

The Lower Triassic Osawa Formation in the South Kitakami Belt, Northeast Japan, consisting mostly of mudstone of shallow-marine environment, was deposited during the late Olenekian (ca. 250 Ma), and is an important unit through which to examine the biotic recovery process after the end-Permian mass extinction. The Osawa Formation is the only unit in Japan that yields thylacocephalans (Arthropoda). Three species belonging to three genera have been reported before: Ankitokazocaris bandoi, Kitakamicaris utatsuensis and Ostenocaris sp. In addition to the known species, some thylacocephalans, including one new genus and three new species, are described in the present paper: Ankitokazocaris tatensis n. sp., Concavicaris parva n. sp., Miyagicaris costata n. gen. n. sp. and Ostenocaris? sp. Although Thylacocephala have a rather long stratigraphic range (from Silurian to Cretaceous) and are known from a wide geographical region, there are only about thirty genera in this group. The Osawa thylacocephalan fauna comprises at least five genera, making it one of the most diverse in the world at the generic level. During the Triassic Period, the Thylacocephala diversified and spread widely throughout low-latitude regions.