Late Palaeozoic red beds elucidate fluvial architectures preserving large woody debris in the seasonal tropics of central Pangaea

Fluvial red beds containing anatomically preserved large woody debris shed new light on seasonally dry biomes of the Pennsylvanian–Permian transition and elucidate the concurrence of river depositional systems and vegetation. As a result, the occurrence, distribution and preservation of petrified large woody debris accumulations are considered crucial to understanding the role of arborescent vegetation in shaping fluvial environments. This study reports sizeable silicified trunks and corresponding fluvial architectures from the uppermost Pennsylvanian (upper Gzhelian) Siebigerode Formation (Kyffhäuser, central Germany). The origin, taphonomy and depositional environment of the fossil woods are elucidated by using a multidisciplinary approach including geological mapping, lithofacies analysis, sediment petrography, wood anatomical studies and microstructure analyses. Results reflect the gradual burial of a gentle basement elevation by sand-bed to gravel-bed braided rivers at the north-western margin of the perimontane Saale Basin. Facies architectures resulted from a complex interplay of syndepositional tectonics, repeated palaeorelief rejuvenation, high-frequency channel avulsion, seasonally dry climate and woody debris–sediment interactions. The alluvial influx and cut-bank erosion recruited trunks from adjacent semi-riparian slope habitats vegetated by up to 40 m tall cordaitaleans and conifers. High discharge in wide braids facilitated uncongested transport of large woody debris. Trunk entombment and initial preservation resulted from grounding on barforms, anchoring by attached roots and subsequent burial. The post-depositional two-phase silicification was influenced by hydrothermal hematite mineralization and determined a selective wood preservation pattern known as ‘pointstone’. Large woody debris-induced sedimentary structures (‘LWDISS’) are introduced as a class of sediment structures formed by the biogenic impact on terrestrial deposition.     

柴达木盆地始新统沟鞭藻及其油源意义

我国中新生代陆相沉积,特别是咸化湖泊沉积中普遍发现属于“海源陆生”的沟鞭藻化石,由于其良好的生油特性,被认为是我国白垩纪—第三纪陆相油气资源的重要来源。柴达木盆地第三系始新统下干柴沟组是该地区最主要的烃源岩,生油岩及原油中富含公认的沟鞭藻生物标志物4 甲基甾烷和甲藻甾烷,但迄今该地区尚未发现可靠的沟鞭藻化石。本次研究在柴达木盆地北缘昆2井下干柴沟组发现了类型单调但化石丰富的以Subtilisphaera为主的沟鞭藻化石组合,为肯定柴达木盆地第三系原油沟鞭藻的贡献提供了直接化石证据。研究表明,沟鞭藻发育的第三系中始新统可能是本地区最有利的生油层,形成于湿热气候所控制的陆相咸水湖泊。     

青藏高原多年冻土沉积物中埋藏植物DNA特征的初步分析

多年冻土沉积物长期处于负温及封闭条件下,使得其中埋藏植物材料得到较好的保存,成为获取古DNA分子的理想材料.采用常规的CTAB法提取多年冻土中埋藏植物材料的DNA,并用琼脂糖凝胶凝胶电泳检测.结果表明,从多年冻土埋藏植物材料中可以提出DNA,而且所提出的DNA不仅具有降解的小分子量DNA分子,而且还有大分子量DNA.提取的埋藏植物材料的DNA多呈棕褐色,指示了在埋藏过程可能发生一定的聚合.电泳结果表明,随埋藏时间的增加(深度增加),埋藏植物材料中DNA含量呈下降趋势.由于埋藏植物材料在不同时代的多年冻土中均有发现,其DNA分子的提取为深入研究其特征所带遗传信息,重现植物大分子物质在地质历史中的演化提供了可能。     

A note on rare structure of fossil coralline algae from the southwest coast of India

The coralline algae (Rhodophyta) are well preserved in the sediments of the Dwarka Formation in and around Porbandar area, southwest coast of India. There are few records of the preservation of genicula in the fossil coralline algae. Three algal fragments with genicula are noted and recorded from the area.     

Tectonic and climate driven fluctuations in the stratigraphic base level of a Cenozoic continental coal basin,northwestern Andes

Changes in the sedimentologic and stratigraphic characteristics of the coal-bearing middle Oligocene–late Miocene siliciclastic Amagá Formation, northwestern Colombia, reflect major fluctuations in the stratigraphic base level within the Amagá Basin, which paralleled three major stages of evolution of the middle Cenozoic Andean Orogeny. These stages, which are also traceable by the changes in the compositional modes of sandstones, controlled the occurrence of important coal deposits. The initial stage of evolution of the Amagá Basin was related to the initial uplift of the Central Cordillera of Colombia around 25 Ma, which promoted moderate subsidence rates and high rates of sediment supply into the basin. This allowed the development of aggradational braided rivers and widespread channel amalgamation resulting in poor preservation of both, low energy facies and geomorphic elements. The presence of poorly preserved Alfisols within the scarce flood plains and the absence of swamp deposits suggest arid climate during this stage. The compositional modes of sandstones suggest sediment supply from uplifted basement-cored blocks. The second stage of evolution was related to the late Oligocene eastward migration of the Pre-Andean tholeitic magmatic arc from the Western Cordillera towards the Cauca depression. This generated extensional movements along the Amagá Basin, enhancing the subsidence and increasing the accommodation space along the basin. As a result of the enhanced subsidence rates, meandering rivers developed, allowing the formation of extensive swamps deposits (currently coal beds). The excellent preservation of Entisols and Alfisols within the flood plain deposits suggests rapid channels migration and a humid climate during deposition. Moderate to highly mature channel sandstones support this contention, and point out the Central Cordillera of Colombia as the main source of sediment. Enhanced subsidence during this stage also prevented channels amalgamation and promoted both, high preservation of geomorphic elements and high diversity of sedimentary facies. This resulted in the most symmetric stratigraphic cycles of the entire Amagá Formation. The final stage of evolution of the Amagá Basin was related to the early stage of development of the late Miocene northwestern Andes tholeitic volcanism (from ∼10 to ∼8 Ma). The extensive thrusting and folding associated to this volcanism reduced the subsidence rates along the basin and thus the accommodation space. This permitted the development of highly aggradational braided rivers and promoted channels amalgamation. Little preservation of low energy facies, poor preservation of the geomorphic elements and a complete obliteration of important swamp deposits (coal beds) within the basin are reflected by the most asymmetric stratigraphic cycles of the whole formation. The presence of greenish/reddish flood plain deposits and Alfisols suggests a dry climate during this depositional stage. The presence of channel sandstones with high contents of volcanic rock fragments supports a dry climate, and suggests an incipient phase of the Combia tholeiitic magmatism present during deposition of the Amagá Formation. The subsequent eastward migration of the NW Andes magmatic arc (after ∼8 Ma) may have produced basin inversion and suppressed deposition along the Amagá Basin.     

Remarkable preservation of microbial mats in Neoproterozoic siliciclastic settings: Implications for Ediacaran taphonomic models

It is beyond doubt that the appearance of infaunal bioturbation and metazoan biomineralization across the Ediacaran–Cambrian transition irreversibly affected the nature of marine sediment architecture and biogeochemistry. Here we review those changes in relation to their likely effect upon the processes of fossil preservation, especially within siliciclastic sediments. Processes of soft-tissue preservation in siliciclastic settings from the Ediacaran Period, including microbes and microbial mats as well as Ediacaran macrofossils, are here reviewed within this context. Highlighted examples include the exceptional preservation of microbes found in association with wrinkle structures and Ediacaran macrofossils in England and Newfoundland (replicated by silicate minerals) and in the White Sea region of Russia (replicated by iron sulphide). These occurrences show that soft-tissue preservation in siliciclastic settings went well beyond that typical for Ediacaran macrofossils alone and also extended to similar modes of preservation in associated microbes. Using these new observations it can be argued that several existing explanations for Ediacaran fossil preservation can be united within a biogeochemical model that involves evolution of the sediment mixed layer across this transition.     

Carotenoid diagenesis in recent marine sediments—I. The Peru continental shelf (15°S, 75°W)

We report here the distribution of carotenoids in Peru marine surface sediments, including partial identification of 37 pigments, 33 of which have not been previously reported to occur in marine sediments. Our analysis demonstrates that zooplanktonic crustacea, diatoms, dinoflagellates, cryptomonads, purple nonsulfur photosynthetic bacteria, and unidentified species of photosynthetic bacteria are contributors to sedimentary organic matter. Fucoxanthin, fucoxanthinol, diadinoxanthin, peridinin and peridininol, the principal carotenoids of diatoms and dinoflagellates observed in sediment traps, are nearly absent from our sample, even though these phytoplankton are the primary source of organic matter. We attribute this to the presence of 5,6 epoxides in these pigments, a feature which causes rapid cleavage of the polyene and fragmentation to low molecular weight compounds.     

Fossil pigments as a guide to the paleolimnology of Browns Lake, Ohio

Some aspects of the paleolimnology of Browns Lake, Ohio, have been ascertained by a study of preserved sedimentary plant pigments and conductivity of interstitial water. Temporal changes in the sedimentary environment, especially redox conditions, along with changes in the flora of the lake and the development of peat in the basin have brought about differential sedimentation and preservation of pigments. Measurement of changes in total and relative concentration and diversity of chlorophyll derivatives and carotenoids has provided important clues to late-glacial and postglacial evolution of the lake. Laminated sediments, rich in fossil remains, near the base of the core indicate eutrophic conditions and meromixis for several thousand years beginning shortly after lake inception. As meromixis broke down, the lake evolved gradually to holomictic conditions when sapropel was deposited. An advancing complex of reed swamp and fen forest began during midpostglacial time, providing ever-increasing amounts of highly organic, peaty sediments and continues to the present. The pond is now dystrophic, and increasing deposition of inorganic sediment is apparent at the top of the core, concomitant with land clearance and agriculture. In the same interval, an increase of water conductivity reflects recent agricultural practices and industrialization in the region.     

Tectonic and climate driven fluctuations in the stratigraphic base level of a Cenozoic continental coal basin, northwestern Andes

Changes in the sedimentologic and stratigraphic characteristics of the coal-bearing middle Oligocene–late Miocene siliciclastic Amagá Formation, northwestern Colombia, reflect major fluctuations in the stratigraphic base level within the Amagá Basin, which paralleled three major stages of evolution of the middle Cenozoic Andean Orogeny. These stages, which are also traceable by the changes in the compositional modes of sandstones, controlled the occurrence of important coal deposits. The initial stage of evolution of the Amagá Basin was related to the initial uplift of the Central Cordillera of Colombia around 25 Ma, which promoted moderate subsidence rates and high rates of sediment supply into the basin. This allowed the development of aggradational braided rivers and widespread channel amalgamation resulting in poor preservation of both, low energy facies and geomorphic elements. The presence of poorly preserved Alfisols within the scarce flood plains and the absence of swamp deposits suggest arid climate during this stage. The compositional modes of sandstones suggest sediment supply from uplifted basement-cored blocks. The second stage of evolution was related to the late Oligocene eastward migration of the Pre-Andean tholeitic magmatic arc from the Western Cordillera towards the Cauca depression. This generated extensional movements along the Amagá Basin, enhancing the subsidence and increasing the accommodation space along the basin. As a result of the enhanced subsidence rates, meandering rivers developed, allowing the formation of extensive swamps deposits (currently coal beds). The excellent preservation of Entisols and Alfisols within the flood plain deposits suggests rapid channels migration and a humid climate during deposition. Moderate to highly mature channel sandstones support this contention, and point out the Central Cordillera of Colombia as the main source of sediment. Enhanced subsidence during this stage also prevented channels amalgamation and promoted both, high preservation of geomorphic elements and high diversity of sedimentary facies. This resulted in the most symmetric stratigraphic cycles of the entire Amagá Formation. The final stage of evolution of the Amagá Basin was related to the early stage of development of the late Miocene northwestern Andes tholeitic volcanism (from 10 to 8 Ma). The extensive thrusting and folding associated to this volcanism reduced the subsidence rates along the basin and thus the accommodation space. This permitted the development of highly aggradational braided rivers and promoted channels amalgamation. Little preservation of low energy facies, poor preservation of the geomorphic elements and a complete obliteration of important swamp deposits (coal beds) within the basin are reflected by the most asymmetric stratigraphic cycles of the whole formation. The presence of greenish/reddish flood plain deposits and Alfisols suggests a dry climate during this depositional stage. The presence of channel sandstones with high contents of volcanic rock fragments supports a dry climate, and suggests an incipient phase of the Combia tholeiitic magmatism present during deposition of the Amagá Formation. The subsequent eastward migration of the NW Andes magmatic arc (after 8 Ma) may have produced basin inversion and suppressed deposition along the Amagá Basin.     

Trilobites,scolecodonts and fish remains occurrence and the depositional paleoenvironment of the upper Monte Alegre and lower Itaituba formations,Lower – Middle Pennsylvanian of the Amazonas Basin,Brazil

This study aims to characterize the scolecodonts, trilobite pygidium fragments and fish remains of an outcropped region in the southern Amazonas Basin, comprising the uppermost section of the Monte Alegre Formation and the basal section of the Itaituba Formation. These, correspond to part of the marine portion of the Tapajós Group, related to an intracratonic carbonate platform. The Monte Alegre Formation includes a deposition of fluvial-deltaic and aeolian sandstones, siltstones and shales of interdunes and lakes, intercalated with transgressive carbonates of a shallow restrict nearshore marine environment. The Itaituba Formation comprises a thickest deposit of marine carbonates, representing the establishment of widespread marine conditions, and is the richest interval containing organisms of shallow marine environment in the Pennsylvanian of the Amazonas Basin. The associated fauna includes brachiopods, bivalves, gastropods, crinoids, echinoids, bryozoans, corals, foraminifers, sponges, ostracods, trilobites, scolecodonts, fish remains and conodonts, mainly in the packstones, and subordinately in the wackestones and mudstones. Conodonts Neognathodus atokaensis, Diplognathodus orphanus, Idiognathodus incurvus, and foraminifers Millerella extensa, Millerella pressa, Millerella marblensis, Eostaffella ampla, Eostaffella pinguis and Eostaffella advena characterizes a predominant Atokan age to the analyzed profile. The fossil association herein presented is taxonomically diversified and biologically interesting, comprising an important and well preserved, for the first time occurrence of two molds and two fragments of Proetida trilobites. Well preserved Eunicida and Phyllodocida scolecodonts and paleonisciform fish remains. These fossils help in the paleoenvironmental establishment of the studied interval in the Amazonas Basin and as a potential biostratigraphic and paleoecological tool to correlate regionally and globally the Pennsylvanian.     

华东白垩纪鸭嘴龙类恐龙蛋化石的发现

浙江天台白垩纪地层中最常见的蛋化石类型之一是赤城山组地层（锆石U-Pb法同位素年龄约92Ma）的树枝树枝蛋（Dendroolithus dendriticus）。对比河南西峡含恐龙胚胎的蛋化石,确定其为鸭嘴龙类（Hadrosaurs）恐龙所产。鸭嘴龙类恐龙在系统分类上归鸟脚亚目（Ornithopoda Marsh,1881）鸭嘴龙超科（Hadrosauroidea Cope,1869）鸭嘴龙科（Hadrosauridae Cope,1869）,建议树枝蛋化石也相应归入圆形蛋化石亚目（Spheroolithineae账oosubord．nov．）树枝蛋化石超科（Dendroolithoidea oosuperfam．nov．）树枝蛋化石科（Dendroolithidae Zhaoand Li 1988）,以便对应研究。从已知的鸭嘴龙类恐龙产蛋尺寸推算,浙江天台的树枝树枝蛋（Dendroolithus dendriticus）为身长不超过7m的恐龙所产,个体大小类似东北一蒙古发现的萨哈林日本龙（Nipponosaurus sachaIinensis）、李氏黑龙江龙（Amurosaurus riabinini）和姜氏巴克龙（Bactrosaurus johnsoni）。该蛋在巢穴里,无序放置,至少3层,常超过20枚,蛋壳具韧性,重力作用下呈扁球形。     

Exceptional fidelity of preservation in a reworked fossil,Chalk drift,South London,England

Reworking of fossils commonly leads to loss of morphological detail and inferior preservation; the main contributions of such specimens to geology are in sedimentology, regional geology and neoichnology. A reworked specimen of the Late Cretaceous (chalk) sponge boring Entobia cretacea Portlock is unusually well preserved. This specimen is from superficial deposits and is well enough preserved that delicate apertural and intercameral canals are apparent. Two factors are recognized as important in maintaining the fine features of this trace fossil: preservation in flint and, presumably, minimal fluvial transport. Copyright © 2013 John Wiley & Sons, Ltd.     

Exceptionally preserved fossil assemblages through geologic time and space

Geologic deposits containing fossils with remains of non-biomineralized tissues (i.e. Konservat-Lagerstätten) provide key insights into ancient organisms and ecosystems. Such deposits are not evenly distributed through geologic time or space, suggesting that global phenomena play a key role in exceptional fossil preservation. Nonetheless, establishing the influence of global phenomena requires documenting temporal and spatial trends in occurrences of exceptionally preserved fossil assemblages. To this end, we compiled and analyzed a dataset of 694 globally distributed exceptional fossil assemblages spanning the history of complex eukaryotic life (~ 610 to 3 Ma). Our analyses demonstrate that assemblages with similar ages and depositional settings commonly occur in clusters, each signifying an ancient geographic region (up to hundreds of kilometers in scale), which repeatedly developed conditions conducive to soft tissue preservation. Using a novel hierarchical clustering approach, we show that these clusters decrease in number and shift from open marine to transitional and non-marine settings across the Cambrian-Ordovician interval. Conditions conducive to exceptional preservation declined worldwide during the early Paleozoic in response to transformations of near-surface environments that promoted degradation of tissues and curbed authigenic mineralization potential. We propose a holistic explanation relating these environmental transitions to ocean oxygenation and bioturbation, which affected virtually all taphonomic pathways, in addition to changes in seawater chemistry that disproportionately affected processes of soft tissue conservation. After these transitions, exceptional preservation rarely occurred in open marine settings, excepting times of widespread oceanic anoxia, when low oxygen levels set the stage. With these patterns, non-marine cluster count is correlated with non-marine rock quantity, and generally decreases with age. This result suggests that geologic processes, which progressively destroy terrestrial rocks over time, limit sampling of non-marine deposits on a global scale. Future efforts should aim to assess the impacts of such phenomena on evolutionary and ecological patterns in the fossil record.     

Petroleum surface oil seeps from a Palaeoproterozoic petrified giant oilfield

Early Palaeoproterozoic rocks from the Onega Basin in Russian Fennoscandia contain evidence for substantial accumulation and preservation of organic matter (up to 75 wt% total organic carbon) with an estimated original petroleum potential comparable to a modern supergiant oilfield. The basin contains a uniquely preserved petrified oilfield including evidence of oil traps and oil migration pathways. Here, we report the discovery of the surface expression of a migration pathway, along which petroleum was flowing from the sub-surface. This surface oil seep, the first occurrence ever reported from the Palaeoproterozoic, appears as original bitumen clasts redeposited in Palaeoproterozoic lacustrine turbidites. The δ¹³C_org of clastic pyrobitumen ranges between −35.4 and −36.0‰ ( n  = 14), which is within the range of interbed- and vein-trapped fossil oil (−46 and −24‰), suggesting similar source. Biogenic organic matter, whose isotopic composition was modified during thermal maturation, is the likely source for the migrated hydrocarbon.     

Diminutive trace fossils in the Chengjiang Lagerstätte

Diminutive trace fossils described here have been well preserved in connection with certain pliable carapaces or skeletons of the Chengjiang animals. Taphonomic evidence suggests that these traces were formed in situ. The peculiar preservation indicates that some bilaterians of uncertain affinities seem to have been active at the burial site, constituting an important group of the hidden majority of Cambrian marine community. This may be an essential feature closely associated with the palaeoecology and exceptional preservation of the Cambrian fossil Lagerstätten. The rare preservation of such millimetre‐sized trace fossils raises further doubts about the timing of the initial benthic bilaterians by applying trace fossil evidence.     

Seasonal to sub-seasonal palaeoenvironmental changes in Lake Sihetun (Lower Cretaceous Yixian Formation, NE China)

Sedimentary properties of the fossil-bearing deposits of Lake Sihetun (Yixian Formation, Lower Cretaceous) were investigated on a high-resolution, sub-millimetric scale. Data were obtained from three excavations and 50 thin-sections. Lake evolution is subdivided into four phases, of which Phases 2 and 3 provided suitable conditions for excellent fossil preservation. Six microfacies are recognized within these two phases: (1) allochthonous, siliciclastic laminae (26.1 μm thick on average), (2) chrysophycean cyst accumulations, (3) tuffaceous silt, (4) lacustrine chemical precipitates, (5) tuff and (6) normal-graded, sandy to silty siliciclastics. Phase 2 is characterized by Microfacies 1–5 and Phase 3 by Microfacies 6. Biofilms are common, and mass occurrences of framboids (pyrite pseudomorphs) are occurring in sediments of Phase 2. Varves can be verified for Microfacies 2 and 4 (179 μm thick). Thicknesses of Microfacies 2 highly fluctuate depending on the occurrence of seasonal heavier rains, which led to deposition of tuffaceous silt layers (Microfacies 3). Meromictic conditions dominated Phase 2, but recurrent mixing is demonstrated by short-lived colonization events by a benthic invertebrate fauna. The transition of Phase 2 to holomictic Phase 3 is marked by a dramatic increase in sediment yield associated with a change from dry to humid climates. Fossil preservation differs according to the diverse physical and chemical conditions during lake evolution. Phase 2 yields framboid replacement of organic tissue and excellent preservation of growth increments of clam-shrimp carapaces, which are poorly preserved in Phase 3. Conversely, though exhibiting a different mode of preservation, insect fossils are superbly preserved as dark stains sealed by silica coatings during Phase 3.     

Functional groups of fossil marattialeans: chemotaxonomic implications for Pennsylvanian tree ferns and pteridophylls

Marattialean-fossil foliage, assigned to Pecopteris Brongniart, was an important and widespread floral component in Late Pennsylvanian mires, with phylogenetic affinity to extant marattialean taxa in tropical regions. Marattialean fossil taxonomy is, however, still uncertain. Specimens from the Pilsen limnic Basin, Westphalian D, Czech Republic, represent fertile marattialean foliage of Pecopteris (Asterotheca) nyranensis and Pecopteris (Asterotheca) miltonii, and sterile foliage of Pecopteris aspidioides and Pecopteris polypodioides. Taxonomic parameters for their assignments included cuticle, stomatal morphologies (studied for the first time), and in situ reproductive organs and spores. Chemotaxonomic interpretations hinge on fidelity of preservation of compounds, or molecular fragments thereof, that were synthesized by the once-living plants. This preservation state was possibly due to the thermal history (maximum temperature of 130 °C) in the Pilsen Basin, acidic preservation conditions, lithology and facies stability.Although subtle, the four pecopterid species are differentiable from one another by combined FTIR characteristics, supporting taxonomy. The ratio of CH₂/CH₃ is hypothesized to be a chemotaxonomic parameter for Pennsylvanian pteridophylls, both in seed and true ferns that have previously been studied. It will, however, be supplemented by additional biochemical markers.     

Microbial mat structures in profile: The Neoproterozoic Sonia Sandstone,Rajasthan, India

Ubiquitous microorganisms, especially cyanobacteria preferably grow on the sediment surface thereby producing microbial mats. In the absence of grazers and bioturbators, microbial mat is a unique feature of the Proterozoic. Most of the papers so far published described a wide variety of bed surface microbial mat structures with rare illustrations from sections perpendicular to bedding. Nonetheless, bed surface exposures are relatively rare in rock records. This limitation of bed surface exposures in rock records suggest that a study of microbial mats in bed-across sections is needed. The 60 m thick coastal marine interval of the Sonia Sandstone Formation is bounded between two terrestrial intervals, a transgressive lag at the base and an unconformity at the top, and has been chosen for exploration of microbial mat structures in bed-across sections. A wide variety of microbial mat-induced structures in bed-across sections are preserved within the coastal interval of the Sonia Sandstone. Though many of these structures are similar in some aspects with bed surface structures, some of those presented here are new. The palaeogeographic range of these microbial structures extends from supralittoral to neritic. Diagenetic alterations of microbial mats produce pyrite and those zones are suitable for the preservation of microbial remains. SEM and EDAX analyses show fossil preservation of filamentous microbial remains that confirm the presence of microbial mats within the coastal interval of the Sonia Sandstone. Effects of proliferation of microbial mats in the siliciclastic depositional setting are numerous. The mat-cover on sediment surfaces hinders reworking and/or erosion of the sediments thereby increases the net sedimentation rate. Successive deposition and preservation of thick microbial mat layer under reducing environments should have a great potential for hydrocarbon production and preservation and therefore these Proterozoic formations could be a target for exploration.     

比较埋藏学与埋藏相及其环境意义简介及评述

在地层中,各种生物的骨骼具有多种埋藏类型,因而据此可很好地了解骨骼所处位置的沉积环境.Speyer和Brett(1988)用化石保存特征及类型,即骨骼的搬运,解体、破碎及侵蚀,建立了七个晚元古代化石埋藏相.由于本学说诞生不久,所以还有许多必须进一步完善之处:1.埋藏相仅是大陆架沉积边缘环境中化石保存类型的简化模式,而在地质历史中,具有众多的不同沉积环境,不仅有沉积边缘,而且还有陡斜坡跌积边缘.如分布于华南晚古生代的跌积边缘就不适于Speyer等的埋藏相理论.2.怎样建立适用于浊流沉积、风暴沉积及淡水河湖沉积环境的埋藏相.淡水沉积环境与海洋沉积环境十分不同,因而淡水沉积环境的化石保存特征也具有不同于海洋沉积环境的特征.     

Systematic and taphonomic insights of fossilized feathers: A new occurrence from the Oligocene of Taubaté Basin (SE,Brazil)

Feathers are rare in the fossil record because they have a low fossilization potential. Despite their palaeobiological significance, they also provide important palaeoecological and taphonomic information. Here, we report a new occurrence of three isolated feathers from the shales of the Oligocene Tremembé Formation (Taubaté Basin, SE Brazil). Their possible taxonomic affinities and taphonomic features are also discussed. Analyses identified the specimens as representatives of two pennaceous morphotypes (i.e., a contour and a rectrice feather). Both are preserved as carbonized traces, although, due taphonomic processes, they show different degrees of preservation. Since the Tremembé Formation is responsible for the most diverse record of Cenozoic birds, and because water-adapted birds (e.g., anseriformes and phoenicopteriformes) occur in this unit, it is highly possible that these feathers belonged to these aquatic taxa. Further investigations should concentrate on geochemical and microscopic techniques in order to reveal additional taxonomic and paleoecological features currently unknown in Paleogene birds of Brazil.