Reworked Devonian (Givetian-Frasnian) spores from a Permian glacially-derived sequence at Bacchus Marsh, Victoria

Emphanisporites rotatus McGregor emend. McGregor 1973 is a distinctive Devonian spore with a known primary source age range in Australia spanning the upper Givetian to early Frasnian (Middle to Late Devonian). This is the first record of the species from Victoria. It occurs as a reworked element in an Early Permian assemblage belonging to the Granularisporites confluens Zone derived from glacigene diamictite in the Bacchus Marsh area. As the predominant direction of Permian ice movement recorded in the Bacchus Marsh district was south-west to north-east, it is possible that the reworked spores were transported from Antarctica.

Magnetic susceptibility dataset from the early Givetian to early Frasnian in the La Thure section

Recent advances in radiometric dating result in significant improvements in the geological timescale and provide better insight into the timing of various processes and evolutions within the Earth's system. However, no radiometric ages are contained within the Givetian. Consequently, the absolute ages of the Givetian Stage boundaries, as well as the stage's duration, remain poorly constrained. As an alternative, the analysis of sedimentary cycles allows for the estimation of the duration of this stage. We examined the high-resolution magnetic susceptibility signals of four Givetian outcrops in the Givet area for a possible astronomical imprint, to fully understand the rates of evolutionary and environmental change. All four sections are firmly correlated and wavelet analyses of the magnetic susceptibility signals reveal the imprint of astronomical eccentricity forcing. The highly stable 405 kyr cycles constrain the duration of the Givetian Stage at 4.35±0.45 Myr, which is in good agreement with the International Chronostratigraphic Chart (5.0 Myr). The studied sections also exhibit an imprint of obliquity, suggesting a climatic teleconnection between low and high latitudes. The corresponding microfacies curves demonstrate similar astronomical imprint, and thereby indicate that the observed 10**5 year-scale cyclicity is the result of climatic and environmental change.

A late Devonian (Frasnian) microbiota from the Farewell-Lyman Hills area, west-central Alaska /

Mode of access: Internet.

华南泥盆纪植物原蕨属的发现和原真蕨亚纲的研究

本文详细研究在我国华南泥盆系地层中发现的一种新的原真蕨植物—原蕨属（新属）propterophyton gen. nov.并详细探讨原真蕨植物的分类问题。 原真蕨植物在早期陆地维管植物系统发育中占有十分重要的地位。它是处于原始的裸蕨植物和进步的真蕨植物之间的一种过渡类型，兼具这两类植物的主要特征。 原始蕨植物的研究已有几十年的历史。但往往由于化石材料的奇缺和破碎，限制人们对它的正确认识，因而研究工作的进展一直十分缓慢。近二十多年来，一方面随着原裸子植物的确认和原裸子植物纲（progymospermopsida）的建立，一些所谓的原真蕨植物经研究后被转移到这个新钢里。另一方面，特别是近十年来，世界各国尤其是欧美的古植物学家对新发现的不少珍贵的原真蕨植物化石进行了深入研究，而使人们对这类灭绝植物的认识得以深化，并就它的分类问题，古植物学家不断提出新的见解。 在我国首次发现的原蕨属的标本十分丰富，保存完整。经过深入细致的研究，使我们对这种植物的外部形态和内部结构有了较全面的认识。并由此涉及到对整个原真蕨植物的认识得以进一步的完善，从而提出一个有关原真蕨植物的新概念。在此研究的基础上，综合国际植物学界人士近二十多年来对原真蕨植物研究的资料，本文拟把原真蕨植物归入原真蕨亚纲（primofilices）置于真蕨纲（Filicopsida）之下，与真蕨亚纲（Filices）并列。 大部分原蕨属的标本采自湖北省汉阳县米粮山采石场。化石层位于上泥盆统珞珈山群的下部，距该群底界与下伏中志留统地层之间的假整合面大约有9米。该层为—巨大的粘土岩透镜体，夹在厚至巨厚层的石英砂岩中。依据分散孢子组合的资料，这种植物的地质时代不会晚于晚泥盆世早期，即弗拉斯期（Frasnian）。另有一部分标本则采自湖南市长沙县跳马涧。其时代大约是中泥盆世晚期，即吉维特期（Givetian）。 原蕨属的化石主要保存为炭化的压型标本，部分黄铁矿化。这些标本经过精心修整，采用多种技术处理，并运用扫描电子显微镜观察，显示出了这种植物主要的外部形态和内部组织的特性。 泥盆原蕨（proptrophyton devonicum sp. Nov.）由根状茎、蕨叶和不定根三部分组成。根状茎横生地下，以细而少分枝的不定根固着于土壤中。蕨叶中仅有一枚直接由根状茎顶部生出，余为侧生，以螺旋排列为主。蕨叶由三次羽状分枝的枝系组成，单轴，不具叶片。成对的羽片在叶轴两侧互生。小羽片也以同样的方式成对互生在羽轴两侧。从而形成一种立体生长的四列式蕨叶。小羽片多为六次等二岐式分枝，没有蹼化。生殖小羽片顶部生出成对孢子囊。估计每枚小羽片上可以生长六十四个孢子囊。幼小的孢子囊圆至纺锤形，下垂。成熟的孢子囊弯眉形，直立。两个孢子囊在小羽片顶部排列成山羊角状。四个孢子囊成两对着生，形成一束。孢子囊沿囊壁内面纵裂，不具环带。孢子同型，具三裂缝。蕨叶具轴有两侧对称的维管结构：两个椭圆柱状的维管束在一侧相连，形成一个v字型结构。在维管束的另一侧具有原生木质部腔（lacuna）。后生木质部管胞放射状相连，具有梯形，椭圆形至圆形的具缘纹孔。成对的小羽片迹由两个维管束不相连的一侧交互产生。皮层分为具薄壁组织的外层和具后角组织的内层。表皮上的气孔器很小，散生，气孔与轴行，无副卫细胞。 泥盆原蕨的蕨叶由不具叶片的枝系组成，立体方式生长。小羽片等二岐式分枝。根状茎顶部直接生长一枚蕨叶。孢子囊定生，纵向开裂。这些属于裸蕨植物的原始性状，明显地不同于真蕨植物。但根、茎、叶的初步分化、蕨叶的单轴生长和羽片在叶轴两侧排列以及与之相对应的蕨叶轴内两侧对称的维管结构，表明泥盆原蕨已部分发展到真蕨植物的水平。由此可见，原蕨属即具有裸蕨植物的原始性状，又具有真蕨植物的进步性状，属于一种典型的原真蕨植物。 综合原蕨属及其它原真蕨植物如指蕨属（pseudosporochnus）,羽裂蕨属（Rhacophyton）和十字蕨属（Stauropteris）的特征，归纳出原真蕨植物的孢子体具有以下主要性状：（1）植物体由茎、蕨叶和不定根组成。（2）茎直立或匍伏生长，具放射状对称的内部结构。（3）不定根自茎生出，有的也从叶柄或叶轴生出。（4）蕨叶由完整的羽状分枝的枝系组成。由此形成的蕨叶与枝系在形态上的差异不甚明显。（5）蕨叶单轴式生长，一次多次羽状，呈背腹状或至少叶轴具备背腹性。（6）羽片和小羽片成对的或单个的侧生在轴两侧，形成立体或平面生长的蕨叶。（7）小羽片等二岐式分枝，不具叶片。（8）叶轴和羽轴具两侧对称的，中始式的维管结构。（9）孢子囊远端位着生，无环带，具简单的开裂机制。(10)孢子多为同形，稀有大小两种。简言之，原真蕨植物是一类蕨叶由羽状枝系组成，不具叶片和孢子囊不具环带的原始的真蕨植物。 这种原真蕨植物的新概念为原真蕨植物的分类和蕨叶的起源提供新的解释。 裸蕨植物与原真蕨植物的主要区别，在于后者已经出现根、茎、叶的初步分化，在系统发育中达到一个新的演化水平。但是，原真蕨植物的蕨叶仅由枝系组成，还没有形成叶片，孢子囊叶不具环带，这些特征在系统发育中又低于真蕨植物所达到的一般水平。因此，有无蕨叶叶片和孢子囊有无环带作为区分原真蕨植物和真蕨植物的主要标志。原真蕨植物应以蕨叶未形成叶片和孢子囊不具环带为特征。而真蕨植物则至少应以有叶片的蕨叶或孢子囊具环带为特征。 原真蕨植物，原裸子植物和原始楔叶植物都起源于裸蕨植物，是共同生活在泥盆，演化水平彼此接近的三大分类群。它们之间的区别主要在于叶器官和生殖器官的不同。这里又涉及到蕨叶起源的问题。 历史人们认为蕨叶（复合叶）起源于一个等二岐式分枝的侧枝。但根据已发现的化石资料，特别是原蕨属所表现的性状，蕨叶可能直接起源于具有完整的至少一次羽状分枝枝系的植物。枝系的扁化和蹼化则发生在以后的演化过程中，逐步形成具叶片的枝状复合蕨叶。而仅仅由一个等二岐式分枝的侧枝起源的叶则应归属于简单的枝状叶。本文所讨论的原裸蕨子植物和原始楔叶植物的叶，就是在茎上螺旋排列或轮生的单叶。在蕨叶中，只有小羽片才是由等二岐式分枝的侧枝起源，排列在羽轴两侧。因此，在系统发育中，原裸子植物和原始楔叶植物的茎及其着生的单叶与原真蕨植物的复合蕨叶是同源的。而单叶则与小羽片同源。 根据上述对原真蕨植物的概念和蕨叶及单叶起源的观点，结合化石植物形态学和解剖学两方面的性状，特别是以生殖器官的性状作为分类的依据，纵观几十年来原真蕨植物的分类，大致经历了三个时期。 第一个阶段于本世纪六十年代以前。这个时期的原真蕨植物的分类，受材料限制，研究的程度不够深入，基本上仅以解剖性状作为分类的主要依据。这一时期归属原真蕨植物的“蕨状植物”包括原始蕨类（protopterids）,枝木类（cladoxylaeans）和合生蕨类（coenopterids）这实际上是一个庞杂的类群，包括了后来分出的原裸子植物，原始楔叶植物以及真蕨植物。 第三个阶段从六十年代至七十年代末。由于美国 C. B. Beck博士的重大发现和深入研究的结果，不仅确立了原裸子植物是一类处于裸蕨植物和裸子植物之间的过渡类型，而且为古植物学的研究提供了很好的范例。即化石植物的正确分类也必须依据形态学和解剖学两方面的证据。生活在中泥盆世至晚泥盆世的原裸子植物既有原始维管植物自由孢子生殖的特征，又具有裸子植物木材的组织特征，即次生木质部的管胞具有典型的松柏类的圆形具缘纹孔。一些所谓的“蕨状植物”经过细致地研究被证实应属于原裸子植物，从而被转移到原裸子植物纲内。 六十年代中期，比利时古植物学家 S. Leclercq 和西德古植物学家H. J. Schweitzer 发现芦形木（Cala-mophyton）的维管结构为枝木形。因而将原来归属于原始楔叶植物叉叶目（Hyeniales）的芦形木和叉叶（Hyenia）转移到枝木目中，作为蕨状植物看待。对此，国际古植物学界尚有不同的看法。主要是由于这两种植物的生殖器官业已分化为原始的孢子囊梗，而且单叶的排列也由螺旋着生演化到假轮生的水平。 在此期间，合生蕨植物的自然分类的问题日趋被人重视。 第三个阶段开始于本世纪八十年代。这个时期有关原真蕨植物分类的核心问题。是如何确定芦形木等属的正确的分类位置和如何对合生蕨植物进行更接近于自然的分类。 枝木目(Cladoxylales）目1 9 2 7年建立以来，主要包含了一些生活在早石炭世的植物。这些植物的轴具有多维管束的组织结构。而植物体的整体形态不详。归入此目的有具枝木型维管结构的中泥盆植物指蕨，帚枝木(Cladoxylon scoparium )和芦形木都显示出相似的掌状分枝的外形．但是指蕨的叶为羽状蕨叶，小羽片两侧排列，孢子囊纺锤形，成对顶生，纵向开裂。而帚枝木和芦形术的叶为螺旋排列在茎上的单叶。芦形木的孢子囊已形成了雏形孢囊梗。帚枝木的生殖器官最初被认为是扇状深裂叶具边缘着生的孢子囊。但是1 9 8 0年Scheitger 和Giestn重新研究后，发现它的生殖结构类似芦形木，为原始的孢子囊梗。帚枝木，芦形木和叉叶的单叶与原其蕨植物的蕨叶不仅形态上截然不问，而且在排列上已趋向于轮生。与此同时，孢子囊梗已初步形成。这些性状表明这些植物与楔叶植物有密切的亲缘关系。本文不仅赞同J．E．Skog 及L. P. Banks （1973年）和W．N. Stevart （1983年）将芦形木和叉叶仍归回原始楔叶植物叉叶目，而且将蒂枝木也归入同—个目内。另外，指蕨属根据蕨叶和孢子囊的性状应属于原真蕨植物。到此为止，枝木目（狭义的）只包括具有多维管束的硅化轴的器官属，其分类位置不明。 合生蕨目（Coenopteridales)历来被认为是原真蕨植物的主要代表。过去对这类植物的认识主要建立在解剖材料上，特别是依据叶轴维管结构的形态。在某种程度上，这个目也是一个庞杂的类群。随着合生蕨的生殖结构的不断发现，人们对这类植物的分类，逐渐转移到以孢子囊的性状作为主要的分类依据。本文赞同根据孢子囊的结构，特别是依据环带的形态结构，把该目中的五个科Botryoptoridaceae, Anacboropteridaceae,　Sermaytaceae, Tedeleacoae 和 Psallxochlaenacoae转移到真蕨亚纲的真蕨目(Filicales ）内。另外本文还对比了该目中的孪生蕨科（Zygopteridaceae )的几个属的囊群，孢子囊及环带的性状与莲座目(Marattiales )中莲座科的一个化石属和一个现代属（Angiopteris ）的生殖器官的性状。根据它们之间的相似程度，建议将孪生蕨科移至莲座目。Iridopterids曾被认为是合生蕨植物。根据新的研究资料， lridopterids 与原始楔叶植物的关系比与其它植物的关系更为密切。合生蕨植物中的羽裂蕨属和十字蕨属因蕨叶不具叶片和孢子囊不具环带，似应归入原真蕨亚纲，置于各目的目下。至此为止，合生蕨植物分别归属不同类群而使该目趋于解体。 原真蕨亚纲包括四个目(指蕨目Pseudosporochnales，原蕨目Propterophytales，羽裂蕨目Rhacophytales，十字蕨目Stauropteridales)六个属( Pseudosporochrmus, Propterophyton, Rhacophyton，Protocaphalopteris, Chlidanophyton, Stauropteris) 代表两条演化路线。指蕨目独自代表一条路线。蕨叶为两度空间生长的二列式蕨叶，即单个羽片侧生在叶轴上，与现代蕨叶相似。但与现代真蕨植物之间的演化关系不详。原厥目，羽裂蕨目和十字蕨目代表另一条路线。蕨叶为立体的四列式蕨叶，即成对的羽片侧生在叶轴上。在后一条演化路线中，原蕨目处于较原始的水平。原蕨属可能直接起源于一种与裸蕨植物Pertica 相近似的祖先。羽裂蕨目较为进化。而十字蕨目则达到极为特化，即蕨叶高度简化，出现异形孢子的水平。真蕨亚纲的祖先植物可能自后一条路线中产生。

湖南、广西泥盆纪硅岩地球化学与沉积构造背景

During the Devonian, a complicated carbonate platform-basin configuration was created through transtensional rifting in the context of opening of Devonian South China Sea; extensive bedded chert, commonly interbedded with tuffaceous beds, occurred in the narrow, elongate interplatform basins (or troughs) in South China, where they occurred earlier (Early Devonian) in southern Guangxi and later (early Late Devonian) in northern Guangxi-south central Hunan. In order to unravel the origin and distribution of the bedded chert successions, and their relationships to basement faulting activities during the opening of the Devonian South China Sea, studies of element (major, minor and REE) geochemistry and Rb-Sr, Sm-Nd isotopic systematics are carried out upon the chert deposits. These chert deposits commonly have high SiO2 contents and (average 94.01%) and low TFe2O3 (average 0.55%), together with other geochemical parameters, suggestive of both biogenic and hydrothermal origins. However, Fe/Ti ratio are high along the elongate interplatform basins(troughs) to the northwest along Wuxiangling-Zhaisha-Chengbu, and to the southeast along Xiaodong-Mugui-Xinpu, suggesting relatively intense hydrothermal activities there. They generally contain very low total REE contents (∑REE average 31.21ug/g) with mediate negative Ce anomalies (mean Ce/Ce*=0.83) and low Lan/Cen values (average 1.64), indicating an overall continental margin basin where they precipitated. The northward increases in Ce/Ce* values, particularly along the elongate troughs bounded both to the east and west of the Guangxi-Huanan rift basin, suggest a northward enhancement of terrigenous influences, thereby reflecting a gradual northward propagation of open marine setting. Generally low positive Eu anomalies in the chert, except for the apparently high Eu anomalies in the chert from Chengbu (Eu/Eu* up to 4.6), suggest mild hydrothermal venting activities in general, except for those at Chengbu. The initial 87Sr/86Sr (0) ratios of chert generally vary from 0.712000 to 0.73000 , suggesting influences both from terrigenous influx and seawater. The Nd isotopic model ages (tDM or t2DM) and initial εNd (0) values of chert vary mostly from 1.5 to 2.1 Ga, and from –16 to –21, respectively, implying that the silica sources were derived from the provenances of the Palaeoproterozoic crust relics at depth. The high εNd (0) values of chert (-0.22 to 14.7) in some localities, mostly along the elongate troughs, suggest that silica sources may have been derived from deeper-seated mantle, being channeled through the interplate boundary fault zones extending downwards to the mantle. At Wuxiangling, Nanning, chert occurs extensively from the Emsian through the Frasnian strata, both U/Th ratios and tDM ages of chert reached up to a maximum in the early Frasnian corresponding to the extensive development of chert in South China, pointing to a maximum extensional stage of Devonian South China basin, which is supported by the Ce/Ce* values as is opposed to the previous datasets as the coeval minimum values.

Electron microprobe results of clay minerals from samples of the Frankenwald and the Thüringer Wald

Late Devonian (Frasnian) pillow basalts from the Frankenwald and Thüringer Wald within the Saxothuringian zone in Germany were found to contain abundant putative biogenic filaments, indicating that the volcanic rocks once harbored microbial life. The mineralized filaments are found in calcite-filled amygdules (former vesicles), where they started to form on internal surfaces of vesicles after seawater ingress. The filaments postdate an early fibrous carbonate cement but predate later equant calcite spar, revealing syngenetic formation. A biogenic origin of filaments is indicated by their size and morphology resembling modern microorganisms, their independence of crystal faces and cleavage plans, complex branching patterns, and internal segmentation. The filamentous microorganisms represent cryptoendoliths that lived in structural cavities of the basalt. They became preserved upon microbial clay authigenesis similar to the encrustation of modern prokaryotes in iron-rich environments. Filaments consist of clay minerals with the endmember composition berthierine-chamosite and illite-glauconite. Based on the discovery of fossilized filamentous microorganisms in Late Devonian pillow basalts of the Saxothurigian zone that are similar to filaments previously found in Middle Devonian pillow basalts of the Rhenohercynian zone, it is apparent that cryptoendolithic life was more widespread than previously recognized. Structural cavities within seafloor basalt may thus represent a common, perhaps universal niche for life in the oceanic crust.

A redescription of Atopacanthus dentatus Hussakof and Bryant, 1918 (Acanthodii, Ischnacanthidae)

The holotype specimen of the ischnacanthid acanthodian Alopacanthus dentatus comprises most of the posterior half of a dentigerous jaw bone, rather than a fragment from the middle of the jaw as was previously believed. A new diagnosis and revised description for the taxon are based on the holotype from the Rhinestreet Shale (Frasnian) and other specimens front the North Evans and Genundewa limestones (early Frasnian) of the Genesee Formation (late Givetian-early Frasnian); all of: these dentigerous jaw bones were collected near Hamburg, New York state, U.S.A. An emended diagnosis for Atopacanthus clarifies the differences between it and other ischnacanthid genera.

Histological structure of the cancellous bone layer in Bothriolepis canadensis (Antiarchi, Placodermi)

The Placodermi are extinct basal gnathostomes which had extensive dermal and perichondral bone, but which lacked the endochondral bone which characterizes the more derived bony fishes. Thin sections of bone from a specimen of the antiarch placoderm Bothriolepis canadensis, from the Escuminac Formation ( Frasnian, Upper Devonian), Quebec, Canada, reveal that part of the cancellous layer in its dermal and endoskeletal bone formed from perichondral bone trabeculae growing around cartilage spheres. The resultant structure mimics that of osteichthyan endochondral bone. The layout and dimensions of this polygonal mosaic patterning of the bone trabeculae and flattened cartilage spheres resemble those of the prismatic layers of calcified cartilage in chondrichthyans. If the lack of endoskeletal bone in chondrichthyans is a derived character, then the structure identified in B. canadensis could represent a 'template' for the formation of prismatic calcified cartilage in the absence of bone.

Upper Devonian biostratigraphy of the Iberian Pyrite Belt, southwest Spain Part Two: Organic-walled microphytoplankton

Upper Devonian rocks of the Iberian Pyrite Belt (IPB) in southwest Spain, comprising the Phyllite-Quartzite Group (PQ) and the lower part of the overlying Volcano-Sedimentary Complex (VSC), contain a diversity of terrestrial and marine palynomorphs (miospores and organic-walled microphytoplankton, respectively), which constitute the basis of this biostratigraphically oriented research project. Part One of the report has previously detailed the miospore content of the constituent 117 palyniferous samples. In the present paper (i.e., the concluding Part Two), the organic-walled microphytoplankton (acritarchs and prasinophyte phycomata) are systematically described and illustrated, and their occurrence in the study material is fully documented. The acritarchs are represented by 23 species (including one species complex) allocated among 14 genera (one of which, Dupliciradiatum, is newly established), together with a very rare and novel category (informally termed Gen. nov. A). The following new acritarch species are formally instituted: Dupliciradiatum crassum (type species), D. tenue, Histopalla languida, and Winwaloeusia repagulata. Five genera allied with the prasinophycean algae are identified; these accommodate a total of 15 species of which two - Cymatiosphaera tenuimembrana and Maranhites multioculus - are formally proposed as new. In addition, representatives of the prasinophyte genera Leiosphaeridia and Tasmanites are recorded but are not discriminated at species level. The microphytoplankton suite is clearly consonant, from previously published occurrences in other regions, with a Late Devonian dating. However, most of the species are known to be relatively long ranging through (and in some cases beyond) that epoch and hence are not amenable to detailed biozonal subdivision of the IPB succession. Moreover, the distribution of the species therein tends to be erratic in comparison with the more consistently occurring miospores, possibly due to stress factors induced by fluctuating conditions in the IPBs Upper Devonian marine environment. By contrast, the land-derived (miospore) assemblages are readily applicable in a blostratigraphic context: they can be correlated precisely with the Devonian miospore biozonation scheme for Western Europe. In those terms, the sampled PQ strata are assignable to the Diducites versabilis-Grandispora cornuta (VCo) Biozone of late Famennian age; while the samples from the anoxic sequence at the base of the VSC belong to the Retispora lepidophyta-Verrucosisporites nitidus (LN) Biozone (latest Famennian = latest Devonian). The biochronostratigraphic data, in conjunction with the findings from earlier IPB studies, imply two appreciable palynostratigraphic breaks within the PQ. These are representative, respectively, of the lower Frasnian-middle Famennian interval and of part of the Strunian/upper Famennian. Speculation currently remains as to whether the inferred gaps are more apparent than real; i.e., whether one or both represent actual hiatuses in IPB sedimentation or are simply a manifestation of hitherto unsampled and/or non-palyniferous PQ strata.