长江源各拉丹冬地区上三叠统巴贡组沉积特征及菊石生物群

上三叠统巴贡组分布于长江源各拉丹冬地区南北两侧 ,南部靠近羌塘盆地中央隆起带 ,沉积环境为三角洲至浅海相 ,陆源物资供应丰富 ,以砂岩沉积为主 ,地层厚度大。北部雀莫错一带沉积环境为陆棚相 ,陆源物资供应相对较少 ,以泥质岩、灰岩沉积为主 ,生物丰富 ,沉积古地理格局显示出南浅北深的特点。在雀莫错一带采集了大量的菊石化石 ,建立 N odotibetitescf.nodosus- Paratibetitescf.wheeleri组合 ,生物组合所反映的地质时代为诺利早—中期 ,与藏南珠穆朗玛峰地区、藏北唐古拉山地区及青海玉树地区同期地层中的菊石生物群可以很好对比。     

Correlation of Mississippian (Upper Viséan) foraminiferan,conodont, miospore and ammonoid zonal schemes,and correlation with the Asbian–Brigantian boundary in northwest Ireland

The microbiota of the upper Viséan (Asbian–Brigantian) rocks in the Lough Allen Basin in northwest Ireland is analysed. The Middle Mississippian sequence studied extends from the upper part of the Dartry Limestone/Bricklieve Limestone formations of the Tyrone Group to the Carraun Shale Formation of the Leitrim Group. The rocks have been traditionally dated by ammonoid faunas representing the B_2a to P_2c subzones. The Meenymore Formation (base of the Leitrim Group) also contains conodont faunas of the informal partial‐range Mestognathus bipluti zone. The upper Brigantian Lochriea nodosa Conodont Zone was recognized by previous authors in the middle of the Carraun Shale Formation (Ardvarney Limestone Member), where it coincides with upper Brigantian ammonoids of the Lusitanoceras granosus Subzone (P_2a). Foraminifera and algae in the top of the Dartry Limestone Formation are assigned to the upper Cf6γ Foraminifera Subzone (highest Asbian), whereas those in the Meenymore Formation belong to the lower Cf6δ Foraminifera Subzone (lower Brigantian). The Dartry Limestone Formation–Meenymore Formation boundary is thus correlated with the Asbian–Brigantian boundary in northwest Ireland. For the first time, based on new data, a correlation between the ammonoid, miospore, foraminiferan and conodont zonal schemes is demonstrated. The foraminiferans and algae, conodonts and ammonoids are compared with those from other basins in Ireland, northern England, and the German Rhenish Massif. Historically, the Asbian–Brigantian boundary has been correlated with several levels within the P_1a Ammonoid Subzone. However, the new integrated biostratigraphical data indicate that the Asbian–Brigantian boundary in northwest Ireland is probably located within the B_2a Ammonoid Subzone and the NM Miospore Zone, but the scarcity of ammonoids in the Tyrone Group precludes an accurate placement of that boundary within this subzone. Copyright © 2006 John Wiley & Sons, Ltd.     

First and Second Orders of Suture Complexity in Ammonites: A New Methodological Approach Using Fractal Analysis

The study of septal patterns in ammonoids has been centered on functional and/or constructional issues. Complexly fluted septa have been considered as complementary structures that reinforce the ammonite shell, their frilled sutures possibly manifesting the demand for strength. Ammonitic sutures display features that denote typical fractal behavior, since they can present very long perimeters relative to the contiguous shell areas, and most provide evidence of statistical self-similarity when observed at varying scales of magnification. However, there is a lower limit of scale measurements below which the fractal behavior of the curve no longer holds, and the perimeter length/step size relationship approaches an Euclidean geometry. This paper describes a new methodology that allows the accurate characterization of suture complexity in ammonoids using the technique of fractal analysis (step-line procedure). The proposed methodology helps to fix the position of this cut-off point, allowing for independent estimates of the fractal dimensions of the curve for both large and small measurement scales (i.e., first and second orders of suture complexity). This approach improves the resolution of fractals in the analysis of suture complexity, thus facilitating the potential interpretation of suture patterns in functional/constructional, evolutionary and paleoecological terms.     

新疆西准噶尔晚泥盆世法门晚期菊石动物群的发现及其意义

首次在新疆准噶尔盆地西北缘和什托洛盖以北地区的晚泥盆世法门晚期地层中发现板海神石及大型弓海神石菊石动物。板海神石动物群由Platyclymenia （Pl.） subnautilina （Sandberger）、Sporadoceras sp.和Prionoceras frechi （Wedekind）等分子组成;可能与Annulata事件有关。弓海神石动物群中Protactoclymenia sp.和Cyrtoclymeniasp.以壳体硕大为显著特征,直径可达20cm。这些菊石可与西欧晚泥盆世标准菊石带第Ⅳ带的菊石组合进行对比（相当于牙形石Upper trachytera至Lower expansa带）,而且在区域上的分布具有一定的稳定性,尤其是弓海神石动物群,其产出层位可作为和什托洛盖以北地区地层对比的标志层。