【作者】 刘桂春；

【导师】 冯庆来；

【作者基本信息】 中国地质大学 ， 古生物学与地层学， 2009， 硕士

【摘要】 在广西省东攀深水相地层中,发现有大量的硅质海绵骨针,且保存良好分异度高。海绵骨针很难进行系统学分类,只能按照其形态,如按照“轴”数,大小等进行分类,共有48种可确定类型和4种未确定类型,其中确定类型又可分为75中亚类型未确定类型分为10种亚类型。这些骨针包含了单轴、三轴、四轴、多轴和网状类型,同时也按照大小进行了分类。在东攀剖面,海绵是深海生物群落中较为重要的组成分子,该生态群落还有大量的放射虫、腕足类、有孔虫等生物。深水海绵多以骨针形式保存下来,而海绵骨骼是由多种类别类型的骨针构成,一个海绵可能有几种到几十种类型的骨针,不同种级甚至属级的海绵可能含有同样的类型骨针,所以很难把这些骨针归属于确定的海绵种中,只有一些特征型的分子可以分辨。东攀的硅质海绵骨针多属于普通海绵纲（Demosponges）和六射海绵纲（Hexactinellids）。在此文中,各种类型的骨针被详细的描述并与其它地区或时代的相似的海绵骨针进行对比。为了进步研究海绵生物的演化,我们对广西东攀和贵州马鞍营海绵骨针进行了统计。马鞍营剖面骨针类型远不如东攀海绵骨针类型丰富,且马鞍营海绵骨针类型都出现于东攀剖面（共52种类型,85中亚类型）。这些海绵骨针在接近二叠纪和三叠纪（P/T）界线附近分异度迅速降低,88%～90%的类型和88%～92%的亚类型消失,只有5种亚类型延续到了早三叠世,包括Oxeas A、Oxeas B、Strongles B、Oxy-orthpentactines和Oxy-orthohexactines A。不同轴数骨针类型的灭绝顺序不同:三轴和四轴骨针最先消失,然后是多轴和网状骨针消失,单轴骨针消失偏晚。不同表面结构特征的海绵骨针灭绝顺序也不同:分枝型和多刺型骨针较早灭绝,光滑型的骨针较晚灭绝或延续到了下三叠统地层中。其灭绝过程表现为逐渐的灭绝模式,并且可以分为两个灭绝阶段:第一阶段呈现出较慢的灭绝速度和较低灭绝率,第二阶段灭绝速度和灭绝率急剧升高。何卫红等通过测量大量的腕足类,发现其个体存在小型化特征,即越靠近二叠-三叠纪界线腕足个体越小。以此为例,我们选择了丰度非常高、且一直幸存到三叠纪的四种海绵骨针类型进行统计、测量,结果发现,海绵骨针在整个东攀剖面内存在四个大小波动的旋回,最终在第7层开始快速变小,其个体只有原来的一半左右。进一步研究表明,海绵骨针大小变动主要与生产力有密切关系,与水体中的氧浓度关系较小,即食物越多、氧浓度越高越有利于海绵个体的发育。海绵骨针小型化的结果充分支持了Twitchett所论述生物在灭绝后产生小型化作用（Lilliput effect）,同时也佐证了食物缺乏是生物个体变小的原因。通过小型化研究,作者发现海绵骨针的大小和其形态分异度有较好的耦合关系。对海绵骨针大小、分异度和灭绝量进行相关性投图,发现生产力是海绵骨针大小和分异度变化的直接原因,而海绵骨针也限于其大小和分异度降低开始大量消失。利用粘土、地球化学、碳屑和菌藻类与海绵骨针各种变化对比发现,大量的火山作用可能是这些变化的根源。海绵动物在每个火山活动旋回初期（依据粘土岩的密度和厚度把火山活动分为四个旋回）就大量的灭绝,而研究的四种海绵骨针个体和海绵骨针分异度直到火山最弱的阶段才减小,这个结果看似矛盾,事实是因为大量的火山灰和火山作用导致陆地产生的大量炭质碎屑为低等的菌藻类提供了充足的营养源,但充足的食物并没有完全缓解环境对海绵的压力,海绵骨针在整体上还是逐渐减小。然而,在东攀剖面第8层到第11层之间,长期的、持续的火山重要摧毁了整个生态系,水体里可能充满了有毒的物质（H₂S）、大量的火山灰和陆源物质,致使海绵动物、放射虫等动物乃至低等的菌藻类都承受着摧毁性的打击。更多还原

【Abstract】 The investigations on the Upper Changhsingian deep-water deposits in southern Guangxi, South China allow us to trace, an abundant, diverse and well-preserved siliceous sponge spicule assemblage. This assemblage contains 48 types including 75 forms and 4 uncertain types including 10 forms in morphologic classification. These spicules can be divided into "monaxons", "triaxons", "tetraxons", "polyaxons" and "demas" with axis number, and further classified by the number of rays or needlelike terminations corresponding to directions of growth and size. The sponges take an important role in the high-diversity community including radiolarians, brachiopods, foraminifera and other animals in Dongpan Section. However, without co-occurrence of appropriate sponge body fossils, it is difficult to assign these disarticulated sponge spicules to species or genus, only some representative spicules of demosponges and hexactinellids can be recognized. In this paper, all spicule types are given morphologic descriptions and briefly discussion with uniform or similar known assemblages in geologic history.For further research, we also accounted the spicules for understanding extinction patterns and processes of deep-water sponges at Maanying Section besides Dongpan Section, South China, all the types and forms of Maanying Section （including 52 types and 85 forms） exhibited in Dongpan Section. These sponge spicules rapidly decreased below the Permian/Triassic boundary （PTB）, and the extinction rates reach up to 88%—90% for types and 88%—92% for forms. Their extinction pattern is a gradual one that consists of two stages: the first is characterized by a gentle and slow extinction speed and low extinction rate, and the second by sharp and fast extinction speed and high extinction rate. The morphological extinction process is involved in the disappearance first of the triaxons and tetraxons, then of the polyaxons and demas, and last of monaxons. In exterior structure extinction, the complex spicules with branches and spines became extinct more easily than did smooth spicules. After the end-Permian mass extinction, only five common and smooth forms survived: Oxeas A, Oxeas B, Strangles B, Oxy-orthpentactines and Oxy-orthohexactines A.It is necessary to research spicule size to well known how the paleoenvironment changed during the end Permian. Four common forms extending to the early Triassic （exhibiting at Maanying Section） are assessed the size variation for discussing the cause of miniaturization in the whole extinction event in Dongpan Section, South China. A lot of data show that siliceous spicules fluctuated in size, reduction and recovery, and occurring concurrently with the extinction event. Most significant changes in spicule size are not controlled by simple environment factors, but by all-around causes. The reductions of size are well explained with anoxic condition and low productivity in lower section, and the associated stresses of collapse of paleoproductivity could be the adopted cause of being in "Lilliput effect" near the Permian-Triassic boundary （PTB）.Of course, the research of spciule size miniaturization can reflect indirectly the cause of sponge extintion, even other marine animals during the end-Permian mass extinction. Using several biotic changes, we not only understand the relationship of sponge spciule size, diversity and the extinction, but also well research the cause of sponge extinction. With statistic method, we found that the productivity decrease was the direct cause of spicule size miniaturization and low form diversity, and low oxygen concentration could be an unimportant reason, while many sponges could be extinct due to the poisonous, acidic and "dirty" water bringing by frequent and large volcanisms. While abundant minerals dissolved from volcanic ash and organic fertilizer of charcoals not all burning were the result of prosperous fungus and acritarchs interval the volcanisms from beds 3 to 7, siliceous mudstone and cherts deposit, during the short-term and discontinuous volcanic explosions. Then the doom occurred from beds 8 to 11, many lives were extinct during the long-term and lasting volcanisms, the world was aphotic, the atmosphere contained low oxygen concentration and high carbon dioxide concentration, and was full of ruinous gas （H₂S）.更多还原