The Classification And Evolvement Of Siliceous Spicules And The Cause Of The Extinction During The End-Permian

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).