Extinction pattern and process of siliceous sponge spicules in deep-water during the latest Permian in South China

Abstract

Diverse and abundant siliceous sponge spicules were found in the latest Permian beds, Dongpan andMa'anying sections, South China, including 52 types and 85 forms. Further investigation on these spicules allows us to understand extinction patterns and processes of deep-water sponges. 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, Strongles B, Oxy-orthpentactines and Oxy-orthohexactines A.siliceous sponge spicules, Permian-Triassic extinction, pattern, process, South ChinaThe end-Permian mass extinction is the largest event among the "Big Five" during the Phanerozoic history in terms of the severity of taxonomic diversity losses [1,2] . Marine animals largely disappeared, resulting in about 51%-57% families extinction, 83%-84% genus extinction and more than 95% species extinction [3][4][5][6][7][8] . This mass extinction was finely recorded in South China, thanks to the well-preserved marine strata (from shallow to abyssal). The end-Permian extinction patterns and processes of marine animals have been widely reported, and some paleobiologists thought that this extinction is sudden with only one crisis stage [9][10][11][12][13] , while the others suggested the extinction was gradual and consisted of several crisis stages [14,15] .The fossil rate is affected by biotic shape, abundance, ecological behavior, distribution and average age, and others. The first and last occurrences of one species are rarely recorded in fossils and most fossils disappeared before their extinctions. Therefore, the time recorded by fossils does not necessarily represent the real living time of biota. In other words, the biotic extinction pattern is not always represented by the fossil extinction pattern [16] . As to biologic extinction patterns, Signor and Lipps [17] showed that a random distribution of errors at the end points of biostratigraphic ranges may produce range truncations and appear gradual decline preceding a sudden extinction boundary. This phenomenon had been known as the "Signor-Lipps effect" [18,19] . Meldahl [20] empirically confirmed the "Signor-Lipps effect", noting

Decline of Siliceous Sponges and Spicule Miniaturization Induced by Marine Productivity Collapse and Expanding Anoxia During the Permian-Triassic Crisis in South China

“…The PE can be placed at the base of Bed 6 at Dongpan and at the base of Bed 8 at Maanying. This level coincides with the first pronounced decreases in fossil abundance in these sections, for example, with declines in radiolarians and sponges at Dongpan and sponges at Maanying (Chen et al, 2005Feng et al, 2007;Liu et al, 2008). The significance of this level is further underscored by the fact that it coincided with deposition of relatively thick volcanic ash layers in the two study sections, i.e., Bed 6 at Dongpan and Bed 8 at Maanying (Fig.…”

“…This technique is successful in recovering siliceous microfossils from a siliceous rock matrix because the compact microcrystalline structure of the fossils makes them less susceptible to solution than the chert matrix, which often contains a large fraction of clay minerals (Pessagno and Newport, 1972). In the present study, all of the recovered spicules were composed of microcrystalline quartz (i.e., chalcedony) (see also Liu et al, 2008).…”

“…Both study sections exhibit stratigraphic variations in spicule form diversity (Liu et al, 2008). At Dongpan, diversity is high (.40 forms) until the middle of Bed 3, where a contraction is observed, although diversity recovers in the upper part of Bed 3 and Bed 4 ( Fig.…”

“…In the modern, demosponges favor shallow-marine habitats, whereas hexactinellids are mostly restricted to water depths between 200 and 1000 m in the open ocean (Leys and Lauzon, 1998). Siliceous sponges experienced many declines through their long evolutionary history, including at the PTB, when most species of both classes went extinct (Liu et al, 2008). The demosponges were relatively less decimated, however, especially hypercalcified forms, among which 31 out of 104 genera survived (Finks, 2010).…”

“…Siliceous sponges thrived globally during the Permian, depositing large quantities of biogenic chert in many shelf and slope settings, including on the northwestern Pangean margin (Beauchamp and Baud, 2002), the northern Pangean margin (Ezaki et al, 1994;Reid et al, 2007), and even the equatorial Tethyan region (Liu et al, 2008). This Permian Chert Event, which was possibly the result of vigorous thermohaline circulation and nutrient upwelling in the global ocean, lasted from the Artinskian Stage (mid-early Permian) to the midChanghsingian Stage (late late Permian) (Finks, 1960;Murchey and Jones, 1992;Beauchamp and Baud, 2002).…”