钙质海绵之古生态

PALEOECOLOGY OF CALCISPONGES (INOZOANS, THALAMID SPONGES, SCLEROSPONGES)

古生代生物礁中钙质海绵 (纤维海绵、房室海绵、硬海绵 )的生态位在中三叠世以后被生态竞争能力更强的六射珊瑚所占据。在古生代和中三叠世的钙质海绵礁上 ,0— 10m深度内钙质海绵很发育。由于与钙藻共生 ,典型的造礁钙质海绵生活在透光带以内 ,并且在其上部更丰富。钙质海绵礁也会生长到破浪带内并受风浪的破坏而形成倒骨岩和骨屑岩。对古生代的钙质海绵礁而言 ,倒骨岩和骨屑岩形成于 0— 3m水深范围内 ,亮晶骨架岩形成于 3— 10m深度范围内 ,灰泥骨架岩形成于 10— 2 0m的水深 ,障积岩形成于 2 0— 30m的水深 ,潜障积岩形成于30— 40m的水深。钙质海绵的生长形态与水深的关系与六射珊瑚与水深的关系一样 :细枝状的钙质海绵生长在最浅的水中 (相当于礁生长带的上部 ) ,在稍深的水中 (相当于礁生长带的中部和下部 )各种形态的海绵都会出现 ,在更深的水中可以出现特别大的。

In Paleozoic calcisponge reefs calcisponges (inozoans, thalamids, sclerosponges) occurred not only at more than 10 m but also at 0—10m water depth. In Permian and Middle and early Late Triassic (Carnian) calcisponge reefs, calcisponges were dominant reef builders, being the most abundant at 0—10 m deep part of the reefs. In post Carnian reefs, the 0—10m deep parts were occupied by scleractinian corals, which won calcisponges in the ecological competition, that may accounts for the extinction of the dominant reef building calcisponges of Paleozoic and Middle early Late Triassic reefs. A statistic study by me shows that all calcisponge species of Permian and Middle early Late Triassic reefs disappeared at end Carnian and all calcisponge species in late Late Triassic (Norian and Rhaetian) are new. The most striking evidences for the shallow water occurrence of calcisponges in Paleozoic and Middle early Late Triassic reefs are (1) the association of calcareous algae such as Archaeolithoporella, which should live in the shallow photic zone, (2) the occurrence of the cemented framestones which lack micritic matrix but have marine fibrous sparry cements, which indicates the occurrence of wave action. By comparison with the occurrence of scleractinian corals and calcisponges in modern reefs, I assume that calcisponge bioliestones (bioliestone=bio+lie+stone; composed overturmed whole skeletons of main reef building organisms) and biorudstones (composed of the skeleton fragments of the main reef building organisms) might have formed in a water depth 0—3 m, cemented calcisponge framestones (i.e., the calcisponge framestones with sparry cements) formed in 3-10m; micritic calcisponge framestones formed in 10—20m; calcisponge bafflestone formed in 20—30 m, calcisponge prebafflestone formed in 30—40m.