A NEW ORDOVICIAN CHIASTOCLONELLID SPONGE FROM INNER MONGOLIA, CHINA

Abstract

Lower paleozoic facies relationships, fossils, and depositional systems of the Northwest Ordos Basin, northern China, are sparsely documented in western world literature (Meng et al., 1997; Kessel, 2005). Recent field work in this area during the summer of 2004 recovered a single specimen of a new chiastoclonellid sponge. That sponge, described here, was collected from a measured section of Lower Paleozoic rocks exposed in the Suhaitu area, in the northern part of the Zhuozi Shan Range, northwestern Ordos Basin (Fig. 1), in southern Inner Mongolia Province. The Zhuozi Shan Range is part of the western Ordos fold and thrust belt, a Late Jurassic–Early Cretaceous tectonic feature, that brought Lower Paleozoic rocks to the surface (Darby and Ritts, 2002; Darby, 2003). Early Paleozoic rocks exposed in the area are dominantly carbonates with minor siliciclastic rocks and they span from the Early Cambrian through the Middle Ordovician (Yang et al., 1992; Meng et al., 1997). They are unconformably overlain by Middle Carboniferous units across the North China Block (Meng et al., 1997). Figure 1 —Index and geologic maps of the northern Zhuozi Shan, northwestern Ordos Basin China, showing the locality of the Suhaitu Section (star 1), from which the specimen of Craterospongiella sinica n. gen. and sp. was collected. Star 2 shows a second occurrence of the species at a similar stratigraphic position. Wuhai City is indicated by the W. The map area designated in the inset shows the position of the study area relative to China and the western Ordos fold and thrust belt. Structural interpretations are adapted from Darby (2003), and the geologic map is adapted from Ma (2002) The sponge-bearing part of the Suhaitu section (Figs. 1, 2) is located at latitude 39°50.71′N and longitude 107°E01.28′E, in the northern Zhouzi Shan Range, and …