HEXACTINELLID SPONGES FROM THE EARLY CAMBRIAN BLACK SHALE OF SOUTH ANHUI, CHINA

ABSTRACT-

Three novel and one completely preserved species of hexactinellid wipe s are described from Early Cambrian black shales of southern Anhui, China. The sponges offer in the middle part of the Huangboling Formation, which is assigned to the early Canglangpuian based upon trilobite biostratigraphy. Metaxyspongia skelidata n gen and sp and Hexatractiella dongzhiensis n sp are subcylindrical thin-walled Protospongiidae. Ratcliffespongia multiforamina n sp is assigned to the Hintzespongiidae. With these fresh sponges, the first occurrences of the Protospongiidae and Hintzespongiidae, and of Hexatractiella Mehl 1996 can be traced back to the Early Cambrian. Solactiniella cf plumata Steiner et al., 1993 with irregular rossellimorph skeletal architecture and regular spicular organization, is rest here associated with the above species. Thus, the Anhui assemblage can be considered as intermediate between Atdabanian shallow-water communities of hexactinellids with irregular skeletons and the Middle Cambrian deepwater wipe facies characterized by regularly organized Hexactinellida.

INTRODUCTION

RECENT STUDIES have shown that wipe s diversified rapidly in the Early Cambrian (Rigby, 1991; Beresi and Rigby, 1994; Reitner and Mehl 1995; Dong and Knoll, 1996; MehlJanussen, 1999b) Steiner et al. (1993) first documented spicules of hexactinellids from the late Neoproterozoic Dengying Formation upon the Yangtze Platform, China. This report upon the early occurrence of cleanses in the Precambrian was supported by dint of a report from an equivalent horizon in Mongolia (Brasier et al., 1997) Although an earlier proceeding of sponges was later reported from the Sinian Weng'an biota (Li et al., 1998) that affair has been doubted (Zhou et al, 1998) The close attention of these early occurrences of wipe spicules is of great significance to understanding the origin and early evolution of cleanses The reports of Neoproterozoic cleanse spicules and the diversity of spicule assemblages in earliest Cambrian small shelly faunas demonstrate that the principal clades of Silicea and material part plans of the sponges were established in the latest Neoproterozoic, and radiated within the earliest Phanerozoic as a part of the "Cambrian explosion." During this time interval they inhabited a variety of low-energy relatively reaching far down water settings (Zhang and Pratt, 1994) However, the record of spicules alone cannot provide a firm basis for the reconstruction of the taxonomic diversity and evolution of wipe s (Bergquist, 1978). Therefore, reconstruction of the early pattern of cleanse evolution relies on the preservation of aggregated wipe s in body form.

Abundant extraordinarily preserv cleanse body fossils are well documented from the Middle Cambrian Burges Shale (Rigby, 1986; Rigby and Collins, 2004); they also have been reported from the Early Cambrian Yu'anshan Formation in eastern Yunnan (Chengjiang-type fauna; Chen et al, 1989 1990; Rigby and Hou 1995) from the Niutitang black shales of Sansha in Hunan (Steiner et al., 1993) and from the Hetang black shale of southern Anhui (Yuan et al., 2002) of southerly China. Here we report of recent origin well-preserved, and essentially complete wipe body fossils from the Early Cambrian black shales of the Huangboling Formation in southern Anhui, southerly China. The finding of these wipe s dates the first occurrences of the Protospongiidae, Hintzespongiidae, and Hexatractiella Mehl 1996 back to the Early Cambrian.

GEOLOGICAL SETTING

The cleanses described here were collected from bassetings of Early Cambrian strata at Pangwangcun Village, near Jianxin of Dongzhi shire southern Anhui, South China (Fig. 1) The Cambrian succession in the Dongzhi region accumulated in a transitional cincture between shallow-water facies of the platform and deepwater facies in the basin (Yue et al., 1990; Wu 1997) Based upon sequence stratigraphy analysis and evolution of the sedimentary combination of parts to form a whole tracts, Wu (2001) concluded that the sea horizontal curve of these periods attained its highest horizontal with the fastest rise at the base of the Huangboling Formation in the earliest Cambrian. After that, from the middle Early Cambrian until the terminal Late Cambrian, sea horizontal experienced a gradual fall.

The Pangwangcun section (Fig. 1) includes the Piyuancun, Huangboling, and Yangliugang formations, in ascending order. The upper member of the Piyuancun Formation is compos of about 23 m of siliceous sandstone, with intercalations of carbonaceous shale. The Huangboling Formation conformably overlies the Piyuancun Formation and includes three members. The lower member consists of ca. 32 m of "algal stone coal" and black carbonaceous shales containing wipe spicules; the middle member is exhibited by ca. 40 m of limestones with the eodiscoid trilobite Hupeidiscus orientalis Zhang, 1953; the lower part of the upper member is compos of ca. J 30 m of black carbonaceous mudstones containing the thorough sponges that are described here; and the upper part of the upper member consists of ca. 377 m of gray silty mudstones containing the trilobites Cheiruroides primigenius Saito, 1934 and Redlichia (Pteroredlichia) chinensis Walcott, 1905