SUBSTRATE CONDITIONS AND SETTLING STRATEGY OF GOGIID EOCRINOIDS (ECHINODERMATA) FROM THE KAILI BIOTA (MIDDLE CAMBRIAN), GUIZHOU PROVINCE, SOUTH CHINA

Eocrinoids are the most pandemic Cambrian echinoderm and are well known from Laurentia, Prague Basin, and Spain. Unlike other blastozoans, which commonly cement to objects or hardgrounds, eocrinoids are attached but not cemented to skeletal debris in the fine-grained siliciclastic settings. Well-preserved gogiid eocrinoid faunas from South China offer new insights to understand the settling strategy in stalked echinoderms.

In Kaili, eocrinoids occur in three microfacies: 1) softground and/or firmground with fine-grained (silty and/or muddy) substrate and a few organophosphatic brachiopods; 2) firmground with abundant organic/algal debris, a few skeletal grains, and trace fossils; 3) pseudo-hardground with concentrated skeletal fragments, which were dominated by either organophosphatic brachiopods, trilobites, or a mixture of both.

In order to test whether eocrinoids had a preference for particular substrates, the relative abundance of skeletal coverage types was determined. 11 eocrinoid-bearing slabs were point counted. Among them, skeletal coverage varied from slightly more than 7% in the softground and/or firmground microfacies up to 64% in the pseudo-hardground microfacies.

Among 123 articulated specimens examined, 73% of eocrinoids are preserved definitely attaching to skeletal substrates. Types of skeletal substrates for eocrinoid holdfasts are organophosphatic brachiopods; large trilobite fragments, such as cranidium, free cheek, thoracic segment, and pygidium; and mollusks, such as hyoliths and Scenella. The high frequency of Gogia globosa attaching to inarticulate brachiopods is due to the high richness of organophosphatic brachiopods rather than a host-specific association in Kaili Biota. However, the preference of not attaching to small trilobites, such as Pagetia sp., requires further investigation.