GEOGRAPHIC DIFFERENCES IN THE DIVERSIFICATION OF BIOLOGICAL ACTIVITIES IN CAMBRIAN EXPLOSION BASED ON ICHNOFOSSIL RECORD

In order to clarify diversifyling pattern and process of biological activities during the Cambrian radiation, ichnofossils were comparatively studied in the several sections of earliest Cambrian; Newfoundland, China and Mongolia. Special attention was paid for the size distributions of the most common ichnogenus Planolites and the densities of all the observed ichnofossils. Besides, bedding plane bioturbation indices (BPBI) were measured and compared to understand animal activities in different ages and sections.

In Newfoundland, almost all the Planolites were small (1-2 mm) in the earliest Cambrian Treptichnus pedum Zone. The BPBI indicate that the biological activity was not intense in the T. pedum Zone. The sizes of Planolites, however, became large in the overlying Rusophycus avalonensis Zone. Some beds also show higher BPBI values (III) than those in the T. pedum Zone. In Meishucun, China and Gobi Altai, Mongolia, however, a variety of Planolites sizes already appeared in the T. pedum Zone. The BPBI in the T. pedum Zone are sometimes comparable to those in the R. avalonensis Zone in Newfoundland. These results demonstrate that there were some regional differences about the diversification of biological activities in the earliest Cambrian. The large Planolites producers appeared earlier in the lower latitudes than in Newfoundland, and the biological activities also show a similar diachronous pattern in a large geographic framework.