THE REFUGIA CONCEPT FOLLOWING THE END-PERMIAN MASS EXTINCTION

The term refuge is used in both modern ecology and paleoecology to describe an ecosystem that remains unchanged during times of environmental stress, and thus acts as a sanctuary for endangered organisms. However, this definition is too simplistic as it paints a picture of a closed, isolated, long-lived ecosystem with a rich population of Lazarus taxa. In order to define this concept, it is important to determine critical ecologic and environmental relationships that support the development of a refuge. The end-Permian mass extinction at 251.95 Ma resulted in the elimination of 95% of oceanic species. Refugia would have played a substantial role in the survival and recovery during and immediately following this event. The study of a Lower Triassic bedding surface (H. parvus Zone) at the Shangsi section of South China, suggests that a refuge might be better described as a constantly shifting, ephemeral, habitable setting. Here an oligophotic outer-shelf ocean floor contains a significant Lazarus echinoid community that lived on microbial mats, which would have provided a firm substrate and acted as a food and oxygen source. This community was terminated by a volcanic ash event that smothered the echinoids and led to higher primary productivity, the proliferation of the opportunistic Claraia and loss of microbial mats. These events occurred after a major temperature spike in shallow water suggesting that the deeper setting may have offered relief from such conditions. In addition, at the previously reported Wadi Wasit block of Oman a diverse shallow water community within the later Griesbachian Isarcicella zones demonstrates that oxygen levels are critical for enhancing recovery. Oxygen levels were also critical on wave-swept shallow shelves along NW Pangea during the lower Griesbachian where a diverse soft-bodied community found refuge in what would have been a slightly cooler setting in Western and Arctic Canada. A picture is emerging where timing, oxygenated levels and amelioration from green-house temperature spikes are critical relationships to consider in refugia development. Work is in progress to test this concept in Panthalassic seamounts in Japan and the Cache Creek Group of British Columbia. A refined concept will inform approaches to understanding modern refugia at a time when many communities are stressed.