For the past decade, Constance Soja from Colgate University has been working with U.S. and Russian colleagues and her students compiling fossil and other geological evidence to understand the origins of the Alexander terrane.
“Until recently, the unclear affinities of many of the Alaskan fossils provided inconclusive information about which islands or continental margins were the source of some of the species that eventually colonized the Alexander terrane,” Soja explained. “But the strong similarities in Silurian marine fossils in southeast Alaska, the Urals, and Siberia indicate that all these areas in the Silurian must have shared a contiguous seaway in the Northern Hemisphere that allowed organisms, generation upon generation, to transmigrate, intermingle, and undergo genetic exchange.”
The distinctive sponge-microbial fossils the team found in limestone bedrock in Alaska and the Ural Mountains formed barrier reefs in the Uralian Seaway. This confutes a competing hypothesis that the Alexander terrane had been located in the Southern Hemisphere during the Silurian.
“All of the data agree that the location of the Alexander terrane can be circumscribed to the Uralian Seaway for a particular interval of time,” Soja said. “Thus by placing the origin and distribution of Alaskan fossils in an evolutionary and tectonic context, our research has contributed new insights into the geologic history of the Alexander terrane, the Northern Urals, and, to some extent, other areas.”
Soja will co-present the team’s findings with her student, Alicia Newton, at the Geological Society of America’s Northeastern Section Meeting on March 27 in Springfield, Massachusetts. Newton has been working on sponge-microbial fossils found in the western slope of the Ural Mountains to refine the team’s understanding of the similarities and differences between the Alaskan and Russian fossils. Distinctive microorganisms that formed the reefs include Ludlovia, Sphaerina, and Hecetaphyton, which are preserved with aphrosalpingid (sphinctozoan) sponges—the very same sponges that are characteristic of the Alexander terrane in southeast Alaska and, to some extent, the Farewell terrane in southwestern Alaska.
By Kara LeBeau, GSA Staff Writer
CONTACT INFORMATION:
Constance M. Soja
Geology Department
Colgate University
Hamilton NY 13346 USA
E-mail: csoja@mail.colgate.edu
Phone: 315-228-7200
FAX: 315-228-7187
Abstract available at: http://gsa.confex.com/gsa/2002NE/finalprogram/abstract_30926.htm .
Northeastern Section, Geological Society of America
36th Annual Meeting
March 25-27, 2002
Sheraton Springfield Hotel
Springfield, Mass.
For information and help during the meeting, please see the media assistant at the GSA registration table or call 413-263-2185.