Influence of T-R Events and Eustasy on the Reorganization of Late Jurassic Biota in the Arctic Basin (Siberia-Northern Alaska)

By

B.N. Shurygin, B.L. Nikitenko (Institute of Petroleum Geology of SB RAS), and M.B. Mickey (Micropaleo Consultants, Inc.)

The lithostratigraphy and the recurrence of benthic associations in Upper Jurassic T-R cycles in Alaska and Siberia bear much similarity. The comparison of Late Jurassic T-R curves from Siberia and Alaska with the quantitative eustatic curve from the Russian Platform shows good correlation. Consequently, eustatic fluctuations can be considered to be the major factor controlling parallel sea level changes.

Late Jurassic fluctuations of benthos taxonomic diversity in the Arctic are considered to be the result of episodic immigrating waves and autochthonous phylolines. The comparative analysis of the main stages in reconstructions of the assemblages of bivalves, foraminifers and ammonites in paleobasins of Siberia and Alaska shows good correlation.

In certain basins of the Late Jurassic Arctic, the benthos was irregularly distributed: taxonomically richer assemblages inhabited the upper (external) and middle (internal) parts of the sublittoral area. Several synchronous levels are recognized in the Late Jurassic, when migrant-taxa of circumboreal distribution made their appearance in the catenas of both the Siberian and Alaskan seas. These migrant-taxa are well represented in the assemblages from the middle part of the benthic catenas. The migrants were most widely distributed in bionomic zones of paleobasins commonly during the circumboreal sea level rise (eustasy).

In the Upper Jurassic successive oryctocoenoses, we can observe the effects of reconstructions of benthic catenas under the influence of local factors (controlled by local T-R events) and also in response to global biotic reconstructions in the boreal basins (often related to eustasy).

AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.