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.