About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 68 (1984)

Issue: 4. (April)

First Page: 466

Last Page: 466

Title: Biostratigraphic Restudy Documents Triassic/Jurassic Section in Georges Bank COST G-2 Well: ABSTRACT

Author(s): Harold L. Cousminer, William E. Steinkraus, Raymond E. Hall


In 1977, the COST G-2 well was drilled in Georges Bank, 132 mi (212 km) east of Nantucket Island to a total depth of 21,874 ft (6,667 m). Biostratigraphic studies of 363 sidewall and conventional cores and 695 cutting samples resulted in a detailed zonation from the Late Jurassic to the present. Restudy of the original samples, as well as new preparations from previously unstudied core material, resulted in revision of the zonation of the Late Jurassic and older section.

On the basis of our study of pollen and spores, dinoflagellates, nannofossils, and foraminifers, we revised the age sequence as follows: 5,856 ft (1,785 m) Late Jurassic (Tithonian); 6,000 ft (1,829 m) Kimmeridgian; 6,420 ft (1,957 m) Oxfordian; 6,818 ft (2,078 m) Callovian; 8,200 ft (2,499 m) Bathonian; 9,677 ft (2,950 m) Bajocian; 14,567 ft (4,440 m) Norian (Late Triassic). Norian dinoflagellate cysts and Tasmanites sp. indicate that intermittent normal marine sedimentation was taking place on Georges Bank as early as Norian time, although most of the Triassic section (+14,500 ft or 4,420 m to T.D.) is composed of barren anhydrite, dolomite, and halite (at T.D.) interpreted as having been deposited under evaporitic sabkha-like conditions. The Norian dinoflagellates (Noricysta, Heibe gella, Hebecysta, Suessia, Dapcodinium, and Rhombodella) include species common to both Arctic Canada and the Tethyan region, indicating a possible Late Triassic marine connection.

End_of_Article - Last_Page 466------------

Copyright 1997 American Association of Petroleum Geologists