Subsidence History of Williston Basin in North Dakota

Richard D. Lefever

The tectonic subsidence history of the Williston basin in North Dakota has been estimated through the examination of wireline logs from 30 wells that penetrated to Precambrian basement.

The initial subsidence of the basin in North Dakota began at a time not later than during deposition of the middle portion of the Deadwood Formation (earliest Ordovician; about 495-490 Ma), significantly earlier than had been estimated by most workers. The initial subsidence was centered in a north-south-trending elongate area in western North Dakota; the maximum calculated tectonic subsidence rate for this event is about 15 m/m.y.

Since the Early Ordovician, exclusive of the basin initiation event, the basin has undergone at least five distinct episodes of tectonic subsidence: (1) from about 450-420 Ma, (2) from 420-355 Ma, (3) from 355-315 Ma, (4) from 270-245 Ma, and (5) beginning in the interval between about 90 and 70 Ma.

Each of the subsidence episodes was characterized by a rapid initial subsidence, followed by a decline to very low subsidence rates. The maximum calculated initial subsidence rates for these episodes are 26, 32, 16, 9, and 15 m/m.y, respectively.

The time between episodes 4 and 5 seems to have been one of relative quiescence; the few rocks preserved from that time interval were deposited during highstands of sea level. The subsidence history curves for episodes 1-4 are consistent with a thermal expansion model; however, with the exception of episode 3 and possibly episode 4, none of the first four subsidence events appears to be temporally coincident with major tectonic events elsewhere in North America.

AAPG Search and Discovery Article #91033©1988 AAPG Rocky Mountain Section, Bismarck, North Dakota, 21-24 August 1988