Corresponding to eons, eras, periods, epochs and ages, the terms "eonothem", "erathem", "system", "series", "stage" are used to refer to the layers of rock that belong to these stretches of geologic time in Earth's history.
Geologists qualify these units as "early", "mid", and "late" when referring to time, and "lower", "middle", and "upper" when referring to the corresponding rocks. For example, the Lower Jurassic Series in chronostratigraphy corresponds to the Early Jurassic Epoch in geochronology. The adjectives are capitalized when the subdivision is formally recognized, and lower case when not; thus "early Miocene" but "Early Jurassic."
Banded Iron Formations (BIFs)
Ordovician Black Island Formation (Winnepeg Group)
The total cumulative oil production from these 18 wells is little more than 200,000 barrels. The cumulative gas production, however, is over 115 BCF of dry gas (Table 1). Converting the gas to barrels of oil equivalent (BOE), assuming 5,620 cubic feet of dry gas (methane) equals 1 barrel of oil, over 17 million BOE have been produced from wells that have completed and produced from the Black Island Formation, while the water production total is ~450,000 barrels. Overall, the average Black Island well has cumulatively produced 960,463 BOE with only 24,960 barrels of water. Even after 15+ years of production, Black Island completions produce very little water.See also this blog post on the Ordovician (Winnepeg Group).
Consulting geologist's evaluation of the Tyler formation, 2011, a PDF.
Monograph on oil potential in eastern North Dakota, 1963, but remains relevant, a PDF.
USGS Fact Sheet, April, 2008
Williston Basin Geology with an emphasis on the Bakken Pool.
The "Bakken Pool" is an administrative term that includes the Bakken formation and the Three Forks formations. In some areas, the Three Forks is referred to as the Three Forks Sanish. The Pronghorn Sand(s) was first talked about around 2011, delineated by Whiting, and in southwest North Dakota.
During the "Bakken boom," there seems to be confusion with "Three Forks Sanish." Early on, that was how it was referred to: the "Three Forks Sanish." Over time, the "Sanish" was dropped, and it was simply "Three Forks." But on file reports, especially Whiting file reports, one sees "Sanish" standing alone. According to the "Petroleum Geology of North Dakota's Williston Basin (linked above also), "Sanish" was another name for the Bakken formation (Table 1, 1977). Further down in the article, it states that the Three Forks overlies the Birdbear formation; and, in turn, the Three Forks overlies the Bakken. (So, there is still a bit of confusion between the geologists and the NDIC administrative nomenclature.) According to the report at the link, the "Sanish" is an "informal unit," Sanish sandstone which overlies the Sanish itself.
The Bakken is a "world class source rock." Click here for a comprehensive 2007 study/report of this source rock.
Click here for an outstanding presentation with emphasis on the Three Forks Sanish formation, undated, but probably 2010, since that was the year that the Three Forks Sanish started getting peak attention "in the Bakken."
Click here for estimated original oil in place (OOIP) and estimated ultimate recovery (EUR) by county.
How and where the "sweet spot" of the Bakken was formed.
A collection of articles / internet sources on the Bakken / Three Forks.
Early review of the Bakken (PDF), undated, probably published about 1993; geologic review up to that time
Salt deposits, July, 2012, article:
The Original Post
See Stratigraphic update, 2009, by Stephan Nordeng and Julie Lefever.
Gamma Ray Logging
Units of gas while drilling
Interpretation of subsurface hydrocarbon shows