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Book Cliffs (Re: howdy ya'll and stratigraphy ?)
basically the Latest cret and tertiary of the book cliffs is Mancos
Shale - part of the western interior seaway, and is deep(ish) marine.
But, the "sea level" was fluctuating at the time, so shoreline was
prograding (aka sealevel trans- and regressing). Each time the
"shore" and the "land" behind it moved seaward, i.e. INTO the basin,
a sandy unit was deposited. Then the sea would transgress and so
vertically above the sandy unit, you get back into Mancos shale.
Anyway, each sandy unit has a name, eg Star Point, Blackhawk (and
various members), North Horn.
Each sand unit represents a different time interval. None are
equivalent to the others even though if you look vertically at a
cliff near Green River and another near Price, you see a similar
pattern of Mancos shale and "sandstones" - these sands are NOT
I've scanned a fig from Franczyk et al that shows the strat. of the
But in reference to fig. 5.5 in Fillmore (2000):
North Horn Fm is ABOVE Tuscher/Canaan Peak Fms
Star Point is lat. equivalent to Blue Gate Shale Mbr of Mancos Shale
Black Hawk Fm is lat. equiv. to youngest Star Point, and Blue Gate,
but everywhere younger than Castlegate Ss and Buck Tongue
Recommended refs w/ strat correlations within Book Cliffs:
Rigby, J.K., MP Russon, RE Carroll, 1987, The Book Cliffs Cretaceous
section: western edge of the interior seaway; GSA Centennial field
guide, Rocky Mountain Section, pp. 251-256
Franczyk, KJ et al, 1989 Evolution of resource-rich foreland and
intermontane basins in eastern utah and western colorado, vol. T324,
pp 1-15; 28th IGC Field trip guidebook, AGU.
Emma C. Rainforth
Geosciences Rm. 206E
Lamont-Doherty Earth Observatory
ph. (845) 365-8621
fax (801) 838-4126