ENIGMATIC BUT APPARENTLY USEFUL CONTINENTAL MOLLUSKS OF THE PALEOCENE–EOCENE GOLDEN VALLEY FORMATION, NORTH DAKOTA
Exposed as numerous isolated butte-associated outcrops, the Golden Valley members (lower: Bear Den and upper: Camels Butte) are both lithologically and chronostratigraphically distinctive. Studies of fossil plants, mammals, palynomorphs, and isotopes confirm the importance of the Golden Valley stratigraphic record. Indication of the PETM in the Bear Den Member at Murray Ranch and Farmers Butte provide a basis for P/E boundary correlation in Hickey’s (1977) sections. The Wa3 NALMA assessed for mammals from the “[upper] Golden Valley Formation” (Robinson et al., 2004) indicate a relatively condensed window into the lower Eocene of North Dakota.
Fossil continental mollusks are uncommon in the Golden Valley Formation. The species from the two localities reported from the Bear Den Member were identified by J.T.-C. Yen with “cf.,” “comparable to the referred species.” Yen indicated poor preservation for the Bear Den mollusks, but typically, a “?” is used in such cases. Better-preserved specimens from the same number of localities in the Camels Butte were more definitely identified and asserted as early Eocene by Yen.
Rethinking identifications as preservation rather than morphological issues, the Bear Den Member taxa indicate a Ti3-Ti4 NALMA. The Camels Butte Member is more difficult to interpret. Most of the taxa are probably misidentified, with over 50% indicative of upper Paleocene strata as identified, with others also suggesting older strata (in Utah and Wyoming). A Wasatchian Stage, however, is more likely based on their typical misidentifications. Note that two other localities are known to the authors; one collected without location by a Golden Valley school boy (David Miller). The other from an undiscussed Hickey locality relocated by JHH and crew in 1998. The former was given to JHH as a marl block that produced lovely late Paleocene snails. The latter, a Camels Butte locality from fissile chips in a lignitic shale, produced flattened shells and fragments indicative of quiet water and an organic-rich lake bottom.