Intertidal and Associated Deposits of the Prairie du Chien Group (Lower Ordovician) in the Upper Mississippi Valley

Paleomagnetism can provide useful information about the stratigraphic relationships between the host rocks and the ore of some ore deposits.Four North American mines with stratabound ore deposits of Mississippi Valley type were sampled and the direction and intensity of the natural remanent magnetization (NRM) were measured. Two of the sites sampled (Newfoundland Zinc Co. property near Daniel's Harbour in western Newfoundland and the St. Joe Minerals Co., #8 Mine in southeast Missouri) had a weak, but measurable NRM in both host and ore rocks. This magnetization proved to be highly stable upon alternating field (AF) demagnetization. The other two mines (Magmont Mine, southeast Missouri, and Pine Point Mine, Northwest Territories, Canada) had intensities of magnetization too low to be measured after demagnetization.The pole positions computed for the ores and their corresponding hosts are identical within the statistical uncertainty, strongly suggesting that the ore and the host are, geologically speaking, of roughly the same age. This study gives two reliable pole positions, one for late lower Ordovician dolostone and sphalerite ore from Newfoundland of 26 °N, 126 °E, and the other for the upper Cambrian, based on the Bonneterre dolostone and galena ore from southeast Missouri of 35 °S, 170 °W.Within the present limitations of the method the results agree with published opinions concerning the age of the ore, i.e. that host rock and ore formation were relatively close in time. Therefore, when significant time differences occur between epigenetic ores and their host rocks, the method may be expected to define this. The method will become progressively more valuable as the apparent polar wandering curves for various continental areas become better defined.

Download Full-text

Cross sections of Lower Ordovician carbonate depositional lithofacies and Mississippi Valley-type zinc-and iron-sulfide mineralization in the Caufield district, east-central part of Harrison 1 degree by 2 degrees Quadrangle, Arkansas and Missouri

10.3133/mf1994c ◽

1992 ◽

Keyword(s):

Cross Sections ◽

Iron Sulfide ◽

Mississippi Valley ◽

Sulfide Mineralization ◽

East Central ◽

Lower Ordovician ◽

Mississippi Valley Type ◽

Valley Type

Download Full-text

Late Cambrian conulariids from Wisconsin and Minnesota

Journal of Paleontology ◽

10.1017/s0022336000033035 ◽

2000 ◽

Vol 74 (5) ◽

pp. 828-838 ◽

Cited By ~ 18

Author(s):

Nigel C. Hughes ◽

Gerald O. Gunderson ◽

Michael J. Weedon

Keyword(s):

Cross Sections ◽

Lower Cambrian ◽

New Genus ◽

Mississippi Valley ◽

Upper Cambrian ◽

Late Cambrian ◽

Lower Ordovician ◽

Two New Species ◽

First Time ◽

Taxonomic Evaluation

Several localities within the heterolithic facies of the St. Lawrence Formation (Upper Cambrian) of Wisconsin and Minnesota yield specimens with phosphatic exoskeletons, quadrate cross sections composed of four equidimensional faces each bearing a midline, and possible holdfast attachment during life. These specimens are here referred to the order Conulariida, class Scyphozoa. Their fine, tuberculate surface ornament and serially invaginated midline structure serve to define a new genus, Baccaconularia, to which two new species, B. robinsoni and B. meyeri, are assigned. Conularia cambria Walcott 1890, also from the Cambrian of the northern Mississippi Valley and long dismissed as a misidentified trilobite fragment, is illustrated photographically for the first time. This species occurs in rocks stratigraphically beneath the St. Lawrence Formation. Specimens assigned to this species by Walcott are conulariids, but lack features now considered diagnostic of either Conularia or Baccaconularia. Walcott's material is insufficient to permit detailed taxonomic evaluation, and we isolate this name to this material, pending the collection of additional, better preserved specimens. Together, Baccaconularia and Conularia cambria contain the oldest large conulariids, and these narrow a stratigraphic gap between other large conulariids known from the Lower Ordovician onwards, and smaller fossils with conulariid affinities known only from Lower Cambrian rocks.

Download Full-text