PLANT MICROFOSSILS FROM A FORT UNION COAL OF MONTANA

Abstract

FOSSIL SPORES and pollen are abundant in coals occurring in the Fort Union series near Red Lodge, Carbon County, Montana. Previous to this discovery only a single species of fossil spore (Miner, 1935) and no pollen grains were known from the Paleocene rocks. In North America, very few of the extensive Tertiary coal deposits have been explored for plant microfossils, although such study has great possibilities for the advancement of knowledge concerning the composition and stratigraphy of coal. The coal field in the vicinity of Red Lodge and Bear Creek, Montana, is extensive. According to Dr. Erling Dorf (personal written communication), coals are very high in the Fort Union series, are definitely post-Lebo, and probably postTongue River as now restricted (see Wood et al., Bull. Geol. Soc. Amer., vol. 52, plate 1, 1941). Woodruff (1909) has shown that there is a total of more than eighty-one feet of coal in the numerous seams. These occur through an 825-foot section of the Fort Union series. The coals range from smuts to seams twelve feet in thickness. There is a general thinning of the seams toward the southwest and thickening toward the northwest. The areal distribution of the seams indicates that they are more extensive than local lenticular deposits. The structure of the coal field is an eroded monocline which dips southwestward from the Pryor Mountains. At the foot of the Beartooth Range the monocline is terminated by a fault whose throw is several thousand feet. The dip of the beds in the vicinity of Red Lodge is 180, but south of Bear Creek the dip is much less. Minor undulations occur in the beds, and a small dome is present near the latter town. In 1940 and 1941 twenty-seven channel samples of coal were collected from seams one to eight inclusive. The seams are numbered from the top down. Maceration of the samples has revealed the presence of spores and pollen in varying degrees of abundance. Those coals composed mostly of modified woody tissues contain very few spores or pollen and have proved unsatisfactory for statistical correlation. This paper describes the fossil spores and pollen from one deposit, the Kolarich Mine. This mine is located in Section 25, Township 7 S., Range 20 E. It is approximately two miles east of Red Lodge. Some uncertainty exists concerning the position of this coal seam. Opinions of local residents are di1 Received for publication August 22, 1945. The authors wish to express their appreciation to Dr. Erling Dorf for information concerning the age of the Kolarich coal, to Dr. J. C. Gilman for examining the fungus spores, and to Dr. Theodor Just for reading the manuscript and checking the construction of the new names and combinations. For a grant-in-aid, the authors are indebted to the American Association for the Advancement of Science. vided as to whether the Kolarich Mine is exploiting seam No. 1 or No. 3. No conclusive evidence has yet been secured from microfossil studies that will solve the problem. The coal sample was secured from the wall several yards from the entrance of the drift mine. The rock section in the Kolarich Mine consists of (1) a gray undershale, (2) coal, 6 feet, (3) shale parting, 6 inches, (4) coal, 6 inches, (5) gray roof shale. METHODS.-Tertiary coals require various maceration treatments because they range widely in composition and structure. Since the Kolarich coal is both woody and close to sub-bituminous rank, it was necessary to use Schultz's solution for maceration. Pieces of coal were selected that did not contain visible woody structure. These were broken into pieces approximately one-half centimeter in diameter and covered with Schultz's solution for 24 hours. In the course of the maceration the mass was frequently stirred. This treatment was followed by washing with water, and decantation, until the odor of Schultz's solution was no longer apparent. The coal was then covered with ammonium hydroxide for another 24 hours. Again the material was washed and decanted until the odor of the ammonium hydroxide disappeared. The remaining sediment was examined for megaspores, but none were found. The finer sediment was stained with safranin, washed, centrifuged and transferred to glycerine jelly. Permanent slides were made from this preparation. All specimens are in the collection of the senior author.