Bulletin of the Geological Society of America Vol. 68. Pp. 413-420. 1 Pl. April 1957 Frenchman Formation of Eastern Cypress Hill
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BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 68. PP. 413-420. 1 PL. APRIL 1957 FRENCHMAN FORMATION OF EASTERN CYPRESS HILLS, SASKATCHEWAN, CANADA BY W. O. KTJPSCH ABSTRACT In the eastern Cypress Hills the Frenchman Formation (Upper Cretaceous), a correla- tive of the Hell Creek in Montana, consists of a clay lithosome and a sand lithesome. Study of sections shows that either lithological unit may form the lowest unit of the Frenchman and that they may alternate vertically. Equivalence of the two lithologies is suggested also by their similar fossil content. The Frenchman is distributed over a larger area than previously assumed. Certain sands formerly interpreted as belonging to the Eastend Formation (the Fox Hills of Montana) are assigned to the Frenchman because of their fossil content. Differences in grain size, color, accessory minerals, stratification, and other characteristics can be used to distinguish Eastend sands from the sand lithosome of the Frenchman. The Frenchman rests on a surface of erosion; the upper contact is abrupt but conforma- able. CONTENTS TEXT ILLUSTRATIONS Page Plate Facing page 1. Distribution of Frenchman Formation in the Introduction and acknowledgments 413 eastern Cypress Hills, Saskatchewan, General stratigraphy 413 Canada 418 Definition of the Frenchman Formation 414 Distribution and thickness 415 TABLES Lithology 415 Table Page Description of two Frenchman lithostrati- 1. Development of stratigraphic nomenclature graphic units 415 in the Cypress Hills 414 Relationship of the two lithostratigraphic 2. Lithological characteristics of Eastend and units 417 Frenchman sands 416 Paleontology 419 3. Fossils from Frenchman Formation, eastern References cited 419 Cypress Hills 418 INTRODUCTION AND ACKNOWLEDGMENTS and Mr. N. L. Mclver who assisted in measur- ing stratigraphic sections in the field, and Mr. The Frenchman Formation of southwestern B. K. Smith who conducted heavy-mineral and Saskatchewan presents three problems: (1) mechanical analyses. Mr. R. Rudichuk of the sands belonging to the Frenchman Formation University of Saskatchewan prepared the map are not everywhere easily distinguishable from for publication. Thanks are also due the Sas- sands belonging to the stratigraphically lower katchewan Research Council for financial aid. Eastend Formation; (2) the relationship of The author is indebted to Dr. F. H. McLearn, two different lithostratigraphical units of the Dr. L. S. Russell, and Mr. William E. Benson Frenchman has been differently interpreted for offering valuable criticism of the manuscript. by various workers; (3) some geologists de- scribed the upper boundary of the Frenchman GENERAL STRATIGRAPHY as conformable with the overlying Ravenscrag, others suggested a disconformable relationship. Rocks of late Cretaceous and early Tertiary The writer wishes to thank Mr. S. P. Jordan age are well exposed in the eastern part of the 413 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/68/4/413/3426947/i0016-7606-68-4-413.pdf by guest on 29 September 2021 414 W. O. KUPSCH—FRENCHMAN FORMATION, SASKATCHEWAN Cypress Hills, especially in the valley of the ous day and impure lignite, and the upper of Frenchman River (formerly called White Mud refractory white, gray, and mauve clays, sandy River) between Ravenscrag and Eastend, in places. In addition McLearn recognized Saskatchewan. The stratigraphic section in this an uppermost or fourth member consisting of valley attracted geologists as early as 1883, dark, bentonitic, nonrefractory shales. Lithol- TABLE 1.—DEVELOPMENT or STRATIGRAPHIC NOMENCLATURE IN THE CYPRESS HILLS Correlatives in adjacent McConnell, 1885 McLearn (in Eraser et al., 1935) Furnival, 1946 areas of the U.S.A. Upper Ravenscrag Fort Union Ravenscrag Lower Frenchman Hell Creek No. 4 zone Battle Laramie No. 3 zone Colgate \ Whitemud member / No. 2 zone Whitemud No. 1 zone / Fox Hills Fox Hill Eastend Eastend Pierre Bearpaw Bearpaw Bearpaw and a lithologic description was published ogy and stratigraphic position indicate that the (McConnell, 1885, p. 27c). White sands and Whitemud Formation is the Canadian equiva- clays, now referred to as the Whitemud Forma- lent of the Colgate member of the Fox Hills tion, constitute the most conspicuous unit of Formation in Montana and North Dakota. the section. These and all overlying strata were Furnival (1946) adopted McLearn's divi- assigned to the Laramie by McConnell, whereas sions for the lower part of the section but he designated the underlying sands as Fox Hill. removed the uppermost dark-shale member The Pierre shales are at the base of McConnell's from the Whitemud and called it the Battle section, the division of which has undergone Formation. Through his work the Lower many changes introduced by various workers Ravenscrag became known as the Frenchman (Table 1). Formation, whereas the Upper Ravenscrag Detailed work was done by McLearn in the became simply Ravenscrag Formation. Eastend area, and the results were summarized in Fraser et al. (1935). McLearn used the name DEFINITION or THE FRENCHMAN FORMATION Bearpaw Formation for the Upper Cretaceous marine shales, which were referred to as Pierre Furnival (1946, p. 94) defines the Frenchman by McConnell. The overlying very fine sands Formation as the strata lying above the Battle and silts, representing the youngest marine Formation and underlying the restricted deposits of the plains, were no longer called Ravenscrag Formation. The type area of the Fox Hill but Eastend. The name Whitemud Frenchman is along the Frenchman River was used for the conspicuous white sediments between Ravenscrag and Eastend, but no type which were treated as a separate formation. section was designated by Furnival. McLearn divided the Whitemud Formation of The upper boundary of the Frenchman is the Cypress Hills into three members, or zones the lowest commerical and mappable coal as he called them. The lowest consists of gray seam, which is placed in the Ravenscrag For- kaolinitic sand, the middle of brown carbonace- mation. In the Eastend area this lignite seam Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/68/4/413/3426947/i0016-7606-68-4-413.pdf by guest on 29 September 2021 DEFINITION OF THE FRENCHMAN FORMATION 415 is called the No. 1 or Ferris seam. It is several These banks are mapped as Eastend on the feet thick and has a break of carbonaceous Regina sheet (Fraser et al., 1935, map) and no shale of about 6 inches separating a lower Ravenscrag (which would include the French- thicker bed from an upper. In Montana, where man) is shown east of the creek. From these the Hell Creek is the correlative of the French- key outcrops the Frenchman sand can be man and the Fort Union of the Ravenscrag, followed north where other fossil localities the lowest mappable lignite is also taken as the verify in places the lithologic correlations. base of the Fort Union (Colton, 1955). Plate 1 does not show the distribution of the The lower boundary of the Frenchman is Eastend, but it can be seen from the abbrevi- marked by a surface of erosion as McLearn ated sections that no Eastend beds are present had already recognized (in Fraser et al., 1935, north of T. 8, where the Frenchman everywhere p. 37). Where the pre-Frenchman erosion is lies directly on Bearpaw. nil or very slight, the Frenchman Formation The thickness of the Frenchman varies with rests on the Battle. In other places the French- the depth of erosion that took place before the man rests on one of the three members of the formation was deposited. It ranges from a Whitemud, the Eastend, or the Bearpaw. The minimum of 28 feet to more than 222 feet greatest amount of erosion took place in the where the Frenchman rests on some horizon northern and eastern parts of the area on the in the Bearpaw. The Frenchman increases in flanks of the Cypress Hills, where as much as thickness from the town of Eastend to the 200 feet of older formations was removed before north and to the east. deposition of the Frenchman. Less material was removed from the center of the hills in the LITHOLOGY Ravenscrag-Eastend area. Here the Frenchman commonly rests on Battle or on some stratum Description of Two Frenchman Lithostratigraphic of the Whitemud Formation and has some Units local channelling down to the Eastend sands. Two lithostratigraphic units make up the To the east the Frenchman lies on progressively Frenchman Formation. One is here referred lower strata down to some part of the Bearpaw to as the sand lithosome, the other as the clay shale at the eastern boundary of the map area. lithosome. These units were previously referred On the northern slope of the Cypress Hills also, to as zones (McLearn, in Fraser et al., 1935, the Frenchman overlies the Bearpaw. p. 41), phases (Russell, 1948, p. 32), and facies (Kupsch, 1956, p. 20). The increased knowledge DISTRIBUTION AND THICKNESS of the stratigraphical relationships between the Plate 1 shows the distribution of the French- two lithological units of the Frenchman and man Formation in the eastern Cypress Hills. the recent redefinition and clarification of many On older geological maps covering this general lithostratigraphical terms seem to justify the region (Fraser et al., 1935, Regina sheet) the adoption of the term lithosome. Wheeler and Frenchman was included in the Ravenscrag. Mallory (1956, p. 2718-2719) define a lithosome In general the Frenchman on Plate 1 coincides as a lithostratigraphic body which is mutually with the outer, lower border of the Ravenscrag intertongued with one or more bodies of differ- as mapped on the Regina sheet. Important ing lithic constitution. They point out that differences are noticeable in the northeastern several writers previously referred to such sector of Plate 1 where large areas previously vertico-laterally delineated units as "facies," mapped as Eastend are now shown as French- but that the restricted definition of lithofacies man.