Brigham Young University BYU ScholarsArchive Theses and Dissertations 1972-05-01 Three new species of petrified wood from the upper jurassic Morrison formation of southern Utah David Arthur Medlyn Brigham Young University - Provo Follow this and additional works at: https://scholarsarchive.byu.edu/etd BYU ScholarsArchive Citation Medlyn, David Arthur, "Three new species of petrified wood from the upper jurassic Morrison formation of southern Utah" (1972). Theses and Dissertations. 8091. https://scholarsarchive.byu.edu/etd/8091 This Thesis is brought to you for free and open access by BYU ScholarsArchive. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. THREE NEW SPECIES OF PETRIFIED WOOD FROM THE UPPER JURASSIC MORR.ISON FORMATION ! OF SOUTHE+ UTAH I A Thes~s Presented to the Department of Botany ajnd Range Science Brigham Young tJniversity In Partial Fulfillment of the Requirements !for the Degree Master of Sqience by David A. M~dlyn May, 19V2 ACKNOWLEDGMENTS I wish to express my appreciation and sincere thanks to the chairman of my advisory committee, Dr. William D. Tidwell of the Department of Botany and Range Science of Brigham Young University. His technical advice and critical reading of the manuscript proved invaluable. Thanks are also expressed to Dr. Samuel R. Rushforth, and Dr. Dayna L. Stocks of the same department, and also Dr. J. Keith Rigby of the Geology Department, all of whom reviewed this manuscript and contributed many valuable suggestions as members of my advisory committee. I also wish to express thanks to Naomi Hebbert for her help in preparing the illustrations. Grateful acknowledgment is also expressed to Thomas and Beth Hopkins of Hanksville, Utah, who were kind enough to take the author to the collecting site. iii TABLE OF CONTENTS Page ACKNOWLEDGMENTS •• . iii LIST OF ILLUSTRATIONS . vi INTRODUCTION . 1 Location and Area 2 Previous Studies . 2 Geology • • 4 METHODS 5 SUMMARY . 6 Distribution . 6 Paleoecology • • • . 7 SYSTEMATIC PALEOBOTANY • 8 Genus Protopigeo~lCfil • . • • • • • • 8 Description • • • • • • • • • • • • • • • 8 Discussion • 11 Historical ·Summary f • 11 Comparison with Living Conifers 13 Comparison with Fossil Conifers 13 Genus T5:xaceoxylon • • • • • • • • • • • • • • • • • 18 iv De.s·cription . 18 Discussion . 20 Historical Summary . 20 Comparison with Living Conifers 22 Comparison with Fossil Conifers 23 Genus Mesembrioxvlon 27 Description 27 Discussion 29 Historical Summary 29 Comparison with Living Conifers 30 Comparison with Fossil Conifers 31 LITERATURE CITED • • . 34 V LIST OF ILLUSTRATIONS Figure Page 1. Index Map of Collecting Locality . 3 2. Transverse Section of ProtQpiceoxvlon . 9 3 • Tangential Section of :P...rotoQiceoID;:lon . 11 4. Radial Section of Pr.Q!QQiceoxylon . 11 5. Tangential Section of Taxaceoxylon . 19 6. Radial Section of Ta~~ceo2r1:lon . 19 7. Radial Section of Mesembrioxylon 28 8. Tangential Section of MesembrioID1.Qn 28 Plate I. Protopiceozylon . 37 II. TaxaceoxYlon . 39 III. Taxaceoxylon, Mesembr!ox:ylon 41 43 vi INTRODUCTION The petrified wood fo"r this study was collected from the Upper Jurassic Morrison Formation in the south central part of Utah on the Colorado Plateau. The exact site was shown to me by Mr. and Mrs . Hopkins of Hanksville, Utah. The study area, located near Clay Point, Garfield County, Utah, is south of the Henry Mountains. The site is relatively undisturbed containing many well preserved specimens. The Morrison Formation is locally abundant with petrified woods some of which are highly siliceous and variously colored. The preservation of some specimens is often poor. However, many specimens exhibit excellent preservation and are generically comparable to previously studied floras of similar age. This study constitutes the first detailed study of fossil coniferous woods of the Morrison Formation. Although this formation contains abundant petrified wood, its floral composition has been vir- tually unknown. Three genera have been identified in this study: Protopiceoxvlon Gothan, Mesembrioxylon Seward, and Taxaceoxylon (Unger) KrcYuseL Protopiceoxylon has only been reported once before from strata of the Jurassic age in North America (Knowlton, 1900). Mesembrioxylon and Taxaceoxylon have not been reported previously from the Jurassic of North America. 2 Location and Area The exposure of the Morrison Formation from which these woods were collected is located in Hansen Canyon, south of the Henry Mountains in Garfield County, Utq.h. Hansen Canyon is approximately 50 miles south of Hanksville near the Star Springs Road (Text-fig. 1). Stratigraphically the woods occur between the Brushy Basin and Salt Wash Members of the Morrison. Previous Studies The Morrison Formation has had a paucity of researchers in spite of the fact that it is very rich in plant and animal fossil material. Ward (1899) was probably the first paleobotanical worker in the Morrison, although he did not cite the formation by name, but referred to it as the fresh water Jurassic which was overlain by the Dakota Sandstone Forma- tion. He named Cycadella, a new genus of cycad, and assigned twenty new species to that genus. Numerous charophytes occur in the fresh water limestones of the Morrison (Peck, 1957). Scott (1961) undertook a study of coniferous wood from the Morrison Formation. He noted two .undescribed species of AraucarioxYlon and further stated that, "all structurally preserved woods collected from the Colorado Plateau belong to Araucarioxylon Kraus". A Rhexoxylon-like stem was described by Arnold (1962) from Hansen Creek at a locality near our collecting site. Chandler (1966) reported some unusual fruiting structures found in the Brushy Basin Member of the Morrison which she classified with the 3 '.__ ..... ~-- . \ t • - ) . ~·1()0 miles 0 S.ALTLAKE ' r---··. ..-~- '-----,----,' ------- --'·•,I\ ' ---· --••v· •' "J-t'' _.., , .... .r•- , ·I' '...• _,. I ! I I I l , PR?Y.O ! I •t I I -------------·''"""''\'.. ,-;,r-.t-•iRici7 : I I ' , -•-••••••-•--•} I J I \ ----•• l ...,••-' Ir T! -·-----j { ; I \ -4'' I \ ------- -----(. L i - _________ .,___ • ~:_:_j______ .,:-~-~::,svttiE 1 •• ••••••••• •H l l\~j~';;:il" ,.J ~:·•:'\f --•'"\._l____________ :r···:,; '\,.._-•, i JJ I .1••-.-• • I ,. a• 20 miles Fig. 1 • Index map (x) indicating the approximate collecting site. 4 Cycadophyta and Coniferales. Recently a new osmundaceous species, 1 , Osmundacaulis wadei, was reported from the Morrison of Utah (Tidwell and Rushforth, 1970). The Morrison Formation is best known for its dinosaur remains (Cope, 1878; Mook, 1916; Lull, 1915). Lull stated that, "The American Morrison contains the greatest profusion of sauropod dinosaurs which any formation or locality has produced. " Mollusks, ostracods, and other invertebrates have also been reported from the Morrison (Stanton, 1915). Geology The Morrison Formation is widely exposed over the western interior of the United States. Cross (1894) named the formation after the type locality near Morrison, Colorado. The formation is accepted as Late Jurassic in age but the exact age of the upper beds have not been · determined (Imlay, 1952). At the collecting locality near Clay Point, Hansen Canyon was mapped by the U.S. Geologic Survey (Hunt, 1953) as eroded in all Morrison beds. However, the author has observed that the Morrison Formation is overlain unconformably by the Lower Cretaceous Cedaf Mountain Formation at the collecting site. The contact is placed below the basal conglomerate (Buckhorn Member) of the latter formation. , The formation underlying the Morrison is not exposed at the collection site, I \ but according to Craig (1955) the Bluff Sandstone, a tongue of the ! Cowspring Sandstone, is present nearby at the top of the Summerville 5 Formation and below the Morrison Formation. The Morrison Formation is composed of four members. The lowest member is the Salt Wash followed upward by the Recapture, Westwater, and the Brushy Basin-Members, although in the vicinity of the Henry Mountains in southeastern Utah only the Salt Wash and Brushy Basin Members are exposed (Craig, 1955). Specimens studied during the present investigation were collected from the Brushy Basin Member, although the Salt Wash is present. The exact contact between the two is not easily determined in the Clay Point area . Lithologically, the Brushy Basin Member consists predom- inantly of variegated claystone containing varying amounts of silt and sand. Sediments are variously colored with reds, purples, pinks, and varying shades of green. Lenses of conglomeratic sandstone composed mainly of red, green, white, and black chert pebbles are present. METHODS Petrified wood was collected in the field and where possible embedded material was preferred. Forty-two specimens were colle,cted, of which six were identifiable . Identification of the petrified wood was accomplished using strictly anatomical criteria as no external morphologi.cal features were · present which would facilitate identification. Standard transverse, tangential, and radial cuts were made. The initial cuts were made on a ten-inch Highland Park rock saw, and then polished on two twelve-inch 6 lap wheels • The sections were then mounted with a thermal cement, Lakeside-70, to glass microscope slides. The final cutting and grinding was done on Ward-Ingram thin sectioning machines. The specimens were described and photographed with the aid of