X4 Bareau of Mines and :dinera1Resources Open File Xeport 49 STRATIGRAPHY AND SEDIMENTARY PETROLOGY OF JURASS.IC AND PRE-GRANEROS CRETACEOUS ROCKS, NORTHEASTERN NEW MEXICO APPROVED: APPROVED: Dean of the Graduate School STRATIGRAPHY AND SEDINIENTARY PETROLOGY OF JURASSIC AND PRE-GRANEROS.CRETACEOUSROCKS,NORTHEASTERN NEW MEXICO Charles John -in, B.S., M.A. DISSERTATION Presented to the Faculty of the Graduate School of The University of Texas in Par.tial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY THE UNIVERSITY OF TEXAS June 1958 STRATIGRAPHY AND SEDIMENTARY PETROLOGY OF JURASSIC AND PRE-GRANEROS CRETACEOUS ROCKS, NORTHEASTERN NEW MEXICO Charles J. Mankin ABSTRACT A field and petrologic study of the continental Exeter, Todilto and Morrison (Jurassic) formationsin northeastern New Mexico,. has revealed their source area, environment of deposition and paleoclimate. The-Exeter sandstone, an interior arid-region dune sand, was derived .from a north- western granitic, metamorphic and older sedimentary source. The Todilto limestone, exposed only in the southwestern part of the area, was deposited as a nonmarine, algal limestone. The Morrison formation contains sedi- ments of alluvial flat, fluvial, lacustrine and aeolian environments. The principal source area of the Morrison was from the northwest and similar to that of the Exeter sandstone, a,lthough the southern margin of the basin had local contributions. Volcanic ash, bentonite beds, plagioclase laths, quartz phenocrysts, apatite, euhedral zircon, and.glass shards indicate volcanic activity in the source area. The upward increase of vacuolieed feldspar, ka,olinite, fluvial sandstones, petrified wood and absence of unstable heavy minerals shows that the paleoclimate changed from arid to humid during Morrison deposition. .An Early Cretaceous transgression from east to west is represented by the Purgatoire formation. The presence of euhedral (volcanic) zircon iii inboth the upper Morrison formation and the Purgatoire formation suggests the possibility of depositionat contemporaneity during this transgression. A second marine transgression, from east to west, is represented by the Dakota formation (Late .Cretaceous). Although the source area for the Dakota was the same as for all of the preceding units, the grain size is co;trser and zircon.is only a minor constituent. The coarser grain size is attributed to a change innrelative amountsof contribution.from igneous, metamorphic and sedimentary rocks. The coarser mode is attributed to a sedimentary source. The decrease in zircon is a result of cess+tion.of volcanic activity. , Theabsence of unstable minerals, abundant silica-cementationand vacuolization of the feldspar indicates a humid paJeoclimate for both.the Purgatoire and.Dakota formations. iV V CONTENTS TEXT Page Introduction ............................ 1 Location ............................ 1 Physicalgeography ...................... 3 Scope of problem ....................... 8 Thin-section.analysis ................... 10 X-raydiffraction analysis ................ 11 Grain-sizeanalysis ................... 12 .Heavy mineralanalysis ................. 12 Previouswork ......................... 13 Early geologic explorationof northeastern Nes Mexico ....................... 13 Recentinvestigations ................... 17 Acknowledgments ........................ 19 Stratigraphyand sedimentary petrology ............. 22 Triassicsystem ....................... 22 Dockum group ...................... 22 .Nomenclature. ................... 22 Lithostratigraphy .................. 24 Jurassicsystem ....................... 27 . Exetersandstone .................... 27 Nomenclature .................... 27 Lithostraitgraphy .................. 30 Grain-sieeanalysis ................. 34 Mineralcomposition ................ 41 Heavyminerals ..................... 46 Cementation ....................... 49 Paleoctimate .................... 52. Todiltoformation .................... 53 Nomenciature .................... 53 Lithostratigraphy .................. 55 Sedimentarypetrology ............... 55 Morrisonformation ................... 56 Nomenclature .................... 56 Lithostratigraphy .................. 63 Grain-size analysis ................. 67 Mineralcomposition ................ 71 .Claymineralogy .................. 77 Heavyminerals .................... 84 Cementation....................... 92 Paleoclimate ..................... 94 vi Page : 8. : ...................... 95 1, +t cretaceous': '.; system 'e; yw7,-@urgatoire formation .................. 95 '9 * i ,; , :& e,' __ ' Nomenclature .................... 95 .. ',.-, : ?,' ? ? d.i Lithostratigraphy .................. 99 1 !i ?, Grain-size analysis. ................. 102 5 ij' ,;:, '! "" +, Mineral composition ................ 105 ? ': 'J .. ~~,,i Cementation, .................... 107 ,~ ,.;i' ;' .. Clay mineralogy. ................... 108 .. ,, ..... Heavy minerals ................... 108 .. , Paleoclimate .................... 113 i ... ;:> . r2Dakota formation. .................... I14 ., 'i ".%...< .... ~ ..; ", Nomenclature. ................... 114 i .., '..I..... *! ...... 1, .. .. Lithostratigraphy .................. 115 ~ ......'7 ................ 118 ', , .. Grain-sizeanalysis. '6 .:; Mineralcomposition ................. 121 >. % ....,. '4 ,::;. Heavyminerals ................... 123 \,, ..~.. .... ,y,% .{ .Cementation. .................... 126 :\ :\ '' Geologic history. ......................... 130 Triassic period ......................... 130 Deposition of Dockum group. .............. 130 Jurassic period. ....................... 13 1 Depositioaof Exeter sandstone ............. 131 Deposition of Toditto limestone ............. I34 .Deposition of Morrison formation. ........... 134 .Cretaceousperiod ...................... 137 Deposition of Purgatoire formation ........... 137 Deposition of Dakota formation .............. 138 Conclusions. .......................... 139 References. ............................. 141 Appendix. .............................. 148 Measured sections ....................... 149 Mitchell Ranch section. ................. 150 Romeroville Gap section. ................ 154 San Agustin section ..................... 158 Trujillo Hill section ................... I62 Sabinoso.Canyon .section. ................ 165 Canadian River section ................. 168 Otd Mills .section. .................... 171 Burro Canyon section ................... 175 Gallegos Ranch section ................. 178 San Jon section. ..................... 182 Pa.ge Thin.section descriptions .................. 185 Vita ................................ 233 ILLUSTRATIONS Figures Page 1. Prominentphysiographic features of northeastern New Mexico ....................... 2 2. Location of map area, measuredsections and sub- surfacecontrol points ................. 9 3. Geologicalexploration .of thesouthern high plains. .. 14 4. Locationmap of geologicinvestigations since 1945, northeastern.New Mexico. ............... 18 5. Geologicmap of Bueyerosarea, Harding'County, New Mexico ........................ 21 6. Paneldiagram of Exeter,Todilto, Morrison, Purga- toire and Dakota formations, northeastern New Mexico. ........................ 31 7. Thickness of theExeter sandstone, northeastern New Mexico. ........................ 33 8. Mean grain size in phi units of the upper part of the Exetersandstone, northeastern NewMexico ..... 36 9. Percentage of feldspar in the.Exetersandstone, northeastern New Mexico ............... 43 10. Arealdistribution of percentage of compositeand stretched composite type quartz in the Exeter sand- stone,northeastern NewMexico ........... 45 11. Cementtypes of theupper part of theEketer sand- stone,northeastern NewMexico ........... 51 12. Thickness of theMorrison formation, northeastern .New Mexico. ...................... 66 viii Page 13. , Comparison of sorting values vs. mean .size for the Exeter, Morrison, Purgatoire and Dakota forma- tions. * . , . , * . 70 14.Panel diagram showing clay mineral zonation.of the Morrison formation, northeastern New Mexico , . 83 15. Percentage of apatitein the non-opaque heavy mineral suite from the Morrison formation, northeastern New Mexico e . , . 91 16. Ratio of euhedrat to anhedralzircons.in the Purga-- toire formation, northeastern New Mexico, . , 111 17. Zirconpercentage vs. meangrain size of samples from the Purgatoire and Dakota formations, north- eastern NewMexico. .. , , . , . , 127 Tables 1. Evolution of nomenclature of theDockum group. 25 2. Grainsize data from the Exeterformation . , . , 35 3. Roundnessdata from the Exetersandstone . , . 40 4. .Heavymherat data from theExeter sandstone . , . 47 5.Grain .size data from the Morrisonformation . 68 6. Percentage of feldsparvs. location .and stratigraphic position in theMorrison formation. , . 73 7. Heavymineral data from the Morrison formation. 85 8. Grainsize from the Purgatoire formation. 103 9. Heavy mineraldata from the Purgatoire formation .. 109 10. Grain sizedata from the Dakotaformation . 119 11. Heavymineral data from the Dakota formation . 124 Plates Page 1 . Photographs of Exeter sandstone ........... 209 2 . Photographs.of Exeter sands.tone ........... 210 3 . Photographs of . Exeter sandstone ........... 211 4. Photomicrographs.of Exeter sandstone ........ 212 5 . Photomicrographs of Exeter sandstone ........ 213 6 . Photomicrographs of Exeter sandstone ........ 2 14 7 . Photomicrographs of heavy minerals from Exeter sandstone ......................... 215 8 . Photomicrographs of heavy