Geology of South-central Hidalgo and Northeastern Mexico, Mexico By KENNETH SEGERSTROM GEOLOGIC INVESTIGATIONS IN MEXICO GEOLOGICAL SURVEY BULLETIN 1104-C Prepared in cooperation with the Insti- tuto Nacional para la Investigacio'n de Re cursos Miner ales, under the auspices of the Technical Cooperation Adminis­ tration of the Department of State and the Foreign Operations Administration ., UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1962 For sale by the Superintendent Of Documents, U.S. Government Printing Office Washington 25, B.C. CONTENTS Page Abstract..___-__________-___--___-_--_------_-_--_--_______,-._ 87 Introduction __________________---.____-----------_---_--_-_._._-._ 87 Location _____________________________________________________ 87 Fieldwork and acknowledgments._______________________________ 88 Geography._ __ _____________________________________________ 89 Accessibility _______.__-___._____------_-_---__---.___..___ 89 Topography and drainage.___________________________________ 91 Climate.;__.______.-_-__-_.-----------___--_--_----____-_ 92 Vegetation._____________________________________________ 92 Agriculture and stockraising.._________-_.____...___.._._... 93 Archeology.______________________________________________ 94 Stratigraphy. _____________________________________________________ 95 Jurassic system______________________________________________ 95 Las Trancas formation _____________________________________ 95 Cretaceous system.____________________________________________ 97 Santuario formation. _ _____________________________________ 97 El Doctor limestone.__-_____-----------------------___---_ 99 Cuautla formation.._______________________________________ 101 Soyatal formation_________________________________________ 103 Mexcala and M^ndez formations._________________ __._______ 105 Tertiary system.______________________________________________ 108 El Morro fanglomerate.__________------_____-_-_---_____-__ 108 Pachuca group__________________------_____-_-__---___---_ 110 Zumate and Tezuantla formations and Don Guinyo tuff.._._-_. 113 San Juan group.________________-----___-___--'------_____- 115 Tarango and Atotonilco el Grande formations-...------------- 118 Quaternary system.____-____-___----------_--_-_-------_____-- 123 Basalt of Pleistocene age._______-__--_-________-_---__.-_-_ 123 Clastic deposits and soils of Pleistocene and Recent ages...__.-_ 125 Intrusive rocks.___________________________________________________ 130 Structure. ________________________________________________________ 131 Folds._._-------.........----_-----------------.------------- 131 Fracture cleavage_________-____--___---_-_-__--_-_-----___--- 135 Thrust faults.....______..---___._-----------.------------------ 135 Normal faults.________________________________________________ 137 Joints. ________________________-_-_______--______------_-__--- 139 Geomorphology ___________________________________________________ 140 Erosional forms in rocks of Mesozoic age. ___-.__---_--------._--- 140 Erosional forms in rocks of Cenozoic age__-_- ___________-_____--- 142 Surfaces of basin-fill deposits__________._______-______--_-__-_- 143 Superposition of streams... _________________*_____---_---_-____- 144 Downcutting and stream capture._________--____-_-_-_---_____-- 147 Recent deposition along streams....----__----_----.---_-----_--- 149 IV CONTENTS Page Geologic history.__________________________________________________ 150 Mineral deposits.__________________________________________________ 153 Metals.... _____--____________-_-_______--_..______--________-_ 153 Nonmetals. __-.-_-_______^_^____- ____________________________ 156 Thermal springs..__-____----______-______-_-_--___--__-__--___ 160 References.--___-__--______---_____-_-__._.____--___--_-___-__-_._ 160 ILLUSTRATIONS PLATE 3. Geologic map and sections of south-central Hidalgo and north­ eastern Mexico, Mexico________-____-_l-_-_-_____._ In pocket FIGURE 35. Index map of Mexico ___________________________________ 88 36. Impure limestone and calcareous shale qf the Las Trancas formation __.:____..__ _________________________________ 96 37. Stratigraphic correlation of geologic units in parts of Mecico.. 98 38. Cliffs of El Doctor limestone along the gorge of the Rfo de Tonaltongo- _____-___._..-..._____-.__.__-_____-_____ 100 39. The rudistid Hippurites mexicana Barcena on the weathered surface of a limestone bed-_____.__.__________ ________ 102 40. Folded limestone beds and shale partings of the Soyatal formation ____-______-_____________-_-.-_-_________.,_ 103 41. Landslide scars (gray slopes) in the poorly resistant Me"ndez formation _______________________________________ _'^._ 106 42. Splintery fracture of the Mexcala or Me"ndez formation...... 107 43. Well-indurated conglomerate of the El Morro fanglomerate lying unconformably on the El Doctor limestone. _______ 109 44. Andesitic flow breccia in the Pachuca group______________ 112 45. Pinnacle composed of explosion breccia of the Zumate forma­ tion. ________________________________________________ 114 46. Weathered surface of Don Guiny6 tuff _ _________._______._ 115 47. Water-laid tuff of the San Juan group along the Rio Tula.___ 116 48. Volcanic conglomerate of the San Juan group...--......-... 117 49. Silt, sand, and pumice of the Tarango formation ._._______-_ 120 50. Contact between crossbedded sand and underlying silt, both of the Tarango formation. _ ._._.___-.____-_-_.___.___._ 121 51. Contact between basalt lava flow and underlying silt stone beds, both of the Atotonilco el Grande formation __.___,_ 122 52. Undissected basaltic cinder cone near Zempoala, Hidalgo.... 123 53. Basaltic ash and lapilli of Pleistocene age in road cut south­ east of Zempoala.___________ _________________________ 125 54. Jawbone of Mammuthus (Parelephas) columbi, found near Tula, Hidalgo... _._._-.-____.._-_-_-_-_-_--_--_-__.._ 127 55. Caliche (white) <in volcanic soil near Pachuca Hidalgo.. _____ 129 56. Flow structure in a small rhyolite plug near San Bartolo, Hidalgo. _______.____ ________________-.---__-_-__-._ 132 CONTENTS V Page FIGURE 57. Fracture .cleavage in marl of the Me"ndez formation near Los Venados, Hidalgo_---------_-_____-----------_--__---_ 136 58. Eroded surface of El Doctor limestone, showing fracture cleavage dipping 45° and nearly horizontal undulating bedding._____________________________________________ 137 59. Ripplelike expression of fracture cleavage in shale beds of the Mexcala formation ___________________________________ 138 60. Coarse gravel faulted against interbedded silt, sand, and gravel of the Tarango formation____________-___-____--_ 139 61. Los Frailes, resistant pinnacles of dacite at the crest of the Sierra de Pachuca.___________________________________ 142 62. The terraced El Tabl6n surface (in shadow) and a small remnant of the higher Actopan surface.--_-_-___-_______ 144 63. View up the Rfo Tula from the rim of Can6n del Abra to the broad plain of the Ixmiquilpan valley______.____________ 145 64. Gorge of the Rio Amajac, cut in El Doctor limestone in the shoulder of an ancient valley___________________________ 146 65. View southeast from Escuela Plomosas, showing gorge cut in El Doctor limestone __________________________________ 147 66. Gully cut in Recent sediments in the Ixmiquilpan valley... __ 148 67. Valley of the Rio Metztitlan, looking upstream from near Los Venados, Hidalgo, before floods of 1954 and 1955_____ 150 68. Valley of the Rio MetztitUln, after floods of 1954 and 1955. _ 151 69. Paricutin mine, 1}_ km southeast of Pachuca, Hidalgo.--.___ 156 70. Loreto mill, in Pachuca__ ______________________ _________ 157 71. El Paje, a mine shaft in the Magdalena district.___________ 158 72. Arrastre used at San Clemente, Hidalgo.-_________________ 159 r T :r -r r r GEOLOGIC INVESTIGATIONS IN MEXICO GEOLOGY OF SOUTH-CENTRAL HIDALGO AND NORTHEASTERN MEXICO, MEXICO By KENNETH SEGERSTROM ABSTRACT The area described extends from Pachuca in east-central Mexico northwest­ ward approximately 100 km to Zimapan, Hidalgo, and southward to within a few tens of kilometers of Mexico City. Folded rocks of Mesozoic age are uncomformably overlain by conglomerate of Eocene to Oligocene age and volcanic rocks of Oligocene to Pliocene age, which locally exhibit slight warping and strong fault-block tilting. Sedimentation, re- excavation, and blocking of drainage are indicated by extensive terrace deposits of late Pliocene silts and gravels. The lava flows that occupy successively lower levels of the Valley of the Rio Tula and the thermal springs that occur throughout the area indicate late Pleistocene volcanic activity. Silver, gold, lead, and zinc ore deposits in Upper Jurassic and Cretaceous marine formations and in lower and middle Tertiary nonmarine rocks are mined extensively. Non- metallic materials of economic importance include limestone and shale for ce- nient manufacture, kaolin and other clays, ocher, and a variety of building stones. INTRODUCTION LOCATION- This report covers ah area extending from 40 to 145 km north of Mexico City and from 215 to 285 km west of the Gulf of Mexico. It lies mostly between lat. 19°50/ and 20°50' N. and between long. 98°40' and 99°24'30" W. A large part of central and southern Hidalgo and the adjacent northeastern corner of the State of Mexico are included (fig. 35). Pachuca, the capital of Hidalgo, is in the eastern part of the area. The southern edge corresponds roughly to the northern edge of the great belt of volcanoes that extends east and