Some Aspects of Younger Pr Ec Am Brian Geology In

Some aspects of younger Precambrian geology in southern Arizona Item Type text; Dissertation-Reproduction (electronic) Authors Shride, A. F. (Andrew Fletcher), 1918- Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 05/10/2021 06:31:52 Link to Item http://hdl.handle.net/10150/565591 SOME ASPECTS OF YOUNGER PR EC AM BRIAN GEOLOGY IN SOUTHERN ARIZONA ■ ' by Andrew F.^Shride A Thesis Submitted to the Faculty of the DEPARTMENT OF GEOLOGY In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY In the Graduate College THE UNIVERSITY OF ARIZONA 1961 THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE I hereby recommend that this dissertation prepared under my direction by Andrew F. Shride entitled nSome Aspects of Younger Pre- cambrian Geology in Southern Arizona” be accepted as fulfilling the dissertation requirement of the degree of Doctor of Philosophy. Dissertation Dit&ctor Date After inspection of the dissertation, the following members of the Final Examination Committee concur in its approval and recommend its acceptance:* i t rw-*<i_ 'AAAx. ♦This approval and acceptance is contingent on the candidate’s adequate performance and defense of this dissertation at the final oral examina tion. The inclusion of this sheet bound into the library copy of the dissertation is evidence of satisfactory performance at the final examination. SOME ASPECTS OF YOUNGER PRECAMBRIAN GEOLOGY IN SOUTHERN ARIZONA : ■ " .. by : • ■ : - i .v ■ > - ■ ; / . Andrew F. Shride, ABSTRACT Feldspathic and quartzose sedimentary formations and cherty dolomites—the latter now largely metamorphosed to silicate-bearing limestones—form a sequence about 1? 500 feet thick that comprises most of the Apache group. Individual formations, which represent shallow marine deposits accumulated through a long period of geologic time, are remarkably uniform in stratigraphic details throughout an area of 15,000 square miles in southern Arizona. Tuffaceous sedi ments in the lowest formation and basalt flows at the top of the group indicate volcanic activity. The Apache group was mildly folded and eroded before deposi tion of the Troy quartzite, which accumulated in thicknesses of at least 1,200 feet. After lithification of the Troy these younger Precambrian formations were folded and faulted along widely spaced northerly trending belts, then intruded by minor dikes and extensive sills of ii diabase, which locally equal the sedimentary rocks in volume. The Troy and older formations were much faulted and displaced as a con sequence of diabase inflation. Thereafter the formations were deeply eroded. In the southern part of the region Middle and Late Cambrian sandstones and quartzites, here referred to the Bolsa and Abrigo for mations, overlie them. In the northern part of the region the Cambrian formations were eroded away before the Martin limestone of Devonian age was deposited on the Precambrian formations. These relations indicate that the Troy quartzite should be redefined and designated Pre cambrian in age, and that the major diabase intrusions, heretofore generally considered Laramide, should be assigned to the Precambrian. Wider appreciation that deformation preceded and accompanied diabase intrusion during later Precambrian time will aid in deciphering the structural settings of the mining districts of southern Arizona. iii STATEMENT BY AUTHOR This thesis has been submitted in partial fulfillment of require ments for an advanced degree at The University of Arizona and is de posited in The University Library to be made available to borrowers under rules of the Library. Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in their judgment the proposed use of the material is in the interests of scholar ship. In all other instances, however, permission must be obtained from the author. SIGNED: 6 ^ TABLE OF CONTENTS . .. Page INTRODUCTION........................................................................................ 1 Geographic settings of the outcrops of younger Precambrian ro ck s........................................................................ 1 Scope of the report ................................................ 7 Acknowledgments .................. 8 Previous nomenclature and correlations of the younger Precambrian ro ck s....................... 10 Principal conclusions of this report .......................................... 15 ROCK TYPES OF THE OLDER PRECAMBRIAN BASEMENT . 18 PR E-APACHE UNCONFORMITY ......................................................... 22 YOUNGER PRECAMBRIAN ROCKS .......................... 26 Apache group .................................................................................... 28 Pioneer s h a le ............................................................................ 28 Dripping Spring quartzite....................................................... 43 Lower member.................................................... 45 Upper member ................................................................. 51 Mescal limestone............................. 67 Stratigraphy of unmetamorphosed sections ............. 70 Lower member ......................................................... 70 Algal m em ber........................... 85 Upper m em b er......................................................... 87 Late-formed chert in the M e sca l................................ 92 Lithology of the metamorphosed M escal................... 102 Thickness ......................................................................... 108 iv / Page Stratigraphic nomenclature............................................ I l l Basalt flo w s ................................................................................ 113 Troy quartzite ................... .............................................................. 117 Arkose member................... ...................................................... 118 Chediski sandstone member .................................... 122 Quartzite member .................................... ...................... .. 139 Diabase ................................................................. ............................. 145 Form and distribution of intrusions .................................... 145 Petrology ................... 156 LATE PRECAMBRIAN DEFORMATION............................... 177 Pre-diabase deformation ................... 177 Deformation associated with diabase intrusion................ 186 RELATIONS OF PALEOZOIC FORMATIONS TO PRECAMBRIAN ROCKS.................. 193 Relations of the Bolsa and Abrigo formations ........................... 195 Relations of the Martin lim estone......................................... 205 GEOLOGIC HISTORY OF THE YOUNGER PRECAMBRIAN FORMATIONS ................. 210 AGE OF THE YOUNGER PRECAMBRIAN FORMATIONS ....----- 223 REFERENCES CITED ............................... 228 v LIST OF FIGURES Figure Page 1. Distribution of outcrops of younger Precambrian rocks in Arizona in relation to the three principal physiographic regions ............................................................ 2 2. Map showing outcrops of younger Pr ecambrian strata and coextensive diabase intrusions in southeastern Arizona ............................. ......................................... .. in pocket 3. Index map showing positions of some paleogeographic features of the younger Pr ecambrian formations ... in pocket 4. Sketch map showing outcrops of the older Pre- cambrian terrane ............................................................. in pocket 5. Delicate cross-lamination in tuffaceous siltstone of the Pioneer shale ....................................................... 34 6. Photomicrograph of tuffaceous siltstone of the Pioneer shale .......................................................... 35 7. Typical lamination and irregular bedding in upper member of Dripping Spring quartzite ............. 59 8. Sc our - and- fill structures and compaction features in upper member of the Dripping Spring quartzite .... 61 9. Scour-and-fill structures of Dripping Spring quartzite viewed in longitudinal section ............................ 65 10. Structures typical of the stromatolite beds of the middle member of the Mescal limestone ........................ 88 11. Reconstruction of north-south geologic section after the Troy quartzite was deposited..................................in pocket 12. Diagrammatic sections showing relations of multiple injections of diabase to plates of host rock isolated between intrusions ........................................................... 153 vi Figure Page 13. Outcrop of diabase showing characteristic effects of disintegration caused primarily by weathering........... 158 14. Diagrams showing effects of sill inflation on dis placement along a pre-existing fault.............................. 184 15. Idealized geologic section showing relations of faults to diabase intrusions and to pre-Paleozoic un conformities ......................

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