Stratigraphy of the North Half of the Western Sierra Nevada ~Etamorphic Belt, California
Total Page：16
File Type：pdf, Size：1020Kb
Stratigraphy of the North Half of the Western Sierra Nevada ~etamorphic Belt, California r;EOLOGICAL SURVEY PROFESSIONAL PAPER 923 repared in cooperation with the alifornia Division of Mines and Geology Stratigraphy of the North Half of the Western Sierra Nevada Metamorphic Belt, California By LORIN D. CLARK GEOLOGICAL SURVEY PROFESSIONAL PAPER 923 Prepared in cooperation with the California Division of Mines and Geology UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1976 UNITED STATES DEPARTMENT OF THE INTERIOR THOMAS S. KLEPPE, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress Cataloging in Publication Data Clark, Lorin D. Stratigraphy of the north half of the western Sierra Nevada metamorphic belt, California. (Geological Survey Professional Paper 923) Bibliography: p. 25-26. Supt. of Docs. no.: I 19.16:923 1. Geology, Stratigraphic-Paleozoic. 2. Geology, Stratigraphic-Mesozoic. 3. Rocks, Metamorphic. 4. Geology-Sierra Nevada Mountains. I. California. Division of Mines and Geology. II. Title. III. Series: United States. Geological Survey Professional Paper 923. QE654.C54 557.94'4 76-608016 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 Stock Number 024-001-02785-2 CONTENTS Page Page 1\bstract _________________________________________________ _ 1 Paleozoic rocks-Continued Introduction --------------------------------------------- 1 Volcanic rocks---------------------------------------- 15 . Previous work ---------------------------------------- 3 Paleozoic and (or) Mesozoic rocks -------------------------- 15 Fieldwork and scope of this in:vestigation _____________ _ 3 Volcanic and sedimentary rocks________________________ 15 1\cknowledgments ___________________________________ _ 4 Epiclastic rocks -------------------------------------- 16 Terminology _________________________________________ _ 4 Metavolcanic rocks____________________________________ 16 Summary of geology -------------------------------------- 5 Mesozoic rocks-------------------------------------------- 16 Paleozoic rocks ___________________________________________ _ 8 Triassic(?) rocks -------------------------------------- 17 Shoo Fly Formation --------------------------------- 8 Jurassic rocks ---------------------------------------- 18 Lithology --------------------------------------- 9 Sailor Canyon Formation-------------------------- 18 Stratigraphic relations ---------------------------- 10 Milton Formation -------------------------------- 19 1\ge ____________________ ~------------------------- 11 1\mador Group of Taliaferro (1942, 1943) __________ 20 Calaveras Formation _________________________________ _ 11 Cosumnes-type rocks__________________________ 21 Fossils and age ---------------------------------- 12 Logtown Ridge Formation ____________________ 22 Relief Quartzite _________________________________ _ 12 Monte de Oro Formation __________________________ 22 Cape Horn Slate--------------------------------- 13 Unnamed epiclastic rocks__________________________ 23 Delhi Formation--------------------------------- 13 Unnamed volcanic rocks -------------------------- 24 Clipper Gap Formation--------------------------- 13 References cited ------------------------------------------ 25 Tightner Formation ----------------------------- 14 Kanaka Formation-------------------------------- 14 ILLUSTRATIONS Page PLATE 1. Geologic map of the northwestern Sierra Nevada -------------------------------------------------------------- In pocket FIGURE 1. Generalized geologic map of the western Sierra Nevada metamorphic belt -------------------------------------------- 2 2. Index of topographic quadrangle maps within and bordering the north half of the western Sierra Nevada metamorphic belt __ 4 3. Sketch offault-bounded structural blocks of the north half ofthe western Sierra Nevada metamorphic belt-----'------------ 7 III STRATIGRAPHY OF THE NORTH HALF OF THE WESTERN SIERRA NEVADA METAMORPHIC BELT, CALIFORNIA By LORIN D. CLARK ABSTRACT INTRODUCTION A belt of metamorphic rocks, about 180 miles (290 km) long and This report is based on fieldwork by L'orin D. Clark 20-40 miles (32-64 km) wide, crops out in the western foothills of the during the period 1955-61 and is an extension of his Sierra Nevada from the latitude of Yosemite Valley northward. It lies between the Sierra Nevada batholith on the east and overlapping earlier work in the southern half of the western Sierra unmetamorphosed Tertiary strata on the west. The metamorphic Nevada metamorphic belt. He prepared the bulk of the rocks were derived from sparsely fossiliferous eugeosynclinal volcanic report in the mid-1960's, but various factors, including and epiclastic rocks of Paleozoic and Mesozoic age. Regional illness, delayed its completion. This illness also pre metamorphism is generally of low grade, in the greenschist facies. vented the preparation of a proposed major chapter on Lithologic similarities between Paleozoic and Mesozoic rocks preclude correlation by lithology alone. The paleontologic record is the structure of the metamorphic belt, and so this report incomplete, and some map units are undated. The Shoo Fly Formation is limited largely to stratigraphic considerations. The is questionably correlated with the lithologically similar Taylorsville basic data that led to the interpretations herein are Formation of Silurian age exposed north of the report area. An being released separately as a series of geologic maps unnamed unit of volcanic and sedimentary rocks has yielded fossils of and cross sections at a scale of 1:62,500, with lithologic probable Devonian age; the Calaveras Formation has yielded gastropods and corals of late Paleozoic age; an unnamed limestone annotations, along the American, Bear, and Yuba Riv contains fossils of Late Triassic(?) age; the Sailor Canyon Formation ers, and Camp Creek, a tributary to the Cosumnes River contains ammonites of Early and Middle Jurassic age; Cosumnes-type (Clark and Huber, 1975). rocks have yielded ammonites of early Late Jurassic age; and the N. King Huber, who spent the summer of 1955 in the Monte de Oro Formation bears. a Late Jurassic fauna. field with Clark, assembled the final manuscrupt. Many As a result of successive deformations, the structure of the metamorphic belt is complex and incompletely understood. The of the internal inconsistencies inherent in most draft structure can be generalized in terms offour blocks separated by three manuscripts and maps have been reconciled, but some steeply eastward-dipping reverse faults along which younger strata remain, particularly with respect to the regional map in have been thrust beneath older. These include, from west to east, (1) a this report and the larger scale separate maps. block of predominantly Jurassic and probable Jurassic rocks, (2) a In the western SierraNevada, metamorphic rocks are block of predominantly Jurassic rocks, (3) a disconnected block of upper Paleozoic and Mesozoic rocks, including the Calaveras exposed in a 20-40-mile-wide (32-64 km) belt that ex Formation, and ( 4) a block of Paleozoic and Mesozoic rocks including tends about 180 miles (290 km) from about the latitude the Shoo Fly Formation. Mesozoic rocks lie on both sides. of the of Yosemite Valley northwestward to the north end of metamorphic belt, and the eastward-facing bedding tops predominat the Sierra Nevada (fig. 1). On the south and east they ing over westward-facing ones suggest the central position of the are bounded by granitoid rocks of the Sierra Nevada Paleozoic strata results chiefly from faulting. Major fault zones are marked by zones of flaser rock ·or schist or both, batholith, and on the north and west they pass beneath which vary in width from about 100 feet (30m) to nearly 3 miles (4.8 unmetamorphosed volcanic and sedimentary rocks of km) iflarge horses are included. Most major faults strike north or N. Tertiary age. The pre-Tertiary surface can be traced 30° W. Planar structures in the fault zones dip eastward more steeply westward by means of drill-hole and seismic evidence to than 70°. Lineations consisting of elongate rock fragments, amphibole about the center of the Great Valley of California. crystals, and axes of minor folds of slip surfaces plunge steeply. In general, Paleozoic rocks are more deformed than Mesozoic rocks Sparse samples suggest that basement rocks under the in the report area, but exceptions are readily found. The present valley fill are similar to those exposed in the metamor structure results from several stages of regional deformation. The phic belt. greater deformation of the older rocks results partly from greater The southern part of the metamorphic belt was de lithologic susceptibility or geographic position or both, but Silurian scribed in an earlier report (Clark, 1964), and the north rocks were deformed at least twice before deposition of Triassic(?) and Jurassic strata. Jurassic rocks were folded about moderately plunging ern part is described herein. Throughout the belt the axes, and older rocks were refolded, before major faulting was metamorphic rocks were derived from eugeosynclinal completed. Paleozoic and Mesozoic volcanic and epiclastic rocks. 1 2 WESTERN SIERRA NEVADA METAMORPHIC BELT, CALIFORNIA EXPLANATION D Cenozoic sedimentary and volcanic rocks Granitic rocks of the Sierra Nevada batholith, chiefly of Mesozoic age ~ Mesozoic sedimentary and volcanic rocks, in places strongly metamorphosed Ultramafic rocks, chiefly of Mesozoic age Paleozoic sedimentary