Read Before Llie Paleontological Society January 2, 1918

Downloaded from gsabulletin.gsapubs.org on July 30, 2015

BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA

V O L . 29, PP. 281-296 JUN E 30, 191S PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY

MEGANOS GROUP, A NEWLY RECOGNIZED DIVISION IN THE EOCENE OP CALIFORNIA * (Read before llie Paleontological Society January 2, 1918)

BY BRUCE L. CLARK CONTENTS Page Introductory statement...... 281 Previous literature concerning the Eocene of the Mount Diablo quadrangle 282 Meganos group north of Mount Diablo...... 283 Stratigraphy and lithology...... 283 The area under consideration...... 283 Summary of lithology of section...... *...... 285 Evidence for unconformity between Meganos and Tejon...... 288 Faunal list...... 289 Comparison of Meganos and Tejon faunas...... 28.9 Meganos group to south and west of Mount Diablo...... 290 General statement...... 290 Stratigraphy and lithology...... 291 Fauna...... ' 292 Other occurrences of Meganos...... 292 General reference...... 292 Coalinga district...... 292 Eocene of Calabasis quadrangle, Ventura County.. :...... 294 Summary of conclusions...... 295

I ntroductory S t a t e m e n t During the summer of 1917, while studying the Tertiary formations on the north side of Mount Diablo, in the Mount Diablo quadrangle, the writer noticed a marked difference in strike between certain of the beds which up to this time had been considered a part of the Tejon (Upper Eocene). This discordance, a difference of nearly 50 degrees, meant one of two things: either it was due to faulting or to an unconformity. Later * Manuscript received by the Secretary of the Geological Society March 5, 1918. XXII—Bull. Geol. Soc. Am., Vol. 29, 1917 (281) Downloaded from gsabulletin.gsapubs.org on July 30, 2015

282 B. L. CLARK----THE MEGANOS GROUP detailed work has shown conclusively that here we have an unconformity, which was the result of crustal movements of considerable magnitude. Briefly stated, it is the writer’s conclusion, after studying the uncon formity mentioned above, together with fairly large collections of fossil invertebrates from both above and below the line of contact, that we have here the evidence of a structural break of more than local importance; that the fauna found above the unconformity in beds associated with the coal strata is typically Tejon in aspect, while the fauna found below is very different from that of the Tejon and comes from beds which ap parently belong to a distinct epoch of deposition, which has not previously been recognized as such. Thus, formerly only two divisions of the Eocene have been recognized in the region of Mount Diablo, the Martinez (Lower Eocene) and the Tejon (Upper Eocene). The new division, described in this paper, is a part of a series of beds which in this vicinity had previ ously been considered as being of Tejon age. I t is the writer’s belief that beds belonging to this epoch of deposition are fairly widespread through out the State. In some localities in California they have been referred to the Tejon, in others to the Martinez. The beds of the newly recognized epoch of deposition are designated in this paper as the Meganos Group.

P revio us L iter a tu r e c o n c e r n in g t h e E ocene of t h e M o u n t D ia blo Quad r an g le It is surprising how little detailed work has been done on the Eocene of the Mount Diablo quadrangle. Only a brief statement concerning this portion of the section in this area was given in the early report of the Geological Survey1 of California. The invertebrate fauna obtained from beds above the coal, which is found in the vicinity of the old mining towns of Nortonville, Sommerville, and Stewartville, was referred to the Tejon formation. This division was regarded at that time as a part of the Upper Cretaceous (Cretaceous B ). A few species were also found in strata below the coal and were referred by Gabb, the paleontologist of the survey, to a horizon intermediate between his Cretaceous A and B—that is, the Martinez. Gabb2 described a number of invertebrate species from the beds immediately above the coal strata of this section. Turner,8 in a paper entitled the “Geology of Mount Diablo, California,” mentioned only very briefly the Eocene section of this area. He included all of the Eocene in the Tejon. Even up to this time(1891) the Eocene 1G. D. Whitney : Report of progress and synopsis of the field-work from 1860-1864. Geol. Surv. of California, vol. 1, 1865, pp. 23-32. 2 W. M. Gahh: Paleontology of California, vols. 1 and 2, 1864-1869. 3 T. W. Turner: Bull. Geol. Soc. Am., vol. 2, 1891, p. 395. Downloaded from gsabulletin.gsapubs.org on July 30, 2015 PREVIOUS LITERATURE OF MOUNT DIABLO EOCENE ‘283 age of these deposits was still questioned by many geologists, and Whit ney’s original statement that here was a continuous and conformable series, extending from the center of the mountain mass out to the valley and including beds from Lower Cretaceous to uppermost Tertiary, re mained unchallenged. T. W. Stanton,4 in 1896, made a special study of the Eocene beds of California in order to determine if possible their stratigraphic and faunal relationships to the Upper Cretaceous deposits of this general region. His work showed conclusively that there was a decided faunal break between these two horizons. Stanton at this time studied the Eocene sec tion on the north side of Mount Diablo, and in his paper are given several lists of fossil invertebrates. With regard to the position of this fauna he states:5 “The fauna represented by these lists is clearly the original Tejon fauna, that occurs in the neighborhood of Fort Tejon, New Idria, and elsewhere along the Coast Ranges of Washington. Its Eocene char acter has been recognized by Conrad, Marcou, Heilprin, White, and others.” R. E. Dickerson6 has described in considerable detail the stratigraphy and fauna of the Martinez Group of this section. He described the un conformity between the Martinez and the Chico (Upper Cretaceous) and also an unconformity at the top of the Martinez, which he believed to be the contact between the Martinez and the Tejon. I t will be shown in this paper that this latter unconformity is not between the Martinez and the Tejon, as he believed, but between the Martinez and a series of beds, here referred to as the Meganos Group, which are intermediate between the Martinez and Tejon, and separated also from the Tejon by an uncon formity.

M eganos Gbo up N o r th of M o u n t D iablo STRATIGRAPHY AND LITHOLOGY The area under consideration.— The principal area under discussion is a strip extending from about one mile to the west of the old coal-mining town of Nortonville, east and a little to the south of the eastern edge of the Mount Diablo quadrangle. The outcrops, including the Martinez, Meganos, and Tejon groups, dip to the north, the angle of dip varying 4 T. W. Stanton: Faunal relation ot the Eocene and Upper Cretaceous on the Pacific coast. Seventeenth Ann. Rept. U. S. Geol. Surv., pt. 1, 1896, pp. 1011-1059. s Op. cit., p. 1021. 8 R. E. Dickerson : The stratigraphic and faunal relations of the Martinez formation to the Chico and Tejon, north of Mount Diablo. Univ. of California Publ. Bull. Dept. Geol., vol. 6. no. 8, 1911, pp. 171-177 ; Fauna of the Martinez Eocene of California. Upiv. of California Publ. Bull. Dept. Ool., vol. 8, no. 6. 1914, pp. 61-180. Downloaded from gsabulletin.gsapubs.org on July 30, 2015

I>:) 00 ~

~ !:"' () t-< ;> ~ p:: I >-3 II: t;j :s: t:Z:J Tmk Markley trJ 0 > [:SJ T!J Tejon >;;i 0w Tsr Mega nos IT=rJ 0 ~ 1:2:2] Tmr Martinez 0 d '"d c=:JKc Chico ----Thrust "- - _: Base of Dlv. D

FIGUUE 1.-Areal Map of the Eocene D eposits to the north of Mount Diablo Downloaded from gsabulletin.gsapubs.org on July 30, 2015

NORTH OS' MOUNT DIABLO 285 from 15 to 40 degrees. The greatest width of these outcrops is about two and a half miles. The beds of the Meganos Group in this area rest unconformably on those of the Martinez Group. This unconformity, as stated above, was first described by E. E. Dickerson. The Lower Tejon, as recognized at that time, is the base of the Meganos, as described in this paper. The Meganos beds in this area have a maximum thickness of approximately

F ig u r e 2.— Cross-section showing the Eocene Groups as found on the north side of Mount Diablo Kc = Chico. Tmt = Martinez. Tst = Meganos. Ttj = Tejon. Tmk = Markle> (Oligocene). 3,000 feet. The section may be roughtly divided into five lithologie mem bers; these, beginning at the base, will be designated divisions A, B, C, D, E. Summary of Ethology of section.— The following is a generalized sec tion of the Eocene groups as found on the north side of Mount Diablo. The Martinez portion of the section is copied from Dickerson’s paper,7 “Fauna of the Martinez Eocene, California.”

Feet 6. Clay shales with minor amount of sandstone.. 500 5. Fine, buff-colored sandstone; in places hard, calcareous layers contain marine fossils...... 175 4. Sandy shales; exposures poor ; soil very red... 75 3. Light gray to white, angular-grained sand stones, coarse to medium in texture; cross bedding common, with minor layers of choco Tejon Group. late-colored shales; two important coal layers ...... '...... 75-400 2. Chocolate-colored shales, ashy in places, with thin lenticular layers of coarse sandstone; coal layer locally known as Black Diamond vein ...... 50 1. Conglomerate ...... 0-20 -----Unconformity------7 H. E. Dickerson : Univ. of California Pubi. Bull. Dept. Geol., vol. 8, no. 6. 1914, p. 71. Downloaded from gsabulletin.gsapubs.org on July 30, 2015

286 B. L. CLARK----THE MEGANOS GROUP Feet Olay shales and sandstones at top, grades down Into fine, massive, poorly indurated sandstone; exposures of the beds of this division are very poor ...... 0-1,500 Sandstone of medium texture; thin-bedded near bottom; more massive at top; yellow brown to D. gray in color. The massive sandstones near top contain lenses of harder, calcareous and fossiliferous sandstones...... 0-300 5. Dark slate-gray shales; bedding planes fairly distinct; light calcareous nodules and lenses. 0-230 §* 4. Sandstone, fine to coarse in texture; in places uo forms a grit; contains thin clay lenses; in O places contains considerable carbonaceous cOa m aterial...... 110 8 CJ 3. Dark slate-gray shales, similar to (1) and (5). 90 9 2. Sandstone, medium to fairly coarse; weathers S on surface a rusty brown; grains chiefly of quartz and mica...... 50 1. Dark slate-gray, clay-shale; bedding planes in distinct ; carbonaceous material abundant... 75 ( Coarse to medium fine, quartzitic, gray to gray- B. J brown sandstones, with some fine conglomeratic layers ...... 700 Heavy conglomerates; boulders composed of quartzites, chert, limestone and large angular slabs of sandstone, containing typical Chico (Upper Cretaceous) fossils...... 50 -Unconformity - 5. Gray-green shale ...... 300 4. Gray-green, glauconitic sandstone; Trocho- cyathus zitteli beds...... 50 Martinez Group... 3. Fine-grained, gray sandstone...... 200 2. Shales and sandstones...... '...... 100 1. Brown conglomeratic sandstone; Meretrix dalli beds...... 50 Unconformity------Chico. The conglomerates at the base of the Meganos Group, division A, because of their peculiar character, are worthy of mention. Here great angular slabs of fossiliferous Chico sandslone, sometimes 5 or 6 feet in Downloaded from gsabulletin.gsapubs.org on July 30, 2015 NORTH OF MOUNT DIABLO 287 length, or even more, are found associated with the well rounded quartzitic and igneous boulders, and with these are found numerous smaller Limestone and sandstone pebbles, which were derived either from the Martinez or the Chico, thus showing conclusively that these beds may be considered as a true basal conglomerate. The shales of division C of the Meganos are especially noticeable in that they are so different from anything found in the Tejon on either the north or south side of Mount Diablo. The dark color, calcareous lenses and nodules, mode of slaking on the surface into small fragments, presence of carbonaceous material and layers of coarse sandstone which separate the different shale members are all very similar to lithological characters of the Knoxville shales (Lower Cretaceous or Upper Jurassic), as seen in certain sections of this general area. These sediments probably represent shallow-water conditions of deposition, and were perhaps laid down in land-locked or partially land-locked basins. In the basal chocolate-colored shales of the Tejon great quantities of impressions of leaves, rushes, and fossil wood are found. These beds, which may be traced for many miles to the east and beyond the eastern boundary of the quadrangle, contain everywhere the leaf impressions in abundance. They will undoubtedly yield a large and well preserved flora for the paleobotanists who wish to study them in the future. These leaf shales were apparently laid down in marginal marine swamps. The pres ence of shells, belonging to the genus Corbicula, in a layer of standstone in the shales testifies as to the brackish or fresh-water conditions during deposition. The most important of the coal beds of this region, and one which was mined throughout most of the area, is found near the top of these lower Tejon shales. In the vicinity of Nortonville this bed is known as the “Black Diamond Vein.” I t is reported to have a maximum thickness of about 4 feet. Above this coal layer at Nortonville is a sandy, conglom eratic bed varying from 1 to 3 feet in thickness, which is very highly impregnated with iron, so much so in places that it may be called an iron ore. Rush and leaf impressions were found also in this layer. The close association of this bed with the leaf shales and coal, together with the fact that the iron deposit is limited to a definite layer over a considerable area, suggests a primary rather than a secondary origin. The coarse, cross-bedded, light-colored sandstones immediately above the shale may well have been deposited under somewhat similar condi tions. Two of the important coal-layers, the “Little” and “Clark” veins, mined for many years at Nortonville and Somerville, are found in these sandstones. The coal of the Clark vein, which is about 2y2 to 3 feet in Downloaded from gsabulletin.gsapubs.org on July 30, 2015

288 B. h. CLARK— THE HEGANOS GROUP thickness as exposed in the mine at Nortonville, is found intercalated between the coarse, white, quartzitic sands without a trace of shale. Evidence for unconformity between Meganos and Tejon.— The most important evidence for unconformity between the Meganos and the Tejon is the great difference in strike between the beds of the two horizons, seen at numerous localities; this is very noticeable at the coal mine at Stewartville, where the difference approximates 50 degrees. The basal sandstone of division D is here in contact with the Tejon, the thickness of the standstone being approximately only 150 feet. When followed to the west of Stewartville, the sandstone soon disappears and the basal beds of the Tejon rest directly on the upper dark-colored shale (division (!), and a little to the west and south of Nortonville the Tejon rests on the first sandstone member from the top of division C. To the south east of Stewartville the sandstone of division D emerges from under the Tejon very rapidly, forming the ridge north of Deer Yalley; the shaly sandstones and shales of division E also appear, and within 3 or 4 miles of Stewartville they show their maximum thickness of 1,500 feet. In the canyon to the south of the Star mine, a distance of not much more than a mile from Stewartville, these upper shales of division E are well developed. In going to the southeast, besides this difference in strike and the rapid emergence of the upper Meganos beds from beneath the Tejon, a marked difference in dip was obtained at a number of localities. In general it appears that there is a difference in dip between the two horizons through out the entire length of the area. At the west end of the area southwest of Nortonville there is a maximum difference in dip of 18 degrees between the Upper Meganos beds and those of the Lower Tejon. In the vicinity of Stewartville the difference approximates only about 5 degrees, while in the vicinity of West Hartley the difference is between 15 and 20 degrees. In the western part of the area under discussion, heavy conglomerates are found at the base of the Tejon. In some places the conglomerate has a thickness approximating 20 feet. To the east, in the vicinity of Stew artville and West Hartley, the conglomerate disappears and the chocolate shales at the base of the Tejon rest on the shales and shaly sandstones of division E of the Stewartville, making it impossible to find a sharp con tact anywhere. As has been already stated, in the western part of the area the basal Tejon conglomerate rests on the dark shale of division C, and at a number of localities a sharp contact was located. This contact is decidedly irregular, and the bedding planes of the shale are cut off and butt into the conglomerate. I t is a noticeable fact, also, that there is con siderable carbonaceous material at the contact. Downloaded from gsabulletin.gsapubs.org on July 30, 2015 NORTH OS' MOUNT DIABLO 289 FAUN AL LIST The following is a preliminary list of the Meganos species obtained from the section described above. The majority of these came from one horizon, the sandstones of division D ; a few species were found in the fine sandstones of division E : Pelecypoda : Gastropoda : Aoila gabbiana Dickerson. Actwon, n. sp. Antigona, n. sp. Aplustrum? n. sp. A vietila, n. sp. Architectonica, n. sp., sp. A. Cardium marysvillensis Dickerson. ArcMtectonica, n. sp., sp. B. Cardium brewerii Gabb, n. subsp. Brachyspingusf n. sp. Corbula, n. sp. Chrysodomus, n. sp. Crassatellites grandis (Gabb), n. Chrysodomus, n. sp. subsp. Fusinus, n. sp. Crassatellites, n. sp. Calleodea, n. sp. Crassatellites, n. sp. Calleodea sutterensis Dickerson. Dosinia, n. sp. Haminea, n. sp. Diplodonta, n. sp. Natica gesteri Dickerson. Ficopsis, n. sp. Natica hornii Gabb. Glydmeris, n.‘ sp. Neptunea, n. sp. Leda gabbi Conrad, n. subsp.? Oliva, n. sp. Leda, n. sp. Pseudoliva, n. sp. Leda sp. Siphonalia? sp. Marcia (?) conradi Dickerson. Surcula, n. sp. Meretrixf dalli Dickerson. Scaphander, n. sp. Meretrixf cf. ovalis Gabb. Turris, n. sp., sp. A. Meretrixf n. sp. Turris, n. sp., sp. B. Macrocallista, n. sp. aff. M. conradi Turris, n. sp., sp. C. (Gabb). Turritella reversa Waring. Modiolus omatus Gabb. Turritella merriami Dickerson, Ostrea sp. n. var. Phacoides, n. sp. Turritella n. sp. Pholasf sp. Scaphoda: Psammobia, n. sp. Dentalium cooperii Gabb. Solemya, n. sp. Cephalopoda :

290 B. L. CLARK----THE MEGANOS GROUP were listed either by Stanton or Dickerson in the papers already referred to. This upper fauna, referred by Dickerson to his Balaniphyllia zone, contains many of the species 'which are so typical of the type section of the Tejon, such as Meretrix hornii Gabb, Meretrix tejonensis Dickerson, Conus remondii Gabb, Ficopsis cf. cowlitzensis Weaver, Turritella uvasana Conrad, Turritella uvasana bicarnata Dickerson. The fauna of the Meganos, as obtained from the section described above, is very different from that of the Tejon. Sixty-five species, listed above, have been recognized in this fauna; of these, 4, possibly 6, are found in the Tejon beds immediately above; 2 or 3 more are found in the Tejon of other sections. I t is interesting to note that over half of the Meganos species are new; also that a number of these forms are found in beds in the southern part of the State, which have been referred to as being Martinez in age. Reference will be made to this occurrence further on in the paper. I t is the writer’s conclusion, after comparing this fauna from the Meganos beds with that of the Tejon, that here is good evidence which points to a marked faunal as well as stratigraphic break between these two horizons.

Meganos Group to South and West of Mount D iablo GENERAL STATEMENT A study of the Eocene section on the south and west sides of Mount Diablo has shown that here also the Meganos beds are present and lie unconformably below the Tejon. One of the best known sections of the Eocene of the Mount Diablo region is found on the south and west sides of the mountain, the maximum thickness in this area being about 2,500 feet. These beds are described in a recent publication by Dr. R. E. Dick erson.8 Here he established three faunal zones, all of which he referred to the Tejon. The lowest zone he called the Turbinolia zone; the fauna from near the middle of the section he referred to his Rimella simplex zone, while that found in the upper beds was referred to his Balanophyllia variabilis zone. The writer’s conclusions, after studying the fauna from the south and west side of Mount Diablo, is that the beds containing the faunas desig nated by Dickerson as the Turbinolia and Rimella simplex zones are not 8 R. E. Dickerson : Note on the faunal zones of the Tejon Group. Univ. of California Publ. Bull. Dept. Geol., vol. 8, no. 2, 1914, pp. 17-25; Stratigraphy and fauna of the Tejon Eocene of California. Univ. of California Publ. Bull. Dept. Geol., vol. 9, no. 17. 1916, pp. 363-524. Downloaded from gsabulletin.gsapubs.org on July 30, 2015

SOUTH AND WEST OF MOUNT DIABLO 291 Tejon, but belong to the Meganos period of deposition; that neither are to be correlated with the typical Tejon of the type section. The first true Tejon in this section is represented by the beds of Dickerson’s Balano- phyllia zone. In this section as well as on the north side of the mountain these latter beds, the true Tejon, are found unconformable on top of the Meganos. Near the western edge of the Mount Diablo quadrangle, beds belonging to the Meganos Group are found unconformably beneath beds containing the “Balanophyllia fauna.” These outcrops are found 011 the north side of the ridge north of Pine Canyon, extending to the west onto the Con cord quadrangle. Not as much detailed work has been done by the writer on the Meganos portion of the section in this area to the west of Mount Diablo as has been done on the section in the area to the north of the mountain; for this reason only a very general statement as to the lithology and fauna of this section can be made.

STRATIGRAPHY AND LITHOLOGY The basal conglomerate of the Meganos in this western area is found on the ridge to the south and west of the mouth of the Arroya del Cerra. Here the conglomerate rests on dark shales and carbonaceous brown sand stones, which very probably are of Cretaceous age. The conglomerate has a maximum thickness of close to 20 feet. The lower portion of the conglomerate is fairly coarse, the pebbles being composed largely of shale, limestone, sandstone, and conglomeratic sandstone, together with some quartzitic and igneous boulders. Some of the boulders of sandstone are angular and are as much as a foot to a foot and a half in length. Typical Chico fossils were found in some of the conglomeratic sandstone boulders. The pebbles in the upper beds of this conglomerate consist chiefly of fine angular fragments" of shale, derived apparently from the dark shales im mediately below. Above the basal conglomerate, just described, is, roughly estimated, 150 to 200 feet of medium fine, yellow-brown, fossiliferous sandstone, and above this about 1,800 feet of dark-colored shales, fine sandstone, and shaly sandstone. The line of division between the Meganos and Tejon is marked by a narrow band, possibly two feet thick, of fine conglomerate. The pebbles at the base consist of quartz, black chert and red chert similar to the cherts of the Franciscan, and shale. Above this the pebbles consist almost entirely of angular fragments of shale in a matrix of coarse, light gray sandstone. Thus here again we apparently have a true basal conglom erate. Downloaded from gsabulletin.gsapubs.org on July 30, 2015

292 B. L. CLARK— THE MEGANOS GROUP The Meganos beds of this section have a strike of approximately north 40o west, while those of the Tejon have a general strike of about north 70° west. Thus, in following the Meganos beds to the southeast they are rapidly overlapped by those of the Tejon, disappearing entirely within a short distance. FAUNA Up to the present time only a comparatively small fauna has been ob tained from the Meganos of this section. More detailed work will un doubtedly yield a larger fauna. Some of the species found are: Cardium, 'brewerii Gabb, n. subsp. Glycimeris sp. Psammobia, n. sp.; also found on north side of Mount Diablo. Macrocallista, n. sp.; also found on north side. Meretrix, n. sp.; also on north side of mountain. Amauropsis, n. sp. RimeUa n. sp. Galleodea sutterensis Dickerson; also found on north side. Mitra, n. sp. Scaphander, n. sp.; also found on north side. V enericardia, n. sp.?

Other Occurrences of Meganos GENERAL REFERENCE It is the writer’s opinion that there are other localities in different parts of California where beds are found which apparently belong to the same general epoch of deposition as those of the Meganos. Two of the better known localities will be discussed here.

COALINGA DISTRICT In the Eocene to the north of Coalinga there is a contact, which has been discussed by several writers. The beds above this contact contains a typical Tejon fauna—a fauna which contains a considerable number of the highly ornamented molluscan species found in the Lower Tejon of the Mount Diablo region and in the type section at the south end of the San Joaquin Valley. One of the most common species found in the beds below this contact is Turritella andersoni Dickerson. This species is so abundant in these beds in this general area that they will be referred to as the Turritella andersoni beds. In 1912 J . A. Taff9 described an uncon formity between the Turritella andersoni beds and the lower sandstones 9 J. A. Taff: Pal. Soe. Am., 1912, p. 127. Downloaded from gsabulletin.gsapubs.org on July 30, 2015 OTHER OCCURRENCES 293 of the Tejon, locally known as the Domengine sands. He suggested that the Turritella andersoni beds might be Martinez in age. E. T. Bumble10 was so impressed with the importance of this contact that he unhesitat ingly expressed the belief that the Turritella andersoni beds were Martinez in age. In his paper entitled “Notes on Tertiary deposits near Coalinga oil field and their stratigraphic relations with the Upper Cretaceous” occurs the following statement: “Our work now proves that this lower member of the Eocene (the Martinez) is of very considerable extent southward on the west side of San Joaquin Valley; that it consists of three or more clearly defined members, and that, in addition to the unconformity already described between it and the Cretaceous, there also exists a decided unconformity between it and the overlying Tejon.” Eobert Anderson and Robert W. Pack/1 in their paper entitled “Geol ogy and oil resources of the west border of the San Joaquin Valley north of Coalinga, California,” referred the Turritella andersoni beds to the Martinez ? Their point of view is stated as follows: “The relation of the Martinez? formation to the overlying Tejon formation may be stated with more assurance“ to be one of unconformity. . . . The writers believe that the beds here described as Martinez? are probably the equivalent partly of the Martinez and partly of the Tejon, and that the uncon formity here registered in the Eocene is not to be correlated with that between the Martinez and Tejon formations in the Mount Diablo region.” Thus in the foregoing we have the suggestion that possibly the Turri tella andersoni beds are transitional between true Tejon and true Mar tinez. Dickerson,13 in his paper entitled “ Stratigraphy and fauna of the Tejon Eocene of California,” states his belief that the unconformity be tween the Turritella andersoni beds and the beds regarded as the base of the Tejon by the writers just quoted is not important. He says: “Several workers in this field report a well marked unconformity in the middle of the section. The time represented by this unconformity is difficult to evaluate. The only method at present available is the faunal one, and, as has been previously shown, the faunas from above and below the unconformity are as a whole quite similar. There is no well marked difference in dip and strike reported along the unconformable contact; but the evidence consists of a sharp change in lithology and the penetration of the underlying strata by 10 E. T. Dumble: Jour, of Geology, vol. 20, 1912, pp. 28-37. 11 Robert Anderson and Robert W. Pack: U. S. Geol. Survey, Bull. no. 603, 1915, p. 66. 12 More assurance than the unconformity between the Chico and the Martinez, just described In the paragraph preceding this. ** R. E. Dickerson : Univ. of California Publ. Bull. Dept. Geol., vol. 9, no. 17, 1916, pp. 428-429. Downloaded from gsabulletin.gsapubs.org on July 30, 2015 294 B. L. CLARK----THE MEGANOS GROUP Cretaceous bore holes 'which are filled with sands of the overlying stratum. The unconformity reported is at least not of the same order as the uncon formity between the Tejon and Martinez, as the structural and faunal break between these two groups is a great one. A very large number of Martinez species failed to bridge the gap. Such is not the case in the vicinity of Do- mangine Creek. The writer believes that the time break represented by this unconformity is at most of secondary order—that is, such as might separate two formations in a group.” After studying the fauna from the Turritella andersoni beds, the same material on which Dickerson based his conclusions, the writer was im pressed with the fact that there are, in this fauna, so few typical Tejon species. He does not agree with a number of the specific determinations that Dickerson made, as given in his list from locality 1817. Evidently Dickerson did not consider the possibility of there being a third group coming in between the Martinez and the Tejon, and that if this were so one might well expect to find a larger number of species bridging the gap between this intermediate horizon and the Tejon than the gap between the Martinez and the Tejon. While the paleontological evidence for the correlation of the Turritella andersoni beds with the Meganos epoch of deposition may possibly not be the best at the present time, yet the strati graphie evidence, together with the difference between the fauna of the Turritella andersoni beds and that of the Tejon above, makes it highly probable that here we are dealing with the same epoch of deposition as that to which the Meganos beds belong.

EOCENE OF CALABASIB QUADRANGLE, VENTURA COUNTY C. A. Waring,14 in a recent publication, has described the Eocene of the Calabasis quadrangle. Waring has divided this series in this area into the Martinez and the Tejon. I t is stated that apparently the Marti nez in this area grades up into the Tejon, the division between the two being entirely based on paleontological evidence. The fauna from these so-called Tejon beds, as he has listed and illustrated it, undoubtably be longs to the same epoch of deposition as the Turritella andersoni beds to the north of Coalinga. I t is interesting to note that several of the species in the so-called Tejon fauna, listed and figured by Waring, are apparently identical with certain of the new species or new subspecies in the Meganos beds of the Mount Diablo region. This is also true of several of the so-called Martinez spe cies. One of the most striking examples is the fact that one of Waring’s 14 C. A. Waring : Stratigraphie and faunal relations of the Martinez to the Chico and Tejon of southern California. Proc. California Acad, Scl., 4th ser., vol. vii, no. 4, 1917, pp. 41-124, pis. 7-16. Downloaded from gsabulletin.gsapubs.org on July 30, 2015 OTHER OCCURRENCES 295 new species of Turritella in his so-called Martinez, Turritella reversa, is found very abundantly in the Meganos beds of the Mount Diablo region. N ote.— During the summer of 1918 a number of the most important Eocene sections in southern California were studied by the writer; these included the Coalinga section and that of the Calabasis quadrangle, both mentioned above. The details of this work will be published in the neaT future. Briefly stated, the results are as follows: In the Coalinga section a marked unconformity was found separating the Turritella andersoni beds (now known to belong to the Meganos epoch of deposition) from those of the typical Tejon. Not only is the contact irregular between the beds of these two groups, but also there is a notice able difference in dip and strike at many localities, together with a true basal conglomerate at the base of the Tejon. In this general region the Martinez is absent; the Meganos group rests on the Upper Cretaceous shales. In the Calabasis quadrangle, the section studied by C. A. Waring, whose paper was referred to above, the Martinez, the Meganos (Turritella andersoni beds), and the Tejon are all present. The Tejon of this section rests unconformably on the Meganos, the unconformity being indicated by an irregular contact, a marked difference in strike, and a possible dif ference in dip, together with a basal conglomerate. A very good typical Tejon fauna was obtained above this contact. The writer’s conclusion is that the Meganos group is to be correlated, at least in part, with the marine phase of the lone as found at Table Mountain, near Oroville, California, the fauna from which latter beds has been referred by Dickerson15 to his Siphonalis sutterensis zone. The writer has refrained from using the name lone for the beds belonging to this epoch of deposition as found in different parts of California, for it is believed that the lone very probably is composed of beds belonging to more than one epoch of deposition.

Summary of Conclusions 1. Mapping of the sedimentary series of the Eocene in the Mount Diablo quadrangle shows that there are three distinct stratigraphic units in these deposits instead of two, as was formerly recognized. 2. The beds of this newly discovered epoch of deposition come between the Martinez (Lower Eocene) and the Tejon (Upper Eocene). 3. The name Meganos has been given to this group of deposits. 16 R. E. Dickerson : Note on the faunal zones of the Tejon group. Univ. of California Publ. Bull. Dept. Geol., vol. 18, no. 2, 1914, p. 23. Downloaded from gsabulletin.gsapubs.org on July 30, 2015

296 B. L. CLARK----THE MEGANOS GROUP 4. The Meganos beds have a maximum thickness of close to 3,p00 feet and lie unconformably below beds of typical Tejon age and unconformably above beds of typical Martinez age. 5. Both of the unconformities, the one found at the top, the other at the base of the Meganos, are indicated by a difference in dip and strike, as well as by the presence of true basal conglomerates, together with other evidences of erosion. 6. I t is believed that the Meganos epoch of deposition has a fairly wide distribution throughout the State; in some localities it has been included with the Martinez, in others with both the Tejon and the Martinez. 7. I t is believed that the beds of the Meganos group are to be corre lated, at least in part, with the marine beds of the lone found at Table Mountain, near Oroville, California. Downloaded from gsabulletin.gsapubs.org on July 30, 2015 Geological Society of America Bulletin

Meganos group, a newly recognized division in the Eocene of California

BRUCE L. CLARK

Geological Society of America Bulletin 1918;29, no. 1;281-296 doi: 10.1130/GSAB-29-281

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