GEOLOGY AND PALEONTOLOGY OF PALOS - Pubs Warehouse

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spring of 1938. Owing to urban and other develop ments exposures change rapidly or are completely ob literated, particularly in San Pedro. Even under natural conditions exposures are rapidly obscured by slump and talus or by growth of vegetation. On the other hand, new and important exposures are contin ually being uncovered. At least along the water front, however, the net result is a distinct loss geologically. Many of Arnold's famous fossil localities are not acces sible, Deadman Island being, for example, no longer in existence. Small areas of fossiliferous San Pedro sand at Second and Beacon Streets, bounded by streets ex cavated to grade, are a few hundred feet inland from Arnold's lower San Pedro locality (now destroyed) at the San Pedro blufi\ By 1943 this entire area was exca vated to grade and exposures of the San Pedro sand, comparable to Arnold's San Pedro Bluff locality, can no longer bo seen. Arnold's upper San Pedro locality at the north end of San Pedro bluff, near the lumber yard (locality 113, on the east side of Harbor Boulevard), has been destroyed recently. His upper San Pedro locality at Crawfish George's (locality 108, at the north bound ary of the Fort McArthur Lower Reservation) and his Pliocene locality at Timms Point were still accessible in 1938, but the point at Timms Point is concealed by fill. LOMITA MARL, TIMMS POINT SILT, AND SAN PEDRO SAND GENERAL FEATURES STRATIQKAPHIC RELATIONS Strata assigned to the lower Pleistocene are found along and near the northeast and north borders of the hills from San Pedro northwestward to Malaga Cove. They lie unconformably on the Repetto siltstone or lap up on different members of the Monterey shale. At many places they are concealed by overlapping terrace deposits. Sections of the lower Pleistocene strata are shown on plate 13. At most localities the lower Pleistocene deposits con sist chiefly or entirely of the San Pedro sand. At places calcareous beds or silt, or both, of varying thickness are found at the base of the section. The calcareous beds are designated the Lomita marl, and the silt is desig nated the Timms Point silt. In central San Pedro, where the three units Lomita marl, Timms Point silt, and San Pedro sand are superimposed, they are found in upward sequence in the order named. If each unit represents a distinct time interval, discontinuities might be expected to account for the varying thickness of the Lomita marl and Timms Point silt and for their local absence. With the following exceptions, however, no marked discontinuities are apparent. On Deadman Island, which has been destroyed, the San Pedro sand overlay the Timms Point silt along an abrupt and irregular contact. At Lomita quarry sand doubtfully identified as the San Pedro appears to overlie the Lomita unconformably. At other localities where contacts be tween the three units were observed the change in lith- ology is generally gradational. Though continuous exposures along the strike are not extensive, the ob served relations appear to be most satisfactorily ex plained by the inference that the lower part of the San Pedro sand grades laterally into the Lomita marl and Timms Point silt and by the further inference that minor discontinuities are found locally between the three units and also within them, as shown in figure 10. Inasmuch as the Lomita marl and Timms Point silt are PLEISTOCENE SERIES 43 considered facies of a major stratigraphic unit, the San Pedro sand, the view that they are to be assigned member rank under the San Pedro sand may be justified. To avoid violation of current usage and also to avoid cumbersome stratigraphic ramrs, the three units are- assigned formatior rank. GENERAI CHARACTER AND DISTRIBUTION The maximum outcrop thickness of the lower Pleis tocene strata is not more than 350 feet; the maximum subsurface thickness is estimated to be about 600 feet. The thickness varies, however, from place to place- owing to the unconformity at the top. Wherever the Lomita marl was found it is at the base of the lower Pleistocene deposits. It has an extensive- but discontinuous distribution from San Pedro to the- region west of Walteria. It is thickest in the Gaffey syncline and in San Pedro. On the north flank of the- Gaffey anticline it is absent generally or if present is thin. The maximum exposed thickness is 60 to 70 feet. The computed thickness in San Pedro is about 100 feet.. Subsurface sections in the Gaffey syncline show a. thickness as great as 275 feet. The Timms Point silt is the least extensive of the three units. The only area of considerable size is in San Pedro, where the silt rests oh the Miocene or over lies the Lomita marl. Isolated exposures of strata, assignable to the Timms Point silt were found on the- north flank of the Gaffey anticline and along the north border of the hills near Agua Magna Canyon. The exposed thickness in San Pedro is 30 to 80 feet, but the- maximum computed thickness is about 120 feet. The San Pedro sand is found throughout the area, where the lower Pleistocene strata are exposed. It rests directly on the Pliocene or Miocene or overlies the- Lomita marl or Timms Point silt. The maximum ex posed thickness is about 175 feet. In subsurface sec tions the thickness is as much as 300 feet. The Lomita marl consists of a variety of calcareous rocks, principally marl and calcareous sand. The term "calcareous sand" is used for unconsolidated calcareous material of sand or granule size -composed chiefly of calcareous organic remains calcareous algae, Forami- nifera, Bryozoa, small shells, and shell fragments. There appears to be no simple term for such calcareous, sediments. The calcareous sand of the Lomita marl is representative of a particular type hi that the calcareous, material which is its principal constituent is derived from contemporaneous or penecontemporaneous organ isms. The term " calcarenite" 5 has been proposed for clastic limestone or dolomite composed of coral sand, shell sand, or of lime sand derived from the erosion of older limestones. That term is, however, hardly suit able for the unconsolidated sediments under discussion, and a special term such as "biocalcigranulyte" 8 is cumbersone and meaningless to most geologists. The proportions of different organic constituents in the calcareous sediments change from place to place and from layer to layer. Foraminifera or mollusks are the usual most abundant constituents; locally Bryozoa or calcareous algae are most abundant. Echinoids, represented generally by spines, are less frequent. Corals, brachiopods, ostracodes, barnacles, and decapod crustaceans are relatively rare. At some places the calcareous sediments contain little detrital material, about 10 percent or less; at other places they 6 Grabau, A. W., Paleozoic coral reefs: Geol. Soc. America Bull., vol. 14, p. 349,1903. 6 Grabau, A. W., Principles of stratigraphy, 2d ed., p. 283, New York, 1924.
44 NW. GEOLOGY AND PALEONTOLOGY OF PALOS VERDES HILLS, CALIFORNIA GAFFEY SYNCLINE 1 ^.'.YjÎLl'.:^ >'. ' ' -{ - - ' i* - /.'.*.'.' . , . . ^j . ...... j_* ........ LOMITA MARL-Y-'.' ' ' ' ' ' 4r^j^^-'_2='-:v'sAN' iî^S^: GAFFEY STREET, SAN PEDRO SECOND STREET, SAN PEDRO TIMMS POINT i uZ^ L^înf7 - i.^:.-_L-l- ' ' ' .-'. IX-'-. ' .' .- .'j-i/^r. .'-TT ^f Ljrr1 -~rj^"r "=^ i= ; TrT: ~:^P:irriTy_1J 0% 0 . oVo 0 0 0 0. ....... /. . 'SAN '. PEDRO -SANI v.- :-\ :.-'.':.':'.-'/.-'.-'.- . : '. . . '. . .-. ::. .-. :'. . . '. '. ^ . ::::::.^^--. . . . . . . . . . . . ,'. :. :::. . . : . . :. . : . . :::. . :: .v. .-.-. -.v: : : ::. . . .4V-:: : . . . . ::. . . . . . . . . . . . . . . . . . . . . . . . . . . ''.'.' . . .'.'.'.'. .'.'' '-^--rrr ' ' ^ r-r~. V '. ..'. .'.'.'.': .' .' .' .' .'.' ' . . :;.-. .-. . . . .^- - ...- -.... . .v.v.: . . . . . .-. .-. . . . . . . .'_. ...: -... :-ii ... -^V... flMMS POINf SMT-A PEDRO'SAND.' '. '. '. '. . . . . '. irf-^fT^-T^- .ZE^.f^- ^-^.^ f^Zli .'. .'. . .. . . . . .: . -Jz^r LOMITA MARL J. "r . . iu. -r^-r -r^ V- '. -=-= i i.-r-rr- i i r-1- , -1- , J r' ,- i ' > -L~ . ' T- ' -^ ' =-v^ 100 Feet FIGURE 10. Chart showing inferred relations of Lomita marl, Timms Point silt, and San Pedro sand. sandy or silty. In excavations or fresh outcrops the calcareous sediments are unc'emented or poorly cemented. In most natural outcrops, however, they consist of hard rocks cemented by secondarily deposited calcareous material. At many localities glauconite and limy phosphatic nodules are abundant in some layers. The Lomita marl includes also beds of gravel consisting chiefly or entirely of limestone pebbles and cobbles derived from the Monterey shale. Locally huge boulders of soft Miocene mudstone and Pliocene siltstone are embedded in calcareous strata. The petrology of the calcareous sediments has been studied by Reed, 7 but only summaries of the results of his studies have been published. The Timms Point silt consists of brownish generally, massive sandy silt and silty sand. At Timms Point the silt is marly near the base of the member. At that locality the silt and sand contain pebbles of limestone like that in the underlying Miocene strata. The San Pedro sand is made up chiefly of regularly bedded and cross-bedded sand, but includes gravel,^ silty sand, and silt. In San Pedro, where the San Pedro sand overlies the Timms Point silt, a transition zone between the two units consists of thin-bedded sand and thin-bedded silt and silty sand. At many localities where the San Pedro overlies the Lomita a transition zone is marked by the gradual addition of i Reed R D , Petrology of the calcareous beds of San Pedro Hills, Calif, (abstract): Oeol Soc. America Bull., vol. 42, pp. 310-311,1931; Geology of California, pp. 259-260, .Am. Assoc. Petroleum Geologists, Tulsa, Okla., 1933. detrital material. . The petrology of the sand and gravel in the San Pedro has not been studied. For the most part these sediments consist apparently of granitic debris, derived presumably from granitic areas' north of the Los Angeles Basin. Some of the beds of gravel, however, contain pebbles of limestone, cherty shale, and schist, which are assumed to represent local debris derived from the Palos Verdes Hills. SE. TYPE REGION OF STRATIGEAPHIC UNITS The name "San Pedro beds" was used by Dall 8 in 1898. It is not certain but is now immaterial whether the strata briefly described represent the San Pedro sand of this report, the Palos Verdes sand, or both. The term "lower San Pedro series" was used by the Arnolds, 9 for the San Pedro sand of this report. When the lower San Pedro series was named particular attention was devoted to exposures on Deadman Island. Localities along the San Pedro water front were mentioned, however, and that general region is regarded as the type region of the San Pedro sand. The strata assigned to the Timms Point silt were designated Pliocene by the Arnolds 10 and were assigned 8 Dall, W. H., A table of the North American Tertiary horizons, correlated with one another and with those of western Europe, with annotations: U. S. Geol. Survey 18th Ann. Rept., pt. 2, 335,1898. 9 Arnold, Delos and Ralph, The marine Pliocene and Pleistocene stratigraphy of the coast of California: Jour. Geology, vol. 10, pp. 120, 124-126, 1902. Arnold, Ralph, The paleontology and stratigraphy of the marine Pliocene and Pleistocene of San Pedro, Calif.: California Acad. Sci. Mem., vol. 3, pp. 12,18-23,1903. 10 Arnold, Ralph and Delos, op. cit., pp. 120,121-123. Arnold, Ralph, op cit. (Cali fornia Acad. Sci. Mem., vol. 3), pp. 12, 14-17, 1903.
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UNITED STATES DEPARTMENT OF THE INT
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IV CONTENTS Stratigraphy and paleon
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GEOLOGY AND PALEONTOLOGY OF PALOS V
Page 8 and 9: and paleontology and a general acco
Page 10 and 11: 1902. Arnold, Delos, and Arnold, Ra
Page 12 and 13: 1933. Davis, W. M., Glacial epochs
Page 14 and 15: GEOGRAPHY FIOUIIE 1. Sketch map of
Page 16 and 17: year on the north slope, and small
Page 18 and 19: correlation with the Franciscan of
Page 20 and 21: LITHOLOGIC UNIT MIOCENE SERIES ' 15
Page 22 and 23: shale and porcelaneous mudstone rat
Page 24 and 25: GEOLOGICAL SURVEY PROFESSIONAL PAPE
Page 26 and 27: GEOLOGICAL SURVEY ^ HnMMHMHMHBMHMHM
Page 28 and 29: part of the Altamira shale in the P
Page 30 and 31: slide debris that may conceal a fau
Page 32 and 33: Section of middle part of Altamira
Page 34 and 35: pi) a tic shale, and limestone in t
Page 36 and 37: is in the upper part of the sandsto
Page 38 and 39: Section of upper part of Altamira s
Page 40 and 41: Section of Monlerey shale, includin
Page 42 and 43: MIOCENE SERIES Foraminifera from up
Page 46 and 47: GEOLOGICAL SURVEY PKOFESSIONAL PAPE
Page 50 and 51: there appears to be no displacement
Page 52 and 53: oad from Girard to Mohn Spring in t
Page 54 and 55: nose of a spur on the north side of
Page 56 and 57: is used for the formation in that a
Page 60 and 61: y Crickmay u to the Santa Barbara f
Page 62 and 63: The base of the San Pedro sand is d
Page 64 and 65: y Dr. Hampton Smith, Bryozoa and mo
Page 70 and 71: including numerous specimens of Bit
Page 72 and 73: gravel as much as 20 feet thick mad
Page 74 and 75: fossils were found near the seaward
Page 76 and 77: NORTHERN SAN PEDRO In the northern
Page 82 and 83: is at an 1 altitude of 365 feet, mu
Page 84 and 85: son tod by 43 collections in the ma
Page 86 and 87: fiocl as M. cf. M. varitosa. M. var
Page 88 and 89: a width of 3.3 millimeters. Only th
Page 90 and 91: ased on fossils from San Pcdro, is
Page 92 and 93: Pedro district, is recognized in th
Page 94 and 95: According to Arnold's description o
Page 96 and 97: midellids are on record, half of wh
Page 98 and 99: fortis is widespread and locally ab
Page 100 and 101: Progabbia cooperi occurs in the Lom
Page 102 and 103: ANOM1IDAE The Recent California spe
Page 104 and 105: opuntia survived from the Pliocene
Page 106 and 107: millimeters) from Puget Sound. The
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lower Pleistocene units, in deposit
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in interpreting the Pleistocene pal
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PLEISTOCENE SERIES 89 Pleistocene m
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There are no shallow-water Littorin
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localities therefore are inferred t
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locality 70 species of gastropods a
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is better known. Calicantharus is a
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The species in the preceding list b
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It is apparent from the preceding t
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graphic or depth range have taken p
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Pedro district. The close faunal si
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age extend over an entire terrace.
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eludes volcanic agglomerate or brec
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San Pedro district, where those str
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during cutting of the Pleistocene m
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GEOLOGICAL SURVEY PROFESSIONAL PAPE
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GEOLOGICAL SURVEY AIIil'LANE VIEW O
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116 GEOLOGY AND PALEONTOLOGY OF PAL
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G92787 45 10 PLATES 28-37 127
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GEOLOGICAL SUEVEY PROFESSIONAL PAPE
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PLATE 29 [Species and varieties ill
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PLATE 37 [Species illustrated still
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Page Calicantharus fortls..........
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142 INDEX Page kennerlyi, Mercenari
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144 INDEX Page Rissoinidae_________
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