Mohnian Stage Research Articles

Facies Analysis of the Monterey Formation in the Northern Santa Barbara Channel (1)

The Monterey Formation in the northern Santa Barbara Channel was deposited in three distinct depositional environments during the early Mohnian (middle Miocene). Along the northern margin of the channel, the Monterey was deposited in a banktop environment, resulting in a thin and clay-rich (chert-poor) lower Mohnian Stage that is punctuated by disconformities. In contrast, in the middle of the Santa Barbara Channel, the Monterey was deposited in a basinal setting, resulting in a thick and continuous lower Mohnian Stage that is clay poor and chert rich. Between the banktop and the basinal depositional settings is an area that is transitional in character and represents deposition on the slope. These changes in average composition and thickness cause a southward increase in the quality of the fractured Monterey reservoir within the northern Santa Barbara Channel.

Middle Miocene planktonic microfossils and lower bathyal foraminifera from offshore southern California

Lower bathyal sediments representing portions of the Luisian and Mohnian stages of Kleinpell (1938) occur on a submarine ridge near Tanner Bank, offshore southern California. The presence of abundant and well-preserved calcareous nannofossils, diatoms, silicoflagellates, radiolarians and foraminifera allows accurate correlations with the onshore type sections of these stages. In terms of the calcareous nannofossil zones, the age range is from the Sphenolithus heteromorphus Zone to the Discoaster kugleri Zone. Although abundant benthic foraminifera indicative of the Luisian and Mohnian are present, they are accompanied by species more characteristic of the Pliocene Repettian Stage of Natland (1952) and the Pliocene-Miocene “Delmontian” Stage of Kleinpell (1938). Many of these latter species live today at lower bathyal depths (below 2,000 m), others occur in lower bathyal sediments as old as Oligocene, but are absent in the onshore type sections of the Luisian and Mohnian stages in coastal California. We ascribe their absence in onshore sequences to deposition at middle bathyal depths. The known chronostratigraphic ranges of several species are extended and five new species and two new subspecies of benthic foraminifera are described.The following new taxa are described: Bolivina pelita n. sp., Cassidulinella inflata n. sp., Globocassidulina undulata n. sp., Cibicidoides mckannai miocenicus n. subsp., C. mckannai sigmosuturalis n. subsp., Pullenia fragilis n. sp., Parafissurina inornata n. sp.

Geochronology Bearing on Age of Monterey Formation, California: ABSTRACT

The name Monterey Formation or Monterey Shale has been applied to lithologically similar pelitic marine rocks of Miocene age exposed in the coastal regions of California. These rocks, characterized by unusually high proportions of silica, have been variously termed diatomite, porcelanite, porcelaeous shale and mudstone, chert, and cherty shale. The type area for the Monterey Formation was designated near Monterey, California. Although the Monterey Formation in general contains numerous ash, tuff, and bentonite beds, only a few of these volcanic units have been dated. It has been necessary to make use of both the isotopically dated horizons and Kleinpell's Miocene benthonic foraminiferal stages to construct a time-stratigraphic framework for the Monterey Formation at different locations. Ages for the various stage and zone boundaries, based on published and unpublished data, are as follows: Repettian-Stratotype B. oblique (Delmontian), ca. 5 m.y.B.P.; Stratotype B. oblique-Mohnian, ca. 7 m.y.B.P.; Mohnian-Luisian, ca. 12 m.y.B.P.; Luisian-Relizian, 14.0 to 14.9 m.y.B.P.; Relizian-Saucesian, 15.7 m.y.B.P. At the type area, an ash from the Canyon del Rey Diatomite Member, the uppermost member of the Monterey Formation, was dated at 11.3 ± 0.9 m.y. (F-T on zircon). Coupled with a Luisian age for the oldest strata, the type Monterey Formation spans, at most, the time interval from 15 to 10 m.y.B.P. In contrast, the Monterey Shale in the Palos Verde Hills encompasses the time interval from 15 to 5 m.y.B.P. based on isotopic data from the Altamira Shale, Valmonte Diatomite, and Malaga Mudstone Members, which contain foraminiferal assemblages characteristic of the Relizian, Luisian, and Mohnian Stages, and the B. oblique zone (Delmontian). At other localities where biostratigraphic and isotopic data are available, the rocks termed Monterey are not exact time equivalents of the type foramation, an observation made earlier by both Kleinpell and Bramlette. End_of_Article - Last_Page 966------------

Planktonic Calibration of Provincial Miocene Stages of California: ABSTRACT

Age assignments and correlations of Miocene marine strata in California are usually made with reference to a sequence of benthic foraminiferal stages. During the past decade refined calcareous and siliceous planktonic microfossil biochronologies have been developed that provide a means for calibrating the California provincial stages to international standards while also testing the chronostratigraphic reliability of correlations derived by equating stage diagnostic benthic foraminifer assemblages in different areas. Diatoms are particularly useful for dating the upper, silica-rich part of the Monterey Formation whereas calcareous nannofossils are useful for dating the lower part of the Monterey Formation and older Miocene units. Data from type sections show that the base of the Saucesian Stage is near the Oligocene-Miocene boundary of international usage, the base of the Relizian Stage falls at the base or in the lower part of the early Miocene Helicosphaera ampliaperta Zone (nannofossil), and the Luisian Stage essentially coincides with the middle Miocene Sphenolithus heteromorphus Zone (nannofossil) and the Denticulopsis lauta Zone to Subzone a of the Denticulopsis hustedtii--D. lauta Zone (diatom). The top of the type Mohnian Stage is within the latest Miocene to early Pliocene Nitzschia reinholdii Zone (diatom), whereas the type section of the Delmontian Stage is within Subzones b and c of the middle Miocene Denticulopsis hustedtii-D. lauta Zone. The type Delmontian is therefore equivalent to the lower Mo nian of most California sections. Compilation of data from throughout California indicates some overlap in time of benthic foraminifer assemblages diagnostic of the Zemorrian and Saucesian Stages and of the Relizian and Luisian Stages. The transition from Luisian to Mohnian benthic foraminifer assemblages, however, consistently occurs near the top of the Sphenolithus heteromorphus Zone and within Subzone a of the Denticulopsis hustedtii-D. lauta Zone. End_of_Article - Last_Page 974------------

Comparison of Miocene provincial foraminiferal stages to coccolith zones in the California Continental Borderland

Research Article| April 01, 1979 Comparison of Miocene provincial foraminiferal stages to coccolith zones in the California Continental Borderland James K. Crouch; James K. Crouch 1U.S. Geological Survey, Scripps Institution of Oceanography, La Jolla, California 92093 Search for other works by this author on: GSW Google Scholar David Bukry David Bukry 1U.S. Geological Survey, Scripps Institution of Oceanography, La Jolla, California 92093 Search for other works by this author on: GSW Google Scholar Author and Article Information James K. Crouch 1U.S. Geological Survey, Scripps Institution of Oceanography, La Jolla, California 92093 David Bukry 1U.S. Geological Survey, Scripps Institution of Oceanography, La Jolla, California 92093 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1979) 7 (4): 211–215. https://doi.org/10.1130/0091-7613(1979)7<211:COMPFS>2.0.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation James K. Crouch, David Bukry; Comparison of Miocene provincial foraminiferal stages to coccolith zones in the California Continental Borderland. Geology 1979;; 7 (4): 211–215. doi: https://doi.org/10.1130/0091-7613(1979)7<211:COMPFS>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Biostratigraphic ages determined by planktic coccoliths and benthic foraminifera for the same core samples from the California Continental Borderland suggest that a significant overlap exists among provincial Miocene stages of California and that some of the benthic foraminifera commonly used to recognize these stages are time-transgressive. For example, samples assigned to the middle Miocene Discoaster exilis Zone of coccoliths (∼ 14 ± 1 m.y.) are also assigned to the Relizian, Luisian, and lower Mohnian Stages on the basis of benthic foraminifera. Significantly, most past and current geologic interpretations of Cenozoic marine sequences in California rely heavily on provincial benthic foraminiferal stages and zones. Thus, the apparent overlapping of provincial stages has serious implications for geologic studies of the California Cenozoic and should be further investigated in sections onshore. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Santa Monica and Santa Ana Mountains--Relation to Oligocene Santa Barbara Basin

An analysis of the stratigraphy and structure of the Santa Monica and Santa Ana Mountains demonstrates a close affinity between the two, one that can be explained only by a much closer original geographic relation of the two ranges. The Santa Monica Mountain block, bounded by the Malibu Coast fault on the south and the Las Posas fault on the north, began a westward movement across the ancestral basin during the Luisian stage of the middle Miocene. Approximately 33 mi (53 km) of left-lateral displacement took place prior to the Mohnian stage of the upper Miocene, breaking the original basin into the separate Ventura and Los Angeles basins joined by a San Fernando subbasin. This displacement took place in no more than 2.5 m.y. at a minimum rate of movement of 0.8 in. (2 cm) year. Four mi (6.4 km) of post-Mohnian left-lateral displacement subsequently occurred. The magnitude of displacement is determined by projecting the Santa Ana Mountains parallel with the San Andreas direction, to a point of intersection with the Raymond fault, and then by matching similar stratigraphy on opposite sides of the fault. Restoration of the Santa Monica Mountains block to its pre-Luisian location, combined with the addition of known thicknesses of sections of the Sespe Formation, permits the construction of original Sespe isopachs and the reconstruction of the Oligocene basin, herein called the Santa Barbara basin. This basin was bounded, south of the present Ventura basin and west of the present Los Angeles basin, by a positive Franciscan area, the Anacapia of Reed and Hollister. The Luisian orogeny, responsible for the westward rifting of the Santa Monica Mountains, also produced the breakup of Anacapia, and exerted the most profound influence on southern California geology of any Cenozoic event.

Late Miocene and Early Pliocene Correlations in California Province: ABSTRACT

The late Miocene of California was divided into four Oppelian zones by Kleinpell. He grouped these zones into larger time-stratigraphic units, the Mohnian and Delmontian Stages. As a discipline for these zones and stages, Kleinpell used benthonic foraminifers and larger invertebrates in continuous stratigraphic sequences. The Bolovina modeloensis, Bulimina uvigerinaformis, and the Bolovina hughesi Zones represent the Mohnian, and the Bolovina obliqua Zone represents the lower half of the Delmontian Stage. No foraminiferal zone was designated for the upper half of the Delmontian Stage. These two stages and four foraminiferal zones can be found in continuous stratigraphic (superpositional) relation with demonstrable middle Miocene, late Luisian, faunas below and early Plioc ne faunas above in the following areas: Palos Verdes Hills, Huasna-Nipomo, Monterey, San Pablo Bay area. Additional continuous stratigraphic sections representing the middle Miocene and early late Miocene, the Luisian and Mohnian Stages, are found in Newport Beach; the Luisian, Mohnian, and Delmontian Stages are found in the Naples Bluff section; the Mohnian and Delmontian Stages are found in Woodland Hills (type Mohnian); the Delmontian and early Pliocene are found in the Reef Ridge area. All of these stratigraphic sections contain one or more of the following groups of microfossils: diatoms, radiolarians, silicoflagellates, and planktonic foraminifers. These microfossil groups, together with the benthonic foraminifers and larger invertebrates corroborate Kleinpell's original zonal sequ nce. End_of_Article - Last_Page 440------------

Luisian and Mohnian Biostratigraphy of Monterey Shale at Newport Lagoon, Orange County, California: ABSTRACT

Sediments of Luisian and Mohnian age are exposed almost continuously in a 1,400-ft section of Monterey Shale along the margin of Newport Lagoon. The lowermost 200 ft appears to be barren of fossils, consequently, no definite age assignment can be demonstrated for this part of the section. Overlying this barren interval is approximately 265 ft assigned to the Luisian Stage on the basis of occurrence of Brizalina advena striatella, Brizalina imbricata, Pullenia miocenica, Siphogenerina spp. and Valvulineria californica californica. Approximately 40 ft of section directly above the Luisian sediments is assigned to the Brizalina modeloensis Zone of the lower Mohnian Stage as defined by the restricted occurrence of the nominate species (sensu stricto); also present, but not restricted to the zone, are Bulimina unigerinaformis, Cassidulina monicana, and Concavella gyroidinaformis. Overlying the Brizalina modeloensis Zone is 325 ft of sediments End_Page 438------------------------------ which is assigned to the Bulimina uvigerinaformis Zone of the lower Mohnian Stage. The Bulimina uvigerinaformis Zone can be readily divided into an older subzone designated the Concavella gyroidinaformis Subzone and a younger subzone here designated the Brizalina woodringi Subzone. The top of the older subzone is marked by the last occurence of Concavella gyroidinaformis; the Concavella gyroidinaformis Subzone is approximately 210 ft thick at this locality. The overlying Brizalina woodringi Subzone is based on the continued occurrence of Bulmina uvigerinaformis after the extinction of Concavella gyroidinaformis. This subzone is approximately 115 ft thick with its top, and the top of the lower Mohnian Stage, marked by the last occurrence of Bulimina uvigerinaformis. Above the lower Mohnian Stage at Newport Lagoon is approximately 470 ft of foraminiferal Monterey Shale assigned to the upper Mohnian Stage. Among the many species present are Bolivina hughesi, Brizalina benedictensis, Brizalina decurtata, Brizalina giradensis, Brizalina granti, Cassidulinella renulinaformis and Discorbinella valmonteensis. No foraminifers were found in the uppermost 100 ft of Monterey Shale which overlies the sediments of demonstrable Mohnian age. Cyclococcolithina neogammation, a fossil coccolith, was found to have its last occurrence coincident with the top of the lower Mohnian Concavella gyroidinaformis Subzone at Newport Lagoon. Another coccolith, Reticulofenestra pseudoumbilica, was observed to have its first occurrence at the base of the lower Mohnian Brizalina modeloensis Zone. The last occurrence of Sphenolithus heteromorphus was confirmed to be in the uppermost Luisian Stage. End_of_Article - Last_Page 439------------

Late Paleogene-Neogene Planktonic Biostratigraphy and Its Geologic Implications, California: ABSTRACT

Planktonic microfossils indicate that at least in some typical sections, the Narizian Stage (Kreyenhagen Shale) is middle Eocene, spanning part of the range for the P10-P14 zones (about 49-45 m.y. ago). The Refugian Stage is essentially late Eocene, representing Paleogene zones P15-P17 (about 45-37.5 m.y. ago). Oligocene time is represented approximately by the Zemorrian Stage, defined by Paleogene zones P18-P22 (about 37.5-22.5 m.y. ago). Miocene subdivisions are: early Miocene, Saucesian Stage (Neogene zones N4-N8), radiometric age span about 23-15 m.y. ago; middle Miocene, Relizian, and Luisian Stages (Neogene zones N9-N12), radiometric age span about 15-11 m.y. ago; and the late Miocene Mohnian Stage (Neogene zones N13-N18), radiometric age span about 11-3 m.y. ago. T e Pliocene is represented by the Repettian, Venturian, and the lower part of the Wheelerian Stage (Neogene zones N19-N21) with a radiometric age span of about 3-1.79 m.y. ago. The Quaternary is younger than 1.79 m.y., embracing the upper part of the Wheelerian Stage, the Hallian, and younger units, representing Neogene zones N22 and N23. Employing planktonic criteria, boundaries of stages based on benthic species are clearly time-transgressive. A major structural change occurred in the Zemorrian Stage, the Oligocene, introducing a new set of basin patterns with the destruction of the Farallon plate and the adjacent spreading center, about 29-24 m.y. ago. A second important structural change occurred about 4 m.y. ago, in the late Miocene, with the development of a different pattern of basins and the formation of the Gulf of California. This new tectonic pattern resulted from, or was related to, the development of a westerly motion of the Pacific plate. The major volcanism of the California Tertiary occurred following the destruction of the Farallon plate, during the early and middle Miocene. End_Page 429------------------------------ Maximum sedimentation rates for the middle Eocene Narizian Stage (Kreyenhagen Shale) are less than 100 m/m.y., for the late Eocene (Refugian Stage) about 100 m/m.y., for the Oligocene Zemorrian Stage about 166 m/m.y., for the early Miocene about 140 m/m.y., for the middle Miocene about 500 m/m.y., for the late Miocene about 250 m/m.y., and for the Pliocene-Pleistocene they are almost 2,000 m/m.y. The very rapid sedimentation rates, following the second major change in tectonic patterns about 4 m.y. ago, are similar to those today in Santa Barbara basin; they are less than the much higher rates recognized for the late Pleistocene in basins of the continental borderland. End_of_Article - Last_Page 430------------

Paleoclimatic Interpretations for Late Miocene of California Based on Marine Diatoms: ABSTRACT

The diatom assemblages of a 1,600-ft section of diatomites in the Monterey and Sisquoc Formations near Lompoc, California, give evidence of a warming trend within the late Miocene. Frequency changes of individual warm and cold water species, ratios of different ecologic types, and variations in the overall assemblage indicate a general increase in temperature during the period of deposition. The lower third of the section (upper Mohnian Stage) contains a cool-temperate microflora, characterized by relatively high frequencies of Denticula hustedtii Simonsen and Kanaya. A mixed warm- and cold-temperate assemblage predominates through the overlying 1,000 ft of diatomites, and the highest 80 ft (Delmontian Stage?) contains a warm-temperate microflora, with Coscinodiscus excen ricus Ehrenberg, C. lineatus Ehrenberg, Thalassionema nitzschioides Grunow, and Thalassiosira sp. Diatom evidence for these temperature changes is further supported by that from the fossil fish and sparse Foraminifera of the Lompoc section. The changes may reflect a general climatic warming, but also may result from local variations in current distribution, such as the fluctuations in the cold-water California Current proposed for the late Miocene of southern California. Diatoms may provide valuable paleoecologic evidence for this extensive diatomite facies in California, which lacks the more commonly utilized foraminiferal and invertebrate paleoecologic indicators. End_of_Article - Last_Page 769------------

Preliminary Revaluation of Late Miocene Biostratigraphy of California: ABSTRACT

Preliminary studies of the type Mohnian and Delmontian Stages and regional biostratigraphic studies of other late Miocene sections of California by the use of benthonic Foraminifera and fish indicate the following. 1. The Delmontian Stage of Kleinpell is correlative with his Mohnian Stage on the basis of the occurrence of (a) Epistominella gyroidinaformis (Cushman and Goudkhoff) in the lower part of the type Delmontian (this species does not range stratigraphically above early Mohnian in California); (b) Bolivina hughesi Cushman (=Bolivina sinuata alisoensis Cushman and Adams of others), Bulimina delreyensis Cushman and Galliher, and Etringus scintillans Jordan in the upper part of the type Mohnian in California; and (c) Late Miocene megafossils in the Santa Margarita Sandstone, which overlies with apparent conformity beds that are near, and correlate with, the upper part of the type Delmontian. 2. Kleinpell's Bolivina obliqua Concurrent-range Zone (Delmontian) overlaps the range of species characteristic of his subjacent Bolivina hughesi Zone in the type are of the Mohnian Stage and all other Mohnian zones at other localities in California. 3. Many of the species characteristic of his late Mohnian Bolivina hughesi Zone overlap both his subjacent Bulimina uvigerinaformis Zone and his superjacent Bolivina obliqua Zone. 4. Many of the species characteristic of his Bulimina uvigerinaformis Zone overlap both his subjacent Bolivina modeloensis Zone and his superjacent Bolivina hughesi Zone. 5. Bulimina uvigerinaformis Cushman and Kleinpell and Bulimina delreyensis Cushman and Galliher have the same stratigraphic range and appear not to range above middle Mohnian in California. Therefore, all of Kleinpell's late Miocene concurrent-range zones are in need of revision or redefinition. End_of_Article - Last_Page 559------------

Tropical Planktonic Zones and Calcareous Nannoplankton Correlations in Part of the California Miocene

THE material used in this study is from exposures along the east shore of Newport Bay, California (Fig. 1). This section contains good assemblages of benthonic foramini-fera of Kleinpell's upper Luisian and lower Mohnian stages1. The Luisian and Mohnian stages are represented by the upper middle and the lower upper part of the Miocene Monterey Shale. These stages are traditionally denned by their characteristic benthonic foraminiferal species. In recent years emphasis has been placed on worldwide planktonic foraminiferal zonation and correlation. Calcareous nannoplankton have also proved to have great biostratigraphic value because of their extreme abundance in many samples, wide geographic distribution and the very short geological range of some species.

Middle Tertiary Planktonic Foraminiferal Facies, San Joaquin Basin, California: ABSTRACT

Biofacies analyses of the middle Tertiary marine units of the San Joaquin basin, California, show that the most continuous deep-water areas were near the southern end of the basin and close to the San Andreas fault system which bounds the basin on the west. Isopach maps demonstrate that the major sediment accumulation was generally in the more rapidly subsiding and deeper water areas of the basin, suggesting that mechanisms such as turbidity currents, sand flow, etc., must have been important in the deposition there. Planktonic foraminiferal facies are restricted to the southern part of the basin. Minor planktonic facies occurred in the Zemorrian and Saucesian Stages, perhaps 28 to about 20 million yr B.P. A major expansion of planktonic facies occurred during the Relizian Stage, about 20 to perhaps 17 million yr B.P. Only minor planktonic faunas are identified with the Luisian Stage, about 17 to perhaps 14 million yr B.P. A second major expansion of planktonic faunas occurred during the Mohnian Stage, perhaps 14 to about 11 million yr B.P. After the Mohnian, the deeper oceanic connection was attenuated rapidly and planktonic faunas disappeared in the latest Miocene. Abundance variations and distribution patterns of middle Tertiary planktonic foraminiferal facies of the San Joaquin basin indicate that (1) there was an important deep-water opening toward the west across the San Andreas fault system, (2) other possible connecting channels must have been of a much smaller magnitude, allowing no major influx of oceanic planktonic populations, (3) the main distribution pattern is counterclockwise indicating a similar counterclockwise current pattern around the southern boundary of the basin, (4) there were two major expansions End_Page 518------------------------------ of the current system and planktonic facies, and (5) the shallow-water facies west of the San Andreas fault at the south end of the San Joaquin Valley are anomalous. The facies anomaly across the San Andreas fault is consistent with the concept of major right lateral-slip movement since the middle Tertiary. End_of_Article - Last_Page 519------------

Foraminifera from the experimental Mohole drilling near Guadalupe Island, Mexico : Parker F.L., 1964. J. Paleont., 38 (4): 617–636

Thirty-four planktonic and 132 benthonic species of Foraminifera from the cored section of the Experimental Mohole drilling near Guadalupe Island, off Baja California, are listed. The benthonic species represent a deep-water fauna from deeper than 1,000 meters. The sampled section is believed to be Miocene and Pliocene. The Miocene section is correlated tentatively, in part, with the Luisian and Mohnian stages of California; the lower portion shows some affinity with the Globorotalia fohsi Zone of the Caribbean region. Two new species are described: Bolivina guadalupae and Melonis guadalupae.

Review of Biostratigraphy of Los Angeles Basin: ABSTRACT

The Los Angeles basin contains a thick sedimentary sequence, mainly of late Miocene and Pliocene age. Sedimentary rocks from Cretaceous through Oligocene age crop out in places along the fringe of the basin, but these strata have not been encountered in the central portion of the basin. A rich foraminiferal assemblage makes it possible to subdivide the Miocene and Pliocene into a number of stages and zones. Luisian fauna, generally the oldest encountered within the basin, is indicated by Valvulineria californica and Anomalina salinasensis. Strata of the overlying late Miocene, lower Mohnian stage, contain the marker fossils Bulimina uvigerinaformis, Bolivina modeloensis, and Epistominella gyroidinaformis. The upper Mohnian fauna is recognized by the presence of Cassidulinella renulinaformis and Bolivina hughesi. The upper Miocene Delmontian stage has fauna similar to the early Pliocene Repettian stage, but contains the marker Rotalia garveyensis and abundant Radiolaria. The Pliocene is divided into three stages, these being--from oldest to youngest--Repettian, Venturian, and Wheelerian. The Repettian stage is divided into 18 zones. Typical Repettian forms are: Ellipsonodosaria verneuili, Karreriella milleri, Bulimina rostrata, and Nonion pompilioides. The Venturian stage has the markers Bulimina subacuminata and Bolivina sinuata. Fauna of the Wheelerian stage includes Uvigerina peregrina, Epistominella pacifica and Bolivina interjuncta. The early Pleistocene guide fossils include Cassidulina limbata and C. tortuosa. The late Pleistocene fauna has the forms Elphidium poeyanum and Elphidiella hannai. Water depth during Luisian time was about ±1,500 feet. Water depth increased at a fairly steady rate, through the Miocene and early Pliocene, until a maximum depth of about ±5,000 feet was reached during mid-Repettian time. The water depth then slowly decreased through late Repettian and sharply decreased during the Venturian. Wheelerian water depths commenced at ±2,000 feet and ended at ±1,000 feet. The basin was filled by the close of Pleistocene time. The main production in the basin is from strata of Repettian age. This is followed by production from the late Miocene. Rocks of other ages produce relatively minor amounts of oil. End_of_Article - Last_Page 1081------------

Geology of the Honor Rancho Oil Field, Los Angeles County: ABSTRACT

The Honor Rancho field was discovered by The Texas Company's Honor Rancho (NCT-1) well No. 1 which was completed on August 22, 1950, flowing 1,414 barrels per day, 35.3° clean oil from the interval 5,302-5,340 feet. Six wells have subsequently been drilled, of which one, the Honor Rancho (NCT-1) No. 4, is a dry hole. The section penetrated consists of approximately 4,000 feet of Pleisto-Pliocene Saugus and Pico, 700 feet of Pliocene Repetto, and 5,000 feet of upper Miocene shale, sand, and conglomerate within the Delmontian and Mohnian stages. The discovery well was drilled on the assumption that the west-plunging anticlinal nose mapped at the surface in the area west of Castaic Creek would rise eastward across the Rancho to the San Gabriel fault and be closed by this fault. Two productive horizons have been discovered: the upper Rancho zone; and the lower, Wayside zone. In the dry hole, Honor Rancho (NCT-1) No. 4, which was drilled to 10,086 feet, deeper sands and conglomerates were found non-productive. The lithology of the oil zones varies from very fine thin-bedded sand to massive conglomerate. The fine sand, generally, is highly permeable while the conglomerate tends to be tight. The thickness of oil sand interval varies considerably from well to well and the electric logs are difficult to correlate. The field appears to be complexly faulted with, possibly, both normal and reverse faults present. In view of the variable lithology and the complex faulting, the writers believe it is impossible to predict the extent of this field at the present time. End_of_Article - Last_Page 2633------------

Correlation Sections Prepared by the Geological Names and Correlations Committee of the A.A.P.G. Castaic Junction Field, Los Angeles County: ABSTRACT

The Humble Oil and Refining Company discovered Castaic Junction in January, 1950, with its fifteenth California wildcat. The discovery well, Newhall Land and Farming Company No. 1, was completed from 11,792-11,841 feet, flowing 156 barrels of 34.2° API gravity oil, gas-oil ratio 3,945, tubing pressure 825 pounds, ¼-inch positive choke, 2.8 per cent salt water. After drilling through a continuous upper Miocene shale section from 8,000-10,900 feet, the well encountered a lower Mohnian gas-condensate sand at 11,638 and an oil sand at 11,775 feet. Subsequently, N. L. & F. 2, located 3,000 feet west-northwest of the discovery, was completed from 100 feet of net gas-condensate sand between 11,198 and 11,371 feet. These wells are producing from the deepest known sa d in the field, Reservoir 21. N. L. & F. 3, located down structure, 2,400 feet southeast of the discovery well, encountered a new reservoir sand near the top of the Mohnian stage of the upper Miocene. Three additional wells have been completed in this sand which has been designated Reservoir 10. Net oil-stained sand and conglomerate range in thickness from 95 feet in N. L. & F. 3 to 221 feet in N. L. & F. 4. A minimum oil column of 998 feet has been proved in Reservoir 10 with no bottom water yet encountered. There is an apparent natural stratification of oil, structurally low wells producing 18.5° gravity oil increasing to 21.3° gravity higher on the structure. In August, 1951, N. L. & F. 6, located 726 feet north of N. L. & F. 3, drilled through Reservoir 10 End_Page 2632------------------------------ and discovered a new upper Mohnian sand, Reservoir 15, approximately 1,000 feet below the base of Reservoir 10. Formation tests of this new reservoir indicate excellent productivity of between 27° and 29° gravity oil and condensate. Subsurface information is so limited to date that the mechanics of reservoir closure are not definitely known. Since the field lies on the southeasterly plunging Del Valle nose, the most logical cause seems to be either strong cross faulting between the Del Valle and the Castaic Junction fields, or merely the development of stratigraphic traps by lensing sands along the anticlinal structure. The highly lenticular nature of the sands and the general structure are depicted on the cross sections and maps. A strong northward shift of the subsurface structural axis is apparent. Current production is approximately 1,100 barrels per day with individual well potentials ranging from 450 to 750 through ¼-inch choke. End_of_Article - Last_Page 2633------------

Miocene-Pliocene Boundary in Los Angeles Basin from Viewpoint of Microstratigrapher: ABSTRACT

Wells drilled in the central portion of the Los Angeles basin normally penetrate an unbroken depositional sequence from the upper Pliocene into the Mohnian stage of the upper Miocene. For some twenty years oil company microstratigraphers have placed the Miocene-Pliocene boundary at the base of the continuous occurrence of such typical Repetto foraminifera as Karreriella milleri Natland, Hopkinsina hispida (Schwager), Bulimina rostrata Brady, etc., and at the approximate upward limit of Rotalia garveyensis Natland, Uvigerina hootsi Rankin, and a related costate Uvigerina. Furthermore, there is a pronounced change in the preservation of the forams as the tests of the Miocene forms are generally so badly crushed by compaction that only a small portion of the fauna can be ext acted by washing. Many foraminiferal species are common to both the lower Pliocene Repetto and the upper Miocene Delmontian, and in the Delmontian there are rare intermittent occurrences of some of the more typical lower Pliocene forms. There is no marked lithologic break at the boundary, but the Miocene shales in general tend to be more laminated, and short intervals of hard, platy, poker chip type shale are commonly encountered a short distance below the contact. Platy shales become more abundant with depth, and the color gradually changes from the dominant hair brown of the lower Repetto to the dark chaetura drab of the upper Miocene. In the laminated Miocene shales, the foraminifera normally are concentrated in thin layers, while in the more massive Pliocene shales they are rather evenly distributed throughout the matrix. End_of_Article - Last_Page 2322------------