RICE UNIVERSITY
RADIOLARIAN DENSITIES, DIVERSITIES, AND
TAXONOMIC COMPOSITION IN RECENT SEDIMENT AND
PLANKTON OF THE SOUTHERN CALIFORNIA
CONTINENTAL BORDERLAND: RELATIONSHIP TO WATER
CIRCULATION AND DEPOSITIONAL ENVIRONMENTS
BY
MICHAEL N. CLEVELAND
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE
MASTER OF ARTS
APPROVED, THESIS COMMITTEE:
Richardichard E. Casey ly Professor of Geolc Chairman fs / Jooh B. Anderson reociate Professor of Geology
* H. C. Clark Associate Professor of Geology
Houston, Texas
October, 1984
3 1272 00289 1065 ABSTRACT
The California Current, the eastern limb of the North Pacific
gyre,‘exhibits the following characteristics‘common to eastern boundary currents: wide, shallow, slow, diffuse boundaries, common upwelling, great seasonal variation, invasions of water masses from
outside the system, and cold, low salinity waters. Studies on
plankton tows and Holocene sediments have correlated components of the
siliceous microplankton (radiolarians and some diatoms) with a number
of those characteristics such as: the main directions of movement of
the invading waters, the provenance of these waters, the presence and
degree of upwelling, seasonality and its impact on the underlying
sediments. Certain types of radiolarians have been found to be
potentially useful in determining fossil anoxic and oxic conditions as well as paleodepth.
This study involved analysis of box core sediment and plankton tow
samples from the southern California continental borderland for
radiolarian density, diversity, taxonomic makeup, and other features which were related to oceanographic and environmental conditions.
Depositional environments were defined for the sediment samples and
radiolarian indicators useful for paleoenvironmental interpretation were defined. A number of borderland environments were identified and » the anoxic nearshore basin was found to have the best preservational
qualities for radiolarians and thus the most representative
radiolarian biocoenosis. ACKNOWLEDGEMENTS
I thank Cities Service Company and Occidental Exploration and
Production Company, my employers during the course of this thesis project, for financial and clerical support. Partial support of this project came from the Petroleum Research Fund, administered by the
American Chemical Society. I am grateful to Victoria Cleveland, Abel
Garcia, Michelle Marrufo and Cynthia Vamay for drafting and typing assistance. I am especially indebted to my committee chairman, Dr.
Richard E. Casey, for providing exceptional instruction and guidance throughout the term of my study. TABLE OF CONTENTS
PAGE
INTRODUCTION 1
PREVIOUS INVESTIGATIONS 2
GEOLOGY OF THE STUDY AREA 5
CALIFORNIA CURRENT SYSTEM AND OCEANOGRAPHY OF THE STUDY AREA 12
SAMPLE ACQUISITION, PREPARATION, AND ANALYSIS 20
RELATIONSHIP OF RADIOLARIAN TAXA TO WATER MASSES 22
RESULTS AND DISCUSSION 25
CONCLUSIONS AND APPLICATIONS 71
BIBLIOGRAPHY 86 LIST OF FIGURES
1 Map of Southern California ‘Continental Borderland, 6 Bathymetry and Physiographic Provinces
2 Schematic Model of Modern Environmental Conditions 9 in the Borderland
3 Flow of Bottom Water Between Basins 17
4 Temperature-Depth Curves for Borderland Waters 18
5 Circulation Patterns in a Hypothetical Ocean 23
6 Sampled Environments 27
7 Reworked Radiolarians 29
8 Radiolarian Number and Radiolarian Density 30
9 Radiolarian Density, Depths Less than 40-60 Meters 31
10 Radiolarian Density, Depths from 40-60 to 32 200 Meters
11 Radiolarian Number 34
12 Radiolarian Number versus Depth, Depth Transect A-L 35
13 Radiolarian Number versus Depth, Depth Transect U-Z 36
14 Radiolarian Number versus Depth 37
15 Diversity 39
16 Nassellarian/Spumellarian Ratio, Depths Less than 41 40-60 Meters
17 Nassellarian/Spumellarian Ratio, Depths from 50-60 42 to 200 Meters
18 Nassellarian/Spumellarian Ratio, Sediment Samples 43
19 Nassellarian/Spumellarian Ratio versus Depth 44 FIGURE PAGE
20 Nassellarian/Spumellarian Ratio versus Depth, Ratios 45 Corrected for Water Masses and Oxygen Concentration
21 Symbiotic Radiolarians, Percent 47
22 Symbiotic Radiolarians, Depth Transect A-L 48
23 Percent Collosphaerids in a Hypothectical Ocean 50
24 Stylodictids and Spongodiscids, Percent 51
25 Warm Water Sphere Radiolarians, Percent 53
26 Percent Warm Water Sphere Radiolarians in a 54 Hypothetical Ocean
27 Cold Water Radiolarians, Percent 56
28 Percent Cold Water Radiolarians in a Hypothetical Ocean 58
29 Intermediate and Deep Water Radiolarians, Percent 59
30 Intermediate and Deep Water Radiolarians, San Miguel 60 Island Shelf, Percent
31 Percent Intermediate and Deep Radiolarians in a 61 Hypothetical Ocean
32 Radiolarian/Sponge Spicule Ratio 63
33 Radiolarians/Sponge Spicules versus Depth 64
34 Phaeodarians, Presence or Absence 65
35 Depths of Preservation of Phaeodarians 66
36 Phaeodarian Presence and Oxygen Concentration versus Depth 67
37 Phaeodarian Preservation, Composite Depth Transect 68 LIST OF TABLES
TABLE PAGE
1 Properties of Basin Waters 74
2 Sediment Station Coordinates and Depths 75
3 Geographic Locations of Sediment Stations 76
4 Sediment Station Counts 77
5 Plankton Station Coordinates 78
6 Plankton Tow Counts 79
7 Operational Taxonomic Units Encountered in this Study 80
8 Numbers of Operational Taxonomic Units Encountered 83 at Sediment Stations
9 Radiolarian Counts versus Environments 85 1
INTRODUCTION
Many workers have shown that radiolaria, marine planktonic protozoans with tests of amorphous silica» can be used as indicators of oceanographic conditions and specific water masses (Kling, 1966;
Renz, 1976; Molina-Cruz, 1977; Casey, 1966; Casey et al 1982; Romine,
1982). Casey et al (1983) showed that paleoceanographic environments such as the warm and cold water spheres can be recognized on the basis of fossil radiolarian assemblages. The main objectives of this thesis were to test radiolarian assemblages as indicators in the southern
California continental borderland and develop indicators that could be used for older rocks in this region, specifically the Miocene Monterey formation. For this study, radiolaria were utilized to investigate the California Current System over the southern California continental borderland. Box core sediment and plankton tow samples from the borderland were analyzed for radiolarian density, diversity, taxonomic makeup, and other features related to oceanographic and environmental conditions. These data were related to the water masses which are carried into the borderland by the California Current System. The boundaries of these currents as they cross the borderland were outlined by a number of radiolarian measurements. Radiolarians were also used to distinguish between shallow shelfal areas and slopes.
Zones of upwelling were identified. Depth and potential paleodepth indicators were recorded. Environmental controls on radiolarian preservation were noted, including the excellent preservational qualities of the anoxic basin. 2
PREVIOUS INVESTIGATIONS
Haeckel (1887), Lo-Bianco (1903), Haecker (1907), Popofsky (1913),
Reshetnjak (1955), Hulsemann (1963) and Petrushevskaya (1966) determined that certain species of radiolarians are limited to living in particular water depths. Kling (1966) found radiolarians were zoned with not only depth, but water masses and hydrographic conditions as well. Casey (1966) noted depth specific zonations of radiolarians and correlated them with such physical, chemical and biological characteristics as thermoclines, pycnoclines, light penetration, water mass boundaries, pressure, biological associations, biologic history of the water, microconstituents of the water, oxygen minimum zones, deep water circulation, and many other parameters. He also noted that vertical and horizontal distributions are closely related. Working off the southern California coast he correlated radiolarian assemblages with the local and general pattern of water masses and circulation patterns in the region. The current systems set up parameters for radiolarian distribution.
Renz (1976), in a study which spanned more than 50° latitude in the central Pacific where radiolarian preservation is good, showed that the radiolarian assemblages in both the water column and in the bottom sediments corresponded to the major water masses.
Molina-Cruz (1977), Casey et al (1982) and Romine (1982), also found that the water masses appear to establish the major environmental packages that control most radiolarian distributional patterns. They showed that many individual species and groups appear 3 to be Indicative of specific water masses. Radiolarian distributions are also controlled by other physical, chemical and biological conditions.
Casey et al (1982) fitted radiolarian data from Holocene sediments of the world oceans to a hypothetical ocean exhibiting characteristics of all oceans. They defined regions of enhancement and/or boundaries to distribution of warm water and cold water sphere radiolarians, intermediate and deep water radiolarians, collosphaerids, and others.
The regions of enhancement and boundaries to distribution of radiolarian assemblages reflect oceanographic conditions such as currents, divergences, convergences, and oligotrophism to eutrophism.
Casey et al (1983) show that, based on distributions of fossil radiolarians, paleoceanographic conditions could be defined, at least through the Neogene. It is the distribution of radiolarian assemblages that defines the paleoceanographic conditions. Ancestors of living species which are indicators of recent oceanographic conditions cannot be assumed to define similar paleoceanographic conditions because they do not necessarily live in the same environments as their descendants (Wigley, in manuscript).
Hickey (1979), on the basis of extensive oceanographic investigations, showed that water movement over the southern
California continental borderland is governed by the California
Current system. This system consists primarily of the California
Current, an eastern boundary current, and the California
Undercurrent. In addition, there is a local component of the system, the Southern California Countercurrent or Eddy. 4
Ecosystems occupying eastern boundary currents are quite complex since, in addition to being open to mass and energy channeled directly into organic production, they are also open to the large-scale input of mechanical energy in the form of advection or local wind forcing.
McGowan (1971; 1974) proposed that, because of the biologically disruptive effects of the physical conditions in these regions, classical biological interaction (competition and predation) might not have an opportunity to play a dominant role in determining the composition of species assemblages nor in modulating the differences in abundances of the species.
Chelton et al (1982) examined thirty years of California
Cooperative Oceanic Fisheries Investigations (CALCOFI) to explore the causes of large scale biological variability in the California
Current. They found that in contrast to the classical view of the dynamics of epipelagic ecosystems in eastern boundary currents, wind-forced coastal upwelling of nutrient rich deep water played a relatively minor role in controlling the large scale zooplankton biomass. Zooplankton abundance is primarily influenced by large scale variations in the flow of the California Current. 5
GEOLOGY OF THE STUDY AREA
The topographically complex region between the coastline and the deep oceanic floor off southern California and northern Baja
California (fig. 1) was named the southern California continental borderland (Shepard and Emery, 1941) to distinguish it from normal, less complex continental margins. Covering an area of more than
64,000 square kilometers, the borderland is composed of a series of northwest-southeast to east-west trending basins separated by narrow banks and ridges, a few of which extend above sea level as islands.
These structural trends strike more or less parallel to the topographic trends of the nearby land areas (Emery, 1960).
Prior to the middle Miocene, western California was an area of broad marine onlap with locally prograding non-marine clastic wedges
(Cole and Armentrout, 1979). Formation of the present borderland began in the Miocene as the result of translational tectonics and rotation along a broad zone of transform faulting at the border between the Pacific and North American plates (Atwater, 1970; Howell et al, 1980). Progressive lateral shifts in the position of the San
Andreas transform transferred successive slices of the North American continent to the Pacific plate. Displacements of these crustal slices relative to the interior of the continent resulted in complex deformation within the borderland where many key tectonic relations are still unclear (Dickinson, 1979). Widespread subsidence and an eastward migration of the strandline in early Miocene time, accompanied by volcanism which peaked in the late Miocene, initiated Figure 1. Map of southern California continental borderland bathymetry and physiographic provinces. basin, filling and a cycle of Neogene basin development in California which continues to the present time (Ingle, 1980). The numerous
structurally controlled deep basins formed adjacent to fault bounded
uplifts under a dominantly extensional stress field. Sediments poured
in from the structural highs, rapidly filling the eastern basins and
spilling over to successively more westward basins (Yerkes et al,
1965; Campbell and Yerkes 1976).
The mainland shore is bordered by a shelf which ranges in width
from less than 1.6 kilometers to 24 kilometers and averages 6
kilometers and the depth at its base is about 3.7 kilometers (Emery,
1960).
The borderland province contains approximately 20 basins. These
basins vary considerably in geometry and water depth but there is a
general trend of increasing water depth away from the shore and toward
the south (Douglas, 1981). Basically oval in outline, the basins
range in sill depth from 200 to more than 2,000 meters (Emery, 1960).
Los Angeles and Ventura basins (including the San Fernando basin) are
filled with sediments and are part of the mainland. Prior to the late
Pleistocene (Hallian) they were accumulating slope and littoral
deposits (Ingle, 1980) and their depositional environments must have
been similar to the present-day nearshore basins. Santa Barbara,
Santa Monica, and San Pedro basins and San Diego trough, located next
to the continent, are all less than 1,000 meters deep and have broad
flat floors (fig. 1). Santa Cruz, San Nicolas, and Tanner basins are
deep (greater than 1,500 meters) offshore basins with high, relatively
steep walls and somewhat irregular floors. Santa Catalina Basin, 8 which is intermediate between the nearshore and offshore basins, has a
relatively flat floor but higher walls (Douglas, 1981).
All basins within the borderland are silled, (i.e., their rims are
cut by inlets which are shallower than the basin floor), a
characteristic feature of all marginal basins. The location,
elevation, and depth of the sill are important in determining the water quality and oxygen levels in the deeper parts of the basin (see
fig. 2). In the borderland, most of the sills are fault controlled
and modified by later deposition and/or erosion (Douglas, 1981).
Where the bottom waters of a basin are anoxic, as in the Santa Monica
and Santa Barbara basins, hemipelagic laminae are preserved because of
the absence of burrowing organisms (Gorsline, 1978).
Based on numerous cores and grab samples taken from a variety of
environments in the borderland, rock bottom is encountered at the
surface of the sea floor in only about 3 percent of the area. This
rock is mainly Miocene shale, mudstone, and phosphorite (finery,
1960). The remainder of the surfaces are covered by unconsolidated
sediments. The following sediment descriptions are based on Emery
(1960):
1. Mainland shelf
Recent detrital sediments cover most of the area. They
consist mainly of sands and silts which form seaward continuations
of the beaches. Primary minerals are quartz and feldspar with
plagiodase 4-100 times as abundant as orthoclase. Grain size
decreases seaward. Sorting is good. Heavy minerals include
hornblende, augite, and epidote, corresponding closely with those 9
NORTHERLY r—r~UJIMD^ CA.IF. CUCREMT J?AT»DSOO cgourm FUVJmfc) i cxx/NTLRojrKriir MAINLAND r 4» 200"!///Ss////////M'r'L.. A- »c*P r - \. v.-y •.£./..•• :yj # TEEP .;?*;.;r: «•<*» • •• . 1 l SIUI» \xi: * » v—■■■ tmcitomic. ct U»ATeR.\v.at^er; ?eEil: c^oiznac^/i) VLU LAMINATED Cpaer* * -%&DiM>EVir& MMH4 LOvO cxv&eu C>o.r<-o.s mi *7O f*LotO 1*0 C*lC dewpmoMi t\/1) *“**“ »« (£££ ^ OUTER DASIN CSEFWMEB fg* *rc SCHEMATIC totTDEL ICouî L O» Ç.MVIROKJ ME NTAL COU'DITICAI W4 THE "BORDER LAMB Figure 2. Schematic model of modern environmental conditions in the borderland. From Douglas (1981). 10 of the adjacent beaches. Organic sediments consist chiefly of broken and corroded shell fragments, mostly of pelecypods and gastropods. The grain size is coarse, and the sorting poor. Foraminifera are a minor constituent. 2. Island shelves Organic sediment is more abundant than on the mainland shelf. Moreover, the detrital sediment also contains fairly large percentages of foraminifera, fragments of gastropods and pelecypods, and bryozoans. There is also appreciable glauconite. If organic, authigenic, and the minor residual sediments are ignored, the remaining present day detrital sediments present a general seaward decrease in grain size. Sorting is good. There is a seaward increase in percentage of calcium carbonate due to organic remains. 3. Bank tops Calcareous organic debris comprises more than 80% of the sediment. Glauconite and phosphorite are abundant. Sediments are coarse (average medium diameter is 310 microns for all sediments on Cortes and Tanner Banks) and rock can be found outcropping here. The inorganic sediments are mainly gray colored quartz and feldspar. There is little organic matter. 4. Basin slopes Some sediments occur on slopes, but they are patchy on many slopes that are distant from the mianland. Thus, rock is usually exposed or only thinly mantled. 11 5. Basins and troughs The bulk of the sediment consists of detrital materials and foraminiferal tests with only minor amounts of authigenic minerals and up to 10 percent organic matter. Grain size is thus controlled by the detrital and calcium carbonate fractions. The detrital fraction of the sediment decreases in grain size in more seaward basins (8.1-2.9 microns average median diameters). This is mostly green mud, the color being attributed to illite and montmorillonite. Sorting is poor. The organic matter is found in least abundance in basins closest to and farthest from shore, and greatest abundance in basins in between. The peak concentration of organic matter at intermediate distance from the mainland is attributed to a very rapid rate of deposition of detrital sediments near shore, resulting in the dilution or masking of organic matter there and to a very slow rate of deposition far from shore, resulting in extensive oxidation of organic matter before it can become protected by burial. Thus, the highest concentration occurs under optimum conditions of neither too rapid nor too slow a rate of deposition of detrital sediments. The chief producer pf organic matter in basin sediments is diatoms. 12 CALIFORNIA CURRENT SYSTEM AND OCEANOGRAPHY OF THE STUDY AREA Hater movement over the southern California continental borderland is governed by the California Current System (CCS), an eastern boundary current. Like all eastern boundary currents, it flows in a broad complex stream toward the equator. The CCS consists primarily of: 1) the California Current, a south-southeasterly surface flow along the west coast of the U.S. and Baja California; and 2) the California Undercurrent, a northerly flow which is concentrated over the continental slope and passes beneath the California Current. A local component of the system is the Southern California Countercurrent or Eddy, a northwesterly flow which is found south of Pt. Conception inshore of the Channel Islands in the California Bight (the area between Pt. Conception and San Diego). Other examples of such systems are the Benguela Current System, the Peru Current System, and the Canary Current System (Hickey, 1979). The eastern boundary currents of subtropical gyres have long been recognized as among the most biologically active areas in the world oceans. Productivity levels typically exceed those elsewhere by at least an order of magnitude. This is attributable to the high rates of supply of dissolved plant nutrients (primarily phosphate and nitrite) which result in high plant phytoplankton productivity (Chelton et al, 1982). 1. California Current The California Current is the eastern limb of the clockwise current gyre in the North Pacific. It exhibits the following 13 characteristics common to eastern boundary currents: wide, shallow, slow, diffuse boundaries, common upwelling, great seasonal variation, and cold, low salinity waters. The large scale wind pattern derives from the gradient between the North Pacific High, an atmospheric pressure zone centered between Alaska and Hawaii, and the continental thermal low over California. The North Pacific High produces westerly winds in the "Roaring Forties" and easterly winds (the Trades) to the south. These winds drive the gyre. Seasonally, the California Current is strongest (strongest southerly flow) in the late spring and summer (with strongest boundary current upwelling at that time) and weakest in winter with strengthening of the Southern California Countercurrent. The California Current has a complex and variable shape with a width greater than 600 kilometers in some places. It transports 10 million cubic meters of water per second (Emery, 1960), moving at a mean speed of 15 centimeters per second (Pavlova, 1966). Flowing generally southeast along the California coast, it is deflected to the west upon reaching Pt. Conception at the northern end of the southern California borderland (Reid et al, 1958). The California Current then turns shoreward again at 32°N latitude near the Mexican border. The mean annual location of the current off Pt. Conception is 270 kilometers offshore (Hickey, 1979). The water is apparently comprised of a combination of Kuroshio Aleutian Surface Water and North Temperate Surface Water (Casey, 1966). The characteristics of this water, which is found down to 100 meters, appear to be relatively independent of the characteristics of the deeper water. It is low in temperature and 14 salinity and high In oxygen. Some Central Pacific Water Is also Included In the current (south of Pt. Conception). It Is high In temperature and salinity and relatively low In oxygen and nutrient content. As the California Current passes Pt. Conception, surface water from the northern borderland Is entrained (Emery, 1960). This in turn causes subsurface water to rise and replace the deficit left by the removal of surface water. The upwelling water, centered near the Santa Rosa-Cortes Ridge (fig. 1), is cooler and enriched in nutrients compared to the normal surface water (Allan Hancock Foundation, 1965). In fact, the area above the ridge exhibits the coldest surface water in the borderland (Emery, 1960). As the nutrient enrichment occurs in the photic zone, high levels of primary productivity result. During seasonal climatic variations % (especially during spring and early summer), wind induced upwelling is also possible over the borderland (Sverdrup and Fleming, 1941). This type of upwelling is usually associated with coastal areas and topographic highs. It plays a relatively minor role in controlling the large scale zooplankton biomass (Chelton et al, 1982). 2. California Undercurrent The California Undercurrent consists of Eastern Pacific Tropical Water which travels northeastward from 20°-30° N latitude across the ocean. It flows north along North America, seaward of the continental shelf, over the continental slope, and beneath the California Current at depths of 200-1900 meters (Hickey, 1979). In the California Bight the Undercurrent shoals in the fall and may actually reach the surface 15 in November and December (Wyrtki, 1974). The undercurrent reaches the surface year round north of Pt. Conception and is named the Davidson Current there. The water is high in temperature, salinity, and phosphate, and low in dissolved oxygen. Near the boundary between this intermediate water and the overlying surface (California Current) water there is a broad mixing of the two water masses. A 50/50 mixture of northern and southern waters occurs at depths between 200 and 300 meters, but can occur locally as deep as 500 meters (Emery, 1960). The dissolved oxygen concentration of the intermediate water is lower than that of the surface water. This is a result of the oxidation of organic matter filtering through the water column. 3. Southern California Countercurrent As was mentioned above, the California Current turns eastward at 32°N latitude. When it approaches the coast, some of the water flows southward and some northward. This latter forms an eddy north of 32°N latitude. This is the Southern California Countercurrent. The majority of the water in the Countercurrent is recirculated into the California Current at Pt. Conception. The remainder flows north around the Point and becomes part of the Davidson Current (Hickey, 1979). The cyclonic Countercurrent has its axis above the Santa Rosa -Cortes Ridge (Allan Hancock Foundation, 1965). Some water on the eastern side of the eddy turns and flows southeastward along the coast (Allan Hancock Foundation, 1965; Emery, 1960). The circulation patterns at depth are similar but not as dynamic (Emery, 1960). Estimates of surface speed in the Countercurrent are comparable to 16 that observed in the California Current itself, 12 to 18 centimeters per second (Sverdrup and Fleming, 1941). Transport estimates for this branch of the eddy are only slightly less than that calculated for the California Current (Pavlova, 1966). The basins of the borderland are mainly filled by the Undercurrent water, although a few of the most northerly and westerly basins fill from the west and southwest (fig. 3). As deep water moves northward into the borderland, progressively shallower sills are encountered so that progressively shallower levels of water fill the basins (Emery, 1954). Water below the sill depth of a given basin is quite uniform, being essentially the same as the water outside the basin at sill depth (Emery, 1954; 1960). This is especially true of the temperature component (see fig. 4). The range of salinity among the basins is only 34.25%o to 34.58Zo (Emery, 1960). The oxygen content of the basin water is maximum near the top, being 5.5-6.0 ml/L and decreases to less than 0*5 ml/L between 500 and 600 meters, which is considered the oxygen minimum zone (Emery, 1954). Physical and chemical properties of the basin waters are given in table 1. The primary water masses encountered over the Southern California borderland are summarized below (Casey, 1966; Emery, 1960): 1. Surface Water - This consists of a mixture of Kuroshio-Aleutian Surface Water and North Tropical Surface Water, both of which flow from the northwest, a. Northern Borderland - Temperature ranges from 12.5°C in spring to 17.0°C in fall. With respect to the southern borderland surface water, salinity here is slightly Figure 3. Paths followed by waters in flow from basin to basin Width of lines serves as rough indicator of transport volume. From Emery (1954). bottoms of basins.(AfterEmery, 1954) basin sills.Short horizontallinesindicatedepthsofsills and Figure 4.Temperature-depth curvesforopenseaand waters below DEPTH IN METERS 18 19 higher (33.5%o), oxygen slightly lower, and phosphate-phosphorous, much higher, all due to upwelling of intermediate water. b. Southern Borderland - Temperature ranges from 14.0°C in spring to 19.5°C in fall. With respect to the northern borderland surface water, salinity is slightly lower (33.4%o), oxygen slightly higher, and phosphate-phosporous much lower. 2. Intermediate Water - This consists primarily of North East Central Pacific Water and North Pacific Intermediate Water from the south and is found at 200-1900 meters. Temperature is a uniform 8-9°C year round. Between 200 and 500 meters there is a zone of mixing of intermediate and surface waters; intermediate water dominates below 500 meters. The California Current System is also influenced by supra-seasonal effects such as El Ninos that have a northern counterpart, the California El Nino (Chelton et al, 1982). In general, these California El Ninos appear to influence the California Current System by: slowing the California Current and its advection of water southward; and allowing warmer waters to invade the California Current System (Chelton et al, 1982). 20 SAMPLE ACQUISITION, PREPARATION, AND ANALYSIS The sediment samples used in this study comprise a subsample of box cores and grab samples collected by Dr. R. Douglas of the University of Southern California as part of the Bureau of Land Management's 1975-76 Southern California Baseline Studies and Analysis. In addition, box core sample SB was collected by Dr. R. Dunbar of Rice University in 1979. A tabulation of the samples used in this study and their locations are given in tables 2 and 3. The tops of the samples were used for the radiolarian analysis. The samples were weighed (dry) and then processed for radiolarians by boiling in HC1 and I^C^, washed over a 63 micron screen and mounted on a glass slide with Permount. Plankton tow samples were obtained on an Allan Hancock Foundation supported University of Southern California cruise in November, 1964. Samples were collected with Nansen nets, treated with H& and and mounted on slides. Coordinates for sampling locations are given in table 5. All slides were examined with a binocular, transmitted light microscope. On the initial examination, I counted all radiolaria and classified them as either nassellarians or spumellarians. In consultation with Dr. R. E. Casey, the environmental habitats for the operational units on table 7 were designated using the method described by Casey et al (1983). The first 100 radiolarians encountered were counted. On this pass, assumed to be representative of the entire sample, radiolarians were identified as to species or 21 lowest operational taxonomic unit and assigned to habitats. Also recorded for the sediment samples were the numbers of obviously reworked radiolarians (mainly Miocene reworking, counts are conservative because many Miocene species are extant), the number of phaeodarian radiolarians and the numbers of sponge spicules and diatoms. The results of sediment and plankton counts are recorded in tables 4 and 6. 22 RELATIONSHIP OF RADIOLARIAN TAXA TO WATER MASSES Tables 7, 8 and 9 show>-the radlolarlan taxa and water mass relationships used for this study. The water masses appear to set up the major environmental packages that control most radlolarlan distributional patterns, although other physical, chemical, and biological conditions also affect distributions. Casey et al (1982) set up a hypothetical ocean for plotting radlolarlan data collected from Holocene sediments because: 1) only sediments with very good or excellent preservation of radlolarlan assemblages were used (there are few of these and it appeared that the best way to present these data was on a composite ocean); and 2) in using a hypothetical ocean to present Recent data, it might be easier to extrapolate Recent data into the past. The hypothetical ocean is shown on figure 5. Plots of radlolarlan indicators of the different water masses found in sediments in the hypothetical ocean are shown on figures 23, 26, 28 and 31 for comparison with this study's findings. Because the main objectives of this study were to develop radlolarlan indicators that could be used in older rocks, specifically the Miocene Monterey formation, radlolarlan assemblages rather than individual species were studied. Casey et al's (1982) hypothetical oceans show how currents and water masses can be extrapolated back through time, and the radlolarlan assemblages are tied to the water masses. Wigley (in manuscript) has shown that study of individual species is not useful for paleoceanographic interpretation because ancestors of living species do not necessarily live in the same 23 PO • POLAR DIVERGENCE W0C • WESTERN BOUNDARY CURRENT PC • POLAR CONVERGENCE EBC • EASTERN BOUNDARY CURRENT STC - SUBTROPICAL CONVERGENCE POr • POLAR DRIFT TC - TROPICAL CONVERGENCE PCr • POLAR CURRENT NED * NORTH EQUATORIAL DIVERGENCE NEC * NORTH EQUATORIAL CURRENT ED • EQUATORIAL DIVERGENCE ECC • EQUATORIAL COUNTER CURRENT • WINOS AT SURFACE OF OCEAN SEC • SOUTH EQUATORIAL CURRENT • CURRENTS AT SURFACE OF OCEAN • • WATER UPWELUNG + - WATER OOWNWELLING Figure 5. Circulation patterns for surface waters and major convergences and divergences in a hypothetical ocean• (After Casey et al, 1982) 24 environments as their descendants. The radiolarian-water mass relationships used in this study follow Casey (1977), Casey et al (1982), Casey et al (1983), and Casey (pers. comm.). Some specific relationships include: 1. Collosphaerids are one of the warm water sphere indicators. They are colonial radiolarians which live in symbiosis with zooxanthellae (algae). This symbiosis, perhaps their size (a few to a hundred centimeters in greatest dimension), and their ability to remain at the surface or drop to a nutricline apparently enable them to dominate the warm water sphere of the gyres where nutrients are low. The zooxanthellae may act as nutrient collectors, enabling the collosphaerids to occupy a primary producer niche. In general, among the polycystine radiolarians, the symbiotic forms (which include Dictyocoryne profunda-truncatum, spongasters, and artiscins, besides the collosphaerids), predominate in the shelfal waters of the tropical and temperate seas. Most of the non-symbiotic radiolarians are excluded from the modern shelfal environments because of either the physical and chemical conditions of the shelfal waters (lowered salinities, radical and sudden changes, unstable and non-stratified environment), or because of direct or indirect competition (Casey et al, 1982). 2. Robust artostrobids, theocalyptrids, and spongodiscids are cold water sphere and intermediate and deep water indicators. These are especially useful as indicators of upwelling and have been used as such in the fossil record (Weaver et al, 1981). 25 RESULTS AND DISCUSSION After identifying radiolarians to the lowest possible division, or operational taxonomic unit (O.T.U.), tallies were made for each of the following categories or characteristics at each station (the following refer to sediment samples only except as noted): 1. Percent of sample that is reworked 2. a) Radiolarians per cubic meter of seawater, or radiolarian density (plankton tows) b) Radiolarians per gram of sediment, referred to as radiolarian number (sediment samples) 3. Diversity, which is number of operational taxonomic units 4. Nassellarian/spumellarian ratio. These are the highest divisions of the polycystine radiolarians. Nassellarians are the cone shaped and spumellarians the spherical group. Counts were made for plankton tows also. 5. Percent symbiotic forms. These radiolarians live in symbiosis with zooxanthellae (algae). The zooxanthellae may act as nutrient collectors, enabling the radiolarians to occupy a primary producer niche. 6. Percent stylodictids and spongodiscids. These two radiolarians, brought into the borderland with the California Current, may indicate upwelling. 7. Percent Warm Water Sphere taxa. Table 7 lists radiolaria demonstrated to be Warm Water Sphere indicators. 26 8. Percent Cold Water Sphere taxa. See table 8 for list of radiolaria demonstrated to be Cold Water Sphere indicators. 9. Percent Intermediate and Deep Water Spheres taxa. See table 9 for list of radiolaria demonstrated to be Intermediate and Deep Water Spheres indicators. 10. Radiolarian/sponge spicule ratio 11. Presence or absence of phaeodarians. This type of radiolarian is composed in large part of organic matter which "glues" its siliceous parts together. Once the organic matter is oxidized the phaeodarian disintegrates. Thus, preservation of phaeodarians occurs only under anoxic conditions. After station by station tabulations were completed, eight environments were identified in the borderland and the sediment stations were each assigned to one or more environments. These environments are mainland shelf, island shelf, offshore shelfal bank, shelf to slope (four depth transects), anoxic nearshore basin, oxic nearshore basin, mid-borderland oxic basin, and open ocean slope (see fig. 6). Ranges and averages of ten categories and characteristics (the same categories and characteristics enumerated above with the exception of reworking) were made for each environment. Figure 6 SAMPLED ENVIRONMENTS Sampled environments ? '© © T . OXIC NEARSHORE BASIN A SEDIMENT STATION . MID-BORDERLAND OXIC BA8IN . OPEN OCEAN 8LOPE 27 28 1. Reworking The reworking shown on figure 7 is mainly from the Miocene. The high reworking value shown at Tanner Bank probably reflects erosion from the mid and upper Miocene outcrops there (Greene et al, 1975). Likewise, the values seen on the San Miguel Island shelf represent simple erosion and transport from outcropping Tertiary rocks there. 2a. Radiolarian Density Figure 9 shows radiolarian density in shallow waters (less than 40-60 meters). The California Current stands out at the northwest comer of the borderland because of its low radiolarian density. The California Current taps Transitional and Sub-Polar Waters where abundant diatoms tend to inhibit radiolarians at shallow depths (Casey et al, 1982). Figure 9 also shows the high density warm, Southern California Countercurrent waters entering the borderland from the southeast. At depths of 40-200 meters, a high density tongue is seen to enter the borderland from the west (fig. 10). This is the California Current wherein radiolarian density is high at greater depths. 2b. Radiolarian Number Johnson (1974) notes that there is a tendency for deeper depositional sites to have slightly better preserved siliceous assemblages at many latitudes. Reasons for this relationship include decreasing temperature and increasing dissolved silica concentration with depth (Berger, 1968; Hurd, 1972). Johnson Figure 7 if i*o'o" »to*o‘o* IlfOO' «••O’O* REWORKED RADIOLARIANS PERCENT (MID-MIOCENE SPECIMENS EXCEPT AS NOTED) Reworked radiolarians P o Ï T e o T Jt SEDIMENT STATION 29 30 Figure 8 Radiolarian number and radiolarian density Figure 9. Radiolarian density, depths less than 40-60 meters. Figure 10 ttl*0*0* 110*0*0* 110*0*0* RADIOLARIAN DENSITY DEPTHS FROM 40-80 TO 200M (RAD3./M3 WATER) Radiolarian density 1 » J.rom T u < §*1 I PLANKTON TOW t 32 33 (1974), studying sediments from depths greater than 2,000 meters, concluded that hydraulic sorting by bottom currents was redepositing siliceous microfossils as a group in preference to other sedimentary components, apparently due to their relatively greater resistance to dissolution and their general durability. Because it is probable that they settle out at depths equal to or greater than the depth from which they were eroded, deeper deposltional sites should be receiving a statistically higher input of siliceous microfossils than shallower sites. Casey et al (1981) note that radiolarian densities in the Caribbean and Gulf of Mexico are lowest in the waters over the shelf. Once deposited on the shelves, they may be swept off, masked by other sediments (as sedimentation rates are greater there), and dissolved in the warm shallow waters. The Radiolarian Number (r.n.) map, 2 depth transects, and the r.n. versus depth plot (figs. 11-14) all show that r.n. stays low on the shelf and increases with depth on the slope. If a best fit line is drawn through the data on the r.n. versus depth plot (fig. 14), the shelf-slope boundary can be seen as the depth beyond which r.n. begins to increase. This r.n. depth relationship might also work as a paleodepth Indicator for rocks from California borderland type basins, for example, Monterey formation. On the environment table (table 9), a large range in r.n. is seen among the different environments. Offshore shelfal bank (r.n. * 231 avg.), anoxic nearshore basin (r.n. • 154 avg.) and mid-borderland oxic basin (r.n. ■ 603 avg.) exhibit the highest T 1 Figure 11. Radiolarian number 35 Figure 12. Radiolarian number versus depth, depth transect A-L. 36 IU VERTICAL EXAQ.:37X Figure 13. Radiolarian number vs. depth, depth transect U-Z. RADIOLARIAN NUMBER VS. DEPTH 24 SEDIMENT SAMPLES (RADS./GM ) 100 200 300 400 600 600 TOO 600 Figure 14 Radiolarian numbervs.depth (suaxaw) Midaa 37 38 values while mainland shelf shows the lowest average (r.n. ■ 66). In general, the shallow environments have low r.n.Cs) and the deep environments have high. The anoxic nearshore basin value is high because the water is acidic, good for preservation of radiolarians (but oxic basins are more basic, which is bad for preservation of radiolarians). Also, in anoxic basins, there are few benthic fauna to ingest and strip protective metallic coatings from the radiolarians (Kunze, 1980). Thus, even though radiolarian density is lower over shelfal areas than farther offshore, the excellent preservation under anoxic conditions results in a high r.n. in the anoxic nearshore basins (even the less resistant taxa are preserved, which increases the r.n., whereas these same taxa might not be preserved at greater depths in an oxic environment). 3. Diversity The high diversities seen along the coastline may represent the northward flowing warm southern waters (see fig. 15). The low diversities to the west probably represent the southeastward flowing California Current. The environment table shows little variation in diversity among the different environments (average number of OTUs is 23) with one exception. The anoxic nearshore basin has a diversity of 42. This value is probably high for the same reason that the anoxic basin r.n. is high: under anoxic conditions even the less resistant taxa are preserved. 4. Nassellarian/Spumellarian Ratio Casey and Bauer (1976), studying living radiolarians on the 39 Figure 15 Diversity 40 south Texas outer continental shelf, showed that the nassellarian/spumellarian (n/s) ratio generally decreases onshore. McMillen (1976) found this same relationship apparently held for Pleistocene-Holocene aged sediments from the Pacific coast of Guatemala. The fact that many nassellarians are thinner shelled (Takahashi and Honjo, 1981) hinders their preservation. These radiolarians are more likely to be preserved where oxygen content is low. Oxygen content is high onshore but low in many basins of the borderland. The n/s sediment sample map generally shows low ratios in shallow areas and higher ratios at greater depths (see fig. 18). However, the n/s ratio versus depth plot shows no clear trend (fig. 19). The scatter on the plot probably reflects at least two complicating factors: 1) n/s ratio is high where oxygen content is low and; 2) the different water masses which enter the borderland exhibit different n/s ratios. The plankton tow n/s maps (figs. 16 and 17) show a high n/s ratio in the warm southern waters which is especially pronounced at depth (California Undercurrent). If these two factors are subtracted out, and assuming there are no other factors affecting n/s ratio, then n/s should decrease onshore. Fig. 20 represents one way to subtract the effects of water masses and low oxygen concentration. An addition of 0.05 was made to the ratios of stations lying in the path of the California Current (which has low n/s ratios), while 0.05 was subtracted from stations lying in the path of the 41 Figure 16. Nassellarian/spumellarian ratio, depths less than 40-60 meters. 42 Figure 17. Nassellarian/spumellarian ratio, depths from 50-60 to 200 meters. Figure 18.Nassellarian/spumellarian ratio,sedimentsamples 111*0*0* irr**oo" »it*o,o' ||*»0*0* NASSELLARIAN/8PUMELLARIAH RATIO i SEDIMENT STATION 43 26 SEDIMENTARY STATIONS Figure 19 . Nassellarian/spumellarian ratiovs. depth DEPTH (METERS X10 44 Figure 20.Nassellarian/spumellarian ratioversusdepth, ratios NASSELLARIAN/SPUMELLARIAN RATIO VS. DEPTH RATIOS CORRECTED FOR WATER MASSES AND OXYGEN CONCENTRATION 26 SEDIMENT 8TATIONS corrected for watermassesand oxygenconcentration. f-Q 5l rw UJ C < < DEPTH (METERS X1 California Undercurrent/Davidson Current (which has high n/s ratios). For stations with oxygen concentrations of less than 0.5 ml/L, 0.10, was subtracted. After these corrections are made it appears that stations on the shelf and upper slope generally record ratios less than 0.20 while mid and lower slope stations generally exhibit ratios greater than 0.20. The complexity of oceanographic variables present in the borderland apparently precludes the straighforward use of the n/s ratio as a depth indicator here, even though a n/s-depth relationship is seen in other less complex areas. 5. Symbiotic, Percent Casey et al (1982) point out that, in general, the symbiotic forms are the dominant radiolarians occupying the shelf waters of the tropical and temperate seas. The symbiotic radiolarian map and depth transect (figs. 21 and 22) bear this out, showing high values along the coast and island shelfal areas. These high values may also reflect, in part, the presence of warm, southern water moving north from the south. The symbiotic-poor California Current water appears to converge with symbiotic-rich Davidson Current water on the slope southwest of San Miguel Island (herein designated the San Miguel convergence). Symbionts may be brought in to the west side of the borderland with Central Gyre water. The symbiotic radiolarian percentage is shown on the environment table to be fairly uniform, ranging from 12 to 18, averaging 16, with one exception. The anoxic nearshore basin contains only 6 percent symbionts. Because symbionts are among Figure 21. Symbiotic radiolarians, percent DEPTH TRANSECT A-L Figure 22 Symbiotic radiolarians, depth transectA-L OFF SHELF•SHELFAL 48 49 the most resistant to dissolution, (Kunze, 1980) and because the radiolarian number maps and plots show that a. much higher percentage of radiolarians is preserved under anoxic conditions, it can be concluded that the absolute number of symbionts is no less in the anoxic basin, but the abundance of other preserved radiolarians masks the number of symbionts. The plot of warm water collosphaerids (symbiotits) on a hypothetical ocean confirms that a low percentage (less than 2%) of symbionts would be expected in well preserved sediments at this location (see fig. 23) . 6. Stylodictids and Spongodiscids, Percent Stylodictids and spongodiscids (s. and s.) are cold water and intermediate and deep water forms (R. E. Casey, pers. comm.). They are commonly found at shallow depths and there indicate upwelling. Such a phenomenon is seen on the s. and s. map (fig. 24) . The deep penetratioon of the California Current into the borderland may reflect upwelling and mass mortality of s. and s. The environment table shows a fairly uniform s. and s. percentage among all but two of the areas, ranging from 30 to 37, averaging 32. At the offshore shelfal bank the value is 22 and in the anoxic nearshore basin there are 8 percent. Because they are resistant to dissolution (R. E. Casey, pers. comm.), their low percentage in the anoxic basin probably reflects masking by the high percentages of preserved radiolarians (as in the case of the symbionts) rather than an absolute low value. The low percentage in the deep (offshore shelfal bank) environment probably occurs 50 80° 80° Q- 2% OH GREATER E3- 10ft Oft GREATER Figure 23. Percent warm water collosphaerids of entire radiolarian fauna in well preserved (radiolarians) sediments in a hypothetical ocean with all oceanic depths 4,000m. (After Casey et al, 1982) Figure 24 STYLODICTIDS AND SPONQODISCIDS PERCENT Stylodictids andspongodiscids , percent SEDIMENT STATION 52 because this environment happens to lie south of the axis of the fall-winter California Current (see eg. figs. 10 and 27) and the fall-winter current leaves the greatest radiolarian imprint on the sedimentary record. 7. Warm Water Sphere, Percent Because symbionts dominate the warm water sphere, the warm water sphere map (fig. 25) looks very similar to the symbiont map. In both cases the high values are found on the shelf. The cool California Current cuts through the borderland, reducing the percentage of warm radiolarians there. Some warm forms may be carried to the southwestern corner of the borderland with Central Pacific Gyre water. As on the symboint map, the San Miguel convergence stands out as a boundary between Davidson and California Current Water. Warm water sphere radiolarians maintain a uniform percentage among all of the environments, ranging from 19 to 29 and averaging 25 with the exception of the anoxic nearshore basin. There the value is 13. As in the case of other parameters, such as the percentage of symbiotic radiolarians, the low percentage in the anoxic basin represents masking due to excellent preservation of all radiolarians. The plot of warm water radiolarians on a hypothetical ocean suggests lower percentages of warm water forms might be expected in well preserved sediments of the borderland (fig. 26). 8. Cold Water Sphere, Percent The cold water sphere is represented in the borderland by the WARM WATER SPHERE RADIOLARIANS Figure 25 PERCENT ’© © Warm watersphereradiolarians , percent. À SEDIMENT STATION 54 B • 2-5* _ EJ» 5-10* Q • 10* 0* GREATER Figure 26. Percent warm water forms of entire radiolarian fauna in well preserved (radiolarians) sediments in a hypothetical ocean with all oceanic depths, 4,000m. (After Casey et al, 1982) 55 California Current. Thus, the cold water map (fig. 27) clearly portrays the California Current as a tongue of cold water cutting through the borderland from the west-northwest. This path of the California Current directly into the borderland is a seasonal (fall-winter) phenomenon (seen in November, 1964). Because this path shows up strongly in the sediments, it suggests that this is the main season for radiolarian input into the sedimentary record, as was seen in figures 10 and 24. The percentage of cold water radiolarians varies among the environments. High values are recorded on the island shelf (34), mid-borderland oxic basin (32), and open ocean slope (32). These highs probably result from: 1) These environments lie in the path of the cold, radiolarian-rich California Current; and/or 2) are upwelling areas (some of the radiolarians used as cold water sphere indicators are probably intermediate and deep forms). Low cold water percentages are recorded at: 1) one shelf to slope transect, SD1-SD2 (14), probably because these stations are at the southern end of the borderland and more influenced by warm southern waters than cool California Current waters; and 2) the anoxic nearshore basin (15) where excellent preservation of all forms masks the cold water percentage. The cold water radiolarians are usually very resistant, so it is unlikely that the low percentage in the anoxic basin reflects an absolute low number of cold water forms. The plot of cold water radiolarians on a hypothetical ocean COLD WATER RADIOLARIANS PERCENT Figure 27. Cold waterradiolarians , percent. 01 0 <3 SEDIMENT STATION 56 57 suggests that 20-30% cold water forms should be expected in well preserved sediments at this location (see fig. 28). The slightly smaller percentage (15) seen in the anoxic basin may represent the influence of the warm California Undercurrent here. 9. Intermediate and Deep Water, Percent Intermediate and deep forms are carried into the borderland by the California Current. The map (fig. 29) is similar to the Cold Water Sphere map, showing a swath of high values cutting into the borderland from the northwest. The large scale map of the San Miguel Island shelf (fig. 30) shows that these forms are frequently deposited at shallow depths after being upwelled. In fact, on the San Miguel slope (at the San Miguel convergence) and at the southeastern end of the borderland (stations SD1 and SD2), greater numbers of deep and intermediate forms are sometimes found in shallow sediments than in deep. Wigley (1982) studying a southern California borderland assemblage, also found examples of deep living taxa being most abundant in shallow thanatocoenoses. The average intermediate and deep percentage among the environments is 18. However, the variation in this percentage among the environments mainly reflects the path of the California Current rather than influences of the environments themselves. The plot of intermediate and deep radiolarians on a hypothetical ocean suggests we should find greater than 10% of these in well preserved sediments at this location (see fig. 31). 10. Radiolarian/Sponge Spicule Ratio The map and radiolarians/sponge spicules vs. depth plot 58 80° 80* Figure 28. Percent cold water forms of entire radiolarian fauna in well preserved (radiolarians) sediments in a hypothetical ocean with all oceanic depths 4,000m. (After Casey et al, 1982) Figure 29 ttl«0‘0* l»0*0*0“ Mt*0'0** INTERMEDIATE AND DEEP WATER RADIOLARIANS PERCENT Intermediate anddeep waterradiolarians, percent SEDIMENT STATION 59 60 INTERMEDIATE AND DEEP WATER RAD10LARIANS SAN MIGUEL ISLAND SHELF PERCENT Figure 30. Intermediate and deep water radiolarians, San Miguel Island Shelf• Dashed lines are bottom contours in meters. 61 80“ 80“ 2 • «TO 10% E3» 10» on GREATER Figure 31. Percent intermediate to deep water forms of entire radiolarian fauna in well preserved (radiolarians) sediments in a hypothetical ocean with all oceanic depths 4,000m. (After Casey et al, 1982) 62 (figs. 32 and 33) show that the ratio is less than or equal to 1.0 (sponge spicules outnumber radiolarians) at all stations except P, Q, and S. This ratio might be expected to increase with depth because sponges preferentially inhabit shelfal areas while most radiolarians are intolerant of shelves. The cold water radiolarians map (fig. 27) suggests that the high ratios at P and Q represent upwelling of radiolarians which have been brought into the borderland with the California Current. The current flows head-on into Santa Catalina Island and is forced to upwell upon encountering that barrier. Station S is low in cold water forms and has the highest percentage of both symbiotic (35) and warm water (51) forms but the radiolarian number is low (12). Thus, it must be concluded that some factor in the environment at S discourages the growth of sponges. Perhaps some other organism competes successfully with sponges in this area. The radiolarians/sponge spicules ratio shows no clear re¬ lationship with depth in the borderland, probably because of the complicating influences of upwelling, multiple water masses, and perhaps some factor which inhibits the sponge population in local areas. 11. Phaeodarians, Presence or Absence The maps, the composite depth transect, and the phaeodarian presence-oxygen concentration-depth plot (figs. 34-37) all show that phaeodarian radiolarians are preserved only within a specific depth range, approximately 225-925 meters. This interval is low in oxygen and includes the oxygen minimum zone at 500-600 meters 63 Figure 32 Radiolarian/sponge spicule ratio RADIOLARIANS/SPONGE SPICULES VS. DEPTH Figure 33 (RADS./3P.SP.) 17 SAMPLES . Radiolarians/sponge spicules versusdepth. Table 2. Letters by dotsarestations referred toon DEPTH (METERS X10 64 65 Figure 34 Phaeodarians presence or absence Figure 35 u^•o,o*, Ito'o'o* Ht *00- m*o‘o“ DEPTHS OF PRESERVATION OF PHAEODARIANS METERS • Depthsofpreservation ofphaeodarians. X SEDIMENT STATION 66 67 PHAEODARIAN PRESENCE AND OXYGEN CONCENTRATION VS. DEPTH OXYGEN CONTENT PHAEODAR1ANS (ML/L) Figure 36. Phaeodarian presence and oxygen content versus depth Figure 37 PHAEODAHIAN PRESERVATION COMPOSITE DEPTH TRANSECT - ALL STATIONS PRESENCE OR ABSENCE (+/-) Phaeodarian preservation, compositedepthtransect 1250 68 69 (Emery, 1954). Phaeodarians are present in all environments. Their presence is tied not to an environment per se, but to low oxygen concentration which is essential for their preservation. As such, they are excellent indicators of low oxygen concentration in recent environments and paleoenvironments. This dependence of phaeodarian preservation on low oxygen concentration is one of the most significant and potentially useful findings of this thesis. Fossil anoxic environments are likely places to find hydrocarbon source rocks. The one environment which differs markedly from the rest is the anoxic nearshore basin. In five of the ten parameters which were plotted against environment (nassellarian/spumellarian ratio, diversity, symbionts, stylodictids and spongodiscids, and phaeodarians), the anoxic nearshore basin had an extreme value, and in one other (radiolarian number) it was close to the extreme. Low oxygen concentration is important both directly and indirectly: 1) In the case of the phaeodarians, low oxygen concentration directly inhibits dissolution of the organic matter which holds the siliceous components together; 2) Benthic burrowing organisms cannot live in anoxic environments. Thus, the radiolarians which are deposited there are not crushed in the digestive tract 70 of a burrower. Runze (1980) notes that radiolaria acquire metallic coatings while living which aid in preservation of their shells even after death. This • coating would be more likely to remain intact if the shell does not pass through the digestive tract of an organism. The anoxic nearshore basin, because it preserves radiolarians better than any other environment, is probably the best representative of the actual concentrations of the various living radiolarians. In other words, what is found in the anoxic nearshore basin should be closer to what actually lived in the water column above than what is found in any other environment. 71 CONCLUSIONS AND APPLICATIONS 1. Maps of living radiolarian concentrations (radiolarian density) during November, 1964 at depths less than 40-60 meters show the California Current to be relatively poor in radiolarians. The California Current is seen to enter the northwest corner of the borderland from the north and flow south. The California Undercurrent rises toward the surface at this time of year and can be seen as a radiolarian-rich tongue of water flowing northwesterly into the borderland from the southeast. At greater depths (40-200 meters), the California Current is rich in radiolarians and is seen to flow east-southeasterly into the borderland from the west. Chelton et al (1982) designate 1964 as an El Nino year off southern California. Since the radiolarian distributions in the plankton and surface sediments match so well, it may be that either the winter season (November) or a California El Nino (like 1964) may have the largest impact on the sedimentary record. 2. Radiolarian concentration in the sediments (radiolarian number) is low on the shelf and increases with depth on the slope. This radiolarian number-depth relationship may serve as a paleodepth indicator for rocks from California borderland type basins such as the Monterey formation. 3 Diversity in radiolarian taxa is low in the California Current. Low oxygen concentrations result in preservation of 72 even the less resistant taxa, so diversities measured in anoxic basins are high. This should serve as a good fossil anoxic basin indicator. 4. Nassellarian/spumellarian ratios have been shown to decrease onshore in other localities, but no clear relationship is observed in the southern California continental borderland. The presence of several water masses and local anoxic basins precludes the straightforward use of the n/s ratio as a depth indicator in the borderland. 5. The warm water sphere radiolarians and symbiotic radiolarians (which are the dominant warm water radiolarians) are found in greatest abundance in shelfal areas. Abundance of these groups of radiolarians in older sediments should also signify shelfal conditions. Warm water and symbiotic radiolarian -poor California Current water appears to converge with warm water and symbiotic-rich Davidson Current water over the slope southwest of San Miguel Island (San Miguel convergence). 6. Stylodictids and spongodisclds and other intermediate and deep water radiolarians are carried into the borderland with the California Current. They are frequently upwelled and deposited at shallow depths. In some areas there are greater numbers of intermediate and deep water forms preserved in shallow sediments than in deep. Relatively high numbers of these forms in older rocks should reflect the path of the paleo-eastern boundary current. 7 The California Current brought cold water sphere radiolarians 73 into the borderland in a tongue of water from the west-northwest during November, 1964. Because the- radiolarian assemblage in the sediment samples is similar to the plankton assemblage, it seems that the season when the California Current swings into the borderland is the main season (November or winter) which leaves an imprint on the sedimentary record; or the supra seasonal California El Nino may leave this same imprint. 8. Preservation of phaeodarian radiolarians occurs only in areas with low oxygen concentration in the water. This study found phaeodarians preserved only at depths of 225-925 meters in the southern California borderland. Phaeodarian presence in older sediments should be an excellent indicator of fossil anoxic conditions. 9. The one borderland environment which is found to differ markedly from the rest is the anoxic nearshore basin. The low oxygen concentration results in the best radiolarian preservation of all of the environments. For this reason, anoxic basin sediments are the best representative of the radiolarians that actually lived in the water column above. PROPERTIES-- OF BASIN WATERS Deoths, meters Temperature, Salinity, Oxygen, PO-?r NO-N SI Effective Basin •c m ml/liter U 3. tom/liter Bottom Sill Sill Santa Barbara 6.26 34.25 0.3 3.1 40 135 627 475 510 San Pedro 5.06 34.29 0.2 - - - 912 737 750 Santa Monica 5.05 34.31 0.3 3.2 35 160 938 737 750 Santa Catalina 4.02 34.42 0.4 3.0 35 165 1357 982 1010 Santa Cruz 4.15 34.52 0.3 - - - 1966 1085 980 San Nicolas 3.71 34.52 0.5 - - - 1833 1106 1100 Tanner 3.85 34.56 0.6 - - - 1551 1165 1060 West Cortes 3.37 • - - - - 1796 1362 - East Cortes 3.13 34.52 0.9 - - - 1979 1415 1370 No Name 2.97 • - - - - 1915 1553 - Long 2.77 - - • - - 1938 1697 - San Clemente 2.60 34.56 1.3 - - - 2107 1816 1750 Velero 2.52 34.58 2.07 - • « 2571 1902 1700 After Emery (1960) 75 TABLE 2 SEDIMENT STATION COORDINATES AND DEPTHS Station Latitude Longitude Depth (Degrees North) (Degrees West) (Meters) A 33.9995 120.3668 63 B 33.9995 120.4340 96 C 33.9833 120.3177 86 D 33.9833 120.3832 98 E 33.9668 120.4822 295 F 33.9497 120.3197 103 G 33.9517 120.3682 185 H 33.9293 120.3350 139 J 33.9318 120.5330 934 K 33.8825 120.2673 332 L 33.8633 120.4660 905 M 34.0830 119.3022 233 N 34.0992 119.2810 140 P 33.5187 118.6687 342 Q 33.4860 118.6672 231 R 33.5515 118.2853 750* S 33.5835 118.2365 92 T 32.6847 119.6032 242 U 32.4993 119.7062 1256 V 32.5502 119.2665 90 W 32.5167 119.2335 89 X 32.5165 119.3343 144 Y 32.5658 119.0693 436 Z 32.5993 118.9505 1008 SD1 32.6000 117.3667 192 SB 34.2467 120.0200 510* SP1 33.5000 118.3333 750* CB1 33.1667 118.5000 1010* SD2 32.4667 117.4833 1188 *These depths are the lowest sill depths for the basins from which the sample was obtained, not the actual depth at the sample site. 76 TABLE 3 GEOGRAPHIC LOCATIONS OF SEDIMENT STATIONS Station Location A, B, C, D, F, H Shallow C 150m) shelf off southern coast of San Miguel Island and western coast of Santa Rosa Island, San Miguel Gap E, G, K Moderately deep (150-350m), just seaward of locations named above, San Miguel Gap J, L Deep ( 900m), just seaward of locations named above, San Miguel Gap N Shallow (140m) shelf south of Ventura M Moderately deep (233m), south of N, at southeastern end of Santa Barbara Basin P. Q Moderately deep (200-350m) shelf off northwest coast of Santa Catalina Island s Shallow (92m) shelf south of Long Beach R Deep (800m, effective sill at 750m), south of S in San Pedro Basin T Moderately deep (242m), southern slope of Tanner Basin Ü Deep (1256m), northwest of Northeast Bank v, w, X Shallow ( 150m), Cortes Bank Y, Z Deep (436, 1008m), northwest end of East Cortes Basin SD-1 Moderately deep (192m) Coronado Bank SB Deep (581m, effective sill at 510m), Santa Barbara Basin SP-1 Deep (806m, effective sill at 750m), San Pedro Basin CB-1 Deep (1074m, effective sill at 1010m), Catalina Basin SD-2 Deep (1188m) San Diego Trough SEDIMENT STATION COUNTS 29 •o co P* W 2 . iH X (HI w d o CO £d 52 0 60 4J "O CD U 0) § W • * CD co • CD CO a H o. CO • > I COH^aOHiOMOHiOOO'OOOOOtN OOOOOOOOOOOOOOOOOOO||IOOOOOOH HCMCMCMHtMrlHCMHCMCMnHHHCMOM HCMCMCMCMCMCMHCMCMCM HCM VOO^CMinNCMOVCM^N |NCOHCT 106 2 154 77 78 TABLE 5 PLANKTON STATION COORDINATES Station Latitude Longitude (Degrees North) (Degrees West) 35 33.7250 119.5056 36 44.4875 121.1583 37 34.0000 121.0833 38 33.5000 120.9167 39 33.0000 120.6667 40 32.5000 120.5000 41 32.9583 119.7500 42 33.0500 119.0417 43 33.3625 118.7683 79 TABLE 6 PLANKTON TOW COUNTS Split Total Rads./ Nass./ Station Depth (m) Fraction Rads. Spurn. 10135 0-40 1 144 72 0.57 10136 0-50 1 10 4 0.43 0-200 1/2 62 12 0.82 50-200 1/2 52 14 0.93 10137 0-200 1/2 30 6 0.36 10138 0-50 1/2 1 1 0-200 1/2 423 85 0.89 50-200 1/2 422 113 0.89 10139 0-60 1/2 50 33 0.25 0-200 1/2 323 65 1.20 60-200 1/2 273 39 1.55 10140 0-50 1/2 25 20 1.08 10141 0-50 1/4 316 506 1.47 0-200 1/4 367 147 2.75 50-200 1/4 51 68 10.6 10142 0-50 1/2 165 132 1.06 0-200 1/2 659 132 1.20 50-200 1/2 494 66 1.26 10143 0-50 1/2 96 77 1.82 0-200 1/2 582 116 1.14 50-200 1/2 486 65 1.04 80 TABLE 7 OPERATIONAL TAXONOMIC UNITS ENCOUNTERED IN THIS STUDY Only Recent specimens are recorded here. Taxa representative of the warm water sphere are denoted by "W". Taxa which live in symbiosis with zooxanthellae (algae) are denoted by "S". Taxa representative of the cold water sphere are denoted by "C". Taxa representative of intermediate and deep water are denoted by "ID." Taxa from broad or uncertain habitats are denoted by OTU Habitat 1. Anthocyrtidlum spp. gr. W 2. Botryostrobus aurltus/australis spp. gr W (actually central water mass) 3. Euchltonla fureata spp. gr. W 4. Eucyrtldium acuminatum (Hirenberg) W 5. E. hexagonatum Haeckel W 6. Heliodiscus asterlscus Haeckel W 7. Lamprocyclas marltails spp. gr. W 8. Larcospyra quadrangula Haeckel W 9. Pterocanlum praetextum spp. gr. W 10. P. trilobum (Haeckel) W 11. P. zancleus (Mueller) W 12. Spongocore spp. gr. W 13. Theocorythlum trachellum (Ehrenberg) W 14. Acanthodesmiidae spp. W,S 15. Amphlrhopalum ypsllon Haeckel w,s 81 16. Collosphaeridae spp. W,S 17. Dlctyocoryne profunda-truncatum spp. gr. W,S 18. Ommatartus tetrathalamus (Haeckel) W,S 19. Pyloniidae spp. W,S 20. Spongaster tétras spp. gr. W,S 21. Botryostrobus aquilonaris (Bailey) C 22. B. corbula (Harting) C 23. Dictyophimus infabricatus Nigrini C 24. Heliotholus spp. C 25. lophophaenid gr. C 26. Porodlscus/Stylodictya spp. gr. C 27. Spongopyle osculosa Dreyer C 28. Spongotrochus glacialis Popofsky C 29. Spongotrochus venustum (Bailey) C 30. Theocalyptra craspedota (Jorgensen) C 31. Anthrocyclas blcornls (Jorgensen) ID 32. Axoprunum stauraxonlum Haeckel ID 33. Lamprocyrtls hannal (Campbell and Clark) ID 34. Larcopyle butschlil Dreyer ID 35. Litheliidae (tightly coiled species such as Llthellus minor Jorgensen) ID 36. Peripyramls clrcumtexta Haeckel ID 37. Stylatractus spp. gr. ID 38. stylosphaerids ID 39. Theocalyptra spp. gr. ID 40. tholonids ID 41. actinomids 42. Artophormis spp. 43. astrosphaerids 44. carpocanllds 45. cenosphaerids 46. Calocyclas amlcae (Theocorythlum trachellum) spp. 47. Cornutella profunda Ehrenberg 48. cubosphaerlds 49. eucyrtidins 50. Eucyrtldium anomalum Haeckel 51. Lamprocyclas nlgrlnlae (Caulet) 52. Lamprocyrtls neoheteroporos (Fling) 53. Lamprocyrtls ? 54. Larcopyle ? 55. Larcospyra ? 56. Lltharachnlum tentorium Haeckel 57. lithelids 58. nassellarians 59. Perldlnlum splnlpes Haeckel 60. pterocorlds 61. sethophormins 62. spongodlsclds 63. spongoplegma 64. spumellarians 65. spyroids 66. theocalyptrids Numbers of Operational Taxonoaic Units Encountered at Sediment Stations 84 40UPH(kOB*lWaSZOiOgl«HD» OMP< flQ v» nu M TABLE 9 RADIOLARIAN COUNTS VERSUS ENVIRONMENTS 85 86 BIBLIOGRAPHY Allan Hancock Foundation, 1965. An oceanographic and biological survey of the southern California mainland shelf. California State Water Quality Control Board, Publ. No. 27, 232 pp. Atwater, T., 1970. Implications of plate tectonics for the Cenozoic tectonic evolution of western North America. Geol. Soc. America Bull., 81î 3513-3536. Berger, W. H., 1968. Radiolarian skeletons: Solution at depth. Science, 159 (3820): 1237-1238. Campbell, R. H., and Yerkes, R. F., 1976. Cenozoic evolution of the Los Angeles basin area — relation to plate tectonics. In: Howell, D. G., Ed., Aspects of the geological history of the California continental borderland: AAPG, Pacific Section, Mise. Publ. 24: 541-558. Casey, R. E., 1966. A seasonal study on the distribution of polycystine radiolarians from waters overlying the Catalina Basin, S. California. Ph.D. diss., Univ. S. California, 145 pp. . 1977. The ecology and distribution of Recent Radiolaria. In: Ramsay, A. J. S., Ed., Oceanic micropaleontology, Vol. II. Academic Press: 809-845, pis. 1-6. . 1982. Lamprocyrtis and Stichocorys lineages: Biogeographical and ecological perspectives relating to the tempo and mode of polycystine radiolarian evolution. Third N. Amer. Paleontological Conv., Proceedings, Vol. I: 77-82. Casey, R. E., and Bauer, M. A., 1976. A seasonal study of Radiolaria and Foraminifera in the waters overlying the south Texas outer continental shelf. Geol. Soc. America. Abs. with programs, 8 (1): 11. Casey, R. E., Leavesley, A., Spaw, J. M., McMillen, K., and Sloan, J. R., 1981. Radiolarian species composition, density, and diversity as indicators of water structure and circulation on the south Texas shelf. Gulf Coast Assoc. Geol. Socs., Trans., 31: 257-263. Casey, R. E., Partridge, T. M., and Sloan, J. R., 1971. Radiolarian life spans, mortality rates, and seasonality gained from recent sediment and plankton samples. Proceedings, II Planktonic Conf., Rome: 159-165. 87 Casey, R. E., Spaw, J. M., and Kunze, F. R., 1982. Polycystine radiolarian distributions and enhancements related to oceanographic conditions in a hypothetical ocean. Gulf Coast Assoc. Geol. Socs., Trans., 32: 319-332. Casey, R. E., Wigley, C. R., and Perez-Guzman, A. M., 1983. Biogeographic and écologie perspective on polycystine radiolarian evolution. Paleobiology, 9 (4): 363-376. Chelton, D. B, Bernal, P. A., and McGowan, J. A., 1982. Large scale interannual physical and biological interaction in the California Current. Journal of Marine Research, 40 (4): 1095-1125. Cole, M. R., and Armentrout, J. M., 1979. Neogene paleogeography of the western United States. S.E.P.M., Pacific Section, Pacific Coast Paleogeography Symposium 3: 297-323. Dickinson, W. R., 1979. Cenozoic plate tectonic setting of the cordilleran region of the western United States. In: Armentrout, J. M., Cole, M. R., and Ter Best, H., Eds. Cenozoic Paleogeography of the Western United States, Pacific Section, S.E.P.M.: 1-13. Douglas, R. G., 1981. Paleoecology of continental margin basins: A modern case history from the borderland of southern California. In: Douglas, R. G. Colburn, I.P., and Gorsline, D. S., Eds. Depositional Systems of Active Continental Margins: Short course notes, Pacific Section, S.E.P.M.: 121-156. Emery, K. 0., 1954. Source of water In basins off southern California. Jour. Mar. Res., 13: 1-21. . 1960. The sea off southern California. John Wiley & Sons, Inc., New York, 366 pp. Gorsline, D. S., 1978. Anatomy of margin basins. Journal of Sed. Pet., 48 (4): 1055-1068. Greene, H. G., Clarke, S. H., Jr. Field, M. E., Linker, F. I., and Wagner, H. C., 1975. Preliminary report on the environmental geology of selected areas of the southern California Continental Borderland. U.S. Geol. Survey, Open File Report 75-596, 70 pp. Haeckel, E., 1887. Report on the Radiolaria collected by H.M.S. Challenger during the years 1873-76. In: Rept. Voyage ’Challenger’, Zool. 18 (188), 1803 pp. Haecker, V., 1907. Altertumliche, Spharellarien and Crytellarien aus grossen Meerstiefen. Archiv Protistenk, 10: 114-126. 88 Hickey, B. M., 1979. The California Current System — hypotheses and facts. Oceanography, 8: 191-279. Howell, D., Alpha, T., and Joyce. J., 1980. Plate tectonics, physiography, and sedimentation of the northeast Pacific. Pacific Section, S.E.P.M. Pacific Coast Paleogeography Symposium 4: 43-54. Hulsemann, K. 1963. Radiolaria in plankton from the Arctic Drifting Station 'T-3', including the description of three new species. Arctic Inst. N. America, Tech. Paper, 13: 1-52. Hurd, D. C., 1972. Factors affecting solution rate of biogenic opal in seawater. Earth Planet. Sci. Lett., 15: 411-417. Ingle, J. C., 1980. Cenozoic paleobathymetry and depositional history of selected sequences within the southern California continental borderland. Cushman Found. Foram. Res., Spec. Publ. 19: 163-195. Johnson, T. C., 1974. The dissolution of siliceous microfossils in surface sediments of the eastern tropical Pacific. Deep Sea Research, 21: 851-864. Kling, S.A., 1966. Castanellid and Circoporid radiolarians: Systematics and zoogeography in the eastern N. Pacific. Unpub. Ph. D. thesis, Univ. California, San Diego. Kunze, F* R., 1980. Silica preservation in the oceans. Unpub. Ph. D. thesis, Rice Univ. Lo-Bianco, S., 1903. La pesche abissale eseguite da F. A. Krupp col Yacht 'Puritan' nelle adiacenze di Capri ed in altre localita del Mediterraneo. Mitte Zool. Sta. Neapol, 16 (1-2): 109-279. McGowan, J. A., 1971. Oceanic biogeography of the Pacific. In: Funnell, B. M., and Riedel, V. R., Eds., The micropaleontology of oceans. Cambridge Univ. Press: 3-74. . 1974. The nature of oceanic ecosystems. In: Miller, C. J., Ed., Oregon State Univ. Press, Corvallis: 9-28. McMillen, K. J., 1979. Radiolarian ratios and the Pleistocene - Holocene boundary. Gulf Coast Assoc. Geol. Socs., Trans., 29: 298-301. Molina-Cruz, A., 1977. Radiolarian assemblages and their relationship to the oceanography of the subtropical southeastern Pacific. Marine Micropaleontology, 2: 315-352. Nigrini, C., and Moore, T. C., 1979. A guide to modern Radiolaria. Cushman Found. Foram. Res., Spec. Publ. 16. 89 Pavlova, Y. Y., 1966. Seasonal variations of the California Current. Oceanology, 6: 806-814. Petrushevskaya, M. G., 1966 Radiolaryii v planktone i v donnykh osadkakh. Geokhimiya Kremnesema. Nauka, Moscow: 21SI-245. Popofsky, A., 1913. Die Nassellarien des Warm wassergebietes. Dt. Sudpol Exped. 1901-1903, 14: 217-416. Reid, J. L., Roden, G. I., and Wyllie, J. G., 1958. Studies of the California Current System. Calif. Cooperative Oceanic Fisheries Investigations Progress Report, 7-1-56 to 1-1-58, Marine Resources Comm., Calif. Dept, of Fish and Game, Sacramento, Calif.: 27-56. Renz, G. W., 1976. The distribution and ecology of Radiolaria in the central Pacific: plankton and surface sediments. Bull. Scripps. Inst. Oceanography, 22, 267 pp. Reshetnjak, V. V., 1955. Vertikalnoe raspredelenie radiolaryii Rurilo-Kamchatskoi vpadiny. Trudy Zool. Inst. Akad. Nauk, U.S.S.R., 21: 94-101. Romine, K., 1982. Late Quaternary history of atmospheric and oceanic circulation in the eastern equatorial Pacific. Marine Micropaleontology, 7: 163-187. Shepard, F. P., and Emery, K. 0., 1941. Submarine topography off the California coast: Canyons and tectonic interpretation. Geol. Soc. America, Spec. Papers No. 31, 171 pp. Sverdrup, H. U., and Fleming, R. H., 1941. The waters off the coast of Southern California, March to July 1937. Scripps Inst. Oceanography. Bull., 4 (10): 261-387. Takahashi, K., and Honjo, S., 1981. Sinking speed, residence time, and dissolution of radiolaria. In: Abstracts with Programs - G.S.A., 13(7): 564. Tchernia, P., 1980. Descriptive regional oceanography. Pergamon Press, New York, 253 pp. Yerkes, R. F., McCulloh, T. H., Schoellhamer, J.E., and Vedder, J. G., 1965. Geology of the Los Angeles basin — an introduction. U.S. Geol. Surv. Prof. Paper 420-A: A1-A57. Weaver, F. M., Casey, R.E., and Perez, A. M., 1981. Stratigraphic and paleoceanographic significance of early Pliocene and Miocene radiolarian assemblages from northern to Baja California. In: Garrison, R.E., Douglas, R. G., Pisciotto, K. E., Isaacs, C. M., and Ingle, J. C., Eds., the Montery Formation and Related Siliceous Rocks of California. Pacific Section, S.E.P.M., Spec. Publ. 90 Wigley, C. R., 1982. Radiolaria in the Holocene sediment of the Gulf of Mexico and the basins off southern California: assemblage changes with water depth and eutrophism. Unpub. Master’s thesis, Rice Univ., 140 pp. Wyrtki, K., 1974. The dynamic topography of the Pacific Ocean and its fluctuations. Hawaii Inst, of Geoph., Rep. 74-5, 37 pp.