LATE PLEISTOCENE SEDIMENTS AND FOSSILS NEAR THE MOUTH OF MAD RIVER, HUMBOLDT COUNTY, CALIFORNIA: FACIES ANALYSIS, SEQUENCE DEVELOPMENT, AND POSSIBLE AGE CORRELATION

by

Erik W. Harvey

A Thesis

Presented to

The faculty of Humboldt State University

In Partial Fulfillment

of the requirements for the Degree

Master of Science

July, 1994 LATE PLEISTOCENE SEDIMENTS AND FOSSILS NEAR THE MOUTH OF MAD RIVER, HUMBOLDT COUNTY, CALIFORNIA: FACIES ANALYSIS, SEQUENCE DEVELOPMENT, AND POSSIBLE AGE CORRELATION

by

Erik W. Harvey

APPROVED BY THE MASTER'S THESIS COMMITTEE

William C. Miller, III

Raymond M. Burke

Kenneth R. Aalto

APPROVED BY THE DEAN OF GRADUATE STUDIES iii

TABLE OF CONTENTS

TABLE OF ILLUSTRATIONS v

ACKNOWLEDGMENTS viii

ABSTRACT ix

INTRODUCTION 1 General 1 Purpose of Study 1 Previous Work 4 Geologic Setting 8 Area of Study 9

SEDIMENTOLOGY 10 Facies Names 10 Methods 10 Field 10 Laboratory 12

PALEONTOLOGY 15 Methods 15 Field 15 Laboratory 15

STRATIGRAPHY 20 General 20 Underlying Unit 20 Overlying Unit 22 Mouth of Mad unit 22 Estuarine Mud 22 Nearshore Sand 22 Nearshore Sand and Gravel 25 Strand-Plain Sand 27 Bay fades 27 Bioturbated Sand 31 Lower Tidal Flat Mud 31 Mixed Sand and Mud 31 Bay Mud 33 Upper Tidal Flat Mud 36 iv

DISCUSSION 38 Depositional Environments 38 Estuarine Mud 38 Nearshore Sand 39 Nearshore Sand and Gravel 40 Strand-Plain Sand 42 Bay 43 Bioturbated Sand 43 Lower Tidal Flat Mud 43 Mixed Sand and Mud 44 Bay Mud 44 Upper Tidal Flat Mud 45 Summary 45 Depositional Sequence 46 Age of Pleistocene Deposits 50 Elk Head 50 Trinidad Head 52 Moonstone Beach 53 Crannell Junction 54 Falor Formation 55 Mouth of Mad unit 55 Correlation 56

CONCLUSIONS 58

APPENDIX A: Sediment Sample Data 60

APPENDIX B: Fossil Sample Data 67

REFRENCES CITED 71 V

TABLE OF ILLUSTRATIONS

FIGURES

Figure 1. Map showing location of studied Pleistocene fossil deposits (EH=Elk Head, TH=Trinidad Head, MB=Moonstone Beach, CJ=Crannell Junction, MOM= Mouth of Mad unit, SRG=School Road gravel, F=Outcrops of Falor Formation). 2

Figure 2. Map showing location of Mouth of Mad unit (MOM) and the School Road gravel (SRG) 3

Figure 3. Composite stratigraphic column for the sediments exposed at the Mouth of Mad river, showing the Mouth of Mad unit and portions of overlying marine terrace and underlying unit. Also shown is variation of Bay facies between northern (N) and southern (S) areas of the exposure. Lower unit contact used as datum because it provides a stable reference level for measurement. Column is incomplete because thickness of overlying and underlying units could not be measured completely (UTFM=Upper Tidal Flat Mud, LTFM= Lower Tidal Flat Mud). 11

Figure 4. In situ tree roots in paleosol below lower unconformity. Hand lens in photograph is 32 mm long. 21

Figure 5. Tresus sp. in living position in the Estuarine Mud fades, just above lower unconfomity. 23

Figure 6. Trough cross-beds in the Nearshore Sand facies. Pebble stringer marks lower boundary of one set. Approximately 10 m above top of Estuarine Mud facies. 24

Figure 7. Fossiliferous sand lens in the Nearshore Sand fades conaining the clam Macoma nasuta and the gastropod Nassarius mendicus. Approximately 6 m above top of Estuarine Mud facies. 26

Figure 8. Gravel lenses in the Nearshore Sand and Gravel facies (A). Marine terrace deposits are also visible (B). Upper surface is top of bluff. Lenses are approximately 3 m above top of Nearshore Sand facies. 28 vi

Figure 9. Tabular gravel beds in the Nearshore Sand and Gravel facies. Also visible is the Strand-Plain Sand facies. Lowest bed is approximately 2 m above top of Nearshore Sand facies. 29

Figure 10. Lower boundary of gravel bed in Nearshore Sand and Gravel facies indicating scour-and-fill processes. The bedding in the underlying sand is truncated. Large pebbles above the boundary suggest reworking by a later storm event. Approximately 3 m above lower contact of unit. 30

Figure 11. Abrupt contact between the Bioturbated Sand and Lower Tidal Flat Mud subfacies. 32

Figure 12. Mixed Sand and Mud subfacies, showing mixture of sandy and muddy sediments. Fossils include Tresus sp. and Ostrea lurida. 34

Figure 13. Tresus sp. in living position near the upper contact of the Bay Mud subfacies with the Upper Tidal Flat Mud subfacies. Smaller fossils in the surrounding matrix include Ostrea lurida and Balanus sp. 35

Figure 14. Upper Tidal Flat Mud subfacies showing contact with subjacent Bay Mud subfacies. Contact is just below handlens 37

Figure 15. Paleogegraphic reconstruction of depositonal environments at the mouth of Mad River locality at the time of deposition of the Bay facies. Size of the bay and location of the inlet are arbitrary. 47

Figure 16. Correlation chart of pre-terrace Pleistocene units and marine terrace deposits in northern coastal Humboldt County, California. Age estimates for lightly stipled units are very tentative. Isotope stages are based on Chappel and Shackelton (1986). (Age data mostly from: Wehmiller et al., 1977; Wehmiller, Lajoie et al., 1977; Kennedy, 1978; Carver, 1987; Carver and Burke, 1992). 51

TABLES

Table 1. Summary descriptions of facies within the Mouth of Mad unit (Fig. 3). 13

Table 2. Fossils from the Bioturbated Sand subfacies 17

Table 3. Fossils from the Mixed Sand and Mud subfacies 18

Table 4. Fossils from the Bay Mud subfacies 19 vii

PLATES

Plate 1. Panel diagram of the exposure of Pleistocene beds at the mouth of the Mad River as it apperaed in April, 1993. View is from sand spit 15 m west of bluffs. (In Pocket) ACKNOWLEDGMENTS

I would like to thank my advisor, Dr. William C. Miller, III, for his help and guidance in the research and preparation of this thesis. I would also like to thank the other members of my committee, Dr. Raymond M. "Bud" Burke and Dr. Kenneth R.

Aalto, for their helpful suggestions and for reviewing this thesis. Dr. Gary A. Carver was also of great assistance with sea level curve interpretations.

The library of Humboldt State University provided the reference materials so necessary in the research of this thesis. The Department of Geology provided the necessary materials and laboratory space.

I also wish to thank my fellow graduate students, and the faculty and staff of the

Department of Geology for their support. I especially extend thanks to Eileen M.

Weppner for her willingness to listen and her understanding.

I would like to sincerely thank my family for their constant encouragement, especially my parents Michael and Margo Harvey, to whom this thesis is dedicated.

Finally a special thanks goes to my wife Kelly Decker, without whose support this thesis would not have been possible. To all -- many thanks.

viii ABSTRACT

Study of late Pleistocene sediments near the mouth of the Mad River revealed a sequence of nearshore marine and shallow bay deposits. This sequence, bounded by unconformities, is informally named the Mouth of Mad unit. The Mouth of Mad unit can be divided into four distinct depositional facies at the study site. The lowest facies are the Nearshore Sand and Estuarine Mud, which lie unconformably on a paleosol. The sand facies grades upward into a high-energy, interbedded Nearshore Sand and Gravel facies containing storm and rip-channel deposits. Above the sand and gravel is a Strand-

Plain Sand facies. This sand is overlain by a laterally variable sequence of shell-rich Bay facies. The bay deposits can be further divided into five subfacies: 1) a Bioturbated

Sand; 2) a Lower Tidal Flat Mud; 3) a Mixed Sand and Mud; 4) an oyster-rich Bay

Mud; and 5) an Upper Tidal Flat Mud. The bay sequence is overlain unconformably by younger late Pleistocene marine terrace deposits. The depositional environments represented by these facies progress from a shoreline estuary to nearshore deposits, above storm wave base, and slowly back to shoreline, and finally to shallow bay conditions. The Mouth of Mad unit represents a transgressive-regressive sequence, involving the development of a protective spit. The uppermost mud within the Mouth of

Mad unit has been dated, using thermoluminesence age estimation, at 176 ± 33 ka, placing it in the late Pleistocene. Amino acid racemization dating, fossil evidence, and the thermoluminesence date can be used to establish a tentative correlation between the

Mouth of Mad unit and other nearby Pleistocene fossil-bearing deposits. The Mouth of

Mad unit appears to be younger than the fossiliferous deposits at Elk Head, Crannell

Junction, Trinidad Head, Moonstone Beach, and the Falor Formation near Maple Creek, and possibly time equivalent with gravel deposits exposed at the western end of School

Road in McKinleyville. ix INTRODUCTION General

Northward migration of the Mouth of the Mad River has produced extensive exposure of marine sediments along the western margin of Dows Prairie, coastal

Humboldt County (Figs. 1 and 2). Included in this exposure is an unconformity- bounded unit consisting of Pleistocene marine and estuarine deposits. Since it was first described by Miller and Morrison (1988), the exposure of these deposits has improved revealing a complex sequence of depositional facies. This unit was informally named the

Mouth of Mad unit (Harvey and Weppner, 1992a). An informal name was used because the Mouth of Mad unit is known only from this exposure.

Five distinct depositional facies can be delineated within the Mouth of Mad unit based on sedimentologic and paleontologic properties. These facies represent nearshore marine and shallow bay environments. Abundant fossils, primarily mollusks, are present only in the upper and lower facies.

Continued erosion by the Mad River threatens to eliminate this exposure, making the documentation and interpretation of the unit important. Exposure reduction and destruction of important deposits have already occurred. Purpose of Study

The primary purpose of this study is to characterize the Mouth of Mad unit while the unit is still well exposed. Additional purposes include the correlation of the Mouth of Mad unit with other local Pleistocene deposits, determination of environmental history, and the interpretation of any paleoclimatic implications. Specifically the purposes are: 1) description of the varied sedimentary structures, textures and lateral variations; 2) characterization of the fossil assemblages; 3) determination of depositional

1 2

Figure 1. Map showing location of studied Pleistocene fossil deposits (EH=EIk Head, TH=Trinidad Head, MB=Moonstone Beach, CJ=Crannell Junction, MOM= Mouth of Mad unit, SRG=School Road gravel, F=Outcrops of Falor Formation). 3

Figure 2. Map showing location of Mouth of Mad unit (MOM), the School Road gravel (SRG) and bore holes drilled by Woodward Clyde. 4 environments and depositional history; 4) determination of age of the unit; 5) correlation with other Pleistocene deposits in the region; and 6) interpretation of the relationship of the Mouth of Mad unit in terms of eustatic sea level changes.

Outcrops of late Pleistocene deposits in northern coastal California are fairly

common but mostly undescribed. The relationships between Pleistocene deposits

cropping out in different localities are poorly understood. Correlation of these deposits is difficult to establish even over short lateral distances owing to discontinuous exposure and faulting.

The results of this study will help to clearify the relationship among Pleistocene deposits in nothern coastal California and provide a framework for further stratigraphic study. Environmental interpretations, by indicating relative sea level at the time of

Mouth of Mad unit deposition, can be used to determie the rate and timing of tectonic uplift. Determination of facies progression and description of sedimentologic features provides another example of high-energy wave-and-storm dominated coastal deposits, which remains a poorly documented environment of deposition.

Previous Work

Study of Pleistocene deposits in Humboldt County began around the turn of the century. Lawson (1894) described "Wild-Cat Series" sediments in the vicinity of

Ferndale and Scotia. On the basis of fossil evidence he assigned a Pliocene age to the

Wildcat and correlated it with the "Merced Series" exposed near San Francisco. Diller

(1902) also described Neogene rocks in Humboldt County, including exposures on the

Mad River upstream from Blue Lake (Falor Formation of Manning and Ogle, 1950).

The first comprehensive field studies were conducted in the late 1940's and

1950's (Manning and Ogle, 1950; Ogle, 1953; Evenson, 1959). Manning and Ogle 5

(1950) described the geology of the Blue Lake 15' quadrangle. They proposed the name

Falor Formation for a sequence of marine sandstones and clays in the vicinity of Maple

Creek. Based on megafossil evidence they assigned a Pliocene age to the Falor, and

suggested a correlation with the upper portion of the Wildcat Group. Ogle (1953)

divided the Wildcat Group into five units: the Rio Dell, Eel River, Carlotta, and Pullen

Formations, and the Scotia Bluffs Sandstone. He mapped Pleistocene deposits above the

Wildcat as the "Hookton formation". Included in the Hookton were both marine and

nonmarine sediments. He inferred a middle to upper Pleistocene age for the

Hooktonbased on limited fossil evidence. He proposed a broad valley plain bordering

the Pacific, including swamps, lagoons, estuaries, and barred bays, as well as terrestrial environments, as the likely depositional setting. Evenson (1959) extended the Hookton to include sediments exposed near Arcata and McKinleyville, including sediments

underlying Dows Prairie.

The deposits at Moonstone Beach (Fig. 1) were briefly noted by Allison et al.

(1962). In a systematic treatment of Wildcat Group megafauna, Faustman (1964) correlated the Moonstone Beach deposits with the Rio Dell Formation and lower Scotia

Bluffs sandstone. Durham and MacNeil (1967) assigned a middle Pleistocene age to the

Moonstone deposits based on the presence of three species of echinoids,

Strongylocentrotus droebachiensis, S. purpuratus, and S. franciscanus. Wehmiller et al.

(1977) reported an age of 710 ± 100 ka for the same deposits based on amino acid racemization analysis.

The deposits at Crannell Junction (Fig. 1) were first studied in the 1960's and

1970's (Fitch, 1970; Howard, 1970; Kilmer, 1972; Kern at al., 1974; Kohl, 1974). Fitch

(1970) documented diverse fossil fish remains, and referred the deposit to the late 6

Pleistocene. Howard (1970) identified a bone of an extinct flightless auk from the

Crannell deposits. Kilmer (1972) described a new species of sea otter from this same site. Kern et al. (1974) described a fossil annelid tube occurring in specimens of Nucella lamellosa from "Arcata, Humboldt County", with the source probably being the Crannell deposits. Kohl (1974) listed a diverse fossil biota from Crannell Junction. He

determined the age of the deposits as late Pleistocene (Rancholabrean) based on the

occurence ofthe sea lion Eumetopias jubata, good shell preservation, and poorly

consolidated sediments. Reppening (1976) reported evidence for a maximum age of

Irvingtonian, or early Pleistocene, for the sea otter described by Kilmer (1972). He also

used the presence of a mammoth scaphoid bone to propose that the Moonstone Beach

deposits are also Irvingtonian or younger in age.

Kennedy (1978) examined Pleistocene fossils from San Francisco to Puget

Sound. He examined several localities in northern California as part of his dissertation research, including Elk Head, Trinidad Head, Moonstone Beach, and Crannell Junction

(Fig. 1). He presented age estimates for these deposits based primarily on amino acid racemization rates. Deposits at Elk Head were placed in oxygen isotope stage 11,

Trinidad Head deposits in stage 15, Moonstone Beach deposits as 730-780 ka in age, and Crannell Junction deposits in stage 13.

Roth (1979) examined Trinidad Head, Elk Head, Moonstone Beach, and

Crannell Junction (Fig. 1) as part of another dissertation on late Cenozoic fossils in

northern California and southern Oregon. He suggested a possible correlation between the Moonstone Beach deposits and those at Trinidad Head. He also proposed that the

deposits be named the "Moonstone Beach Formation" (although the proposal was never 7 published), and dated them at 1.25 to 1.5 Ma based on fossil evidence. He further placed the age of the deposits at Elk Head in the late Pleistocene.

Carver (1985) mapped marine deposits in the drainages along the western margin of Dows Prairie as part of the Falor Formation. Sarna-Wojcicki et al. (1987) reported an age estimate for a volcanic ash layer 100 m from the base of the Falor Formation as between 1.8 and 2.0 Ma. Using this date, and average sedimentation rates, Carver

(1987) calculated an age for the top of the Falor Formation in the Mad River Fault Zone of 800-900 ka.

The Mouth of Mad unit itself was first studied by Miller and Morrison (1988).

They identified fossil associations for two fossiliferous facies, a sandflat facies

(Bioturbated Sand subfacies of this study) and a slough-basin mud facies (Bay Mud subfacies of this study). Other fossiliferous facies and the lower contact of the unit were not exposed at the time of their study. They dated the unit as late Pleistocene in age based on fossil evidence. In this case, it appeared that all the mollusks belonged to extant species.

Berger et al. (1991) reported a thermoluminesence date for the uppermost mud within the Mouth of Mad unit of 176 ± 33 ka. They further reported a soil correlation age of 70 ka for a soil formed in the overlying terrace deposits (Berger et al., 1991, p.

36).

More recently, the Mouth of Mad unit was studied by Harvey and Weppner

(1992 a, b). They briefly described the entire unit, but only an informal name was applied owing to the limited exposure (1992a). The facies presented in their study were delineated and environmental interpretations made based on sedimentologic and paleontologic evidence. These workers placed the unit in the late Pleistocene, based on 8 the thermoluminesence age estimate mentioned above and lack of extinct species. A possible time equivalence with the Hookton Formation in its type area south of Eureka was suggested.

The late Pleistocene marine terraces near the Mouth of Mad river, and in the surrounding area, have been studied by Carver et al. (1986) and by Carver and Burke

(1992) marine terraces in these studies being defined as topographic benches cut into nearshore marine sediments. These studies focused on determination of uplift rates and on age estimation of terrace surfaces based on soil profiles. Geologic Setting

Northern coastal California has undergone extensive folding and faulting following the passage northward of the Blanco Fracture Zone (Carver, 1987; Kelsey and

Carver, 1988). With the passage of the fracture zone deformation associated with the subduction of the Gorda Plate beneath the North American Plate dominated the tectonic setting in this region. The active tectonism, coupled with eustatic fluctations, have resulted in the deposition and exposure of Pleistocene marine sediments along the northern California coast. The Mouth of Mad unit lies within the Mad River Fault Zone

(Carver et al., 1986; Clarke, 1987; Nilsen and Clarke, 1987; Carver and Burke, 1992).

The unit is deformed at the northern end of the exposure by a splay of the McKinleyville fault, a northeast-dipping thrust fault (Carver, 1991; Carver and Burke, 1992). Beds at the northern end of the exposure dip 30-35° south to southwest. Beds become nearly horizontal near the southern end toward Widow White Creek (Fig. 2; Plate 1).

Late to middle Pleistocene exposures in coastal Humboldt County are patchy and often separated by multiple faults. These deposits are underlain by either late Mesozoic rocks of the Franciscan Complex or by Plio-Pleistocene marine sediments. Younger late 9

Pleistocene marine terrace deposits often overlie the older Pleistocene deposits (Carver and Burke, 1992), as is the case in the study area. Area of Study

The Mouth of Mad unit is exposed in the bluffs along the eastern bank of the

Mad River, extending from 250 m south of the Highway 101 vista point to 100 m north of Widow White Creek, east halves of sections 24 and 25, T. 7 N, R. 1 W (Figs. 1 and

2). The bluffs reach a maximum height of approximately 30 m at the northern end of the exposure and decrease gradually to approximately 4 m at the southern end of the exposure near Widow White Creek. South of the bluffs for 1-2 km the deposits are covered by vegetation, but presence of the unit is suggested by shell material in the channels of small tributary creeks along the Mad River.

Additional Pleistocene localities in the vicinity were studied in order to propose time correlations. These localities included Elk Head, Trinidad Head, Moonstone

Beach, Crannell Junction, exposures of the Falor Formation near Maple Creek, and gravel deposits at the western end of School Road in McKinleyville (Figs. 1 and 2). SEDIMENTOLOGY Facies Names Facies names are introduced at this time as a matter of convenience. The facies names are based on the sedimentologic and paleontologic features of the deposits. The interpretations and reasoning for the names are discussed in the Stratigraphy and Discussion sections of this thesis. Methods Field A total of 18 sediment samples was collected for grain-size analysis from the three lowest sandy facies. Of these samples, five came from the Nearshore Sand facies, eight from the Nearshore Sand and Gravel facies, and five from the Strand-Plain Sand facies (Fig. 3). Additional data were collected as observations in the field. Field descriptions and photographs of sedimentary structures were made. Sediment color was determined using a Geological Society of America rock color chart. Grain shape was determined by handlens observations. Bed geometry was determined using the inclinometer on a Brunton compass. Bed thickness was measured using a combination of a 50 m reel tape, and a 1.7 m Jacob staff and hand level. The extensive lateral exposure of the Mouth of Mad unit affords a unique opportunity to study lateral facies transitions. For this reason a series of overlapping photographs was taken from the western bank of the river, approximately 15 m from the outcrop. These photographs were then enlarged and a panel diagram constructed by tracing facies boundaries (Plate 1).

10 Figure 3. Composite stratigraphic column for the sediments exposed at the Mouth of Mad river, showing the Mouth of Mad unit and portions of overlying marine terrace and underlying unit. Also shown is variation of Bay facies between northern (N) and southern (S) areas of the exposure. Lower unit contact used as datum because it provides a stable reference level for measurement. Column is incomplete because thickness of overlying and underlying units could not be measured completely (UTFM=Upper Tidal Flat Mud, LTFM= Lower Tidal Flat Mud). 1 1 12

Laboratory

The samples collected for grain-size analysis were processed in the following manner. First the samples were split to obtain smaller representative samples weighing approximately 100 g. These samples were then dried for approximately 12 hours and weighed again. After weighing, the samples were placed in a Ro-tap sieving device and the dry sieved for fifteen minutes on nested screens. Following the Udden-Wentworth grain-size classification, screens of 4, 3, 2, 1, 0, -1, and -2 phi size were used. The resulting fractions were then weighed and weight-percents for each size class were calculated (Appendix A).

The results of the laboratory analysis are displayed graphically in Figure 3 using standard Udden-Wentworth size categories: very fine (3 to 4 fine (2 to 3 medium

(1 to 2 coarse (0 to 1 ,very coarse (-1 to 0 granule (-2 to -1 and pebble (-

6 to -2 Some categories are grouped together for better display in Figure 3. Some graphs are averages of two or more samples. The raw data are contained in Appendix

A. Summary descriptions are recorded in Table 1. 13

Table 1. Summary descriptions of fades within the Mouth of Mad unit (Fig. 3). Average FACIES Thickness Subfacies Description (m) OVERLYING UNIT Sand, fine to medium, subangular to subrounded; gravel interbeds; no fossils present; moderate yellow brown (10 R 4/6); unconformable contact with underlying Bay facies,extends to top of bluff —5.0

BAY Upper Tidal Flat Mud Clay, silty; thin horizontal laminations; seagrass fragments concentrated on bedding planes; olive gray (5 Y 4/1), upper 2 m weathered to reddish brown (10 R 4/6); unconformable contact with terrace deposits above, grades abruptly to Bay Mud below; found in northern area of exposure 0.9 Bay Mud Clay, silty, some sand near upper contact; shelly throughout; bioturbated; abundant fossils, primarily Ostrea lurida and Balanus sp.; olive gray (5 Y 4/1); grades downward to mixed Sand and Mud in the northern area of the exposure, or abruptly to Lower Tidal Flat Mud in southern area 1.7-1.1 Lower Tidal Flat Mud Clay, silty; thin parallel horizontal laminations; seagrass fragments concentrated on bedding planes; olive gray (5 Y 4/1); abrupt contact with Bioturbated Sand Below; found in southern area of exposure 0.4 Mixed Sand and Mud Sand, clayey, silty clay in burrows with increased mixing of sand and clay upward; bioturbated; fossils common, primarily Ostrea lurida and Protothaca staminea; light brown (5 Y 4/4-5/6); grades gradually downward to Strand-Plain Sand; found in northern area of exposure 1.8 Bioturbated Sand Sand, fine to medium; subangular to subrounded, well-sorted, bioturbated; fossils common, primarily Balanus sp. and Protothaca staminea; moderate yellow brown (10 YR 5/4); grades gradually downward to Strand-Plain Sand; found in southern area of exposure 0 6 STRAND-PLAIN SAND Sand, fine to medium, subangular to subrounded, single-grain-thick pebble beds near lower contact; parallel horizontal laminations, abundant burrows in upper 1 - 2 m; rare Tresus sp. preserved in the largest burrows; moderate yellow brown (10 YR 5/4); lower contact defined as first gravel laterally continuous over 10's-of-m's 2.5 14

Table 1. (continued) Average FACIES Thickness Subfacies Description (m) NEARSHORE SAND AND GRAVEL Sand, gravel interbeds; sand fme, subangular to subrounded, well-sorted, occasional pebbles in sand layers near contact with gravel interbeds; trough cross-beds in lower portion of facies, changing to parallel horizontal laminations near upper contact; occasional vertical burrows 10-15 mm in diameter; no fossils; moderate yellow brown (10 YR 5/4) changes to light olive gray (5 Y 5/2) near lower contact; gravel in fme to coarse sand matrix includes imbricated mud clasts, rounded to subrounded, poorly- to very poorly-sorted; trough cross-beds; gravel occurs in lenses and tabular beds, irregular lower boundaries; up to 0.64 m thick; moderate yellow brown (10 YR 5/4); lower contact is defined as lowest gravel bed laterally continuous over 10's of m's 5.7

NEARSHORE SAND Sand, fme, subangular to subrounded, well-sorted, single-grain-thick pebble beds near upper and lower contacts; trough cross-beds and hummocky cross-stratification present throughout; occasional vertical burrows 10-15 mm in diameter in upper and lower third; rare Olivella biplicata and Dendraster sp. in lower third, shell lens containing Macoma nasuta, Nassarius mendicus, and fish vertebrae occur in lower third; light olive gray (5 Y 5/2); abrupt lower contact with Estuarine Mud, gravel bed occurs at lower contact with paleosol 20.9

ESTUARINE MUD Silt, gravelly; gravel rounded to subrounded, poorly sorted; Tresus sp. in living position, molar from Mammut americana found at lower contact; discontinuity surface of unconformable contact with paleosol below marked by burrow underprints 0.4

UNDERLYING UNIT Sand, fme, subangular to subrounded, well sorted; some places muddy sand;gravel interbeds; paleosol at top; light olive gray (5 Y 5/2); in situ tree stumps and roots; possible burrow underprints in upper surface; lower contact not visible 10+ PALEONTOLOGY Methods Field Twenty-five bulk samples were collected from the fossiliferous deposits for analysis. Samples were collected from all points along the exposure, wherever access was possible. Ten samples were taken from the Bay Mud subfacies, eight from the Bioturbated Sand subfacies, and seven from the Mixed Sand and Mud subfacies (Fig. 3). Laboratory One-litre bulk samples, measured by water displacement, were soaked in a 10% sodium hexametaphosphate solution for 24-48 hours, and then washed on a 2 mm screen. After drying, the fossils were identified using the literature on eastern Pacific invertebrates (Abbott, 1974; Griffith, 1975; Smith and Carlton, 1975; Morris et al., 1980; Abbott and Dance, 1982; Kozloff, 1987), and counted. For broken mollusk specimens, an apical fragment had to be present to count as one gastropod, a beak fragment to count as 1/2 bivalve. In order to estimate the number of Balanus sp., the total number of disarticulated side plates was divided by six. These adjusted counts provide a conservative estimate of original species abundance. Estimation of original abundance of individuals gives a more realistic sense of original community composition than a simple count of fragments, because the number of fragements per individual varies with species (Stanton and Dodd, 1990). The taphonomic characteristics of the fossils were evaluated by examination of individual shells. Shells that exhibited wear or discoloration were considered to have been transported from adjacent environments within the bay (Driscoll, 1967; Driscoll and Weltin, 1973; Parsons and Brett, 1991).

15 16

Summaries of the fossil inventories are given for each of the three fossiliferous subfacies that were examined (Tables 2, 3, and 4). Complete inventories for the fossil samples are contained in Appendix B. Discussion of the environmental implications of the fauna can be found in latter portions of this thesis. Examination of microfossils was beyond the scope of this study. 17

Table 2. Fossils from the Bioturbated Sand subfacies

Average no. individuals/ Type/ litre Standard Substrate Taxa samplel deviation /Depth3 (n=7) 2 Autochtonous Balanus sp.4 57.1 122.0 Ci/H/ML Protothaca staminea (Conrad, 1837) 17.1 12.1 Bi/S/ML Tresus sp. 7.1 8.2 Bi/sM/ML Saxidomus giganteus (Deshayes, 1839) 2.8 3.2 Bi/SsM/LS Brachiura indet. 1.1 1.7 Cr/-/- Odostomia sp. 0.7 1.5 Ga/H/L Littorina scutulata Gould, 1849 0.3 0.8 Ga/H/HM Nassarius mendicus (Gould, 1849) 0.1 0.4 Ga/MS/L Turbonilla sp. 0.1 0.4 Ga/-/-

Transported Ostrea lurida Carpenter, 1864 34.2 - - Mytilus edulis Linne, 1758 6.6 - - Macoma nasuta (Conrad, 1837) 2.7 - - ?Cylichnella sp. 0.3 - - Mopalia sp. 0.3 - - Zoosteraceae indet. common5 - - 1 Refer to methods for count criteria. 2 Standard deviations are given to show variability of number of individuals between samples. 3 Type organism: Substrate: Prefered Depth: Bi - bivalve M - Mud H - High Intertidal Ga - gastropod S - Sand M - Middle Intertidal Pp - polyplachophoran sM - Sandy Mud L - Low Intertidal Ci - Cirriped H - Hard S - Subtidal P1- Plant Cr - Crustacean 4 Some specimens may have washed in from adjacent Bay Mud subfacies. 5 Where counts of individuals were not possible, owing to fragmentation, the general categories common, uncommon, and rare are used. 18

Table 3. Fossils from the Mixed Sand and Mud subfacies

Average no. individuals/ Type/ litre Standard Substrate Taxa samplel deviation /Depth3 (n=8) 2 Autochtonous Ostrea lurida Carpenter, 1864 91.9 47.6 Bi/H/L Protothaca staminea (Conrad, 1837) 41.6 10.0 Bi/S/ML Balanus sp.4 7.5 6.9 Ci/H/ML Tresus sp. 4.3 8.8 Bi/sM/ML Saxidomus giganteus (Deshayes, 1839) 3.4 1.7 Bi/SsM/LS Macoma nasuta (Conrad, 1837) 2.4 1.1 Bi/SM/LS Littorina scutulata Gould, 1849 1.8 1.7 Ga/H/HM Clinocardium nuttallii (Conrad, 1837) 1.7 2.1 Bi/MsM/LS Brachiura indet. 1.1 1.4 Cr/-/- Mytilus edulis Linne, 1758 0.9 1.7 Bi/H/LS Mitrella gausapata Gould, 1850 0.1 0.4 Ga/M/LS Zoosteraceae indet. commons - -

Transported Bittium eschrichtii (Middendorf, 1849) 44.5 - - Odostomia sp. 1.9 - - Diodora aspera (Rathke in 1.0 - - Eschscholtz, 1833) Mopalia sp. 0.4 - - Hinnites giganteus (Gray, 1825) 0.3 - - Ayes indet. (bones) 0.1 - - Echinoidea indet. (spines) 0.1 - - Subscripts and abbreviations explained in foot of Table 2. 19

Table 4. Fossils from the Bay Mud subfacies

Average no. Type/ individual Standard Substrate Taxa s/ deviation /Depth3 litre 2 samplel (n=10) Autochtonous Ostrea lurida Carpenter, 1864 136.4 49.4 Bi/H/L Balanus sp.4 41.2 41.8 Ci/H/ML Protothaca staminea (Conrad, 1837) 25.9 21.5 Bi/S/ML Bittium eschrichtii (Middendorf, 1849) 4.2 5.6 Ga/S/L Cryptomya californica (Conrad, 1837) 2.4 7.6 Bi/M/MLS Odostomia sp. 2.4 2.1 Ga/H/L Tresus sp. 2.1 4.0 Bi/sM/ML Macoma nasuta (Conrad, 1837) 1.8 1.4 Bi/SM/LS Mytilus edulis Linne, 1758 1.1 1.8 Bi/H/LS Brachiura indet. 1.0 1.2 Cr/-/- Clinocardium nuttallii (Conrad, 1837) 0.8 1.0 Bi/MsM/LS Littorina scutulata Gould, 1849 0.6 0.5 Ga/H/HM Nassarius mendicus (Gould, 1849) 0.4 0.5 Ga/MS/L Mitrella gausapata Gould, 1850 0.2 0.4 Ga/M/LS Alvania sp. 0.1 0.3 Ga/H/LS ?Cylichnella sp. 0.1 0.3 Ga/M/H Mysella tumida (Carpenter, 1864) 0.1 0.2 Bi/SM/LS Zoosteraceae indet. common5 - Pl/M/MLS

Transported Saxidomus giganteus (Deshayes, 1839) 4.0 - - Mopalia sp. 3.7 - - Diodora aspera (Rathke in Eschscholtz, 0.2 - - 1833) Hinnites giganteus (Gray, 1825) 0.2 - - Crepidula sp. 0.1 - - Turbonilla sp. 0.1 - - Subscripts and abbreviations explained in foot of Table 2. STRATIGRAPHY General The term facies has been used for several different purposes since it was first introduced (see review in Hallam, 1981). For this reason the International Stratigraphic Guide (Hedberg, 1976, p. 15) states "The general term 'facies' has been greatly overworked...If the term is used it is desirable to make clear the specific kind of facies to which reference is made". The facies in this study are defined based on sedimentologic and paleontologic features, and are named based on their inferred environment of deposition and predominant sediment type. The Mouth of Mad unit contains five facies, representing a sequence of nearshore marine and shallow bay environments (Fig. 3). The unit is bounded by unconformities; it is underlain by a paleosol marking the top of the underlying unit, and overlain by younger late Pleistocene terrace deposits (Fig. 3).

The majority of the unit consists of unconsolidated sand and gravel, but some mud is found near the top and bottom of the unit. Underlying Unit The unit underlying the Mouth of Mad unit consists of well-sorted, subangular to subrounded, light olive gray (5 Y 5/2) fine sand, with gravel interbeds. In some places it is a muddy sand. A paleosol is developed at the top of the unit, although only the C- horizon remains. At the contact with the Estuarine Mud facies, this paleosol contains in situ tree stumps and roots (Fig. 4).

The contact between the Mouth of Mad unit and the underlying paleosol is very irregular. Depressions in the discontinuity surface may represent the underprints of clam burrows, although they have been alternatively interpreted as terrestrial vertebrate tracks

20 21

Figure 4. In situ tree roots in paleosol below lower unconformity. Hand lens in photograph is 32 mm long. 22

(G. A. Carver, personal communication,1991). These probable underprints are gravel-filled oval depressions up to 10 cm long and 4 cm deep. Overlying Unit

Overlying the Mouth of Mad unit are marine terrace deposits. These deposits consist mostly of subangular to subrounded, moderately- to well-sorted, moderate yellow brown (10 R 4/6) fine to medium sands. Gravel interbeds are found throughout, including a basal gravel bed. A soil is developed in the unit at the top of the exposure.

Terrace deposits in the study area have been studied by Carver et al. (1987) and by

Carver and Burke (1992).

Mouth of Mad unit

Estuarine Mud

The Estuarine Mud facies consists of poorly-sorted, olive gray (5 Y 4/1) gravelly sandy mud, with the gravel component being typically well rounded. Tresus sp. are found within the facies in living position (Fig. 5). A single molar of the mastodon,

Mammut americana, was found just above the contact between the Estuarine Mud and the paleosol (G. A. Carver, personal communication, 1993). Striations on one side of the tooth seem to indicate transport by fluvial processes. Deposits of this facies crop out only on the river beach and were not observed in the bluff exposure (Plate 1).

Nearshore Sand

Overlying the Estuarine Mud and the paleosol is a well-sorted, subangular to subrounded, light olive gray (5 Y 5/2) fine sand. Scattered pebbles and pebble stringers

(single-grain-thick discontinuous gravel layers) occur near the upper and lower contacts.

Some mud rip-up clasts occur in the lower third of the facies. Trough cross- stratification sets, approximate ly 20 cm thick, are poorly visible throughout the exposure 23

Figure 5. Tresus sp. in living position in the Estuarine Mud facies, just above lower unconfomity. 24

Figure 6. Trough cross-beds in the Nearshore Sand facies. Pebble stringer marks lower boundary of one set. Approximately 10 m above top of Estuarine Mud facies. 25 of this facies. Hummocky cross-stratification can also been seen throughout. The bottoms of some of the cross-bed sets are marked by pebble stringers (Fig. 6).

Occasional vertical burrows, 10-15 mm in diameter, are also present.

A fossil sample taken from the sand near the lower contact contains the gastropod Olivella biplicata (Sowerby, 1825) and fragments of the sand dollar

Dendraster sp.

Abrasion of the gastropod shells, fragmentation of the sand dollars, and the typical occurence of these organisms in modern shallow-water environments suggests that the specimens were transported prior to deposition (Driscoll, 1967; Driscoll and Weltin,

1973; Staff and Powell, 1990; Parsons and Brett, 1991). A lens of gravely sand 5-10 m above the lower contact of the facies contained abundant fossils, including Macoma nasuta (Conrad, 1837), Nassarius mendicus (Gould, 1849), and fish vertebrae (Fig. 7).

Nearshore Sand and Gravel

The Nearshore Sand facies grades upward into an interbedded sand-and-gravel facies. Scattered pebbles occur near the top of the Nearshore Sand and increase in frequency upward until small gravel stringers are found. The contact between the two facies is defined here as the lowest gravel bed laterally continuous for 10's-of-meters.

The sand is well-sorted, subangular to subrounded, fine- to medium-grained sand. The color changes from light olive gray (5 Y 5/2) near the lower contact to moderate yellow brown (10 YR 5/4) near the upper contact. Scattered pebbles occur throughout the sand. Trough cross-beds are prevalent near the lower contact, changing to plane-parallel laminations near the upper contact. Occasional vertical burrows 10-15 mm in diameter occur throughout and are often truncated by superjacent gravel beds.

Gravel layers consist of a poorly to very poorly sorted, subangular to subrounded, moderate yellow brown (10 YR 5/4) gravel and sand mixture. Pebbles 26

Figure 7. Fossiliferous sand lens in the Nearshore Sand facies conaining the clam Macoma nasuta and the gastropod Nassarius mendicus. Approximately 6 m above top of Estuarine Mud facies. 27

average approximately 15 mm in diameter, but reach a maximum diameter of 9 cm.

Gravels occur in lenses (Fig. 8) and tabular beds (Fig. 9). Normal grading and trough cross-beds are present in most of these gravel beds. Some of the gravels contain imbricated eliptical mud clasts approximately 6-10 cm in length. Gravel beds increase in thickness to a maximum of 63.5 cm in the middle of the facies, but decrease to single- pebble thickness at the upper and lower contacts. The highly irregular boundaries of the superposed gravel beds indicate scour-and-fill processes (Fig. 10).

Strand-Plain Sand

Above the highest laterally continuous gravel bed is a well-sorted, subangular to subrounded, moderate yellow brown (10 YR 5/4), fine to medium sand (Fig. 3). The sand occurs as plane-parallel laminations 1 - 4 mm thick. Pebble stringers occur near the lower contact. Burrows occur near the upper contact with the Bay facies, and increase in abundance upward resulting in a gradational contact. The most prominent of these burrows are 8-10 cm wide and extend up to 1 m below the contact with the overlying bay deposits. One such burrow contained a specimen of Tresus sp. in living position.

Other burrows tend to be narrower, 4 - 6 cm, and much shallower, up to approximately

20 cm.

Bay facies

The Bay facies has been divided into five subfacies (Fig. 3) based on sedimentologic and faunal properties. The vertical sequence of these subfacies changes laterally (Plate 1). 28

Figure 8. Gravel lenses in the Nearshore Sand and Gravel facies (A). Marine terrace deposits are also visible (B). Upper surface is top of bluff. Lenses are approximately 3 m above top of Nearshore Sand facies. 29

Figure 9. Tabular gravel beds in the Nearshore Sand and Gravel facies. Also visible is the Strand-Plain Sand facies. Lowest bed is approximately 2 m above top of Nearshore Sand facies. 30

Figure 10. Lower boundary of gravel bed in Nearshore Sand and Gravel facies indicating scour-and-fill processes. The bedding in the underlying sand is truncated. Large pebbles above the boundary suggest reworking by a later storm event. Approximately 3 m above lower contact of unit. 31

Bioturbated Sand

Near the southern end of the exposure the lowest division within the Bay facies is a heavily bioturbated sand (Fig. 3 and Plate 1). The sand is a well-sorted, subangular to subrounded, moderate yellow brown (10 YR 5/4), fine to medium sand. Bioturbation has apparently eliminated all original physical sedimentary structures. An increasing abundance of burrows, as described for the Strand-Plain Sand facies, marks the contact with the subjacent Strand-Plain Sand facies. The fauna of this highly fossiliferous deposit was dominated numerically by the bivalves Protothaca staminea (Conrad,

1837), Tresus sp., and Saxidomus giganteus (Deshayes, 1839) and by the cirriped

Balanus sp. (Table 2). Occurring with these taxa were the transported fragments and whole shells of the bivalves Ostrea lurida (Carpenter, 1864), Mytilus edulis Linnè,

1758, and Macoma nasuta (Conrad, 1837), and small amounts of transported eel grass

(Table 2). Transportation is indicated by abrasion of the shells, fragmentation of the sanddollars, and the typical occurence of these forms in different environments(Driscoll,

1967; Driscoll and Weltin, 1973; Ricketts et al., 1985; Staff and Powell, 1990; Parsons and Brett, 1991).

Lower Tidal Flat Mud

Where it occurs, the bioturbated sand is always overlain by an olive gray (5 Y

4/1), finely laminated mud (Fig. 3). Contact between these two subfacies is abrupt but conformable (Fig. 11). This mud contains no shells, but has abundant fragments of eel grass along bedding planes. Oval ironoxide stains found along some bedding plains could be the result of dissolution of shell material.

Mixed Sand and Mud

Where the Lower Tidal Flat Mud and Bioturbated Sand are absent, a poorly sorted, subangular to subrounded, light brown (5 YR 4/4-5/6) clay-rich sand deposit 32

Figure 11. Abrupt contact between the Bioturbated Sand and Lower Tidal Flat Mud subfacies. 33 occurs (Fig. 3). Bioturbation has thoroughly mixed what was likely a backshore sand with the overlying bay mud (Fig. 12). Dominantly muddy sediment occurs in burrows near the lower contact, but toward the upper contact there is a mixture of mud with sand. This deposit contained abundant fossils, including: the bivalves Ostrea lurida, Protothaca staminea, Tresus sp., and Saxidomus giganteus; the gastropods Littorina scutulata Gould, 1849 and Mitrella gausapata Gould, 1850; the cirriped Balanus sp.; crab dactlys; and plant fragments (Table 3). Also found were the transported gastropods Bittium eschrichtii (Middendorf, 1849), Odostomia sp., and Diodora aspera (Ratlike in Eschscholtz, 1833) (Table 3). Bay Mud Overlying both the Mixed Sand and Mud, and the Lower Tidal Flat Mud, is an olive gray (5 Y 4/1) mud, which is slightly sandy near the contact with the overlying

Upper Tidal Flat Mud (Fig. 3). Bioturbation coupled with abundant fossils has produced a hash of shells and mud with no obvious structure. The dominant fossil, numerically, is Ostrea lurida. Also present are the bivalves Protothaca staminea, Cryptomya californica (Conrad, 1837), Tresus sp., Macoma nasuta, and Mytilus edulis; the gastropods Bittium eschrichtii, Odostomia sp. and Littorina scutulata; the cirriped Balanus sp.; crab dactyls; and plant fragments (Table 4). The transported component includes the bivalve Saxidomus giganteus, the polyplacophoran Mopalia sp., and the gastropod Diodora aspera (Table 4). The clam Tresus sp. is found in situ near the upper contact where the sand content increases (Fig. 13). 34

Figure 12. Mixed Sand and Mud subfacies, showing mixture of sandy and muddy sediments. Fossils include Tresus sp. and Ostrea lurida. 35

Figure 13. Tresus sp. in living position near the upper contact of the Bay Mud subfacies with the Upper Tidal Flat Mud subfacies. Smaller fossils in the surrounding matrix include Ostrea lurida and Balanus sp. 36

Upper Tidal Flat Mud

At the top of the Mouth of Mad unit, underlying the younger late Pleistocene terrace deposits, is another olive gray (5 Y 4/1), finely laminated mud (Figs. 3 and 14).

This mud is thicker than the Lower Tidal Flat Mud. The upper 20 cm is deeply weathered and features a moderate reddish brown color (10 R 4/6). This mud also contains abundant eel grass fragments and oval iron stains. 37

Figure 14. Upper Tidal Flat Mud subfacies showing contact with subjacent Bay Mud subfacies. Contact is just below handlens. DISCUSSION Depositional Environments The depositional settings for each facies and subfacies were determined by comparing sedimentologic features and faunal content to published descriptions of both modern and ancient nearshore deposits (Clifton et al., 1971; Clifton and Phillips, 1980; Hunter and Clifton, 1982; Clifton, 1983; Leithold and Bourgeois, 1984; Duke, 1985; Clifton, 1988). By ordering the facies in stratigraphic succession, a detailed depositional history can be constructed. Estuarine Mud Heavily bioturbated gravelly mud deposits similar to the Estuarine Mud facies deposits have been observed in modern estuaries (Elliott, 1975; Clifton and Phillips, 1980; Frey and Howard, 1980; Clifton, 1983). In modern estuarine settings, such as Williopa Bay, Washington, these deposits are found in the accretionary banks of tidal channels. A gravel lag is overlain by muddy bank sediments and later bioturbation mixes these sediment types (Clifton and Phillips, 1980). Clams of the genus Tresus, the only fossil found in the Estuarine Mud subfacies, can be found today in river estuaries along the coast of California (J. D. DeMartini, personal communication, 1992). They occupy the banks of tidal channels in gravelly or sandy mud (J. D. DeMartini, personal communication, 1992). The stratigraphic position of the Estuarine Mud further argues for a marginal marine setting. The Estuarine mud lies between undoubtedly terrestrial deposits, including in situ tree roots and the remnant of a paleosol, and shallow marine deposits of the lower Nearshore Sand facies. This positioning supports a transitional environment

38 39 such as a tidal coastal estuary. Only a small portion of these estuary deposits remains, the rest having been eroded away.

Nearshore Sand

The trough cross-bedding, hummocky cross-stratification, and texture of the

Nearshore Sand facies are very similar to properties of nearshore sediments in modern and ancient high-energy nearshore environments (Clifton et al., 1971; Kumar and

Sanders, 1976; Clifton, 1981; Leithold and Bourgeois, 1984). Additionally, the vertical succession of fades is typical of other ancient high-energy nearshore deposits (Clifton et al., 1971; Leithold and Bourgeois, 1984). The deposits of this facies correspond to the lunate megaripple and outer planar structural facies defined by Clifton et al. (1971).

This is a zone of wave build up and the outer regions of the surf zone.

The presence of hummocky cross-stratification within the Nearshore Sand is indicative of storm-related deposition (Hunter and Clifton, 1982; Duke, 1985; Morton,

1988). Clifton (1988) used the presence of hummocky cross-stratification to suggest a depth of deposition for such sediments well above maximum storm wave base, and just below fairweather wave base. Clifton (1988) also noted extensive interbeddings of firmer grained material in sediments deposited near maximum storm wave base. These finner grained sediments are present only as rip-up clasts and small lenses in the

Nearshore Sand subfacies indicating depths of deposition likely well above maximum storm wave base (Clifton, 1988). Modern maximum storm wave base off coastal

Humboldt County is approximately 50-60 m, and fairweather wave base approximately

15-20 m (J. C. Borgeld, personal communication, 1993). Assuming conditions were similar at the time of deposition, this suggests that the maximum depth of deposition represented in the Mouth of Mad unit is approximately 20-50 m, and owing to the lack of fine grained sediments is likely to be less than 50 m. This maximum is represented 40

within the first 5 m of the facies above the lower contact with the Estuarine Mud or the

underlying unit.

The increased gravel content near the upper boundary of the Nearshore Sand facies indicates an increase in the energy regime. The sediments with pebble stringers just below the upper contact with the Nearshore Sand and Gravel facies were deposited in the outer region of the surf zone (Clifton et al., 1971).

Nearshore Sand and Gravel

The boundary between the Nearshore Sand and the Nearshore Sand and Gravel facies was defined by the first laterally continuous gravel bed, representing a slight change of depositional environment. The Nearshore Sand and Gravel facies represents a gradual transition toward higher energy and shallower water environments. The characteristics of this facies are similar to Miocene coarse-grained sediments in southwestern Oregon studied by Leithold and Bourgeois (1984). They (Leithold and

Bourgeois, 1984) interpreted these sediments to represent a river influenced, high- energy nearshore environment.

The gravel beds contain well-rounded large clasts suggesting deposition near a fluvial source. The fluvial source of these gravels raises the question of their place of origin. The proximity of the deposits to the Mad River and the origin of the Mad River drainage prior to deposition of the Mouth of Mad unit (R. M. Burke, personal communication, 1993) suggests the possibility that the ancestral Mad River was the source of the gravel. Gravel deposits of fluvial origin, as evidenced by well-rounded clasts, a single dominant direction of orientation of grains measured in the field, and normal grading, are found approximately 4 km to the south at the western end of School

Road in river bank exposures (Figs. 1 and 2)(K. R. Aalto, personal communication,

1993). While these deposits cannot be directly correlated to the Mouth of Mad unit, 41

they underlie the same terrace and are thus older than 70 ka (Berger et al., 1991; Carver

and Burke, 1992). Examination of the lithology of the gravel, notably chert and

metasedimentary rocks, in the Mouth of Mad unit reveals an exclusively Franciscan

Complex origin. Of the three nearest modem rivers of sufficient size to carry sediment

this coarse -- the Mad, Eel and Klamath Rivers -- only the Eel and the Mad erode

Franciscan Complex bedrock. However, the Eel also erodes other lithologies, and

sediments deposited by it would typically contain these other lithologies. Finally, the

drainage basin of the Mad River can be dated, using uplift rates at the headwaters, as

being older than 500 ka (R. M. Burke, personal communication, 1993). These factors

taken together suggest an ancestral Mad River as the origin of the gravels in the Mouth

of Mad unit.

After deposition on the inner continental shelf by a flooding river, the gravel was

then reworked by marine storm events. The two types of bedding geometries of the

gravels in the Nearshore Sand and Gravel facies indicate different modes of

accumulation. The lenticular beds could represent coarse sediments transported by rip

currents during storms (Leithold and Bourgeois, 1984). The thick laterally continuous gravel beds indicate deposition by an agent acting uniformly over a broad area. The size

of the clasts suggests very high energy. The gravel was probably first introduced to the

nearshore by a flooding river. Temporary accumulations of gravel were then reworked

laterally by storm waves. The channeled lower surfaces of the beds indicate scour by storm generated waves and currents, followed by deposition of graded sandy-gravel beds as storm energy decreased. The cross-bedding, grading, and irregular lower boundaries of the gravel beds are typical of proximal tempestites (Kumar and Sanders,

1976; Dupre et al., 1980; Clifton, 1981; Leithold and Burgeois, 1984). 42

As the water depth decreased into the surf zone, due to sedimeent accumulation, eustatic selevel change, and tectonic uplift, the gravel accumulated in thicker beds as wave energy neared its peak. The thickest beds near the middle of the facies are probably amalgamated storm deposits that to represent several superimposed events. As the water became shallower and wave energy decreased, the gravel beds became thinner and sand was deposited with little to no gravel by normal day to day wave action.

The sand beds within the facies were deposited during relatively quiet intervals between large storms, perhaps seasonally. The much finer grain size within these beds indicates lower energy (Clifton, 1981; Hunter and Clifton, 1982). Near the upper contact with the Strand-Plain Sand facies these deposits probably represent the landward edge of the surf zone, as evidenced by thin plane parallel laminations (Clifton, 1969). As the influence of storm activity decreased, because of falling relative sea level, swash zone processes dominated resulting in deposition of the Strand-Plain Sand facies.

Strand-Plain Sand

The thin plane-parallel laminations, graded bedding, and fine sand of the

Strand-Plain Sand facies are indicative of a beach swash zone (Clifton, 1969; Clifton et al., 1971). the vertical change of facies from nearshore to swash and then to shallow bay environments indicates a change from an open to a protected coast setting. The protection from wave energy can be accomplished by formation of an offshore bar or sand spit. The stand-Plain Sand facies sediments then represent open coast deposition prior to the formation of the bar or spit. An alternative would be the migration or progradation of a sand spit. in this case the Strand-Plain Sand sediments represent a beach along the seaward margin of th spit prior to migration or progradation. Each of these situations allows for the colonization of the former beach by quiet-water fauna. 43

BioturbatedBay Sand

The three dominant bivalve species in the Bioturbated Sand (Protothaca staminea, Tresus sp., and Saxidomus Giganteus) prefer a protected sandy-bottom environment (Ricketts et al., 1985). Protection from surf would have been provided by development or migration of a sandy spit similar to those found today along northern coastal California between rocky headlands. The presence of the clam Protothaca staminea indicates a reduction of wave influence, as it cannot live in shifting sand because its weak foot makes it a poor burrower (Ricketts et al., 1985, p. 281).

The extensively burrowed and irregular lower contact of the Bioturbated Sand with the Strand-Plain Sand facies, along with the quiet water fauna, suggests that, following migration or progradation of a spit, the sand was colonized by organisms that typically inhabit protected sandy bottoms. The resulting bioturbation eliminated any sedimentary structure that might have been previously present.

Lower Tidal Flat Mud

The thin laminations and fine sediment size of the Lower Tidal Flat Mud subfacies indicate a very low energy environment such as a tidal flat (Elliott, 1978;

Clifton and Phillips, 1980). The presence of eel grass, probably belonging to the family

Zoosteraceae, is also suggestive of tidal flat conditions (Smith and Carlton, 1975).

Clifton and Phillips (1980), in a survey of Willapa Bay, Washington, found grasses of the same family growing on the intertidal flats. These flats accumulate algal growths that create anoxic conditions and inhibit endobenthic organisms from colonizing them

(Clifton and Phillips, 1980). 44

The Lower Tidal Flat Mud sediments lack evidence of abundant animal life. No body fossils are found, and the thin laminations are undisturbed by bioturbation suggesting the absence of large organisms. Additionally, the chemistry of the pore water within the sediments of the tidal flat would have produced pH and Eh conditions unsuitable for preservation of shell material (Frey and Howard, 1986). Oval ironoxide stains along bedding planes suggest possible dissolution of shells. All of this taken together indicates a depositional environment similar to the intertidal flats described by

Clifton and Phillips (1988) for the Lower Tidal Flat Mud subfacies.

Mixed Sand and Mud

The fauna of the Mixed Sand and Mud subfacies contains elements characteristic of both the Bioturbated Sand and the Bay Mud subfacies. The gradual change in sediment and the change in burrow fill proceeding upward within the facies indicate a change of depositional environment. The character of the Mixed Sand and

Mud/Strand-Plain Sand contact is similar to that of the Bioturbated Sand/Strand-Plain

Sand contact suggesting a transition of environments like that described for the

Bioturbated Sand subfacies. Colonization of the protected sand was followed by further shallowing and a change to a muddy bottom bay environment, resulting in mixing of the sediments and faunas by subsequent bioturbation.

Bay Mud

The organisms found in the Bay Mud subfacies are indicative of a shallow bay environment, such as Humboldt Bay (Ricketts, 1985; DeMartini, personal communication, 1992). Ostrea lurida occurred in clumps on the bay bottom, thus forming an oyster garden (see community reconstruction in Miller and Morrison, 1988). 45

Balanus sp. would have taken advantage of any hard substrate, in this case exploiting the shells of oysters and other living bivalves or their exposed dead skeletons. The activity of burrowing organisms apparently destroyed any layering that may have been present and produced an homogenous mixture of shell fragments and sediment. The greater sand content near the upper contact is probably the result of washover into the bay during large storms (Schwartz, 1982). A sandy mud substrate will favor the development of the Tresus populations seen in the upper portions of the facies, as it is better able to burrow in sandy mud than pure sand or mud (Ricketts et al., 1985, p. 377; J. D. DeMartini, personal communication, 1992). Upper Tidal Flat Mud The Upper Tidal Flat Mud subfacies is nearly identical to the Lower Tidal Flat Mud subfacies, the only difference being the thickness of the unit. This similarity indicates a similar depositional environment. In a modern bay (Elliott, 1975; Clifton and Phillips, 1980; Clifton, 1983), tidal flats can be found on both the spit and the landward side of the bay. The vertical succession of facies within the Mouth of Mad unit indicates a consistant drop in relative sea level, and accompaning progradation of environments, from the lower portion of the Nearshore Sand Facies uppward. Following this trend, and using Walther's Law, it is resonable to suggest that the Upper Tidal Flat Mud subfacies represents the landward tidal flat of the Bay. Summary The vertical succession of the five subfacies of the Bay facies approximates a lateral transect accross the bay. The Bioturbated Sand and the Mixed Sand and Mud subfacies both represent a transition from the strand-plain of a beach or sand spit to protected marine conditions. This sandy substrate was then exploited by a quiet-water fauna. In the southern area of the outcrop this sandy bottom was replaced by a tidal flat, 46 with the possible algal accumulations inhibiting further animal activity (Clifton and

Phillips, 1980) and preverting the mixing of sediment types seen in the north within the mixed Sand and Mud subfacies. In the northern area of the outcrop the vertical transition was directly to a muddy bottomed bay environment and later bioturbation thouroghly mixed the two sediment types. The tidal flat in the south was also later replaced by muddy bottom bay deposits. The bay deposits were then overlain by another tidal flat, this time on the landward side of the bay. The deposits of this tidal flat are not seen in the northern area of the outcrop and were probably eroded away by later wave action associated with marine terrace formation. Depositional Sequence

The environmental interpretations for the sediments in the Mouth of Mad unit can be used to reconstruct the sequence of environmental change that occurred at the

Mouth of Mad locality during the deposition of the Mouth of Mad unit. These changes were induced by the rise and fall of relative sea level. Figure 15 shows the relationship of the different environments at the time of deposition of the Bay facies.

Prior to deposition of the first deposits in the Mouth of Mad unit the area of the

Mouth of Mad locality was subaerially exposed. This exposure lasted long enough for a soil to form and for trees to develop to maturity. At this time the relative sea level rose, resulting in an erosional transgression. During this transgression a estuary developed at the Mouth of Mad locality. Deposits of this estuary are preserved in the Estuarine Mud facies complete with Tresus clams in life position. Erosion of the estuary deposits and the abrupt transition to marine deposits produced a ravinment surface (Demarest and

Kraft, 1987) at the contact between the Estuarine Mud facies and the Nearshore Sand facies. 47

Figure 15. Paleogeographic reconstruction of depositional environments at the mouth of Mad River locality at the time of deposition of the Bay facies. Size of the bay and location of the inlet are idealized. 48

As relative sea level continued to rise the Estuarine Mud was covered by nearshore marine deposits of the Nearshore Sand facies. At approximately 5 m above the lower contact of this facies, maximum inundation occurred. At this time the depth was between 20 and 50 m, although it was likely to have been much less than 50 m.

Following maximum inundation the relative sea level began to fall. The depth of

deposition represented at the site continually shallowed from this time onward. As

depths began to approach wave base the increased hydraulic energy transported coarser sediment, resulting in the pebbles and pebble stringers found in the upper portions of the

Nearshore Sand facies deposits. Eventually, the water depth was shallow enough, and

thus the energy great enough, that storms could lay down a sheet of gravel producing the laterally continuous gravel bed that marks the contact between the Nearshore Sand facies and the Nearshore Sand and Gravel facies.

As relative sea level continued to fall the energy acting on the bottom increased,

both during storms and during fair weather wave activity. At this time the influence of the ancestral mad river on clast size is felt. When the river flooded, it brought large well rounded clasts into the nearshore marine environment. These clasts were later entrained by waves associated with large storms and reworked. The storms scoured the bottom during their peak. Then as the storm waned the energy decreased and the entrained sediment was deposited in graded sandy gravel beds. These beds take two forms: laterally continuous and lenticular. The lenticular deposits are the result of seaward movement of sediment in rip channels. The thick laterally continuous beds are the result of storm deposition along the entire coast. Near the center of the Nearshore Sand and

Gravel facies deposits the thickest gravel beds consist of several superposed storm beds.

The deposits of one storm were reworked by the following, storm and thick sequences 49 of gravel were produced. The sandy interbeds are the result of more normal fair weather wave action and deposition. During deposition of thick gravel beds the storm energy acting on the bottom reached its peak. After this peak, as relative sea level continued to fall, the energy also decreased and the amount of gravel that was deposited diminished, resulting in thinner beds again toward the upper contact of the Nearshore Sand and

Gravel facies. Eventually the energy decreased to the point were deposition of laterally continuous gravel beds was no longer possible. At the same time, the fair weather intervals were less influenced by waves, and swash zone conditions dominated . This marks the transition from Nearshore Sand and Gravel facies deposition to Strand-Plain

Sand facies deposition.

At the time of Strand-Plain Sand facies deposition the environment at the Mouth of Mad locality was that of a beach. This beach was probably located on the seaward side of a sandy spit. As sea level dropped further and paralic depositional environments shifted seaward, beach sand was protected by the spit and colonized by a quiet-water fauna. Deposits other than beach sand that may have accumulated locally, such as dune sands higher on the beach, were either eroded away or their structure was eliminated by subsequent bioturbation.

The action of this quiet-water fauna thoroughly bioturbated the sand eliminating any structure that may have been present. In the southern area of the site this sandy bottom community was replaced by a tidal flat fauna and conditions unsuitable for further endobenthic organism activity. In the north, however, the transition was directly to a muddy bottom bay, and the two sediment types were mixed by bioturbation to form the Mixed Sand and Mud facies. In the northern area, the resulting bay deposits continue to the upper unconformity of the Mouth of Mad unit. In the south, the Bay

Mud subfacies deposits were replaced by a second, landward tidal flat identical in 50 character to the seaward tidal flat below. Any deposits above this were removed by later erosion during the formation of the overlying marine terrace. Age of Pleistocene Deposits

Data used for previous age assignments of the Pleistocene deposits were analyzed and their accuracy was assessed (Manning and Ogle, 1950; Durham and

MacNeil, 1967; Kilmer, 1972; Kohl, 1974; Wehmiller et al., 1977; Kennedy, 1978; Roth,

1978; Carver, 1987; Miller and Morrison, 1988; Berger et al., 1991; Carver and Burke

1992). These data included stratigraphic ranges for various fossil species, amino acid racemization ratios for Saxidomus clams, a thermoluminecence age estimate, and magnetic polarity of sediments. Additional unpublished data and Uranium-series coral dates were also considered (Szabo, letter to William Miller, 1986). The combination of these data was then used to establish tentative age estimates (Fig. 16).

Elk Head

Fossiliferous sand deposits at Elk Head, 1.3 km north of Trinidad (Fig. 1), overly an abrasion platform cut into rocks of the Franciscan Complex. The deposit is 2 - 3 m thick and exposed between paleotopographic highs in the Franciscan Complex. The presence of large numbers of hard substrate species, along with many endobenthic bivalves and gastropods, indicates a sublittoral rocky environment protruding above an area of sandy seafloor (Kennedy, 1978, p. 250-265). The surface of the underlying abrasion platform contains numerous pholadid clam borings assignable to the ichnogenus

Gastrochaenolites. A hard substrate crevice fauna, consisting primarily of barnacles and bryozoans occurring within a shell fragment matrix, is also found within cracks in the

Franciscan rocks (E. M. Weppner, personal communication, 1993). The borings and crevice fauna preceeded the deposition of the fossiliferous sand. 51

Figure 16. Correlation chart of pre-terrace Pleistocene units and marine terrace deposits in northern coastal Humboldt County, California. Age estimates for lightly stipled units are very tentative. Isotope stages are based on Chappel and Shackelton(1986). (Age data mostly from: Wehmiller et al., 1977; Wehmiller, Lajoie et al., 1977; Kennedy, 1978; Carver, 1987; Carver and Burke, 1992). 52

The overlying terrace has been dated at approximately 64 ka (Fig. 16) (Carver and Burke, 1992). Kennedy (1978, p. 250-265) tentatively placed the Elk Head deposits in oxygen isotope stage 11 (middle Pleistocene). Kennedy (1978) based this age estimate on a single amino acid racemization ratio and the presence of two possibly extinct species, Calliostoma sp. aff. C. ligatum and Scutellaster sp., which were thought to occur in the middle to lower Pleistocene of northern California. However, the uncertainty in identification of these possibly new species makes their usefulness as age indicators problematic. This means the age determinaiton was based on a single amino acid date, creating uncertainty in the age of these deposits.

Trinidad Head

A fossiliferous sand deposit is found between Trinidad Head and Little Head approximately 1.5 km south of Elk Head (Fig. 1). The deposit is 5 - 6 m thick and extends for approximately 50 m along the beach in a seacliff. The fossil evidence suggests a sandy substrate with abundant shell fragments in an intertidal to subtidal environment, with input of hard-substrate fauna, including Mytilus californianus Conrad

1837, Hinnites sp., Nucella sp., and balanid barnacles. The skeletal material was derived from the adjacent sea stacks consisting of Franciscan rocks (Kennedy, 1978, p.

243-249).

The overlying terrace has been dated at approximately 64 ka (Fig. 16) (Carver and Burke, 1992). Wehmiller et al. (1977) reported an amino acid date of 500±

75 ka for this deposit. Kennedy (1978, p. 246) used this information to assign the deposits to oxygen isotope stage 15 (middle Pleistocene) (Fig. 16). 53

Moonstone Beach

The deposits at Moonstone Beach, approximately 4.6 km south of Trinidad Head

(Fig. 1), consist of cross-bedded sands, bioclastic sands, and a basal fossiliferous boulder bed overlying Franciscan Complex rocks. The uppermost shell bed is moderately well cemented. The broken, graded and oriented shell material, cross-beds, and channeling of the deposit suggest a current-deposited shell accumulation (Kennedy, 1978, p. 228-242;

E. M. Weppner, personal communication, 1993). The presence of hard substrate organisms and the proximity of the deposits to a relict sea stack consisting of Fransican rocks suggest that most of the fossils were derived from the submerged sides of the adjacent sea stack (E. M. Weppener, personal communication, 1993).

As at the previously mentioned fossil localities, the overlying terrace has been dated at approximately 64 ka (Fig. 16) (Carver and Burke, 1992). Kennedy (1978, p.

235) and Wehmiller et al. (1978) reported amino acid ratios from the uppermost shell bed that indicate an age for the Moonstone deposits of 700±100 ka. Kennedy (1978, p.

235) reported that sediments he regarded as fluvial in origin overlying the Moonstone deposits are paleomagnetically reversed. This places the deposits below the

Burnhes-Matuyama boundary (approximately 600-700 ka). Repenning (1976) identified a mammoth scaphoid from Moonstone and considered it to be no older than Irvingtonian

(1.5 Ma or middle Pleistocene). Durham and MacNeal (1967) determined the deposits to be middle Pleistocene in age based on the presence of three species, Strogylocentrotus droebachiensis, S. pupuratus, and S. fransiscanus. Szabo (letter to William

Miller,1986) reported a Uranium-series date for the coral Balanophilla elgans as 350-

1000 ka. Roth (1978, p. 168) cited an undescribed species of Scutellaster, and propsed an age range for the deposits between 1.25 and 1.5 Ma based on the age range of the 54 sand dollar and the mammoth. The age range for the genus Scutellaster is now in question because specimens have been found in deposits younger than 1.25 Ma (E. M.

Weppner, personal communication, 1992). The combination of evidence suggests a possible age for the Moonstone Beach deposits of —700-800 ka (Fig. 16).

Crannell Junction

The fossiliferous sand deposits at Crannell Junction (Fig. 1) were divided into an upper and lower unit by Kohl (1974). The deposits are no longer well exposed. The fossils within the lower unit were thought to represent a sandy, offshore, subtidal environment (Kohl, 1974; Kenndey, 1978, p. 204-227). Based on the presence of many species from shallow subtidal depths and rocky coasts, Kohl (1974) proposed a partially protected bay having a rocky headland to the north as the probable depositional setting for the lower unit. This proposal was supported by Kennedy (1978, p. 206).

Citing the abundance of articulated shallow water bivalves in the upper unit,

Kohl suggested (1974, p. 218) "... a shallow semi-protected bay replaced the more exposed bay environment of the lower unit...". He further suggested that a bar slowly developed seaward of the bay and was responsible for this change of environment.

The marine terrace overlying the deposits at Crannell Junction has been dated at approximately 130 ka (Fig. 16)(Carver and Burke, 1992). Both Kilmer (1972) and Kohl

(1974), based on the presence of the sea lion Eumetopias jubata, suggested that the

Crannell Junction deposits are Rancholabrean (late Pleistocene) in age. Kennedy (1978) using a combination of Kohl's (1974) data, the presence of several extinct species not found at other sites, amino acid age estimates, and paleomagnetic data, tentatively assigned a middle Pleistocene age (approximately stage 13) to the Crannell Junction deposits. Considering the available data, Kennedy's (1978) age assignment is the more reasonable (Fig. 16). 55

Falor Formation The Falor Formation, in the vicinity of Maple Creek (Fig. 1), is an alternating sequence of nearshore marine and terrestrial sediments (Manning and Ogle, 1950; Carver, 1987). The Falor Formation is exposed in the upper Mad River drainage and adjoining areas (Fig. 1) and is approximately 900 m thick. The faunal evidence suggests a shallow sublittoral to intertidal environment for the marine sands within the Falor (Manning and Ogle, 1950). Sarna-Wojcicki et al. (1987) chemically correlated a volcanic ash layer 100 m above the base of the Falor Formation with an ash dated at 1.8 - 2.0 Ma. Using this date, and net sedimentation rates, Carver (1987) estimated the age of the uppermost deposits of the Falor as roughly 800-900 ka (Fig. 16). Owing to faulting and unconformities within the Falor, the age estimate for the top of the Falor is tentative (G. A. Carver, personal communication, 1993). Mouth of Mad unit Berger et al. (1991) obtained a single thermoluminesence date for the Upper Tidal Flat Mud of the Mouth of Mad unit of 176 ± 33 ka. This age estimate is consistent with the position of the unit below a soil , dated by soil correlation, at 83 ka (Carver and Burke, 1992). Carver (personal communication, 1993), suggests that the unit underlying the Mouth of Mad unit contains sediments deposited during oxygen isotope stage 8 (Fig. 16). He bases this age estimate on the consitent preservation of successive isotope stage deposits observed in coastal Humboldt County, California. There is not as yet any firm data to support this age assignment. It is also possible that the underlying unit may be part of the Falor Formation, as it was mapped by Carver (1987) (Fig. 16). 56

All of the fossil taxa present in the Mouth of mad unit appear to be extant, whereas older deposits in the area, such as the Wildcat Group and the Falor Formation, or even the deposits at Elk Head and Crannell Junction, contain extinct species. Miller and Morrison (1988) used this fact to propose a late Pleistocene age for the unit. Some of the bivalve specimens collected still retained their periostracum, hinge ligaments, and color patterns. This is not the case in the older deposits. These factors taken together strongly suggest a late Pleistocene (post-Wildcat or post-Falor) age for the Mouth of

Mad unit (Fig. 16).

In order to achieve better age control for the Mouth of Mad unit further research is required. Closer analysis of other fossils from the Bay and Nearshore Sand facies may provide more age constraints. Identification of the foraminiferids in the Bay facies would be particularly useful for determining the age of the unit. Additionally, more refined identification of vertebrate and plant fossils, if possible, could provide useful data. Amino acid recemization studies of clams, both from the Bay and Estuarine facies would also provide a firmer estimage of the age of the Mouth of Mad unit. An age estimate of the underlying unit based on any of the above methods would also help by limited the maximum age of the unit. Correlation

One of the purposes of this study was to attempt to correlate the Mouth of Mad unit with other Pleistocene deposits in northern coastal Humboldt County. The proposed relationship between the various units is shown in Figure 16.

The stratigraphic position of the Mouth of Mad unit, relative to the other deposits in the same area, can be established using several pieces of fossil evidence. The entire fauna of the Mouth of Mad unit is extant. All other fossil bearing deposits contain species of extinct organisms, even the relatively young Elk Head and Crannell Junction 57

deposits (Kennedy, 1978; Roth, 1978; Kohl, 1974). This indicates that the Mouth of

Mad unit is younger than the other fossiliferous deposits in the same area (Fig. 16).

The stratigraphic position of the Mouth of Mad unit relative to marine terrace

deposits is easily established (Fig. 16). The Mouth of Mad unit lies directly beneath the

83 ka terrace and is thus older by superposition (Fig. 16). The timing of formation of

the terraces, relative to the sea level curve, has been carefully worked out by Carver et

al. (1986) and by Carver and Burke (1992). Terrace deposits equivalant in age to the

Mouth of Mad unit have not be identified in the McKinnleyville area (Carver et al.,

1986, Carver and Burke, 1992).

Woodward Clyde Consultants (1980) drilled boreholes approximately 1.2 km

due west of the Arcata Airport (Fig. 2). Data reported from these boreholes were

analyzed to determine if the Mouth of Mad unit could be identified. Shelly sandy

sediments were, in fact, reported from the boreholes (Woodward Clyde Consultants,

1980, Fig. B-22). The strata were considered equivalent to the Crannell Junction

deposits (Woodward Clyde Consultants, 1980). However, the lack of detailed lithologic

descriptions and no mention of specific taxa, only "seashells", make it impossible to

determine if the shelly sandy strata are equivalent to the Mouth of Mad unit, Crannell

Junction deposits, or another unit.

More refined age estimates are necessary before the Pleistocene stratigraphy of

the are can be fully understood and better correlations made. One way of achieving this is to reevaluate the fossil faunas from some of the less studied units, mainly Elk Head,

Trinidad Head, and the Falor Formation. Amino acid racemization studies hold some promise, but the database is as yet too small for effective age estimation and correlation to be possible. CONCLUSIONS

Depositional environments represented by facies within the Mouth of Mad unit were reconstructed using sedimentologic and paleontologic evidence. The lowest facies are a nearshore marine sand and an estuarine mud that lie unconformably on a paleosol.

The estuarine mud and the lower portions of the sand were deposited during a transgression that eroded away the upper layers of the paleosol. A more gradual regression, following a maximum depth of approximately 20-50 m, produced a thick storm-influenced sand deposit. As depth further decreased and energy acting on the bottom increased, the environment gradually changed to produce an interbeded sand and gravel facies containing storm and rip-channel deposits. Further decrease of depth and decrease in energy resulted in transition to a strand-plain sand facies.

This sand was then covered by a laterally variable sequence of shell-rich bay sediments. The bay sediments are further divided into five subfacies. In the northern part of the outcrop these include: 1) a bioturbated backshore sand; 2) an oyster-rich bay mud; and 3) overlying tidal flat mud. In the southern part these include: 1) a mixed sand and mud; overlain by 2) a lower tidal flat mud; and 3) the same bay mud sediments as in the north. These regressive deposits are the result of coastline progradation, resulting from sediment accumulation, tectonic uplift and falling eustatic sea level.

Using data from earlier studies, including presence or absence of extinct species, a thermoluminesence date, amino acid racemization ratios, and paleomagnetic data, an attempt was made to correlate Pleistocene exposures in northern coastal Humboldt

County. Correlation between the Mouth of Mad unit and other sequences in the region was difficult owing to extensive folding and faulting, and a lack of continuous exposures. Sediments at the top of the Mouth of Mad unit have been dated, by

58 59 thermoluminesence, at 176 ± 33 ka, placing them in the late Pleistocene. The Mouth of

Mad unit appears to be younger than fossiliferous deposits at Elk Head, Crannell

Junction, Trinidad Head, and at Moonstone Beach, and is definitely younger than the

Falor Formation near Maple Creek. The Mouth of Mad unit is possibly time equivalent with gravel deposits at the western end of School Road in McKinleyville. Comparison to the eustatic sea level curve suggests that the Mouth of Mad unit was deposited during a shallowing stage of isotope stages 7 and 6.

The environmental and age interpretations of this study will help in the understanding of the chronology of tectonic processes and eustatic sea-level changes by providing further information on timing of sea-level changes and rates of tectonic uplift.

This information can be used to support earlier, and future, work done with marine terraces and the evidence they provide of uplift rates and timing. To date studies of tectonics in coastal Humboldt County have focused on marine terraces, the Mouth of

Mad unit provides the possibility of using older deposits exposed along the coast to confirm the results of these studies.

Studies of coarse clastic sediments in high-energy nearshore environments are few. The facies analysis in this study contribute to the further understanding of the character and evolution of high-energy wave dominated coasts by providing another example of such an environment in the stratigraphic record. Data from this and other studies can be used to construct a general facies model for nearshore high-energy environments. APPENDIX A: Sediment Sample Data

This appendix contains the results from the sieving of eithtenn sediment samples obtained fromthe non-fossiliferous facies of the Mouth of Mad unit. Samples are numbered in the order of collection. Each sample number is followed by the date on which it was processed.

Facies are designated as follows:

B - Nearshore Sand facies C - Nearshore Sand and Gravel facies D - Strand-Plain Sand facies

Sample 1 10/24/92 Dry Weight: 98.47 g Facies: B Location: -1 m above lower contact Size (Phi) Weight (g) Weight % Cumm. Wt. % >-2 0.00 0.00 0.00 -1 0.00 0.00 0.00 0 0.00 0.00 0.00 1 0.04 0.04 0.04 2 0.75 0.76 0.80 3 56.67 57.55 58.35 4 34.73 35.27 93.62 <4 6.28 6.38 100.00

Sample 2 10/24/92 Dry Weight: 98.92 g Facies: B Location: -7 m above lower contact Size (Phi) Weight (g) Weight % Cumm. Wt. % >-2 0.00 0.00 0.00 -1 0.00 0.00 0.00 0 0.00 0.00 0.00 1 0.03 0.03 0.03 2 1.08 1.09 1.12 3 58.51 59.51 60.27 4 33.06 33.42 93.69 <4 6.28 6.31 100.00

60 61

Sample 3 10/24/92 Dry Weight: 99.90 g Facies: B Location: -10 m above lower contact Size (Phi) Weight (g) Weight % Cumm. Wt. % >-2 0.00 0.00 0.00 -1 0.00 0.00 0.00 0 0.02 0.02 0.02 1 0.61 0.61 0.63 2 2.18 2.18 2.81 3 57.73 57.79 60.60 4 33.41 33.44 94.04 <4 5.95 5.96 100.00

Sample 4 10/25/92 Dry Weight: 98.80 g Facies: B Location: -13 m above lower contact Size (Phi) Weight (g) Weight % Cumm. Wt. % >-2 0.00 0.00 0.00 -1 0.14 0.14 0.14 0 0.00 0.00 0.14 1 0.02 0.02 0.16 2 0.17 0.17 0.33 3 84.59 85.62 85.95 4 12.99 13.15 99.10 <4 0.89 0.90 100.00

Sample 5 10/25/92 Dry Weight: 99.55 g Facies: B Location: -0.5 m below upper contact Size (Phi) Weight (g) Weight % Cumm. Wt. % >-2 0.00 0.00 0.00 -1 0.00 0.00 0.00 0 0.01 0.01 0.01 1 0.03 0.03 0.04 2 0.13 0.13 0.17 3 88.98 89.38 89.55 4 9.96 10.01 99.66 <4 0.44 0.44 100.00 62

Sample 6 10/25/92 Dry Weight: 99.00 g Facies: C Location: Just above lower contact Size (Phi) Weight (g) Weight % Cumm. WL % >-2 0.00 0.00 0.00 -1 0.18 0.18 0.18 0 0.04 0.04 0.22 1 1.20 1.21 1.43 2 15.52 15.68 17.11 3 78.00 78.79 95.90 4 2.90 2.93 98.83 <4 1.16 1.17 100.00

Sample 7 10/25/92 Dry Weight: 99.36 g Facies: C Location: -5 m above lower contact Size (Phi) Weight (g) Weight % Cumm. Wt. % >-2 0.00 0.00 0.00 -1 0.04 0.04 0.04 0 0.00 0.00 0.04 1 0.02 0.02 0.06 2 0.34 0.34 0.40 3 90.82 91.41 91.81 4 7.51 7.56 99.37 <4 0.63 0.63 100.00

Sample 8 10/24/92 Dry Weight: 100.18 g Facies: C Location: Below thickest gravel Size (Phi) Weight (g) Weight % Cumm. Wt. % >-2 0.35 0.35 0.35 -1 0.38 0.38 0.73 0 0.78 0.78 1.51 1 3.68 3.67 5.18 2 4.62 4.61 9.79 3 86.74 86.58 96.37 4 2.70 2.70 99.07 <4 0.93 0.93 100.00 63

Sample 9 10/26/92 Dry Weight: 97.63 g Facies: C Location: Above thickest gravel Size (Phi) Weight (g) Weight % Cumm. Wt. % >-2 0.00 0.00 0.00 -1 0.07 0.07 0.07 0 0.02 0.02 0.09 1 0.94 0.96 1.05 2 18.96 19.42 20.47 3 75.15 76.97 97.44 4 1.81 1.86 99.30 <4 0.68 0.70 100.00

Sample 10 10/26/92 Dry Weight: 102.30 g Facies: C Location: Near upper contact Size (Phi) Weight (g) Weight % Cumm. Wt. % >-2 0.35 0.34 0.34 -1 0.73 0.71 1.05 0 1.23 1.20 2.25 1 3.49 3.41 5.66 2 8.58 8.39 14.05 3 85.02 83.11 97.16 4 2.18 2.14 99.30 <4 0.72 0.70 100.00

Sample 11 10/26/92 Dry Weight: 98.92 g Facies: D Location: Near lower contact Size (Phi) Weight (g) Weight % Cumm. Wt. % >-2 0.00 0.00 0.00 -1 0.00 0.00 0.00 0 0.00 0.00 0.00 1 0.68 0.69 0.69 2 14.50 14.66 15.35 3 80.66 81.54 96.89 4 2.13 2.15 99.04 <4 0.95 0.96 100.00 64

Sample 12 10/26/92 Dry Weight: 98.52 g Facies: D Location: Near upper contact Size (Phi) Weight (g) Weight % Cumm. Wt. % >-2 0.00 0.00 0.00 -1 0.08 0.08 0.08 0 0.14 0.14 0.22 1 10.21 10.36 10.58 2 34.41 34.93 45.51 3 51.99 52.77 98.28 4 1.04 1.03 99.31 <4 0.68 0.69 100.00

Sample 13 10/26/92 Dry Weight: 100.51 g Facies: D Location: - Middle of facies Size (Phi) Weight (g) Weight % Cumm. Wt. % >-2 0.00 0.00 0.00 -1 0.00 0.00 0.00 0 0.02 0.02 0.02 1 0.24 0.24 0.26 2 8.31 8.27 8.53 3 89.99 89.53 98.06 4 1.30 1.29 99.35 <4 0.65 0.65 100.00

Sample 14 10/27/92 Dry Weight: 98.21 g Facies: D Location: - Middle of facies Size (Phi) Weight (g) Weight % Cumm. Wt. % >-2 0.69 0.70 0.70 -1 0.55 0.56 1.27 0 1.14 1.16 2.43 1 14.63 14.89 17.32 2 17.49 17.81 35.13 3 60.08 61.18 96.31 4 2.11 2.14 98.45 <4 1.52 1.55 100.00 65

Sample 15 10/27/92 Dry Weight: 99.09 g Facies: D Location: - Middle of facies Size (Phi) Weight (g) Weight % Cumm. Wt. % >-2 0.00 0.00 0.00 -1 0.00 0.00 0.00 0 0.04 0.04 0.04 1 2.82 2.85 2.89 2 34.85 35.17 38.06 3 59.54 60.09 98.15 4 1.00 1.00 99.15 <4 0.84 0.85 100.00

Sample 16 10/27/92 Dry Weight: 112.25 g Facies: C Location: Lowest gravel Size (Phi) Weight (g) Weight % Cumm. Wt. % >-2 56.63 50.45 50.45 -1 25.98 23.14 73.59 0 2.99 2.66 76.25 1 1.27 1.13 77.38 2 0.24 0.21 77.59 3 22.14 19.72 97.31 4 2.57 2.29 99.60 <4 0.45 0.40 100.00

Sample 17 10/27/92 Dry Weight: 114.31 g Facies: C Location: Thickest gravel Size (Phi) Weight (g) Weight % Cumm. Wt % >-2 34.42 30.11 30.11 -1 34.15 29.88 59.99 0 17.12 14.98 74.97 1 10.09 8.83 83.80 2 5.07 4.44 88.24 3 12.09 10.58 98.82 4 0.72 0.63 99.45 <4 0.63 0.55 100.00 66

Sample 18 10/27/92 Dry Weight: 115.30 g Facies: C Location: Upper gravel Size (Phi) Weight (g) Weight % Cumm. Wt. % >-2 37.51 32.53 32.53 -1 9.07 7.87 40.40 0 8.97 7.78 48.27 1 19.73 17.11 65.38 2 13.04 11.31 76.69 3 25.44 22.06 98.75 4 0.92 0.80 99.55 <4 0.52 0.45 100.00 APPENDIX B: Fossil Sample Data

This appendix contains the results from the sorting, identification, and counting of 25 fossil samples. The samples are divided into three tables based on the subfacies from which they were collected. Numbers indicate counts of individuals fo each taxa for each sample. For broken mollusc specimens, the apex had to be present to count as one gastropod and the beack to count as 0.5 bivalves. In order to estimate the total number of individual Balanus the total number of side plates was divided by six. Where counts of individuals were not possible presence is indicated by an X. The Autochthonous or transported character of the taxa is based on weathering and abrassion of individual specimens.

67 68

Fossils form the Bioturbated Sand subfacies Sample # Taxa 8 9 10 20 22 23 24 Autochthonous Balanus sp. 73 - 356.7 Protothaca staminea 9.5 17 16 41 5 8.5 23 Tresus sp. 8 13 0.5 2.5 3 22.5 Saxidomus gigantea 6 8 1 3.5 1 Clinocardium nuttalii 0.5 4.5 1.5 - Odostomia sp. 4 1 Littorina scutalata 2 Nassarius mendicus 1 Turbonilla sp. - 1 Brachiura indet. 3 4 - 1 Transpoted Ostrea lurida 33.5 0.5 - 205.5 - Mytilus edulis 2.5 0.5 41.5 1 0.5 1 Macoma nasuta 1 6.5 3.5 3.0 1 4 Cylichnella sp. 1 1 - Mopalia sp. 2 Zoosteraceae X X X X X X Fossils from the Bay Mud subfacies Sample # Taxa 1 2 3 5 6 14 15 16 17 Autochthonous Ostrea lurida 185 110 179.5 110 63.5 39 156 162 155 Balanus sp. 142.8 59.2 57.8 0.7 1 12.8 23.3 29.5 29.7 Protothaca stamines 28 11.5 61 6.5 1 4 43.5 48.5 42 Bittium eshcrichtii - 1 4 10 2 - 1 7 17 Cryptomya sp. 24 ------Odostomia sp. 1 3 5 - 5 3 - 2 - Tresus. 2 11 ------Macoma nasuta 2 2.5 3.5 1.5 1.5 - 0.5 - 2 Mytilus edulis - - 0.5 1 1 - 0.5 6 2 Brachiura indet. 3 - 3 - - 1 - - 2 Clinocardium nuttallii 1 2.5 1 - - - - - 0.5 Littorina scutulata 1 1 1 - - - 1 1 - Nassarius mendicus 1 1 1 ------Mitrella gausapata - - - - 1 - - - 1 Alvania sp. 1 ------Cylichnella sp. ------1 Mysella tumida ------0.5 Zoosteraceae X X - - - - X - X Transported Saxidomus gigantea 11 4.5 4.5 - - - 2.5 4 3.5 Mopalia sp. 12 3 3 6 7 - - - - Diodora aspera - - - - 2 - - - - Hinnites giganteus - - - 0.5 - - 0.5 0.5 - Crepidula sp. - - - 1 - - - - - Turbonilla sp. ------69

70

Fossils from the Mixed Sand and Mud subfacies Sample # Taxa 4 7 12 13 19 25 26 27 Autochthonous Ostrea lurida 125.5 1 155.5 63.5 103.5 68 97 121.5 Protothaca staminea 37.5 22 34.5 44.5 37 41.5 51.5 44.5 Balanus sp. 6.3 0.6 19.7 4.3 5.8 4.2 4.8 17.8 Tresus sp. 26 2 2 0.5 1.5 1 1 SazSaxidomisgantea 5 4.5 4.5 2.5 2 2 5.5 1 Macoma nasuta 0.5 2.5 3.5 2.5 2.5 1.5 4 2 Littorina scutulata 3 1 5 2 1 2 Clinocardium nuttallii 0.5 1 1 6.5 2.5 0.5 1.5 Mytilus edulis 0.5 5 0.5 1 Brachiura indet. 4 1 2 1 1 Mitrella gausapata 1 Zoosteraceae X X X X X X Transported Bittium eshchrichtii 68 29 54 55 39 41 70 Odostomia sp. 2 3 1 5 3 1 Diodora aspera 1 1 1 2 2 1 Mopalia sp. 2 Hinnites giganteus 0.5 0.5 0.5 0.5 Ayes Echinoidea 1 REFRENCES CITED

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