Rice University
SEDIMENTARY FACIES AND TRACE FOSSILS IN THE EOCENE DELMAR FORMATION AND TORREY SANDSTONE, CALIFORNIA
by
Jannette Elaine Boyer
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF
Master of Arts
Thesis Director's Signature:
Houston, Texas ABSTRACT
SEDIMENTARY FACIES AND TRACE FOSSILS IN THE
EOCENE DELM&R FORMATION AND TORREY SANDSTONE, CALIFORNIA
Jannette Elaine Boyer
The Delmar Formation and Torrey Sandstone were studied in sea- cliff outcrops at Solana Beach, about 15 km north of San Diego.
There, they represent lagoonal and barrier bar or shoal deposits, respectively.
Five subfacies were recognized in these outcrops, utilizing observations on sediments, physical sedimentary structures, body fossils and trace fossils. The Delmar exhibits three subfacies that formed as oyster reefs, tidal flats, and sublittoral tidal channels and ponds. The Torrey contains two subfacies, representing suba¬ queous dunes and tidal channels on a tidal delta or interior side of a barrier bar or s.hoal, and large, temporary channels generated by drainage of the lagoon after periods of high run-off or storms.
Trace fossils contribute significantly to the description and interpretation of these subfacies. Their density and diversity indi¬ cate brackish to marine conditions. The abundant lebensspuren
Ophiomorpha nodosa and Gyrolithes indicate deposition in littoral to inner sublittoral zones; Gyrolithes is especially common in brackish environments of the Delmar lagoon. Sandy, high-energy facies of the Torrey Sandstone are characterized by large, vertically- oriented dwelling burrows and by vertical locomotion traces generated by infauna migrating up and down in response to sedimentation and erosion. Muddy, more protected environments of the Delmar Formation exhibit lese robust, horizontally-oriented dwelling burrows and an abundance of feeding burrows constructed by animals mining the or¬ ganic-rich sediment for food. Sedimentation and physical reworking were very active in Torrey environments, so trace fossils there dis¬ tort but do not obliterate physical sedimentary structures and bedding characteristics. In contrast, much of the Delmar has been heavily bioturbated, indicating predominance of biological reworking over physical processes. 1
ACKNOWLEDGEMENTS
Dr. John E. Warme suggested the project, supervised the research, made available his collection of books, journals and reprints, and offered valuable comments and criticisms on the text. His generous, unwavering support as mentor and friend are deeply appreciated.
A grant to Dr. Warme by the Henry L. and Grace Doherty Charitable
Foundation financed this research.
Dr. Michael P. Kennedy of the California Division of Mines and
Geology furnished copies of his geologic quadtangle maps of the San
Diego area, imparted freely of his experience and knowledge, and introduced me to other workers in the field. Among them, Dr. C. R.
Givens was especially helpful; Dr. Givens made available much un¬ published information about the molluscan assemblage in the Delmar
Formation.
Dr. William C. Elsik of Esso Production Research studied pollen in several samples from my field area. Dr. Elsik furnished lists of identified pollen and spores and provided valuable paleoclimatlc information; I appreciate his help and his wonderful enthusiasm.
I am especially grateful to Dr. J. Philip Kern (California
State University, San Diego) and Claudia Kern, who cheerfully provided housing for one field season and helped me with the field work.
I appreciate very much the advice and comments of Drs. J. L.
Wilson (Rice), Cortez Hoskins (Union Oil Research), and R. J. Moiola
(Mobil Oil Research). Drs. R. E. Casey and John J. W. Rogers of
Rice University served with Dr. Warme as my thesis committee; both read the manuscript critically. il
Mr. Michael L. Johnson of Rice kindly ran an oxygen isotope survey on an Ostrea valve. I enjoyed and benefited from discussions with several other past and present graduate students at Rice. Ms. Mary
Hodge typed part of the manuscript when I thought there wasn't a typist left in Houston; Dr. Pat Rudd finished it in the wee hours of the morn.
I also want to thank my family for welcoming without comment my all-too-short, usually working vacations at home and at the farm, and for their unwavering emotional and financial support. lii
TABLE OF CONTENTS
Page
INTRODUCTION
SIGNIFICANCE OF FACIES STUDIES UTILIZING TRACE FOSSILS 1 SCOPE AND AIM OF THIS STUDY 2
PREVIOUS WORK 5 -
GEOLOGIC SETTING 8
SAN DIEGO AREA 8 LOCAL SETTING, DELMAR FORMATION AND TORREY SANDSTONE 12 SELECTION OF OUTCROPS 14
DESCRIPTION OF THE DELMAR FORMATION 17
STRATIGRAPHY AND GENERAL DESCRIPTION 17 PALEONTOLOGY 19 Microfossils 19 Macrofossils 23 SEDIMENTS 28 Composition 28 Texture 28 Depositional processes affecting texture 29 PHYSICAL SEDIMENTARY STRUCTURES 33 Interbedded sand and mud 33 Depositional processes affecting interbedded sand/mud 33 Micrograded beds 40 Thicker mud beds 40 Laminated sand 40 Cross-stratification 43 Sedimented shell beds 44 Bored claystone beds 45 BIOGENIC SEDIMENTARY STRUCTURES 47
DESCRIPTION OF THE TORREY SANDSTONE 52
STRATIGRAPHY AND CENERAL DESCRIPTION 52 PALEONTOLOGY 54 Microfossils 54 Macrofossils 54 SEDIMENTS 55 Composition 55 Texture 56 iv
PHYSICAL SEDIMENTARY STRUCTURES 58 Trough cross-bedded sandstone 58 Large channels 60 Wedge-sets of cross-bedded sandstone 61 Interbedded sandstone and mudstone 61 BIOGENIC SEDIMENTARY STRUCTURES 63
DESCRIPTION AND INTERPRETATION OF SUBFACIES 66
GENERAL SETTING 66 SUBFACIES 67- Subfacies A: Oyster beds 68 Subfacies B: Flaser-bedded sequences 71 Subfacles C: Fining-upward sequences 73 Subfacies D: Large-scale trough cross-bedded sandstone 75 Subfacies E: Large channels 77
SIGNIFICANCE AND USEFULNESS OF TRACE FOSSILS IN THIS STUDY 81
CONCLUSIONS 85
REFERENCES CITED 87
APPENDIX I. TRACE FOSSILS 98
METHOD OF STUDY 98 DESCRIPTIONS OF TRACE FOSSILS 100 Domichnia 102 Ophlomorpha Lundgren and Thalassinoidea Ehrenberg 102 Gyrolithes Saporta 107 Fat, mud-lined burrows 114 Vertical burrows with sprelten 115 Borings in claystone 116 Fodinichnla 119 Ardella Chamberlain and Baer 119 Phycodes Richter 122 Small horizontal and vertical burrows 130 Dendritic burrows 130 Replchnla 133 Conostlchus 134 Vertical movement paths 139 Palaeophycus Hall 142 Cublchnla 145 Surface depress ions 145 Other trace fossils 148 Collapse structures 148 V
APPENDIX II. GRAIN-SIZE ANALYSIS OF SEDIMENTS 153
TABLE OF CHARACTERISTICS OF SAMPLES FROM THE DELMAR FORMATION 154 TABLE OF CHARACTERISTICS OF SAMPLES FROM THE TORREY SANDSTONE 155 CUMULATIVE CURVES, SAMPLES FROM THE DELMAR FORMATION 156 CUMULATIVE CURVES, SAMPLES FROM THE TORREY SANDSTONE 157
APPENDIX III. CARBON AND OXYGEN ISOTOPE ANALYSIS 159
PLATES 160
ILLUSTRATIONS
Figure Page
1 INDEX MAP, SAN DIEGO COASTAL AREA 3
2 GEOLOGIC COLUMN, SAN DIEGO COASTAL AREA 9
3 SCHEMATIC COLUMN AND FACIES DIAGRAM, DEL MAR QUADRANGLE 10
4 GEOLOGIC MAP, DEL MAR QUADRANGLE 13
5 LOCATIONS OF MEASURED SECTIONS 16
6 MEASURED SECTIONS (in pocket)
7 COMPOSITE STRATIGRAPHIC SECTION, DEIMAR FORMATION 18
8 PALYNOMORPHS 21
9 FLORA REPRESENTED BY PALYNOMORPHS 22
10 AGE OF FLORA 22
11 MOLLUSCS IN THE DEIMAR FORMATION 26-27
12 HISTOGRAMS OF SAND FRACTIONS 30
13 FLASER BEDDING AND RIPPLE CROSS-LAMINATION 36 vl
14 OCCURRENCES OF FUSER, WAVY, AND LENTICUUR BEDDING 38-39
15 MICROGRADED BEDS 41
16 LAMINATED SAND 42
17 TERMS EXPRESSING REUTIVE DENSITY OF BIOGENIC STRUCTURES 48
18 COMPOSITE STRATIGRAPHIC SECTION, TORREY SANDSTONE 53
19 URGE-SCALE TROUGH CROSS BEDDING 59
20 WEDGE-SETS OF CROSS BEDDED SANDSTONE 62
21 SUBFACIES A: OYSTER BEDS 69
22 SUB FACIES B: FUSER-BEDDED SEQUENCES 72
23 SUBFACIES C: FINING-UPWARD SEQUENCES 74
24 SUB FACIES D: URGE-SCALE TROUGH CROSS-BEDDED SANDSTONE 76
25 SUB FACIES E: URGE CHANNELS 78
26 CHARACTERISTICS OF SUBFACIES 80
27 DISTRIBUTION OF ETHOLOGICAL CUSSES OF TRACE FOSSILS 83
28 OPHIOMORPHA NODOSA GRADING INTO THAUSSINOIDES 103
29 OPHIOMPRPHA NODOSA (URGE FORM) 104
30 WALL STRUCTURE OF OPHIOMORPHA NODOSA 105
31 DIMENSIONS AND MORPHOLOGIC TERMINOLOGY OF GYROLITHES 109
32 GYROLITHES 111
33 GYROLITHES 112
34 GYROLITHES 113
35 VERTICAL BURROWS WITH SPREITEN 117 vil
36 ARDELIA 120
37 INTERNAL STRUCTURE OF PHYCODES 123
38 MORPHOLOGIC TERMINOLOGY OF PHYCODES 124
39 PHYCODES 126
40 HYPOTHETICAL ORIGIN OF PHYCODES 129
41 DENDRITIC BURROWS 131
42 MODERN PROGENITORS OF CONE-IN-CONE STRUCTURES (CONOSTICHUS) 136
43 CONOSTICHUS 137
44 CONOSTICHUS 138
45 VERTICAL MOVEMENT PATHS 141
46 PALAEOPHYCUS 144
47 SURFACE DEPRESSIONS 147
48 COLLAPSE STRUCTURE 150
49 COLLAPSE STRUCTURE 151
50 COLLAPSE STRUCTURE 152
Plates
1 FOSSILS IN THE DEIMAR FORMATION 160
2 SUBFACIES IN THE DEIMAR FORMATION 161
3 SEDIMENTS AND SEDIMENTARY STRUCTURES IN FLASER- BEDDED UNITS, DEIMAR FORMATION 162
4 MEDIUM-SCALE CROSS-BEDDING IN THE DEIMAR FORMATION 163
5 BORED CLAYSTONE BEDS AND CLAYSTONE CLASTS, DEIMAR FORMATION 164 viii
6 RELATIVE DEGREES OF BIOTURBATION 165
7 DUELLING BURROWS IN THE DEIMAR FORMATION 166
8 OPHIOMORPHA NODOSA (SMALL FORM) IN THE DEIMAR FORMATION 167
9 FEEDING BURROWS IN THE DEIMAR FORMATION 168
10 LARGE-SCALE TROUGH CROSS-BEDDED SANDSTONE, TORREY SANDSTONE 169
11 BOUNDARY BETWEEN DEIMAR AND TORREY FACIES 170
12 LARGE CHANNELS IN THE TORREY SANDSTONE 171
13 LARGE CHANNEL IN THE TORREY SANDSTONE 172
14 TRACE FOSSILS IN THE TORREY SANDSTONE 173
15 TRACE FOSSILS IN THE TORREY SANDSTONE 174 SEDIMENTARY FACIES AND TRACE FOSSILS IN THE EOCENE DELMAR FORMATION AND TQRREY SANDSTONE, CALIFORNIA
INTRODUCTION
Significance of Facies Studies Utilizing Trace Fossils
Studies of recent depositional environments of terrigenous sediments have been carried out for several decades in coastal and shelf areas of the North Sea. The' scientists include German and Dutch biologists, sedimentologists, and oceanographers^; their approach is multidisciplinary, descriptive and pragmatic. The focus of research is to answer a single question: how would these sediments look in the geologic record?
Similar types of studies have more recently been initiated in the 2 United States, mainly on the Atlantic coast . The American scientists have found, as did the Europeans, that clastic depositional environ¬ ments can be defined most readily by four characteristics: sediment texture, physical sedimentary structures, organic life, and biogenic sedimentary structures (lebensspuren, or trace fossils). Although the first three features have long been studied and utilized by geologists working in ancient rocks, the fourth — trace fossils -- has until recently experienced comparative neglect.
*f| At the Senckenberg Institute at Wilhelmshaven on Jade Bay: Walter Hantzschel, Rudolf Richter and Wilhelm Schafer, and more recently, J. Dorjes, S. Gadow, W. Gutmann, G. Hertweck, H.E. Reineck, I.B. Singh, and F. Wunderlich, among others. In the Netherlands: Ph. H. Kuenen, H. Postma, and L. M. J. U. van Straaten, among others. 2 At the Skidaway Institute of Oceanography, Georgia: R.W. Frey, S.A. Greer, V.J. Henry, Jr., J.D. Howard, J.H. Hoyt, T.V. Mayou, G.F. Oertel, R.J. Weimer, and Charlie, among others. In New England, Miles 0. Hayes and students in the Coastal Research Group, University of Massachusetts. Some work of this kind has been done on the west coast of the United States by H.E. Clifton and J.E. Warme, among others. 2
Within the past two decades the biogenic structures have been successfully employed as interpretationai tools in ancient rocks by 1 several geologists. Still it is not a common practice, particularly in North America, to note presence and types of biogenic structures in a stratigraphic section. Thus it seems appropriate to evaluate the usefulness of trace fossils in re-interpretation of rocks that have been analyzed by geologists using other kinds of information — chiefly of stratigraphic and paléontologie nature.
Scope and Aim of This Study
The seacliffs at Solana Beach, California (Fig. 1) expose a section of mid-Eocene sedimentary rocks that have a rich and varied suite of trace fossils. Authors of major geologic studies that include these rocks judge them to be of shallow marine origin (Hanna, 1926,
1927; Kennedy and Moore, 1971b), but do not mention the lebensspuren.
Recent workers have noted their presence (J. P. Kern, 1972, pers. commun.; M. P. Kennedy, 1973, pers. commun.)'but no detailed studies have been pursued.
The purpose of my study of the Solana Beach outcrops is twofold:
(1) to determine those processes — biologic and physical — that contributed to the original character of the sediments, and thus to describe the depositional environments; and
(2) to investigate in detail the biogenic structures and textures and to evaluate their usefulness in defining and interpreting sedimentary
1 E.g., Seilacher (1954, 1964, 1967 ); Goldring (1962); Farrow (1966); Howard (1966); Wunderlich (1970); Osgood (1970); Frey (1970 ), volume of papers edited by Crimes and Harper (1970); Chamberlain (1971 ); guide¬ book edited by Perkins (1971); and Kern and Warme (1974), among others. 3
FIGURE 1. MAP OF BEDROCK GEOLOGY OF THE SAN DIEGO COASTAL AREA, INDICATING STUDY AREA. QUATERNARY DEPOSITS NOT SHOWN. REDRAWN FROM KENNEDY AND MOORE (1971a:Fig. 1). 4 facie3.
To accomplish this purpose 1 studied in detail two formations exposed at Solana Beach — the Torrey Sandstone and Delmar Formation -- noting sediment textures, physical sedimentary structures, body fossils, ' and biogenic sedimentary structures. The types of lebensspuren are individually described and discussed in Appendix I. Their distribu¬ tion and significance, along with descriptions and interpretations of fossils, sediment textures and structures, are discussed separately for the Delmar Formation and Torrey Sandstone* For comparison, I have utilized published descriptions of clastic depositlonal environments in the Holocene. Using this information I divided the rocks into five subfacies which are interpreted in terms of depositlonal environ¬ ments. Finally, the significance and usefulness of trace fossils in determining and interpreting facies are discussed. 5
PREVIOUS WORK
Despite its delightful location and pleasant climate, the Del Mar -
Solana Beach coastal area was studied only sporadically by geologists until the late 1960's. The first geologic map and account of geology of the area was published by Blake (1856) as part of a railroad survey.
Gabb (1864, 1869), working with the Second Geological Survey of Cali¬ fornia, described many Cretaceous and Eocene fossils from the San
Diego area. Several stratigraphic sections and logs of wells near
Del Mar were prepared by Ellis and Lee (1919)'as part of a more extensive report on groundwaters and geology of San Diego County.
Useful for my research in the area are the works of Hanna (1926,
1927), in which he presented a new geologic map of the coastal region, established stratigraphic nomenclature, and described invertebrate
fauna from the Eocene formations. Hanna defined the "Delmar Sand" and "Torrey Sand" as members of the La Jolla Formation and assigned
Delmar macrofossils to the Domengine molluscan stage (middle Eocene).
His faunal list for the Delmar has been modified only slightly since
it appeared in 1927.
In 1944 Hertlein and Grant published a memoir on the San Diego
Pliocene that also contains information on older rocks in the area.
Milow and Innis (1961) discussed the stratigraphy of Cretaceous
through Pleistocene sedimentary rocks in a field guidebook to San
Diego County. They divided the Delmar into a muddy lower member and a sandy upper member with biostrome interbeds, and assigned it to the
Ynezian-Bulitian benthonic forminiferal stages (uppermost Paleocene
and lowermost Eocene). They were the first to recognize marine fossils 6
in the Torrey sand (Milow and Innis, 1961:38).
The last £ew years have witnessed a flourishing of geologic work
in the San Diego Eocene -- much of it by students at the University of
California at Riverside and at California State University, San Diego,
and much of it based on work done by Michael F. Kennedy. Kennedy mapped the coastal area from Point Loma to Oceanside at a scale of
1:24,000, including the entire 7%-rainute Del Mar quadrangle in which
this study took place. The maps constitute part of his Ph.D. disser¬
tation entitled "Stratigraphy of the Eocene San Diego Embayment"
(Kennedy, in preparation). Kennedy and Moore (1971b) redefined the
Cretaceous and Eocene formations and discussed their stratigraphic
and facies relationships. The Delmar and Torrey members were raised
to formational status and included in the La Jolla Group.
Recent paleontological studies on the Delmar and correlative
formations have confirmed the middle Eocene age assigned by Hanna
(1927). Bukry and Kennedy (1969) studied coccolith assemblages in
the Ardath Shale and correlated them to the lower middle Eocene Dis-
coaster sublodoensis Concurrent-range Zone. Because the Delmar inter¬
fingers with the Ardath (Fig. 3), these formations were also assigned
a mid-Eocene age (Kennedy and Moore, 1971b). Direct evidence of age
comes from a palynologie study: an assemblage of pollen and spores
collected from the Torrey Sandstone and Delmar Formation in my study
area correlates with middle Eocene assemblages from the Gulf and Pacific
coasts (W. C. Elsik, 1974, personal communication). Age relationships
of Eocene formations in the San Diego area have also been discussed
by Moore (1968) on the basis of molluscs, and by Gibson (1971) and
Steineck et al.,(1972)using benthonic and planktonic foraminifera, 7 respectively.
An interesting guidebook on "geology and geologic hazards" of the
San Diego area (Ross and Dowlen, 1973) appeared recently; it contains a wealth of information on Eocene sedimentary rocks. Kennedy (1973) discussed petrographic and engineering characteristics of the Delmar and Torrey, and Elliot (1973) put together a correlation chart in which he compared older stratigraphic nomenclature to that more recently proposed, and listed equivalent formations in southern Orange County
(50-100 km north of the study area) and northern Baja California.
Also in the same guidebook there is a paper on Eocene terrestrial vertebrate fossils (Lillegraven, 1973), and a discussion of pre-
Eocene topography, weathering profiles and paleoclimate (Peterson and Abbott, 1973). The guidebook includes an extensive bibliography of works on San Diego area geology that were written between 1963 and 1973 (Flynn and Dowlen, 1973); it contains listings of numerous unpublished senior research papers and master's theses by students at California State University, San Diego. 8
GEOLOGIC SETTING
San Diego Area
The San Diego coastal area is underlain by Cretaceous and Ter¬
tiary sedimentary strata that rest unconformably on an igneous and metamorphic basement of late Jurassic and Cretaceous age (Bushee et al,
1963; Fife et al.,1967) (refer to Fig. 2). Basement rocks are the
Santiago Peak Volcanics (Black Mountain Volcanics of Hanna, 1926)
and parts of the southern California batholith. The former includes
predominently dacitic and andesitic flows with associated volcanoclastic deposits and some interbedded, marine metasedimentary rocks (Kennedy,
1973; Peterson and Abbott, 1973). Batholithic rocks are the Woodson
Mountain Granodiorite, Bonsall Tonalité, and San Marcus Gabbro (Larsen,
1948).
Pronounced uplift in middle and late Cretaceous time brought these
rocks to the surface, where they contributed debris westward to a belt
of nonmarine conglomerates and marine siltstones, sandstones, and
conglomerates known collectively as the Rosario Group (Kennedy and
Moore, 1971b; Jones and Peterson, 1973; Peterson and Abbott, 1973).
During latest Cretaceous and early Tertiary time a widespread erosion
surface with several thousand feet of relief developed across the base¬
ment complex and the most landward deposits of the Rosario Group
(Lusardi Formation). Analysis of paleosols generated on this terrane
suggests a climate much more humid than today's (Peterson and Abbott,
1973) .
The next record of deposition in the San Diego area is an elon¬
gate complex of Eocene fluviatile, marginal marine, and fully marine 9
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TERTIARY JURASSIC and CRETACEOUS Figure 2. Columnar section of the San Diego coastal area, California. From Kennedy (]973:Fig. 2) SW NE 10 11 clastic strata that together are approximately 700 m thick (Kennedy,
1973). Kennedy and Moore (1971b) divided these strata into a mid- Eocene La Jolla Group and late Eocene Poway Group; these two groups include nine formations. Figures 1 and 3 illustrate stratigraphic relationships of these formations.
The Eocene formations record a series of interdigitations of marine and terrestrial deposits over a rather short distance laterally Physiographically, then, the Eocene terrane must have been much the same as it is today: uplifted source rocks not far to the east sup- plied mineralogically and texturally immature, coarse detritus west¬ ward to low-lying marginal marine environments.
Shelf and bathyal environments lay still further to the west. They are preserved now in the Ardath Shale of the San Diego coastal plain (Gibson, 1971; Kennedy and Moore, 197lb;721; Gibson and Steineck
1972; Steineck et al., 1972) and in conglomeratic units with "Poway type clasts" (Woodford et al., 1968:1464) that outcrop on San Miguel,
Santa Rosa, Santa Cruz and San Nicholas Islands of the continental borderland (Woodford et al., 1968; Weaver et al., 1969; Merschat, 1971 McCracken, 1972; Howell et al., 1974; Yeats et al., 1974). Post-Eocene tectonic activity may have separated Eocene sediments in the coastal plain from source areas to the east and some bathyal equivalents to the west (Merriam, 1968; Minch, 1972; Howell et al.,
1974; Yeats et al., 1974). Evidence for this separation is based on occurrences of the distinctive Poway clasts in conglomeratic units, one of which forms a thin lens at the base of the Delmar Formation
(Kennedy and Moore, 1971b:715). There is no known source area east of San Diego for these reddish-gray clasts of soda rhyolite and other 12 siliceous tuffs (Woodford et al.,1968). Nevertheless, because of the large size (up to 2 m in diameter) of some Poway clasts, Wood¬ ford et al. (1972) believe that they must have been derived from a nearby source terrane that has since been completely removed by erosion.
If instead the Poway clasts were derived from similar rocks in
Sonora, Mexico, as suggested by Merriam (1968), at least 200 km of right-lateral displacement along northwest-southeast trending faults is required to match the Sonoran source with the San Diego depocenter
(Minch, 1972). This would place depositional environments of Eocene formations in the San Diego area much further to the south. Peterson and Abbott's (1973) study of the pre-Eocene weathering profile supports the latter hypothesis. The ancient soil is laterite, a type of soil that develops today in humid, tropical regions within 25 degrees of the equator (Goode and Espenshade, 1953).
Local Setting
Delmar Formation and Torrey Sandstone
The Delmar and Torrey are enclosed stratigraphically, paleo- environmentally, and chronologically by the Ardath Shale to the southwest and the Friars Formation to the northeast (Figs. 3 and 4).
The Ardath Shale contains coccoliths, planktonic and benthonic fora- minifera and marine molluscs; benthonic forams indicate water depths of 500-1500 m (upper middle bathyal) (Gibson, 1971), and coccolith zonation by Bukry and Kennedy (1969) suggests correlation with Lute¬ tian strata in France («middle Eocene). The Friars Formation contains terrestrial vertebrate fossils that according to Lillegraven (1973) 13
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Eocene).
The Torrey Sandstone and Delmar Formation are time-transgressive units deposited in an interface zone between marine and terrestrial environments. Torrey sands are white to medium-brown and coarse, characterized by large-scale cross-bedding and, as shown below, by large trace fossils. The Delmar is composed of dark green claystone and mudstone, green to gray muddy sandstone, and biostromic inter¬ beds of mollusc shells. It is characterized by planar and ripple lamination, medium-scale cross-bedding, smaller trace fossils and more intense bioturbation. The two facies interfinger extensively, so
Kennedy (1973, pers. commun.) defined the base of the Torrey Sandstone at the lowermost appearance of Torrey-facies strata. Thus strata that are clearly of Delmar character can and do appear in rocks mapped as Torrey Sandstone.
Both formations crop out in a northwest-southeast trending linear belt from 5-6 km north of Encinitas to Torrey Fines State Park, 20 km south (Fig. 1 and 4). The Torrey extends from the coast about
8 km inland; the Delmar, about 13 km inland (Delmar Formation and
Friars Formation, undifferentiated) (Kennedy, 1967; Kennedy and
Moore, 1971b). They are believed to extend southeastward in the sub¬ surface and to have been eroded at their northwestward extent (Kennedy and Moore, 1971b).
Selection of Outcrops
Many Torrey and Delmar outcrops are not suitable for detailed study: weathering crusts form on exposure surfaces so that small- 15 scale, low-contrast features — such as trace fossils and some physical sedimentary structures — are obscured. Sea cliffs, in contrast, pro¬ vide excellent vertical exposures and fairly clean surfaces on which such features are easily visible. For this reason -outcrops in a
2.8 km stretch of sea cliffs from the mouth of San Dieguito Valley north to San Elijo Lagoon (Fig. 1 and 4) were chosen for this study.
Kennedy (1967) mapped these outcrops as Torrey Sandstone; however, within the cliff face there are exposures of strata in both Torrey and
Delmar facies. Herein I shall refer to rocks of these outcrops as
"Delmar Formation" «* "Delmar facies" and "Torrey Sandstone" * "Torrey facies". Eighteen stratigraphic sections along the Solana Beach sea cliffs were measured and described. Figure 5 maps locations of sections that are graphically presented in Figure 6, in pocket. 16
FIGURE 5. LOCATIONS OF MEASURED STRATIGRAPHIC SECTIONS. GENERAL DISTRIBUTION
OF TORREY AND DELMAR FACIES ARE PRESENTED SCHEMATICALLY AT FAR RIGHT.
» DELMAR FACIES = TORREY FACIES 17
DESCRIPTION OF THE DELMAR FORMATION
(as exposed at Solatia Beach)
Stratigraphy and General Description
Approximately 15 m of stratigraphic section in Delmar facies were measured and described at eleven localities (sections 1-10 and 18).
Localities 1-10 begin at the southern tip of the cliff outcrops and continue northward about 0.5 km; section 18 is located in the northern most sea cliffs, at the southern edge of San Elijo Lagoon (Fig. 5).
Delmar strata exposed at the south end of the sea cliffs dip gently northeast; those exposed at the northern extreme dip southward
(Fig. 5). If these strata can be loosely correlated (a chancy business as the Delmar is highly variable laterally), it would appear that the sequence is folded into a shallow syncline, with younger Torrey sedi¬ ments exposed in the fold axis and older Delmar-type deposits out¬ cropping on the flanks.
A composite stratigraphic section has been constructed for the
Delmar (Fig. 7) to illustrate rock types present and the general sequence in which they occur. The lower 9 m of the Delmar consists primarily of oyster beds, intensely bioturbated muddy sandstone, burrowed sandy mudstone, and interbedded silty sandstone, mudstone and clay-shale. The oyster beds are composed overwhelmingly of Ostrea idriaensis Gabb but also contain a variety of other bivalve and gastro pod shells in a sandy, calcite-cemented matrix. Muddy sandstones form 0.3-1.2 m thick beds that commonly are finer-grained upward and are capped by a layer of sandy mudstone. These beds contain scattered shells and molds of Ostrea and other molluscs. They 18
1egend
A Qstrea idriaensls bioturbated muddy sandst. bi val ve and snail shells cross-stratified sandst. 1 Gyrolithés £=» ThaiIassinoides clay-draped sand ripples £r» Ophî omorpha nodosa (flasers) (J vertical burrows sandy mudstone TPhycodes ÎPalaeophycus mudstone Jj^coal lens $ Conostichus
FIGURE 7, GENERALIZED, COMPOSITE STRATIGRAPHIC SECTION OF THE DELMAR FORMATION AS EXPOSED AT SOLANA BEACH. COMPARE TO COMPOSITE SECTION OF THE TORREY SANDSTONE, FIGURE 18 (p. 53) 19 also have abundant trace fossils, but in some beds distinct biogenic
structures have been destroyed by intense and/or prolonged bioturbation.
Interbedded silty sandstone, mudstone and clay-shale are characterized by a remarkable rarity of biologic reworking. Thus delicate planar and ripple lamination and flaser bedding have been preserved. There
is much carbonaceous material and even a small lens of coal in these beds (PI. 3C).
The upper 6-7 m of Delmar contains some scattered shell material but no biostromic oyster beds. The sediments are primarily muddy
sandstones and sandy claystones; a vestige of medium-scale cross-bedding is preserved in some sandstone beds, but in general bioturbation is intense. A trough-shaped erosional surface marked by concave-downward pelecypod valves signals initiation of Torrey deposition.
Paleontology
The Delmar Formation at Solana Beach contains both microfossils and macrofossils. The calcareous microfossils and many of the macro¬
fossils have been badly leached, thus much of the original assemblage is not preserved or is present only as molds and casts.
Microfossils.
Pollen, spores, a single cast of an ostracode valve, fecal pellets, and some questionable arenaceous foraminifera are preserved in the
Delmar Formation.
Pollen and spores. Dr. W. C. Elsik conducted a palynologie study on nine samples from the Delmar Formation and Torrey Sandstone at
Solana Beach and at Torrey Pines State Park. The following discussion is based entirely on information furnished by him. 20
The assemblage is diverse, containing A4 genera of pollen and spores as well as several undescribed genera and species (Fig. 8).
All samples appear to represent the same floral assemblage.
The palynomorphs represent evergreen and broadleaf trees, some shrubs and herbs, and possibly mangroves. As shown in Figure 9, each of these plants is presently native to either a tropical, subtropical, temperate, or tropical high-altitude climate. The modern mangrove is a lowland tropical form occupying brackish water environments
(Smith, 1966:219); identification of mangrove pollen in the Delmar is uncertain, however (Fig. 8).
In summary, there are climatically divergent elements in the
Delmar flora. In this respect it resembles the Chalk Bluffs flora
(middle Eocene lone Gravels) of north central California (Andrews,
1961:200). The two assemblages also have several species in common
(W. C. Elsik, 1974, pers. commun.; Leopold, cited in Penny, 1969).
The Chalk Bluffs flora are thought to have existed in a warm (mean annual temperature in 60's and 70's degrees F.), humid climate (Andrews,
1961:200). It seems likely that the Delmar flora thrived in a similar climate, based on its similarity to Chalk Bluffs flora, and on the abundance of pollen of broadleaf trees and several tropical plant genera.
The Delmar palynomorph assemblage correlates well with assemblages of middle Eocene age from the Gulf and Pacific coasts (Fig. 10).
Although rare elements of Oligocène and Paleocene age are present, the overall aspect is middle Eocene based on angiosperm pollen type and diversity.
Ostracoda. A single cast of an ostracode valve (Pi. 1A) was 21
PTER1D0PHYTE SPORES ANGIOSPERM POLLEN, continued
Polypodiaceoisporites (Pteris) Diporopollenites sp. aff. spp. Psilodiporites hatnmenii Varma Aff. Polypodiaceoisporites & Rewat 1963 marxheimensis (Murr* & Ulmus spp. Pflug 1952) Krutzch 1959 Malpighiaceae sp. Deltoidospora spp. Tilia sp. Laevigatosporites sp. Erdtmanipollis (Pachysandra) sp. Divisisporites sp. Bombacacidites spp. Triplanosporites spp. Nyssaceae spp. Selaginella sp. Bursera sp. Lusatisporis spp. ? Rhizophorus sp. Perotrilites spp. ? Amanoa sp* several undescribed species ? Alangiaceae sp* undescribed genera and species Aff* Bombacacidites claibornensis
GYMNOSPERM POLLEN
Pinus spp. FUNGAL SPORES Picea spp. ? Sequoiapollenites sp. Pluricellaesporltes spp. ? Tsugapollenites sp. Inapertisporites spp. Rugobivesiculites sp. Lacrimasporonites spp* Exesisporites sp. cf. E. "magnus" Diporisporites spp. Notothyrites sp. ANGIOSPERM POLLEN Dicellaesporites ? cf. "atrophus*' Diporicellaesporites sp. Liliacidites sp. numerous undescribed species Quercus sp. Aff. Momipites (Engelhardia) triradiatus Nichols 1973 Ericaceae spp. INCERTAK SEDIS Myrica spp. Ilexpollenites spp. Schizosporis parvus ? Oculopollis spp. Schizosporis spp. . ? Salixpollenites sp. ? Platycarya sp. ? Fraxinus sp. Vacuopollis sp. WOODY TISSUE Malvaceae sp. Trudopollis sp. Woody tissue 5 types Alnus sp. Proteaceae spp. !
Figure 8. Palynomorphs and other plant remains preserved In the Delmar Formation and Torrey Sandstone, Solana Beach and Torrey Pines State Park. Figure 9. Flora represented by palynomorphs and their present-day climatic distribution.
Flora represented by palynomorphs Climatic distribution of present-day species
Pinus spp. - pines Picea spp# - spruces Liliacidites sp. Trudopollis sp. Erdtmanipollis sp. — Pachysandra Amanoa sp. - mangrove Tropical to subtropical ? Rhizophorus sp. - mangrove Tropical to subtropical Ilexpollenites spp. - holly?, yupon? Oculopollis spp. - evening primroses, etc. ? Proteaceae spp. Tropical; dry climate Malpighiaceae sp. Tropical Myrica sp. — bayberry, wax myrtle, etc. Temperate and subtropical Ulmus sp* elm Temperate and mountains of Tropical Asia Pteris spp. Cosmopolitan Alnus sp. — alder Temperate, northern hemisphere and Andes
Figure 10. Age of flora.
Palynomorphs in the Delmar Formation and Torrey Sandstone that are middle Eocene age in Gulf Coast assemblages:
Lusatisporis spp. Polypodiaceoisporites (Pteris) spp. Tricolporopollenites spp. — unpublished Bursera sp. undescribed genera and species
Palynomorphs in the Delmar Formation and Torrey Sandstone that are middle Eocene age in Pacific Northwest assemblages:
Ulmus sp. (small) common Lacrimasporonites sp. — unpublished Bursera sp. undescribed genera and species
Other:
Rare elements of latest Paleocene - late Eocene of Gulf Coast; of Oligocène of Venezuela; of lower-middle Eocene of India.
Conclusion: overall aspect of flora is middle Eocene based on angiosperm pollen type and diversity. 23 observed in a mud-shale layer in the Delmar Formation. Ostracodes can be found in almost any aquatic environment; a single, unidentified cast certainly is inadequate to provide paleoecological or strati¬ graphic information.
Fecal pellets. Fecal pellets (PI. IB) were recovered from the same mud-shale in which the ostracode was observed. The pellets are
1 mm long and about 0.4 mm wide; a slight depression runs parallel to the length of the pellet and divides it into two "pillows". It is
interesting, though certainly not diagnostic, that the Delmar fecal pellets closely resemble those of modern Ostrea (Sch'dfer, 1972:Fig. 245), a genus that is preserved in abundance in Delmar strata. In a more general sense, the geometry of these pellets corresponds to "segmented faecal pellets" described by Schdfer (1972:421). Such pellets can be transported in water without disintegrating, because they are highly dehydrated, pressed and formed, and because they are small and not adhesive (Schafer, 1972:421,422). This property is advantageous to animals that live attached to a substrate or that live in semi¬ permanent dwelling burrows. These animals must depend on extraneous or self-propelled water currents to remove feces.
Arenaceous foraminifera. A few small cylinders constructed of sand grains were found associated with the ostracode and fecal pellets.
The tubes are 0.3 - 0.5 mm long and 0.1 mm in diameter (Pi. 1C); they are similar in size, shape, and composition to some arenaceous foraminifera. Small, simple arenaceous foraminifera are common in paralic environments (Bandy, 1960).
Macrofossils.
Macrofossils in the Delmar Formation - all mollusc shells - 24 occur in three types o£ deposits. The most diverse assemblage is preserved in cemented beds composed largely of Ostrea idriaensis
Gabb. Less common are sedimented shell beds of broken and dis¬ articulated valves of pelecypods and gastropods. Molds and casts of gastropods and pelecypods are scattered through intensely bioturbated beds of muddy sandstone.
The oyster beds are flat-lying and continuous for up to 30 m along strike (Fl. 2); they are quite hard and form résistent banks that project several meters from the base of the cliffs into the surf zone. These beds are particularly Interesting because many of the oys¬ ters are preserved in living position with valves articulated; I be¬ lieve they represent in situ oyster reefs.
The mollusc assemblage has been studied by Hanna (1927), Mande1
(1971) and most recently by Dr. C. R. Givens. Hanna identified 16 species of Pelecypoda and 16 of Gastropoda; he correlated them with the
Domengine molluscan stage (mid-Eocene) defined by Clark (1926) and
Vokes (1939). Hanna (1927:257) considered the assemblage to indicate
"brackish water conditions".
C. R. Givens (1973, pers. commun.) has recognized an additional four molluscs, two of them species misidentified by Hanna (Fig. 11).
He did not, however, find either Turritella applinae or Turricula praeattenuata, two typically marine species. His environmental inter¬ pretation follows:
"In my opinion, the fauna of the Delmar Formation is definitely 'brackish'. This conclusion is based upon the abundant oysters and on the presence and abundance of certain other species, including Loxotrema turritum, Potamides carbonicola, Pelecyora aequilateralis, Crommium andersoni, Nerita triangulata, Cuneocorbula torreyensis and Myrtea roseburgensis, which are consistently associated with oysters in Eocene strata interpreted to be brackish-water deposits elsewhere 25 on the pacific Coa3t. Thus, for example, these species were reported by Vokes (1939) only from portions of the Domengine Formation charac¬ terized by oyster beds and lignites and interpreted by him to be of brackish-water origin. The association of Potamides carbonicola and Loxotrema turritum with oysters is particularly marked. These two species are almost always associated with oysters. Although both of these genera are extinct, they belong to families which are largely or entirely confined to brackish- and fresh-water environments. Living members of the Family Potamididae characteristically occur in mud flat and mangrove swamp environments in brackish-water bays and lagoons. Loxotrema is referable to the Family Melaniidae, which is largely a fresh-water group but includes some brackish-water species. The sharp contrast in taxonomic composition between the Delmar fauna nad the typically inner sublittoral marine assemblages that characterize the other Eocene units in the San Diego area also supports a brackish-water environment for this fauna. Relatively few species in the Delmar fauna also occur in the marine molluscan assemblages of the other for¬ mations, and vice versa. Most of those species that are shared in common belong to taxa (e.g., Brachidontes, Barbatia)that commonly occur in the littoral zone or in very shallow water and that are able to tolerate a range of salinity conditions. The salinity of the water in which the Delmar fauna lived may have been in the upper part of the brackish range. The oyster in the Delmar fauna is Ostrea rather than Crassostrea. According to Stenzel (1971:N1039), Ostrea occurs in water ranging from euhaline to the upper part of the brackish range but cannot tolerate water as brackish as that in which Crossostrea thrives." 26 Figure 11• Molluscan species identified from the Delmar Formation (continued next page) 27 Figure 11 (continued). Molluscan species identified from the Delmar Formation 28
Sediments
Textural and compositional characteristics of the Delmar Formation reinforce the paleontological evidence for deposition in protected environments within a shoreline complex. As shown below, fine-grained sediments and carbonized plant debris are more abundant in Delmar sediments than in the Torrey, suggesting that these constituents were concentrated and trapped shoreward of the Torrey by a variety of processes that operate in very shallow-water, transitional environments.
Composition.
The sand fraction of a typical Delmar sediment is composed of
80-85% quartz, 10-15% biotite, and a trace of hematite, topaz, pyroxene, tourmaline, chlorite, and glauconite; the clay-sized fraction consists of smectite and kaolinite (Kennedy, 1973). Delmar sediments at Solana
Beach are compositionally similar, but they contain more potassium feldspar than plagioclase, plus 2-3% muscovite, a trace of metamorphic rock fragments, some claystone clasts and 1-2% carbonaceous material.
Abundant plant remains in the Delmar are preserved as imprints, casts and carbon films. These include recognizable remains of grass blades and wood fragments that are concentrated along bedding planes in mudstone and muddy sandstone. The Delmar also contains a small coal lens from which amber has been recovered (J. P. Kern, 1972, pers. commun.). The coal appears to be limited to a meter-wide pocket, and may represent a carbonized tree or large wood fragment (pi. 3C).
Texture.
Grain size analyses of selected samples from the Delmar Formation are presented in Appendix II. These analyses confirm rock names
(after Folk, 1968) assigned to samples on the basis of hand lens 29
inspection in the field and inspection under a binocular microscope
in the lab.
An interesting feature of Delmar sediments is the ubiquitous
presence of mud. Sandstone beds contain at least 10-15% mud; mud¬
stone lenses and beds are abundant; and a common rock type is inter-
bedded and interlaminated sandstone, mudstone, and claystone. There
is much more mud in Delmar sediments than in the Torrey (cf. Figs.
7 and 18).
Sand populations in the Delmar are also finer than those in the
Torrey. Three of four analyzed sand fractions from the Delmar exhibit
primary and secondary modes of fine (2.25-2.5(9 and medium (1.5-1.750)
sand, respectively (Fig. 12). In contrast, fine sand is a secondary
mode or non-modal in all but one Torrey sand; medium sand (1.5-1.750)
is dominant and very coarse sand and minor gravel are present in all
samples.
It has been established stratigraphically that the Torrey over-
lies the Delmar in a transgressive sequence (Kennedy and Moore, 1971b)
(see Fig. 3, this paper). Therefore Torrey facies must have been
deposited seaward of Delmar facies. This implies that fine sediment was concentrated shoreward.
Depositional processes affecting texture.
The perponderance of mud in the Delmar relative to the Torrey
echos a pattern exhibited in Holocene depositional environments in
many nearshore areas of the world: sediment that accumulates near the
shoreline in protected bays, lagoons and tidal flats is finer than
that deposited immediately offshore (Shephard, 1960:215 and Fig. 13;
Warme, 1971:25). There are many processes that operate to trap fine 30 TORREY SANDSTONE (RIGHT). WEIGHT PERCENT MUD (SILT + CLAY) GIVEN IN COLUMNS TO RIGHT OF EACH HISTOGRAM FIGURE 12. HISTOGRAMS SHOWING GRAIN-SIZE DISTRIBUTION OF SAND FRACTIONS SAMPLES FROM THE DELMAR FORMATION (LEFT) 31 sediment nearshv*»e; they have been discussed by van Straaten and Kuenen
(1957, 1958), Postma (1961), Kuenen (1961:492-495), and van Straaten
(1965:63-65) and summarized by Warme (1971:25).
(1) Invertebrate £auna, whose populations are very dense in pro¬ tected shoreline environments, remove fine-grained sediment from suspen¬ sion in water and incorporate them into fecal and other types of pellets.
These are sand-sized and thus are more rapidly deposited than their con¬ stituent particles.
(2) Plants growing on the sediment surface damp currents, promoting deposition.
(3) Algal films trap sediment and protect it from erosion.
(4) Organic detritus in suspension initiates growth of clay floccules that are much larger and therefore sink faster than the fine floccules of the open sea.
(5) Wave energy is lower than on the open coast, reducing turbu¬ lence .
(6) In tidal flats mud is deposited at flood tide in a broad sheet.
Ebb currents, however, are confined to gullies and channels, leaving large areas of mud intact.
(7) Lag effects - (a) "settling lag effect" — Within protected environments currents tend to slow as they approach land. A particle begins to sink at some critical velocity level, but is then carried still further inland because there is a time "lag" between initiation of sink¬ ing and hitting bottom. At the eventual site of deposition, currents are slower than the "critical velocity", (b) "scour lag effect" — A stronger current is required to pick up a settled particle than is required to keep it in suspension. 32
(8) Particles are floated landward on bubbles, foam, and surface tension as the tide rises. The material sinks or becomes stranded before ebb tide.
(9) If there is very strong influx of fine suspended sediment from rivers or estuaries, much of it will be deposited nearshore regard¬ less of energy levels (McCave, 1971 ).
All of these processes may well have contributed to deposition of fine sediment in Delmar environments. There is direct evidence for pro¬ duction of mud pellets (trace fossils of burrowing fauna, and some preserved fecal pellets and pellets in lined burrows) and for deposition of clay as silt-sized floccules (mud beds suggestive of simultaneous deposition of silt and clay).
I have not observed traces of algal films or plant rootlets in the
Delmar, but certainly there is abundant, macroscopic plant debris. Too, algal films are ubiquitous in modern nearshore environments and are well- known in the geologic record (especially from carbonate rocks); thus it is quite possible that both algae and grasses contributed to retention of fines in the Delmar.
There is indirect evidence for operation of processes 5-8. Since
Torrey strata indicate higher energy conditions seaward, Delmar environ¬ ments must have been protected from wave action to some degree (process 5).
The other processes depend on tidal activity. Some paléontologie, compo¬ sitional, and textural evidence for deposition of Delmar facies in protected shoreline environments has been presented above; since there was an ocean to the west, and since these environments were at least marginally marine, they must have been tidally controlled to some degree.
Finally, there is some textural evidence that the overlying water 33 was turbid nearly all the time and very turbid on occasion. For example, even the very coarse, large-scale cross stratified sands of the Torrey
contain some mud (Fig. 12), and there are thicker mud beds (>5 cm) associ¬
ated with them and in the Delmar that must have accumulated rapidly
under high influx of fine sediment.
Physical Sedimentary Structures
Physical sedimentary structures and bedding characteristics of the
Delmar Formation indicate physical processes that commonly operate in
shoreline environments. There is evidence for frequent and radical fluc¬
tuations in physical energy levels, for both wave and current activity,
for close juxtaposition in time and space of erosional and sedimentary events, and more generally, for heterogeneity of depositional processes
in time and space.
Specific structures are individually described and discussed below.
Interbedded sand and mud.
Not only is there abundant mud in the Delmar Formation, but it occurs
in intimate association with sand: interlaminated and interbedded sand and
mud, and flaser, wavy, and lenticular bedding (terminology after Reineck
and Wunderlich, 1968) are common bedding types, particularly in the lower
half of the Delmar outcrops (see sections 1-3, Fig. 6). These bedding
types as they occur in the Delmar are illustrated in Figures 13, 15, and
16 and Plate 3.
Depositional processes affecting interbedded sand/mud.
The several processes acting to deposit mud in close association with
sand have been studied in Holocene nearshore environments, particularly on
the North Sea coasts of Germany and Holland and along the east coast of
the United States. These processes are summarized below. 34
(1) Fluctuations in physical energy. -- Sand is deposited during periods of current or wave activity; mud settles from suspension during slack water. Such conditions are commonly present in very shallow-water environments and particularly in intertidal to subtidal zones, where energy fluctuations are related to the tidal cycle. (Reineck, 1960b,
1972; Reineck and Wunderlich, 1968; van Straaten, 1952:501).
(2) Biogenic pelletization. -- Invertebrate fauna produce fecal and pseudofecal pellets that are composed of mud and organic matter but are hydrodynamically equivalent to coarse silt and fine quartz sand.
Pellets are deposited both from the traction load and from suspension.
(Haven and Morales-Alamo, 1968; Pryor, 1972; t'cward and Dorjes, 1972;
Oertel, 1973).
(3) Deposition from very turbid water. --If the concentration of suspended sediment in water is sufficiently high, mud will be deposited at flow velocities that would normally keep such material in suspension.
This results in accumulations of thinly-laminated mud that are associa¬ ted with layers of much coarser sediment. In areas in which sand is normally deposited, mud beds accumulate after periods of increased physical energy, such as storms or spring tides, when waters are except¬ ionally turbid. Where suspended-sediment concentrations are normally high and current velocities moderate, mud is deposited relatively continuously, interrupted occasionally by sand layers that originate during the early periods of storms, high run-off, or spring tides.
(McCave, 1970, 1971 ; Oertel, 1973; Howard and Reineck, 1972:102).
(4) Mud-pebble beds. -- Mud pebbles eroded from contacted mud
layers and exhumed marsh deposits accumulate in foresets and are pre¬
served as wavy or lenticular beds (Oertel, 1973). 35
Identification of processes by texture and structure. Processes of mud deposition can be differentiated by textures and sedimentary struct¬ ures; textures, however, frequently are not well-preserved. For instance, Howard and Dorjes (1972) reported that fecal pellets cannot be identified at one-meter depth in cores from Recent tidal flats in
Georgia. Mud pebbles are more likely to retain morphologic integrity, particularly if there is sufficient sand matrix to outline their shape.
Sedimentary structures are more likely to be preserved and can be helpful in identifying processes of mud deposition. Mud that settles from suspension during slack water is draped over sand in thin laminae.
If the sand surface is rippled, mud will be thicker in the troughs and thinner over crests. If a drape is deposited within a tidal cycle, it must be fairly thin (less than 1 cm) (McCave, 1971), and the ripplèd sand should exhibit bipolar current directions (herringbone pattern)
(Reineck, 1967) .
Mud pellets that settle from suspension form laminated drapes very similar to those described above, but can be much thicker (Klein, 1971).
Mud pellets deposited from the traction load, however, give rise to very different structures: the pellets are concentrated in thin laminae between inclined laminae of fine sand and coarse silt. In this manner, delicate flasers, like those illustrated in Figure 13, are formed in
foresets of rippled sand.
Mud pebbles are deposited in foresets in which the pebbles some¬
times are imbricated. Wavy and lenticular bedding result.
Identification of processes operating in the Delmar Formation.
Mud layers in interbedded sand/mud sequences of the Delmar appear
to have accumulated both by settling and traction deposition of pellets 36
DOMINANT ORIENTATION OF RIPPLE FORESETS
CM
10
a. SIMPLE FLASER BEDDING
b. BIFURCATED WAVY FLASER BEDDING
c. WAVY MUD LAYER
d. LENTICULAR BEDDING WITH CONNECTED LENSES
e. LENTICULAR BEDDING WITH SINGLE LENSES
TERMINOLOGY AFTER REINECK AND WUNDERLICH (1968)
FIGURE 13. FLASER, WAVY, AND LENTICULAR BEDDING IN THE DELMAR FORMATION. THESE STRUCTURES ARE DEVELOPED ON CURRENT RIPPLES. FORESET LAMINAE ALTERNATELY DIP IN TWO OPPOSING DIRECTIONS (SEE COLUMN AT RIGHT); PREDOMINANT DIRECTION OF RIPPLE MIGRATION WAS RIGHT TO LEFT IN SKETCH. BLACK2 MUD AND CLAY; DOT PATTERN2 MUDDY SAND AND SANDY SILT. 37 and by settling of suspended mud. Pellets in the traction load probably composed the inclined laminae (A) in Figure 13; thicker drapes (B, Fig.
13) might have formed from pellets or suspended mud. Foreset orienta¬ tions are bipolar, but no herringbone patterns were observed. Mud clasts are present in several beds (Pi. 5 A & B); they do not form solid mud layers, however.
Modern occurrences of flaser, wavy and lenticular bedding.
Flaser, wavy and lenticular bedding have been described from sever¬ al Recent depositional environments. These occurrences are summarized in Figure 14: marine littoral, inner sublittoral, lacustrine and allu¬ vial environments are listed.
Alluvial and lacustrine environments can be elimated from con¬ sideration because body and trace fossils in the Delmar indicate brackish to normal marine salinities (Hanna, 1927; C. R. Givens, 1973, pers. commun.; see discussion of trace fossils and Appendix I, this paper). The remaining occurrences of flaser, wavy and lenticular bedding have been described from two general areas (see Fig. 14):
(1) protected environments within a shoreline complex (littoral and inner sublittoral zones, water depth less 4 m) e.g.,
tidal flats and channels
beach and shoal runnels
interdistributary bay (lenticular bedding only)
lagoons ;
(2) areas immediately offshore major sources of fine sediment
(inner sublittoral zone, water depth about 3-15 m), e.g.,
channel in front of estuary entrance
flanks of estuary entrance shoals 38
Figure 14. Occurrences of flaser, wavy, and lenticular bedding described from Holocene depositional environments.
Location (zones after Hedgpeth, 1957:18) Source
Littoral zone (intertidal, between low and high water lines)
tidal flats, North Sea coast Reineck, 1960a; Hântzschel, 1939:202 low tidal flats, Dutch Wadden Sea van Straaten, 1952:502 Misch (sand/mud) tidal flats, Jade Bay ... Reineck, 1967:201 tidal flats, Sapelo Is., Georgia Howard and Dorjes, 1972 mud tidal flat, Mississippi River delta .. Coleman and Gagliano, 1965:146 beach: lee side of ridges and in backshore runnels, Sapelo Is., Georgia Wunderlich, 1972:52 beach sediments, North Sea coast Wunderlich, 1969 runnels behind swash bar, estuary mouth shoal, Doboy Sound, Georgia Oertel, 1972 lateral (tidal) channel deposits Reineck and Wunderlich, 1969
Inner littoral zone (low water to 40 m depth)
tidal channels, Dutch Wadden Sea van Straaten, 1952:502 lagoons (flaser on oscillation ripples) Reineck and Wunderlich, 1968 flanks of estuary entrance shoals, Doboy Sound, Ga. (fecal origin, depth 2-4.7 m).. Oertel, 1973 channel offshore estuary entrance, Doboy Sound, Ga. (mud pebble origin, depth 4-10 m) Oertel, 1973 offshore of estuary entrance, Doboy Sound, Ga. (3-12.5 m depth) Oertel, 1973 interdistributary bay, Mississippi River delta Coleman and Gagliano, 1965:146 "near source" on prodelta, Mississippi River delta (best development at depths less than 2.4 m) Moore and Scruton, 1957:2753 subaqueous levee, Mississippi River delta (with distorted laminations) Coleman and Gagliano, 1965:145 39
Figure 14, continued. Occurrence of flaser, wavy and lenticular bedding described from Holocene depositional environments.
Location (zones after Hedgpeth, 1957:18) Source
Lacustrine
shallow lakes on delta plain, Mississippi River delta (depth 5 m, lenticular bedding only, clay and silt only) ...... Coleman and Gagliano, 1965:148
Alluvial
alluvial levee deposits ... Allen, 1965 40
"near source" on prodelta (Mississippi River delta)
inner German Bay, opposite mouths of Weser and Elbe Rivers.
These possibilities for the Delmar Formation will be discussed below under Identification and Interpretation of Subfacies.
Micrograded beds.
A meter-thick, flaser-bedded sequence at section 1 (Fig. 6) exhibits four pairs of micrograded laminae (Fig. 15). Each lamina grades upward from gray silt and fine sand to dark gray-green clay and is 2-4 mm thick.
The laminae are persistent laterally for at least two meters (width of outcrop undisturbed by faults); the grains are we11-segregated verti¬ cally according to size. Probably the laminae were deposited from sus¬ pension in a very slow-moving or still body of water. The paired occurrences are quite striking and suggest deposition through tidal cycles.
Thicker mud beds.
The Delmar also contains relatively thick (greater than 5 cm) mud layers (Pi. 10) that exhibit millimeter laminae of pure claystone.
These beds appear to be unrelated to overlying and underlying beds (as opposed to interbedded sand and mud). They may have accumulated in areas of persistent high turbidity, or as plugs of abandoned channels.
Laminated sand.
Planar laminated sands compose a small part of Delmar sediments; they are associated with interbedded sand and mud and with flaser, wavy and lenticular bedding as shown in Figure 14. Laminated sands are com¬ posed of fine and medium sand with some silt. They may or may not exhi¬ bit erosional contact with underlying sediments.
Laminated sands have been observed to form by swash and backwash 41 FIGURE 15. VERTICAL EXPOSURE IN THE DELMAR FORMATION AT SECTION 2, SHOWING PHYSICAL SILTY SANDSTONE. SEDIMENTARY STRUCTURES IN INTERBEDDED AND INTERLAMINATED MUDSTONE, CLAY-SHALE, 42
FIGURE 16. EXPOSURE PERPENDICULAR TO BEDDING, DELMAR FORMATION, SHOWING CHARACTERISTIC PHYSICAL AND BIOGENIC SEDIMENTARY STRUCTURES IN LAMINATED SANDSTONE BEDS. 43
(Reineck, 1963; Clifton, 1969; Oertel, 1972), by currents in plane- bed phase of the upper flow regime (Simons et al., 1965:36,37), by deposition from suspension clouds produced by channel currents or shoaling waves (Reineck, 1963), and by deposition from suspension clouds in still or very slowly moving waters (less than 20 cm/sec)
(Reineck and Singh, 1972).
The latter sands, called "storm-sand layers", are found in graded rhythmites in which laminated sands become interbedded upward with mud laminae that thicken in the same direction; the entire rhythmite is only a few centimeters thick. In contrast, laminated sands in the Delmar are approximately a decimeter in thickness and grade upward either into interbedded sand/mud or into rippled and cross-bedded sand.
Most of the remaining processes operate in very shallow water: in swash zones of beaches and shoals in the upper offshore of Georgia at
2-5 m depth (Howard and Reineck, 1972:93), on submerged parts of sand bars, and on washover fans (Mikesh et al., 1968).
Cross-stratification.
At least four general types of cross-stratification are exhibited in Delmar outcrops.
(1) cross-stratification of current ripples and
(2) cross-stratification of oscillation ripples.
Current and oscillation ripples associated with mud flasers (Fig.
13) are composed of fine sand and silt. Oscillation ripples are formed by wave action; in Delmar strata they are much rarer than current ripples. Ripples associated with larger scale cross-bedding (Pi. 4A) are composed of muddy fine and medium sand. They occur above larger cross-sets and indicate waning currents. 44
(3) medium-scale trough cross-stratification. -- Trough cross- stratified sets are 15-20 cm thick and composed of muddy sand. One set
(Pi. 3D) clearly was deposited in a shallow channel 18 cm deep and 1.6 m wide. Other sets (Pis. 3A & B and 4A, lower part). appear to be deposits of megaripples. A reactivation surface followed by steepening of in¬ clined beds appears in one example of this type (Pi. 3A & B).
(4) tabular sets of planar inclined beds. -- Tabular sets occur at the base of 0.5-1.0 m-thick units of muddy sandstone that grade up¬ ward to sandy mudstone (Pi. 4B-D)* The lower bounding surface is planar to slightly irregular; inclined laminae dip 15-24 degrees and are dis¬ cordant with the basal surface. These structures probably were formed by migration of a megaripple or by deposition on a point bar of a shallow channe1.
Sedimented shell beds.
Mollusc shells in the Delmar occur in three types of shell beds: oyster reefs, decimeter-thick shell hashes, and thin stringers of Ostrea shells. The reefs are chiefly biostromic; shell hashes and stringers result from physical processes of sedimentation.
The shell hashes observed in the Delmar are lenses about 10 cm thick and a meter or two long that are composed of bivalve and gastropod shells other than Ostrea. Pelecypod valves occur in almost all orientations but exhibit a slight preference for concave upward positions. The shells are in a matrix of muddy sand that grades upward to sandy mudstone. The entire bed is about 20 cm thick and is intensely bioturbated.
Somewhat similar but more extensive deposits have been observed at inner sublittoral depths (1-10 m) immediately offshore Sapelo Island,
Georgia (Howard and Reineck, 1972:102) and from the German (Heligoland)
Bay at 10-15 m depth (Reineck et al., 1968:293 and Fig. 13). The shells 45 are transported and concentrated during storms. Storm activity would satisfactorily account for the Delmar shell hash; the absence of Ostrea suggests hydrodynamic sorting, and the graded sequence above it could represent waning of current and wave strength after a storm.
A more common shell deposit is thin stringers of large shells, chiefly Ostrea, that define the base of approximately meter-thick, in¬ tensely bioturbated, graded beds (Pi. 6D). Biogenic reworking has so thoroughly homogenized these beds that shell stringers are the sole indi¬ cation of bedding.
There are at least two processes that could give rise to these shell stringers in the Delmar. (1) The shells could be a lag deposit marking the base of a migrating channel. As a channel moves laterally, it erodes along one side and finer sediment is carried away or deposited on a point bar. Coarse fragments (in this case, Ostrea valves) are left behind on the floor of the channel and are eventually covered by point bar deposi¬ tion. Burrowers then reworked the entire sequence during periods of non¬ deposition. (2) Alternatively, the shells might have been eroded from nearby oyster reefs by physical (wave) or biologic (burrowers) undercut¬ ting. Currents and waves then redistributed the shells and concentrated them slightly. This process, on a smaller scale, would also account for the occasional large shell isolated in a matrix of muddy sand or sandy mud (Pi. 6D).
Bored claystone beds.
Claystone clasts in Delmar sediments indicate exposure and erosion of cohesive claystone beds. In fact, there is direct evidence for this process: a claystone bed that was exposed and bored (by clams?) is over- lain by claystone clasts derived from it (PI. 5). The claystone 46 conformably overlies a muddy sandstone; its upper contact is very irregu lar but sharply defined, as shown in Plate 5C. Cylindrical borings penetrate the bed from the top down and are filled with sediment from the overlying bed.
Exhumed and bored claystones and mudstone are known from coastal environments in many areas of the world; such a bed is presently exposed for example, on Cabretta Island Beach, Georgia, There, old marsh depos¬ its have been invaded by boring clams and by polychaetes and small deca¬ pods that re-occupy old burrows (Frey and Howard, 1969:435, Pi. 4(3) and
Table 1). A cohesive mudstone can be exhumed intertidally by waves (as at Cabretta Island) or by erosive currents in the inner sublittoral zone: its presence does not necessarily indicate subaerial exposure.
The bored claystone in the Delmar is covered by sand, claystone clasts and carbonized wood fragments (Pi, 5A), The clasts probably were derived directly from the claystone layer below. This conclusion is supported by (1) location of the deposit and (2) presence of a large
(8 cm long) clast with two sand-filled holes that probably are borings
(Pi. 5B). 47
Biogenic Sedimentary Structures
Burrowers have left their mark on almost every bed and lamination in the Delmar outcrops. The physical environment apparently was at all times hospitable to a diverse and plentiful infauna; variations in abun¬ dance of trace fossils depended on faunal densities supported by each subenvironment, and on sedimentation rates and frequency and depth of physical reworking. Hospitable physical environments for burrowers are marine and marginal marine environments. Although lake and river bottoms and terrestrial deposits (e.g., beach dunes) are disturbed by some crust¬ aceans and/or fish, the structures and textures they produce are not near¬ ly so varied and dense as those exhibited in Delmar strata.
Biogenic sedimentary structures observed in the Delmar are listed below (for detailed descriptions and photographs refer to Appendix I).
Ophiomorpha nodosa and Thalassinoides (small form=»s.f.)
Gyrollthes (small form = s.f.)
small horizontal and vertical burrows
vertical burrows with internal spreiten
vertical movement paths
dendritic burrows
collapse structures over open burrows
? Paleophycus
? Phycodes
bioturbate textures (sediment homogenized by thorough biogenic re¬
working)
The distribution of these trace fossils with respect to lithology is summarized below. Figure 17 contains explanations of terms express¬ ing relative abundance of traces. 48 Figure 17. Definitions of terms expressing relative density biogenic sedimentary structures 49
Laminated and rippled sand, sand channels -
Rare burrows.
Trace fossils (listed in order of decreasing abundance):
0. nodosa and Thalassinoides (s.f.), vertical orientations
predominant.
vertical burrows with spreiten
collapse structures over open burrows.
Interbedded sand and mud -
Rare to abundant burrows, also partial bioturbate texture (rare).
Trace fossils:
0. nodosa and Thalassinoides (s.f.), all orientations
small vertical burrows
vertical movement paths
Gyrolithes (s.f.)
chewed-through mud layers.
Cross-stratified to burrowed muddy sandstone -
Abundant burrows to partial and complete bioturbate textures.
Trace fossils:
vertical movement paths
small vertical burrows
bioturbate textures .
Bioturbated muddy sandstone and sandy mudstone -
Partial to complete bioturbate textures. A few distinct structures
(mostly mud-lined or mud-filled) overprinted on bioturbate text¬
ures.
Trace fossils:
bioturbate textures 50
0. nodosa and Thalasslnoides (s.f.), horizontal orientations
predominant
Gyrolithes (s.f.)
small horizontal barrows
vertical burrows with spreiten
? Phycodes
? Paleophycus
dendritic burrows.
Mudstone and mud-shale -
'Abundant burrows to partial and complete bioturbate textures.
Trace fossils:
bioturbate textures
vertical and horizontal burrows
0. nodosa and Thalasslnoides, without mud linings (extensions
into mud from sandstone beds).
Eroded beds of cohesive claystone -
Trace fossils:
borings.
In summary, the trace fossils in the Delmar are distributed as
follows:
(1) Laminated and rippled sands contain the simplest assemblage of
lebensspuren; the dominant form is stoutly-lined, vertically-oriented
0. nodosa (Fig. 16). The sand appears to have been deposited quickly,
under high-energy conditions.
(2) Interbedded sands and muds exhibit more diverse trace fossils
(Pi. 3A & B). The vertical movement paths, and the preservation of
physical sedimentary structures, suggest rapid sedimentation and, perhaps, 51 occasional physical reworking.
(3) Cross-stratified to burrowed sandstones (Pi. 4) exhibit in¬ creasing bioturbation upward. Apparently these units were deposited rather quickly, then invaded by burrowers from the top down during periods of non-deposition.
(4) Slow and continuous or very sporadic deposition and a favor¬ able habitat for infauna are indicated by diverse and dense traces in strata of muddy sandstone and sandy mudstone, (Pis. 7 and 8).
(5) Favored substrates for burrowers are muddy sand, interbedded mud and sand, and sandy mud. Pure mud or clay-shale and relatively clean sandstone and silty sandstone exhibit markedly fewer lebensspuren. 52
DESCRIPTION OF THE TORREY SANDSTONE
(as exposed at Solatia Beach)
Stratigraphy and General Description
At least 18 m of section in Torrey facies were measured in six locations (sections 11 - 17» Fig. 5). This figure is only approximate because the Torrey is composed of large-scale» cross-stratified sand, and thus it is impossible to correlate accurately from one section to the next. Torrey beds outcrop continuously along a 2.3 km stretch of beach between sections 11 and 17, with the exception of one location
(between sections 13 and 14) where Quaternary terrace deposits are faulted down to sea level.
A composite section of the Torrey Sandstone (Fig. 18) illustrates rock types present and the general sequence in which they occur. The lower and upper parts of the Torrey at Solana Beach are composed of broad, shallow troughs of cross-bedded muddy sandstone with mudstone lenses. Trace fossils are abundant, but overall bioturbation is not so intense that physical sedimentary structures are destroyed, in contrast with much of the underlying Delmar Formation. There are some large,
2-6 m deep channels in the Torrey that are filled with steeply dipping beds of slightly granular muddy sandstone. Burrows are rare and in some cases absent in these beds.
The stratigraphic position, lithologies, physical sedimentary struct¬ ures, and body and trace fossils in the Torrey Sandstone are consistent with deposition in estuary mouth shoals or in tidal deltas behind a barrier bar 53
C3> Ophiomorpha nodosa V . bioturbated muddy sandst £» Thalassinoides H cross-stratified sandst. 4. Gyrolithes ü sandy mudstone iSi Ardelia US mudstone 0 vertical burrows & Conostichus FIGURE 18. GENERALIZED, COMPOSITE STRATIGRAPHIC SECTION OF THE TORREY SANDSTONE AS EXPOSED AT SOLANA BEACH. COMPARE TO COMPOSITE SECTION OF THE DELMAR FORMATION, FIGURE 7 (p. 18). 54
Paleontology
The oyster reefs and shell beds characteristic of Delmar facies are not present in the Torrey Sandstone. In part this may be owing to poor preservation frequently encountered in coarse-grained, terrigenous rocks.
Certainly the trace fossils attest to an active fauna that probably in¬ cluded crustaceans, pelecypods, and gastropods (refer to section on
Biogenic Sedimentary Structures and to Appendix I).
Microfossils.
Pollen and spores, hystrichospheres and dinoflageHates were recovered from the only thick mudstone bed in the Torrey outcrops: bed
1302 (section 13, Fig. 6), a 1.8 meter-thick unit of light gray, thin- bedded, slightly sandy mudstone. The pollen and spores are from the same floral assemblage collected from Delmar strata (W. C. Elsik, 1974, pers. commun.).
Two genera of hystrichospheres - Hystrichospheridium spp. and
Hystrichokibotlum spp. - and two unidentified dinoflageHate genera were recognized. Dinoflagellates thrive in fresh, brackish, or normal marine waters. Hystrichospheres, which are secreted by dinoflagellates during reproductive or resting stages, are more limited in distribution.
With the exception of a few isolated species reported from Pleistocene sediments and Holocene environments (W. C. Elsik, 1974, pers. commun.), hystrichospheres appear to be indicative of marine conditions (Pokorn/,
1963:502).
Macrofossils.
The only macrofossils I observed in Torrey outcrops were iron- stained outlines of a few, completely leached pelecypod valves resting concave downward on an erosional surface that marks the boundary between 55
Delmar and Torrey facies. However, as stated above, the Torrey exhibits abundant lebensspuren, many of which probably were made by pelecypods, gastropods, and crustaceans. The mollusc shells either were abraded and broken by currents and waves, or they were transported into the quieter environments of the Delmar, or they have been leached.
Ostrea shells in Delmar, however, are exceptionally thick and re- sistent to leaching, so their absence in the Torrey probably indicates that they did not live in Torrey environments. Possibly they could not survive because they were repeatedly buried by rapid deposition of sand.
Sediments
Sediments of the Torrey Sandstone have a composition similar to that of Delmar sediments, except that there is less shell material and plant debris, and no coal. Texturally, however, the two formations are quite different. Torrey sediments are much coarser and are indicative of stronger wave and current activity.
Composition.
Typical minéralogie composition of Torrey sand as determined by
Kennedy (1973) is 85% quartz, 5-10% potassium feldspar (orthoclase and some microcline), 3-5% biotite, 1% plagioclase, and a trace of hematite, epidote, chlorite, zircon, tourmaline, pyroxene, and amphibole. Compo¬ sition of the Torrey at Solana Beach is very similar, but here it also contains 1-27. muscovite and a trace of metamorphic rock fragments and shell material. In addition, where channels have eroded down into clay- stone beds, clay clasts up to 30 cm across have been Incorporated into the channel fill 56
Texture.
Grain-size distributions of selected samples from the Torrey Sand¬ stone are presented in Figure 12 and in Appendix II. These analyses and my field descriptions indicate three general sediment types in the
Torrey: mudstone and mud-shale, muddy sandstone and slightly granular muddy sandstone, and slightly granular sandstone.
Mud. As in the Delmar, mud is ubiquitous as laminae and beds and in interstices between sand grains. However, there are fewer mud beds and fewer sequences of interbedded sand and mud as described from the Delmar so the total amount of fine-grained sediment is considerably less.
Mud occurs in three types of deposits: (1) intermixed with sand
(interlaminated and interstitial), (2) in thick mud beds, and (3) inter bedded with sand.
(1) In trough cross-bedded sandstones, mud appears to be concen¬ trated along inclined beds of sand (Pi. 9). This mud must have been deposited as biogenic pellets, because it is intimately associated with textures and structures indicative of high-energy depositional processes
Mud is also disseminated within the sand, either because the water was turbid and mud settled out of suspension regardless of physical energy levels, and/or because burrowers dispersed mud by mixing sandy and muddy beds and by producing mud pellets.
(2) Mud also accumulated in decimeter-thick lenses associated with
cross-bedded sands (Pi. 9), and in a single 1.8 meter-thick unit at
section 13 (Fig. 6, see also Fig. 18). These beds have very sharp,
sometimes erosional contacts with under- and over-lying sediments.
Even given the processes of mud deposition discussed above (section on
Depositional processes affecting texture, Delmar Formation), there must 57 have been major changes in energy levels or the sand would continue to migrate, preventing accumulation of extended mud beds.
These beds contain thin laminae of fine sand, including high con¬ centrations of mica, and thin laminae of silty clay. There are no foresets of mud with sand or of mud pebbles, so this material probably settled from suspension during periods of slack water when processes of sand deposition were not active. However, silt and clay were deposited simultaneously, so the clay must have settled as silt-sized floccules and/or as biogenic pellets.
(3) At one locality in the Torrey (bed 1701, see Fig. 6) there is a sequence of sand interbedded with millimeter-thick laminae and flasers of mud (Pi. 6B). This mud appears to have been deposited from suspension during periods of slack water (laminae) and, as pellets, from the tract¬ ion load contemporaneous with sand deposition (flasers), as discussed under Physical Sedimentary Structures, Interbedded sand and mud, Delmar
Formation.
Sand. The sand fraction of Torrey sediments is coarser and slightly better sorted than that of Delmar sediments. Four of the five samples analyzed are essentially unimodal in the medium sand range (1.25-1.750); two of these samples exhibit minor secondary modes of fine sand (2.25-
2.50) (refer to Fig. 12). The fifth sample is unimodal in the fine sand range. All but one sample contains some granule-sized grains.
These textural characteristics indicate that Torrey sediments were subject to stronger and more frequent physical reworking than were sedi¬ ments of the Delmar. 58
Physical Sedimentary Structures
Physical sedimentary structures are on a considerably larger scale in the Torrey than in the Delmar. Exposed in the Solana Beach outcrops are large-scale trough cross-bedding, large channels, large-scale wedge sets of cross-bedding, and a minor amount of interbedded sandstone and mudstone with flaser bedding. Most of these structures formed by migra¬ tion of channels, subaqueous dunes and megaripplesand by construction of sand lobes and bars into local depressions. There is no evidence in these outcrops for sand deposition in the wave swash zone of beaches or exposed bars. Rather, the Torrey structures are those characteristic of shoals and tidal deltas.
Trough cross-bedded sandstone.
A large part of the Torrey is composed of large-scale trough cross- bedded sandstone, illustrated in Plate 9 and Figure 19. The troughs are
5-30 m wide and 1-4 m deep; some of the sets are terminated by an erosion- al surface and/or a mud lens. Stratification has in most cases been disrupted but not destroyed by burrowers (see Pi, 13C & D); apparently
sedimentation rates were sufficiently rapid to prevent complete destruct¬ ion of bedding by infauna.
These structures probably were formed by migration of subaqueous
dunes and/or by migration and filling of channels. Both of these
processes result in deposition of curved, inclined beds in a trough¬
shaped scour. The mud lenses suggest that large-scale movement of bed
* As defined by Coleman (1969), dunes are distinguished from megaripples by size. Dunes are larger forms, with heights of 5-25 feet (1.5-7.5 m) and lengths of 140-1600 feet (42-480 m). Megaripple wave heights are greater than 10 cm (Imbrie and Buchanan, 1965:155). 59
FIGURE 19. OBLIQUE VIEW OF CLIFF FACE NEAR SECTION 13, SOLANA BEACH. LARGE-SCALE TROUGH CROSS-BEDS OF SLIGHTLY GRANULAR MUDDY SANDSTONE (TORREY SANDSTONE) ARE EXPOSED IN A SECTION PERPENDICULAR TO BEDDING. 60 forms was sporadic, perhaps related to storms or spring tides, and that mud accumulated in depressions and scours during times of less vigorous current and wave activity.
Large channels.
Four large channels are exposed in the Solana Beach sea cliffs: one cuts down into the uppermost part of the Delmar (Pi. 10); the other three erode into trough cross-bedded sandstones of the Torrey (Pis. 11A &
B and 12). These channels are 2-6 m deep and up to 80 m wide. Very coarse sand and gravel, and some claystone clasts up to 30 cm across, mark the base of the channels, which are filled with slightly granular muddy sandstone.
Host of the internal structures are on the same size scale as the trough itself; the channels are filled in down-bowed beds that follow the shape of the scour surface (Pi. 11A). Two of the channels exhibit more complex internal structures. Reactivation or reintensification of channel scour and migration is evidenced by reactivation surfaces shown in Plate 12. In the channel at the top of the Delmar (Pi. 10), megaripple cross-stratification is superposed on a larger-scale pattern of lateral channel fill.
All four channels are characterized by a unique lack of biogenic sedimentary structures (Pi. 6A) that is especially striking because surrounding sediments exhibit abundant trace fossils. This condition is in contrast to major tidal channels and inlets in Recent environments, which normally support an active infaunal population (Warme, 1971:38-39).
The channels either were created by fresh-water flow and/or they were scoured and filled very rapidly, before burrowers were able to invade the substrate 61
Possibly the channels formed after periods of high rainfall. At this time brackish water would be flushed out of the lagoon, through the sand dunes and channels of the Torrey. Scour and fill would occur quickly, perhaps in a period of a few hours or days.
Wedge-sets of cross-bedded sandstone.
Outcrops at section 11 (see Fig. 6) of wedge-sets of cross-bedded sandstone are shown in Figure 20. The sediment is slightly granular muddy sandstone; the sand fraction is better sorted (°x * 0.695, or moderately well sorted, Folk, 1968:46) than any other sand collected from the Torrey or Delmar. Like the channels,'these beds have exper¬ ienced little or no biogenic reworking.
The cross-beds appear to have been generated by sand avalanching down the back of a bar or lobe of sand. The absence of trace fossils again suggests rapid deposition, perhaps related to storm activity.
Interbedded sandstone and mudstone.
A thin sequence of interbedded sandstone and mudstone is exposed in the lower part of the Torrey, at section 17 (Figs. 5 and 6). The beds are flat-lying but are interrupted by low-angle erosion surfaces draped with mud (Pls.l3A,B and 6B). Trace fossils are abundant (Pi. 13A,B).
The mud accumulated both in millimeter-laminae and in flaser beds, as discussed above (section on Texture, Hud, Torrey Sandstone).
The interbedded sandstone and mudstone beds were deposited by much weaker currents than those responsible for much of Torrey sedimentation.
They are similar to Delmar deposits and appear to be transistional to them, as the oyster and flaser beds characteristic of Delmar facies crop out only a few tens of meters to the north, at section 18 (see Fig. 5).
Interbedded sandstones and mudstones probably accumulated in the 62
FIGURE 20. CLIFF FACE AT SECTION 13, SOLANA BEACH, EXPOSING SECTION OF TORREY SANDSTONE PERPENDICULAR TO BEDDING. WEDGE SETS OF LARGE-SCALE CROSS-BEDDED SAND¬ STONE REST CONFORMABLY ON HORIZONTAL BEDS OF BURROWED, MUDDY SANDSTONE. 63 intertidal zone, in tidal flats or in local depressions protected by shoals and bars.
Biogenic Sedimentary Structures
The Torrey Sandstone exhibits diverse and abundant lebensspuren, most of them quite different in form and size from those of the Delmar.
Complete bioturbate textures are much less common, locomotion traces such as Conostichus are much more abundant, and ichnogenera common to both formations are larger in the Torrey relative to the Delmar. These characteristics of the trace fossils assemblage reflect higher rates of sedimentation, coarser sediment, and stronger currents and waves in
Torrey environments.
Trace fossils observed in the Torrey are listed below in order of decreasing abundance (for photographs and detailed descriptions of trace fossils types refer to Plates 13 and 14 and to Appendix I).
Ophiomorpha nodosa and Thalassinoides (large and small forms)
Conostichus
surface depressions
Vertical burrows with spreiten
collapse structures over open burrows
vertical movement paths
fat, mud-lined burrow
Gyrolithes (large form =l.f.)
Ardelia
The distribution of these traces defines three distinct ichnofacies, described below: 64
Large channels -
Rare burrows (as defined in Figure 17).
Trace fossils:
A very few Ophlomorpha nodosa (l.f.) and Conostlchus
Large-scale, trough cross-bedded sandstone -
Abundant burrows to partial bioturbate textures.
Trace fossils: the most varied suite of trace fossils,
including all types listed for the Torrey except vertical
movement paths and fat, mud-lined burrows. Ophlomorpha
nodosa (l.f,)(Pl. 14B) and Conostlchus (Pis. 13C and 14C)
are particularly abundant.
Interbedded sandstone and mudstone -
Abundant burrows.
Trace fossils:
vertical movement paths
Ophlomorpha nodosa (s.f.) (Pi. 13A,B)
fat, mud-lined burrows (Pi. 13B)
As was the case in the Delmar, these lchnofacies are readily char- acterizable by a dominant lithology and suite of physical sedimentary structures. The physical processes that affect texture and structure, then, also largely govern the composition and/or behavior of the infauna.
For example, traces of vertical to oblique movement (Conostlchus, vertical burrows with spreiten) dominate the cross-bedded sands of the
Torrey, whereas a variety of mud-filled or mud-lined feeding burrows characterize Delmar sediments. Dwelling burrows such as Ophlomorpha nodosa, Thalassinoides and Gyrolithes are present in both formations, but are much larger and more stoutly-lined in the Torrey. Vertical 65 burrows with spreiten exhibit similar contrasts in size between forma¬ tions. Furthermore, several units in the Torrey contain few or no lebensspuren, while in the Delmar almost all beds exhibit some degree of biogenic reworking, as well as complete homogenization.
These differences mainly are related to more rapid sedimentation and erosion, to coarser, less cohesive substrates and to stronger waves and currents in Torrey environments relative to the Delmar. Torrey infauna were larger, stronger, more mobile, and more apt to filter feed than were their cousins in the Delmar. 66
DESCRIPTION AND INTERPRETATION OF SUBFACIES
General Setting
The features that I have described in preceding sections of this paper support Kennedy and Moore's (1971b) general conclusions concerning the stratigraphy and paleoenvironments of the Delmar Formation and
Torrey Sandstone. Their analysis can be summarized as follows:
(1) Both formations were deposited in shallow, marginal marine environments.
(2) The Delmar and Torrey are not deltaic in nature. Rather, they are elongate sand bodies deposited approximately parallel to the mid-
Eocene shoreline trend.
(3) Delmar facies developed in a protected, shoreline environment such as estuary, bay, or lagoon.
(4) Torrey facies developed as parts of a shoal or bar separating the Delmar environments landward from an open sea to the southwest.
(5) The Torrey transgressed over the Delmar through time.
These conclusions are supported by Kennedy and Moore's (1971b) stratigraphic and paléontologie observations, as well as by detailed studies conducted by me on the sediments, sedimentary structures and trace fossils. Specifically, the evidence is as follows:
(1) Stratigraphy: The Delmar Formation interfingers laterally with terrestrial deposits to the northeast; the Delmar interfingers with the
Torrey Sandstone; the Torrey interfingers laterally with marine outer shelf and bathyal environments to the southwest.
(2) Shape and size: Both formations are relatively thin, elongate sand bodies oriented approximately parallel to the mid-Eocene pattern of 67 terrestrial-to-marine facies belts.
(3) Variability: Both formations, and particularly the Delmar, are highly variable laterally and vertically. This indicates environ¬ mental heterogeneity in space and time, a feature characteristic of nearshore environments.
(4) Texture: Both formations are composed of a wide range of grain sizes, including large proportions of medium to coarse sand and some granule-sized sediment. Silt- and clay-sized particles are con¬ centrated in the Delmar; coarser sediments predominate in the Torrey.
(5) Composition: The Delmar Formation contains much land-derived plant material, including a small lens of coal.
(6) Physical sedimentary structures: As discussed in previous portions of this paper, both formations exhibit physical sedimentary structures indicating wave and current processes typical of littoral and inner sublittoral environments. Torrey structures were formed under high current velocities; Delmar structures indicate a quieter, more pro¬ tected environment.
(7) Body fossils: The Delmar Formation contains oyster reefs and an assemblage of other molluscs indicative of brackish waters.
(8) Trace fossils: Both formations exhibit trace fossils that are characteristically abundant in littoral to inner sublittoral zones (such as Ophiomorpha and Gyrolithes) and/or indicate physical processes typical of such environments.
Subfacies
Within the general, paleoenvironmental setting described above, five subfacies of the Delmar Formation and Torrey Sandstone have been recognized by me, based on sediments, physical sedimentary structures, 68 body and trace fossils. As illustrated In Figures 21-26, these sub¬ facies are as follows:
A. oyster beds
B. flaser-bedded sequences
C. fining-upward sequences
D. large-scale trough cross-bedded sandstone
E. large channeIs
The subfacies are described below and interpreted in terms of depo- sitional environments.
Subfacies A; Oyster beds (Fig. 21 and Pis. ID, 2 and 9B).
Description. The most distinctive and easily recognized subfacies are oyster beds that occur in the lower part of the Delmar Formation.
These are 15-20 cm-thick, tabular beds of concentrated mollusc shells dominated by Ostrea idriaensis Gabb in living position. The beds are tightly cemented with calcite spar; they are quite hard and form promi¬ nent, broad ledges that jut out into the modern surf zone. Each bed persists no more than a few hundred meters along strike, thinning into a stringer of broken shells along its perimeter.
Oyster beds consistently develop atop surfaces of mudstone or very muddy sandstone, but there is little terrigenous sediment within the shell beds. Muddy beds beneath oyster beds are almost structureless and probably have been thoroughly bioturbated. They exhibit a few sand- filled, cylindrical burrows approximately 1 cm in diameter (Pi. 9B).
Interpretation. The oyster beds are fossilized, in situ oyster reefs*-. They grew in a protected, low energy, shallow-water environment
*As defined by Stenzel (1971:N1041), oyster reefs are "natural accumu¬ lations of oyster shells, dead or alive, that rise above the general level of the substratum they are built on". OYSTER BED TEXTURE SHELLS a SOME SAND 111 < z> t LU ÜJ O LÜ H 3 a Z -, O ° H (/) h" cc < CD C0 H < CD ÜJ o CD (5 < CL O £ O "5 O E Z w H < LU co < -J O „j o CD m ID co co e> < E > CL > z © ° S CD ^ o W 69 CO CO O Li. CD LÜ E o co H CD CL CO < o O a © O (A 0) O D LU Ü O ea» cr H ffi — CDO H CC LU H Ul CD O CD is CD s 2 gw „h- CD 111
FIGURE 21. SCHEMATIC DIAGRAM OF SUBFACIES A: OYSTER BEDS, OF THE DELMAR FORMATION. THE BEDS ARE INTERPRETED HEREIN AS IN SITU, FOSSIL OYSTER REEFS. 70
— such as a bay, lagoon, or estuary -- that experienced broad salinity fluctuations. This interpretation is based on several lines of evidence.
(1) Many Ostrea valves are preserved articulated and in living position.
(2) The associated molluscs either are characteristic of fresh to brackish-water environments or are euryhaline (C. R. Givens, 1973, pers. commun.).
(3) Oyster beds consistently rest conformably on surfaces of mud¬ stone or very muddy sandstone. This relationship suggests biologic selectivity for substrate and energy regime, tather than hydrodynamic concentration of shells.
(4) The beds are capped by sand. Apparently the oysters were able to sweep out most fine sediment, and succumbed only when smothered by a rapidly deposited, relatively thick sand unit.
(5) According to Stenzel (1971:N1041) only coastal, brackish-water species of modern oysters form reefs. Modern reefs grow most abundantly in bays and lagoons and along tidal channels of estuaries. (Note: There are patch reefs that grow far from shore. For example, a large patch reef described by Caspers (1950) and Stenzel (1971:1048) exists in 23-28 m of water in the German Bay (or Bight) of the North Sea, 15 km from
Helgoland island and 50 km from the mainland. Salinities there are less
than 34 parts per mille. However, largely because these reefs are not intertidal, they are associated with rather broad facies belts. Sub¬
facies vary over a distance of kilometers, rather than meters, as is
the case with subfacies associated with oyster reefs in the Delmar
Formation. ) 71
Subfacies B: Flaser-bedded sequences (Fig. 22 and Pis» 2,3,6B and 8A).
Description. Closely associated with the oyster reefs in the Del- mar Formation are interbedded and interlaminated claystone, sandy mud¬
stone, and muddy sandstone. These sequences are moderately bioturbated
(rare to abundant burrows, see Fig. 17); they exhibit flaser, wavy and
lenticular bedding, planar lamination, micro-graded beds, ripple cross¬
lamination, and some medium-scale, trough cross-bedding. Abundant
carbonized plant fragments are concentrated along bedding planes, and
there is a small lens of coal.
Interpretation. Flaser-bedded sequences are tidal flat deposits
of the littoral zone. This interpretation is based on the following
observations:
(1) Flaser, wavy and lenticular bedding are common structures of
tidal flat deposits.
(2) In the Delmar Formation, flaser, wavy and lenticular bedding
are developed on both current and wave ripples, but current ripples pre¬
dominate. This is in contrast to sublittoral zones of lagoons and bays, which display chiefly oscillation ripples, and to deeper (below wave
base) environments offshore that exhibit only current ripples.
(3) Ripple cross-laminations indicate bipolar current directions.
(4) Micro-graded beds occur in pairs, suggesting tidal control.
(5) Small channels are present in this subfacies.
(6) Percent bioturbation is quite variable, but a large proportion
of these beds exhibit only rare to abundant burrows (see Fig. 12). This
indicates locally rapid deposition and/or frequent physical reworking
of the deposits. Such conditions can exist on tidal flats, in contrast
to most offshore sublittoral environments, which usually are intensely FLASER-BEDDED TEXTURE CLAYSTONE, MUDSTONE,
SEQUENCE ÜJ CO < Û CO h o Z 111 CO HI CO h o OC O ÛC CO UJ < =;oc CO _]K * CC£ UJ
FIGURE 22. SCHEMATIC DIAGRAM OF SUBFACIES B: FLASER-BEDDED SEQUENCES, OF THE DELMAR FORMATION. THE SEQUENCES ARE INTERPRETED HEREIN AS TIDAL FLAT DEPOSITS. 73 bioturbated.
Subfacies C: Fining-upward sequences (Fig. 23 and Pis. A, 5, and 6D).
Description. Fining-upward sequences comprise a third subfacies recognized in the Delmar Formation. These sequences are more variable and less well-defined than subfacies A and B, because the beds have been intensely bioturbated and their physical origins obscured. I have in¬ cluded three types of deposits in this subfacies:
(1) Approximately 1.0 m-thick beds consisting of, from bottom to top, an ero3ional surface, a tabular set of medium-scale, planar cross¬ beds of muddy sandstone o£ medium-scale trough cross-beds of muddy sand¬ stone, + ripple cross-laminated muddy sandstone, and a cap of sandy mudstone and mudstone that may exhibit millimeter-laminae of clay-shale.
BioturbatLon increases upward. These deposits are pictured in Plate A.
(2) 0.3-1.0 m-thick beds consisting of, from bottom to top, a stringer of Ostrea shells (as described under Sedimented Shell Beds, p. 44-45), bioturbated muddy sandstone, + cap of sandy mudstone (see Pi.
6D).
Fining-upward sequences include three ichnofacies described in the
section on Biogenic Sedimentary Structures of the Delmar Formation: cross-stratified to burrowed muddy sandstone, bioturbated muddy sand¬
stone and sandy mudstone, and mudstone and mud-shale. Trace fossils in
fining-upward sequences include all of the traces recognized in the
Delmar Formation (see list, p. 47 ).
Interpretation. Fining-upward sequences are polygenetic. They
were deposited on the lower parts of tidal flats and on the sublittoral
floor of the Delmar "lagoon".
Some beds in this subfacies exhibit ghosts of interbedded sandstone 74 CO co O £ ÜJ O CD CD i CO CD CO X OC LU 3 UJ CO CÛ O HH LU CO CD HH DC CO Z CVJ O ce CD CD ►-H O SUBLITTORAL TIDAL CHANNELS AND PONDS. 75 and mudstone and flaser bedding, and are probably bioturbated equi¬ valents of the tidal flat deposits described above (subfacies B). A majority of the beds, however, were deposited by migrating tidal channels. A lag deposit or erosional surface outlines the base of each channel; a cap of fine-grained sediment marks its passage. Sediments accumulating in the channel probably were originally com¬ posed of interbedded sand and mud or of sand with biogenic mud pellets. The latter sediments were deposited as tabular cross-beds on point bars or as trough cross-beds of megaripples in the channel. Channels that were relatively stable were populated by burrowers at a very early stage these deposits have been thoroughly bioturbated. Sediments deposited by rapidly migrating channels were later invaded by infauna from the surface; these are the cross-stratified to burrowed sequences. Apparently these sediments were covered by water much of the time and physical reworking was sporadic, allowing burrowers to rework large volumes of sediment. This contrasts with conditions higher on the flats where animal life was less abundant and/or physical reworking by tidal currents and storms was more frequent. Subfacies D: Large-scale trough cross-bedded sandstone (Fig. 24 and Pis. 10, 14 and 15). Description. The Torrey Sandstone as exposed in Solana Beach sea cliffs is composed mainly of coarse or slightly granular muddy sandstone in large-scale trough cross-beds. The troughs are 5-30 m wide and 1-4 m deep. Thin mud beds are also present that either follow the inclined bedding in the sand or rest on erosional surfaces. Stratification has been disrupted but not destroyed by burrowers: apparently sedimentation rates were sufficiently rapid to prevent TROUGH X-BEDDED TEXTURE SANDSTONE COARSE, MUDDY SANDSTONE MUDSTONE 0) O CL LU <0 3 CL I- 3 H LU a ■ CD h- tr O CO O < -J 1x1 CD ÜJ < (r I co ÜJ o X CD I ÜJ z CO lii CO (0 ? ® (0 Ü <3 O cc LU (5 Z O LU CO 76 < I— tr z a X CO CD 3 X O “<07 2o o uz £ UJ tu z n UJ oc FIGURE 24. SCHEMATIC DIAGRAM OF SUBFACIES D: LARGE-SCALE TROUGH CROSS-BEDDED SAND¬ STONE. THESE BEDS ARE INTERPRETED HEREIN AS DEPOSITS OF SUBAQUEOUS DUNES AND TIDAL CHANNELS ON A TIDAL DELTA OR INTERIOR SIDE OF A BARRIER BAR OR SHOAL. TORREY SS. 77 complete destruction of bedding by Infauna. The most abundant trace fossils In this subfacles are Ophlomorpha nodosa (large form) and Conostlchus. A single Gyrolithes of very large size was observed. Interpretation. Sediments in this subfacies were deposited in subaqueous sand dunes and in channels on a tidal delta or on the inshore side of a barrier bar or shoal. The physical and biogenic sedimentary structures indicate very strong waves and currents. Deep physical re¬ working, however, was not constant, as would be expected on the ocean- ward margin of a shoreline sand body, or much of the mud would have been removed. Fluctuations in energy level were provided by the tidal cycle and accentuated by some shielding from wave action. Turbid waters from the protected (Delmar) environments shoreward contributed fine sediment that settled during periods of slack water in troughs protected by dunes and in depressions of abandoned channels. Nordstrom et al. (1965) have described beds in the Torrey Sandstone, which they attribute to beach or aeolian origins, indicating that the subfacies described here is indeed a part of a barrier bar. In the Solana Beach outcrops, however, there is no evidence of subaerial expos¬ ure of these sediments, either in a swash platform or as wind-blown dunes. Subfacies E: Large channels (Fig. 25 and Pis., 6A and 11-13). Description. Large channels in the Torrey Sandstone comprise the fifth subfacies recognized in the Solana Beach outcrops. The channels are up to 80 m wide and 2-6 m deep; they are filled with slightly granu¬ lar muddy sandstone. The base of each channel is a trough-shaped scour surface marked by lag deposits of coarse sediment and mudstone clasts. These beds exhibit little or no biogenic sedimentary structures. LARGE CHANNELS TEXTURE COARSE, SLIGHTLY GRAVELLY SANDSTONE (/) O DC 0) LU a LU o x * < x 7 CD C û 7 UJ _i Û U. Û _j FIGURE 25. SCHEMATIC DIAGRAM OF SUBFACIES E: LARGE CHANNELS, OF THE TORREY SANDSTONE. THESE STRUCTURES ARE INTERPRETED HEREIN AS TEMPORARY CHANNELS GENERATED BY DRAINAGE OF THE LAGOON AFTER HIGH RUN-OFF OR SPRING TIDES. 79 Interpretation. The large channels were generated by temporary flushing of the Delmar "lagoon" after periods of high rainfall or after storms that piled up water along the coast. This interpretation is based on the following evidence: (1) Trace fossils in the channels are rare or absent. This contrasts with active tidal channels in Recent nearshore environments; they usually support a healthy population of burrowers. Large channels in the Torrey either were created by fresh-water flow or were scoured and filled very quickly, before infauna had an opportunity to settle and to penetrate the sediment. (2) Bipolar current directions are indicated by cross-beds in only one channel, pictured in Plate 12; the other three channels apparently were scoured and filled by unidirectional flow. In summary, the five subfacies that I have recognized are(see fig.26) A. oyster beds « oyster reefs B. flaser-bedded sequences = tidal flat deposits C. fining-upward sequences » lower tidal flats and sublittoral tidal channels and ponds D. large-scale trough cross-bedded sandstone « subaqueous dunes and channels E. large channels « temporary channels generated by drainage of the lagoon after high rainfall and/or storms. 80 (0 CO iH • TJ X CO X Cd TJ no a> U 3 TJ CO 0) •> U C0 p tu 4> a) cd «C TJ P O P P TJ P 6 I > co > a eu cd 43 I O) X ^ o g • cd 4-i •H (D^ d) * O <3 TJ P 43 u CO 60 I TJ /-N eu CS O x M p (0 2 O X -H P* iH • P H ClJ O I CO a. co rH * 1 » , I i 43 eu co Tl * P P P o •H 0) . QJ 43 X CS eu p TJ H P 43 P P rH a > c» Cî 43 TJ cd 60 rH »H M P P O P p 43 Cd N-/ o o * 09 Cd 60 TJ Ü CS TJ Cd P P 60 42 P P P •H M a M P *H P 09 *H p « eu * P Ü O P 43 O P 09 U CU P «H B I TJ cd o - m P rH *H 43 £ M TJ TJ C0 P 43 4-1 X 09 0) TJ > 0 P 44 U O P O •H CU 43 •H O TJ Vl 60 rH O 43 P U 43 p O M TJ TJ cd b* 43 TJ O TJ 4-1 rH rH P P MHO P CUrH 2 2 cd i •H U 3 cd O *H X p P *H *, •H eu cd eu 4J à §*3■ •-3 X > euTj 43 X 49 49 Oj P TJ Ü 09 09 •* p 44 i P 1, 1 1 rH > 1 O « 1 P • o 1 •H P rH O TJ TJ P X rH «•k 1 | 60 P P 1 u\ •H P P P u P P P TJ eu to •H « P 60 P 43 P P w 43 S-i rH o B J4 0 P 0 P 43 eu p TJ P P P p •H p U P o] M eu P •H rH P p Û P • 49 60 «H o P TJ O •H •H > rH P •H P p (U 43 P 43 2 P » •H P 44 1 P 14 p P P TJ P «H eu 43 P «% > •H a «k P P 0 rH O X O 44 49 TJ P P rH 0 X 43 •k U •H P • ££ O P P P u 43 U • A P rH P O p H • •k > P TJ 43 «P N X 43 O rH 43 P U 43 P P P rH P a P P a 43 44 P P X 43 •H 5 P 43 P 43 P P P 43 rH P *H •H <4 • • p TJ P P P )4 i TJ P 43 1 P P P U •H P P •H >4 • o P P 44 O TJ > eu O o 09 P TJ 43 X P P rH |4 rH P 43 TJ TJ 43 43 43 P w • O O 43 es X P P •H P rH P P P O P O « •H O P P P P P u * m 43 M O P 0 s *H U eu O o P eu eu P P O rH 43 O P s-/ u 43 P w p v3 » O P P O p TJ X TJ P w •H P U TJ TJ P p eu P Î5 2 M E X X p ri p 1 •» •H TJ P o O P 43 •H P O •H P 49 a O 0 • C* R TJ TJ p P d rH • p P 43 P eu M 49 «H 43 43 P O 43 «k X U p 43 cy TJ P O H 49 P TJ TJ O 60 P rH O 43 49 P |4 O P 43 rH p 43 u > >4 •• X P P 43 P p O P P M p P P u P p O p •H • •H •H P p a p o p o 09 X P P eu H P 0 43 P rH 0 eu 43 O O eu P4 43 ol P rH a 43 o 43 0 > I . I * I P > I 09 O 43 SI’S HJ cd TJ CU TJ TJ r-l 09 0) 09 09 co P rH g-H èl iu • • 43 eu a eu • H 0 d) u o CO C0 CU iH N P 43 P , J? 43 » TJ Cd eu CD H 43 Cd ‘H P TJ P P •H O * O TJ 09 M M cd H QJ 6 cd -H H o «d o rH 6 H *H P 0 £3 09 eu cd U 43 M «H Ü O P O _eu TJ P rH P O 43 43 * 43 •H C0 CO iH 60 d a) Cd 0) CO 4-1 09 P TJ O 43 U O TJ Cd 0 O 0) 3 d 44 4-4 O P • *H O * 0 P • TJ TJ • eu H O u u o d M eu co TJ P «3 > CU 4-1 P » *J ol » 0) * es eu TJ 4-1 «H o M «H cd P ■3 c • 0 o) cd es TJ 4J *H P •M «es co TJ * O § P H 43 P c o 09 •* 0 0 u cd u O C0 0) C0 09 09 p P P P 43 O * 4J *0*0) rH rH a 4-t u p £ CO 43 43 O £ 0 P 43 (U C0 U 4JH HH Q) cd eu cd o) O P •H Ü •H O P rH TJ (U 09 60 co •H rH d U H CS H H rH P P 43 U p TJ «d CS •W TJ TJ d TJ U g O 431 rH P rH M P H H u u > 43 P 43 Cd c: P d •H a> QJ 0 H 0) d) U o CU 43 0 P 2 JS 09 CO H M TJ «Û O 09 CO o eu cd eu && P P > rO 0 rH I P 0 TJ I X-H p C/9 * O P P P rH P I 43 43 C3 P «O eu p P 60 e P O f*3 rH P &g •H P P •H • P3 «H 43 U *û P 43 «3 P P 8 fi *g P. P *H P P X 43 O 43 P >-S P 6 U osa W P rH P 44 p TJ * TJ o P O P O P *H p g 2 £ Ü t) £§ P eu TJ c g p 4) P P . OOP •H *H 3-° «d *a S P * • P 43 X H eu p 43 *H P d 4-1 rH TJ 43 P TJ P 43 X H 43 *H 43 «a «a rH p P P P O 43 «O P M P K u *o O P P P § P P P P O p «H P 4J <0 S P 0 U» e S3 O rH O o eu eu eu 43 (o ja FIGURE 26. SUMMARY OF CHARACTERISTICS SUBFACIES SUB¬ SEDIMENTS J. PHYSICAL SEDI¬ BODY TRACE FACIES MENTARY STRUCTURES FOSSILS FOSSILS 81 SIGNIFICANCE AND USEFULNESS OF TRACE FOSSILS IN THIS STUDY For the general field geologist with a rudimentary acquaintance with ichnology, even very cursory observations of the biogenic struct¬ ures and textures can yield important paleoenvironmental information. First, the mere presence and abundance of trace fossils immediately characterizes the Solana Beach strata as marginal marine to marine. This is particularly helpful in the Torrey Sandstone, where macrofossils are rare or absent. Second, certain well-defined and easily recognized lebensspuren are good littoral and inner sublittoral indicators in these outcrops, namely Ophiomorpha nodosa and Gyrollthes. Although these traces also occur in deeper water deposits (Kern and Warme, 1974), their abundance and large size in the Delmar and especially in the Torrey confirm their shallow water origin. The prominent vertical orientations of 0. nodosa also support this interpretation. The entire suite of trace fossils can be used for more detailed facies analysis. Host importantly, using presence and relative abun¬ dances of the various lebensspuren, I was able to define ichnofacies that were combined with other types of observations to identify and interpret the five, major subfacies discussed above. Only one of these subfacies — the oyster reefs — could be described without reference to biogenic structures. Ichnofacies contribute significantly to the identification and interpretation of the other four subfacies. The trace fossils and bioturbate textures were also used to estimate relative rates of sedimentation and/or physical reworking. For example, 82 in the large channels of the Torrey the lack of traces indicates very rapid scour and fill — an important clue to the origin of the struct* ure. Contrasts between trace fossils of Delmar facies (subfacies B and C) versus Torrey facies (subfacies D and E) are particularly distinct¬ ive and emphasize the differences between the two formations. As illustrated in Figure 27, the Delmar traces are dominated by Fodinichnia and Domichnia, and bioturbation is much more intense overall compared to the Torrey. Traces in the Torrey Sandstone are chiefly Repichnia and Domichnia; there is less bioturbation overall. In addition, Ophiomorpha nodosa and Gyrolithes in the Delmar are smaller and less thickly lined than the same ichnogenera in the Torrey. Horizontal orientations of 0. nodosa and Thalassinoides are more common in the Delmar, while vertical orientations predominate in the Torrey. These observations indicate that the Delmar facies generally were characterized by lower current velocities and more stable, muddy sub¬ strates rich in organic matter. Therefore feeding burrows constructed by vagile and sessile animals mining the sediment for food are very common, and populations of infauna are denser, as predicted by Purdy (1964) based on studies of Recent animal/substrate relationships. In contrast, the Torrey lebensspuren suggest higher current velocities, unstable, shifting substrates, and less organic matter in the sediment. Therefore the burrowing fauna were dominated by vagile infauna, particularly suspension feeders. The crustacean burrows appear to have been constructed by large, strong species that lived deep in the sediment to avoid exposure by erosion. They built long, vertical DELMAR FORMATION TORREY SANDSTONE DOMICHNIA + FODINICHNIA + REPICHNIA CUBICHNIA Ü PARTIAL TO COM- PLETE BIOTUR- BATE TEXTURES4 U LEGEND SCALE: □ = PRESENCE OF ONE TRACE FOSSIL TYPE. (FOR EXAMPLE, FOUR DOMICHNIA TRACES ARE PRESENT IN THE DELMAR FORMATION -- OPHIOMORPHA NODOSA AND THALASSINOIDES, GYROLITHES, VERTICAL BURROWS WITH SPREITEN, AND BORINGS IN CLAYSTONE — SO THE BAR IS FOUR SQUARES LONG.) + INDICATES MARKED ABUNDANCE OF TRACE FOSSILS IN THAT ETHOLOGIC GROUP * SUBJECTIVE ESTIMATE OF RELATIVE FREQUENCY OF PARTIAL TO COMPLETE BIOTURBATE TEXTURES IN THE DELMAR FORMATION VERSUS THE TORREY SANDSTONE. SUCH TEXTURES ARE APPROXIMATELY FOUR TIMES AS ABUN¬ DANT IN THE FORMER AS IN THE LATTER. FIGURE 27. COMPARISON OF DISTRIBUTIONS OF ETHOLOGICAL CLASSES OF TRACE FOSSILS IN THE DELMAR FORMATION AND TORREY SANDSTONE. DOMICHNIA (DWELLING BURROWS) AND FO- DINICHNIA (FEEDING BURROWS) ARE MOST DIVERSE AND ABUN¬ DANT IN THE DELMAR FORMATION; THE TORREY SANDSTONE IS CHARACTERIZED BY DOMICHNIA AND REPICHNIA (LOCOMOTION TRACES). 84 burrows to the surface; therefore vertical orientations are more common in the Torrey. The above are very broad generalizations and do not apply to all parts of the two formations. For example, in the Delmar Formation there are a few beds of laminated sand that exhibit vertically oriented Ophiomorpha nodosa and some Repichnia, but very little bioturbation overall. Apparently the sands were deposited under high current veloc¬ ities such as those characteristic of Torrey facies. Another example can be found in section 17 of the Torrey Sandstone. A sequence of interbedded sandstone and mudstone is present there that exhibits trace fossils similar to those characteristic of Delmar subfacies B (flaser- bedded sequences). The trace fossil assemblages, then, are very sensitive even to short-term changes in the depositional environment. 85 CONCLUSIONS (1) The Delmar Formation and Torrey Sandstone are elongate sand bodies that were deposited in nearshore environments oriented parallel to the mid-Eocene shoreline trend. (2) The Delmar Formation, as exposed at Solana Beach, is composed of deposits of a shallow lagoon bounded on its landward side by tidal flats and oyster reefs in the intertidal (“littoral) zone, and on its seaward side by deposits of the Torrey Sandstone. (3) The Torrey Sandstone, as exposed at Solana Beach, formed largely as subaqueous dunes and channels on an interior tidal delta or on the interior margin of a barrier bar or shoal. The Torrey sand body enclosed and separated the Delmar lagoon from an open ocean to the southwest. (4) The presence of abundant biogenic structures in the Solana Beach outcrops is a reliable, easy-to-use indicator of marginal marine to marine conditions. (5) The full suite of trace fossils can be employed to define ichnofacies that appear to be very sensitive to depositional environ¬ ments. These ichnofacies contribute significantly to recognition and interpretation of four of the five subfacies listed below. (6) The abundant trace fossils Ophiomorpha nodosa and Gyrolithes appear to be good indicators of littoral and inner sublittoral environ¬ ments in the formations studied; Gyrolithes is especially common in brackish environments of the Delmar lagoon. (7) The size and wall thickness of both Ophiomorpha nodosa and Gyrolithes vary directly with the strength of waves and currents. In 86 addition, vertical orientations of 0. nodosa/Thalassinoides predominate in cross-bedded and planar laminated sandstones indicative of a shift¬ ing, unstable substrate and relatively high current velocities. Horizontal orientations are common in muddy sediments that provided a more stable substrate in a quieter wave and current regime. (8) Traces of vertical migrations of vagile infauna (Repichnia, such as Conostichus and the vertical movement paths described in this paper) are most abundant in the Torrey Sandstone. They are good indi¬ cators of frequent, rapid erosion and sedimentation characteristic of littoral and inner sublittoral environments. (9) Feeding burrows and traces left by vagile deposit feeders and sessile suspension feeders (Palaeophycus, Phycodes, small horizontal and vertical burrows) are more common in muddy sediments of the Delraar Formation. These indicate lower current velocities and more abundant organic matter in the sediment relative to the Torrey sands. (10) Five major subfacies can be identified in the Solana Beach outcrops based on sediments, physical sedimentary structures, body fossils and trace fossils; they are as follows: Subfacies A. oyster beds = oyster reefs Subfacies B. flaser-bedded sequences «* tidal flat deposits Subfacies C. fining-upward sequences « lower tidal flats and sub-littoral tidal channels and ponds Subfacies D. large-scale trough cross-bedded sandstone « subaqueous dunes and channels Subfacies E. large channels « temporary channels generated by drainage of the lagoon after high rainfall and/or storms 87 REFERENCES CITED Allen, J. R. L. (1965) A review of the origin and characteristics of recent alluvial sediments. Sedimentology. ,5:89-191. Andrews, H. N., Jr. (1961) Studies in Paleobotany. John Wiley and Sons, Inc. New York: 487 p. Bandy, 0. L. (1960) General correlation of foraminiferal structure with environment. International Geological Congress Session 21. Norden, Copenhagen. Part 22:7-19. Blake, W. P. 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Grant, IV (1944) The geology and paleontology of the marine Pliocene of San Diego, California. Part 1, Geology. San Diego Society of Natural History Memoir 2; 72 p. 98 APPENDIX I TRACE FOSSILS Method of Study Torrey and Delmar sediments are poorly lithified and trace fossils readily fall apart during attempts to excavate large samples, so most of the descriptive data were recorded in the field by draw¬ ings and photographs. A few samples of lebensspuren were painstak¬ ingly carved from the outcrop and transported to the laboratory. Most of these were impregnated under vacuum with a polyester resin thinned with acetone. I used the following resin mixtures: (1) 1 part acetone 4 parts A-l polyester resin* 20 drops catalyst per pint resin (catalyst* = 607» MEK peroxide in dimethyl phthalate) (2) 1 part acetone 4 parts NATCOL NL-410 polyester resin** 64 drops catalyst per pint resin (catalyst** = #263 for polyester resin) * A-l Plastics, Houston, Texas ** NATCOL Crafts Inc., Redlands, California The second mixture dried much clearer and harder and without cracks. After impregnation samples could be sliced. In order to make thin sections or polished slabs still another procedure was necessary. Slabs were thoroughly dried and heated to 99 about 100°F, then painted with a thin coat of epoxy (one part Versamid 140 Polyamide to three parts R-815 Resin, both manufactured by Ring Chemical Co., Houston, Texas). These samples were heat-cured, then pol¬ ished and each used either "as is" for study under a reflected light microscope or further cut and polished to make a thin section. 100 Descriptions of Trace Fossils Trace fossils are evidences of activity of an organism in or on a substrate such as sediment or rock; they include tracks, trails, burrows, borings and coprolites. The term trace fossil is used syneno- mously in this report with "trace" and "lebensspur" (pi. lebensspuren), a German noun meaning literally "life trace". At Solana Beach, outcrops of the Torrey Sandstone and Delmar Formation reveal a plentiful and diverse assemblage of trace fossils. Body fossils in general are poorly preserved, so the traces constitute a particularly valuable source of paleoecological information. I have grouped the lebensspuren ethologically, following the classi ficatory scheme proposed by Seilacher (1953). Seilacher's scheme is relatively simple and well-defined, and it recognizes gradational rela¬ tionships between trace fossils and body fossils and between his five classes of behavior. A behavior-based organization was adopted because, in my study area, (1) progenitors of the various trace fossils cannot be precisely identified, and (2) as a result of (1), faunal behavior as recorded by lebensspuren appears to be more sensitive to differences in depositional environments than is the gross composition of the burrow ing fauna. My approach to naming trace fossils has been generally conservative It is well known that similar traces are made by different organisms, and that a single organism can produce widely varying traces. As a result there is an unnecessary and confusing proliferation of names in ichnological literature. It is also generally true, however, that "trace fossils must be named to survive" (Osgood, 1970:295). Therefore 101 In this study traces which do not fit readily into previously described and named ichnogenera will wherever possible be assigned to the ichno- genus I feel most closely resembles it. The descriptions that follow apply only to the trace fossils as they appear in Solana Beach outcrops; each synopsis is merely a summary description of that form and is not intended as a définition of the ichnogenus or ichnospecies. 102 Domichnia. Domichnia (after the Latin domus, meaning house or home) are dwel¬ ling burrows of benthic infauna. Generally they are tubes of various configurations. Domichnia serve as a more or less permanent home for filter feeders, predators and scavengers, thus the sides of the burrow may be fortified by some kind of lining or wall structure. Torrey and Delmar representatives are interpreted herein as mostly dwelling burrows of crustaceans and pelecypods. OPHIOMORPHA LUNDGREN 1891 OPHIOMDRPHA NODOSA LUNDGREN 1891 and THALASSINOIDES EHRENBERG 1944 Reference. For extensive synonomy and discussion refer to II Kennedy and McDougall (1969), Hantzschel (1952:145), and Chamberlain and Baer (1973) . 1 Synopsis. Cylindrical, branching dwelling burrow with smooth inner surface and nodose exterior. Each burrow wall is constructed from a single layer of roughly equant balls of mud and fine sand. The burrows divide in side- or Y-branches, usually at an angle of 90-120°. Burrows are observed in all orientations from horizontal to vertical, and can extend at least 1-2 m. in length. *0. nodosa may have served' in part as a feeding burrow (Fodinichnia). The modern ghost shrimp Callianassa major is a deposit feeder, so it digs through the sediment both to find food and to construct a burrow. However, the lined part of its burrow (Ophlomorpha) is kept open and occupied by the organism; therefore I have classified it as being predominantly a dwelling burrow. 103 104 105 FIGURE 30. WALL STRUCTURE OF OPHIOMORPHA NO¬ DOSA, SHOWN IN DRAWING OF SECTimfTUT'TO'AUTEL TTrTENGTH, BUT NEAR PERIPHERY, OF THE BURROW. WALL IS COMPOSED OF PELLETS OF DARK GREEN SANDY MUD; SOME OF THESE EXHIBIT A CORE OF LIGHT GREEN MUD. INNER DIAMETER OF BURROW (EX¬ CLUDING WALLS) = 2.5 CM. 106 Ophiomorpha nodosa, small form Plates 7A & B and 8 Figures 16 and 28 Discussion. 0. nodosa (small form)are common trace fossils in highly bioturbated muddy sandstones of the Delmar Formation. Inner diameters of the burrows range from 0.8 to 2.0 cm (average about 1.0-1.5 cm); pelleted walls are 0.2-0.5 cm thick (average 0.3 cm). o Burrows branch at 90-120 angles, and form extensive horizontal net¬ works up to one meter in length, Burrows are observed in all other orientations as well, however. The pelleted burrow (Ophiomorpha) is continuous with a branching, non-nodose, mud-lined burrow known as Thalassinoides; the two traces probably were constructed by the same animal and thus are considered together in this paper. Where pelleted, the burrow wall is composed of balls of greenish sandy mud. Non-pelleted parts of the wall are composed of similaf material but are somewhat thinner (about 2 mm). This trace clearly fits the descriptions of 0. nodosa as given by Lundgren (1891) and HSntzschel (1952 and 1962:W205-W206). Ophiomorpha nodosa, large form Plate 15B Figures 29 and 30 Discussion. Large, sturdily-built 0.nodosa are abundant in trough cross-stratified, muddy sandstones of the Torrey Sandstone. Inner diameter of the burrow ranges from 2.5 to 5.0 cm; walls are 0.5-1.5 cm thick. All parts of a burrow system are of similar size; there is no distinctive "main shaft". Ophiomorpha nodosa (large form)are preserved in full relief. 107 The mud In the wall Is more resistant than the surrounding sand, so It weathers In positive relief on an exposed surface. The tubercles which make up the wall are composed of green mud and some sand-sized flakes of mica. Some pellets possess a rudimentary internal structure, as shown in Figure 30: mica flakes are oriented parallel to the outer surface, and there is an inner core of finer green sediment, possibly pure clay. This trace also fits the definition of Ophiomorpha nodosa as given by Lundgren (1891) and Hantzschel (1952 and 1962:W205-W206). Interpretation (of both small and large forms). Burrows of similar geometry and structure are presently made by at least two species of the decapod crustacean genus Callianassa; C. major Say (Weimer and Hoyt, 1964; Frey and Mayou, 1971) and C. biformis (Hertweck, 1972:136-137). Both species occur in the nearshore environ¬ ment of the Georgia coast, but C. major thrives in the higher energy foreshore, and its.burrow systems are considerably sturdier and more extensive than those of C. biformis, a characteristic inhabitant of the upper offshore (Hertweck, 1972*136,150-151,154-155). Thus it seems quite likely that 0. nodosa (large form)of the Torrey Sandstone and 0. nodosa (small form)of the Delmar Formation were constructed by two species of a genus of fossorial shrimp, possibly Calliannassa. The known geologic range of Callianassa is upper Jurassic (Rathbun, 1926) or lower Cretaceous through Holocene (Glaessner, 1969); 0. nodosa is Permian to Holocene (Chamberlain and Baer, 1973). GYROLITHES SAP0RTA 1884 Plate 7C & D Figures 31-34 108 Reference. For extensive bibliography and discussion of the environmental significance of Gyrolithes, refer to Gernant (1972). Synposis» Full relief dwelling burrow that is loosely coiled, dextrally or sinistrally, and is oriented upright (i.e., coil axis vertical). The shaft is roughly circular in cross-section and has a smooth mud wall. Discussion. Gyrolithes is a common trace fossil in heavily bioturbated muddy sandstones of the Delmar Formation. It is much rarer in coarser, cross-stratified Torrey sandstones: only a single example, of abnormally large size, was found there. The Delmar specimens are all very similar in size and morpho¬ logy, varying mostly in wall thicknesses, which range from 0.1-1.5 cm. Coil and shaft diameters, 2.0-3.5 cm and 0.5-1.3 cm, respectively, remain nearly constant throughout the length of the coil (for defi¬ nitions of terms refer to Fig. 31b). All observed specimens have 4-5 coils within a-coiled section 4.0-13.0 cm long. The lone Gyro¬ lithes observed in Torrey sediments is considerably larger than those previously described. They are very similar geometrically, however. Several more completely preserved specimens exhibit access shafts similar in size and structure to the coiled part of the shaft. Vertically oriented, sometimes branching access shafts connecting to the upper end of the coiled shaft are preserved in the individuals illustrated in Figures 32, 33, and 34a-c. The horizontal, lower access tube is less well preserved (Fig. 34c & d). Enlargement of the lower¬ most coil and a pronounced lateral flair are all that remain of this structure in most specimens. The wall of the shaft has smooth inner and outer surfaces and 109 SOURCE LENGTH COIL SHAFT COILS (CM) DIAMETER DIAMETER PER 10 (CM) (CM) CM LENGTH DELMAR FORMATION 4.0-13.0 2.0-3.5 0.6-1.3 av. 6.6 TORREY SANDSTONE 35.0 12.5 3.5 1.1 ALL OTHER* 7.4-60.0 2.5-5.0 1.0-1.8 2.0-4.5 (1 speci¬ men 36 cm long) FIGURE 31a. TABLE OF DIMENSIONS OF GYROLITHES FROM THE MID- EOCENE DELMAR FORMATION AND TORREY SANDSTONE AND FROM OTHER LOCALITIES. *DERIVED. FROM MEASUREMENTS OF OVER 400 SPECI¬ MENS OF GYROLITHES FROM NORTH AMERICA AND EUROPE, MIOCENE TO CRETACEOUS IN AGE (VARIOUS AUTHORS, SUMMARIZED IN TABLE 1 OF GERNANT, 1972). DIAMETER FIGURE 31b. SCHEMATIC DIAGRAM OF GYROLITHES ILLUSTRATING MORPHOLOGIC TERMINOLOGY. MODIFIED FROM GERNANT (1972: TEXT-FIG. 1). 110 is composed of dark green mud with some fine sand. Wall thicknesses range from 0.1-1.5 cm, averaging 0.2-0.3 cm. Gyrolithes was constructed infaunally and is preserved in full relief. It is visible chiefly because of color contrasts between the darker green mud wall and the lighter brown- to gray-green sandy matrix. Most Delmar Gyrolithes are separated by a decimeter vertically and several meters laterally. They are not evenly distributed, however; there is some tendency to "group" within a single bed or series of 2-3 adjacent beds for a distance of several meters along the outcrop. Gyrolithes as it occurs in the Delmar Formation and Torrey Sandstone is quite similar in shape and structure to the Gyrolithes described by Gernant (1972). The Delmar specimens are shorter and smaller, however, as demonstrated in Fig. 31a. Interpretation. Stanton and Warme (1971) observed Gyrolithes leading into an irregular, branching burrow system which they feel was constructed by a decapod crustacean. Other workers (Kilpper, 1962; Keij, 1965; Kennedy, 1967; C. T. Siemers cited in Gernant, 1972) have observed Gyrolithes leading into Ophiomorpha and/or Thalassinoides. This suggests that, like Ophiomorpha and Thalas- sinoides, Gyrolithes was constructed by a burrowing crustacean. This interpretation is supported by various aspects of the size, geometry, occurrence, and structure of Gyrolithes - subjects which have been extensively discussed by Gernant (1972:736-738). Gyrolithes from Solana Beach outcrops occur with well-developed Ophiomorpha nodosa and Thalassinoides. The burrow shafts of all three ichnogenera have approximately the same diamter and shape, and all possess some kind of mud wall. Moreover, the same size Ill FIGURE 32a,b. GYROLITHES FROM THE DELMAR FORMATION, VERTICAL EXPOSURES. BLACK - SiûOÎH WALL OF DARK GREEN MUD. 112 FIGURE 33a,b. GYROLITHES FROM THE DELMAR FORMATION, VERTI¬ CAL EXPOSURES. BLAW-""SMOOTH WALL OF DARK GREEN MUD. BOTH SPECIMENS EXHIBIT A VERTICAL, UPPER ACCESS SHAFT; THE LATERAL" FLAIR OF THE LOWERMOST COIL OF 33a HINTS OF A HORIZONTAL, LOWER ACCESS SHAFT. 113 FIGURE 34a-d. GYROLITHES FROM THE DELMAR FORMATION, VERTICAL EXPOSURES. BLACK » SMOOTH BURROW WALL OF DARK GREEN MUD. SPECIMENS 34a-c EXHIBIT VERTICAL, UPPER ACCESS SHAFTS; HORI¬ ZONTAL, LOWER ACCESS SHAFTS ARE PRESERVED IN 34a and d. ALL SPECIMENS LIFESIZE. 114 contrast that was noted in Torrey versus Delmar Ophlomorpha nodosa is imitated in Gyrolithes from the two facies. The cylindrical, sometimes branching, mud-walled access shafts of Gyrolithes may easily be described as Thalassinoides, and 0. nodosa was observed grading into Thalassinoides in a Delmar bed (Pi,. 7A & B and Fig. 28)» Thus, although no direct connections were observed between Gyrolithes and the two branching burrow systems, it is likely that they were constructed by the same or very similar organisms. It is not clear from specimens in Torrey and Delmar sands alone, however, whether Gyrolithes represents the behavior of a related but different organism, or a special behavior exhibited under particular conditions by the same organism. Direct connections between the traces have been observed by other workers, as noted above, and this supports the "special behavior" hypothesis. FAT, MUD-LINED BURROWS Plates 6D and 14B Synopsis. Simple, non-branching (?) dwelling burrow with a mud wall, that has a smooth interior surface and a rough, irregular exterior. The burrow is obliquely oriented. Discussion. A few examples of this lebensspur were observed in interbedded sandstone and mudstone in the Torrey facies, section 17 (Fig. 5) . The burrow penetrates downward at least 18 cm; the inner diameter is about 4-5 dm and the mud wall is 1 cm thick. The burrows appear to be relatively shallow and extend obliquely downward from an erosional surface draped with mud. Possibly they are parts of J- shaped or U-shaped burrow systems. 115 These burrows are most similar to Ophiomorpha nodosa (large form), but are not classified with them because (1) the mud wall is irregular but not distinctly nodose; (2) no branchings were observed. Interpretation. Burrows that are of like orientation and size are constructed by modern crabs such as Ocypode quadrata and Uca pugilator (Frey and Howard, 1969:P1. 3, Fig. 4; Frey and Mayou, 1971: 58-65), but these animals do not construct mud walls. The mantis shrimp Squilla also constructs a large, obliquely-oriented burrow. Squilla burrows are mud-lined in sandy sediment, and branch (Frey and Howard, 1969:Pl. 4, Fig. 2; Hertweck, 1972;136). There are too few examples of fat, mud-lined burrows to define their true geometry. However, because of the size and mud lining, they are most likely to have been constructed by burrowing crustaceans. VERTICAL BURROW WITH SPREITEN Plate 14D Figure 35 Synopsis♦ Full relief dwelling burrow and locomotion trace that is a vertical or nearly vertical, rarely branching tube with hori¬ zontal, concave upward spreiten inside. Discussion. Vertical burrows with spreiten are common traces in muddy sandstones and in interbedded sandstone and mudstone of the Delmar facies, and in cross-bedded sandstone of the Torrey. They are a few centimeters to 17-20 cm long and 0.7-1.5 cm wide; the spreiten are at least 0.3 cm apart vertically. The burrows are preserved in full relief. Some specimens are accented by diagenetic iron or by slight color contrasts between the inside of the burrow and the sediment matrix. 116 I have not yet found a suitable established Ichnogenus to which this trace fossil can be assigned. ft Interpretation. Schafer (1972) has described similar structures produced by the burrowing anemone Cerianthus and by a burrowing lamelli- branch (Fig. 35b & c). Both organisms occupy a cylindrical burrow. Movement of bivalve siphons smooths and compresses the burrow walls; Cerianthus lines its burrow with grains uselectively acquired from the surrounding sediment. In response to moderate sedimentation either animal can migrate upward, leaving a digging core of crescent-shaped layers as small amounts of sediment settle to the bottom of the dwelling tube. Layers of the burrow fill are unrelated to stratification of the surrounding sediment. Similar structures can also be formed by inroganic filling of an open burrow, leaving meniscus-like laminae. Several of the Delmar traces are surrounded by thoroughly bio- turbated, structureless sediment. Thus the burrow must have been occupied and kept open while the surrounding sediment was occupied by various burrowers; it was abandoned close to the time when other infauna also migrated upward in response to sedimentation. BORINGS IN CLAYSTONE Plate 5 Reference. Frey and Howard (1969:435, Pi. 4(3) and Table 1). Synopsis. Roughly cylindrical, non-branching tubes that penetrate downward from the eroded, irregular, upper surface of a claystone bed. The tubes are filled with sediment from an overlying bed. Discussion. The tubes are circular in cross-section and measure 117 - 1 CM 30 CM FIGURE 35. (a) VERTICAL BURROWS WITH SPREITEN IN MUDDY SANDSTONES OF THE DELMAR FORMATION. (b) DWELLING BURROW OF THE ANEMONE CERIANTHUS. SPREITEN ARE CREATED AS SEDIMENT FILLS IN THE BURROW AND THE ANIMAL MIGRATES SLOWLY UPWARD. REDRAWN FROM SCHÂFER (1972: FIG. 165). (c) BIVALVE CREAT¬ ING A "DIGGING CORE" (VERTICAL BURROW WITH SPREITEN) BY MIGRATING UPWARD THROUGH BEDDED SEDIMENT. REDRAWN FROM SCHAFER (1972 : FIG. 223). 118 1.0-1.5 cm in diameter. They are densest near the upper surface of the bçd; a few tubes extend 15 cm downward to its lower, gradation contact with underlying strata (Pi. 5C). The tubes are predominately vertical, but they also curve gently and exhibit all orientations. The tubes do not appear to branch or to cross-cut one another. Interpretation. These structures were open tubes that were filled only when the overlying bed was deposited. The claystone in which they occur was exposed by waves and/or currents as a stiff, cohesive bed; this is evidenced by the irregular, eroded upper surface and by clay- stone clasts in an overlying lag deposit (PI. 5A,B). Because the tubes also penetrate downward from that surface, they probably were excavated when the clay was stiff and cohesive. Therefore they are borings, rather than burrows. Similar holes are present in exhumed claystones and mudstones on the Georgia coast. As described by Frey and Howard (1969:435), the tubes are vertical borings excavated by pelecypods such as Petricola pholadiformis and Cyrtopleura costata. In addition, polychaetes and small decapods reoccupy old burrows preserved as cavities. Borings in the Delmar Formation differ slightly in geometry from the Georgia example; the Eocene borings are chiefly but not entirely vertical. However, like the Georgia borings they are simple, non¬ branching tubes excavated in a cohesive, but not lithified, clay or mud. The tubes in the Delmar Formation, then, are also considered to be borings, probably excavated by suspension-feeding pelecypods. 119 Fodinlchnla. Fodinichnia (from the Latin fodere, meaning to dig) are feeding burrows, produced by vagile infauna that are mining the sediment for nutrients. Fodinichnia may also serve as permanent or semipermanent dwelling burrows for the organism producing them (Osgood, 1970:298), Fodinichnia in the Solana Beach outcrops are predominently sinuous, unlined burrows and mud-filled, bundled tubes. ?ARDELIA CHAMBERLAIN AND BAER 1973 Figure 36 Reference. The only published reference to this ichnogenus is Chamberlain and Baer (1973), in which the new ichnogenus-sp. Ardelia socialia is established and described from the Permian Cedar Mesa Sandstone of Utah. A very similar lebensspur was described from the Sparnacian (uppermost Paleocene) of England by Kennedy and Sellwood (1970:108) but was not named. Synopsis. Small, branching, mud-filled burrows arising from larger burrows and covering them densely. Discussion. Ardelia is a rare trace fossil in trough cross- stratified muddy sandstones of the Torrey Sandstone. The few specimens observed are associated with Ophiomorpha nodosa,(large form). The small tubes are cylindrical and 0.2-0.4 cm in diameter. They arise from a large shaft which appears to be 2-4 cm wide, and which is probably continuous with O. nodosa. The small tubes extend several centimeters out from the main shaft, and some branch in a broad Y (Fig.36 a). Ardelia are full relief burrows filled with dark green mud. 120 . :J?ù . - • . ' . • ' / i'!/ ■ * ' .• • • . /• ■• V : * 10 CM FIGURE 36. (a) ARDELIA IN CROSS-BEDDED MUDDY SANDSTONE, TORREY SANDSTONE. THE MUD-FILLED, SECONDARY GALLERIES ARE CONCENTRATED ALONG THE PERIPHERY OF A LARGE, SAND- FILLED BURROW, (b) RECONSTRUCTION OF ARDELIA SOCIALIA CHAMBERLAIN AND BAER FROM THE PERMIAN ÜFD'ÀR' MESA "SANDSTONE OF UTAH. FINE STIPPLE IN ENLARGED CROSS-SECTIONS REPRESENTS INCREASED CONCENTRATION OF DIAGENETIC IRON TOWARDS CENTRAL GALLERY AND RADIATING TUBES.(FROM CHAMBERLAIN AND BAER, 1973: TEXT-FIG. 5.) 121 The Torrey trace, though generally similar to Chamberlain and Baer's (1973) Ardelia socialia in shape and occurrence, differs from the type species in several respects. For this reason only the generic name is applied here. A. socialia from the Cedar Mesa Sand¬ stone are neither lined nor filled with mud — this despite the fact that they are found in association with classical, mud-walled Ophiomorpha nodosa (Chamberlain and Baer, 1973:79). The Utah, England, and California traces are approximately equal in size. In Utah speci¬ mens, however, the secondary galleries are rather simple, non-branching radial bifurcations from the central gallery (Fig. 36b). The lebens- spuren described by Kennedy and Sellwood (1970:108) and in this report exhibit more complex tubes which bend, curve, and branch, and occasional¬ ly return to the main shaft. Nevertheless, the Torrey lebensspur is more like Ardelia socialia than any other named ichnospecies or ichnogenus, so the name Ardelia will be applied to the California specimens. Interpretation. L. F. Braithwaite (1971, pers. commun to Baer, cited in Chamberlain and Baer, 1973:88) suggested that A. socialia might have been constructed by a crustacean stuffing fecal material into the walls of its burrow. Chamberlain and Baer observed that would have required a tremendous amount of feeding activity, and sug¬ gested instead that A. socialia could be attributed to "radial probing by a deposit feeding organism". Discussing the Paleocene lebensspuren in England, Kennedy and Sellwood (1970:108) felt that the secondary galleries must represent the activity of a small, vermiform animal that either lived commensally with the organism responsible for the main shaft (probably a decapod crustacean), or adopted the 122 the empty burrow after Its abandonment. As noted above, secondary galleries in the Paleocene and Eocene specimens are rather complex, an observation that strongly supports the latter interpretation. Thus they are probably Fodinichnia -- feeding burrows of a small, deposit feeding animal. ?PHYCODES RICHTER 1850 Plates 9C & D, Figures 37-40 Reference. For partial synonomy and discussion, refer to Osgood (1970:341-343). Synopsis. A bowl-shaped grouping of mud-filled tubes. The tubes are bundled together and are indistinguishable near the base and center of the bowl, but separate as they extend outward and upward with concave-upward curvature. Preserved in full relief; probably a feeding burrow. Discussion. These traces are rare and very limited in distri¬ bution within the Delmar Formation: they occur only in a single meter- thick bed, for about 30 m along strike. Within this rather small area of vertical exposure there are at least 22 individual specimens of highly variable morphology. Individuals range in shape from nearly circular (PI. 8D and Fig. 37) to oblong (Pi. 9C and Figs. 38 and 39a), and are from 6 cm to 15 cm wide. The height of the trace is defined as the distance from the lowest point on the base of the bowl to the highest point reached by any one branch (see Fig. 38), and averages 5-6 cm. The mud-filled branches are roughly circular in cross-section and about 2 mm in di¬ ameter, but in general they do not have well-defined boundaries. J^IGHT GREEN MUDDY SAND 123 FIGURE 37. (a) PHYCODES IN MUDDY SANDSTONE, EXPOSED ON A VERTICAL OUTCROP SURFACE, (b) VERTICAL SECTION CUT PARALLEL TO EXPOSURE SURFACE. PURE MUD IS CONCENTRATED IN THE INNER PART OF THE MAIN BRANCHES; SANDY MUD IS PUSHED TO THE PERIMETER. THE BRANCHES EXTEND UPWARD TO A SURFACE OF COLOR CHANGE (ORANGE TO LIGHT GREEN) THAT IS PARALLEL TO BEDDING. LIFESIZE. 12U WIDTH OF BOWL HEIGHT BASE OF BOWL LENGTH OF STEM LIFESIZE FIGURE 38. PHYCODES IN VERTICAL SECTION, ILLUSTRATING MORPH¬ OLOGIC TERMINOLOGY. BLACK = DARK GREEN MUD AND SANDY MUD. 125 They are distributed with no apparent symmetry, with the exception of a few individuals that exhibit rough radial symmetry in the horizontal. Two specimens, one of them shown in Figure 38 , were observed to possess short, cylindrical stems about 1.5-2.5 cm in diameter and up to 5 cm long, extending vertically downward fromthebase of the bowl and also filled with dark green, sandy mud. The traces are preserved in full relief within a single bed of micaceous, highly bioturbated muddy sand. All specimens observed are within 30 to 60 cm of the top of the bed, and are spaced at least 30 cm apart laterally. They are filled with dark green, slightly sandy clay, and weather in positive relief on the exposure surfaces. In one specimen the lining of a bundle of tubes is composed of dark green, sandy mud; the interior of the filling is composed of almost pure clay (Fig. 39b). In another example, some of the mud fill appears to be in roughly ovoid pellets about 0.2-0.5 mm long. I have not yet recognized similar trace fossils in the literature, and assign them to the ichnogenus Phycodes with some reluctance. Phycodes has been defined by Osgood (1970:341) as follows (refer to Fig. 39b) : "Horizontal bundled burrows of infaunal origin preserved out¬ wardly as convex hyporeliefs. Overall pattern flabellate, broora- • like, or occasionally circular. Some forms consist of a few main branches showing a Spreite-like structure which distally gives rise to numerous free branches. In other forms the Spreiten are lacking and branching tends to be more random. Individual branches are terete and finely annulate or smooth. Length of entire burrow 2.5-15.0 cm..." Free branches of topotypes of the type species, Phycodes circinatum, have an average diameter of 1.3 cm (Magdefrau, 1934); those of Phycodes flabellum described by Osgood (1970:344) are 1-3 mm in diameter. 126 a LIFESIZE b FIGURE 39. (a) PHVCODES IN MUDDY SANDSTONE (DOTTED AREA) IN THE DELMAR FORMATION. VERTICAL SECTION CUT PARALLEL TO LONGEST DIMENSION OF TRACE. THE BURROW IS FILLED WITH MUD AND SANDY MUD (WHITE AREA INSIDE HEAVY LINES). (b) SEILACHER’S RECONSTRUCTION OF PHYCODES CIRCINATUM, BASED ON SAMPLES FROM THE SALT RANGE, PAKISTAN^ THE MASTER SHAFT (AT LEFT) EXHIBITS SPREITEN-STRUCTURES NOT OBSERVED IN THE DELMAR PHYCODES. (FROM SEILACHER, 1955 : FIG. 3.) 127 The trace described from the Delmar differs from other Phycodes in three respects: (1) Phycodes spp. described in the literature are preserved as convex hyporeliefs, whereas the Delmar trace is preserved in full relief. There are at least two possible explanations for this dis¬ crepancy: the behavior could be similar but preservation different, or the behavior could be different. Sellacher (1955) considered P. circinatum to have been constructed by an animal mining a nutrient- rich layer along a silt-mud interface, The Delmar unit in which these traces are found is muddy (15-20% mud) and has been thoroughly homogenized by burrowing organisms. Perhaps because the nutrients were evenly distributed throughout the sediment, the mining operation need not have taken place along such an interface. At any rate bedding planes are poorly preserved in the Delmar, both because of intense biological reworking and because the rocks are poorly lithified. Thus the chances of finding any trace preserved on a bedding plane are much reduced. An alternative explanation is that the behavior resulting in the Delmar trace may not have been of the "mining” sort. The organism may have been a filter feeder or scavenger sitting just at or below the water/sediment interface; if that surface were not preserved as a bedding plane, the trace would be preserved in full relief. (2) The Delmar trace also differs from Phycodes with respect to the central shaft. Osgood (1970:344) described a 1 cm-wide central shaft in specimens of P. flabellum that extended vertically downward almost to the bedding plane, then turned at 90° to run along the base of the bed and give rise distally to the typical 128 Phycodes structure. There is no evidence of such a central shaft in Delmar specimens. Although a special effort was made to find exit orentrance paths to the trace, the only likely structure observed was the vertical, cylindrical stem described above and illustrated in Figure 38. This stem, however, extends downward from the base of the Phycodes structure. (3) Delmar traces also do not exhibit the spreiten-structure observed in some, but not all, described species of Phycodes. Interpretation. These bowl-shaped structures were constructed endogenetically, probably by a deposit feeder. There are at least three kinds of organisms whose behavior might have produced such a structure. (1) The brittle star Hemipholus elongata anchors itself in silty fine sand with three or two arms; the remaining arms extend to the surface where they collect edibles to be passed tp the buried central disc. The.upper arms are 1.0-1.5 mm in diameter, and may be surrounded by a muddy burrow lining up to 1 cm thick (Hertweck, 1972: 138 and Fig. 9a; see Fig. 40b, this paper). According to Hertweck (1972:138), movements of the arms generate distinct burrows; thus one can easily imagine a whole series of such burrows that converge downward. The stem observed in some Delmar speciments might represent the position of the central disc (Fig. 40a). The Eocene Delmar ophiuroid would only have to have been shorter armed than modern H. elongata, thus buried less deeply in the sediment and producing a broader, flatter trace. (2) The Delmar Phycodes could also be the feeding burrow of a tentaculate detritus feeder, perhaps an anemone. The stem would then 129 a 1 CM FIGURE 40. (a) HYPOTHETICAL RECONSTRUCTION OF PHYCODES (AS DESCRIBED FROM THE DELMAR FORMATION) AS THE' FEEDING BURROW OF AN ENDOBENTHIC OPHIUROID. BLACK » MUDSTONE AND SANDY MUDSTONE; DOT = MUDDY SANDSTONE, (b) BURROWS OF HEMIPHOLUS ELONGATA (OPHIUROIDEA) IN THE UPPER OFFSHORE (WATëR DéPTïT'6'-T M7 OFF SAPELO ISLAND, GEORGIA, BLACK = MUD; DOT = FINE SAND WITH SILT. (FROM HERTWECK, 1972: FIG. 9a). 130 represent the anchoring anemone body, while the mud-filled branches represent positions of tentacles extended up to or upon the sediment surface In search of food. Mud might have been selectively Intro¬ duced along or below the tentacles along with' finely divided food par¬ ticles. (3) Alternatively, a deposit-feeding worm of appropriate diameter (about 2 mm) could have repeatedly burrowed out and up from a central area, stuffing the burrow with fine fecal material as it returned to its point of origin. It is difficult to explain, however, origin of the rather thick, cylindrical stem observed in some Delmar specimens. SMALL HORIZONTAL AND VERTICAL BURROWS Plate 9A & B Synopsis. Sinuous, cylindrical burrows 1 cm or less in diameter that may or may not branch and are observed in all orientations. Lined in sandy sediments and unlined in muddy sediments. Discussion. The burrows are most abundant in mudstone and very muddy sandstone; in mudstone the burrows show up when filled with sand from overlying sandy sediments. Interpretation. The burrows branch and cross-cut one another. Apparently they are created by vagile deposit feeders, possibly crustaceans and/or worms, that dig in search of food, but also maintain the burrows for a short time as semi-permanent dwelling burrows. DENDRITIC BURROWS Figure 41 131 FORMATION. BLACK = MUD BURROW FILL; DOT = BIOTURBATED MUDDY SAND¬ STONE. 132 Synopsis. Mud-filled burrows that are mainly vertical in ori¬ entation and that branch upward in a dendritic pattern. Discussion. Dendritic burrows are less than 5 mm in diameter but extend several decimeters vertically in the sediment. They branch upward in an irregular pattern illustrated in Figure 41. These burrows are most common in bioturbated, muddy sandstones o£ the Delmar Formation. Interpretation. Burrows of small diameter that branch irregu¬ larly and are mainly vertical in orientation are constructed by modern polychaete worms in the upper offshore off Sapelo Island, Georgia (Hertweck, 1972:132-133). These burrows do not branch in the dendritic pattern described above, but they are similar in size and general form to dendritic burrows at Solana Beach. Therefore I feel that poly- chaetes are the most likely progenitors of dendritic burrows. 133 Replchnla Repichnla (from the Latin repere, to creep or crawl) are simple traces of movement of an organism from one place to another, in or on the sediment. Repichnla is commonly translated as "crawling trace" (Kreichspur of Seilacher, 1953). Delmar and Torrey Repichnla, however, are largely formed infaunally by burrowing organisms so will be referred to here as "locomotion traces". Hertweck (1972j142) defines locomotion traces as "subsurface structures caused by animals pushing or ploughing through sediment without leaving cavities". These traces are abundant in the Solana Beach outcrops and require some further discussion. Almost all infaunal organisms, even those that do not specifically construct feeding or dwelling burrows, will leave some trace of their movements through the sediment. An animal may migrate in search of food, or in response to erosion or sedimentation or to predation. Rates of locomotion can vary considerably. Thus it is not surprising that there is a tremendous abundance and variety of such traces in the Solana Beach outcrops. In the Torrey Sandstone, in which pediment is coarse and perm¬ eable, and shells are rarely and poorly preserved, these traces are the only remaining indication of a plentiful shelled fauna. Locomotion traces in my study area are predominantly vertical or oblique in orientation. This probably reflects rapid and/or frequent changes in position of the sediment surface (due to erosion and sediment¬ ation) characteristic of a shallow, nearshore environment. Poor preserva¬ tion and exposure of bedding planes that would best show horizontal traces, however, are also contributing factors. 134 CONOSTICHUS LESQUEREUX 1876 Plates 14C and 15C Figures 43 and 44 Reference. Branson (1960 and 1961); Chamberlain (1971:220-223); Pfefferkorn (1971); for modern examples of "cone-in-cone" structures, see also Shinn (1968:880-890, Text-fig. 14 and PI. 112) and Schafer(l972; 288-290 and Fig. 165). Synopsis. Full relief locomotion trace in which successive strata are bowed down over a roughly circular area to form a cylinder or cone of disturbed sediment. In axial section the distorted strata look like nested u's or V's, which may be broken through at the base. Discussion. Conostichus is common in moderately bioturbated, trough cross-stratified muddy sandstones of the Torrey facies. They vary greatly in size, from a decimeter to several decimeters long and 5-15 cm wide. The structures are preserved as full reliefs, and are visible chiefly because diagenetic iron or color differences between adjacent laminae emphasize the distortion of the strata. In the fossil record similar structures have been referred to the ichnogenera Conostichus Lesquereux, 1876 (Hantzschel,1962: Fig. 116(2,3)) and Rossella Dahmer, 1937 (Chamber- lain and Clark, 1973). Interpretation. Nested cone structures are known to be produced by the burrowing anemone Phyllactis conguelegia in cross-bedded oolite sands on the Bahama Banks (Shinn, 1968; see Fig. 42a, this paper). The trace pictured by Shinn is 30 cm long and 6 cm wide, and was produced over a period of about 12 hours by upward migration of Phyllactis conguelegia in response to artifically induced sedimentation. Down-bowed lamination 135 is produced as sand trickles into the space left below as the organism moves upward. The sag trail is vertical to gently curving. Cerianthus, another burrowing anemone, produces a similar escape trail when sedimentation is so rapid that it is forced to abandon its dwelling burrow (Schafer, 1972:289-290 and Fig. 165). The resulting sag trail, however, should be preserved in association with the abandoned dwelling tube -- a feature not observed in Solana Beach outcrops. Digging trails of some lamellibranch bivalves and sipunculid worms also give rise to cone-in-cone structures, as shown in Fig. 42b & c (Schafer, 1972:273-275 and 372-380, Fig. 160 and Pis. 18b and 19b; Reineck, 1957 and 1958a,b). Lamellibranch trails are vertical and can represent upward or downward movement as the organism attempts to main¬ tain a characteristic depth of burial. A rapid burrower such as Mya arenaria drags the cut-off strata in the direction of movement (Schafer, 1972:Pl. 18b and Fig. 221). Other lamellibranchs, however, by their pushing and pulling motions can sufficiently loosen surrounding sediment so that penetrated layers sag downward, in response to gravity, regard¬ less of whether the bivalve has moved up or down (Schafer, 1972:377). Sipunculid worms are deposit feeders and produce locomotion traces in all orientations as they plow through the sediment in search of food. Sipunculus has a smooth, elongate body which glides readily through the sediment. Therefore the periphery of the locomotion trace is sharply defined, and cut-off beds always point in the direction of movement (Schafer, 1972:275 and Fig. 160). If Sipunculus moves vertically down¬ ward, so that the cut-off beds point downward, a cone-in-cone, Conostichus- like structure results. One of the difficulties inherent in attempting to interpret a 136 o «oc o Z FIGURE 43. CONOSTICHUS IN CROSS-BEDDED SANDSTONE, TORREY SANDSTONE. 138 FIGURE 44. CONOSTICHUS IN CROSS-BEDDED SANDSTONE, TORREY SAfclbSTONE. 139 cone-in-cone structure is that the morphology of the trace varies significantly with -the orientation of the exposure surface. In axial section one might be able to distinguish a structure created by upward migration of the anemone Phyllactis conguelegia from that produced by downward burrowing of a lamellibranch or sipunculid by close observation of the internal structure. The nested cones of the former structure are U-shaped and unbroken; nested cones of the latter are V-shaped or are broken through at the tip. The two structures look alike, however, in vertical sections cut through the periphery of the cone. Specimens of Conostichus in the Torrey Sandstone (Figs. 43 and 44, Pis. 14C and 15C) are vertical, or nearly vertical, and cut-off beds are invariably down-turned, suggesting that the organisms responsible are vertically migrating suspension feeders (such as anemones and some lamell¬ ibranch bivalves), rather than wandering deposit feeders (such as Sipun- culus). VERTICAL MOVEMENT PATHS Plate 14A Figure 45 Synopsis. Vertically-orientated columns or cone-shaped volumes of disturbed, homogenized sediment. Specimens exhibit a distinct base but become less well-defined upward. Discussion. Vertical movement paths are columns or cones of churned sediment that are up to 60 cm long and 5-10 cm in diameter. These struct¬ ures have a distinct base that is tear-drop-shaped (see Pi. 14A and Fig. 45b) or that is marked by a lined burrow (see Fig. 45a); their outline becomes 140 less distinct and well-defined upward. Some specimens (PI. 14A and Fig. 45a) also widen upward, so that the disturbed sediment is in an inverted cone. Vertical movement paths are restricted to sequences of interbedded sandstone and mudstone. Interpretation. Vertical movement paths are genetically related to Conostichus. but differ in that the path of movement is marked by complete destruction of stratification in the former, versus simple down-warping of stratification in the latter. In part this must be owing to differ¬ ences in the sediment matrix. Vertical movement paths were observed only in interbedded sandstone and mudstone, suggesting that the churned texture results because these sediments were somewhat cohesive. Possibly also the animal was able to induce thixotropy in the path of movement by shoot¬ ing a stream of water or by beating a foot (gastropod or pelecypod) or tall (crustacean) in the sediment. The paths widen upward, indicating that the sediment there was less compacted and more watery. The tear-drop-shaped base shown in Plate 14A and Figure 45b is reminiscent of a gastropod or pelecypod, while the lined burrow at the base of the path in Figure 45a probably was constructed by a crustacean. Apparently the paths were created during rapid, emergency ascents or descents by animals in response to burial under freshly deposited sediment or to exposure by erosion. 141 i Ozxz LU O< OLU OLU OLL M »— *LU CO ex LU co ex LU 2 < LU >OCÛ>- »- < CO LU -J • o ac XI =5 H- ex •*X LU Id I— O U)Q u. co en en STRUCTURES IN (a) PERHAPS ARE CAUSED BY INCREASED WATER CONTENT OF THE SEDIMENT, OR BY THIXOTROPHY INDUCED MOVEMENTS OF THE ANIMAL. 142 ? PALAEOPHYCUS HALL 1847 Figure 46 Reference: For synonomy and extended discussion see Osgood (1970; 373-376). Synopsis. Full relief, unlined, cylindrical burrows that are oriented parallel and obliquely to the bedding plane. The burrows do not branch, but wind back on themselves and interpenetrate, so that the sediment takes on the appearance of a mass of wet, fat macaroni. Discussion. This burrow type has been observed only within a single, meter-thick bed in the Delmar Formation, for about 30 m along strike. Its distribution is the same as that of ? Phycodes described in this report. The sediment matrix is green, micaceous muddy sand. The burrows are quite uniform in size and shape, being nearly circular in cross-section and 0.4-0.5 cm in diameter. The burrows are not lined, and are visible chiefly because mica flakes have been pushed to the peri-* meter of the tubes and thus appear to swirl around them. Other than a slight deficiency in percent mica and slightly paler color, the infilling sediment is similar to the matrix sediment. The burrows are very densely packed. This lebensspur is similar in size and morphology to two named ichno- genera: Palaeophycus Hall, 1847 and Planolites Nicholson, 1873. Palaeo- phycus and Planolites are very similar and thus are difficult to distin¬ guish. Osgood (1970:373-376) discussed the problem at length and concluded that "the only significant difference lies in the nature of the filling". The burrow filling of Planolites differs in texture or composition from the host sediment; that of Palaeophycus does not. Presumably this 143 difference reflects two types of behavior: Planolites may be the stuffed feeding burrow of-a Sedimentfresser (Nicholson, 1873; Richter, 1937; Howell, 1943; Reineck, 1955); Palaeophycus, the locomotion trace of '•errant predaceous or selective feeders” (Osgood, 1970:376). The problem requires further study of type specimens of Planolites. Interpretation. The Delmar burrows are paler in color than the host sediment, but there are no significant differences in texture or composi¬ tion between burrow fill and matrix. Mica flakes swirl around the peri¬ phery of the burrow in a manner reminiscent of the locomotion traces of the irregular echinoid Moira atropos (Hertweck-, 1972:Fig. 9b). The Delmar lebensspur, then, may also be a trace of movement, assignable to the ichnogenus Palaeophycus. However, the burrows are densely packed (see Fig. 46) suggesting that an organism was ploughing through the sediment specifically to sift it for food. In this sense the tybes are also feed¬ ing burrows. According to Seilacher (1964:299), feeding burrows (Fodin- ichnia) "reflect the search for food and at the same time fit the require¬ ments for a permanent shelter”. The Delmar trace does not appear to have been maintained as an open burrow or "permanent shelter”; therefore I have classified it as a locomotion trace attributable to Repichnia. Palaeophycus in the Delmar Formation might have been created by a locally dense population of small crustaceans, worms, or gastropods. 144 FIGURE 46. PALAEOPHYCUS IN FINE, MUDDY SANDSTONE, DELMAR FORMATION. THE INTERIOR OF THE BURROWS IS SOMEWHAT LIGHTER IN COLOR THAN THE MATRIX SEDIMENT, AND HEAVY MINERALS ARE CONCENTRATED AT THEIR PERIPHERY. 145 Cubichnia. Cubichnla (after the Latin cubare, to lie down) are shallow resting tracks or resting burrows left by animals seeking temporary shelter just below the sediment surface (Seilacher, 1964:299). SURFACE DEPRESSIONS Plates 14B and 15A Figure 47 (Note: Surface depressions appear to be a mixture of Cubichnia and shallow, temporary Domichnia). Synopsis. Cone- or bowl-shaped volumes of disturbed sediment that descend from an erosional surface or a bedding plane. Discussion. Surface depressions range in size from 5 cm wide and 12 cm deep to 20 cm wide and 30 cm deep. They descend from a well-defined bedding plane or erosional surface. Surface depressions are particularly well-defined if that surface is draped with mud, because the mud layer is pushed downward and outlines the trace, as shown in Figure 47. Interpretation. Surface depressions vary greatly in size and shape, and probably are caused by several, different types of behavior. The trace illustrated in Figure 47 is broad and shallow; it might have been the resting place of a crab. Schafer (1972:385-388 and Fig. 227) has described a similar resting burrow made by the crab Carcinides maenas on beaches and tidal flats of the North Sea coast (see Fig. 47c). In con¬ trast, the surface depressions shown in Figure 47a and in Plate 15A are much deeper and narrower; perhaps they were shallow dwelling burrows of anemones. A third kind of surface depression is pictured in Plate 14B. 146 Similar cones of disturbed sediment were described by Schafer (1972:392- 393 and Fig. 230)', again from the North Sea. These are generated by small, cumacean crustaceans that dig a shallow, cup-shaped resting burrow. When they leave the burrow they do so with a spring and straightening of the body, putting up a cloud of sediment that then settles back Into the depression as a churned, homogeneous plug. Surface depressions, then, are geometrically variable and are probably polygenetlc. They mark temporary resting burrows and shallow burrows of organisms that must maintain contact with the water-sediment interface, such as some anemones and some crustaceans. 147 i M C£llL ceo< ZO O LU Z HUJZH COIO 00 I- I- sc LU 00 O acûzh LU < O O Z OO LU 2C h- LU O O O O O LU CC < O CL LLûû OC LU LU >- 3XCÛCC CO OO I «c o oo ce LU a. co o I— o Q- < oo >- 3: LU LU LU O O ce LuüHh TIDAL FLATS OF THE NORTH SEA. ABOVE: IN MUD; BELOW: BEDDED SAND. CARCINIDES BURROWS 148 Other trace fossils COLLAPSE STRUCTURES Figures 48-50 (Note: Collapse structures are actually physical sedimentary structures and can form independent of biologic activity. The structures described herein, however, are directly related to faunal activity and therefore are included as trace fossils. Collapse structures do not fit into any of the éthologie catagories of Seilacher (1953).) Synopsis. Full relief cone-in-cone structure in which vertical dis¬ placement of beds increases downward, and diameter of disturbed area decreases downward. Periphery of the cone may exhibit small normal faults dipping toward the axis of the trace. Discussion. This type of cone-in-cone structure is common in Ophio- inorpha-rich, cross-stratified, slightly granular muddy sandstones of the Torrey facies. They vary greatly in size; the structure sketched in Figure 50 is 12 cm long and 5-6 cm across, while that of Figure 49 is four times as long and up to 17 cm across. Large, mud-walled burrows are preserved directly beneath the tip of the cone. In all cases, down-draped laminae are continuous with surrounding stratification. The structures are preserved as full reliefs, and are accented by differential concen¬ tration of diagenetic iron in successive laminae. Interpretation. These structures were created by sudden, downward displacement of sediment into a previously open burrow. Sediment immedi¬ ately above the tube pours in, leaving steeply down-turned cut-off beds along the periphery and a disturbed, homogeneous zone directly abovç the 1U9 tube. Rapid collapse of superjacent laminae may be accommodated by small normal faults dipping toward the axis of the trace. The effect decreases upward and with time. 150 FIGURE 48. COLLAPSE STRUCTURE IN BEDDED SANDSTONE, TORREY SANDSTONE. THE STRUCTURE WAS CREATED WHEN LOOSE SEDIMENT POURED INTO AN OPEN BURROW (LOWER LEFT). 151 FIGURE 49. COLLAPSE STRUCTURE IN CROSS-BEDDED SANDSTONE, TORREY SANDSTONE. THE STRUCTURE WAS CREATED WHEN LOOSE SEDIMENT POURED INTO AN OPEN BURROW (BELOW). 152 FIGURE 50. COLLAPSE STRUCTURE IN BEDDED, MUDDY SANDSTONE, DELMAR FORMATION. THE STRUCTURE WAS CREATED WHEN LOOSE SEDIMENT POURED INTO THE THEN- OPEN BURROW, BELOW. 153 APPENDIX II GRAIN-SIZE ANALYSIS OF SEDIMENTS Methods Grain-size frequency distributions and derivative measures are based on dry-sieve analyses of sand fractions and determinations of weight percents of fine fractions by the pipette replicate method (Folk, 1968). Samples for grain-size analysis were chosen so that all sedi¬ mentary environments would be represented. After having been disaggregated in distilled water with dispersant, each sample was washed on a 6^( wet sieve to separate mud and sand fract¬ ions. The sand fraction was dried, weighed, then sieved on a series of twenty-three U. S. Standard brass sieves eight inches in diameter. Sieve sizes were set at quarter-phi Intervals from 4.00 to -1.00, and at half- phi intervals from -1.00 to -2.00 (phi scale devised by Krumbein and PettiJohn, 1938). Sand remaining on each sieve after fifteen minutes on the RO-TAP was weighed to the nearest milligram on a Sartorius balance. This figure was corrected as necessary to allow for aggregate grains; percent aggregates was estimated using the method described by Folk (1968:35). The weight of sand in each sieve, calculated as a percent of the weight of the whole sample, constitutes the basic data used to pre¬ pare the graphs and charts in Appendix II and in the text. Detailed procedures of these analyses follow the suggestions of Folk (1968:34-38). SOME CHARACTERISTICS OF GRAIN-SIZE DISTRIBUTIONS OF ANALYSED SAMPLES FROM THE DELMAR FM 1# * * z CD OO Z Z LO 10 CM «a- M re 0 00 o> LO CO CO CD =3 • • • CM • H-l 2 CM O Is*. • CO LU 1—1 •—1 CM r-1 3 ** H in LO <ÛÎH £ CM CM 3.0 CM «3- 2 CD CO 00 •« 1 1 1— CO CO CO Z LU CO 1 CO en c 0 LU U U. 3 Z O • 0 1 0 c 1 CO C Lu O •O OC LU cc 0 Z OC 0 z z Z —J CO CO *-* 0 z 0 IxIDh LU LU H D3 JQ LU I— 0 0 Z CO Z _J C LU >*< re 1— oc z to z N fN. hs. * «K SOME CHARACTERISTICS OF GRAIN-SIZE DISTRIBUTIONS ANALYSED SAMPLES FROM THE TORREY SS CUMULATIVE WEIGHT PERCENT 156 40 CUMULATIVE WEIGHT PERCENT -■ ■ ■ r—i —t ■ ■ ■ i r- is -w> -.5 ao +-Si.o 2.0 ao 40 GRAIN SIZE(0) 157 158 I miscounted and had no page 158. So I take this opportunity to thank two people who came through for me in the eleventh hour: my thesis advisor Dr. John E. Warme, without whose advice and generosity the process of manuscript preparation would have been much more difficult, and my sister Ms. Judith B. Derrick, who drafted some of the figures and helped in innumerable ways to get me out of Houston at last! 159 APPENDIX III CARBON AND OXYGEN ANALYSIS M. L. Johnson of Rice University investigated the isotopic composition of a valve of Ostrea ldrlaensls from an oyster bed in the Delmar Formation at Solana Beach. Samples were evolved in 100Z phosphoric acid at 25*C. The result is -10.9°/Oo PDB. 18 Evolved CO2 has a JO value of -5.l°/0o PDB. 160 PUTE 1 Fossils In the Delmar Formation A. External cast of an ostracode valve, In a mud-shale* Bar * 1 mm. B. Segmented fecal pellet from a mud-shale. Bar « 0.5 mm. C. Possible arenaceous foramlnifera from a mud-shale. Bar • 1 mm. D. Upper surface of an oyster reef, showing several, large Ostrea idriaensts (center, right, and upper right), and other mol¬ lusc shells.' Some of the pelecypod valves are articulated (lower right and center left). The oyster shell in the center of the pic¬ ture exhibits numerous, small borings made by clionid sponges. Ruler is 14.5 cm long. 161 PLATE 2 Subfacies in the Delmar Formation A,B. Strata of the Delmar Formation exposed in a cliff face at section 2 (refer to Fig. 5, p. 16). A is a sketch of B, showing approximate distribution of subfacies. Cliff face is about 10 m high. (a) Subfacies A (p. 68-70) ** oyster reefs. The reefs are ce¬ mented by calcite and are quite hard, so they project from the cliff face. (b) Subfacies B (p. 71-73) » interbedded and interlaminated sandstone, mudstone and clay-shale exhibiting flaser, wavy, and lenti¬ cular bedding. Interpreted herein as tidal flat deposits. (c) Subfacies C (p. 73-75) ■ fining-upward sequences -- bio- turbated beds of muddy sandstone and mudstone interpreted herein as deposits of lower tidal flats and sublittoral tidal channels, and as deposits on the floor of the Delmar lagoon. 162 PLATE 3 Sediments and Sedimentary Structures In Flaser-bedded Units, Delmar Formation (Subfacles B, p. 71-73) A,B. Interlaminated muddy sandstone and sandy mudstone exhibiting flaser bedding. Note megaripple cross-stratification in lower center of picture; (a) marks a reactivation surface followed by steepening of inclined laminae. Vertical movement paths (b) (see p. 139-140) extend upward from burrows in the lower part of the picture, suggesting that the sediments immediately above the mega¬ ripple were rapidly deposited. Ruler is 30 cm long. C. Small lens of coal (a) in interlaminated sandstone, mud¬ stone and clay-shale. Note flaser bedding (b), Knife is 17 cm long. D. Small channel cutting down into flaser-bedded sandstone, mudstone, and clay-shale. Scour surface of channel is visible just above handle of knife. Knife is 15 cm long. 163 PLATE 4 Medium-scale Cross-bedding In the Delmar Formation (Subfacies C, p. 73-75) A. Medium-scale trough X-beds grading upward into small-scale (ripple) cross-beds. A few mud-walled burrows (Ophiomorpha nodosa, Thalassinoides, and Gyrolithes) are visible in the lower part of the sequence* Bioturbation increases upward, and the upper part has been completely homogenized by burrowers. Ruler is 15 cm long. B, C. Tabular sets of medium-scale planar cross-bedding in muddy sandstone. The inclined beds are discordant with the lower bounding surface, which is horizontal and conformable to subjacent stratification. Bioturbation increases upward. Ruler in B is 30 cm long. D. Cross-bedded unit shown in A and B can be seen in the lower part of the cliff face. The sediments are in subfacies C. Cliff face is about 7 m high. 164 PLATE 5 Bored Claystone Bed and Claystone Clasts, Delmar Formation A,B. The dark hollows In the center of A marie positions of weathered-out claystone clasts, shown in place In B. The clasts were derived from a claystone bed visible, in the lower right corner of A. This bed was exhumed and eroded before lithification but after some compaction, so that it offered a cohesive surface to boring invertebrates* Two borings can be seen in the large clast in the center left of B. Rulers in both A and B are 30 cm long. C. Detail of a vertical exposure of the claystone bed (black) discussed above. The lower boundary of the bed is gradational; the upper boundary is sharp and highly irregular. Borings, probably made by bivalves, penetrate downward from the upper surface to the base of the bed. Bar ■ 10 cm. 165 * PLATE 6 Relative Degrees of Bioturbation (see Figure 17, p. 48, for detailed definitions of underlined terms) A. Rare burrows in large-scale cross-beds of slightly granular, muddy sandstone. These beds fill a large channel in the Torrey Sand¬ stone that is shown in Plate 12B,C. Hollows mark weathered-out clay- stone clasts. Knife is 15 cm long. B. Abundant burrows in flaser-bedded sandstone and mudstone at section 17 (see p. 61 and 63). Fat, mud-lined burrows (p. 114- 115) extend downward from a thin bed of sandy mud-shale. Entire sequence is about 1.4 m thick. C. Partial bioturbate texture in cross-stratified muddy sandstone of the Delmar Formation. Mud-lined burrows are Thalassinoides (p. 102-107). Ruler is 15 cm long. D. Complete bioturbate texture in muddy sandstone of the Delmar Formation. The Ostrea valves (upper center) form shell stringers as described on p. 45 166 PLATE 7 Dwelling Burrows In the Delmar Formation A,B. Ophlomorpha nodosa (small form) grading into Thalassinoides in a horizontal burrow system exposed on a bedding plane. This same burrow is sketched in Figure 28, p. 103. Ruler in B is 15 cm long. C,D. Gyrollthe8 in a vertical exposure in muddy sandstone. The mud wall has been darkened with ink in C. (The wall is actually smooth; the pelletai appearance is an artifact of my painting tec- nique.) Ruler in D. is 15 cm long. 167 PUTE 8 Ophlomorpha nodosa (small form) In the Delmar Formation A. Vertically-oriented 0. nodosa burrow (left of knife) in medium-scale cross-bedded muddy sandstone. Flaser bedding (subfacies B) visible in lower part of picture. Knife is 15 cm long. B. Horizontally-oriented 0. nodosa burrow in muddy sandstone. Note nodose outer surface and Y-shaped branchings. Ruler is 15 cm long. 168 PLATE 9 Feeding Burrows in the Deltnar Formation A. Small branching burrows in muddy sandstone. Parts of the burrows have mud walls (upper center and lower right). B. Sand-filled, branching burrows in very muddy sandstone be¬ low an oyster reef. Knife is 17 cm long. C. ÎPhycodes (p. 122-130) in muddy sandstone. The burrow is filled with dark green mud. Knife is 17 cm long. D. ÎPhycodes in muddy sandstone. Light-colored burrows of Palaeophycus (p. 142-144) are faintly visible in lower part of pic¬ ture. Blade of knife is 6.5 cm long. 169 PLATE 10 Large-scale Trough Cross-bedded Sandstone, Torrey Sandstone (Subfacies D, p. 75-77) * A,B. Torrey Sandstone exposed in cliff at section 14 (see Fig. 5, p. 16). Large-scale trough cross-beds of coarse, muddy sandstone (dotted areas in A) with lenses of sandy mud-shale (solid black in A) are described in the text as subfacies D = deposits of subaqueous dunes and tidal channels of a tidal delta or interior side of a barrier bar or shoal. Bed at base of cliff has been heavily burrowed and stratification there is obscured. Rod is 1.8 m long. 170 PLATE 11 Boundary Between Delmar and Torrey Facies A large channel (a) (subfacies E) of the Torrey Sandstone cuts down into bioturbated sandstones and mudstones (subfacies C) of the Delmar Formation* Load casts of sand (c) are visible against beds of dark green, sandy mud-shale and mudstone (b). Note contrast be¬ tween rare burrows in the channel (a) and partial to complete bio- turbate textures in subjacent beds. Visible cliff face is about 9 m high. 171 PLATE 12 Large Channels In the Torrey Sandstone (Subfacles E, p. 77-79) A. Large channel filled with slightly granular muddy sandstone cuts into a bed of sandy mud-shale (dark area at lower left). The channel is about 70 m wide and 5 m deep. It filled from right to left and toward the reader (beds dip out of the page, or toward the reader). B, C. Large channel filled with slightly granular muddy sandstone. The lower part of the channel filled from right to left and toward the reader; inclined beds in the upper part dip in the opposite direction (C), forming a herringbone pattern. Bars in B and C are 1 m long. 172 PLATE 13 Large Channel In the Torrey Sandstone (Subfacles E, p. 77-79) A,B. Large channel In the Torrey Sandstone near section 13 (see Fig. 5, p. 16). The channel filled by lateral migration of the banks from left to right. The scarcity of trace fossils (compare to burrowed sandstones into which the channel erodes, lower left of B) suggests that the channel was short-lived, generated perhaps by drainage of the Delmar lagoon after periods of high run-off or high spring tides. The channel is about 80 m wide and 6 m deep. Ver¬ tical exagération in A ■ 2X. 173 PLATE 14 Trace Fossils in the Torrey Sandstone A. Vertical movement paths (p. 139-140) in flaser-bedded sand¬ stone and mudstone. Scale drawn on outcrop. B. Fat, mud-lined burrow (below felt-tip pen) (p. 114-115) and surface depressions (to left of fat, mud-lined burrow) (p. 145- 146) in flaser-bedded sandstone and mudstone. Felt-tip pen is 11 cm long. C. Conostlchus (p. 134-139) in large-scale cross-bedded sandstone. Scale drawn on outcrop. D. Ophiomorpha nodosa (large form) (below left of knife) and vertical burrows with spreiten (above right of knife) (p. 115-117) in large-scale cross-bedded sandstone* Knife is 17 cm long. 174 PLATE 15 Trace Fossils in the Torrey Sandstone A. Surface depressions (p. 145-147) in large-scale trough cross- bedded sandstone. Thin laminae of mud have been pushed downward to outline a cone-shaped structure. Knife is 17 cm long. B. Vertically-oriented Ophiomorpha nodosa (large form) in large-scale trough cross-bedded sandstone. Knife is 17 cm long. C. Conostichus in large-scale trough cross-bedded sandstone. Knife is 17 cm long. FIGURE 6. GRAPHIC PRESENTATION OF STRATIGRAPHIC SECTIONS i METERS - ZZI— z z«c • z to o O QOO LU Q CD O O CD CO LU CD CO LU z *~i CO ZCCH CD O z 1— < z z z . 1— O ox
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