Micropaleontological Evidence of A Submarine Fan in the Lower Coaledo Formation, Southwestern Oregon, USA

Abstract

The middle Eocene lower Coaledo Formation was interpreted as ten shoaling upward delta-margin cycles based on sediments and macrofauna. The strata, however, contains deep-water foraminifers. Explanations to resolve this anomaly included reworking, bathymetric range extension, or upward migration of water masses. Paleoecology analysis of foraminifers indicates that the few shelf species are poorly preserved whereas the well-preserved lower bathyal species dominate, and planktic organisms are present. Evidence for reworking, bathymetric range extension, or upward migration of water masses was not found in any of the cycles. The paleoecologic utility of hummocky cross-bedded sandstones is questioned as these features are controversial. In addition, there is no evidence of sea-level changes or tectonic activity to accommodate the bathymetric changes needed. Deposition of the lower Coaledo Formation on a submarine fan at lower bathyal depths eliminates the need to explain bathymetric anomalies or lack of tectonic movement.

Full text

MICROPALEONTOLOGICAL EVIDENCE OF A SUBMARINE FAN IN THE LOWER
COALEDO FORMATION, SOUTHWESTERN OREGON, USA
KRISTIN MCDOUGALL*
U.S. Geological Survey, Geology, Minerals, Energy and Geophysics Science Center, 2255 N. Gemini Dr., Flagstaff, Arizona, USA, 86001
ABSTRACT
The middle Eocene lower Coaledo Formation was inter-
preted as ten shoaling upward delta-margin cycles based
on sediments and macrofauna. The strata, however, con-
tains deep-water foraminifers. Explanations to resolve this
anomaly included reworking, bathymetric range exten-
sion, or upward migration of water masses. Paleoecology
analysis of foraminifers indicates that the few shelf species
are poorly preserved whereas the well-preserved lower
bathyal species dominate, and planktic organisms are pre-
sent. Evidence for reworking, bathymetric range exten-
sion, or upward migration of water masses was not found
in any of the cycles. The paleoecologic utility of hum-
mocky cross-bedded sandstones is questioned as these fea-
tures are controversial. In addition, there is no evidence of
sea-level changes or tectonic activity to accommodate the
bathymetric changes needed. Deposition of the lower
Coaledo Formation on a submarine fan at lower bathyal
depths eliminates the need to explain bathymetric anoma-
lies or lack of tectonic movement.
INTRODUCTION
The Coaledo Formation is considered a middle to late
Eocene deltaic deposit (Chan & Dott, 1983, 1986), found
along the southern Oregon coast in the Coos Bay basin (Fig.
1). Studies suggest that the Tyee and Coaledo Formations
were deposited in a subsiding forearc basin with an active
magmatic arc to the southeast and east (Dott, 1966; Rooth,
1974; Ryberg, 1978; Dott & Bird, 1979; Chan & Dott, 1983,
1986). The Tyee Formation was believed to contain fluvial,
marsh-swamp, and delta-distributary channel facies, as well as
basinal facies (Chan & Dott, 1983), whereas the Coaledo For-
mation contained marsh-swamp, delta-margin, delta-distribu-
tary channel, delta-front, and prodelta-shelf facies (Chan &
Dott, 1986).
Foraminiferal analyses of the Tyee and Coaledo Formations
have in most cases supported these interpretations (Bird, 1967;
Rooth, 1974; McKeel & Lipps, 1975; McKeel, 1979, 1980).
However, Bird (1967) had difficulty interpreting the depth at
which deposition occurred because the microfossils suggested
bathyal (.150 m) or deeper environments, but macrofossils
and sediments suggested deposition occurred at inner shelf
depths (,50 m). Although Bird (1967) considered reworking
and broader bathymetric ranges for the microfossils, he dis-
counted the reworking as there was no source for the speci-
mens, and he could not find evidence to support a broad
enough bathymetric range that would allow deposition of
lower bathyal species at inner shelf depths. So, the anomaly
remained. Rooth (1974) also suggested that the “lower
member of the Coaledo Formation was deposited in a predom-
inantly shallow marine environment, 120 to 240 feet (36.6 to
73.2 m) based on mollusks, and that there was evidence of
strong current action in the lower and middle parts of the
lower member, whereas deposition of the upper part of the
lower Coaledo was in a quieter environment.”Rooth (1974)
also noted that the bathymetric interpretation of at least two
foraminiferal species (Gyroidina girardana planata of Rooth,
1974, and Cyclammina pacifica) was not consistent with sedi-
mentary or macrofossil evidence; therefore, he suggested that
perhaps the bathymetric ranges may not be as restricted in the
Eocene as today. McKeel (1979, p. 4) noted: “Abundant speci-
mens of the bathyal genus Gyroidina occur with rare inner
neritic Elphidium californicum”and considered this occur-
rence to be incompatible with a deep water interpretation so
suggested that “since the benthonic fauna in this interval repre-
sents cold bottom water (very low species diversity), an outer
neritic environment is suggested here; the deep-water species
of Gyroidina could have migrated onto the outer shelf, finding
similar temperatures to its normal bathyal habitat.”Based on
this interpretation McKeel (1979, 1980) indicated deposition
occurred at neritic depths.
Although suggestions were made to resolve the discrepancy
between the foraminiferal and mollusk/sediment bathymetric
interpretations, none have been accepted. To resolve this issue,
closely spaced samples were taken from cycle 2 of Chan &
Dott (1986) and examined. Cycle 2 is near the top of the lower
member of the Coaledo Formation and one of the shoaling
upward delta-margin sequences of Chan & Dott (1986). This
study documents the foraminiferal assemblages and 1) pro-
vides a detailed analysis of the paleoecology of cycle 2 based
on the foraminiferal assemblages and ecological implications
of the species, as well as 2) examines and compares microfos-
sil assemblages in the other lower Coaledo cycles to those of
cycle 2.
GEOLOGIC SETTING AND STRATIGRAPHY
The Coaledo Formation outcrops in southwestern Oregon
around Coos Bay in what is considered the Coos Bay basin
(Niem et al., 1992; Ryu, 1995; Armentrout, 2021; Fig. 1). The
Coos Bay basin includes 3400 m (11000 ft) of middle Eocene
to Late Miocene deltaic to deep marine sediments (Armentr-
out, 2021; Ryu, 1995; Chan & Dott, 1986; Fig. 2). The adja-
cent Tyee Forearc Basin contains 7600 m (25000 ft) of early
to middle Eocene sediments and overlies the older Umpqua
Group (Baldwin, 1974; Ryu, 1995; Ryu et al., 1996). Late
middle Eocene to middle Oligocene strata most likely
extended across the forearc basin to the foothills of the Cas-
cade arc but were removed by late Oligocene and younger
uplift and erosion (Armentrout, 2021).
* Correspondence author. E-mail: kris@usgs.gov
311
Journal of Foraminiferal Research, v. 53, no. 4, p. 311–337, October 2023
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Kristin McDougall; Micropaleontological Evidence of A Submarine Fan in the Lower Coaledo Formation,
Southwestern Oregon, USA. Journal of Foraminiferal Research 2023;; 53 (4): 311–337. doi: https://
doi.org/10.2113/gsjfr.53.4.311

Deposition in the Coos Bay basin began with the early
Eocene sandstone of Fivemile Point of Wiley et al. (2015),
which was deposited at middle to lower bathyal depths (Fig. 2;
Snavely et al, 1982). This unit is unconformably overlain by
the Tyee Mountain Member of the Tyee Formation, which is
interpreted as a deep-water turbidite unit (Wiley et al., 2015).
The contact between the siltstones and associated channel and
turbidite sandstones of the Sacchi Beach and Tyee Mountain
Members of the Tyee Formation has not been observed (Wiley
et al., 2015). The Sacchi Beach Member is interpreted as lower
slope deposits (Rooth, 1974; Bird, 1967; Ragan et al., 2023)
and is overlain by the Coaledo Formation. The base of the
lower Coaledo Formation is described as a sandstone with
minor conglomerate and pebbly sandstones (Baldwin & Beau-
lieu, 1973). Thin, local coal beds (1–4 inches thick; Bird,
1967) and coalified wood (Armentrout, 2021) are recognized
in some outcrops. Baldwin & Beaulieu (1973) suggested an
unconformity between the Sacchi Beach Member of the Tyee
Formation and the overlying lower Coaledo Formation. How-
ever, Dott (1966), Bird (1967), and Rooth (1974) considered
the contact between the two units to be gradational. Rooth
(1974) believed the upper beds of the Sacchi Beach Member
shallowed to neritic depths. This interpretation was also sup-
ported by Chan & Dott (1986), as they correlated the base of
the Coaledo Formation with a sea level fall in the late early
Eocene [zones NP12/13 of the Vail et al. (1977) sea level
curve].
The overlying Coaledo Formation is divided into three
members that comprise approximately 2000 m (Baldwin,
1974; Chan & Dott, 1986). The lower member of the Coaledo
Formation is composed of ten shoaling progradational succes-
sions and is believed to represent delta progradation and lobe
shifting as well as relative changes in sea level (Dott, 1966;
Frazier, 1967; Baldwin, 1974; Rooth, 1974; Coleman &
Wright, 1975; Ryberg, 1978; Dott & Bird, 1979; Chan & Dott,
1986; Armentrout, 2021). Deposition of this member is
thought to have occurred at shallow depths of #50 m (Chan &
Dott, 1986). Contact between the lower and middle members
of the Coaledo is gradational. The middle member of the Coal-
edo Formation is interpreted as reflecting a period of sudden
124oW
43oN
44oN
Agness
Cape
Blanco
Reedsport
Florence
Powers
Pacific Ocean
Roseburg
Tyee
Umpqua
Coos Bay
Basin
Loon
Lake
Arch
Basin
Forearc
0 5 10 15
Miles
Study Area
(see Fig. 2) Coos
Bay
Bandon
Western Cascades volcanic rocks
Coos Bay basin strata
Spencer Fm.
Batemam Fm.
Elkton Fm.
Tyee Fm. (Baughman, Hubbard
Creek, and Tyee Mtn Mbrs)
Camas Valley & White Tail Ridge Fms.
Umpqua Group, undifferentiated
(Tenmile and Bushnell Rock Fms.)
Siletz River volcanics
Mesozoic rocks of Klamath Mtns.
United States
Canada
Mexico
Coos Bay
FIGURE 1. Index map showing geologic units and tectonic features of southwestern Oregon, modified from Ryu (1995). Coos Bay Basin lies along the
coast near the city of Coos Bay, Oregon, and includes strata of middle Eocene to Late Miocene age. Additional details of the Coos Bay basin geology are
shown in Figure 2.
312 MCDOUGALL
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deepening of hundreds of meters (Rooth, 1974; Armentrout,
2021), which resulted in shelf mudstones being deposited over the
delta-front sandstones. The upper member of the Coaledo Forma-
tion is interpreted as a prograding deltaic sandstone and conglom-
erate, with additional delta-front and delta-distributary channel
facies (Baldwin, 1974; Chan & Dott, 1986). Conformably overly-
ing the upper Coaledo Formation is the late Eocene Bastendorff
Shales, suggesting that deposition occurred near the shelf edge to
upper bathyal biofacies (Baldwin, 1974; Tipton, 1975).
Cycle 2 of the lower Coaledo Formation is exposed in Sun-
set Bay, Oregon. At this location, cycles 1 (youngest) through
4 (oldest) are exposed, as is a portion of the middle Coaledo
Formation (Fig. 3). Cycle 2 represents the delta-front facies of
Chan & Dott (1986) that was previously interpreted as being
deposited at depths of 50 m and shoaling upward. The base of
cycle 2 is composed of a massive mudstone (USGS Micropa-
leontology Laboratory numbers Mf14402–Mf14411) that
becomes a silty mudstone (Mf14412) and a laminated silty
mudstone (Mf14413–Mf14425). The first hummocky cross-
bedded sandstone occurs between samples Mf14425 and
Mf14426. Above this, the middle part of the cycle is described
as a laminated muddy siltstone with thin hummocky sand-
stones or silty sandstones (Mf14427–Mf14453; Ragan et al.,
2023). The upper part of cycle 2 is a hummocky sandstone
Sacchi
Beach
Mbr.
sandstone of
Fivemile Pt.
of Wiley et al.
(2015)
6500
6000
5500
4000
3500
3000
2500
2000
1500
1000
4500
5000
500
0
Cummulative
Thickness (m)
Tyee Formation
Tyee Mtn. Member
EARLY
EOCENE MIDDLE EOCENE LATE EOCENE E. OLIG. MIDDLE
MIOCENE
LATE
MIOCENE
Empire
Formation
“Tarheel
formation”
Armentrout
(1967)
Tunnel
Point Sst.
Bastendorff
Shale
Coaledo Formation
upper
member
middle
member
lower
member
70575-600
245
425
760
570425
1525
420 950
EPOCH
FORMATION
THICKNESS (m)
gravelmud
fine sand
medium sand
coarse sand
<18.1 Ma
<15.9 Ma
<33.5 Ma
<33.5 Ma
<24.5 Ma
37.8 Ma
38.8 Ma
39.8Ma
45.4 Ma
<45.0 Ma
<45.0 Ma
40.9Ma
> 46.5 Ma
<53.9 Ma
Detrital Zircon ages
(Darin et al., 2022)
Paleodepth
Interpretation
23
Paleodepth
(km)
1
LB
LMB
UMB
UB
Lower bathyal
Water depth
Lower bathyal
Fluvio-deltaic
Middle bathyal
Coastal delta
Middle to
Lower bathyal
FIGURE 2. Stratigraphic column for the Coos Bay basin showing Cenozoic formations, contact relationships, thickness, age, lithology, detrital zircons
ages (Darin et al., 2022), and paleobathymetric interpretations based on Snavely et al. (1982) and Chan & Dott (1986). Paleobathymetric interpretations:
Fluvio-deltaic (at or above sea level), coastal delta (0–50 m below sea level), middle bathyal (500–2000 m below sea level), middle to lower bathyal (500
to 4000 m below sea level) and lower bathyal (2000–4000 m below sea level).
MICROPALEO EVIDENCE OF A SUBMARINE FAN 313
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with interbedded sandy siltstones and occasional muddy silt-
stones (Fault block B; Mf14454–Mf14469).
MATERIALS AND METHODS
Microfossil samples from cycle 2 from the lower Coaledo
Formation were collected on three separate occasions (Ragan
et al., 2023): 1) widely spaced samples (seven randomly
spaced samples throughout the cycle) collected in 2017 and
2019; 2) closely spaced samples (»1-m stratigraphic inter-
vals), collected in 2019, to provide detailed analysis of the
paleoenvironmental changes; and 3) samples collected in 2021
from the sandier upper parts of cycle 3, underlying cycle 2,
and upper part of cycle 2, top 20 m of fault block B. Microfos-
sil assemblages were also examined from cycle 10 or older
sediments at Ocean View or Collapse Cave Point; from cycles
9 through 6 in and near Simpson Cove and from cycle 4 along
the Qochyax Island Tombolo (Fig. 4; Ragan et al., 2023).
Samples were assigned laboratory numbers (MfXXXXX),
processed, and examined in the U.S. Geological Survey
Micropaleontology Laboratory in Flagstaff, Arizona (Appen-
dix A). The foraminiferal samples were processed with solvent
Middle CoaledoLower Coaledo
Cycle 1Cycle 2Cycle 3Cycle 4
FIGURE 3. Lower Coaledo Formation cycles 4 through 1 of Chan & Dott (1986) and the middle Coaledo Formation exposed in Sunset Bay State Park.
Photography by John Armentrout, University of Oregon, emeriti.
Bathers Cove
Sunset Bay
Qochyax
Is.
L. Coaledo
M. Coaledo
C4
C7
C8 C6
C10 C5
C9
C8
C9
C2
C3
C1
C4
C3 C2 C1
C4
C5
C9
C7
C10
C6
C7
C6
Simpson Cove
Sacchi Beach
Member of the
Tyee Formation
Lower Coaledo
Formation
Middle Coaledo
Formation
Simpson Reef Overlook
Sea Lion Cove Overlook
Ocean View North
Outer Ocean View and
Collapse Cave Point
Bathers Cove
(C9 to C7)
South Simpson Beach Cove (C7 to C6)
North Simpson Beach
Cove, Shore Acres
(C9 and C7)
Qochyax Island Tombolo (C4)
Sunset Bay (C3 to M. Coaledo)
Not to Scale
C-2
C-10
C-6
C-3
C-7
C-8
C-9
C-1
C-5
C-4
FIGURE 4. Generalized stratigraphic column for the lower Coaledo and adjacent units, and map showing location of cycles (C1, youngest, through C10,
oldest). Cycles of Chan & Dott (1983) are indicated on the stratigraphic column. Faults (dark orange dashed lines) are modified from Wiley et al. (2015).
Location of sections is from J.M. Armentrout (University of Oregon, written communication, 2019). Microfossil samples were collected from the underly-
ing Sacchi Beach Member of the Tyee Formation (location not shown on figure), all cycles except cycle 5 of the lower Coaledo Formation and from the
overlying Middle Coaledo Formation. Contact between Lower and middle Coaledo Formation is indicated by a dashed light orange line. Background
image is from Google Earth Pro 5/2015, and additional information on cycles and sample locations is available in Ragan et al. (2023). C 5cycle.
314 MCDOUGALL
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(kerosene) and Quaternary-O, washed through a 63-lm mesh
screen, and dried at low temperatures (,40°C). The entire
$150-lm fraction or a known split obtained using a micro-
splitter was picked for foraminifers, and the presence of frag-
ments, planktic foraminifers, and other organic remains
(radiolarians, diatoms, ostracodes, and fish debris) were noted
(Tables 1, 2, 3). Benthic foraminifer species identifications
were reviewed for consistency with modern taxonomy and
ecological considerations (Ragan et al., 2023). Foraminiferal
slides and residues are on file at the U.S. Geological Survey
Micropaleontology Laboratory in Flagstaff, Arizona.
Overall preservation of the benthic foraminiferal assem-
blages was assessed based on the absolute preservational scale
(APS) of Nguyen et al. (2009). The condition of the tests
(intact or broken chambers and number), etching, holes, and
pyrite fillings were noted (Table 3). Assemblages that con-
tained ,300 specimens or were barren are believed to have
been subjected to post-depositional factors. Criteria used to
interpret the paleoecological setting of these assemblages
includes bathymetry, species trends, agglutinated foraminiferal
morphogroups, epi/infaunal ratios, and dissolved oxygen in
addition to quantitative measures, such as foraminiferal abun-
dance, species richness, planktic/benthic ratio, and associated
microfossils.
Abundance is given as a percent of the total number of ben-
thic foraminifers counted in Tables 1–3. Diversity is given as
species richness (number of benthic foraminiferal species in
each sample), Shannon H(S), and Evenness indices. The Shan-
non H(S) and Evenness (e^H/S) indices were calculated for
the benthic foraminiferal assemblages using the PAST-soft-
ware program (Hammer et al., 2001).
Paleobathymetric interpretations are based on foraminiferal
bathymetric biofacies of Ingle (1980), which are specificto
the tectonically active East Pacific Margin and reflect the dis-
tribution of foraminiferal species based on water depth, water
mass, and physicochemical parameters. The approach taken
here builds on the biofacies developed by Ingle (1980) and
allows coeval foraminiferal assemblages along the East Pacific
Margin to be compared. Assignment of species to a biofacies
is based on overviews of Pacific benthic foraminifers, calcare-
ous and agglutinated species by Ingle (1980), Ingle & Keller
(1980), and studies of cosmopolitan benthic foraminifers by
Douglas (1981), Tjalsma & Lohmann (1983), Woodruff
(1985), van Morkhoven et al. (1986), Kaminski & Gradstein
(2005), and Hayward et al. (2012). Since foraminiferal assem-
blages can contain indigenous and transported species, the
abundance of each biofacies was determined by the percent
of benthic foraminiferal specimens with upper depth limits
TABLE 1. Distribution and abundance of foraminifers and associated microfossils in the lower Coaledo Formation, North Simpson Beach Cove, South
Simpson Beach Cove, and Bathers Cove, south of Coos Bay, Oregon. Samples are arranged stratigraphically from oldest to youngest. Abundances indicate
the percentage of the total benthic foraminiferal fauna or absent (-). Species richness is the number of species identified in the sample. Samples barren of
microfossils are indicated by light grey shading. Associated microfossils noted are the number of planktic foraminifers and ostracods observed in the sam-
ple and the relative abundance of other microfossils. Relative abundances are indicated by R (rare) 51 specimens; F (few) 52–10 specimens; C (com-
mon) 511–50 specimens; and A (abundant) $50 specimens. Data available from Ragan et al. (2023).
MICROPALEO EVIDENCE OF A SUBMARINE FAN 315
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(UDL) in each of the bathymetrically defined biofacies.
Depths associated with the bathymetric biofacies follows Ingle
(1980): inner neritic (0–50 m), outer neritic (50–150 m), upper
bathyal (.150–500 m), upper middle bathyal (.500–1500
m), lower middle bathyal (.1500–2000 m), lower bathyal
(.2000–4000 m), and abyssal (.4000 m). Species UDLs and
other ecological and environmental information are given in
the Taxonomic Notes (Fig. 5; Appendix B; Ragan et al.,
2023). Further analysis of these assemblages considered: epi/
infauna abundances, dominant species, environmental associa-
tions, habitat, food preferences, and oxygen constraints
(Corliss & Chen, 1988; Kaiho, 1991; Jorissen et al., 1995;
Kaminski & Gradstein, 2005; Jorissen et al., 2007; Thomas,
2007; Alegret et al., 2021).
AGE
The lower Coaledo Formation is Eocene in age: late Eocene
(Bird, 1967; Baldwin, 1974; Armentrout, 1981) and middle
Eocene, late Ulatisian to early Narizian Stages (Rooth, 1974;
Chan & Dott, 1986). Recent work on detrital zircons suggests
that the lower Coaledo Formation is middle Eocene, ranging
TABLE 2. Distribution and abundance of foraminifers and associated microfossils in the lower Coaledo Formation, Qochyax Island Tombolo, Coos Bay,
Oregon. Samples are arranged stratigraphically from oldest to youngest. Abundances indicate the percentage of the total benthic foraminiferal fauna or
absent (-). Species richness is the number of species identified in the sample. Samples barren of microfossils are indicated by light grey shading.
Associated microfossils noted are the number of planktic foraminifers and ostracods observed in the sample and the relative abundance of other microfos-
sils. Relative abundances are indicated by R (rare) 51 specimens; F (few) 52–10 specimens; C (common) 511–50 specimens; and A (abundant) $50
specimens. Data available from Ragan et al. (2023).
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from 43.4 to 42.0 Ma; samples from the top of the lower mem-
ber (cycle 1) were reported as 40.961.1 Ma (Fig. 6; Darin
et al., 2022). Paleomagnetic analysis of the Sacchi Beach
Member of the Tyee Formation and the Coaledo Formation
(Blackwell et al., 2021) suggest that the lower Coaledo Forma-
tion ranges from the latter part of Chron C20r through C19n,
approximately 44.5–42.1 Ma.
Foraminifers in cycle 2 of the lower Coaledo Formation
contain several age diagnostic species that suggest a middle
Eocene age, ranging from the very latest Ulatisian to early
Narizian Stages. This interpretation is based on the first
appearances of Caucasina schencki (coeval with planktic
zones E9–E16), Cibicides natlandi (E10–E15), Eggerella
elongata (E10–E16), Plectofrondicularia packardi (E10–E15),
and Pullenia salisburyi (E11 and younger), and the last
appearance of Spiroplectammina richardi (P4–E8 and ques-
tionably from E9–E14). The planktic foraminifer Pseudohasti-
gerina micra, also present, ranges from zone E7a through O1,
and thus overlaps the range based on benthic foraminifers.
Based on the global ranges of the benthic foraminifers, cycle 2
is correlative with planktic zones E10 through E14 and ranges
from 43.1 to 36.3 Ma. However, restrictions imposed by the
zircon dates (Darin et al., 2022) and paleomagnetic data
(Blackwell et al., 2021) indicate the age of cycle 2 is approxi-
mately 42.0 Ma and coeval with planktic zones late E10
through early E11 (Fig. 6).
FORAMINIFERAL RESULTS FROM CYCLE 2
ABUNDANCE AND DIVERSITY
Foraminifera in cycle 2 are common to abundant in most
samples: 44 samples contained $300 specimens, 16 samples
contained ,300 specimens, and 9 samples were barren
(Appendix C; Fig. 7). Barren samples and low abundance
samples occurred at the top of cycle 2. Species richness aver-
ages 18 species per sample in the lower part (samples
Mf14402–Mf14425), declining to ten per sample in the middle
part (samples Mf14426–Mf14453) and to two species per sam-
ple in the upper part (Fault Block B, samples Mf14454–
Mf14469). The Shannon index declines slightly upsection,
whereas the Evenness index increases (Fig. 8). The decline in
the foraminiferal number and various diversity indices corre-
sponds to the change in lithology and increase in sand content:
massive mudstones in samples Mf14402–Mf14411, laminated
silty mudstones in samples Mf14412–Mf14421, muddy silt-
stones with thin hummocky cross-bedded sandstones or sandy
siltstones from Mf14422–14453, and hummocky sandstones
with interbedded sandy siltstones and occasional muddy silt-
stones in samples Mf14454–Mf14469. The first hummocky
cross-bedded sandstone (HCS) occurs between sample
Mf14425 and Mf14426.
Planktic foraminiferal abundance and the ratio of planktic
to benthic foraminifers (P/B) in cycle 2 of the Coaledo For-
mation are low (Fig. 7). Few planktic foraminifers occur in
the lower part of the cycle but are very rare above sample
Mf14425. Diatoms and radiolarians are common to abundant
in the lower part of the cycle but decline above sample
Mf14425 (Fig. 7).
PRESERVATION
Foraminiferal assemblages containing 300 or more specimens
in lower Coaledo cycle 2 are moderately well preserved, but the
condition of specimens within the assemblage is highly variable.
Neritic and upper bathyal species are poorly to moderately pre-
served, whereas lower bathyal species are well preserved. Rare
inner neritic specimens are characterized by well-rounded and
worn tests (E. californicum;Fig.9.1)withmostofthesurface
ornamentationobscuredbybrokenandpyrite-filled tests with lit-
tle original shell material (Quinqueloculina,Figs.9.5–9.6). Outer
neritic specimens (Eponides,Lenticulina,andPlectofrondicu-
laria) show similar signs of wear and are broken or crushed and
are sometimes filled with pyrite (Figs. 9.7–9.12). Upper bathyal
specimens (e.g., Caucasina; Figs. 9.16–9.17) are moderately well
preserved with little to no breakage. Lower bathyal Gyroidina
specimens are well preserved, generally intact, and show little
sign of wear or breakage, although some tests may contain some
pyrite (Figs. 9.21–9.23). Based on the Absolute Preservation
Scale (APS) of Nguyen et al. (2009), inner neritic species have
TABLE 3. Preservational scale based on the Absolute Preservation Scale (APS) and a description of the observed preservation modified from Nguyen et
al. (2009).
Absolute preservation score (APS)
of Nguyen et al. (2009) Description of degree of preservation (Nguyen et al., 2009)
8 The whole specimen is intact (100%preserved).
7 No chambers missing. Some etching on the surface or the opacity of the test of benthic foraminifa starts to
increase (90–95%preserved).
6 The last chamber is breached or broken, or more or less missing, or it has a few scattered holes on the surface
(80–90%preserved).
5 The penultimate chamber is breached, broken, or missing, or the test has scattered holes, or the wall becomes
thinner, or some parts of the test (costae, ribs, etc.) dissappeared (70–80%presreved).
4 Three last chambers are broken or missing, or the whole test becomes considerably thinner, or scattered holes
are more frequent on the test (55–70%preserved).
3 Less than 70%of the chambers are preserved, or most of the wall of the last whorl is peeled off (40–55%
preserved).
2 Less than 50%of the chambers are present, or the test becomes so thin that it crumbles at the touch of the
brush (20–30%preserved).
1 Practically the entire test is destroyed, having either disappeared altogether, or with only small remains left.
Taxonomic identification is impossible (less than 20%preserved).
MICROPALEO EVIDENCE OF A SUBMARINE FAN 317
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an APS of 2 or 3; outer neritic species have a 3 or 4, upper and
middle bathyal species have a 5 or 6, and lower bathyal species
have a 7 or 8 (Table 3). This preservation pattern occurs in all
cycle 2 assemblages.
BATHYMETRY AND EPI/INFAUNAL CHARACTERISTICS
Biofacies analysis of the foraminiferal assemblages in cycle
2 of the lower Coaledo Formation indicates that species with
UDLs in the inner neritic occur sporadically (#7%); outer
neritic species are common throughout (#42%); upper and
middle bathyal species are few (#10%and #2%, respec-
tively); and lower bathyal species dominate (»54%; Fig. 10).
The dominance of lower bathyal species remains consistent
throughout the entire cycle, decreasing only in the poorly pre-
served samples at the top where barren and low abundance
samples occur. Outer neritic species decline up-section as
upper and middle bathyal species increase. Although speci-
mens are rare in the upper part of cycle 2 (Mf14454–
Mf14469), the outer neritic, upper bathyal, and lower bathyal
biofacies are present and in abundances similar to that seen in
the lower assemblages.
Epifaunal species are not common and occur primarily in the
lower part of cycle 2, whereas infaunal species dominate the
foraminiferal assemblages. Specimens from the inner neritic
biofacies are primarily infaunal (Nonion applini and rare Elphi-
dium californicum) with rare epifaunal (Quiqueloculina good-
speedi and Q. imperialis) specimens. Common outer neritic
epifaunal species are found in the lower part of the cycle, and
several specimens are found in association with the hummocky
cross-bedded sandstones at the top. Few outer neritic infaunal
species occur. Bathyal assemblages are dominated by infaunal
species. Caucasina schencki and Eggerella elongata are partic-
ularly abundant in the upper part of the section. Lower bathyal
infaunal species Haplophragmoides porrectus and Gyroidina
soldanii dominate. Tests of Haplophragmoides walteri and the
deeper water H. porrectus are fine-grained, smoothly finished
and use a dissolution-resistant cement, which is characteristic of
the lower part of the species depth range and below or in prox-
imity to the calcium compensation depth (CCD). Although
Gyroidina soldanii is typically considered an epifaunal species
common to well-oxygenated bottom waters, this species has
been found as shallow infauna in lower oxygen environments,
explained by its dependence on a supply of high-quality food
particles (Jorisson et al., 2007).
REFERENCES:
1. Ingle, 1980
2. Murray, 2006
3. Saelan and Hohenegger, 2018
4. Rau, 1948
5. Beck, 1943
6. Lagoe, 1988
7. Boltolsky et al., 1980
8. Murray, 2013
9. Kaminiski and Gradstein, 2005
10. Hayward et al. 2012
11. Murray et al., 2011
12. McDougall, 1980
13. Smith, 1964
14. Thomas, 1990
15. Pflum and Frerichs, 1976
16. Douglas and Heitman, 1979
17. McGann, 2014
18. Altenbch et al., 1999
19. Bandy, 1953
20. Ingle and Keller, 1980
Benthic Foraminiferal Bathymetric Biofacies
*All species in this genus are assumed to
represent shelf deposition (Murray, 1991).
LOWER BATHYAL
(>2000-4000 m)
Amphimorphina californica 10 I
Amphimorphina jenkinsi 10 I
Bathysiphon spp. 1,11 E
Dentalina consobrina 10 E
Gyroidina soldanii 1,19,20 E/I
Haplophragmoides porrectus 9,11 I
Haplophragmoides walteri 9I
Planktic Organisms1
PF: 5-30% **
R: 500-1000 specimens/gm
Displaced BF 50-100% of total benthics1
MIDDLE BATHYAL
(>500-2000 m)
Alabamina wilcoxensis 1 E
Anomalina garzaensis 1 E
Cibicides lobatulus 18 E
Dentalina jacksonensis 10 E
Eggerella elongata 11,1 2 I
Pseudonodosaria conica 1I
Planktic Organisms1
PF: 5-30% **
R: +500 specimens/gm
Displaced BF 50-100% of total benthics1
OUTER NERITIC
(>50-150 m)
Allomorphina conica1 I
Cibicidoides natlandi 5,6 E
Cornuspira byramensis 7,8 E
Cyclammina placenta 6,9 I
Dentalina dusenburyi 10 E
Eponides mexicanus 1 E
Gaudryina laevigata 1,9,11 I
Guttulina problema 1I
Lenticulina spp* E
Marginulina spp* E
Planularia tolmani 12 E
Plectofrondicularia packardi 1,6 E
Pullenia salisburyi 1,13 I
Robertina washingtonensis 1 E
Spiroplectammina richardi 1,9,11,12 E
Planktic Organisms 1
PF: 10--50%
R: <5 specimens/gm
Displaced BF <50% of total benthics1
INNER NERITIC
(0-50 m)
Elphidium californicum 1I
Nonion applini 1 I
Quinqueloculina goodspeedi 2,3 E
Quinqueloculina imperialis 3 E
Quinqueloculina weaveri 4 E
Planktic Organisms 1
PF: < 10%
R: <5 specimens/gm
Displaced BF: <10% of total benthics 1
UPPER BATHYAL
(>150-500)
Bolivina kleinpelli 5,12 I
Caucasina schencki 1,14 I
Cibicides elmaensis 12 E
Globocassidulina globosa 1,15 I
Globobulimina pacifica 1,16 I
Haplophragmoides spp. 12 I
Nodosaria longiscata 10 E
Oridorsalis umbonatus 1 E/I
Praeglobobulimina ovata 1I
Praeglobobulimina pupoides 1,17 I
Reophax pilulifer 9 I
Trifarina hannai 1 I
Uvigerina cocoaensis 1I
Planktic Organisms1
PF: 20-80%
R: <500 specimens/gm
Displaced BF 50-100% of total benthics1
**Excluding deep sea pelagic oozes
FIGURE 5. Diagnostic benthic foraminifers from East Pacific margin Paleogene bathymetric biofacies and microfaunal trends. The list of diagnostic
taxa has been modified from Ingle (1980) and includes references on new data; more specific information on the UDLs, and other paleoenvironmental data
is given in the Taxonomic Notes. The list has also been modified to include only those species present in the lower Coaledo Formation of southwestern
Oregon. Epifaunal/Infaunal designations are indicated: E 5Epifaunal, I 5Infaunal (Corliss & Chen, 1988; Corliss & Fois, 1990; Jorissen et al., 1994,
1995). Single asterisk (*) indicates a genus that is assumed to represent shelf deposition as this genus is not common in the deep sea [slope and abyssal
plain] in the Cenozoic (Murray, 1991). Double asterisk (**) excludes deep-sea pelagic oozes. Abbreviations: BF 5benthic foraminifers, PF 5planktic
foraminifers, R 5Radiolarians.
318 MCDOUGALL
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AGGLUTINATED BENTHIC FORAMINIFERS
Agglutinated foraminifers are not common in cycle 2 and
average only 25%of the benthic foraminiferal assemblage
(Fig. 11). Exceptions to this low abundance are spikes in the
abundance of H. porrectus and H. walteri (in samples
Mf14407, Mf14412, Mf14454, and Mf14457) that indicate a
physical disturbance, such as current activity. In both samples
Mf14407 and Mf14412, an increase in upper bathyal infaunal
species suggests that an upper slope failure may have
occurred. In samples Mf14453, Mf14454, and Mf14457 from
the top of the cycle, the abundance spike occurs in association
with an increase in sand and a probable increase in current
activity plus poor preservation possibly related to weathering,
as foraminifers are rare in these samples.
Morphogroup B3 (Murray et al., 2011; morphogroup 4 of
Kaminiski & Gradstein, 2005) dominates cycle 2 and includes
species of Haplophragmoides,Cyclammina,andCribrostomoides
(Fig. 11). Peak abundances of H. walteri alternate with H.
porrectus. Few specimens of Cyclammina placenta are present in
cycle 2. Although Ingle (1980) considered C. pacifica an upper
middle bathyal species along the east Pacific margin, subsequent
studies have placed this species in synonymy with Cyclammina
placenta and recognize the UDL, as in the outer neritic biofacies
(Lagoe, 1988; Kaminiski & Gradstein, 2005; Murray et al., 2011).
Morphogroup C1 is only moderately represented in cycle 2 and
includes few to common Reophax,Spiroplectammina,Gaudryina,
and Eggerella. Although Eggerella elongata is characteristic of
similar environmental conditions, it is more common in deeper
water and occurs in association with Haplophragmoides langsda-
lensis and H. walteri. Morphogroup A of Murray et al. (2011)
occurs rarely in cycle 2. Few specimens of Bathysiphon spp. occur
randomly throughout.
CALCAREOUS BENTHIC FORAMINIFERS
Calcareous benthic foraminiferal specimens dominate the
cycle 2 assemblages; few species are inner neritic and upper or
40.9+1.1 Ma, top L. Coaledo Fm.
(Darin et al., 2022)
Age of L. Coaledo Fm., detrital zircons
(43.4-42.0 Ma; Darin et al., 2022)
Age of L. Coaledo Fm., Sunset Bay,
Paleomagnetics (44.5-42.0 Ma;
Blackwell et al., 2021).
Age of Cycle 2, based on foraminifers
a
b
a
a
b
b
c
δ 18O (o/oo)
MPBE
EocenePaleocene
55
52
57
58
54
53
59
56
60
45
42
47
48
44
43
49
46
50
51
36
37
39
40
41
38
Epoch
Polarity
34
35
Time (Ma)
Chrons
Calcareous
Nannoplankton
Zones
Foraminiferal
Stages and Zones
Ulatisian Narizian
Penutian
Bulitian
Ynezian
Refugian
Sea Level
relative to modern
(m)
050 100 150 200
C26
C25
C24
C23
C22
C21
C20
C19
C18
C17
C16
C15
C13
P4
P5
E1
E2
E3
E4
E5
E6
E7
E8
E9
E10
E11
E12
E13
E14
E15
E16
NP5
NP6
NP7
NP8
NP9
NP10
NP11
NP12
NP13
NP14
NP15
NP16
NP17
NP18
NP19-
20
NP21
CP4
CP5
CP6
CP7
CP8
CP9
CP10
CP11
CP12 CP13 CP14
MECO
EECO
ETM
3
ETM2
PET
M
0+3
CP15
CP16
2+1+
late middleearly late
LLTM
(41.52 Ma)
Reticulophragmium
Glomospira acme
Nothia and/or
Trochamminoides
“Biofacies B” with
Glomospira
Karrerulina
Deep Water Agglutinated
Foraminiferal acmes
zones
Karrerulina
Reticulophragmium
amplectens
Spiroplectammina
Ammodiscus latus
1
2
3
4
5
6
7
Eocene Silica Accumulation Events (ESAE; Moore et al., 2008)
Calcium Accumulation Events (CAE; Lyle et al., 2005)
Equatorial
Pacific CCD
(km)
5.0 4.5 4.0 3.5
C.schencki
C. natlandi
E. elongata
P. packardi
P. salisburyi
S. richardi
P. micra
FIGURE 6. The age cycle 2 of the lower Coaledo Formation is based on the ranges of benthic foraminifers which gives an age range of E10 through
E14. This age is further modified based on paleomagnetic ages (Blackwell et al., 2021) and detrital zircon ages (Darin et al., 2022) which suggest that the
upper boundary of the lower Coaledo Formation is within Chron 20r, possibly earliest C19n and that the lower Coaledo ranges from 42.5 to 40.9 Ma. The
overlap of these ages indicates that cycle 2 of the lower Coaledo Formation is »42.75 Ma. These data are plotted on the Paleogene timescale modified
from McDougall (2007). Shown here is the international timescale of Gradstein et al. (2012, 2020), oxygen isotope curve of Zachos et al. (2008), and the
sea level curves of Kominz et al. (2009). The California benthic foraminiferal zonation is modified from McDougall (2007), and the Deep Water
Agglutinated Foraminiferal acme zones (DWAF; Kaminiski & Gradstein, 2005) are modified to include genera commonly used on the West Coast of
North America which are probably synonymous with the genera and species used by Kaminiski & Gradstein (2005). In addition, global events such as
hyperthermals and climatic optima are also identified. Hyperthermals are abbreviated: MPBE 5Mid-Paleocene Biotic Event; PETM 5Paleocene-Eocene
Thermal Maximum; ETM2 5Eocene Thermal Maximum 2; ETM3 5Eocene Thermal Maximum 3; and LLTM 5Late Lutetian Thermal Maximum.
Climatic Optima are abbreviated: EECO 5Early Eocene Climatic Optimum and MECO 5Middle Eocene Climatic Optimum. References for the hyper-
thermals and climatic optimums can be found in Westerhold et al. (2020). Eocene Silica Accumulation Events (ESAE; Moore et al., 2008) and Calcium
Accumulation Events (CAE; Lyle et al., 2005) and the depth of the Calcium Compensation Depth (CCD; Palike et al., 2012) and deep-water sources (Pak
& Miller, 1995; Lyle et al., 2008; Barron et al., 1991) are also plotted on this figure.
MICROPALEO EVIDENCE OF A SUBMARINE FAN 319
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Associated
microfossils
Barren
0
20
40
30
50
60
10
70
80
90
Fault Blk. A
Stratigraphic distance in meters
Mf 14394
Mf 14395
Mf 14396
Mf 14397
Mf 14398
Mf 14399
Mf 14400
Mf 14401
Mf 14402
Mf 14403
Mf 14404
Mf 14405
Mf 14406
Mf 14407
Mf 14408
Mf 14409
Mf 14410
Mf 14411
Mf 14412
Mf 14413
Mf 14414
Mf 14415
Mf 14416
Mf 14417
Mf 14418
Mf 14419
Mf 14420
Mf 14421
Mf 14422
Mf 14423
Mf 14424
Mf 14425
Mf 14426
Mf 14427
Mf 14428
Mf 14429
Mf 14430
Mf 14431
Mf 14432
Mf 14433
Mf 14434
Mf 14435
Mf 14436
Mf 14437
Mf 14438
Mf 14439
Mf 14440
Mf 14441
Mf 14442
Mf 14443
Mf 14444
Mf 14445
Mf 14446
Mf 14447
Mf 14448
Mf 14449
Mf 14450
Mf 14451
Mf 14452
Mf 14453
Mf 144 54
Mf 144 55
Mf 144 56
Mf 144 57
Mf 144 58
Mf 144 59
Mf 144 60
Mf 144 61
Mf 144 62
Mf 144 63
Mf 144 64
Mf 144 65
Mf 144 66
Mf 144 67
Mf 144 68
Mf 144 69
0
20
30
10
Fault Blk. B
1st HCS
0
2000
Benthic
Foraminiferal
number
0200
Planktic
Foraminiferal
number
P/B ratio
0 0.2 0.4 0.6 0.8 1.0
RFC
A
Diatoms
Radiolarians
0
massive mudstone
silty mudstone HCS
muddy sitstone with thin HCS
FIGURE 7. Number of benthic foraminiferal specimens, planktic foraminiferal specimens, ratio of planktic foraminifers to total number of foraminiferal
specimens (P/B), and the abundance of associated microfossils (diatoms and radiolarians) in cycle 2. The relative abundance of associated microfossils is
given as R 51 specimen; F 52–10 specimens; C 511–50 specimens; and A $50 specimens. Barren intervals are indicated by gray bands. HCS 5
Hummocky cross-bedded sandstone.
320 MCDOUGALL
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0
20
40
30
50
60
10
70
80
90
Fault Blk. A Barren
Stratigraphic distance in meters
Mf 14394
Mf 14395
Mf 14396
Mf 14397
Mf 14398
Mf 14399
Mf 14400
Mf 14401
Mf 14402
Mf 14403
Mf 14404
Mf 14405
Mf 14406
Mf 14407
Mf 14408
Mf 14409
Mf 14410
Mf 14411
Mf 14412
Mf 14413
Mf 14414
Mf 14415
Mf 14416
Mf 14417
Mf 14418
Mf 14419
Mf 14420
Mf 14421
Mf 14422
Mf 14423
Mf 14424
Mf 14425
Mf 14426
Mf 14427
Mf 14428
Mf 14429
Mf 14430
Mf 14431
Mf 14432
Mf 14433
Mf 14434
Mf 14435
Mf 14436
Mf 14437
Mf 14438
Mf 14439
Mf 14440
Mf 14441
Mf 14442
Mf 14443
Mf 14444
Mf 14445
Mf 14446
Mf 14447
Mf 14448
Mf 14449
Mf 14450
Mf 14451
Mf 14452
Mf 14453
Mf 14454
Mf 14455
Mf 14456
Mf 14457
Mf 14458
Mf 14459
Mf 14460
Mf 14461
Mf 14462
Mf 14463
Mf 14464
Mf 14465
Mf 14466
Mf 14467
Mf 14468
Mf 14469
0
20
30
10
Fault Blk. B 0 1000 2000 3000
Benthic Foramniferal
number
0
Species
Richness (S)
10 20 30 0 1 200.40.81.2
Evenness_e^H/S
Shannon (H)
1st HCS
MICROPALEO EVIDENCE OF A SUBMARINE FAN 321
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middle bathyal, but outer neritic and lower bathyal species are
common (Fig. 10). Dominant calcareous species (i.e., species
with abundances greater than 10%in multiple samples) con-
tained Nonion applini (average 55%) from the inner neritic
biofacies; Cibicidoides natlandi (2.5%), Epondies mexicanus
(»4%), Lenticulina inornata (13%), and Plectofrondicularia
packardi (1.3%) from the outer neritic biofacies; Caucasina
schencki (4.6%) from the upper bathyal biofacies; and Gyroi-
dina soldanii (28%) from the lower bathyal biofacies (Fig.
12). The abundance of these species drops considerably in the
hummocky cross-bedded sands in the top of the cycle where
Caucasina schencki (13%), Gyroidina soldanii (7%), and Len-
ticulina inornata (5.6%) dominate and the other species
decline [Nonion applini (2.5%), Eponides mexicanus
(0.34%)], or disappear from the assemblages (Cibicidoides
natlandi and Plectofrondicularia packardi). The distribution
of Globocassidulina globosa is also noted, as this is an impor-
tant upwelling indicator species (Gooday, 1994; Mackensen
et al., 1995; Suhr et al., 2003; Ortiz & Thomas, 2015), but
only rare specimens were observed in cycle 2, occurring in the
lower part of the cycle (average ,0.14%; Fig. 12).
OXYGEN CONDITIONS
The dominance of infaunal species in cycle 2 (Fig. 10) sug-
gests that lower oxygen conditions prevailed. Although epifau-
nal species are present in the lower part of the cycle, these
specimens are transported from the shelf and do not represent
the conditions at which deposition was occurring. The benthic
foraminiferal oxygen index (BFOI) of Kaiho (1994, 1999) and
abundances of the species associated with various oxygen lev-
els (Kaiho, 1999; Cannariato & Kennett, 1999) indicates that
the benthic foraminifers in cycle 2 were deposited under sub-
oxic conditions (0.3–1.2 mL O
2
/L; Fig. 13).
Genera characteristic of oxic conditions (.1.5 mL O
2
/L)
include various Cibicides (C. elmaensis,C. lobatulus,C. nat-
landi), Eponides,Globocassidulina, and Quinqueloculina.
This group occurs mainly in the lower part of cycle 2 and rep-
resents neritic biofacies identified as transported, due to pres-
ervation. Suboxic (0.3–1.5 mL O
2
/L) genera include
Lenticulina,Marginulina,Dentalina,Bulimina,Bolivina, rare
Anomalina,Caucasina,Gyroidina, and Nonion. These domi-
nate throughout cycle 2 and are represented by both epifaunal
and infaunal species. Only rare dsyoxic (0.1–0.3 mL O
2
/L)
species are present in cycle 2. The abundance in Mf14424 is
due to a poorly preserved assemblage and low foraminiferal
number.
MICROFOSSILS IN OTHER LOWER COALEDO
FORMATION CYCLES
Ten cycles were identified by Chan & Dott (1986; Fig. 4).
Each cycle, except cycle 5, was examined for microfossils, but
sampling was not as detailed as in cycle 2. No foraminifers
were found in samples from cycle 10 or older sediments at
Ocean View or Collapse Cave Point (Fig. 4). Only samples
from cycles 9 through 6 in and near Simpson Cove and cycle
4 along the Qochyax Island Tombolo contained foraminiferal
assemblages that could be compared with cycle 2.
Samples from cycles 9 through 6 of Chan & Dott (1986)
were collected from several outcrops in North and South
Simpson Coves and Bathers Cove (Figs. 14–17). Microfossil
samples are from the silty mudstones between the hummocky
cross-bedded sandstones (Table 1; Ragan et al., 2023). Most
samples in cycles 9 through lower cycle 7 at all three locations
are poorly preserved due to weathering and contain rare fora-
minifers (,300 specimens/sample), but preservation and fora-
miniferal abundance are better in the middle to upper part of
the section, cycles 7 and 6 (Figs. 14, 16). Preservation of the
benthic foraminifers is similar to that seen in cycle 2: neritic
species are poorly preserved and have an APS score of 3 or
less, upper and middle bathyal species have a 5 or 6, and lower
bathyal species have a score of 7 or 8. Planktic foraminifers
are rare, but diatoms and radiolarians are common (Table 1).
Planktic organisms are preserved as siliceous molds with little
original shell material or pyrite molds with no original shell
material.
Bathymetric biofacies analysis of the foraminiferal assem-
blages at Simpson Cove indicates that the neritic biofacies are
not well represented, averaging about 20%, while the lower
part of the Simpson Cove samples contains abundant upper
bathyal species with the lower bathyal species dominating
cycles 9 through 6 (Fig. 14). At Bathers Cove, the neritic biof-
acies is better represented: 33.3%,0%, 18.9%, 30.2%, and
23.5%, respectively for cycles C10 through C6 (Fig. 16).
However, samples Mf14348 through Mf14351 are large sam-
ples specifically designed to sample lenses rich in macrofos-
sils. These samples are skewed towards the neritic biofacies as
the macrofossils and unidentified shell fragments are primarily
transported and from the shelf edge (C. Hickman, University
of California, written communication, 2022). When these sam-
ples are removed from the analysis, the neritic biofacies, cycle
7, declines to an average of 26.8%.
Distribution patterns of the diagnostic foraminiferal species
observed in cycle 2 are not evident in these cycles, probably
due to lack of detailed samples, low foraminiferal numbers,
and poor preservation (Fig. 14, 16). However, Gyroidina sol-
danii is the dominant species throughout all cycles. Poorly
preserved intervals, intervals with ,300 specimens/sample,
are dominated by agglutinated genera Haplophragmoides and
Eggerella with dissolution resistant tests that are common to
abundant throughout cycles 9 through 7, and Gaudryina (Fig.
9.14) is common in the middle part of cycle 7 at all three loca-
tions. Poorly preserved specimens of Elphidium californicum
are common in samples associated with shell fragments in the
foraminiferal residue or visible in the outcrop.
Cycle 4 was sampled at low tide along the Qochyax Island
Tombolo (Fig. 4). Although detailed sampling was not done
FIGURE 8. Number of benthic foraminiferal specimens, species richness (number of species per sample), and diversity indices for cycle 2 of the lower
Coaledo Formation are shown. Diversity indices shown here are the Shannon and Evenness. Barren intervals are indicated by gray bands. The number of
foraminiferal specimens and species per sample declines slightly up section in the fossiliferous intervals. This trend is reflected in the Shannon index
whereas the evenness (number of specimens per species) shows a slight increase in the upper part of cycle 2, below the barren interval. See Figure 7 for
explanation of lithology. HCS 5Hummocky cross-bedded sandstone.
322 MCDOUGALL
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FIGURE 9. Foraminifera from the lower Coaledo Formation. 1Elphidium californicum Cook, worn, sample Mf14330, cycle 7, North Simpson Cove.Bar equals
40 mm. Magnification X189. 2Nonion applini Howe and Wallace, with broken chambers and pyrite filling, sample Mf14409, cycle 2, Sunset Bay.Bar equals 40 mm.
Magnification X230. 3Nonion applini Howe & Wallace,crushed, sample Mf14423, cycle 2, Sunset Bay.Bar equals 40 mm. Magnification X174. 4Nonion applini
Howe & Wallace,filled with pyrite, sample Mf14370, cycle 4, Qochyax Island Tombolo. Bar equals 40 mm. Magnification X267. 5Quinqueloculina imperialis Hanna
& Hanna, broken chambers and pyrite filling, sample Mf14444, cycle 2, Sunset Bay. Bar equals 40 mm. Magnification X206. 6Quinqueloculina imperialis Hanna &
Hanna, broken chambers and pyrite filling, sample Mf14409, cycle 2, Sunset Bay. Bar equals 40 mm. Magnification X160. 7Lenticulina inornata (d’Orbigny),broken
chambers, sample Mf14409, cycle 2, Sunset Bay. Bar equals 100 mm. Magnification X99. 8Lenticulina inornata (d’Orbigny), broken chambers, sample Mf14409,
cycle 2, Sunset Bay. Bar equals 100 mm. Magnification X82. 9Lenticulina inornata (d’Orbigny), broken chambers, sample Mf14423, cycle 2, Sunset Bay. Bar equals
40 mm. Magnification X166. 10 Plectofrondicularia packardi Cushman & Schenck, broken chambers, sample Mf14370, cycle 4, Qochyax Island Tombolo. Bar equals
40 mm. Magnification X161. 11 Eponides mexicanus (Cushman), broken chambers, sample Mf14409, cycle 2, Sunset Bay. Bar equals 100 mm. Magnification X99. 12
Eponides mexicanus (Cushman), broken chambers, sample Mf14330, cycle 7, North Simpson Cove. Bar equals 100 mm. Magnification X 106. 13 Cibicidoides nat-
landi (Beck), sample Mf14409, cycle 2, Sunset Bay. Bar equals 100 mm. Magnification X142. 14 Gaudryina laevigata Franke,broken chambers, sample Mf14330,
cycle 7, North Simpson Cove. Bar equals 100 mm. Magnification X97. 15 Spiroplectammina richardi Martin, crushed, sample Mf14409, cycle 2, Sunset Bay. Bar
equals 40 mm. Magnification X164. 16 Caucasina schencki (Beck), broken chambers, sample Mf14423. Bar equals 40 mm. Magnification X211. 17 Caucasina
schencki (Beck), sample Mf14370, cycle 4, Qochyax Island Tombolo. Bar equals 40 mm. Magnification X281. 18 Globocassidulina globosa, sample Mf14370, cycle
4, Qochyax Island Tombolo. Bar equals 40 mm. Magnification X399. 19 Haplophragmoides walteri (Grzybowski), sample Mf14423, cycle 2, Sunset Bay. Bar equals
20 mm. Magnification X254. 20 Subbotina eocaena (Gumbel), sample Mf14409, cycle 2, Sunset Bay. Bar equals 40 mm. Magnification X246. 21 Gyroidina soldanii
d’Orbigny, sample Mf14409, cycle 2, Sunset Bay. Bar equals 40 mm. Magnification X197. 22 Gyroidina soldanii d’Orbigny, sample Mf14330, cycle 2, Sunset Bay.
Bar equals 40 mm. Magnification X175. 23 Gyroidina soldanii d’Orbigny, sample Mf14370, cycle 4, Qochyax Island Tombolo. Bar equals 40 mm. Magnification
X203. 24 Haplophragmoides porrectus Maslakova, sample Mf14423, cycle 2, Sunset Bay. Bar equals 40 mm. Magnification X254. 25 Amphimorphina jenkinsi
(Church), sample Mf14370, cycle 4, Qochyax Island Tombolo. Bar equals 100 mm. Magnification X135.
MICROPALEO EVIDENCE OF A SUBMARINE FAN 323
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for this cycle and many samples have few to no foraminifers
(,300 specimens/sample), a number of samples do contain
common to abundant foraminifers (Fig. 18; Table 2). Planktic
foraminifers were not observed in this section, but diatoms
and radiolarians are common to abundant in the lower part of
cycle 4. Preservation of the foraminiferal assemblages is simi-
lar to that seen in cycle 2: neritic species are poorly preserved
and have an APS score of 3 or less, upper and middle bathyal
species have a 5 or 6, and lower bathyal species have a 7 or 8.
Bathymetric biofacies analysis indicates that inner neritic spe-
cies are rare (averages »3%), outer neritic species are com-
mon (average 33.4%), with few upper bathyal species (16%),
rare middle bathyal species (,1%), and common lower
bathyal species (30.6%). The distribution of key species is like
that observed in cycle 2, with outer neritic epifaunal species
with heavy tests (Lenticulina spp., E. mexicanus,C. natlandi,
and P. packardi) most common in the lower part of the section
and poorly preserved (APS of 2–3). Caucasina schencki and
species of Bolivina and Bulimina appear in the middle to upper
part of the section, along with rare Globocassidulina globosa
(Fig. 19). Lower bathyal species, Gyroidina soldanii and Hap-
lophragmoides spp., dominate the section (Fig. 19). The disso-
lution-resistant tests of Haplophragmoides walteri and H.
porrectus allow these species to dominate the poorly preserved
samples. Foraminifers decline in abundance as the sand com-
ponent increases at the top of the section.
DISCUSSION
Deposition of cycle 2 of the lower Coaledo Formation
occurred in the middle Eocene, early Narizian Stage of Mal-
lory (1959; as modified by McDougall, 2007). An age of
41.8–42.0 Ma is indicated for Cycle 2 based on the overlap-
ping age ranges of foraminiferal biostratigraphy, detrital zir-
cons, and paleomagnetic analysis. This age suggests that cycle
2, which is near the top of the lower Coaledo Formation, was
deposited when sea level was approximately 50 m higher than
present (Westerhold & Rohl, 2013; Intxauspe-Zubiaurre et al.,
Barren
Tick marks = 10%
Inner
Neritic
Outer
Neritic
Upper
Bathyal
Lower
Bathyal
infauna, IN
epifauna, IN
infauna, ON
epifauna, ON
infauna, LBinfauna, UB
Epifauna Infauna
Epifauna
Infauna
Middle
Bathyal
Infauna
infauna, MB
Paleodepth
Interpretation
Lower bathyal;
transport from the
shelf edge and
upper slope
23
Paleodepth (km)
1 4
BLA
LMB
UMB
Lower bathyal;
transport from
shelf edge
UB
Lower bathyal;
transported
specimens
reduced
Lower bathyal;
transport from the
shelf edge
Chan and Dott
(1986) Paleodepth
Paleodepth based
on foraminifers
0
20
40
30
50
60
10
70
80
90
Fault Blk. A
Stratigraphic distance in meters
Mf 14394
Mf 14395
Mf 14396
Mf 14397
Mf 14398
Mf 14399
Mf 14400
Mf 14401
Mf 14402
Mf 14403
Mf 14404
Mf 14405
Mf 14406
Mf 14407
Mf 14408
Mf 14409
Mf 14410
Mf 14411
Mf 14412
Mf 14413
Mf 14414
Mf 14415
Mf 14416
Mf 14417
Mf 14418
Mf 14419
Mf 14420
Mf 14421
Mf 14422
Mf 14423
Mf 14424
Mf 14425
Mf 14426
Mf 14427
Mf 14428
Mf 14429
Mf 14430
Mf 14431
Mf 14432
Mf 14433
Mf 14434
Mf 14435
Mf 14436
Mf 14437
Mf 14438
Mf 14439
Mf 14440
Mf 14441
Mf 14442
Mf 14443
Mf 14444
Mf 14445
Mf 14446
Mf 14447
Mf 14448
Mf 14449
Mf 14450
Mf 14451
Mf 14452
Mf 14453
Mf 14454
Mf 14455
Mf 14456
Mf 14457
Mf 14458
Mf 14459
Mf 14460
Mf 14461
Mf 14462
Mf 14463
Mf 14464
Mf 14465
Mf 14466
Mf 14467
Mf 14468
Mf 14469
0
20
30
10
Fault Blk. B
1st HCS
FIGURE 10. Epifaunal/infaunal, biofacies, and paleobathymetry of cycle 2. The abundance of epifaunal and infaunal specimens is based on the percent-
age of each group from the total benthic foraminiferal fauna. Biofacies analysis indicates the abundance of specimens with upper depth limits (UDLs) in
each of the biofacies. Biofacies faunas are also separated into epi- and infaunal species except for the lower bathyal biofacies which contains only infaunal
species. Paleobathymetric interpretation based on benthic foraminifers as well as the paleobathymetry determined by Chan & Dott (1986). See Figure 7 for
explanation of lithology. HCS 5Hummocky cross-bedded sandstone; IN 5inner neritic biofacies; ON 5outer neritic biofacies; UB 5upper bathyal
biofacies; MB 5middle bathyal biofacies; UMB 5upper middle bathyal biofacies; LMB 5lower middle bathyal biofacies; LB 5lower bathyal biofa-
cies; A 5abyssal biofacies.
324 MCDOUGALL
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2018; Westerhold et al., 2020) and the CCD was 4 to 4.5 km
below sea level (Palike et al., 2012). This interval coincides
with the onset of a calcium carbonate accumulation event
(CAE) that is marked by a high-carbonate burial, a relatively
deep CCD, and evidence of cool global conditions (CAE3;
Lyle et al., 2005, 2008; Moore et al., 2008).
Foraminifers are common to abundant in cycle 2 except near
the top of the cycle where hummocky cross-bedded sandstones
dominate. Abundance declines gradually as sand becomes more
common. Foraminifers are scarce or absent at the top of the sec-
tion, as is most organic matter, and occur primarily in the inter-
bedded silty mudstones. Overall preservation of the assemblages
in cycle 2 is moderate; however, preservation within an
assemblage is highly variable. Neritic specimens are poorly pre-
served, often broken, crushed, or dissolved, but bathyal speci-
mens are well preserved. The low abundance and poor
preservation of the neritic species indicates transport from the
shelf, whereas the well-preserved middle to lower bathyal spe-
cies suggest in situ deposition. Displaced or transported speci-
mens are common along an active margin and can comprise
more than 50%of the assemblage at lower bathyal depths (Ingle,
1980). The low numbers of planktic foraminifers suggest prox-
imity to the coast and deposition on an active margin but may
also indicate exclusion due to the influx of freshwater. The abun-
dance of diatoms and radiolarians in the lower part of cycle 2
suggests deposition is occurring near the base of the slope.
Barren
Mf 14403
Mf 14404
Mf 14412
Mf 14419
Mf 14429
Mf 14435
Mf 14443
0200400600
Agglutinated
Foraminiferal
number
0
Species
Richness
246
B3
C1
B3
C1
Morphogroups
of Murray et al.
(2011)
A morphogroup
B3 morphogroup
C1 morphogroup
A
B3
H. porrectus
(LB)
H. walteri
(UMB)
C. placenta
(ON)
G. laevigata
(ON)
E. elongata
(UMB)
Tick marks = 10%
0
20
40
30
50
60
10
70
80
90
Fault Blk. A
Stratigraphic distance in meters
Mf 14394
Mf 14395
Mf 14396
Mf 14397
Mf 14398
Mf 14399
Mf 14400
Mf 14401
Mf 14402
Mf 14405
Mf 14406
Mf 14407
Mf 14408
Mf 14409
Mf 14410
Mf 14411
Mf 14413
Mf 14414
Mf 14415
Mf 14416
Mf 14417
Mf 14418
Mf 14420
Mf 14421
Mf 14422
Mf 14423
Mf 14424
Mf 14425
Mf 14426
Mf 14427
Mf 14428
Mf 14430
Mf 14431
Mf 14432
Mf 14433
Mf 14434
Mf 14436
Mf 14437
Mf 14438
Mf 14439
Mf 14440
Mf 14441
Mf 14442
Mf 14444
Mf 14445
Mf 14446
Mf 14447
Mf 14448
Mf 14449
Mf 14450
Mf 14451
Mf 14452
Mf 14453
Mf 14454
Mf 14455
Mf 14456
Mf 14457
Mf 14458
Mf 14459
Mf 14460
Mf 14461
Mf 14462
Mf 14463
Mf 14464
Mf 14465
Mf 14466
Mf 14467
Mf 14468
Mf 14469
0
20
30
10
Fault Blk. B
1st HCS
FIGURE 11. Abundance and distribution of agglutinated foraminifers in cycle 2 of the lower Coaledo Formation. The abundance of agglutinated fora-
minifers and the species richness indicate that this group is only moderately abundant in this interval. Morphogroup analysis indicates the dominance of
Morphogroup B3 of Murray et al. (2011), moderate numbers of C1 and rare A morphogroups. The distribution of key species present in this interval is
shown. See Figure 7 for explanation of lithology. HCS 5Hummocky cross-bedded sandstone; ON 5outer neritic biofacies; UMB 5upper middle bathyal
biofacies; LB 5lower bathyal biofacies.
MICROPALEO EVIDENCE OF A SUBMARINE FAN 325
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Biofacies analysis of foraminiferal assemblages indicates that
cycle 2 was deposited at lower bathyal depths (2000–4000 m)
in suboxic conditions and with abundant organic material. The
massive and laminated silty mudstones at the base of the cycle
(Mf14402-Mf14425) are dominated by lower bathyal species in
association with planktic organisms (diatoms, radiolarians, and
rare to few planktic foraminifers) and transported benthic spe-
cies. Gyroidina soldanii and several species of Haplophrag-
moides are the dominant lower bathyal species in this interval.
Gyroidina soldanii is a shallow infaunal species found in lower
oxygen environments where there is a supply of high-quality
food particles and increased terrigenous detrital material
(Heinze & Wefer, 1992; Jorisson et al., 2007). Haplophrag-
moides walteri and H. porrectus, members of morphogroup B3,
are tolerant of oxygen-poor environments and significant
organic matter (Wa
skowska, 2021) and have smooth, dissolu-
tion-resistant tests, which implies deposition at the deeper por-
tion of their depth range (bathyal to abyssal; Kaminiski &
Gradstein, 2005). These species also indicate pulsed or seasonal
food sources, lower oxygen conditions, and vigorous bottom
currents and sandy sediments (Gooday, 1994; Schmiedl et al.,
1997; Ortiz & Thomas, 2015). Morphogroup C1, particularily
Gaudryina laevigata, are common in this interval and indicate
low dissolved oxygen, high productivity, and increased organic
matter flux (Kaminiski & Gradstein, 2005; Murray et al., 2011).
The transported benthic foraminifers (Lenticulina,Cibicides,
Eponides,andPlectofrondicularia) are primarily from the outer
neritic biofacies, epifaunal, tend to inhabit areas with current
activity, and have sturdy tests that can withstand transport
(Beck, 1943; Lagoe, 1988). Transported inner neritic species
Barren
Tick marks = 10%
G. soldanii
(LB)
N. applini
(IN)
0.00
E. mexicanus
(IN/ON)
L. inornatus
(ON) C. natlandi
(ON)
P. p a ck a rd i
(ON)
Globocassidulina globosa
*
*
*
*
*
*
*
*
*
*
C. schencki
(ON/UB)
0
20
40
30
50
60
10
70
80
90
Fault Blk. A
Stratigraphic distance in meters
Mf 14394
Mf 14395
Mf 14396
Mf 14397
Mf 14398
Mf 14399
Mf 14400
Mf 14401
Mf 14402
Mf 14403
Mf 14404
Mf 14405
Mf 14406
Mf 14407
Mf 14408
Mf 14409
Mf 14410
Mf 14411
Mf 14412
Mf 14413
Mf 14414
Mf 14415
Mf 14416
Mf 14417
Mf 14418
Mf 14419
Mf 14420
Mf 14421
Mf 14422
Mf 14423
Mf 14424
Mf 14425
Mf 14426
Mf 14427
Mf 14428
Mf 14429
Mf 14430
Mf 14431
Mf 14432
Mf 14433
Mf 14434
Mf 14435
Mf 14436
Mf 14437
Mf 14438
Mf 14439
Mf 14440
Mf 14441
Mf 14442
Mf 14443
Mf 14444
Mf 14445
Mf 14446
Mf 14447
Mf 14448
Mf 14449
Mf 14450
Mf 14451
Mf 14452
Mf 14453
Mf 14454
Mf 14455
Mf 14456
Mf 14457
Mf 14458
Mf 14459
Mf 14460
Mf 14461
Mf 14462
Mf 14463
Mf 14464
Mf 14465
Mf 14466
Mf 14467
Mf 14468
Mf 14469
0
20
30
10
Fault Blk. B
1st HCS
FIGURE 12. The distribution and abundance of key calcareous species present in cycle 2 of the lower Coaledo Formation are shown. Specimens of
Globocassidulina globosa are rare, so asterisks (*) are used to indicate samples where this species is present. See Figure 7 for explanation of lithology.
HCS 5Hummocky cross-bedded sandstone; IN 5inner neritic biofacies; ON 5outer neritic biofacies; UB 5upper bathyal biofacies; LB 5lower
bathyal biofacies.
326 MCDOUGALL
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Barren
0
20
40
30
50
60
10
70
80
90
Fault Blk. A
Stratigraphic distance in meters
Mf 14394
Mf 14395
Mf 14396
Mf 14397
Mf 14398
Mf 14399
Mf 14400
Mf 14401
Mf 14402
Mf 144 03
Mf 144 04
Mf 14405
Mf 14406
Mf 14407
Mf 14408
Mf 14409
Mf 14410
Mf 14411
Mf 144 12
Mf 14413
Mf 14414
Mf 14415
Mf 14416
Mf 14417
Mf 14418
Mf 144 19
Mf 14420
Mf 14421
Mf 14422