Upper Paleocene to Lower Eocene ("Meganos stage") marine megafossils in the uppermost Santa Susana Formation, Simi Valley, southern California

38 Pages·1999·34.9 MB·English

by  Richard L Squires

Upper Paleocene to Lower Eocene (“Meganos
Stage”) Marine Megafossils in the
Uppermost Santa Susana Formation,
Simi Valley, Southern California
Richard L. Squires1
ABSTRACT. Uppermost Paleocene to lowermost Eocene (“Meganos Stage”) marine rocks arerareonthe
Pacific coast of North America, and the upper 100 m of the Santa Susana Formation in Simi Valley
represents the only known “Meganos Stage” rocks in southern California. This report concerns the first
detailed study ofmega-invertebrate fossils in this part ofthe formation. The fossils are inthin lensesthat
formed as storm-lag accumulations in a relatively shallow, offshore environment. Thirtylocalitiesyielded
a total of38 megafossil taxa identifiable to species or subspecies. These include one isidid octocoral,one
solitary coral, two colonialcorals, 17gastropods, 14 bivalves, twocrabs, andonespatangoidechinoid.A
new species of solitary coral, ?Antillopbyllia californica new species, is described and named. A possible
new species ofthecolonialcoralAstrocoeniaisdescribed. Turritellaandersonisusanaeislocallyabundant
and one ofthe most diagnostic species ofthe “Meganos Stage” in the SimiValley area.
Most of the studied megafauna is known from elsewhere in Pacific coast Eocene strata, primarily in
California. The molluscan-stage ranges of approximately one third ofthe studied mega-invertebrates are
extended downward to the “Meganos Stage,” based on their presence in the upper 100 m of the Santa
SusanaFormation.Themolluscan-stagerangesofthegastropodRingicula (R.)pinguis,thebivalveSaulella
undulifera, andthecrab CyclocorystesaldersoniareextendedupwardfromthePaleocene“MartinezStage”
to the “Meganos Stage.” In addition, a few of the mega-invertebrates have their geographic ranges ex-
tended. The isidid octocoral tMopsea sp., aff. M. costata is the first record of an isidid from Paleogene
rocksonthePacificcoastofNorthAmerica.Thestudiedmegafaunaisindicativeofwarm-waterconditions,
and some ofthe taxa are conspecificwith orclosely alliedto Old World Tethyan mollusks.
INTRODUCTION tiallyunfossiliferousoutcropsstratigraphicallylow-
er in the Santa Susana Formation. Many previous
Since the early 1900s, paleontologists have collect-
workers seemed to have assumed that the upper
ed marine megafossils from the Santa Susana For- m
100 are not particularly fossiliferous. Locally,
mation in the Simi Valley area (Fig. 1), Ventura however, megafossils are abundant there, and their
County, southern California. These fossils, which
preservationcan be good. The purpose ofthispres-
are predominantly mollusks, have been studied by
Waring (1917), Nelson (1925), Fantozzi (1955), ent study is to document the taxonomic composi-
tion of the megafossil content in these upper 100
and Zinsmeister (1983a, 1983b), but their studies
m. This informationwillhelpgreatlyinrefiningthe
dealt only with “Martinez Stage” rocks of late Pa-
molluscan stage ranges of these taxa because the
leocene age in the lower part of the formation on m
upper 100 of this formation correlate to the
the south side of Simi Valley. Although various
workers have found a few mollusks in the upper “Meganos Stage” oflatest Paleocene to earliestEo-
100mofthe Santa SusanaFormation,todatethere cene age. Rocks deposited on the Pacific coast of
hasnotbeenacomprehensivestudyofthesefossils. North America during this time interval are rela-
Poor exposures, absence of fossils at many locales, tively rare, and those in the study area represent
and generally poor preservation have discouraged the onlyknown “MeganosStage”rocksinsouthern
such study, and prior to this study no one had ever California.
“walked out” the stratigraphic interval throughout The molluscan stage terminology used in this re-
port includes the upper Paleocene “Martinez
the Simi Valley area. In addition, outcrops of the
upper 100 m of the Santa Susana Formation have Stage,” the uppermost Paleocene to lowermostEo-
the same color and general appearance of essen- cene “Meganos Stage,” the middle lower “Capay
Stage,” the upper lower to lower middle “Domen-
gine Stage,” the lower middle “Transition Stage,”
1. Department of Geological Sciences, California State
University, Northridge, California 91330-8266, and Re- andthemiddlemiddleEocenetoupperEocene“Te-
search Associate in Invertebrate Paleontology, Natural jon Stage.” The stage names are in quotes because
History Museum of Los Angeles County, Los Angeles, they are informal terms and in essence equivalent
California 90007-4000. to formation names. Clark and Vokes (1936) gave
Contributionsin Science,Number479, pp. 1-38
Natural HistoryMuseum ofLos Angeles County, 1999
a historical overview of these stage names. Givens sanaFormationisdisconformablyoverlainbybasal
(1974) modified the use ofthe “Capay Stage,” and conglomerate of the Llajas Formation (Fig. 2), and
it is in this modified sense that the “Capay Stage” the contact is an uneven erosion surface with as
is used here. Saul (1983) and Squires (1984, 1987, much as 1 m ofrelief. Thin beds oflaminatedsand-
1988a) regarded the modified “Capay Stage” of stone alternating with thin beds of bioturbated
Givens (1974) as middle lower Eocene. sandstone containing vertical Ophiomorpha bur-
rows are present at the top of the Santa Susana
STRATIGRAPHY
Formation at two places on the north side of the
The upper 100 m of the approximately 1000-m- valley. One location is at CSUN locality 968, and
thick Santa Susana Formation in the Simi Valley the other location is just north of the Marr Ranch
area consists mostlyofgray, veryfine-grainedsand- (Fig. 3) in the northeastcorner ofsection 31,T3N,
stone, with some gray muddy to sandy siltstone. R17W, where the type section ofthe overlying Lla-
Locally, there are concentrations of fossil-shell jas Formation is located (see Squires, 1981:fig. 3)
hash, and rocks surrounding these localized con- (Fig. 3).
m
centrations are barren of megafossils. The lower Sedimentaryrocksintheupper 100 oftheSan-
part of the upper 100 m of the Santa Susana For- ta Susana Formation are not resistant and are usu-
mation has a gradational lithology fromthe under- ally poorly exposed orcovered. The bestexposures
lying gray mudstone and siltstone. The Santa Su- are onthenorthsideofSimiValley,where 19fossil-
2 Contributionsin Science, Number 479 Squires: “Meganos Stage” Marine Megafossils
ity 959, there is a thin lens containing abundant
<UL>) O) Turritella uvasana infera Merriam, 1941 and the
+0-3> oc lens is traceable laterally for about 6 m. This lo-
0>003> uCL O calOitny itshenoswouutnhdesirdehoomfeSismities.Valley, 11 fossil-col-
u0C3l rcoo lecting localities have been found in the upper 100
_Q 968disconformity m of the Santa Susana Formation (Figs. 1, 4). An
isolated locality (CSUN 1565) is in Bus Canyon,
• LACMIP 26615 and another isolated locality (UCMP loc. 7009) is
• 1349
• LACMIP 26611 near Meier Canyon (Fig. 1); the other localitiesare
• LACMIP 21550 intwogroups,withsixlocalitiesfoundmostlynear
• 1565 the top ofthe Santa Susana Formation in the Run-
Q)
O) • 1347,1348 kle Canyon area and three localities justeastofthe
03
04c1o-0/>3 (CQ~_D> •• 1935484 cRaarulenitksiliesmeiolCanarnttyhoeotnshoofusateuhltosni(Fdtiehg.eof4n)oS.ritmAhitsVmiaodlseletoy,foftthhteehevfsaoelslseliyol-,s
0C3D • 959,960-967 and there are concentrations of unabraded fossil-
<D • 1345,1346 shell hash in thin lenses whose tops and bottoms
• 967-973 are indistinct. Abundant weathered-out specimens
C03 of the solitary coral ?Antillophyllia California new
0C3O • 1343 species, abundant tips (apices) of turritellas, and
0=03 • 1342,LACMIP commonly occurring mostly right valves of the bi-
oo<C0D) (0U3 OCCLD 0c003 77100294,UCMP vSataqluCvierSePUsyNcannlododcaoDlneimtteyet1(rP3ih4oy3ng.,ra1e9a9)0sp.w,erafef.fPo.u(nP.d)pianciffliocaat
03
_C00L3> 0-Nt0-J 0CCL0J gafTohsseilrelloactailvietystirnattihgeraupphpicerpo1s0i0tiomn ooff tehaechSamnet-a
L_ CCD 20m Susana Formation, on both the north and south
<D
Q. side of Simi Valley, is show in Fig. 2.
CL
ZD
00
OCL DEPOSITIONAL ENVIRONMENT
basenotmeasured
Parker (1983) did the most current and detailed
Figure2. Stratigraphiccolumnoftheupper 100 mofthe study ofthe depositional environment ofthe Santa
Santa Susana Formation (and of the immediately under- Susana Formation andreportedthattheverticalse-
lying and overlying strata), showing subseries,provincial
quence of the Simi Conglomerate, Las Virgenes
molluscan stages, calcareous nannofossil biozones (CP
Zones), and stratigraphic position of each of the mega- Sandstone, and Santa Susana Formationrepresents
fossil-collectinglocalities.AgeofthelowerpartoftheLla- a transition from nonmarine to deep-marinefacies.
jas Formation from Squires (1984). The distribution of these facies is, in part, defined
by the Runkle Canyon-BurroFlatsfaultzone inthe
central part ofthe south side ofSimiValley. Parker
(1983) referred to strata west of this fault zone as
the “western facies,” and these include, from base
collectinglocalitieshave beenfound (Fig. 3). CSUN to top, braided river, meandering stream, near-
localities 962 through 967 are approximately shore, transition zone, offshore to shelf, and slope
aligned along the same strike and form a series of deposits. Hereferredto strataeastofthisfaultzone
localities that parallels the top ofthe Santa Susana as the “eastern facies,” and these consist mostly of
Formation. CSUN localities 969 through 973 are slope and inner-fan deposits. The fault zone juxta-
similarly aligned. Four localities (CSUN 968, LAC- posescoevalnonmarineanddeep-marinerocksand
MIP21550, LACMIP26611,andLACMIP26615) accounts for the fact that nonmarine to nearshore
are near the top of the formation. At nearly all of Las Virgenes Sandstone, for example, is present
the localitiesonthenorthsideofSimiValley,fossils only west of the fault (Fig. 5).
are concentrated in lenses about 20 cm thick and Parker (1983) reported that although the Santa
several meters in lateral extent. The tops and bot- Susana Formation was mostly deposited in deep
toms ofthe lenses are indistinct. The bivalvesinthe water, the sedimentology ofthe upper 100mofthe
lenses are almost always single valves and usually formation throughout the Simi Valley area reflects
broken, and many of the associated gastropods upliftto shelfdepthspriortodepositionofthenon-
consistoffragments. Althoughthefossils aremost- marine basal part of the Llajas Formation. New
ly broken, none shows any obvious signs of abra- sedimentologic information obtained during this
sion. Specimens of Turritella andersoni susanae presentstudyshowsthattheshallowingeventPark-
Merriam, 1941 are plentiful and dominate the oth- er (1983) recognized produced, toward the top of
erwise usually meager megafauna. At CSUN local- the Santa Susana Formation, sediments deposited
Contributionsin Science,Number 479 Squires: “Meganos Stage” MarineMegafossils 3
Figure 3. Geologic map showing location ofmegafossil localities (CSUN localities unless otherwisenoted) onthenorth
sideofSimiValley. BasemapisU.S. GeologicalSurvey, 7.5-minute,SantaSusanaquadrangle, 1951 (photorevised1969),
Ventura County, southern California. Geology from Squires (1983b).
in progressively more shallow water. Beds of alter- part of the overlying Llajas Formation, is charac-
nating laminated sandstone and bioturbated sand- teristic of modern and ancient shoreface to upper
stone (e.g., at CSUN loc. 968) were found at the offshore environments (Squires, 1981).
top ofthe formation, and this alternation oflithol- Heitman (1983), on the basis of benthic forami-
ogies,whichisalsopresentintheshallowestmarine niferal assemblages, also reported that the upper-
4 Contributionsin Science, Number 479 Squires: “Meganos Stage” Marine Megafossils
Figure 4. Geologic map showing location ofmegafossil localities (CSUN localities unless otherwisenoted) onthesouth
side ofSimi Valley. Base maps are U.S. Geological Survey, 7.5-minute Calabasas quadrangle, 1952 (photorevised1967);
and Santa Susana quadrangle, 1951 (photorevised 1969), Ventura County, southern California. Geology from Squires
(1983b).
mostpartofthe SantaSusanaFormationrepresents transport of the shallow-marine mollusks was not
a shoaling event associated with basin filling that great.
deposited a silty sandstone just above the shelf- At all of the fossil localities mentioned in this
slope break. Filewicz and Hill (1983), on the basis present report, fossils occur as concentrations in
ofcalcareous nannofossil datums and sediment-ac- small lenses of sandstone surrounded by siltstone
cumulation rates, reported that silty sandstones in usually barren of megafossils. The tops and bot-
m
the upper Santa SusanaFormation (20 belowthe toms of these lenses are indistinct, and Squires
base of the overlying Llajas Formation) were de- (1981) reported similar lenses in the overlying Lla-
posited just above the shelf-slope break. jas Formation, where the shallow-marine facies
Squires (1991a) and Saul and Squires (1997) in- grades into outer shelf to slope facies. In this tran-
m
terpreted that megafossils in the upper 100 of sitional paleoenvironment, the contacts of the fos-
the Santa Susana Formation on the north side of siliferous lenses were rendered indistinct by the ac-
Simi Valley are shallow-marine forms deposited as tivities of burrowing organisms shortly after depo-
storm-lagaccumulationsinarelativelyshallow,off- sition ofthe sediments, undoubtedly just like those
shore environment. This more detailed present inthe upper 100 m ofthe Santa Susana Formation.
study further supports these earlier interpretations. It is readily apparentthat the fossils in the upper
m
Squires (1990) suggested that the fossiliferous 100 of the Santa Susana Formation have under-
lens at CSUN locality 1342, in the upper 100 m of gone some postmortem transport, based on their
the formation on the south side ofSimiValley, rep- broken conditionandlocalizedconcentrations.The
resents a storm deposit in a middle to outer shelf distance of this transport was not great based on
environment, and that the distance of postmortem the absence ofany evidence ofsignificantabrasion.
Contributions in Science, Number479 Squires: “Meganos Stage” MarineMegafossilsH5
Clark
Waring Clark Nelson Clark Parker, 1983, Mollusk
1921,
1917 1 1918 Kew 1925 1926 Saul, 1983, & "Stages"
This Report
1924
W W W
E E E
Tejon Tejon Domen- "Domen-
Meganos Domengine gine Llajas gine"
Fm. Fm.
Fm. Fm. "Capay"
Meganos SSuasnatnaa upper 100 m of "Meganos"
Santa Susana Fm.
Fm.
Martinez
Santa
5
Martinez £- Martinez Susana Santa Susana "Martinez’
marine marine Shales Fm.
c5
Martinez member member
ci'
r
Fm. C_j>
(D 3
Martinez 1ȣ re
5
Las c£ Las er
Virgenes Virgenes a>
I^~
Sandstone Sandstone
Simi Conglomerate Simi Conglom.
Chico Chico Fm Chico Chatsworth Fm. Campanian
Figure 5. Comparative concepts oflowerPaleogene stratigraphic units in the Simi Valley area. The letters “W” and“E”
refer to west and east ofthe Runkle Canyon fault (shown in Fig. 1).
Inaddition,thefossilsareecologicallysimilar.Buri- but the distance of transport was not far. Beds at
alwas rapid because thereis a scarcityofepibionts. the top of the formation were deposited in a shal-
Most of the fossils represent storm-lag accumula- lower environment (shoreface).
tions in a middle-to-outershelfenvironment,where
fine sands accumulated in close proximity to silt- MEGAFAUNA
stone. Bioturbation must have obliterated any ini-
tially sharp contacts that would have been formed A total of 560 megafossil specimens were collected
along the bottoms of the fossiliferous lenses. from 30 localities. Preservation ranges from poor
CSUNlocality 1343,however,isunusualbecause to good, and many of the fossils are badly weath-
the abundant specimens of the solitary coral? An- ered or in hardconcretions. Thirty-eightmegafossil
tillophyllia californica newspeciesfoundtherecon- taxa were identified to genus and species/subspe-
stitute agrowthseries. Thesecoralsmusthavelived cies. These include one octocoral, one solitary cor-
in close proximity to where they were buried and al, two colonial corals, 17 gastropods, 14 bivalves,
experienced much less distance of postmortem two crabs, and one spatangoid echinoid. Other
transport than the other associated fossils. taxa too poorly preserved for generic identification
In summary, the overall fine-grained rock type, include one solitary coral, one scaphopod, three
the assemblages of benthic foraminifera, the local- gastropods (anaticid, acymatiid,andaturrid),and
ized concentrations of unabraded shallow-marine four bivalves (a pinnid, a lucinid, a pitarinid, and
megafossils, and alternating rock types at the top a solenid). The poorly preserved solitary coral was
ofthe formation indicate thatthe bulkoftheupper mentioned by Durham (1943:199, pi. 32, fig. 22),
100 m of the Santa Susana Formation in the Simi who reported two specimens from UCMP locality
Valley area was deposited in a relatively shallow, 7000 (exactlocation notknown). Onlytheexterior
offshore environment (middle-to-outer shelf morphology of this coral is known. It is alate and
depths). Storm surges transported the megafossils, somewhat flabelliform, but better preserved speci-
6 Contributionsin Science, Number 479 Squires: “Meganos Stage” Marine Megafossils
mens and studies of their interiors are needed to (1918), and the type section of this stage is in the
determine the familial or generic assignments. No Deer Valley area north of Mount Diablo, Contra
new specimens were found during this present Costa County, northern California, where Clark
study. Durham (1943) identified the coral as Fla- (1918, 1921) subdivided the Meganos Formation
bellumstantoniDurham, 1943,anamethathealso into five major lithologic members. Starting at the
gave to specimens that Vaughan (1900:67-68, pi. base, he designated the members as Divisions A, B,
4, figs. 5, 6) had misidentified as Flabellum remon- C, D, and E. The molluscan fauna from this series,
dianum Gabb (1864:207, pi. 26, fig. 199). whichwasstudiedindetailbyClarkandWoodford
Vaughan’s specimens were probably collectedfrom (1927), comes from Division D. Almgren et al.
“Martinez Stage” rocks near Benicia in northern (1988: fig. 4) assigned Division D strata oftheMe-
California. Durham (1943) wasprobablycorrectin ganos Formation to the CP9 Zone (lowest Eocene)
giving the name F. stantonitoVaughan’sspecimens of the standard calcareous nannofossil zonation.
from Benicia, but whether or not this name is ap- Most of the “Meganos Stage” correlates with the
propriate for the two poorly known coral speci- CP9Zone, butthelowerpartofthestagecorrelates
mens from the upper part ofthe Santa Susana For- to the CP8 Zone (uppermost Paleocene). The age
mation is an open question. These two coral spec- of the “Meganos Stage,” therefore, corresponds to
imens are not the same as the new species of soli- the latest Paleocene to earliest Eocene (Saul, 1983;
tary coral described here. Squires, 1988a, 1997). Modern workers now refer
Although early workers (Clark, 1921:table 1; to the strata of Division D of the Meganos For-
1926:114-116;Kew, 1924:25;Nelson, 1925:pl.61, mation as the Margaret Hamilton Sand (Edmond-
and foldout between pages 402 and 403) gave fau- son, 1984).
nal lists for so-called “Meganos” age-strata in the Filewicz and Hill (1983:fig. 5) reported calcare-
Simi Valley area, there are serious problems in try- ous nannofossils diagnostic of the lower Eocene
ing to use these lists because (1) detailed locality Diseoaster diastypus (CP9) Zone of the standard
information is lacking, and (2) previously usedfor- calcareous nannofossil zonationfrom siltstonesim-
mation names (e.g., Meganos and Domengine) are mediately below the upper 100 m of the Santa Su-
m
not exact equivalents of the upper 100 of the sana Formation on the north side of Simi Valley.
Santa Susana Formation (Fig. 5). In addition, be- The upper 100 m on the north side of Simi Valley
cause these species names have only been listed, are barren ofany calcareous nannofossils (Filewicz
without illustration or reference to cataloguedmu- and Hill, 1983), as well as any planktonic forami-
seum specimens, there is no way to verify the iden- nifera (Heitman, 1983). Filewicz and Hill (1983)
m
tifications. did notstudy the upper 100 ofthis formationon
Three previously named megafossil species have the south side of Simi Valley. In the course of this
m
theirtype localities in the upper 100 ofthe Santa present study, I collected 12 microfossil samples
Susana Formation in the Simi Valley area. Theyare from the upper 100 m of the Santa Susana For-
the gastropod Corsania (Januncia susana Saul and mation on the south side of Simi Valley. The cal-
)
Squires, 1997andthe bivalvesArea (Area)filewiezi careous nannofossils are rare, poorly preserved,
Squires, 1991a and Netastoma squiresi Kennedy, and, as with those from the north side ofSimi Val-
1993. In addition, the following two species could ley, only present near the bottom of the 100-m-
probably be added to this list. Although the de- thick interval, where the siltstone contentishigher.
scription of the type locality of the bivalve Veneri- Only two samples, those from CSUN localities
eardia (Pacificor) susanaensis Verastegui, 1953, is 1342 and 1343, yielded anycalcareousnannofossil
somewhat vague, this locality is most likely in the data pertinent to geologic age determination. Both
m
upper 100 ofthe formation. As will be discussed samples yielded a late Paleocene age, probably
under“Age,” thetype localityofthegastropodTur- equivalent to the Diseoaster multiradiatus (CP8)
ritella andersoni susanae was reported (Merriam, Zone of the standard calcareous nannofossil zona-
1941) from the basal part ofthe Llajas Formation, tion (M. V. Filewicz, personalcommunication).No
but the actual stratigraphic position ofthis locality planktonic foraminifera were recovered from any
is probably in the upper 100 of the Santa Susana of the 12 microfossil samples (H. L. Heitman, per-
Formation. sonal communication).
As mentionedearlier, thestratigraphicnomencla-
AGE ture of the upper part of the Santa Susana Forma-
tion in the Simi Valley area has been confusingly
The upper 100 m ofthe Santa Susana Formationis inconsistent. Similarly, the concept of the “Mega-
latestPaleocenethroughearliestEocene (“Meganos nos Stage” in this area has lacked biostratigraphic
Stage”) in age, based on calcareous nannofossils, precision. Saul’s (1983) study ofthe turritellas and
mollusks, sporomorphs, and magnetostratigraphy. venericardias in the various Paleogene formations
Assignmentsto thecalcareousnannofossilbiozones in the Simi Valley area helped greatly in clarifying
and provincial Pacificcoast ofNorthAmerica low- theproperassignmentofprovincialmolluscanstag-
er Paleogene molluscan stages are shown in Fig- es to these formations. She reported that Turritella
ure 2. andersoni susanae, T. uvasana infera, T. megano-
The term “Meganos Stage” stems from Clark sensis Merriam, 1941 and Venericardia (Paeifieor)
Contributionsin Science,Number479 Squires: “Meganos Stage” Marine Megafossils 7
) )
hornii susanaensis are important megafaunal com- position of the upper 100 m of the Santa Susana
ponents of the upper 100 m of the Santa Susana Formation was also coincident with an overall
Formation and enable correlation ofthese rocks to global sea-level rise (supercycle TA2 of Haq et al.,
the northern California-based concept ofthe “Me- 1987).
ganosStage.” Turritellameganosensis,furthermore, The latestPaleocene to earliest Eocene age (“Me-
m
is also found at the type section (Margaret Hamil- ganos Stage”) of the upper 100 of the Santa Su-
ton Sand) ofthis stage in northern California. Tur- sana Formation corresponds to an absolute age of
ritella andersoni susanae is locally plentiful in the 53 to 55 Ma (Berggren et al., 1995). Based ontheir
m m
upper 100 ofthe formation and isprobablycon- presence in the upper 100 of the Santa Susana
fined to the “Meganos Stage.” A single specimen, Formation, the molluscan-stage ranges ofnine spe-
which is the holotype of this gastropod, however, cies can be extended downward to the “Meganos
was reported from the basal part (“Capay Stage”) Stage.” These species are: Velates perversus (Gme-
ofthe overlying Llajas Formation on the northside lin, 1791), Pacbycrommium clarki (Stewart, 1927),
of Simi Valley. It seems highly probable that the Arcbitectonica (A.) llajasensis Sutherland, 1966,
stratigraphicposition ofthislocalityisinerror,and Cylicbnina tantilla (Anderson and Hanna, 1925),
that the holotype is actually from the upperpartof Spondylus carlosensis Anderson, 1905, Macoma
the Santa Susana Formation. Turritella uvasana in- rosa Hanna, 1927, Pitaruvasana coquillensisTurn-
fera is found in both the “Meganos Stage” and in er, 1938, Corbula Caryocorbula dickersoniWeav-
( )
the overlying “Capay Stage.” er and Palmer, 1922, and Corbula Caryocorbula
(
The only well-described (Clark and Woodford, parilis Gabb, 1864. Similarly, the presence of As-
1927) megafauna of “Meganos” age is that of the trocoenia sp. and Pycnodonte {Phygraea sp., aff.
Margaret Hamilton Sand at the type section ofthe Pycnodonte (Pbygraea) pacifica Squires and De-
“Meganos Stage” in Deer Valley, Contra Costa metrion, 1990,inthe upper 100moftheformation
County, although strata (“MeganosFormation”) of represents the earliest occurrences of Astrocoenia
this age are also known from south ofRound Val- and Pbygraea in the Paleogene rock record of the
ley on the Middle Fork ofEel River in Mendocino Pacific coast of North America.
County, northern California. Other than Turritella The molluscan-stage ranges of three species in
meganosensis, species found in both the Margaret the study area can be extended upward from the
Hamilton Sand and the upper 100 m of the Santa Paleocene “Martinez Stage” to the “Meganos
Susana Formation are Calyptraea diegoana (Con- Stage.” These species are: Ringicula (R.) pinguis
rad, 1855) [= Calyptraea Galerus calabasaensis (Gabb, 1864), Saulella undulifera (Gabb, 1869),
( )
Nelson, 1925], Bracbyspbingus mammilatus Clark and Cyclocorystes aldersoni Squires, 1980.
and Woodford, 1927, Nuculana Saccella gabbii
( )
(Gabb, 1869) [= Leda gabbii (Gabb, 1869)], and PALEOCLIMATE AND
Schizaster diabloensis Kew, 1920. Gemmula sp., PALEOBIOGEOGRAPHY
aff. G. diabloensisClarkandWoodford, 1927from
m
the upper 100 of the Santa Susana Formation As reviewed by Squires (1987), the world climate
has close affinity to G. diabloensis from the Mar- was relatively warm and equable during most of
garet Hamilton Sand. the Paleocene through early middle Eocene time,
Frederickson (1983) reported early Eocene spo- and a worldwide late Paleocenewarmingtrendcul-
romorphs from the upper 100 m of the Santa Su- minated in a period of peak warming during the
sana Formation on the north side of Simi Valley. earlyEocene. Also reviewed bySquires (1998),dur-
The presence ofthese early Eocene sporomorphs is ing late Paleocene to early middle Eocene time, hu-
best documented near the top of the upper 100 m mid tropical climatic conditions were prevalent in
of the formation. coastal-lowland areas from Baja California, Mexi-
Bottjer et al. (1991) reported that, in terms of co, to southwestern Washington.
m
magnetostratigraphy, the lowermostpartoftheup- Megafossils in the upper 100 ofthe Santa Su-
m
per 100 of the Santa Susana Formation on the sana Formation strongly support the presence of
north side of Simi Valley is correlative to Chron tropical waters. The hermatypic colonial coral ge-
C24R, which is equivalent to an interval that en- nus Astrocoenia lives today only in the WestIndies
compasses the Paleocene-Eocene boundary (Berg- and is a reef dweller in shallow, tropical seas (Dur-
gren et al., 1995). ham, 1942). Although Paleocene and early Eocene
Simi Valley is part of the Western Transverse reef corals seldom formed true reefs, by middle
Ranges tectonic block, which has been rotated by through late Eocene times they started to build
Neogene displacements. Before rotation, this block reefs, and Astrocoenia was one ofthese reefbuild-
lay adjacentto SanDiego andAnaheiminsouthern ers inthe Caribbeanregion (Buddetal., 1992).The
California. During the Miocene, the block was ro- extinct gastropod genus Corsania is indicative of
tated clockwise. Its northern end (which included warm climate (Saul and Squires, 1997), and mod-
Simi Valley) acted as the pivotal area and remained ern Campanile is also indicative of warm waters
essentiallyinplace (Atwater, 1998). TheEocenepa- and very shallow depths (Squires, 1993). The bi-
leolatitude of the Simi Valley area, therefore, was valve Area s.s. most frequently inhabits tropical
probably not much different than it is today. De- waters today (Keen, 1971; Abbott and Dance,
8 Contributionsin Science, Number 479 Squires: “Meganos Stage” Marine Megafossils
1982), and the same is true of the bivalves Spon- ANSP CAS: California Academy ofSciences,
dylus (see Squires, 1984:table 5) and Fimbria (see San Francisco
Nicol, 1950). ANSP CSUN: California State University,
Northridge
The late Paleocene and early Eocene were times ANSP LACMIP: Natural HistoryMuseum ofLos
ofmajor immigration ofOld WorldTethyanmega-
Angeles County, Invertebrate Paleontology
invertebrates into the Pacific coast region ofNorth Section
America via a seaway, mostlikelythroughtheCen- ANSP UCMP: University ofCalifornia, Museum
tral America seaway (Clark and Vokes, 1936; Giv- ofPaleontology, Berkeley
ens, 1978, Zinsmeister, 1983a; Squires, 1984, ANSP UCR: UniversityofCalifornia, Riverside
1987). One of the most important of these is the ANSP USNM: United States National Museum,
gastropod Velates perversus, which dispersedwest- Washington, D.C.
wardly from Pakistan into California (Squires,
1987; Squires and Demetrion, 1992). The new oc- atTChSeUbNu.lkNoefwthespceoclileesctpiroinmsaursyedtyipnethmiastsetruiadlyaarnedhohuyspeo-d
currenceofthisspeciesinthe“Meganos”-ageupper
m types ofthe invertebrates used for illustrations in this re-
100 of the Santa Susana Formation provides it port are depositedat LACMIP.
with a slightly earlier arrival date in California.
Additional mollusk taxa in the upper part ofthe SYSTEMATICS
Santa Susana Formation that have been recognized
asTethyan orofTethyanaffinity (ClarkandVokes, Phylum Cnidaria Hatschek, 1888
1936; Squires, 1984; 1987, 1990, 1991a; Givens, Class Anthozoa Ehrenberg, 1834pqc
1989) and must have accompanied Velates perver-
sus into the waters of the Pacific coast of North Subclass Octocorallia Haeckel, 1866
America are Pachycrommium, Area s.s., and Fim- Order Gorgonacea Lamouroux, 1816
bria. Although Campanile is also indicative ofOld
World Tethyan connections, this genus had already Family Isididae Lamouroux, 1812
arrived onto the Pacific coast region by the late Pa-
Genus Mopsea Lamouroux, 1816
leocene (“Martinez Stage”) (Squires, 1993).
As will be indicated in the “Systematics” section, TYPE SPECIES. Isis dichotoma Linnaeus, 1758,
some other megafossils found in the upper part of by subsequent designation Milne-Edwards and
the Santa Susana Formation are stronglysuggestive Haime, 1850; Recent, Antarctica.
of Old World Tethyan connections. The octocoral
IMopsea sp., aff. M. costata Milne-Edwards and }Mopsea sp., aff. M. costata Milne-Edwards
Haime, 1850 is remarkably similar to M. costata and Haime, 1850
from the lower Eocene London Clay in southern Figures 6, 7
England. The crab CyclocorystesaldersoniSquires,
1980 is most similar to C. pulchellus Bell, 1858, LOCAL OCCURRENCE. CSUN loc. 1343.
also from the lower Eocene London Clay. Cyclo- REMARKS. Twenty-six fragments were collect-
corystes is only known fromthese two species.The ed, and they consist of straight-to-curved,cylinmdrmi-
gastropod ?Ancillarinasp.,whichmightbetheonly cal calcareous internode axial stems up to 23
known record of this genus in the Western Hemi- long. The stemsare longitudinallymarkedbyclose-
sphere, is most similar to A. canalifera (Lamarck, ly spaced ribs that bear small spines.
1802) from the Paris Basin, France. Few published reports exist describing fossil oc-
tocoral remains. The isidid octocorals areprobably
SYSTEMATIC MATERIALS AND METHODS the most common forms preserved because of ex-
tensive calcification of the axis (Kocurko, 1988).
Systematicarrangementofthehighertaxa followsthatof Unfortunately, generic determinations of isidid oc-
Bayer (1956) fortheoctocoral,Wells (1956) forthescler- tocorals cannot be reliably made using onlycalcar-
actinians, Vokes (1980) for the bivalves, and Glaessner eous internode-stem material. Soft-part morpholo-
(1969) for the crabs. The higher classification of gastro- gy and microscopic spicularmaterial are alsoneed-
pods is in a state offlux, and some ofthecategoriesused ed (Bayer, 1956, and personal communication).
hereforsuprafamilialnamesarereferredtoassuperorders The Santa Susana Formation specimens are re-
and generally correspond to major clade names used by
markably similar to the calcareous axial parts of
Ponder and Lindberg (1996, 1997).
Synonymies (primarily including only figured speci- Mopsea costata Milne-Edwards and Haime, 1850,
mens), primarytype material, molluscanstagerange,and from the lower Eocene London Clay in southern
geographic distribution data are given forthe identifiable England. The Santa Susana Formation specimens
species.Termsusedtodenotespecimenabundancearede- differ from M. costata Milne-Edwards and Haime
fined as follows (number of specimens in parentheses): (1850:42, pi. 7, figs. 3, 3a) only by having more
rare(1-4),uncommon(5-9),common(10—29),andabun- elongate spines. To a slightlylesserdegree, the San-
dant (30 or more). Abbreviations for catalog and/or lo- ta SusanaFormationspecimens alsoresembleMop-
cality numbers are: sea encrinula (Lamarck, 1815) that lives today in
ANSP:Academy ofNatural Sciences, New Caledonian waters. The Santa Susana For-
Philadelphia mation specimens differ from M. encrinula, which
Contributionsin Science,Number479 Squires: “Meganos Stage” Marine Megafossils 9
10 Contributionsin Science,Number 479 Squires: “Meganos Stage” Marine Megafossils