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PALEOGEOGRAPHIC IMPLICATIONS OF MOLLUSCAN ASSEMBLAGES IN THE UPPER () PIGEON POINT FORMATION,

William P. Elder LouElla R. Saul U. S. Geological Survey, Natural History Museum Mail Stop 915, of Los Angeles County, 345 Middlefield Road, 900 Exposition Boulevard, Menlo Park, CA 94025 Los Angeles, CA 90007

ABSTRACT formation's place of deposition relative to cratonic . The Pigeon Point Formation crops out along the San Mateo County coastline in a This paleogeographic controversy was northern and southern sequence of folded and generated by paleomagnetic data reported by faulted strata. Correlation of the two se- Champion and others (1981, 1984), which indi- quences remains somewhat equivocal, although cate that the Pigeon Point Formation was de- on the basis of biostratigraphy and a re- posited as much as 2500 km south of its pre- versed magnetic interval both appear to have sent latitude, or at the approximate latitude been deposited during the early to middle of southern in the . Campanian. Sedimentary structures suggest The formation has been considered by many to that the northern sequence was deposited by overlie basement rocks of the Salinian ter- turbidity currents in a continental rise set- rane (e.g. Howell and Vedder, 1978; Champion ting, whereas the southern sequence primarily and others, 1984), causing speculation that reflects deposition in shelf and slope envi- that terrane is far traveled. However, other ronments . geologic and paleomagnetic evidence suggests that Salinia has had more limited tectonic Right-lateral offset on the San Andreas transport (James and Mattinson, 1988; Lund and subsidiary faults to the east of the Pi- and others, 1991; Whidden et al., 1991). In geon Point Formation can account for 100's of addition, sandstone petrology and conglomer- km of northward transport since its deposi- ate clast composition of the Pigeon Point tion. However, Champion and others (1984) Formation is not characteristic of Cretaceous suggested 2500 km of northward transport from strata underlain by Salinian basement else- a tropical setting of about 21'N. Molluscan where (Lee-Wong and Howell, 1977; Grove, assemblages in the formation argue strongly 1989) . Instead, conglomerate clast composi- for a less tropical site of deposition. tion is suggestive of Late Cretaceous rocks Relative abundances of warm and temperate of the Sur-Obispo terrane (Grove, 1989), taxa and the presence or absence of key spe- which coincidentally does contain paleomag- cies are similar to those of the Santa Ana netic evidence of substantial northward Mountains Cretaceous section, and are indica- translation (Lund and others, 1991). tive of a warm-temperate to subtropical site of deposition. This paper will compare molluscan assem- blage data drawn from material collected in INTRODUCTION the Pigeon Point Format .ten, with molluscan distributions found in rocks of similar age Upper Cretaceous sedimentary rocks near along the Pacific margin of North America in Pigeon Point, California, were first recog- order to assess paleobiogeographic con- nized by Arnold (1908), who identified a num- straints on the tectonic transport history of ber of Late Cretaceous species and named sev- the formation. However, before addressing eral new species from the unit. These strata the paleogeographic questions, we will review were formally named the Pigeon Point Forma- the geologic and lithostratigraphic settings, tion by Hall and others (1959), who provided the age control and the paleoenvironmental molluscan evidence for a late Campanian or implications of the assemblage distributions, age. Following these reports, since these factors play an important role in the Pigeon Point Formation generally has been developing paleobiogeographic comparisons. considered sparsely fossiliferous, although Saul and Popenoe (Saul and Popenoe, 1962, GEOLOGIC SETTING 1992; Saul, 1978, 1983, 1989) discussed and named a number of species from it. Continued The Pigeon Point Formation lies west of research of existing collections and analysis the San Andreas fault on a block that is of new collections by the authors indicates bounded to the northeast by the San Gregorio that approximately 100 megafossil species can fault (Fig. 1) . Cretaceous strata have not be identified from the formation, making the been identified between the San Gregorio and fauna one of the most diverse known for a San Andreas fault zones in the Santa Cruz unit apparently confined to middle Campanian Mountains, where Cenozoic strata apparently age on the west coast of North America. This lie directly on granitic basement rocks of paper provides a preliminary report of those the Salinian terrane (Clark and Brabb, 1978; taxa having paleobiogeographic implications McLaughlin and others, 1988). The offshore regarding the controversy surrounding the extent of the Pigeon Point Formation is not known, but some have suggested a hypothetical In Dunn, G., and McDougall, K., eds.,1993, Mcsozoic Palcogcography of the Western United Statcs-II Pacific Section SEPM, Book 71, p. 171-186. / f'-r extension of the Sur-Nacimiento fault zone through exposure or drill hole, identifica- not far offshore (e.g. Howell and others, tion of the amount of offset on the San Gre- 1977; Lowe, 1979), which may truncate the gorio fault is critical in determining the formation to the southwest (Fig. 1). basement rock and terrane to which the Pigeon Point Formation belongs. This is because the Because of the paleomagnetically implied Sur-Nacimiento fault, which separates grani- extensive transport of the Pigeon Point For- tic basement of the Salinian terrane to its mation since deposition (Champion and others, northeast from Franciscan basement of the Sur 1981, 1984), determination of the underlying Nacimiento block to its southwest, is appar- basement rock has been paramount to analysis ently offset by the San Gregorio fault off- of terrane movements. Barring the possibil- shore from Point Sur (Fig. 1) . Franciscan ity of direct investigation of the basement basement rocks dredged from the headward part of Ascension Canyon just south of Pigeon Point (Howell and Joyce, 1981) imply at least 90 km of dextral offset of the Sur-Nacimiento fault by the San Gregorio fault system. How- Point Arena ever, if offset on the San Gregorio fault is slightly greater, on the order of 110-115 km, then the Pigeon Point Formation would lie on the southwest side of the Sur-Nacimiento fault and be underlain by Franciscan basement of the Sur-Obispo terrane (Fig. 1) . Most es- timates of offset on the San Gregorio-Hosgri fault system fall into the range of 105-150 km (see discussion in Griscom and Jachens, 1989). Thus, a narrow adjustment of these constraints in either direction would allow the Pigeon Point Formation to be underlain by either Salinian or Sur-Obispo basement rocks.

Cretaceous rocks nearest to the Pigeon Point Formation lie to the east of the San Andreas fault on Franciscan basement in Palo Alto and near Loma Prieta (Fig. 1). In Pal Alto, a small claystone outcrop on the St a- ford University campus contains foraminxit. and macrofossils of late Campanian ag*_- (Graham and Church, 1963), but exposure is too limited to make proper comparison with the Pigeon Point Formation. Upper Cretaceous rocks near Loma Prieta are turbidite deposits similar to those of the Pigeon Point Forma- tion and are of approximately the same age, as indicated by a number of bivalves in com- mon, including middle Campanian Meekia bella. However, the molluscan fauna near Loma Prieta contains turbidite transported nearshore com- ponents originating in littoral rocky coast- line habitats (Elder, 1991) that are not rep- resented by faunal components in the Pigeon Point Formation.

LITHOLOGIC AND STRATIGRAPHIC SETTING

The Pigeon Point Formation is well ex- posed along 16 km of coastline near Pigeon EXPLANATION Point in San Mateo County. Neither the de- Sur-Obispo positional base nor top of the formation are Salinian terrane exposed due to burial or fault contact and terrane erosional truncation, respectively (Howell and Joyce, 1981). Small to large scale fold- ing, faulting, and rotation of blocks within Figure 1. Map of west-central California the formation are extensive (Joyce, 1981) and showing the position of the Pigeon Point For- inhibit precise reconstruction of the strati- mation relative to nearby localities of simi- graphic section. Correlation is particularly lar age (LP = Loma Prieta; PA = Palo Alto, hampered by an unnamed fault 1.5 km south of Stanford University Campus) and major faults Bean Hollow Beach (Fig. 2), which effectively and terrane boundaries of significance to its divides the formation into northern and tectonic transport history. Fault abbrevia- southern sequences of uncertain relationship. tions are as follows: HF = Hosgri fault, PF = In spite of these structural difficulties, Pilarcitos fault, SAFZ = San Andreas fault reasonably accurate large-scale stratigraphic zone, SGF = San Gregorio fault, SNF = Sur sections through the approximately 2500-3300 Nacimiento fault. Position of offset Sur m of exposed formation have been constructed Nacimiento fault and Salinian/Sur Obispo ter- by Howell and others (1977), Lowe (1979), and rane boundary relative to the Pigeon Point Howell and Joyce (1981) . Formation is not known. / f'-r Northern Sequence

Figure 2. Map showing fossil localities, major structures, and generalized dip directions and lithofacies units of the Pigeon Point Formation. Modified from Howell and Joyce <1981). / f'-r The northern section is inferred to con- and Joyce (1981) correlate the cross-bedded tain the oldest exposed rocks (Lowe, 1979; shelf strata at Bolsa Point with fine-grained Howell and Joyce, 1981), with the section's turbidites and thicker bedded sandstone units base outcropping just south of Pescadero overlying the slumped slope facies to the Beach and exposures continuing upsection to south at Franklin Point (Fig. 2). They con- the fault 1.5 km south of Bean Hollow Beach sidered these facies to be indicative of a (Fig. 2). Strata in this part of the forma- middle-fan environment developed offshore of tion have been largely interpreted as repre- the Bolsa Point•deposits, but these deposits senting deep-sea fan turbidite deposits may reflect turbidites deposited on the (Lowe, 1979; Howell and Joyce, 1981). The outer-shelf below storm wave base (Walker, lowest part of this section is dominated by 1984). Macrofossils are rare in this deeper- thick-bedded to massive sandstone units sepa- water facies. rated by thin intervals of thin-bedded fine- grained turbidites, suggesting deposition in MOLLUSCAN ASSEMBLAGES AND the suprafan environment of the middle-fan DEPOSITIONAL ENVIRONMENTS (Walker, 1978) . Macrofossils are rare in Accurate paleobiogeographic interpreta- this interval except in a thinly bedded por- tions require the comparison of assemblages tion at the very northern end of the outcrop characterizing similar habitats because rocky belt, where abundant inoceramid bivalves oc- shoreline or beach faunas may have a very cur locally in a mudstone matrix, and rudist different composition and latitudinal distri- debris, solitary corals, and scattered ammon- bution than open-shelf or bathyal assem- ites occur in siltstone and sandstone beds blages. The Pigeon Point Formation contains (Fig. 2, Iocs. 1, 2). a fauna characteristic of the inner- to outer-shelf throughout, although in much of Upsection, the formation is character- the formation the shells were transported to ized by thinning-upward megacycles with tur- bathyal depths by turbidity currents. How- bidites containing all or part of the Bouma ever, there are some notable differences in sequence (Howell and Joyce, 1981) . These assemblage composition and taphonomy in the thinning-upward sandy cycles reflect the lat- different facies present. eral shifting of turbidite channels charac- teristic of middle-fan depositional environ- An interesting paradox found in the Pi- ments (Walker, 1978). Macrofossils are very geon Point Formation is that the only rudis- rare in this facies. The uppermost part of tid bivalves, which were nearshore taxa that the 2500 m thick northern section is composed required rocky or shell-rich substrates for of a conglomerate and sandstone unit, ap- attachment, occur near the base of the sec- proximately 250 m thick, that Howell and tion in strata that are interpreted as being Joyce (1981) correlated to a similar conglom- deposited in one of the most offshore, deep- eratic unit exposed at the base of the south- water settings (Fig. 2, loc. 2). These frag- ern section near Pigeon Point (Fig. 2). This mental rudists occur in sandy turbidite beds thick conglomeratic interval suggests a shift and are associated with solitary corals, ser- in environment to a major feeder channel in a pulid worms, and Didymoceras ammonites. The proximal fan setting and implies a regressive presence of* rudists in these middle-fan de- trend upsection through the northern section. posits, but not in the more fossiliferous Few macrofossils are present in the conglom- nearshore slope and shelf facies near the top eratic interval except for scattered oysters of the section, suggests that the rudist and, in a relatively thin conglomerate bed fragments bypassed those coastal regions via near its base, a low diversity assemblage transport in submarine canyon systems fed dominated by Tvrritella (Fig. 2, loc.3). from very nearshore environments.

The overall regressive trend is contin- The clay lithologies of the middle-fan ued through the southern section, which is facies in the basal Pigeon Point Formation based by a thick conglomeratic interval that contain scattered fossils which apparently is overlain by an extensively slump-folded are in sit u or little transported. Just sequence (up to 350 m thick) of discontinuous south of the fault contact at Pescadero Beach units of mudstone, pebbly-to-cobbly mudstone, (Fig. 2, loc. 1), a zone of large, whole (to and conglomerate indicative of a transition 30 cm length) and fragmented inoceramid bi- from an inner-fan to slope setting (Howell valves is found within a 5 m thick interval and Joyce, 1981). Macrofossils are moder- of thinly interbedded mudstones and silt- ately common in this facies, where they typi- stones. This is the only place in the forma- cally occur as isolated specimens or small tion where inoceramids are abundant or even clusters floating in a mudstone matrix. common. In addition, the only pachydiscid These slope deposits are in turn overlain by ammonite known from the Pigeon Point Forma- the apparently youngest deposits in the Pi- tion came from a mudstone bed at the rudistid geon Point Formation near Bolsa Point (Fig. locality mentioned above. This specimen is 2), where a 250 m thick interval of massive quite large (>50 cm in diameter) and was fine-grained sandstone containing hummocky crushed and highly fractured in place. The cross-stratified beds and thin conglomerate few other fossils that have been found in the and shell lenses is found. These features middle-fan facies include rare occurrences of imply a shelf environment shallow enough for probable pelagic ammonites such as Didy- storm waves to impinge on the bottom, perhaps moceras and Hypophylloceras. reworking shallow-water turbidite deposits (i.e. Walker, 1984). The majority of macro- The conglomerate-dominated facies inter- fossils found in the Pigeon Point Formation preted to represent middle- to inner-fan come from the shell lenses developed in these channel environments generally contain very relatively shallow-water deposits. Howell few fossils with one notable exception. This / f'-r is the of Turritella chicoen- served age-diagnostic ammonites. Overall sis pescaderoensis Arnold, which is found at taxonomic composition generally implies an the base of the conglomeratic interval cap- early to middle Campanian age (Fig. 3) . Some ping the northern section (Fig.2, loc. 3) ; of the important age-indicative mollusks are this is also the only locality in the Pigeon shown in Plate 1. In addition to biostrati- Point Formation from which this taxon is graphic control, a reversed paleomagnetic po- known. At this locality, several thin con- larity interval found by Champion and others glomerate beds (1-2 m thick) contain common (1981, 1984) in the apparently older northern to abundant Turritella as well as rare speci- section also provides some potential age con- mens of Idonearca, Volutoderma, and Bacu- straints. Available biostratigraphic data lites. Shale interbeds also contain Tur- indicate that this reversed interval most ritella in association with Glycymeris, Acila likely reflects the early Campanian Chron (Truncacila), and Tessarolax; the latter two 33R. genera are typical of fairly deep, quiet- water shelf environments. Otherwise, the Age control on the. northern sequence is conglomeratic channel facies typically yields based on sketchy ammonite control. Rocks only scattered specimens of a thin-shelled near the base of the section at the south end pink oyster. of Pescadero Beach (Fig. 2, loc. 2), have produced a large, badly fractured pachydiscid The slumped and pebbly mudstone facies ammonite with broad flank ribs similar to of the slope environment contains rare to those of Canadoceras yokoyamai (Jimbo) . If fairly common fossils that typically occur as this identification is correct, then an early individual specimens floating in mudstone, or Campanian age is indicated, and the magneti- as small pockets of fossils that are commonly cally reversed interval in that part of the associated with pebbly mudstone intervals. section would reflect Chron 33R. The pres- Fossil assemblages in this depositional envi- ence of inoceramid bivalves resembling Inoce- ronment typically reflect relatively deep ramus subundatuSantonian in Japan (Matsumoto, 1967). Didy- fauna at Bolsa Point (Fig. 3). This common- moceras (Bostrychoceras) is characteristic of ality reflects the similar shallow water the Santonian and Campanian, whereas Nosto- habitats of the mollusks and is unlikely to ceras is typical of the Maastrichtian (Mat- have been achieved by North Pacific forms sumoto, 1967) . following the thermocline into deeper water to the south, as the co-occurring genera A middle to late Campanian age is sug- Yaadia, Meekia, and Tellina (Tellinella) are gested near the top of the northern section constrained to shallow water habitats. In by the type locality of Turritella chicoensis contrast, the Bell Canyon fauna, which appar- pescaderoensis Arnold (Fig. 2, loc. 3). This ently is more similar to the Pigeon Point taxon has been considered characteristic of Formation in age and water temperature than the late Campanian Metaplacenticeras paci- the Chico fauna (Figs. 4, 5; Table 1), has ficum ammonite zone elsewhere (Saul, 1983), fewer species in common because its taxa rep- but also is found with Hoplitoplacenticeras resent deeper water habitats than the Pigeon sp. near Punta Abreojos, Mexico, and with Point fauna. Hoplitoplacenticeras? bowersi at Dayton Can- yon, Simi Hills (Fig. 4, Iocs. 10, 6); both In spite of these minor inconsistencies occurrences lie below the Metaplacenticeras in age and environment between the sites, the pacificum Zone (Alderson and Saul, 1992). 49 species listed in Figure 4 provide infor- mative comparisons of relative numbers of The most common ammonite in the southern tropical, warm, North Pacific, and other tem- sequence is a species of Baculites with a perate species within each fauna. In the Pi- complex suture, oval cross-section, and gen- geon Point Formation, an eighth of these spe- eral lack of ornamentation comparable to that cies are tropical and nearly a third are of of the late Campanian to early Maas- North Pacific affinities. This mixing of trichtian (?) species B. rex Anderson, but warm and cool water species is not unex- with slightly less deeply incised saddles pected, however, since the Late Cretaceous than typical of that species. Ward (1978) was a time of broad climatic zones and wide considered Baculites rex in the Nanaimo Group latitudinal species ranges (Kauffman, 1973). (Clapp, 1912) to be of middle late Campanian For example, representatives of tropical age and to have evolved from the early Cam- groups such as the cypraeids, which today panian Baculites chicoensis Trask, which has a less complex and deeply incised suture than the former species. It is therefore possible that the Pigeon Point Formation Baculites Table 1. Pigeon Point Formation species represents a previously unrecognized middle that have been recognized at one or more of Campanian intermediate form. ten other Pacific slope localities. Species listed in four provincially significant The common occurrence of the early to groups. Relative age of Pigeon Point middle Campanian species, Meekia bella Saul Formation and other localities are shown in and Popenoe, throughout the shelf deposits of Figure 3. See Figure 4 for geographical the southern sequence perhaps provides the position of localities numbered from north to best age control for that sequence. Although south. 1 Nanaimo Basin, southern British the type specimen of early Maastrichtian Columbia and Sucia Island, San Juan Co., Yaadia hemphilli (Anderson) was reported to Washington; (Clapp, have come from Pigeon Point Formation 1912). 2 = Vicinity of Chico Creek, Butte (Anderson, 1958), Saul (1978) points out Co., CaTTiTSrnia; . = Loma problems with its locality data, and we have Prieta, Santa Clara Co., California; Unnamed thus far only found specimens of Yaadia ques- formation of the Great Valley sequence. = tionably identified as early to middle Cam- York Mountain Quadrangle, San Luis Obispo panian Yaadia tryoniana (Gabb) in the Pigeon Co., California; Atascadero Format-ion. 5 _ = Point Formation. Vicinity of Jalama Creek, Santa Ynez Mts., Santa Barbara Co., California; Jalama For- PALEOBIOGEOGRAPHY mation (Dibblee, 1950). * = ^l1 Canyon, Simi Hills, Ventura Co., California; Chatsworth As seen above, the bulk of evidence sug- Formation. 7= Dayton Canyon, Simi Hills, Los gests that Pigeon Point assemblages primarily Angeles California; Chats-worth represent clastic-dominated sub-littoral to Formation (Colburn and others, 1981). .8 = inner-shelf environments of middle Campanian Santa Ana Mountains, Orange Co., California; age. Therefore, molluscan paleobiogeographic upper part of Holz Shale Member of Ladd comparisons for the Pigeon Point Formation Formation.r- Santa Ana Mountains, Orange are best made with assemblages of similar age Co., California; Pleasants Sandstone Member and habitat. of Williams Formation. __1 n -n Punta Abreojos, Vizcaino Peninsula, Baja California Sur, Table 1 compares the Pigeon Point fauna Mexico; Valle Formation. 1-3 lie east of with 10 other west coast localities (Fig. 4) the San Andreas fault; all other localities that are reasonably well known and that are are to the west. / f'-r

Pigeon Point Tethyan & probably tropical Coralliochama cf. C. orcutti Whit© Cerithium? cf. C. totium-sanctorum White Isogognomon n. sp. Lispodesthes rotundus (Waring) Pseudoglauconia? aff. P. ainiktos Dailey & Popenoe Trinacria cor Popenoe Warm but not 'Tethyan' Ampullina packardi Popenoe Anchura aff. A. fa/ciformis (Gabb) Crassatella aff. C. conradiana (Gabb) Crassatslla saulae Dailey & Popenoe EHipsoscapha cf. E. nortonensis (Anderson) Euspira compressa (Waring) "Fulgur" hilgardi White Glycymeris (Gtycymerita) anae Smith Glycymeris (Glycymerita) apletos Dailey & Popenoe Legumen ooides (Gabb) Laternula? alisoensis (Packard) Nonacteonina obesa Dailey & Popenoe Nonacteonina aff. N. tensa Stephenson Opis cf. O. rosarioensis Anderson & Hanna Pinna calamitoides Shumard Pterotrigonia ovansana (Meek) Tellina (Tellinella) n. sp. Turritella chicoensis pescaderoensis Arnold Volutoderma santana Packard North Pacific Ataphrus compactus Gabb Biplica obliqua (Gabb) Bittiscala tenuisculpta (Whiteaves) ? Bittiscala suciense (Whiteaves) ? Calva (Egelicalva) bowersiana (Cooper) Cymbophora popenoei Saul Cymbophora stantoni (Arnold) Cymbophora triangulata (Waring) Gyrodes (Sohlella) canadensis (Whiteaves) Lysis duplicosta (Gabb) Meekia (Mygallia) bella Saul & Popenoe Meekia (Meekia) peleia Saul & Popenoe Tessarolax distorta Gabb Willimactra (Petromactra) truncata (Gabb) Yaadia tryoniana (Gabb) Temperate but not restricted to North Pacific Acila (Truncacila) demessa Findlay Bacuiites cf. B. rex Anderson Canadoceras cf. C. yokoyami (Jimbo) Clisocolus dubius (Gabb) Idonearca youngi (Waring) Indogrammatodon? cf. /. vancouverensis (Meek) Inoceramus subundatus Meek Panopea cf. P. californica Packard subelongata Meek Totals Number of species in common 19 26 14 6 14 16 18 24 19 14 Tethyan & probably tropical 0 1 0 0 3 1 2 3 2 3 Warm but not "Tethyan" 3 6 4 1 7 5 7 9 8 4 North Pacific 10 12 6 5 3 5 3 8 5 3 Temperate but not restricted to North Pacific 6 7 4 0 2 5 6 4 4 4

Table 1. / f'-r range on the west coast no farther north than Monterey, California, are recognized in the Campanian as far north as the Nanaimo Basin, British Columbia (Sohl, 1971; Groves, 1990). Vancouve On the whole, however, California Campanian Island faunas were not dominated by tropical spe- cies, but rather resembled those of the mod- ern Californian Province, which includes a single cypraeid and several other species of tropical affinity but is predominantly com- posed of North Pacific temperate species.

If, as has been suggested, the Pigeon Point Formation was deposited approximately 2500 km south of its present latitude (i.e. Oregonian near 21 *N, the latitude of southern Mexico), (Temperate) tropical provincial affinities should be re- flected in its fauna. However, the only clearly Tethyan Pigeon Point species listed in Table 1 under "Tethyan and probably tropi- cal" is the rudistid bivalve, Coralliochama. In contrast, Tethyan bivalves such as Trigon- arca, Quadratotrigonia, and Roudairia, and Tethyan gastropods including Uerinea, Wood- salia, and actaeonellids are present in Cali- fornia faunas of other Cretaceous stages, primarily the through . Post- Turonian cooling of the Pacific coast may ex- plain the absence of these taxa from autoch- thonous California Campanian rocks (Saul, 1986), but if the Pigeon Point Formation was deposited at the latitude of southern Mexico, these groups should be well represented. This would be especially true if the northern boundary of Campanian Tethyan assemblages was near 25'N, as suggested by Sohl (1971); that is 2* north of the present Panamic boundary on the west coast of Baja (Fig. 4). Although there are no Campanian molluscan faunas from the Pacific coast of southern Mexico with which to test: this assumption, Olsson (1934, 1944) has documented these Tethyan mollusks in Senonian faunas of Peru. Thus, we do know that these tropical groups inhabited the tropical eastern Pacific when the Pigeon Point Formation was deposited.

There is some possible biasing of these paleobiogeographic comparisons that should be noted, however. One conceivable bias is po- tential upwelling along the Pacific coast CBarron, 1985). If upwelling occurred, it may have depressed the northern boundary of Tethyan assemblages further south than the 25'N suggested by Sohl (1971), who primarily based this latitude on Caribbean distribu- tions. Also, protected bays in the present Surian Province contain more diverse and tropical components than open coastal areas, which have more Californian style faunas (Brusca, 1980) . Therefore, the Pigeon Point Pariamic KM 500 fauna might appear anomalously cool if it (Tropical) mJmm originated in an area of upwelling or an open coastal environment. On the whole, however, it would be remarkable for the Pigeon Point Figure 4. Map showing the geographic Formation to have so many species in common distribution of the ten localities compared with Sucia Island and Chico Creek (Table 1, in Table 1. See Table 1 caption for more Fig. 4) if it were deposited at the latitude specific locality information. Figure also of southern Mexico, but this commonality shows position of modern molluscan provincial would be expected if the formation was depos- boundaries discussed in text (dashed lines), ited north of 25'N. and probable northward expansion of the Cam- panian tropical Tethyan Province to near 25*N is shown by solid line at tip of arrow. Although the Pigeon Point Formation does not appear to have originated in the tropics, there are faunal indications that it was de- / f'-r posited south of its present position. About fornia, Berkeley, for the loan of specimens half of the species listed in Table 1 are in- reported on and illustrated in this paper. dicative of warm water, whereas more than The California Department of Parks and Rec- half of the species in the northern areas reation is thanked for allowing the collec- (Fig. 4, Iocs. 1-4) are North Pacific or tem- tion of fossils on park lands. perate water indicators. For example, the major difference between the Pigeon Point REFERENCES CITED fauna and that of the Chico Formation is the fewer warm and tropical forms present in the Alderson, J.M., and Saul, L. R., 1992, A latter. Additionally, there are some probable occurrence of the ammonite ge- biogeographically significant species in the nus Hoplitoplacenticeras Paulcke, 1907, Pigeon Point Formation that differentiate it on the Vizcaino Peninsula, Baja Califor- from the northern faunas. Plate 2 shows some nia Sur, Mexico, in Carrillo-Ch&vez, of these taxa. Anchura falciformis Gabb is Alejandro, and Alvarez-Arellano, Alejan- common in the northern faunas but is not dro (eds.), Primera reunion interna- found in the Santa Ana Mountains, where two cional sobre geologia de la peninsula de undescribed Campanian species occur. One of Baja California: Memorias, Universidad these, listed as Anchura aff. A. falciformis Aut6noma de Baja California Sur, p. 97- on Table 1, is a species of more southern oc- 99. currence than Anchura falciformis and there- Anderson, F.M., 1958, Upper Cretaceous of the fore suggestive of warmer water. Another Pacific Coast: Geological society of such species is Volutoderma santana Packard, America Memoir 71, ?78 p., pis. 1-75. which otherwise has not been found north of Arnold, Ralph, 1908, Descriptions of new Cre- the Santa Ana Mountains. The less strongly taceous and Tertiary fossils from the shouldered Volutoderma averilli (Gabb) is Santa Cruz Mountains, California: Pro- common at Chico Creek and in the Nanaimo ba- ceedings of the U.S. National Museum, v. sin and is also present in the Santa Ana 34, no. 1617, p. 345-348, pis. 31-32. Mountains but has not been recovered from the Barron, E,J., 1985, Numerical climate model- Pigeon Point Formation. Other Pigeon Point ing.. a frontier in petroleum source rock species listed in Table 1 that have not been prediction — Results based on Creta- found in northern faunas are Isognomon n. ceous simulations: American Association sp., Lispodesthes rotundas (Waring), hztur- of Petroleum Geologists Bulletin, v. 69, nula? alisoensis (Packard),' and Ceritium? p. 448-459. totium-sanctorum White. In addition, the Brusca, R.C. 1980, Common :atertidal inverte- rudist Coralliochama is only found west of brates of the Gulf of California, 2nd the San Andreas fault in California. ed. : University of Arizona Press, Tuc- son, Arizona, 513 p. In conclusion, Table 1 indicates that Champion, D.E., Grc-.^e, C.S., and Howell, warm water faunal elements increase from D.G., 1981, Paleomagnetic study of the north to south in the compared area, and that Upper Cretaceous Pigeon Point Formation, the warm water components of the Pigeon Point in Frizzell, V. (ed.), Upper Cretaceous Formation ally it most closely to the more and turbidites, central Cali- southern localities (Fig. 4, Iocs. 5-10). fornia coast: Los Angeles, Pacific Sec- Molluscan temperature indicators of the Pi- tion, Society of Economic Paleontolo- geon Point Formation are most similar to gists and Mineralogists, p. 53-55. those in middle to late Campanian faunas from , Howell, D,G., and Gromme, the Peninsular Ranges terrane of southern and C.S., 1984, Paleomagnetic and geologic Baja California and correspond particularly data indicating 2500 km of northward well with those of the Santa Ana Mountains. displacement for the Salinian and re- These Santa Ana rocks have been inferred to lated terranes, California: Journal of have been deposited near the paleolatitude of Geophysical Research, v. 89, p. 7736- 26*N (see data in Lund and others, 1991), 7752. and, therefore, north of the Tethyan Prov- Clapp, C.H., 1912, Geology of Nanaimo Sheet, ince, whose northern boundary may have been Nanaimo Coalfield, Vancouver Island: near 25 *N. This inferred paleolatitude for Geological Survey of , Summary Re- the Pigeon Point formation of near 26'N does port 1911, p. 91-105. not clearly indicate the terrane in which the Clark, J.C., and Brabb, E.E., 1978, Strati- Pigeon Point Formation might lie. Lund and graphic contrasts across the San Gre- others (1991) have projected the Sur-Obispo gorio fault, Santa Cruz Mountains, west terrane to be further south than this in the central California, in Silver, E.A., and Campanian (although largely based on the Pi- Normark, W.R. (eds.), San Gregorio- geon Point paleomagnetics of Champion and Hosgri fault zone, California: Califor- others, 1984), and the Salinian terrane to be nia Division of Mines and Geology, Spe- further north than the molluscan assemblages cial Report 137, p. 3-12. in the Pigeon Point Formation imply. Colburn, I.P., Saul, L.R., Almgren, A.A., 1981, Chatsworth Formation: a new forma- ACKNOWLEDGMENTS tion name for the Upper Cretaceous strata of the Simi Hills, California, in We thank Dave Bottjer, John Harris, Link, M.H., Squires, R.L., and Colburn, George Kennedy, Kristin McDougall, Bill I.P. (eds.), Simi Hills Cretaceous Tur- Sliter, and Ed Wilson for reviewing the text bidites, Southern California: Los Ange- and providing useful comments and sugges- les, Pacific Section, Society of Eco- tions. In addition, we acknowledge Peter nomic Paleontologists and Mineralogists, Rodda at the California Academy of Sciences Volume and Guidebook, p. 9-16. and Dave Lindberg at the University of Cali- / f'-r Dibblee, T.W., 1950, Geology of southwestern James, E.W., and Mattinson, J.M., 1988, Meta- Santa Barbara County, California: Cali- morphic history of the Salinian block — fornia Division of Mines and Geology, An Isotopic reconnaissance, in Ernst, Bulletin 150, 95 p. W.G., (ed.), Metamorphism and crustal Elder, W.P., 1991, An unusual Upper Creta- evolution of the western , ceous fauna from an oyster bed interval Rubey Volume 7: Englewood Cliffs, New in the Santa Cruz Mountains, California, Jersey, Prentice-Hall, p. 938-952. in W. Sando (ed.), Shorter Contributions Joyce, J.M., 1981, A deformational history of to Paleontology and Stratigraphy: U. S. the Pigeon Point Formation, in Frizzell, Geological Survey Bulletin 1934-E, p. Virgel (ed.), Upper Cretaceous and Pa- E1-E18, 5 figs., 2 tabs., 5 pis. leocene turbidites, central California Graham, J.J., and Church, C.C., 1963, Cam- coast: Los Angeles, Pacific Section, So- panian foraminifera from the Stanford ciety of Economic.Geologists and Miner- University campus, California: Stanford alogists, p. 57-59. University Publications, Geological Sci- Kauffman, E.G., 1973, Cretaceous Bivalvia, in ences, v. 8, no. 1, 107 p., pis. 1-8. Hallam, A. (ed.), Atlas of Paleobiogeog- Griscom, Andrew, and Jachens, R.C., 1989, raphy: Amsterdam, New York, Elsevier Tectonic history of the north portion of Publishing Co., p. 353-383. the San Andreas fault system. Califor- Lee-Wong, F., and Howell, D.G., 1977, Petrog- nia, inferred from gravity and magnetic raphy of Upper Cretaceous sandstone in anomalies: Journal of Geophysical Re- the Coast Ranges of central California, search, v. 94, p. 3089-3099. in Howell, D.G., Vedder, J.G., and Mc- Grove, Karen, 1989, Upper Cretaceous conglom- Dougall, K.A., (eds.), Cretaceous geol- erates from the Salinian terrane, west- ogy of the , west central California, in Colburn, I. P., of the San Andreas fault, Pacific Coast Abbott, P.L., and Minch, John, (eds.), paleogeography field guide 2: Los Ange- Conglomerates in basin analysis — a les, Pacific Section, Society of Eco- symposium dedicated to A. 0. Woodford: nomic Paleontologists and Mineralogists, Los Angeles, Pacific Section, Society of p. 47-55.. Economic Paleontologists and Mineralo- Lowe, D.R., 1979, Stratigraphy and sedimen- gists, v. 62, p. 143-160. tology of the Pigeon Point Formation, Groves, L.T., 1990, New species of Late Cre- San Mateo County, California, in Nilsen, taceous Cypraeacea (Mollusca: Gastropo- T.H., and Brabb, E.E., (eds.), Geology da) from California and Mississippi, and of the Santa Cruz Mountains, California: a review of Cretaceous Cypraeceans of Geological Society of America, Cordil- North America: The Veliger, v. 33, p. leran Section, Field Trip Guidebook, p. 272-285,' 34 figs. 17-29. Hall, C.A., Jones, D.L., and Brooks, S.A., Lund, S.P., Bottjer, D.J., Whidden, K.J., 1959, Pigeon Point Formation of Late Powers, J.E., and Steele, M.C., 1991, Cretaceous age, San Mateo County, Cali- Paleomagnetic evidence for Paleogene fornia: American Association of Petro- terrane displacements and accretion in leum Geologists Bulletin, v. 43, p. southern California, in Abbott, P.L., 2855-2865. and May, J.A., (eds.), geologic Howell, D.G., and Joyce, J.M., 1981, Field history of San Diego region: Pacific guide to the Upper Cretaceous Pigeon Section SEPM, v. 68, p. 99-106. Point Formation, in Frizzell, V. (ed.), Matsumoto, Tatsuro, 1959, Upper Cretaceous Upper Cretaceous and Paleocene tur- ammonites of California, Part II: Mem- bidites, central California coast: Los oirs of the Faculty of Science, Kyushu Angeles, Pacific Section, Society of University, D, Geology, Special Economic Paleontologists and Mineralo- Volume I, 172 p. gists, p. 61-70. , 1967, Evolution of the , and Vedder, J.G., 1978, Late Nostoceritidae (Cretaceous heteromorph Cretaceous Paleogeography of the Sal- ammonoids): Memoirs of the Faculty of inian block, California, in Howell, 'Science, Kyushu University, Series D, D.G., and McDougall, K.A., (eds.), Meso- Geology, v. 18, p. 331-348. zoic paleogeography of the western McLaughlin, R.J., Clark, J.C., and Brabb, United States, Pacific Coast paleogeog- E.E., 1988, Geologic map and structure raphy symposium 2: Los Angeles, Pacific sections of the Loma Prieta 7 1/2* Quad- Section, Society of Economic Paleontolo- rangle, Santa Clara and Santa Cruz Coun- gists and Mineralogists, p. 523-534. ties, California: U.S. Geological Survey , , McLean, Hugh, Open-File Map 88-752, p. 1-32, 2 Sheets. Joyce, J.M., Clarke, S.H., Jr., and Olsson, A.A., 1934, The Cretaceous of the Smith, Greg, 1977, Review of Cretaceous Amotape Region. Bulletins of American geology, Salinian and Nacimiento blocks, Paleontology, v. 20, no. 69, 104 p. Coast Ranges of central California, in , 1944, Contributions to the pa- Howell, D.G., Vedder, J.G., and McDou- leontology of northern Peru. Part VII. gall, K.A., (eds.), Cretaceous geology The Cretaceous of the Paita region. Bul- of the California Coast Ranges, west of letins of American Paleontology, v. 28, the San Andreas fault, Pacific Coast pa- no. Ill, 114 p. leogeography field guide 2: Los Angeles, Saul, L.R., 1978, The North Pacific Creta- Pacific Section, Society of Economic Pa- ceous trigoniid genus Yaadia: University leontologists and Mineralogists, p. 1- of California Publications in Geological 46. Sciences, v. 119, 65 p., pis. 1-12.