Late Pleistocene Marine Paleoecology and Zoogeography in Central California
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Late Pleistocene I Marine Paleoecology · and Zoogeography in Central California GEOLOGICAL SURVEY PROFESSIONAL PAPER 523-C Late Pleistocene Marine Paleoecology and Zoogeography in Central California By W. 0. ADDICOTI CONTRIBUTIONS TO PALEONTOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 523-C Invertebrate assemblages analogous to the Aleutian molluscan province indicate a former cool-temperate marine climate UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1966 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 35 cents (paper cover) CONTENTS Page Page Abstract __________________________________________ _ C1 Paleoecology-Continued Introduction ______________________________________ _ 2 Substratum ___________________________________ _ C9 Acknowledgments __________________________________ _ 2 Marine hydroclimate ___________________________ _ 9 Earlier studies _____________________________________ _ 2 Regional marine paleoclimate _______________________ _ 11 Geologic setting ___________________________________ _ 3 Outer-coast biotope ____________________________ _ 11 Point Afio Nuevo localities ______________________ _ 3 Protected-coast biotope _________________________ _ 13 Santa Cruz localities ___________________________ _ 3 Zoogeography _____________________________________ _ 1.5 Faunal composition ________________________________ _ 4 Modern molluscan provinces ____________________ _ 16 Paleoecology ______________________________________ _ 6 Late Pleistocene molluscan provinces _____________ _ 16 Mode of formation _____________________________ _ 6 Discussion ____________________________________ _ 17 Probable size of late Pleistocene fauna ____________ _ 8 References ________________________________________ _ 19 BathymetrY--------------------~--------------- 8 ILLUSTRATIONS [Plates follow index] PLATE 1. Mollusks and coral. 2. Mollusks. 3. Mollusks and echinoid. 4. Mollusks and barnacle. Page FIGURE 1. Index map of Half Moon Bay-Monterey area, central California ________________________________ ----------- C3 2. Index map of the Pacific coast showing places referred to in text__________________________________________ 7 3. Average annual temperature at surface and at 100 feet in northeastern Pacific Ocean ____ -- ______ ------------ 10 4. Modern shallow-water molluscan provinces of the northeastern Pacific Ocean ____________________ ----------- 12 5. Modern and inferred late Pleistocene shallow-water marine climate _____________________________ ----------- 14 6. Late Pleistocene shallow-water molluscan provinces---------------------------------~-------------------- 15 TABLES Page T~BLE 1. Late Pleistocene larger invertebrates _____________________________________________________ -------------- C4 I 2. Pleistocene mollusks from Point Afio Nuevo and Santa Cruz, California, listed by Arnold _____ --------------- 4 3. Late Pleistocene Foraminiferida from Point Afio N euvo and Santa Cruz, California _____ -_------------------- 5 4. Late Pleistocene Ostracoda from Point Afio N euvo, Calif_ ___________________________ --------------------- 5 5. Mollusks not previously reported as fossiL ____________________________________________ ----------------- 6 6. Modern bathymetric ranges of selected sublittoral mollusks __________________________ -_------------------- 8 7. Mollusks from the southwestern Santa Cruz Mountains that are extralimitaL_______________________________ 9 8. Southern mollusks in the upper Pleistocene Millerton Formation__________________________________________ 14 9. Late Pleistocene invertebrates from three-quarters mile southwest of Bandon, Oreg _________ ----------------- 17 10. Mollusks from central California to Oregon open-coast assemblages that are now restricted to the Aleutian molluscan province________________________________________________________________________________________ 18 11. Pleistocene invertebrates from Willapa Bay, southwestern Washington_____________________________________ 19 III CONTRIBUTIONS TO PALEONTOLOGY LATE PLEISTOCENE MARINE PALEOECOLOGY AND ZOOGEOGRAPHY IN CENTRAL CALIFORNIA By w. 0. ADDICOTT ABSTRACT surface-water temperatures of about 7.5°0 are suggested for the Open-coast molluscan assemblages of late Pleistocene age from winter-early-spring period. This is ahout 4° lower than present northwestern Baja California to Oregon can be grouped to day temperatures. Yearly high temperatures during the represent three faunal provinces. T'he composition of these late-summer-early-fall period may have averaged about 13°C, units differs significantly from that of modern shallow-water about zo lower than present-day temperatures. T'he late zoogeographic provinces of the near-shore northeastern Pacific Pleistocene marine climate was cool temperate, whereas the Ocean area. Late Pleistocene invertebrates of the outer-coast modern climate is temperate. biotope from central California to Oregon have modern ranges The relatively cooler late Pleistocene hydroclimate indicated that overlap in the vicinity of southern British Columbia (lat by fossil assemblages from the lowes:t emergent terrace in the 48° N.). These assemblages represent the newly recognized coastal area of central California to Oregon differs markedly Nuevan molluscan province named for the relatively large open from that in the southern California area, where contemporane coast assemblages from Point Afio Nuevo, Calif. (lat 37.1 o N.). ous fossil assemblages commonly contain both southward- and To the south, molluscan assemblages broadly comparable to those northward-ranging extralimital species. GreateT climatic ex of the modern Oregonian province (lat 34.5°-48° N.) occur from tremes are required by the faunal distributions in southern Estero Bay (lat 35.5° N.) south to the Channel Islands (lat 34o California. They have been interpreted as occurring within N.). This faunal unit is referred to as the Cayucan province the framework of a generally warmer marine climate because (restricted) . South of the Channel Islands mixed assemblages of the sizeable subtropical to tropical molluscan element. The with both extralimital northern and southern mollusks charac outer-coast assemblages in the northe•rn part of the late Pleisto terize the open-coast biofacies of southern California and north cene Verdean province are bracketed, however, by assemblages western Baja California. This faunal unit has been named the of predominantly northern aspect in central California and in Verdean molluscan province (Valentine, 1961). northern Baja California, suggesting that the near-shore marine In the Santa Cruz-Point Afio Nuevo area of central California, climate of this part of the noDtheastern Pacific Ocean may have the open-coast late Pleistocene biofacies is represented by 101 been somewhat cooler than at present. The more southern po larger invertebrate taxa, principally mollusks. Also represented sition of isotherms during the late Pleistocene in central Cali are 27 taxa of Foraminiferida, the largest late Pleistocene fornia and Oregon refl~ts an overall cooling and relatively assemblage known from the Pacific coast, and 18 species of narrow range of temperature, perhaps due to proximity to gla ostracodes. 'The megafossils represent a fossil assemblage con cial melt water. The cool-water aspect of the northwestern Baja sisting of three principal elements: a rock-boring pelecypod· California assemblages may be related to heightened seasonal element, an epifaunal gastropod element, and a sandy infaunal upwelling as the presence of a few warm-water specimens seems pelecypod element. The mollusks inhabited a level-bottom inner to indicate a relatively broader range of temperatures than sublittoral biotope consisting of a fine sand substratum with now prevails in that area. The cool-water aspect of some of local rock protuberances. The fossil assemblages are compara the faunal units conflicts with relatively warm interglacial ble to Shelford's (1935) Macoma-Paphia and Str·ongylocentrotus paleotemperature estimates from zoogeographic •and oxygen A.ruobuccinum communities of the near-shore northeastern isotope studies of foraminifers from deep-water oceani·c cores, Pacific Ocean. Bathymetric data on living mollusks suggest although these are generally from more equatorial areas of maximum water depths of 15-20 fathoms; physical data suggest other oceans. shallower depths, about 10-14 fathoms. Locally the fossil as The only significant protected-coast assemblages from the semblages are preserved undisturbed. Usually they are re central California-Oregon area occur in the upper Pleistocene worked or transported, but evidence of significant mixing with Millerton Formation of Tomales Bay (lat 38.2° N.). These representatives of other communities is lacking. Zoogeographic assemblages contain extralimital southern species that sug criteria suggest relatively cooler surface-water temperatures gest a warm-temperate hydroclimate. T'he deposits are diffi during the late Pleistocene interval represented by these de cult to relate to the open coastal area and may not be con posit<;. T'here is a moderately large element of extralimital temporaneous.. Population of this protected biotope by species that today range no farther south than the latitude of warm-limited southern mollusks with long larval stages might Puget Sound ( 48o N.). The foraminifers, with one exception,