Geologic Studies in Alaska by the U.S. Geological Survey, 1992

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230 GEOLOGIC STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY, 1992 made up of wave- and current-transported sand. The in- ferred depth range of 20-80 m corresponds to inner sublittoral and shallow middle sublittoral ostracode Assemblages I and I1 of the Gulf of Alaska (Brouwers, 1988), which have annual ranges in temperature of 2-15°C and salinity of 30-32.5 parts per thousand. The rarity and low species diversity of marine ostracodes in the lake samples may imply that these organ- isms are in the initial stage of colonization. The sparse assemblage more probably is a function of high sediment accumulation and consequent dilution of ostracode produc- tivity. Samples M1 and MI0 have a mixture of nonmarine and marine species, implying input either from runoff of the adjacent islands or from erosion of outcrops from the mainland that have been transported by ice into the marine system. The sedimentation rate in Vitus Lake is relatively great because of the high input from iceberg melt. We observed some icebergs which were so dirty that no ice was visible, and they appeared to be floating islands. Sedi- mentation rate is on the order of meters per year. CONTINENTAL OSTRACODES Two species of continental ostracodes, Candona caudata and Limnocythere ceriotuberosa, were recovered from 3 of the 29 samples (Ml, M2, M10; table 1; fig. 4). Two samples were collected from the northern part of an island just inside of proglacial Vitus Lake and one sample was collected from a shallow lagoon at the mouth of the Seal River (fig. 1). Sample MI0 contains a large amount of plant debris from the adjacent coastal plain. Salinity, expressed as total dissolved solids, major dissolved ion composition, water temperature, general hydro- logical setting (lake, pond, stream, or aquifer), and the annual variation of physical and chemical water properties determine the biogeography and local occurrences of continental ostracodes (Forester, 1987, 1991a). A large proglacial lake, for example, is usually sustained by meltwater. Meltwater lakes generally remain cold during the year and are filled with dilute water that has a major ion composition dominated by calcium bicarbonate. Those properties, but especially temperature, limit the occurrence of ostracodes. Candona subtriangulata is an example of a species that can survive under such conditions. Continental ostracodes recovered from the above samples are remarkable because they have no known relationship of any kind with ostracodes from either proglacial lakes or marginal to fully marine environments. Limnocythere ceriotuberosa is a euryhaline ostracode that commonly occurs in inland saline to seasonally saline lakes that have a major dissolved ion composition enriched in carbonate (Forester, 1986). Lakes existing under semi- arid to arid climates in regions with volcanic rocks are often inhabited by this species. Ocean water, by contrast, is depleted in carbonate and enriched in calcium. Candona caudata lives in freshwater to slightly saline lakes and streams having a major ion chemistry dominated by calcium bicarbonate, but is tolerant of either calcium or carbonate enrichment (Forester, 1991b). Stream-supported, seasonally saline, carbonate-enriched lakes in the Great Basin often contain both of these ostracode species. Juveniles compose most of the material. Preservation ranges from pristine to highly frosted, partially dissolved valves. Some of the valves are carbonate coated, which is common for ostracode valves found in slightly to fully saline lakes. None of the material contains soft parts. Juve- nile-dominated assemblages are often transported, as are assemblages composed of taxa that are ecologically incom- patible with their surroundings. Thus, unless evidence to the contrary emerges, these shells must be assumed to have been transported from some as yet unknown sediment in the drainage basin of this lake. Oxygen or strontium isotopes would likely demonstrate that these ostracodes did not calcify their valves in either a proglacial lake or in ocean water. Acknowledgments.-We thank the U.S. Geological Survey Volunteer in Science program for funding Rina Coury, who provided field support. Leonard Wilson and Florian Maldonado assisted in the sample collection. 20 30 80 140 rn 1 VfNfffflllf-lllllf. I Celtia blizhnii 20 30 60 220 rn I mlN/NNfA I Cythere alveolivalva 20 80 220 rn I Cytheromorpha molniai 50 200 rn I I Cytheropteron drybayensis 30 50 90 230 m I I Cytheropteron nodosoalatum 20 25 100 220 rn I vffxffffffffffffffffflfffff~ I Palmoconcha russellensis Pectocythere parkerae Figure 2. Preferred (hachured) and total depth range in the Gulf of Alaska of six marine and one marginal marine ostracode species recovered from Vitus Lake.
OSTRACODE ASSEMBLAGES FROM MODERN BOTTOM SEDIMENTS OF VJTUS LAKE 23 1 REFERENCES CITED Brouwers, E.M., 1988, Palaeobathymetry on the continental shelf based on examples using ostracods from the Gulf of Alaska, in De Deckker, P., Colin, J.-P., and Peypouquet, J.- P., eds., Ostracoda in the earth sciences: Amsterdam, Elsevier, p. 55-76. 1990, Systematic paleontology of Quaternary ostracode assemblages from the Gulf of Alaska, Part 1: Families Cytherellidae, Bairdiidae, Eucytheridae, Krithidae, Cushmanideidae: U.S. Geological Survey Professional Pa- per 1510,43 p., 39 figs., 13 pls. 1993, Systematic paleontology of Quaternary ostracode assemblages from the Gulf of Alaska, Part 2: Families Trachyleberididae, Hemicytheridae, Loxoconchidae, Paracytheridae: U.S. Geological Survey Professional Paper 1531, 40 figs., 11 pls. --- in press, Systematic paleontology of Quaternary ostracode assemblages from the Gulf of Alaska, Part 3: Family Cytheruridae: U.S. Geological Survey Professional Paper, 42 figs., 23 pls. Forester, R.M., 1986, Determination of the dissolved anion composition of ancient lakes from fossil ostracodes: Geology, V. 14, p. 796-798. 1987, Late Quaternary paleoclimate records from lacustrine ostracodes, in Ruddiman, W.F., and Wright, H.E., Jr., eds., North American and adjacent oceans during the last deglaciation: Geological Society of Amererica, Geology of North America, v. K-3, p. 261-276. 1991a, Ostracode assemblages from springs in the western United States: Implications for paleohydrology, in Will- iams, D.D., and Danks, H.V., eds., Arthropods of springs, with particular reference to Canada: Memoirs of the Ento- mological Society. 1991b, Pliocene-climate history of the western United States derived from lacustrine ostracodes: Quaternary Sci- ence Reviews, v. 10, p. 133-146. Molnia, B.F., Trabant, D.C., Post, Austin, and Frank-Molnia, D.G., 1990, Bering Glacier, Alaska: Factors influencing the potential for an irreversible calving retreat: Eos, v. 7 1, no. 43, p. 1314. Post, Austin, 1972, Periodic surge origin of folded medial rno- raines on Bering piedmont glacier, Alaska: Journal of Gla- ciology, v. 11, no. 62, p. 219-226. Reviewers: Thomas M. Bown and Louie N. Marincovich
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Geologic Studies in Alaska by the U
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CONTENTS Introduction Cynthia Dusel
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CONTENTS CONTRIBUTORS TO THIS BULLE
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GEOLOGIC STUDIES IN ALASKA BY THE U
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LATE HOLOCENE LONGITUDINAL AND PARA
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DEEP-WATER LITHOFACIES AND CONODONT
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Table 1. Locality register for key
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Table 1. Locality register for key
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LITHOFACIES AND CONODONTS OF CARBON
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LITHOFACES AND CONODONTS OF CARBONI
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Table 1. Conodont faunules and lith
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DEPOSITIONAL SEQUENCES IN ATIGUN SY
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U-Pb AGES OF ZIRCON, MONAZITE, AND
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APPEAL FOR NONPROLIFERATION OF ESCA
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FAVORABLE AREAS FOR METALLIC MINERA
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GOLD AND CINNABAR IN HEAVY-MINERAL
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EARLY CENOZOIC DEPOSITIONAL SYSTEMS
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EARLY CENOZOIC DEPOSITIONAL S YSTEM
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RESERVOIR FRAMEWORK ARCHITECTURE, C
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GEOCHEMISTRY OF OPHIOLITIC ROCKS FR
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Table 1. Isotopic ages of intrusive
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Table 1. Isotopic ages of intrusive
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GEOCHEMICAL EVALUATION OF STREAM-SE
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Geologic Studies in Alaska by the U.S. Geological Survey, 1992

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