May 9, 2017 - The Oldest Representative (Early Jurassic, middle Hettangian) of the Gastropod. Genus Pleurotomaria in North America (Discovered in the ...
The Oldest Representative (Early Jurassic, middle Hettangian) of the Gastropod Genus Pleurotomaria in North America (Discovered in the Pogibshi formation near Seldovia, Kenai Peninsula, Alaska) Mariel Ferrari1, Robert B. Blodgett2, Montana S. Hodges3 and Christopher L. Hodges3 1
Instituto Patagónico de Geología y Paleontología, IPGP (CCT CONICET-CENPAT), Boulevard Alte. Brown 2915, (9120) Puerto Madryn, Provincia de Chubut, Argentina 2
Blodgett & Associates, LLC , 2821 Kingfisher Drive, Anchorage, Alaska 99502
3
University of Montana Paleontology Center, University of Montana, 32 Campus Drive, Missoula, Montana 59812
Abstract The earliest and only known Jurassic gastropod of the genus Pleurotomaria in North America is reported here from middle Hettangian strata of the lower part of the July member of the informally named Pogibshi formation of Kelley (1980). This unit is restricted to the southwestern part of the Kenai Peninsula west of Seldovia, Alaska. The Pogibshi consists of marine sedimentary and volcanic rocks which are part of the widespread Peninsular terrane of southcentral Alaska. Co-occurring or closely associated with the Pleurotomaria is a new species of the pectinid subgenus Weyla (Lywea), ammonites, and scleractinian corals. Introduction Although Arkell (1956) recognized that the Jurassic of Cook Inlet and the Alaska Peninsula of southern Alaska represented the most complete sedimentary succession for this interval on the North American continent, biostratigraphic and paleontologic studies of this region have lagged far behind other parts of western North America. In the March 2017 issue of this newsletter the oldest representatives of the bivalve genus Weyla in North America were documented from the Seldovia area on the Kenai Peninsula, southcentral Alaska (Hodges and others, 2017a). The genus Weyla is restricted to and characteristic of all four stages of the Lower Jurassic. The occurrence at Seldovia was noted as Weyla (Lywea) n. sp., but this species is intended to be formally named and described in the near future (Blodgett and others, in preparation). Likewise another surprising discovery during the 2016 field season near Seldovia was the occurrence of the oldest and only known Jurassic gastropod of the genus Pleurotomaria to be found in North America. The genus has a wide chronostratigraphic distribution from the Middle Triassic to the Recent (see Begg and GrantMackie, 2003) and is also known from all over the world. Particularly, in the Western Hemisphere it first appears during the Late Triassic in South America. Haas (1953) reported the oldest─although doubtful─occurrence of Pleurotomaria in the Norian-Rhaetian of central Peru. During the Early Jurassic Pleurotomaria has also been reported in South America by Gründel (2001) and Ferrari (2014) who mentioned some species from the early Sinemurian of northern Chile and from the late Pliensbachian-early Toarcian of north and southwestern Argentina. The first occurrence of a middle Hettangian Pleurotomaria species from North America is reported here and it is preliminary assigned to Pleurotomaria sp. This species, together with Weyla (Lywea) n. sp., is also intended to be formally named and described in the near future. Geologic Setting The Peninsular terrane comprises parts of southcentral Alaska and the Alaska Peninsula, and extends from near the tip of the Alaska Peninsula north and eastwards to the Copper River Basin at the east end of the Talkeetna Mountains (Jones and Silberling, 1979; Jones and others, 1981; Poulton and others, 1992; Silberling and others, 1992; Nokleberg and others, 1994). The outboard boundary of the Peninsular terrane is limited by the Border Range fault system that extends from southwest of Afognak Island to the northeast along the western margin of the Chugach Mountains (Fig. 1). The Chugach terrane is accreted on the southern outboard side of the Border Ranges fault system.
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The northeastern limit of the Peninsular terrane occurs in the southern Talkeetna Mountains. Within the Peninsular terrane are the elements of island volcanic arcs including prearc rocks, the sedimentary and lesser volcanic sequences of the Upper Triassic Kamishak Formation and the volcanic arc and postarc sedimentary sequences of the Lower Jurassic Talkeetna Formation (Wilson and others, 2012). The boundary between the Kamishak and Talkeetna Formations had been assumed to be the Triassic-Jurassic boundary but high precision geochronology at Puale Bay on the west side of Shelikof Strait, northeastern Alaska Peninsula, indicates the Kamishak continues into the early Hettangian (Pálfy and others, 1999; Barbacka and others, 2006). On the Kenai Peninsula only a sliver of the Peninsular terrane outcrops on the southwestern side of Kachemak Bay southwest of Seldovia (Fig. 2). The sea cliffs in the area contain a fairly well-exposed continuous sequence of Late Triassic to Early Jurassic age deposits (Martin, 1915, 1926; Kelley, 1980, 1984). The Jurassic portion of the succession has been informally referred to as the Pogibshi formation to distinguish it from the Jurassic Talkeetna Formation (Kelly, 1980, 1984). The Pogibshi formation consists of approximately 5,270 m thickness of volcaniclastic and sedimentary rocks (Kelley, 1980).
Figure 1. Terrane map of south-central Alaska after Rioux and others (2007) showing in green a sliver of the Peninsular terrane known as the Pogibshi formation on the southern Kenai Peninsula near Seldovia. See Fig. 2 for a detail of Seldovia area.
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Although the Pogibshi unit has been referred to as a formation, it has not been formally named and shows many similarities to the Talkeetna Formation to which some authors have assigned it (Magoon and others, 1976; Bradley and others, 1999). The Talkeetna Formation was initially described in the Talkeetna Mountains (Martin, 1926) and later extended to areas west of the Cook Inlet (Detterman and Reed, 1980) and then continuing as far south as Puale Bay on the northeast part of the Alaska Peninsula (Detterman and others, 1996). The Lower Jurassic exposures at Puale Bay had earlier been assigned to the Bidarka Formation of Kellum (1945), which seemingly included even younger strata. Both the Pogibshi and Talkeetna are of Early Jurassic age and consist of thousands of meters of volcanic, volcaniclastic rocks and both marine and non-marine sediments (Martin, 1926, Detterman and Reed, 1980; and Draut and others, 2006), but significant differences between the petrology in the Pogibshi formation and Talkeetna Formation have been noted (Kelley, 1980; Detterman and others, 1996; Wilson and others, 2012). In addition, a variance in age is also to be noted with the Pogibshi formation at Seldovia being Hettangian to early Sinemurian in age, while the Talkeetna Formation in the Talkeetna Mountains ranges in age from late Sinemurian to Toarcian (Imlay, 1981). In relation, different units underlie the Pogibshi formation near Seldovia, the Talkeetna Formation in the Talkeetna Mountains, and also on the west side of Cook Inlet and at Puale Bay. The informally named Port Graham formation (Kelley, 1980, 1984) underlies the Pogibshi formation and has been shown to overlap in age with the Kamishak Formation which underlies the Talkeetna Formation on the west side of the Cook Inlet including at Puale Bay. However, these two units differ in their lithologic content and depositional environments.
Figure 2. Geologic map of the Pogibshi formation (Jp) west and southwest of Seldovia Bay. Localities JL198 and JL3 are shown by red stars. Modified from Wilson and others, 2012.
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Pogibshi formation of Kelley (1980) We report here on fossils and a dated sandstone collected from the middle member of the Pogibshi formation at locality JL198 and a second sandstone collected to robustly confirm the unit age from locality JL3 (Fig. 2). Kelley (1980) divided the Pogibshi into three members on the basis of rock type, modal composition, and depositional texture (Fig. 3). The stratigraphically lowest member, the Dangerous member, consists of volcaniclastic breccia, conglomerate, and sandstone in depositional contact with the also informally defined Port Graham formation of Kelley (1980). Locally tuffaceous dark-gray sedimentary rocks in the Dangerous member make it difficult to distinguish the Dangerous member from the Port Graham formation. The July member consists of dacitic pyroclastic rocks, tuffaceous sandstone, granule conglomerate, and mudstone. Kelley (1980) indicated that the high quartz content and abundance of glassy debris help to distinguish this unit from other parts of his Pogibshi formation. The uppermost member, the Naskowhak member, consists of greenish-gray tuffaceous mudstone, siltstone, and tuff. Locally, the basal part of the Naskowhak member includes laterally extensive coal-bearing units that help to distinguish the Pogibshi formation of Kelley (1980) from the otherwise lithologically similar Talkeetna Formation on the west side of Cook Inlet. Bradley and others (1999) reported that the Pogibshi is intruded by the tonalite of Dogfish (Koyuktolik) Bay and possibly by the diorite of Point Bede, both in the southern Seldovia quadrangle; if so, a Late Triassic U/Pb age (205.1±4.8 Ma) on the diorite (D.C. Bradley, USGS, written commun., 2016) may indicate that the Pogibshi is in part significantly older than the Talkeetna Formation. Stanton and Martin (1905), Moffit (1906), Martin (1915, 1916, 1926), Imlay (1981) and Blodgett (2009) reported a diverse Lower Jurassic fauna along the coast southwest of Seldovia. Bradley and others (1999) erroneously attributed the Jurassic collections of Martin (1915) to the Port Graham formation of Kelley (1980), but those collections were from localities within the outcrop area Bradley and others (1999) assigned to the Talkeetna Formation, which Wilson and others (2012, 2015) reassigned back to the Pogibshi formation of Kelley (1980). Fossils noted in the above cited publications included scleractinian corals, numerous bivalves (mostly pectinaceans), gastropods, and ammonites. Blodgett (2009) briefly visited a section of early Sinemurian age, exposed about 6 km west of Seldovia, and found numerous pectinacean bivalves of the genus Weyla, gastropods, and scleractinian corals. The bivalve Weyla, an Early Jurassic index fossil, is found primarily along western coast of North and South America. At least two species of Weyla are present in the July member, one species being middle Hettangian in age and the other being early Sinemurian (Blodgett, personal observation). Early Jurassic ammonites from these same rocks were discussed and, in part, illustrated in Imlay (1981), who recognized both Sinemurian and Hettangian fossil assemblages. The oldest fossils identified within the Pogibshi formation are early Hettangian ammonites [placed here in the middle Hettangian] found at the base of the July member (Imlay, 1981), suggesting the strong possibility that the lowest member, the Dangerous member may be entirely or in part of Late Triassic age. Connelly (1978) and Connelly and Moore (1979) suggested correlation of these rocks with the Upper Triassic Shuyak Formation of the Afognak Island, which is intruded by the Afognak pluton of Triassic age (see also Wilson, 2013). Rioux and others (2007) reported an age on a metamorphosed volcaniclastic rock within the Border Ranges fault system in the Anchorage quadrangle that may be equivalent to the Pogibshi formation or Port Graham formation. The sample yielded two distinct populations of zircons, reported as 202.1±1.2 Ma and 205.8±0.4 Ma. The geochronology of the lower July member The age of the lower part of the July member was determined by ammonite zonation and confirmed by uranium-lead dating at two locations (Fig. 3). The lower location is referred to as JL198 (Fig. 4) and the upper location as JL3. The respective GPS coordinates of the two locations are 59.43739º N, 151.82033º W and 59.44269º N, 151.78861º W, respectively. The continuation of the beds at JL198 (shown in the far left of Fig. 5) contain ammonites identified by Imlay (1981) as Psiloceras (Franziceras) cf. P. (F.) ruidum (Buckman) which Imlay assigned an early Hettangian age. Subsequent work by Taylor and others (2001) suggests that this ammonite interval should instead be considered as the Coronoides zone which is approximately middle Hettangian. In the beds near JL3 Imlay (1981) identified two ammonites, Paracaloceras rursicostatum Frebold and Coroniceras (Paracoroniceras) sp. which indicated an early Sinemurian age for JL3.
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Sandstone samples were collected from JL3 and from the JL198 beds at an appearance of the same fossiliferous interval at a location approximately 260 meters west of JL198. Detrital zircons were extracted from these sandstones at the Arizona LaserChron Center (ALC) and uranium-lead dated using laser ablation multicollector inductive coupled plasma mass spectrometry (LA-MC-ICPMS) following current ALC protocols (Gehrels, 2012; Hodges and others, 2017b). The preliminary maximum depositional age of JL198 beds is middle Hettangian at 200.5 ±2.5 ±1.8 Ma from 9 zircon grains with the stated errors reported at 2σ for internal and systematic respectively. The upper JL3 sample is early Sinemurian with a preliminary maximum depositional age of 198.9 ±0.62 ±2.2 Ma from 314 zircon grains. These U-Pb ages support the ammonite zonation ages established by Imlay (1981). The geochronology and biochronology will be described in detail in the near future (Hodges and others, in preparation).
Figure 3. Stratigraphic composite section of the middle and upper Pogibshi formation. The position of localities JL198 and JL3 in the July member are indicated. Modified from Kelley (1980).
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The occurrence of the gastropod genus Pleurotomaria in the Pogibshi formation The gastropod genus Pleurotomaria is represented by three specimens from the middle Hettangian age locality JL198 (see Fig. 2 for location and Fig. 3 for stratigraphic position within the Pogibshi formation.). The specimens found at the JL198 locality are represented by rather poorly preserved shells, although one of them shows the typical morphological characters of Pleurotomaria (Fig. 7A-7C). The taxonomic treatment and a detailed morphological description of the Pleurotomaria species are not the aim of this paper, and will be treated in a forthcoming publication. The Pleurotomaria species here reported have been found in association with Weyla and coral-bearing beds exposed at the locality JL198 (see Hodges and others, 2017a).
Figure 4.The Early Jurassic (middle Hettangian) cliffs of site JL198, where Pleurotomaria was discovered. The fossiliferous beds are between the man's feet and shoulders.
Figure 5. The view looking east from site JL198. The fossiliferous beds are marked in red by a 1 meter scale bar. Note the change in bed dip angles shown in the photo between the near right and the far left.
Figure 6. In-situ Pleurotomaria sp. at middle Hettangian locality JL198. This is the same specimen as that shown in Figs. 7A7C.
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The vetigastropod genus Pleurotomaria shows a wide chronostratigraphic distribution from the Middle Triassic to the Recent and is found all over the world. Begg and Grant-Mackie (2003) supported the idea of an origin of Pleurotomaria from the late Anisian-Ladinian (Mid-Triassic) in the south-western Pacific sea. In the European epicontinental seas, Pleurotomaria first appeared during the early Hettangian and reached the European region through dispersal along the southern Tethyan margin (Monari and Gatto, 2013). The Late Triassic?-Early Jurassic radiation of Pleurotomaria from the western Tethys to North and South America may be related to the opening of a mid-Atlantic sea way, the Hispanic Corridor as earliest as the Norian times. According to Blodgett and Frýda (2001) and Frýda and Blodgett (2003) the strong similarities between western North American Late Triassic gastropod with those of the western Tethys suggests that the Hispanic Corridor may have been open as early as the Norian. The first and oldest ─although doubtful─occurrence of Pleurotomaria in the Western Hemisphere dates from the Late Triassic (Norian-Rhaetian) of South America (Haas, 1953). Gründel (2001) and Ferrari (2014) have also mentioned some species from the early Sinemurian of northern Chile and from the late Pliensbachian-early Toarcian of north and south western Argentina. Based on the general shell morphology with a gradate shape and angulated outer edge of the ramp, broad selenizone, strongly prosocyrt nodular elements and spiral ornament dominant on adult shell, our middle Hettangian Pleurotomaria seems to represent a new species and its stratigraphic occurrence suggest it is the first and oldest reported species of the genus in North America. Acknowledgments This work was supported in part by a grant from the Alaskan Geological Society to Montana Hodges in support of her doctoral dissertation. This study greatly benefited from discussions with Dr. John S. Kelley (USGS retired, Anchorage) and Dr. Frederic H. Wilson (USGS, Anchorage). We also appreciate the assistance in field work by Dr. Bretwood Higman and family, Captain Kirby Corwin, Ben Siwiec and the dedicated staff of the Arizona LaserChron Center.
Figure 7. Pleurotomaria sp. from middle Hettangian locality JL198. Scale bar is 20 mm in length. A-C, three views of largest specimen, A, lateral view, B, basal view, and C, opposing lateral view which is a naturally-occurring cross-section showing umbilicate nature of shell with inner whorls margins clearly delineated on left side of view. D-E, intermediate sized (of the three collected) specimens, D, apertural view, E, abapertural view.
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REFERENCES Arkell, W.J., 1956, Jurassic Geology of the World: Oliver and Boyd, Edinburgh, 806 p. Barbacka, Maria, Pálfy, József, and Smith, P.L., 2006, Hettangian (Early Jurassic) plant fossils from Puale Bay (Peninsular terrane, Alaska): Review of Palaeobotany and Palynology, v. 142, p. 33-46. Begg, J.G., and Grant-Mackie, J.A., 2003, New Zealand and New Caledonian Triassic Pleurotomariidae (Gastropoda, Mollusca): Journal of the Royal Society of New Zealand, v. 33, p. 223-268. Blodgett, R.B., 2009, Report on day trip (5/16/07) to visit Mesozoic rocks exposed in Port Graham and near Seldovia, southern Kenai Peninsula, p. 109-116, in LePain, D.L., Preliminary results of recent geologic investigations in the Homer, Kachemak Bay area, Cook Inlet Basin. Progress during the 2006-2007 field season: Alaska Division of Geological & Geophysical Surveys Preliminary Interpretive Report 2009-8C, p. 109-116. Blodgett. R.B. and Frýda, Jiří, 2001, Upper Triassic gastropod biogeography of western North America: Geological Society of America Abstracts with Programs, v. 33, no. 3, p. A-53. Bradley, D.C., Kusky, T.M., Haeussler, P.J., Karl, S.M., and Donley, D.T., 1999, Geologic map of the Seldovia quadrangle, southcentral Alaska: U.S. Geological Survey Open-File Report 99-18, 1 sheet, scale 1:250,000. Connelly, William, 1978, Uyak Complex, Kodiak Islands, Alaska: A Cretaceous subduction complex: Geological Society of America Bulletin, v. 89, p. 755-769. Connelly, William, and Moore, J.C., 1979, Geologic map of the northwest side of the Kodiak and adjacent islands, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF–1057, 2 sheets, scale 1:250,000. Detterman, R.L., Case, J.E., Miller, J.W., Wilson, F.H., and Yount, M.E., 1996, Stratigraphic framework of the Alaska Peninsula: U.S. Geological Survey Bulletin 1969-A, 74 p. Detterman, R.L., and Reed, B.L., 1980, Stratigraphy, structure, and economic geology of the Iliamna quadrangle, Alaska: U.S. Geological Survey Bulletin 1368-B, p. B1-B86, 1 sheet, scale 1:250,000. Draut, A.E., Clift, P.D., and Blodgett, R.B., 2006, Field-trip guide to volcanic and volcanoclastic deposits of the Lower Jurassic Talkeetna Formation, Sheep Mountain, south-central Alaska: U.S. Geological Survey Open-File Report 2006-1124, 21 p. Ferrari, S. M., 2014, Patellogastropoda and Vetigastropoda (Mollusca, Gastropoda) from the marine Jurassic of Patagonia, Argentina: Historical Biology, v. 26, no. 5, p. 563-581. Frýda, Jiří, and Blodgett, R.B., 2003, Silberlingiella, a new purpirinid genus (Littorinoidea, Gastropoda) from the Late Middle Norian (Late Triassic) of the Clan Alpine Range, western Nevada: Mitteilungen des Geologisch-Paläontologischen Instituts der Universität Hamburg, Heft 87, p. 47-54. Gehrels, George, 2012, Detrital zircon U Pb geochronology: Current methods and new opportunities, p. 45-62, in Busby, Cathy, and Azor, Antonio, eds., Tectonics of Sedimentary Basins: Recent Advances, John Wiley & Sons, Inc. Gründel, Joachim, 2001, Gastropoden aus dem Jura der südamerikanischen Anden: Freiberger Forschungshefte C 492, p. 43–84. Haas, Otto, 1953, Mesozoic invertebrate faunas of Peru: Bulletin of the American Museum of Natural History, v. 101, p. 1-328. Hodges, M.S., Hodges, C.L., Blodgett, R.B., and Stanley, George, Jr., 2017a, Preliminary investigations of Early Jurassic fossils and geochronology of the Pogibshi formation near Seldovia, Kenai Peninsula, Alaska: Alaska Geology – Newsletter of the Alaska Geological Society, v. 47, no. 7, p. 5-15. Hodges, M.S., González-León, C.M., Stanley, G.D. Jr., and Hodges, C.L., 2017b (in press), Detrital zircon U-Pb geochronology of the Sierra de Santa Rosa Formation, Sonora, Mexico, and implications for an Early Jurassic retroarc basin, Lithosphere. Imlay, R.W., 1981, Early Jurassic ammonites from Alaska: U.S. Geological Survey Professional Paper 1148, 49 p., 12 pls. Jones, D.L., and Silberling, N. J., 1979, Mesozoic stratigraphy – the key to tectonic analysis of southern and central Alaska: U.S. Geological Survey Open-File Report 79-1200, 39 p. Jones, D.L., Silberling, N.J., Berg, H.C., and Plafker, George, 1981, Map showing tectonostratigraphic terranes of Alaska, columnar sections, and summary description of terranes: U.S. Geological Survey Open-File Report 81-792, 20 p., 2 sheets, scale 1:2,500,000. Kelley, J.S., 1980, Environments of deposition and petrography of Lower Jurassic volcaniclastic rocks, southwestern Kenai Peninsula, Alaska: Davis, University of California – Davis, unpublished Ph.D. dissertation, 304 p. Kelley, J.S., 1984, Geologic map and sections of the southwestern Kenai Peninsula west of Port Graham, Alaska: U.S. Geological Survey Open-File Report 84-162, 1 sheet, scale 1:63,360. Kellum, L.B., 1945, Jurassic stratigraphy of Alaska and petroleum exploration in northwest America: Transactions of the New York Academy of Sciences, ser. 2, v. 7, no. 8, p. 201-209. Magoon, L.B., Adkison, W.L., and Egbert, R.M., 1976, Map showing geology, wildcat wells, Tertiary plant fossil localities, K-Ar age dates, and petroleum operations, Cook Inlet area, Alaska: U.S. Geological Survey Map I-1019, 3 sheets, scale 1:250,000. Martin, G.C., 1915, The western part of the Kenai Peninsula, in Martin, G.C., Johnson, B.L, and Grant, U.S., Geology and mineral resources of Kenai Peninsula, Alaska: U.S. Geological Survey Bulletin 587, p. 41-111. Martin, G.C., 1916, Triassic rocks of Alaska: Geological Society of America Bulletin, v. 27, p. 685-718.
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Martin, G.C., 1926, The Mesozoic stratigraphy of Alaska: U.S. Geological Survey Bulletin 776, 493 p. Moffit, F.H., 1906, Gold fields of the Turnagain Arm region: U.S. Geological Survey Bulletin 277, p. 7-52. Monari, Stefano, and Gatto, Roberto, 2013, Pleurotomaria Defrance, 1826 (Gastropoda, Mollusca) from the Lower Bajocian (Middle Jurassic) sediments of Luxemburg, with considerations on its systematics, evolution and palaeobiogeographical history: Palaeontology, v. 56, p. 751–781. Nokleberg, W.J., Plafker, George, and Wilson, F.H., 1994. Geology of south-central Alaska, p. 311–366, in Plafker, George, and Berg, H.C., eds. The geology of Alaska. The Geological Society of America, Boulder. Colorado, The geology of North America, v. G-1. Pálfy, József, Smith, P.L., Mortensen, J.K., and Friedman, R.M., 1999, Integrated ammonite biochronology and U-Pb geochronometry from a basal Jurassic section in Alaska: Geological Society of America Bulletin, v. 111, no. 10, p. 1537–1549. Poulton, T.P., Detterman, R.L., Hall, R.L., Jones, D.L., Peterson, J.A., Smith, Paul, Taylor, D.G., Tipper, H.W., and Westermann, G.E.G. , 1992, Western Canada and United States, p. 29–92, in Westermann, G.E.G., ed., The Jurassic of the Circum-Pacific: Cambridge University Press, Cambridge. Rioux, Matthew, Hacker, Bradley, Mattinson, James, Kelemen, Peter, Blusztajn, Jurek, and Gehrels, George, 2007, Magmatic development of an intra-oceanic arc: High-precision U-Pb zircon and whole-rock isotopic analyses from the accreted Talkeetna arc, south-central Alaska: Geological Society of America Bulletin, v. 119, p. 1168-1184. Silberling, N.J., Jones, D.L., Monger, J.W.H., and Coney, P J., 1992, Lithotectonic terrane map of the North American Cordillera: U.S. Geological Survey Miscellaneous Investigations Series Map I-2176, 2 sheets, scale 1:5,000,000. Stanton, T.W., and Martin, G.C., 1905, Mesozoic section on Cook Inlet and Alaska Peninsula: Geological Society of America Bulletin, v. 16(1), p. 391-410. Taylor, D.G., Guex, J., and Rakus, M., 2001, Hettangian and Sinemurian ammonoid zonation for the Western Cordillera of North America: Bulletin de la Société Vaudoise des Sciences Naturelles, v. 87, no. 4, p. 381-421. Wilson F.H., 2013, Reconnaissance geologic map for the Kodiak and adjacent islands, Alaska: U.S. Geological Survey Scientific Investigations Map 2999, pamphlet 8 p., 1 sheet, scale 1:500,000. Wilson, F.H., Hults, C.P., Schmoll, H.R., Haeussler, P.J., Schmidt, J.M., Yehle, L.A., and Labay, K.A., 2012, Geology of the Cook Inlet region, Alaska, including parts of the Talkeetna, Talkeetna Mountains, Tyonek, Anchorage, Lake Clark, Kenai, Seward, Iliamna, Seldovia, Mount Katmai, and Afognak 1:250,000-scale quadrangles: U.S. Geological Survey Scientific Investigations Map SIM-3153, pamphlet 71 p., 2 sheets, scale 1:250,000. Wilson, F.H., Hults, C.P., Mull, C.G., and Karl, S.M., compilers, 2015, Geologic map of Alaska: U.S. Geological Survey Scientific Investigations Map 3340, 196 p., 2 sheets, scale 1:584,000, http://dx.doi.org/10.3133/sim3340
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