Eleven widely separated areas in Alaska contain rocks of Precambrian or probable Precambrian age.The age assignment in five areas is based on radiometric dating; in the other six areas stratigraphic evidence is used to infer a Precambrian age.All known Alaskan Precambrian rocks are of Late Proterozoic age except those constituting the Kilbuck terrane of southwestern Alaska and an area in the Yukon-Tanana upland of eastern Alaska, which are Early Proterozoic, and the schist of the northeastern Kuskokwim Mountains in central Alaska, which is Middle and Late Proterozoic.No evidence exists at this time for the presence of rocks of Archean age in Alaska.The Tindir Group along the Yukon River in east-central Alaska, which is considered equivalent to parts of the Windermere, Belt, and Purcell Supergroups of Canada, is the only group of Precambrian rocks in Alaska that can be definitely related to Precambrian stratigraphic sections in other parts of the North American Cordillera.The Neruokpuk Quartzite and underlying strata of northern Alaska are Precambrian on the basis of stratigraphic evidence.The Tindir(?) Group along the Porcupine River in east-central Alaska and low-grade metamorphic rocks in the Livengood-Crazy Mountains region of central Alaska are probably Precambrian, although their precise ages are not known.Tectonomagmatic events in the interval 1,100 to 600 million years ago are recorded in schist of the Yukon-Koyukuk region in west-central Alaska and in gneiss on the Seward Peninsula.The Wales Group of the Alexander terrane of southeastern Alaska and the Kilbuck metamorphic terrane of southwestern Alaska are allochthonous and appear to belong to exotic terranes accreted to the North American craton during Phanerozoic time.Although mineral deposits are known to occur in several areas of Precambrian rocks, many of these deposits were produced during Phanerozoic mineralization episodes.However, banded iron-formation within the Tindir Group of east-central Alaska and certain volcanogenie, stratabound base-metal deposits within the Wales Group in southeastern Alaska are believed to have been formed during the Precambrian era.

Diverse Quaternary surficial deposits are widely distributed throughout the quadrangle but have not been separately studied or mapped.Only major areas of distribution are shown and their delineation has been inferred mainly from the examination of aerial photographs. Qag^DIFFERENTIATED SURFICIAL DEPOSITS Includes mainly alluvium, tidal mudflat, and glaciofluvial deposits BEDROCKS Ts CONGLOMERATE, SANDSTONE, AND CONGLOMERATIC SANDSTONE (Eocene?)At Coal Bay, located on the south shore of Kasaan Bay, rocks consist of light-gray to buff graywacke-type sandstone that contains carbonized logs with branches still attached.Two kilometers to the northeast, at the head of Little Coal Bay, conglomerate and conglomeratic sandstone containing cobbles and boulders of diorite and subordinate black argillite of local derivation are interbedded with graywacke that contains a few discontinuous flat-lying seams of lignitic coal a few inches thick.In the valley of Lava Creek, at head of Thorne Bay, deltaic conglomerate contains abundant pebbles and cobbles of locally derived argillite, gneiss, trachyte and amygdaloidal lava, biotite granite, schist and chert in a lithified matrix that contains rounded clasts of quartz, orthoclase, and microcline in addition to small fragments of the lithologies of the rocks listed.The conglomerate is cut by pitchstone dikes.Northeast of Clarence Strait, similarly constituted and probably correlative conglomerate, sandstone, siltstone, and shale, with minor lignite occur on northeastern Eagle Island and south of Union Point, the northeast headland of Union Bay. Field relations suggest deposition as alluvial fans, piedmont gravels and deltas at the mouths of steep gradient streams that drained terranes of considerable relief (Buddington and Chapin, 1929, p. 267; Sainsbury, 1961, p. 328).Tentative Eocene age assignment based on (1) the presence of igneous and metamorphic detritus in the Prince of Wales Island conglomerates believed to have been derived from a provenance of Middle Cretaceous age, and (2) the possible correlation between the pitchstone dikes that cut the Ts unit in the valley of Lava Creek with rhyolitic detritus abundant in Eocene rocks north of the Craig quadrangle (Sainsbury, 1961, p. 328).Probably not more than 30 m thick NORTHEAST OF CLARENCE STRAIT

Paleozoic limestone, graywacke, sandstone, milestone, red beds and volcanic rocks of the Alexander terrane, southeastern Alaska, have yielded six paleomagnetic pole positions after thermal and alternating‐field demagnetization. These poles are from sample groups of late Middle Ordovician, Late Ordovician, Devonian, Late Devonian, and early and late Carboniferous age. To test various tectonic models for the structural development of this part of western North America, the paleomagnetic results are compared to those for the North American craton. It is found that the observed inclination and declination values deviate significantly from the values predicted for the present‐day position of the Alexander terrane (55.5N, 133.5W). Better matching can be obtained for a paleoposition of the terrane at about 40N, 120W, in the present position of western Nevada and northeastern California. In addition, an in situ 25° clockwise rotation of the terrane is required to restore it to its original position.

A brachiopod fauna from the type locality of the Port Refugio Formation on Suemez Island, 24 km south of Craig, southeastern Alaska, is described and illustrated. The fauna consists of Cyrtospirifer buddingtoni n. sp., Mucrospirifer refugiensis n. sp., Crurithyris alaskensis n. sp., Johnsonathyris adrianensis n. gen., n. sp., Cleiothyridina milleri n. sp., Rugaltarostrum congregabile n. sp., Chapinella bucareliensis n. gen., n. sp., Kindleina suemezensis n. gen., n. sp., Allorhynchoides kirki n. gen., n. sp., and Rhipidomella sp. All these species except Crurithyris alaskensis occur together in what is considered to be a single community named the Johnsonathyris Community. Crurithyris alaskensis occurs in a separate horizon, about 1.3 m above the other species. The Johnsonathyris Community consisted of epifaunal suspension feeders living on a silty calcareous substratum. A middle to late Famennian age is assigned to the fauna. Although the biogeographic affinities of the fauna seem to be mainly with North America, none of the forms is conspecific with previously described material, and the fauna is unusually provincial at a time when brachiopods were generally cosmopolitan. Some degree of isolation from other North American brachiopod faunas is indicated.

Conodonts from a limestone interval exposed above Port St. Nicholas, Prince of Wales Island, southeastern Alaska, include Pandorinellina exigua philipi (Klapper), Eognathodus sulcatus Philip, and Pelekysgnathus serratus Jentzsch. These conodonts indicate an early to middle Pragian age (informal faunal units 5 or 6 of Klapper et al). This middle Early Devonian age is supported by the presence of the graptolites Monograptus yukonensis, M. craigensis, and M. pacificus in shales above the limestone and by some shelly fossils from within the limestone.

No record of production butMaddren.1915.p. staking of lower half of valley 336-138; Hoare and was essentially complete as of Cobb.1977, p. to 1914.Fine colors reported near mouth of creek.Reputed to contain large amount of lowgrade ground that may be suitable for dredging.Bedrock ts graywacke and other elastics of Cretaceous Kuskokwin Group.Some right Unit tributaries head 1n Tertiary granitic stocks of Mt.Plumner and Marvel Dome Numerous claims located and Maddren, 1915, p. small placer gold prospect )o-339 cated in glacial gravels but no mining reported as of 1914 9 FUner Creek H. 9 T.9N..R.58H.

SummaryK—Ar age measurements on Esquibel Island, southeastern Alaska yield a minimum age of about 433±3 Ma for the Zone of Monograptus cyphus of the Lower Silurian. An age of approximately 435—437 Ma is estimated for the Ordovician—Silurian boundary.

Research Article| June 01, 1977 Ancient borderland terranes of the North American Cordillera: Correlation and microplate tectonics MICHAEL CHURKIN, JR.; MICHAEL CHURKIN, JR. 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar G. DONALD EBERLEIN G. DONALD EBERLEIN 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Author and Article Information MICHAEL CHURKIN, JR. 1U.S. Geological Survey, Menlo Park, California 94025 G. DONALD EBERLEIN 1U.S. Geological Survey, Menlo Park, California 94025 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1977) 88 (6): 769–786. https://doi.org/10.1130/0016-7606(1977)88<769:ABTOTN>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation MICHAEL CHURKIN, G. DONALD EBERLEIN; Ancient borderland terranes of the North American Cordillera: Correlation and microplate tectonics. GSA Bulletin 1977;; 88 (6): 769–786. doi: https://doi.org/10.1130/0016-7606(1977)88<769:ABTOTN>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Enigmatic Paleozoic and Precambrian sequences rich in volcanic and plutonic rocks form discrete terranes along the outer border of the North American Cordillera. These borderland terranes occur in California in the northern Sierra Nevada and Klamath Mountains, in central Oregon and eastern Oregon–westernmost Idaho, in Washington in the Northern Cascade Mountains and San Juan Islands, in British Columbia in Vancouver Island, and in Alaska in the Alexander Archipelago. The difficulty in relating the geology of the borderland terranes to that of the North American continent, the recognition of ophiolites and suture zones separating the terranes from the continent, plus the Asiatic affinity of certain of the borderland faunas indicate that the terranes are allochthonous relative to the North American continent. Furthermore, major differences in stratigraphy, magmatic activity, tectonic activity, metamorphism, and particularly the ages and types of basement between the terranes — when considered together with discordant paleomagnetic data — suggest that at least six lithospheric plates are represented.The terranes in the Klamath Mountains have an Ordovician ultramafic rock (ophiolite) basement. The Oregon terranes have ultramafic complexes (ophiolites) in close association with volcanic rocks (volcanic arcs) that form the basement. In the Northern Cascade Mountains and San Juan Islands, the terranes have, respectively, Precambrian and Ordovician crystalline metaplutonic (magmatic arc) basement. The terrane in the southern part of the Alexander Archipelago has a Precambrian crystalline meta-volcanic-metasedimentary (remnant arc) basement, but an Ordovician basaltic-andesitic basement (initial deposits of an upward-shoaling island arc) appears farther north. Transcurrent faults segment and truncate parts of the Cordillera, but since the borderlands are in themselves composed of several plates, models of a single allochthonous plate are difficult to apply. More likely, during Precambrian and Paleozoic time, multiple microcontinental plates and volcanic arcs moved outboard and inboard (away from and toward North America) to accommodate a succession of marginal ocean basins opening and closing behind migrating arcs. This was followed in Mesozoic and Cenozoic time by large-scale northwestward drift. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Continued Page 6. Aquagene tuff overlain by basalt and underlain by chert-shale subunit

Figures 2-31 are photographs] Page 4. Basaltic tuff-breccia_______________________________ 5. Pillow basalt_____________________________________ 6-9.Heceta Limestone: 6. Cuesta formed in massive Heceta Limestone__________ 7. Intraformational limestone conglomerate of the Heceta Limestone ___ ---------------------------------8.Intraformational limestone breccia of the Heceta Lime-stone__________________________________________ 9. Exotic block of

The youngest zones of Monograptus occur in Devonian black shale and slate along the western shore of Prince of Wales Island and on Noyes Island, southeastern Alaska. The following five species of Monograptus, in close association with vascular plants and marine shelly faunas, indicate a Praguian, (Siegenian to Early Emsian), late Lower Devonian and possibly early Middle Devonian age: M. yukonensis Jackson & Lenz, M. n. sp. aff. yukonensis ? Jaeger & Stein, M. aeqimbilis notoaequakilis Jaeger & Stein, M. pacificus Jaeger n. sp. and M. craigensis Jaeger n. sp. The yukonensis zone containing M. craigensis in its upper part is followed stratigraphically higher by the M. pacificus zone – the youngest occurrence of Monograptus. The new species belong to the M. uncinatus group and, like most Praguian monograptids, have long dorsal tongues on their siculae. M. craigensis and M. pacificus increase to seven the number of species of Monograptus known from the Praguian. On the basis of the Alaskan material, the geographical distribution of M. aequabilis notoaequabilis now includes North America in addition to previously recorded occurrences in Australia, Southeast Asia, and Europe. This broad geographic distribution suggests that the last survivors of Monograptus had worldwide distribution and a rather uniform assemblage of species.