West-central Alaska Research Articles

Some Early Pragian Brachiopods from Soda Creek Limestone of West-Central Alaska

Some Early Pragian Brachiopods from Soda Creek Limestone of West-Central Alaska

Early Pragian Rhynchonellids (Brachiopoda) of West-Central Alaska and Northeastern Eurasia and Their Paleobiogeographic Significance

Early Pragian Rhynchonellids (Brachiopoda) of West-Central Alaska and Northeastern Eurasia and Their Paleobiogeographic Significance

Two new brachiopod genera from the Lower Pragian (Lower Devonian, Soda Creek Limestone) of west-central Alaska

New strophomenid and rhynchonellid (Brachiopoda) taxa are described from the Lower Pragian (Soda Creek Limestone) of west-central Alaska: Harperoides gen. nov. with type species H. alaskensis sp. nov. (subfamily Mesodouvillinae Harper et Boucot) and Pedderia gen. nov. with type species P. fragosa sp. nov. (family Pygmaellidae Baranov).

A cold supergene zinc deposit in Alaska: The Reef Ridge case

The Reef Ridge deposit is a typical supergene “nonsulfide” zinc mineralization, located in the Yukon-Koyukuk region of west-central Alaska (USA). It is hosted in sedimentary rocks of the Farewell terrane, a continental fragment sandwiched between the Siberian and Laurentian cratons during the early Paleozoic. The mineralization occurs in Lower–Middle Devonian shallow-water dolomite of a Paleozoic carbonate platform succession belonging to the Nixon Fork tectonic unit. The mineralization consists of oxidized minerals associated with minor remaining sulfides (pyrite/marcasite and sphalerite). In the oxidation zone, smithsonite is the predominant mineral, mixed with Fe-(hydr)oxides (goethite and hematite). A complete petrographic and mineralogical study was performed. Samples were analyzed by X-ray diffraction, inductively coupled plasma–mass spectrometry and emission spectrometry, energy dispersive scanning electron microscopy, and QEMSCAN ® (quantitative evaluation of minerals by scanning electron microscopy). The most abundant mineral in the nonsulfide ore is smithsonite. Similar to other nonsulfide Zn deposits worldwide, the first generation of smithsonite has replaced both primary sphalerite and the host carbonates. A second smithsonite generation precipitated as cement in vugs, cavities, and fractures. Minor zinc amounts also occur in the Fe-(hydr)oxides, and zinc traces have been identified in clay minerals. The carbon and oxygen isotope values of smithsonite at Reef Ridge vary from −0.7 to 2.1‰ relative to Vienna Peedee belemnite (VPDB) and 19.1‰ to 21.9‰ relative to Vienna standard mean ocean water (VSMOW). The δ 13 C values are similar to those of the host rock, suggesting that the predominant carbon source for smithsonite was the host carbonates, with only a limited contribution from organic carbon. The oxygen isotope ratios of Reef Ridge smithsonite are more depleted in 18 O compared to supergene nonsulfides from other parts of the world formed under warm-humid, temperate, or semiarid climates. The oxygen isotope fractionation between water and smithsonite, which relates the δ 18 O value of the mineralizing solution, the formation temperature of smithsonite, and its δ 18 O composition, indicates that the δ 18 O composition of Reef Ridge smithsonite is related to very low formation temperatures (~10 °C), and strong depletion in 18 O of the precipitating waters. The δ 18 O smithsonite composition, the strong 18 O depletion, and the relationship of the formation of the Reef Ridge nonsulfide deposit with the development of the Sleetmute upland surface (which started in the Late Tertiary and continues to the present) indicate that the formation of the Reef Ridge nonsulfide deposit is probably related to cold/humid weathering episodes during a period comprised between Late Tertiary and Holocene. The “traditional” interpretation on the genesis of Zn nonsulfide deposits in warm-humid, temperate, or semiarid conditions should be questioned where other climate zones are indicated.

Emsian (Late Early Devonian) sponges from west-central and south-central Alaska

Relatively common specimens of the hypercalcified agelasiid sponge Hormospongia labyrinthica Rigby and Blodgett, 1983 and specimens of associated species of Hormospongia have been previously reported from Emsian and Eifelian stratigraphic units at several localities in south-central and southeastern Alaska (Rigby and Blodgett, 1983). Those sponges were first described from the type section of the Eifelian Cheeneetnuk Limestone in the McGrath A-5 quadrangle. Since then several additional specimens of Hormospongia labyrinthica have also been collected from a new locality in the Talkeetna C-6 quadrangle in south-central Alaska (Figs. 1, 2.1), and are documented here.

Silurian Gastropoda from southeastern and west-central Alaska

Additional Silurian (Ludlovian) gastropods are described from the Heceta Formation in the Alexander terrane on Prince of Wales Island, southeastern Alaska. Species includeSpinicharybdis krizin. sp.,Spinicharybdis boucotin. sp.,Morania wagnerin. sp.,Haplospira craigin. sp.,Australonemasp.,Pachystrophiacf.gotlandica(Lindström, 1884), andMedfrazyga gilmullin. sp. An additional new Silurian species,Morania nixonforkensisn. sp., is described from the Nixon Fork subterrane of the Farewell terrane of west-central Alaska.The spine-bearingSpinicharybdisis placed into a new subfamily Spinicharybdiinae together withHystricocerasJahn, 1894. Joint occurrences of generaBeraunia, Coelocaulus, andMorania, as well as members of subfamily Spinicharybdiinae in the gastropod fauna from the Heceta Formation, support its close relationship with gastropod fauna of Bohemia. Additionally, the occurrence of the genusMedfrazygasuggests a faunal link between the Alexander and Farewell terranes of Alaska.Medfrazyga gilmullin. sp. is the oldest known and the only early Paleozoic member of the family Palaeozygopleuridae.

New Emsian (late Early Devonian) gastropods from Limestone Mountain, Medfra B-4 quadrangle, west-central Alaska (Farewell Terrane), and their paleobiogeographic affinities and evolutionary significance

A significant number of small-sized gastropods are described from Emsian (late Early Devonian) strata on the south flank of Limestone Mountain, Medfra B-4 quadrangle, west-central Alaska, providing the first detailed taxonomic inventory of Emsian gastropods from the Farewell terrane of southwestern and west-central Alaska. The fauna is distinctly of Old World Realm character, and contains not a single species in common with Emsian faunas of nearby nonaccreted rocks of western Canada and east-central Alaska (“Western Canada Province” of Blodgett et al., 2001a). The genera Balbinipleura Bandel and Frýda, 1996 and Nanochilina Frýda, 1998, as well as the subgenus Palaeozygopleura (Rhenozyga) Frýda, 2000, are reported for the first time in the Devonian of the Western Hemisphere. The gastropod fauna includes members of three (i.e., Archaeogastropoda, Caenogastropoda, and Heterobranchia) of the five modern gastropod subclasses, illustrating that these gastropod lineages were separated from each other since the Early Devonian. New taxa include the new genera Arctozone, Farewellia, and Medfrazyga, represented by the new species Arctozone cooki, Farewellia heidelbergerae, and Medfrazyga clauticae. Further new species include Quadricarina (Quadricarina?) noklebergi, Balbinipleura krawczynskii, Decorospira lepaini, Decorospira? minutula, Palaeozygopleura (Rhenozyga) reifenstuhli, and Nanochilina gubanovi. In addition, the following previously described gastropods are also discussed and illustrated: Alaskiella medfraensis Frýda and Blodgett, 1998; Alaskacirrus bandeli Frýda and Blodgett, 1998; and Kuskokwimia moorei Frýda and Blodgett, 2001a.

Oldest, smallest Newberria (Brachiopoda) from the Eifelian (Early Middle Devonian) of west-central Alaska

Oldest, smallest Newberria (Brachiopoda) from the Eifelian (Early Middle Devonian) of west-central Alaska

Larval Fishes in Relation to Water Masses of the Central North Pacific Transitional Areas, Including the Shelf Break of West-Central Alaska

Larval fishes and corresponding physical data were sampled along two transects from Seward, Alaska to Oahu, Hawaii in February 1991. The first transect was west along the shelf break (SH) off Kodiak Island, 57°38′ to 55°20′ N, between 149 and 156°W. The second transect, North Hawaii (NH), was south along 158°W from 54°40′N, at Shumigan Islands off the Alaskan Peninsula, to 22°00′ N, near the island of Oahu, Hawaii. No other cruise has specifically sampled fish larvae along a similar transect from Alaska to Hawaii in the winter. Myctophidae, Gonostomatidae and Sternoptychidae dominated our catches. A variety of methods have been used to assign faunal provinces and to define distribution of fishes, from descriptive to empirical to statistical to physical. The result is that zoogeographic zones in the North Pacific have been defined in several ways, depending on the taxa and area studied. The multiplicity of nomenclature complicates comparisons, however the difference may be a matter of semantics. We used Roden's (1991) salinity and temperature limits as an objective method for determining water mass boundaries and analyzing faunal provinces. The subtropical domain had the highest diversity, as expected; however, the subarctic front was a close second. Diversity was the lowest in the subarctic domain and the transition zone. The counter-intuitive low values of diversity and evenness in the transition zone are explained by the vertical distributions of fish in these water masses. When temperature divisions are used to calculate diversity, a true “transition zone” appears between 8 and 19°C. The “transition” of taxa apparently occurred north of the physically derived transition zone. This may be a situation unique to the relatively wide transition zone of February 1991. If not, then future analysis should include frontal zones as part of one large transition zone to reflect the broader subarctic-subtropical transition zone. Regardless of the label or the method used to assign faunal provinces, the distribution of larval fishes is regulated by water mass characteristics.

Glacier Regimes, Periglacial Landforms, and Holocene Climate Change in the Kigluaik Mountains, Seward Peninsula, Alaska, U.S.A.

Three glaciers of the Kigluaik Mountains are very small and the only ones on the Seward Peninsula and surrounding west-central Alaska, but they are important climatically. They display the typical recession in response to recent warming, as well as moraine evidence of Little Ice Age worldwide cooling peaks of the 17th and 19th centuries. The terminal moraine of Grand Union glacier, dated lichenometrically at about A.D. 1645, indicates that equilibrium line altitudes fell about 170 m from present levels at this time, or one half the amount estimated locally for late Wisconsin glaciation. Periglacial landforms throughout the Kigluaik Mountains display ample evidence of the earlier Neoglacial cooling of the Holocene. Minimum (lichenometric) ages from active tongue-shaped rock glaciers and protalus ramparts, as well as maximum 14C ages for pingo development are compatible with a wide range of published proxy climate data indicative of middle to late Holocene cooling, particularly from about 4000 to 3000 yr ago. Increasing warmth of the late 20th century is showing its direct effects on Grand Union glacier, the only active glacier remaining in this transitional maritime-continental climatic regime of western Alaska. With an estimated net mass balance of -0.8 m water equivalent, it is, along with the other two stagnant glaciers of the Seward Peninsula, projected to disappear by about A.D. 2035.

Glacier Regimes, Periglacial Landforms, and Holocene Climate Change in the Kigluaik Mountains, Seward Peninsula, Alaska, U.S.A.

Three glaciers of the Kigluaik Mountains are very small and the only ones on the Seward Peninsula and surrounding west-central Alaska, but they are important climatically. They display the typical recession in response to recent warming, as well as moraine evidence of Little Ice Age worldwide cooling peaks of the 17th and 19th centuries. The terminal moraine of Grand Union glacier, dated lichenometrically at about A.D. 1645, indicates that equilibrium line altitudes fell about 170 m from present levels at this time, or one half the amount estimated locally for late Wisconsin glaciation. Periglacial landforms throughout the Kigluaik Mountains display ample evidence of the earlier Neoglacial cooling of the Holocene. Minimum (lichenometric) ages from active tongue-shaped rock glaciers and protalus ramparts, as well as maximum 14C ages for pingo development are compatible with a wide range of published proxy climate data indicative of middle to late Holocene cooling, particularly from about 4000 to 3000 yr ago. Increasing warmth of the late 20th century is showing its direct effects on Grand Union glacier, the only active glacier remaining in this transitional maritime-continental climatic regime of western Alaska. With an estimated net mass balance of −0.8 m water equivalent, it is, along with the other two stagnant glaciers of the Seward Peninsula, projected to disappear by about A.D. 2035.

Two new cirroidean genera (Vetigastropoda, Archaeogastropoda) from the Emsian (Late Early Devonian) of Alaska with notes on the early phylogeny of Cirroidea

Two new cirroidean gastropod genera, Alaskiella (family Porcelliidae) and Alaskacirrus (family Cirridae), from the Emsian (late Early Devonian) of west-central Alaska (Medfra B-4 quadrangle) are described. The shell of Alaskiella medfraensis new genus and species exhibits inclined heterostrophic coiling. This shell character is known among other members of the subclass Archaeogastropoda, but is recorded for the first time within members of the superfamily Cirroidea. Inclined heterostrophic coiling of the shell was probably developed independently in several different groups of the subclass Archaeogastropoda. The new genus Alaskacirrus, represented by Alaskacirrus bandeli new species, is the oldest and only known Paleozoic member of the family Cirridae. This suggests that the family Cirridae was separated from the family Porcelliidae since at least Early Devonian time and that it most probably developed from the subfamily Agnesiinae of the family Porcelliidae. Thus, the stratigraphic range of the family Cirridae is at least from Lower Devonian to Cretaceous, an interval of about 350 million years.

Morphological Differences in Pacific Coast Populations of Greater White-Fronted Geese

We examined morphological relationships of three Pacific coast populations of Greater White-fronted Geese (Anser albifrons). Adult geese were captured and measured at three breeding areas in Alaska and two wintering areas in California, 1980-1991. A two-step discriminant function analysis examined morphological differences among the three populations. Stepwise discriminant function procedures created the simplest measurement models. Each sex was analyzed separately since multivariate analysis of variance indicated that males were significantly larger than females for all three populations. Tule Greater White-fronted Geese (A. a. gambelli) were significantly larger than Pacific Greater White-fronted Geese (A. a. frontalis), hereafter Pacific Geese. The first step of discriminant function analysis created models to differentiate Tule Geese from the Pacific Geese. Bivariate stepwise discriminant function models consisting of only two measurements correctly classified 92% of males (bill height, bill width) and 96% of females (bill height, culmen) of these subspecies. The second step of discriminant function analysis compared a small population of Pacific Geese from the Bristol Bay Lowlands (BBL) of southwestern Alaska with the large population of Pacific Geese that breed on the Yukon-Kuskokwim River Delta (YKD) of westcentral Alaska. We developed models with three (culmen, diagonal tarsus, midtoe) and five (culmen, diagonal tarsus, midtoe, total tarsus, bill height) measurements from stepwise discriminant function analyses to correctly classify 72% of males and 74% of females of these populations. Thus, morphology of Tule Geese differed highly significantly from Pacific Geese, as expected, but differences between populations from the BBL and YKD areas were also significant. Morphometric analyses as these provided supporting evidence for clinal variation in populations of Greater White-fronted Geese. They also underscore a need for further studies of differences among North American populations of Greater White-fronted Geese to resolve classification and to allow formulation of subpopulation/subspecies management strategies.

A new species of Droharhynchia (Brachiopoda) from the lower Middle Devonian (Eifelian) of west-central Alaska

A new species of the genus Droharhynchia Sartenaer is established from lower Eifelian strata of west-central Alaska and the northwestern Brooks Range of Alaska. Droharhynchia rzhonsnitskayae n. sp. occurs in the Cheeneetnuk Limestone of the McGrath A-5 quadrangle, west-central Alaska, and the Baird Group of the Howard Pass B-5 quadrangle, northwestern Alaska. These occurrences extend the lower biostratigraphic range of both the genus and the subfamily Hadrorhynchiinae into the Eifelian. They also suggest close geographic proximity of the Farewell terrane of southwestern and west-central Alaska and the Arctic Alaska superterrane of northern Alaska during Devonian time.

First recognition of the genus Verneuilia Hall and Clarke (Brachiopoda, Spiriferida) from North America (west-central Alaska)

The brachiopod genus Verneuilia Hall and Clarke, 1893, is recognized for the first time in North America, where it is represented by a new species described here, V. langenstrasseni. This occurrence not only extends the geographic range of the genus, but also the lower age and stratigraphic limit into the Eifelian (early Middle Devonian). Previously, the oldest known species was the type, V. cheiropteryx d'Archiac and de Verneuil, 1842, from the Givetian (late Middle Devonian) of Germany. Internal structures of V. langenstrasseni n. sp. are similar to those of genera in the ambocoeliid subfamily Rhynchospiriferinae, providing the first good evidence of a systematic relationship.

Significance of Silurian stromatolite-sphinctozoan reefs

Upper Silurian (Ludlovian) limestones from the Heceta Formation of southeastern Alaska (Alexander terrane) contain skeletal stromatolite reefs and stromatolite mud mounds that were colonized by sphinctozoan sponges. Internal growth cavities, synsedimentary marine cements, and stromatolite debris flows in slope deposits indicate that these reefs grew with relief at the seaward margin of the carbonate platform. The biotas under study have evolutionary significance because they contain the earliest widespread reef-building sphinctozoans and represent a previously unrecognized stage in the evolution of Phanerozoic microbial-metazoan (predominantly poriferan) reefs. On the basis of the presence of Silurian stromatolite-sphinctozoan deposits in southeastern Alaska, southwestern and west-central Alaska, and the Urals, this study also establishes a Late Silurian paleobiogeographic connection between the Alexander terrane, cratonic northwestern North America, and the Uralian region.

Russian Devonian brachiopod genera Cyrtinoides and Komiella in North America

The Middle Devonian brachiopod genus Cyrtinoides, described from the southern Urals, is a senior subjective synonym of Mucroclipeus, previously known only from eastern and western North America. The Middle and Late Devonian cyrtinid brachiopod genus Komiella, previously known only from the Timan Range of eastern Europe, is identified from west-central Alaska and Nevada. A new family Komiellidae is proposed. New species are Komiella gilberti, K. magnasulca, and K. stenoparva. Known species of both genera occupy carbonate platform foreslope facies or shelf basins, allowing open marine migration via peripheral biofacies.

Middle Ordovician carrier shellLytospira(Mollusca, Gastropoda) from Alaska

The euomphalacean gastropodLytospira gerulusn. sp. is described from the Middle Ordovician of west-central Alaska. The species is among the oldest known carrier shell specimens, and also shows evidence of repaired shell breakage; the breakage may have been the result of unsuccessful predation attempts. The interior of the shell shows an unusual spiral groove and ridges that may have been associated with the animal's retractor muscle. This internal groove may be an overlooked feature of all species ofLytospira.

Dutrochus, a new microdomatid (Gastropoda) genus from the Middle Devonian (Eifelian) of west-central Alaska

A new gastropod genus, Dutrochus, is established for members of the family Microdomatidae that are characterized by a reticulate ornament of spiral cords and intersecting, finer collabral threads, with all but one spiral cord being of nearly equal strength, and the single remaining cord being of stronger (nearly twice the order) magnitude and being situated at the periphery. It is represented by the type and only known species, Dutrochus alaskensis n. gen. and sp., from the upper part (lower Middle Devonian; lower Eifelian) of the Lower? and Middle Devonian Cheeneetnuk Limestone, McGrath A-5 quadrangle, west-central Alaska. The genus is very close and nearly homeomorphic to the Permian microdomatid genus Glyptospira, but differs from the latter in possessing an extremely strong, peripheral spiral cord and an extremely thick, multi-layered apertural margin.

Stratigraphy of the Colorado Creek mammoth locality, Alaska

The Colorado Creek mammoth locality in west-central Alaska contains the remains of two mammoths that were scavenged by carnivores. Sedimentologic interpretations of the reworked eolian deposits surrounding the bones, supplemented by 10 radiocarbon dates, indicate that the lower and upper mammoths died and were buried within separate, but superimposed, thaw gullies about 23,000 and 16,000 yr ago, respectively. From our results, we propose a polycyclic taphonomic model for thaw gullies governed largely by slope aspect, rather than regional climate, and in which mixing between faunal horizons is more likely than not. Variations in the rate of silt influx and the position of the permafrost table provide a paleoclimatic proxy record that can be correlated to other records in eastern Beringia.