The Hayes Tephra Deposits, and Upper Holocene Marker Horizon in South-Central Alaska

1990 ◽  
Vol 33 (3) ◽  
pp. 276-290 ◽  
Author(s):  
James R. Riehle ◽  
Peter M. Bowers ◽  
Thomas A. Ager
Keyword(s):  
Cook Inlet ◽  
Radiocarbon Dates ◽  
Fine Grained ◽  
South Central ◽  
Inlet Region ◽  
Tephra Deposits ◽  
Phenocryst Content

AbstractThe most widespread of all Holocene tephra deposits in the Cook Inlet region of south-central Alaska is a set of deposits from Hayes volcano. Because of their unique phenocryst content—biotite in rare amounts and a high proportion of amphibole to pyroxene—the deposits are readily identifiable at all but the most distant sites where they are very fine grained. Eighteen radiocarbon dates from eight upland sites limit the age of the tephra set to between about 3500 and 3800 yr. The set originated at Hayes volcano in the Tordrillo Mountains 150 km northwest of Anchorage; seven or possibly eight closely succeeding deposits, low-silica dacite in composition, compose two main lobes that extend northeast for 400 km and south for at least 250 km from the vent. We estimate the total tephra volume to be 10 km3; multiple layers imply four to six larger and two or three smaller eruptions. The deposits are a nearly isochronous marker horizon that should be useful in future archeologic, geologic, and palynologic studies in the region.

scholarly journals Assessment of undiscovered oil and gas resources of the Cook Inlet region, south-central Alaska, 2011

Fact Sheet ◽  
2011 ◽  
Author(s):  
Richard G. Stanley ◽  
Ronald R. Charpentier ◽  
Troy A. Cook ◽  
David W. Houseknecht ◽  
Timothy R. Klett ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Cook Inlet ◽  
South Central ◽  
Inlet Region ◽  
Oil And Gas Resources

Impact of a Larger Fore‐Arc Region on Earthquake Ground Motions in South‐Central Alaska Including the 2018 M 7.1 Anchorage Inslab Earthquake

2019 ◽  
Vol 91 (1) ◽  
pp. 174-182 ◽  
Author(s):  
Chris H. Cramer ◽  
Eric Jambo
Keyword(s):  
Subduction Zones ◽  
Thermal State ◽  
Ground Motions ◽  
Historical Earthquakes ◽  
Cook Inlet ◽  
Damage Potential ◽  
Motion Models ◽  
South Central ◽  
Inlet Region ◽  
Subducting Plate

Abstract The thermal state of the crust and mantle in subduction zones is controlled by the depth of the subducting plate. With low‐angle subduction, like at the eastern end of the Alaska subduction zone, the less attenuating fore‐arc is extended farther from the trench and can effect ground motions in addition to source and site effects. Recent crustal and subduction earthquakes in south‐central Alaska, including the 2018 M 7.1 Anchorage event, demonstrate these effects. Inslab earthquake waves in the subducting plate can propagate up the slab to the fore‐arc region with less attenuation, causing an increase in observed ground motions. Long‐period ground motions from the 2018 M 7.1 Anchorage earthquake are significantly higher than predicted ground motions from current subduction ground‐motion models within 50–100 km of the epicenter. At short periods, ground motions show reduced amplitudes due to nonlinear sediment effects in the Anchorage area, reducing the damage potential of the earthquake. At long periods, ground motions are little affected by sediment nonlinearity and remain higher than expected. The duration of shaking was too short for widespread liquefaction effects, unlike during the 1964 M 9.2 earthquake. Other historical earthquakes have produced similar increases in ground motions in the Cook Inlet and Kenai Peninsula region. At both short and long periods, ground motions from the 2016 Iniskin M 7.1 inslab earthquake are higher than expected in the Cook Inlet region. The 2015 Redoubt M 6.3 inslab earthquake also shows increased ground motions in the Cook Inlet region at all periods. Crustal Q estimates from Lg waves show less attenuation in south‐central Alaska at longer periods. In the larger south‐central Alaska region crustal Q(f)=336f0.34 compared to Q(f)=217f0.84 for all of Alaska with most of the decrease in attenuation at frequencies below 2 Hz.

Volcanoes of the Wrangell Mountains and Cook Inlet region, Alaska: selected photographs

Data Series ◽  
10.3133/ds39 ◽  
2001 ◽  
Author(s):  
Christina A. Neal ◽  
Robert G. McGimsey ◽  
Michael F. Diggles
Keyword(s):  
Cook Inlet ◽  
Inlet Region

Late-glacial flow patterns, deglaciation, and postglacial emergence of south-central Baffin Island and the north-central coast of Hudson Strait, eastern Canadian Arctic

1996 ◽  
Vol 33 (11) ◽  
pp. 1499-1510 ◽  
Author(s):  
William F. Manley
Keyword(s):  
High Tide ◽  
Ice Sheet ◽  
Late Glacial ◽  
Flow Patterns ◽  
Sediment Provenance ◽  
Radiocarbon Dates ◽  
Ice Cap ◽  
The North ◽  
South Central ◽  
Ice Stream

New georaorphic, sedimentologic, and chronologic data are used to reconstruct late Quaternary ice-sheet flow patterns, deglaciation, and isostatic uplift along the largest marine trough connecting the Laurentide Ice Sheet with the North Atlantic Ocean. The Lake Harbour region was targeted for study given its potential to record flow from several ice-dispersal centers. Striations and sediment provenance indicators define flow patterns. Thirty-four radiocarbon dates constrain a chronology of events. Centuries or millennia(?) before deglaciation, a southeast-flowing ice stream impinged on southernmost Big Island, as recorded by a single striation site and delimited in extent by geomorphic evidence of cold-based ice. During the Cockburn Substagc (9000–8000 BP), the region was scoured by southward to southwestward flow from an ice cap on Meta Incognita Peninsula, as recorded by 60 striation sites along 200 km of coastline. Carbonate erratics are uncommon in till above the marine limit. Where present, they suggest that southward flow reworked older drift. At about 8200 BP, the area was dcglaciated, and the marine limit was established at elevations of 67–141 m above high tide. Iceberg calving and sediment discharge from an ice margin in Ungava Bay, Hudson Bay, or Foxe Basin then blanketed the area with limestone-rich glaciomarinc sediment. Afterward, the region experienced slow but sustained emergence. The data revise the maximum lateral extent of a Late Wisconsinan ice stream in Hudson Strait and emphasize the extent of a late-glacial ice cap on western Meta Incognita Peninsula.

Subsurface sediment profiles below Point Pelee: indicators of postglacial evolution in western Lake Erie

1998 ◽  
Vol 35 (1) ◽  
pp. 88-99
Author(s):  
John P Coakley ◽  
Allan S Crowe ◽  
Patrice A Huddart
Keyword(s):  
Lake Levels ◽  
Dune Sand ◽  
Radiocarbon Dates ◽  
Subsurface Sediment ◽  
Fine Grained ◽  
Western Lake ◽  
Planar Wave ◽  
Point Pelee ◽  
Sediment Data ◽  
Point Pelee National Park

An extensive drilling program, undertaken along the western barrier bar at Point Pelee National Park, Ontario, Canada, yielded considerable subsurface sediment data relevant to the nature and lateral geometry of sedimentary units below the Point Pelee foreland. Four major sedimentary units were identified: a basal clay-rich till, a fine-grained glaciolacustrine sand, a medium-grained sand unit (subdivided into a poorly sorted shoreface sand and an aeolian (dune) sand derived from the shoreface sand), and an organic marsh (gyttja) deposit. The present study confirms the existence of a planar, wave-eroded till surface below the southern portion of Point Pelee at an elevation of approximately 164 m asl. Following this low-water period in the basin, lake levels rose abruptly to an elevation several metres above 172 m asl. This resulted in erosion of the upper part of the glaciolacustrine sand during a later period of stable higher lake levels, perhaps coinciding with the Nipissing flood event (about 4000 BP). This resulted in a planar surface at approximately 169.5 m asl. Several radiocarbon dates on basal gyttja from the marsh (averaging 3200 BP) reflect a subsequent drop in levels to about 2-3 m below present levels. Though undated, the initiation of shoreface and dune sand deposition is roughly coeval with the basal marsh deposits.

New excavations at the late Pleistocene site of Chinchihuapi I, Chile

2019 ◽  
Vol 92 (1) ◽  
pp. 70-80 ◽  
Author(s):  
Tom D. Dillehay ◽  
Carlos Ocampo ◽  
Jose Saavedra ◽  
Mario Pino ◽  
Linda Scott-Cummings ◽  
...  
Keyword(s):  
Late Pleistocene ◽  
Early Holocene ◽  
Occupied Site ◽  
Radiocarbon Dates ◽  
Central Chile ◽  
South Central ◽  
Cool Temperate ◽  
Human Use ◽  
Monte Verde ◽  
Point Type

AbstractThis paper presents new excavation data on the Chinchihuapi I (CH-I) locality within the Monte Verde site complex, located along Chinchihuapi Creek in the cool, temperate Valdivian rain forest of south-central Chile. The 2017 and 2018 archaeological excavations carried out in this open-air locality reveal further that CH-I is an intermittently occupied site dating from the Early Holocene (~10,000 cal yr BP) to the late Pleistocene (at least ~14,500 cal yr BP) and probably earlier. A new series of radiocarbon dates refines the chronology of human use of the site during this period. In this paper, we describe the archaeological and stratigraphic contexts of the recent excavations and analyze the recovered artifact assemblages. A fragmented Monte Verde II point type on an exotic quartz newly recovered from excavations at CH-I indicates that this biface design existed in at least two areas of the wider site complex ~14,500 cal yr BP. In addition, associated with the early Holocene component at CH-I are later Paijan-like points recovered with lithic tools and debris and other materials. We discuss the geographic distribution of diagnostic artifacts from the site and their probable relationship to other early sites in South America.

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