Geology topics

Kenneth P. Helmold

Publications and source records attributed to Kenneth P. Helmold.

9 recordsLinked to original sources

USGS2018

Secular changes in Cenozoic arc magmatism recorded by trends in forearc-basin sandstone composition, Cook Inlet, southern Alaska

A robust set of modal composition data (238 samples) for Eocene to Pliocene sandstone from the Cook Inlet forearc basin of southern Alaska reveals strong temporal trends in composition, particularly in the abundance of volcanic lithic grains. Field and petrographic point-count data from the northwestern side of the basin indicate that the middle Eocene West Foreland Formation was strongly influenced by nearby volcanic activity. The middle Eocene to lower Miocene Hemlock Conglomerate and Oligocene to middle Miocene Tyonek Formation have a more mature quartzose composition with limited volcanic input. The middle to upper Miocene Beluga Formation includes abundant argillaceous sedimentary lithic grains and records an upward increase in volcanogenic material. The up-section increase in volcanic detritus continues into the upper Miocene to Pliocene Sterling Formation. These first-order observations are interpreted to primarily reflect the waxing and waning of nearby arc magmatism. Available U-Pb detrital zircon geochronologic data indicate a dramatic reduction in zircon abundance during the early Eocene, and again during the Oligocene to Miocene, suggesting the arc was nearly dormant during these intervals. The reduced arc flux may record events such as subduction of slab windows or material that resisted subduction. The earlier hiatus in volcanism began ca. 56 Ma and coincided with a widely accepted model of ridge subduction beneath south-central Alaska. The later hiatus (ca. 25–8 Ma) coincided with insertion of the leading edge of the Yakutat terrane beneath the North American continental margin, resulting in an Oligocene to Miocene episode of flat-slab subduction that extended farther to the southwest than the modern seismically imaged flat-slab region. The younger tectonic event coincided with development of some of the best petroleum reservoirs in Cook Inlet.

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USGS2015

Storm-influenced deltaic deposits of the Middle Jurassic Gaikema Sandstone in a measured section on the northern Iniskin Peninsula, Cook Inlet basin, Alaska

Middle Jurassic strata of the Gaikema Sandstone were deposited about 170 million years ago on a delta that was located on the western shoreline of the Cook Inlet basin (Detterman and Hartsock, 1966; LePain and others, 2011, 2013). The delta was built by swift, sediment-laden rivers that flowed southeastward from a mountainous volcanic terrane west of the Bruin Bay fault (fig. 6-1). Upon reaching the edge of the Jurassic sea, the rivers dumped abundant sand, gravel, and mud into a depocenter on the northern Iniskin Peninsula, about 240 km southwest of Anchorage (figs. 6-1, 6-2). This report provides a preliminary description and interpretation of a detailed, 34-m-thick measured section in the Gaikema Sandstone on the south shore of Chinitna Bay at latitude 59.816°N, longitude 153.168°W (figs. 6-1–6-3). The sandstone in this measured section exhibits hummocky cross lamination and other features suggestive of storm-influenced deposition on the shallow-marine, seaward margin of the Gaikema delta. Our field studies of the Gaikema Sandstone were conducted during 2013 and 2014 as part of a collaborative effort by the Alaska Division of Geological & Geophysical Surveys (DGGS), Alaska Division of Oil and Gas (DOG), and U.S. Geological Survey (USGS) to provide the public with reliable information on the geologic framework and petroleum resource potential of Cook Inlet basin (Gillis, 2013, 2014). Jurassic rocks in Cook Inlet, including the Gaikema Sandstone, are of economic interest because they could contain significant undiscovered petroleum resources (Bureau of Ocean Energy Management, 2011; Stanley and others, 2011a, 2011b, 2013a; LePain and others, 2013).

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USGS2015

Petrology and reservoir quality of the Gaikema Sandstone: Initial impressions

The Division of Geological & Geophysical Surveys (DGGS) and Division of Oil & Gas (DOG) are currently conducting a study of the hydrocarbon potential of Cook Inlet basin (LePain and others, 2011). The Tertiary stratigraphic section of the basin includes coal-bearing units that are prolific gas reservoirs, particularly the Neogene sandstones. The Paleogene sandstones are locally prolific oil reservoirs that are sourced largely from the underlying Middle Jurassic Tuxedni Group. Several large structures act as hydrocarbon traps and the possibility exists for stratigraphic traps although this potential has not been fully exploited. As part of this study a significant number of Tertiary sandstones from the basin have been already collected and analyzed (Helmold and others, 2013). Recent field programs have shifted attention to the Mesozoic stratigraphic section to ascertain whether it contains potential hydrocarbon reservoirs. During the 2013 Cook Inlet field season, two days were spent on the Iniskin Peninsula examining outcrops of the Middle Jurassic Gaikema Sandstone along the south shore of Chinitna Bay (fig. 7-1). A stratigraphic section approximately 34 m in thickness was measured and a detailed description was initiated (Stanley and others, 2015), but due to deteriorating weather it was not possible to complete the description. During the 2014 field season two additional days were spent completing work on the Gaikema section. Analyses of thin sections from six of the samples collected in 2013 are available for incorporation in this report (table 7-1). Data from samples collected during the 2014 field season will be included in future reports.

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USGS2015

Reconnaissance stratigraphic studies in the Susitna basin, Alaska, during the 2014 field season

The Susitna basin is a poorly-understood Cenozoic successor basin immediately north of Cook Inlet in south-central Alaska (Kirschner, 1994). The basin is bounded by the Castle Mountain fault and Cook Inlet basin on the south, the Talkeetna Mountains on the east, the Alaska Range on the north, and the Alaska–Aleutian Range on the west (fig. 2-1). The Cenozoic fill of the basin includes coal-bearing nonmarine rocks that are partly correlative with Paleogene strata in the Matanuska Valley and Paleogene and Neogene formations in Cook Inlet (Stanley and others, 2013, 2014). Mesozoic sedimentary rocks are present in widely-scattered uplifts in and around the margins of the basin; these rocks differ significantly from Mesozoic rocks in the forearc basin to the south. Mesozoic strata in the Susitna region were likely part of a remnant ocean basin that preceded the nonmarine Cenozoic basin (Trop and Ridgway, 2007). The presence of coal-bearing strata similar to units that are proven source rocks for microbial gas in Cook Inlet (Claypool and others, 1980) suggests the possibility of a similar system in the Susitna basin (Decker and others, 2012). In 2011 the Alaska Division of Geological & Geophysical Surveys (DGGS) and Alaska Division of Oil and Gas, in collaboration with the U.S. Geological Survey, initiated a study of the gas potential of the Susitna basin (Gillis and others, 2013). This report presents a preliminary summary of the results from 14 days of helicopter-supported field work completed in the basin in August 2014. The goals of this work were to continue the reconnaissance stratigraphic work begun in 2011 aimed at understanding reservoir and seal potential of Tertiary strata, characterize the gas source potential of coals, and examine Mesozoic strata for source and reservoir potential

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USGS2013

Status of a reconnaissance field study of the Susitna basin, 2011

The Alaska Division of Geological & Geophysical Surveys (DGGS) and Alaska Division of Oil and Gas (DOG), in collaboration with the U.S. Geological Survey (USGS) performed reconnaissance field studies for ten days in late June 2011, in the Susitna basin, directly north of Cook Inlet, south-central Alaska (fig. 1). The purpose of our investigation was to reconnoiter outcrops in the basin and along its periphery to gather new information towards understanding the basin formation history and stratigraphy. This reconnaissance data represents the first step toward better understanding the basin’s hydrocarbon potential, a key component of DGGS’s multi-year In- State Gas Program. This program is focused on collecting baseline geologic information from potential frontier gas basins to encourage new exploration to help, in part, reduce the high cost of energy in rural Alaska. Our work represents the first season of this three-year project. Preliminary results from year two, a companion project within the Nenana and Tanana basins in interior Alaska, are described by Wartes and others (2013). DGGS plans to return to the Susitna basin for follow-up fieldwork during the third and final year of the program. The motivation for developing a better understanding of the Susitna basin stems from the recognition that the Susitna basin shares similar age coal-bearing strata with the adjacent, petroliferous Cook Inlet forearc basin (Barnes, 1966; Reed and Nelson, 1980) and with exhumed strata in the Matanuska Valley forearc basin (Trop and others, 2003) (figs. 1 and 2). Cook Inlet basin has eight producing oil fields, more than 25 producing gas fields, and likely contains many additional undiscovered oil and gas accumulations (LePain and others, in press). Most of the Cook Inlet gas is of microbial origin and apparently was sourced from abundant coalbeds of primarily Miocene age in the Tyonek, Beluga, and Sterling Formations (Claypool and others, 1980; Magoon, 1994). If the biogenic gas model for Cook Inlet is applicable to the Susitna basin, then the latter may be a viable source for Alaska Railbelt and rural energy needs. This brief overview report summarizes the reconnaissance field data collected in the Susitna basin during the first summer of the program. As the data are developed, this report will be followed by interpretive technical reports addressing the stratigraphy, reservoir quality, coal quality and gas potential, hydrocarbon seal integrity, subsurface structure, and uplift history of the basin and sub-basin margins.

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USGS2013

Summary of 2012 reconnaissance field studies related to the petroleum geology of the Nenana Basin, interior Alaska

The Alaska Division of Geological & Geophysical Surveys (DGGS) recently initiated a multi-year review of the hydrocarbon potential of frontier sedimentary basins in Alaska (Swenson and others, 2012). In collaboration with the Alaska Division of Oil & Gas and the U.S. Geological Survey we conducted reconnaissance field studies in two basins with recognized natural gas potential—the Susitna basin and the Nenana basin (LePain and others, 2012). This paper summarizes our initial work on the Nenana basin; a brief summary of our work in the Susitna basin can be found in Gillis and others (in press). During early May 2012, we conducted ten days of helicopter-supported fieldwork and reconnaissance sampling along the northern Alaska Range foothills and Yukon–Tanana upland near Fairbanks (fig. 1). The goal of this work was to improve our understanding of the geologic development of the Nenana basin and to collect a suite of samples to better evaluate hydrocarbon potential. Most laboratory analyses have not yet been completed, so this preliminary report serves as a summary of field data and sets the framework for future, more comprehensive analysis to be presented in later publications.

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USGS2013

Reconnaissance studies of potential petroleum source rocks in the Middle Jurassic Tuxedni Group near Red Glacier, eastern slope of Iliamna Volcano

Previous geological and organic geochemical studies have concluded that organic-rich marine shale in the Middle Jurassic Tuxedni Group is the principal source rock of oil and associated gas in Cook Inlet (Magoon and Anders, 1992; Magoon, 1994; Lillis and Stanley, 2011; LePain and others, 2012; LePain and others, submitted). During May 2009 helicopter-assisted field studies, 19 samples of dark-colored, fine-grained rocks were collected from exposures of the Red Glacier Formation of the Tuxedni Group near Red Glacier, about 70 km west of Ninilchik on the eastern flank of Iliamna Volcano (figs. 1 and 3). The rock samples were submitted to a commercial laboratory for analysis by Rock-Eval pyrolysis and to the U.S. Geological Survey organic geochemical laboratory in Denver, Colorado, for analysis of vitrinite reflectance. The results show that values of vitrinite reflectance (percent R o ) in our samples average about 2 percent, much higher than the oil window range of 0.6–1.3 percent (Johnsson and others, 1993). The high vitrinite reflectance values indicate that the rock samples experienced significant heating and furthermore suggest that these rocks may have generated oil and gas in the past but no longer have any hydrocarbon source potential. The high thermal maturity of the rock samples may have resulted from (1) the thermaleffects of igneous activity (including intrusion by igneous rocks), (2) deep burial beneath Jurassic, Cretaceous, and Tertiary strata that were subsequently removed by uplift and erosion, or (3) the combined effects of igneous activity and burial.

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USGS2013

Hydrocarbon-bearing sandstone in the Upper Jurassic Naknek Formation on the south shore of Kamishak Bay

The presence of an active petroleum system in Kamishak Bay is demonstrated by an outcrop of hydrocarbon-bearing sandstone in the Upper Jurassic Naknek Formation near the south shore of the bay (fig. 1). The outcrop is about 140 km southwest of Homer on a small, unnamed island near the mouth of the Douglas River (fig. 17). The existence of this outcrop was kindly reported to us by Les Magoon (U.S. Geological Survey, emeritus), who also provided a topographic map showing its exact position. The outcrop was mentioned very briefly in publications by Magoon and others (1975, p. 19) and by Lyle and Morehouse (1977, p. E-1), but to our knowledge there are no detailed descriptions of this outcrop or its hydrocarbons in the published scientific literature.

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USGS2013

Preliminary stratigraphy and facies analysis of the Upper Cretaceous Kaguyak Formation, including a brief summary of newly discovered oil stain, upper Alaska Peninsula

The Alaska Division of Geological and Geophysical Surveys has an ongoing program aimed at evaluating the Mesozoic forearc stratigraphy, structure, and petroleum systems of lower Cook Inlet. Most of our field studies have focused on the Jurassic component of the petroleum system[this report.] However, in late July and early August of 2012, we initiated a study of the stratigraphy and reservoir potential of the Upper Cretaceous Kaguyak Formation. The Kaguyak Formation is locally well exposed on the upper Alaska Peninsula (fig. 25) and was named by Keller and Reiser (1959) for a sequence of interbedded siltstone and sandstone of upper Campanian to Maastrichtian age that they estimated to be 1,450 m thick.Subsequent work by Detterman and Miller (1985) examined 900 m of section and interpreted the unit as the record of a prograding submarine fan.This interpretation of deep-water deposition contrasts with other Upper Cretaceous rocks exposed along the Alaska Peninsula and lower Cook Inlet that are generally described as nonmarine to shallow marine (Detterman and others, 1996; LePain and others, 2012).Based on foraminifera and palynomorphs from the COST No. 1 well, Magoon (1986) concluded that the Upper Cretaceous rocks were deposited in a variety of water depths and environments ranging from upper bathyal to nonmarine. During our recent fieldwork west and south of Fourpeaked Mountain, we similarly encountered markedly varying lithofacies in the Kaguyak Formation (fig. 25), and we also found oil-stained rocks that are consistent with the existence of an active petroleum system in Upper Cretaceous rocks on the upper Alaska Peninsula and in lower Cook Inlet. These field observations are summarized below.

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