GENERALIZED THERMAL MATURITY MAP OF ALASKACompiled by

Mark J. Johnsson and David G. Howell1996

INTRODUCTION

Thermal maturity is a measure of the level of thermal alteration of organic matter in sedimentary rocks. Inasmuch as different types of organic matter respond differently to heat, thermal maturity is operationally defined differently for different substances. Accordingly, many organic and mineral indicators of thermal maturity have been proposed and, to a certain degree, crosscorrelated (see, for example, Hood and others, 1975; Scholle and Schluger, 1979; Héroux and others, 1979). The thermal maturity of organic matter provides a means of ascertaining the maximum temperatures to which sedimentary rocks have been exposed. Diagenetic or low-grade metamorphic temperatures, in regions where igneous or hydrothermal heat sources have been insignificant, are largely a reflection of burial heating. The level of thermal maturity of rocks at the surface can thus be used to infer relative uplift and erosion subsequent to maximum burial, providing valuable insights into tectonic processes and histories. In addition, the maximum temperature to which sedimentary rocks have been exposed is an important parameter in evaluating hydrocarbon potential.

VITRINITE REFLECTANCE

Vitrinite is one of several types of organic matter commonly disseminated in clastic sedimentary rocks. Representing the remains of woody plant material, vitrinite is the major constituent of most coals and is abundant in most terrestrially derived shales. It is often present, although much less abundant, in coarser sediments, limestones, and marine rocks as well. Upon diagenesis, loss of volatile components and graphitization of carbon result in an increase in the reflectivity of vitrinite. Reflectivity increases regularly proportional to temperature, is not influenced by pressure or chemical reactions with most diagenetic waters, and is not susceptible to retrograde alteration (Bostick, 1979). Accordingly, vitrinite reflectance has become the most widely used measure of thermal maturity in sedimentary rocks. Recent kinetic models (Burnham and Sweeney, 1989; Sweeney and Burnham, 1990) and field studies in areas where the duration of heating has been well constrained (Barker and others, 1983; Barker, 1991) suggest that, for heating periods of greater than approximately 104 years, maximum temperature and not the duration of heating largely determines the level of vitrinite reflectance. Vitrinite reflectance thus may be used, with caution, to establish absolute maximum paleotemperatures. Many workers have proposed equations relating temperature and vitrinite reflectance (Bostick, 1979; Price, 1983; Barker and Pawlewicz, 1986; Barker, 1988). We prefer the correlation of Barker (1988; T(ϒC)=104(lnRo)+148) as it most closely matches the results predicted by kinetic models (Burnham and Sweeney, 1989; Sweeney and Burnham, 1990).

Vitrinite reflectance is quantified by measuring the percentage of light reflected from randomly oriented polished vitrinite particles through the use of a photomultiplier photometer attached to a microscope and calibrated through the use of polished glass or mineral standards. Because an oil-immersion objective is used, the reflectance measured is that in oil. Vitrinite-reflectance units are, therefore, the percentage of light reflected in oil (Ro). Anisotropy of reflectance results from the structure of vitrinite and increases with increasing reflectivity (Stach and others, 1982). Accordingly, a vitrinite-reflectance determination involves measuring the reflectance of a number of particles in random orientation and taking the mean value of the determinations. Determining the mean reflectance, occasionally referred to as Rm, involves identification of the indigenous vitrinite population, exclusive of recycled material. Such material is usually identified by constructing a histogram of individual vitrinite-reflectance measurements and isolating suspect material from the calculation of the mean.

CONODONT COLOR ALTERATION INDEX

Conodonts are toothlike microfossils of an extinct group of primitive vertebrates (probably related to jawless fishes), commonly 0.1 to 1 mm in length, that are found in marine rocks of Late Cambrian through Triassic age. They are common in carbonate and some marine clastic rocks, and their abundance generally varies inversely with sedimentation rate. Conodonts grew throughout the life of the animal by periodic addition of a relatively coarse lamella of apatite followed by a fine lamella of organic matter. During diagenesis, the organic matter sealed between transparent apatite lamellae becomes carbonized, producing visible color changes. Colors range from pale yellow, to amber, light brown, dark brown, and black corresponding to temperatures ranging from 50ϒ to 300ϒC (Epstein and others, 1977). Above 300ϒC, conodonts change from black to gray, to opaque white, and finally to crystal clear as a result of carbon loss, release of water of crystallization, and recrystallization. All of these color changes have been observed in natural samples and reproduced and calibrated by pyrolysis experiments in the laboratory (Epstein and others, 1977; Rejebian and others, 1987). The Condont Color Alteration Index (CAI) is the quantification of these color changes through the use of established standards.

SYNOPSIS OF THERMAL MATURITY PATTERNS IN ALASKA

This map was produced from nearly 10,000 vitrinite-reflectance and CAI determinations from surface, offshore, and subsurface localities across the state. From these data, a number of generalities can be made. For example, rocks exposed at the surface of the Tertiary interior basins and in the Aleutian forearc and backarc basins are uniformly of very low thermal maturity, indicating that these basins are at or near maximum burial, have seen little uplift, and are probably thermally immature with respect to hydrocarbon generation. In contra st, many sedimentary basins—for example, the Yokon-Koyukuk and Colville Basins—show elevated levels of thermal maturity at the surface, commonly with the highest values at basin margins. This geometry suggests a pattern of greater uplift along basin margins, possibly reflecting isostatic readjustments as crustal loads are removed by erosion.

Johnsson and others (1993) investigated thermal maturity relations in three sedimentary basins—the Colville, Cook Inlet, and Kandik Basins—in more detail. Thermal maturity patterns in the Colville Basin are broadly asymmetric, suggesting systematic differential uplift ranging from a minimum of no uplift at the Arctic coastline to 9 to 13 km of uplift in the central Brooks Range; even greater uplift further to the south is indicated by the presence of greenschist facies and higher grade metamorphism. This Johnsson and others (1993) investigated thermal maturity relations in three sedimentary basins—the Colville, Cook Inlet, and Kandik Basins—in more detail. Thermal maturity patterns in the Colville Basin are broadly asymmetric, suggesting systematic differential uplift ranging from a minimum of no uplift at the Arctic coastline to 9 to 13 km of uplift in the central Brooks Range; even greater uplift further to the south is indicated by the presence of greenschist facies and higher grade metamorphism. This pattern may reflect the deflexing of the lithosphere subsequent to the principal episode(s) of crustal convergence and thickening. The continuity of this pattern across the region suggests a similar thermal history for the proximal Colville Basin and the northern foothills belt. Thermal maturity isograds within the Brooks Range cut major thrust faults, indicating that maximum burial postdated the principal phases of thrusting. In contrast, isograds in the foothills belt to the north are broadly warped by local structure, indicating continued north-south shortening subsequent to maximum burial. A broad southward extension of thermally immature rocks in the central portions of the foothills belt suggests relatively young east-west shortening (parallel to the strike of the orogen), a feature that to date has not been included in regional tectonic syntheses. Alternatively, this thermal-maturity pattern could be explained by tectonically unrelated uplift episodes in the eastern and western parts of the Brooks Range.

In the Cook Inlet Basin, vitrinite-reflectance isograds also are indicative of relatively greater uplift at the basin margins than at the basin center. The basin center appears to be presently at its maximum burial depth. Uplift in the Cook Inlet Basin may reflect compression along the faults bounding the basin. High thermal maturity along the western margin of the basin also may reflect magmatic heat sources from the Alaska Peninsula-Aleutian Volcanic Arc. The Seldovia Arch, a major structural feature trending across the southern end of the basin (see Johnsson and others, 1993), does not appear to deform vitrinite-reflectance isograds, implying that deformation on that structure ceased prior to maximum burial (Johnsson and others, 1993).

In the Kandik Basin, a thermal-maturity anomaly—thermally mature younger rocks in fault contact with thermally immature older rocks—provides clues to the nature and timing of east-west thrusting. Mesozoic foreland basin deposits associated with thrusting buried Paleozoic rocks of the easternmost part of this fold-and-thrust belt to relatively shallow depths, driving potential hydrocarbon source rocks into the oil-generation window. The western foreland basin deposits were overridden by advancing thrusts and tectonically buried to as deep as 10 km. These disparate thermal domains are juxtaposed along the Glenn Creek Fault, which may represent a terrane boundary in east-central Alaska (Johnsson and others, 1993).

Although complicated by the effects of convective heat transfer by fluids and spatial variations in heat flow, thermal maturity data from sedimentary rocks isolated from igneous activity largely reflect burial heating and thus provide a means of assessing vertical movements in the upper crust. Thermal-maturity patterns in Alaska reflect the complex tectonic history of the region. The amalgamation of terranes with different thermal and uplift histories produces a patchwork of sharply contrasting thermal maturity. Sedimentary basins developed on these terranes record the history of terrane accretion through differential regional uplift. A varied thermal-maturity pattern in these deposits indicates a complex pattern of uplift that is not readily apparent from traditional mapping of stratigraphic and structural relations.

ACKNOWLEDGMENTS

We would like to express our sincere thanks to all of those individuals who have contributed unpublished data or samples to this project. Special thanks are extended to A.G. Harris, who made available her complete Alaskan inventory of Conodont Color Alteration Index data, and to M.L. Miller, A. Anderson, R.R. Reifenstuhl, H.A. Cohen, S.E. Box, W.W. Patton, Jr., J.M. Murphy, and R.G. Stanley, who provided samples from critical areas. M.J. Pawlewicz produced hundreds of vitrinite reflectance determinations. L.B. Magoon was instrumental in organizing data collected over the past decade by USGS workers, and C.N. Threlkeld oversaw database management during submittal of new samples. K.J. Bird's familiarity with North Slope geology and the USGS sampling program proved invaluable in analyzing the data. Both L.B. Magoon and K.J. Bird also helped to solicit data from industry sources. Generous contributions of unpublished data were provided by the Shell Oil Company, British Petroleum, and Chevron. C. Dusel-Bacon made available her then unpublished metamorphic facies map of Alaska and helped interpret inorganic indicators of low-grade metamorphism. Z.C. Valin extracted hundreds of vitrinite reflectance determinations from industry reports and the literature; he and C.F. Hamilton also assisted with data input. Assistance in the field was provided by M.B. Underwood, D.L. Gautier, C.J. Schenk, T. Brocculeri, L. Huafu, P.B. O'Sullivan, W. Arendt, P. McClung, N. Fehri, F. Roure, and P. Desegaulx. P.A. Swenson assisted with drafting. Help with computational aspects of data manipulation was provided by C.H. Degnan, C.A. Madison, R.C. Obuch, M.J. Rachlitz, C.K. Runge, R. Sanders, and W.S. Weber. D.S. Aitkin, B.S. Bennet, T.T. Fitzgibbon, D.L. Knifong, P.K. Showalter, W.C. Steele, C.M. Wentworth, Jr., and F.L. Wong provided valuable advice on geographical information systems. This map benefited from critical reviews by K.J. Bird, S.E. Box, D.C. Bradley, J.L. Clayton, C. Dusel-Bacon, H.L. Foster, P.J. Haeussler, J.S. Kelley, L.B. Magoon, M.L. Miller, C.G. Mull, J.M. Murphy, G. Plafker, A.B. Till, and F.H. Wilson.

REFERENCES CITEDBarker, C.E., 1988, Geothermics of petroleum systems: Implications of the stabilization of

kerogen thermal maturation after a geologically brief heating duration at peak temperature, in Magoon, L.B., ed., Petroleum systems of the United States: U.S. Geological Survey Bulletin 1870, p. 26–29.

———1991, Implications for organic maturation studies of evidence for a geologically rapid increase and stabilization of vitrinite reflectance at peak temperature: Cerro Prieto geothermal system, Mexico: American Association of Petroleum Geologists Bulletin, v. 75, p. 1,852–1,863.

Barker, C.E., Dalziel, M.C., and Pawlewicz, M.J., 1983, A surface vitrinite reflectance anomaly related to Bell Creek Oil Field, Montana, USA: U.S. Geological Survey Open-File Report 83-826, 17 p.

Barker, C.E., and Pawlewicz, M.J., 1986, The correlation of vitrinite reflectance with maximum paleotemperature in humic organic matter, in Buntebarth, G., and Stegena, L., eds., Paleogeothermics: New York, Springer-Verlag, p. 79–93.

Bostick, N.H., 1979, Microscopic measurement of the level of catagenesis of solid organic matter in sedimentary rocks to aid exploration for petroleum and to determine former burial temperatures—A review, in Scholle, P.A., and Schluger, P.R., eds., Aspects of Diagenesis: Tulsa, Oklahoma, Society of Economic Paleontologists and Mineralogists Special Publication 26, p. 17–44.

Burnham, A.K., and Sweeney, J.J., 1989, A chemical kinetic model of vitrinite reflectance maturation and reflectance: Geochimica et Cosmochimica Acta, v. 53, p. 2,649–2,657.

Epstein, A.G., Epstein, J.B., and Harris, L.D., 1977, Conodont color alteration—An index to organic metamorphism: U.S. Geological Survey Professional Paper 995, 27 p.

Héroux, Y., Chagnon, A., and Bertrand, R., 1979, Compilation and correlation of major thermal maturation indicators: American Association of Petroleum Geologists Bulletin, v. 63, p. 2,128–2,144.

Hood, A., Gutjahr, C.C.M., and Heacock, R.L., 1975, Organic metamorphism and the generation of petroleum: American Association of Petroleum Geologists Bulletin, v. 59, p. 986–996.

Johnsson, M.J., Howell, D.G., and Bird, K.J., 1993, Thermal maturity patterns in Alaska: Implications to tectonic evolution and hydrocarbon potential: American Association of Petroleum Geologists Bulletin, v. 77, p. 1,874–1,903.

Price, L.C., 1983, Geologic time as a parameter in organic metamorphism and vitrinite reflectance as an absolute paleogeothermometer: Journal of Petroleum Geology, v. 6, p. 5–38.

Rejebian, V.A., Harris, A.G., and Huebner, J.S., 1987, Conodont color and textural alteration: An index to regional metamorphism, contact metamorphism, and hydrothermal alteration: Geological Society of America Bulletin, v. 99, p. 471–479.

Scholle, P.A., and Schluger, P.R., 1979, Aspects of diagenesis: Tulsa, Oklahoma, Society of Economic Paleontologists and Mineralogists Special Publication 26, 443 p.

Stach, E., Mackowsky, M., Teichmuller, M., Taylor, G.H., Chandra, D., and Teichmuller, R., 1982, Stach's textbook of coal petrology: Berlin, Gebruder Borntreger, 535 p.

Sweeney, J.J., and Burnham, A.K., 1990, Evaluation of a simple model of vitrinite reflectance based on chemical kinetics: American Association of Petroleum Geologists Bulletin, v. 74, p. 1,559–1,570.

SOURCES OF DATA

Data for this map have been compiled from the literature cited below, unpublished industry reports provided to the Alaska Division of Geological and Geophysical Surveys, previous USGS investigations, data contributed by industry, academic and government colleagues, and by our own sampling and analysis where needed. Quantitative data used in the preparation of the map were restricted to vitrinite-reflectance and Conodont Color Alteration Index analyses because these types of data are the most common and best quantifiable thermal-maturity data available in Alaska. The database behind this map (Johnsson and others, 1992), consists of 3,716 vitrinite-reflectance determinations from 2,123 outcrop localities, 1,474 Conodont Color Alteration Index determinations from 1,306 outcrop localities, and 4,482 vitrinite-reflectance determinations from 217 wells.

Where vitrinite-reflectance or Conodont Color Alteration Index data were sparse or unavailable, other organic and inorganic thermal-maturity data from the literature cited below were used to help constrain thermal maturity. Such data include: rock-evaluation pyrolysis (Tmax), thermal-alteration index (TAI), fluid inclusion, illite crystallinity, zeolite mineralogy, and fission-track data. In particular, the laumontite-prehnite-pumpellyite facies of Dusel-Bacon (1994) generally correlates with the supermature thermal-maturity unit defined by vitrinite-reflectance and Conodont Color Alteration Index data, and Dusel-Bacon (1994) was accordingly used to constrain the supermature thermal-maturity map unit in places.

The geologic base (metamorphic, plutonic, and unmetamorphosed bedrock, surficial units, and faults) is modified from Dusel-Bacon (1994) and Beikman (1980).

Bayliss, G.S., and Magoon, L.B., 1988, Organic facies and thermal maturity of sedimentary rocks in the National Petroleum Reserve in Alaska, in Gryc, G., ed., Geology and exploration of the National Petroleum Reserve in Alaska, 1974 to 1982, p. 489–518.

Belowich, M.A., 1986, Basinal trends in coal, petrographic, and elemental composition with applications toward seam correlation, Jarvis Creek Coal Field, Alaska, in Rao, P.D., ed., Focus on Alaska's Coal '86, Proceedings of the Conference held at Anchorage Alaska October 27–30, 1986: Fairbanks, Alaska, Mineral Industry Research Laboratory, p. 300–335.

Beikman, H.M., 1980, Geologic map of Alaska: U.S. Geological Survey, 1:2,500,000, 2 sheets.

Bird, K.J., 1987, The framework geology of the North Slope of Alaska as related to oil-source rock correlations, in Tailleur, I., and Weimer, P., Alaskan North Slope geology: Bakersfield, California, and Anchorage, Alaska, Pacific Section, Society of Economic Paleontologists and Mineralogists and Alaska Geological Society, p. 121–143.

Bird, K.J., and Magoon, L.B., 1987, Petroleum geology of the northern part of the Arctic National Wildlife Refuge, northeastern Alaska: U.S. Geological Survey Bulletin 1778, 329 p.

Brosgé, W.P., Reiser, H.N., Dutro, J.T., Jr., and Detterman, R.L., 1981, Organic geochemical data for Mesozoic and Paleozoic shales, central and eastern Brooks Range, Alaska: U.S. Geological Survey Open-File Report 81–551, 17 p.

Bruns, T.R., von Huene, R., Curlotta, R.C., Lewis, S.D., 1985, Summary geologic report for the Shumagin Outer Continental Shelf (OCS) Planning Area, Alaska: U.S. Geological Survey Open-File Report 85–32, 58 p.

Cameron, A.R., Norris, D.K., and Pratt, K.C., 1986, Rank and other compositional data on coals and carbonaceous shale of the Kayak formation, northern Yukon Territory, in Current Research, Part B: Geological Survey of Canada, p. 665–670.

Claypool, G.E., and Magoon, L.B., 1988, Oil and gas source rocks in the National Petroleum Reserve in Alaska, in Gryc, G., ed., Geology and exploration of the National Petroleum Reserve in Alaska, 1974 to 1982, p. 451–481.

Dusel-Bacon, C., 1994, Metamorphic history of Alaska, in Plafker, G., and Berg, H.C., eds., The geology of Alaska: Boulder, Colorado, Geological Society of America, The Geology of North America, v. G1, plate 4, 1:2,500,000, 2 sheets.

Fisher, M.A., 1982, Petroleum geology of Norton Basin, Alaska: American Association of Petroleum Geologists Bulletin, v. 66, p. 286–301.

Fisher, M.A., and Magoon, L.B., 1978, Geologic framework of Lower Cook Inlet, Alaska: American Association of Petroleum Geologists Bulletin, v. 62, p. 373–402.

Gautier, D.L., Bird, K.J., and Colten-Bradley, V.A., 1987, Relationship of clay mineralogy, thermal maturity, and geopressure in wells of the Point Thomson area, in Bird, K.J., and Magoon, L.B., eds., Petroleum geology of the northern part of the Arctic National Wildlife Refuge, northeastern Alaska: U.S. Geological Survey Bulletin 1778, p. 199–207.

Gryc, G., editor, 1988, Geology and exploration of the National Petroleum Reserve in Alaska, 1974 to 1982: U.S. Geological Survey Professional Paper 1399, 940 p.

Harris, A.G., Ellersieck, I.F., Mayfield, C.F., and Tailleur, I.L., 1983, Thermal maturation values (conodont color alteration indices) for Paleozoic and Triassic rocks, Chandler Lake, De Long Mountains, Howard Pass, Killik River, Misheguk Mountain, and Point Hope quadrangles, northwest Alaska, and subsurface NPRA: U.S. Geological Survey Open-File Report 83–505, 15 p.

Harris, A.G., Lane, H.R., Tailleur, I.L., and Ellersieck, I., 1987, Conodont thermal maturation patterns in Paleozoic and Triassic rocks, northern Alaska—Geologic and exploration implications, in Tailleur, I., and Weimer, P., Alaskan North Slope geology: Bakersfield, California, and Anchorage, Alaska, Pacific Section, Society of Economic Paleontologists and Mineralogists and Alaska Geological Society, p. 181–191.

Howell, D.G., Johnsson, M.J., Underwood, M.B., Lu Huafu, and Hillhouse, J.W., 1992, Tectonic evolution of the Kandik region, east-central Alaska: Preliminary interpretations, in Bradley, D.C., and Ford, A.B., eds., Geologic studies in Alaska by the U.S. Geological Survey during 1990: U.S. Geological Survey Bulletin 1999, p. 127–140.

Howell, D.G., Bird, K.J., Lu Huafu, and Johnsson, M.J., 1992, Tectonics and petroleum potential of the Brooks Range fold and thrust belt—A progress report, in Bradley, D.C., and Ford, A.B., eds., Geologic studies in Alaska by the U.S. Geological Survey during 1990: U.S. Geological Survey Bulletin 1999, p. 112–126.

Johnsson, M.J., Pawlewicz, M.J., Harris, A.G., and Valin, Z.C., 1992, Vitrinite reflectance and conodont color alteration index data from Alaska: Data to accompany the thermal maturity map of Alaska: U.S. Geological Survey Open-File Report 92–409, 3 diskettes.

Laughland, M.M., Underwood, M.B., and Wiley, T.J., 1990, Thermal maturity, tectonostratigraphic terranes, and regional tectonic history: An example from the Kandik area, east-central Alaska, in Nuccio, V.F., and Barker, C.E., eds., Applications of thermal maturity studies to energy exploration: Rocky Mountain Section, Society of Economic Paleontologists and Mineralogists, p. 97–111.

Magoon, L.B., and Bird, K.J., 1988, Evaluation of petroleum source rocks in the National Petroleum Reserve in Alaska, using organic-carbon content, hydrocarbon content, visual kerogen, and vitrinite reflectance, in Gryc, G., ed., Geology and exploration of the National Petroleum Reserve in Alaska, 1974 to 1982, p. 381–450.

Magoon, L.B., and Claypool, G.E., 1981, Petroleum geology of the Cook Inlet Basin—An exploration model: American Association of Petroleum Geologists Bulletin, v. 65, p. 1,043–1,061.

———1988, Geochemistry of oil occurrences, National Petroleum Reserve in Alaska, in Gryc, G., ed., Geology and exploration of the National Petroleum Reserve in Alaska, 1974 to 1982, p. 519–549.

Magoon, L.B., Woodward, P.V., Banet, A.C., Jr., Griscom, A.B., and Daws, T.A., 1987, Thermal maturity, richness, and type of organic matter of source rock units, in Bird, K.J., and Magoon, L.B., eds., Petroleum geology of the northern part of the Arctic National Wildlife Refuge, northeastern Alaska: U.S. Geological Survey Bulletin 1778, p. 127–179.

McLean, H., 1977, Organic geochemistry, lithology, and paleontology of Tertiary and Mesozoic rocks from wells on the Alaska Peninsula: U.S. Geological Survey Open-File Report 77–813, 63 p.

Merritt, R.D., 1985a, Coal atlas of the Matanuska Valley, Alaska: Alaska Department of Natural Resources, Division of Geological and Geophysical Surveys Public Data File 85–45, 270 p.

———1985b, Coal atlas of the Nenana Basin, Alaska: Alaska Department of Natural Resources, Division of Geological and Geophysical Surveys Public Data File 85–41, 197 p.

———1986a, Geology and coal resources of the Wood River Field, Nenana Basin: Alaska Department of Natural Resources, Division of Geological and Geophysical Surveys Public Data File 86–68, 11 p.

———1986b, Depositional environments and resource potential of Cretaceous coal-bearing strata at Chignik and Herendeen Bay, Alaska Peninsula: Alaska Department of Natural Resources, Division of Geological and Geophysical Surveys Public Data File 86–72, 20 p.

———1990, Coal resources of the Susitna Lowland, Alaska: Alaska Department of Natural Resources, Division of Geological and Geophysical Surveys Report of Investigations 90–1, 181 p.

Rao, P.D., 1980, Petrographic, mineralogical, and chemical characterization of certain Arctic Alaskan coals from the Cape Beaufort region: Alaska Department of Natural Resources, Division of Geological and Geophysical Surveys, Mineral Industry Research Laboratory Report No. 44, 66 p.

Rao, P.D., and Smith, J.E., 1983, Petrology of Cretaceous coals from northern Alaska: Alaska Department of Natural Resources, Division of Geological and Geophysical Surveys, Mineral Industry Research Laboratory Report No. 64, 141 p.

Reifenstuhl, R.R., 1990, Vitrinite reflectance data for some early Tertiary through Jurassic outcrop samples, northeastern Alaska: Alaska Division of Geological and Geophysical Surveys Public Data File 90–5a, 3 p.

———in press, Gilead sandstone, northeastern Brooks Range, Alaska: An Albian to Cenomanian marine clastic succession, in Reger, R., ed., Short Notes on Alaskan Geology, Alaska Division of Geological and Geophysical Surveys Professional Report 111.

Robinson, M.S., 1989, Kerogen microscopy of coal and shales from the North Slope of Alaska: Alaska Division of Geological and Geophysical Surveys Public Data File 89–22, 19 p.

Smith, J., and Rao, P.D., 1986, Geology and coal resources of the Bering River Coal Field, in Rao, P.D., ed., Focus on Alaska's Coal '86, Proceedings of the Conference held at Anchorage Alaska October 27–30, 1986: Fairbanks, Alaska, Mineral Industry Research Laboratory, p. 266–299.

Stanley, R.G., 1987, Thermal maturity and petroleum source-rock potential of the Cantwell Formation (Paleocene), Alaska Range, in Hamilton, T.D., and Galloway, J.P., eds., Geologic Studies in Alaska by the U.S. Geological Survey during 1986: U.S. Geological Survey Circular 998, p. 104–107.

———1988, Hydrocarbon source potential and thermal maturity of the Sanctuary Formation (Middle Miocene), northern foothills of the Alaska Range, in Galloway, J.P., and Hamilton, T.D., eds., Geologic Studies in Alaska by the U.S. Geological Survey during 1987: U.S. Geological Survey Circular 1016, p. 117–120.

Stanley, R.G., McLean, H., and Pawlewicz, M.J., 1990, Petroleum source potential and thermal maturity of the Tertiary Usibelli Group at Suntrana, Central Alaska, in Dover, J.H., and Galloway, J.P., eds., Geologic Studies in Alaska by the U.S. Geological Survey, 1989: U.S. Geological Survey Bulletin 1946, p. 65–76.

Underwood, M.B., Laughland, M.M., Wiley, T.J., and Howell, D.G., 1989, Thermal maturity and organic geochemistry of the Kandik basin region, east-central Alaska: U.S. Geological Survey Open-File Report 89–353, 41 p.

Underwood, M.B., Brocculeri, T., Bergfeld, D., Howell, D.G., and Pawlewicz, M., 1992, Statistical

1Onset of oil generation

Limit of oil generation

Limit of wet gas preservation

Limit of oil preservation

Undermature

Mature

Overmature

1.5

2

3

2.5

3.5

4

4.5

5

UUndermature

M1Mature I

M2Mature II

OOvermature

SSupermature

Ig-MIgneous/

Metamorphic

0.6

3.5

5.0

1.3

2.0

Vitrinitereflectance

(R , %)

Conodont coloralteration index

(CAI)

Hydrocarbongeneration†

Mapunits

o

Correlation of thermal maturity indicators and definition of map units

Maximumtemperature

(ϒC)*

95

278

315

175

220

* Barker, C.E., 1988, Geothermics of petroleum systems: Implications of the stabilization of kero-gen thermal maturation after a geologically brief heating duration at peak temperature in Magoon, L.B., ed., Petroleum Systems of the United States: U.S. Geological Survey Bulletin 1870, p. 26–29.

† Poole, F.G. and Claypool, G.E., 1984 Petroleum source-rock potential and crude-oil correlation

in the Great Basin, in Woodward, J., Meissner, F.F., and Clayton, J.L., eds., Hydrocarbon source rocks of the greater Rocky Mountain region: Denver, Colorado, Rocky Mountain Association of Geologists, p. 179–229.

MISCELLANEOUS INVESTIGATIONS SERIESMAP I-2494

BULLETIN 2142PLATE 1

U.S. DEPARTMENT OF THE INTERIORU.S. GEOLOGICAL SURVEY

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey

For sale by U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225

-500 m

Area of diagram

Colville BasinSubsurface perspective

-1000 m

-1500 m

-2000 m

-2500 m

-3000 m

Sea level

< 0.3

0.3–0.6

0.6–0.9

0.9–1.2

1.2–1.5

1.5–1.8

1.8–2.1

> 2.1

Prudhoe Bay

Point Barrow

ALASKA

EXPLANATION

Oil well

Thrust fault

Basement

Boundary between thermal-maturity units, dashed where uncertain

Point Thomson

U.S.

CANADA

Well name

Kelly bushing elevation, meters above sea level

Vitrinite reflectance at surface (%)

Vitrinite reflectance at total depth (%)

Hole bottom, meters below sea level

Contacts between thermal map units, meters below sea level

Becharof #1Ro, Surf(67m): 0.25Ro, TD(-2683m): 1.77U/M1: -2351mM1/M2: -2501mM2/O: -2754m

EXPLANATIONThermal-maturity units—Ro, reflectance value in oil; CAI, Conodont Color

Alteration Index. See text for explanation

U Undermature—Ro < 0.6, CAI < 1.0

M1 Mature I—Ro 0.6–1.3, CAI 1.0–2.0

M2 Mature II—Ro 1.3–2.0, CAI 2.0–3.0

O Overmature—Ro 2.0–3.6, CAI 3.0–4.0

S Supermature—Ro 3.6–5.0, CAI 4.0–4.5

Ig-M Igneous-Metamorphic—Ro > 5.0, CAI > 4.5

? No data

Qs Quaternary sediments (unconsolidated)

Glacial cover

Thermal-maturity unit contact—Dashed where inferred, dotted where concealed

High-angle fault—Dashed where inferred, dotted where concealed

Thrust fault—Dashed where inferred, dotted where concealed

Detachment fault—Dashed where inferred, dotted where concealed

Contour on U/M1 unit boundary—Elevation of U/M1 thermal maturity map-unit boundary (0.6% vitrinite reflectance isograd). Values, meters below sea level

Sample localities—Many localities represented by multiple samples. Where shown, color indicates thermal maturity map unit

Vitrinite reflectance

Conodont Color Alteration Index

Subsurface data

Selected oil well with vitrinite reflectance data—All elevations and vitrinite reflectance values are from regression lines drawn through the data; this line may be extrapolated slightly below the well bottom

Other oil well—Used to constrain contoured U/M1 thermal maturity map-unit boundary (0.6% vitrinite reflectance isograd) in Cook Inlet and North Slope regions

City

Anchorage

Seward

Sea level

-500 m

-1000 m

-1500 m

-2000 m

-2500 m

-3000 m

0.2–0.30.3–0.40.4–0.50.5–0.60.6–0.70.7–0.8Area of diagram

Cook Inlet BasinSubsurface perspective

ALASKA

Bruin

Fault

BayBorder Ranges Fault

EXPLANATION

Oil well

Fault

Boundary between thermal-maturity units

Mean Ro—In percent. See text for description

Lake Clark-Castle Mountain Fault

Mean Ro—In percent. See text for description

50 350 KILOMETERS0 50 100 150 200 250 300

SCALE: 1:5,000,00050 250 MILES0 50 100 150 200

BATHYMETRIC CONTOUR INTERVAL 1000 METERSSUPPLEMENTARY CONTOUR AT 200 METERS

Geology modified from Dusel-Bacon (1994) and Beikman (1980)

Map edited by Dale Russell and Taryn A. Lindquist; cartography by Karen L. Wheeler and Taryn A. Lindquist

Map approved for publication July 1, 1994

Johnson, Mark J., and Howell, David G., eds., 1996, Thermal evolution of sedimentary basins in Alaska: U.S. Geological Survey Bulletin 2142

Base prepared by Geological Society of America from U.S. Geological Survey National Atlas, 1:7,500,000, 1970. Bathymetry north of lat 60ϒ plotted by U.S. Geological Survey from GEBCO digital data; bathymetry south of lat 60ϒ (SYNBAPS) plotted by National Oceanographic and Atmospheric Administration

Transverse Mercator projection. Central Meridian, 100ϒ W. Scale factor, 0.926. Reference ellipsoid, (6371204 m, 6371204 m)

K.E. Adams

T.S. Ahlbrandt

American Oil Co.

A. Anderson

H.C. Berg

R.B. Blodgett

D.A. Bodnar

D. Bohn

S. Boundy-Sanders

S.E. Box

E.E. Brabb

D.A. Brew

British Petroleum

W.P. Brosgé

T.K. Bundtzen

C. Carlson

R.M. Chapman

Chevron Oil Co.

M. Churkin, Jr.

K.H. Clautice

J.G. Clough

H.A. Cohen

H.E. Cook

S.M. Curtis

J.T. Dillon

J.H. Dover

J.A. Dumoulin

J.T. Dutro, Jr.

I.F. Ellersieck

P. Folger

H.L. Foster

W.G. Gilbert

P.D. Gruzlovic

G. Hakkila

C.L. Hanks

P.J. Haeussler

B.K. Holdsworth

A.C. Huffman, Jr.

D.L. Jones

S.M. Karl

J.S. Kelley

M.M. Laughland

C.F. Mayfield

M.L. Miller

C.M. Molenaar

T.E. Moore

C.G. Mull

M.W. Mullen

J.M. Murphy

S.W. Nelson

W.J. Nokleberg

A.T. Ovenshine

W.W. Patton, Jr.

G. Plafker

A.W. Potter

B.L. Reed

R.R. Reifenstuhl

H.N. Reiser

S.B. Roberts

J.M. Schmidt

Shell Oil Co.

N.J. Silberling

J.P. Siok

R.G. Stanley

I.L. Tailleur

W. Thompson

A.B. Till

M.B. Underwood

K.F. Watts

F.R. Weber

T.J. Wiley

INTERIOR__GEOLOGICAL SURVEY, RESTON, VA__1995

PRINCIPAL CONTRIBUTORS

Kenneth J. Bird, Cynthia Dusel-Bacon, Christopher F. Hamilton, Anita G. Harris, Leslie B. Magoon,

Mark J. Pawlewicz, and Zenon C. Valin

Previously unpublished data and samples contributed by:

2000

140ϒ145ϒ150ϒ155ϒ160ϒ165ϒ170ϒ175ϒ180ϒ170ϒ

155ϒ 150ϒ 145ϒ 140ϒ 135ϒ 130ϒ160ϒ165ϒ170ϒ

55ϒ

135ϒ

130ϒ

60ϒ

65ϒ

70ϒ

70ϒ65ϒ

175ϒ

170ϒ

60ϒ

180ϒ

55ϒ

175ϒ

175ϒ

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