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Previous HitMAGNETICNext Hit GLACIAL AND FLUVIAL SEDIMENTS IN THE HOLITNA BASIN AND OTHER CENOZOIC BASINS IN ALASKA - RELEVANCE FOR THE AEROMAGNETIC SEARCH FOR HYDROCARBONS

CADY, John W., GeoPeregrino, 3955 Douglas Mountain Drive, Golden, CO 80403-7701, [email protected]

A high-resolution aeromagnetic survey was flown in the Cenozoic Holitna basin in interior Alaska for coal bed methane exploration. Interpretation of the survey shows that many short-wavelength Previous HitmagneticNext Hit highs are caused by Previous HitmagneticNext Hit sediments derived from both igneous rocks of the Wrangellia composite terrane (WCT) and Tertiary granodiorite to tonalite superimposed on the WCT. The Previous HitmagneticNext Hit sediments were transported as glacial till and outwash. At their greatest (pre-Wisconsin) advance, glaciers crossed the Denali fault and deposited glacial till in the pull-apart Holitna basin, producing Previous HitmagneticNext Hit highs aligned with the fault. The short-wavelength Previous HitmagneticNext Hit highs occur as peaks on a low-amplitude (100-200 nT) regional Previous HitmagneticNext Hit high in the Holitna and other interior basins. Isolated igneous outcrops within the basins cause only local weak Previous HitmagneticNext Hit anomalies. Thus igneous rocks within or beneath the basins are not a compelling explanation for the regional Previous HitmagneticNext Hit high over the basins. In contrast, regional Previous HitmagneticNext Hit anomalies over igneous rocks in the WCT have high amplitudes (500-2500 nT). I conclude that the regional Previous HitmagneticNext Hit high in interior Alaska is partially caused by Previous HitmagneticNext Hit sediments derived from the WCT. Late Cenozoic uplift (5 km at Denali) of Previous HitmagneticNext Hit igneous rocks provided abundant Previous HitmagneticNext Hit sediments. Glaciers were larger and more active on the southern flank of the Alaska Range and Wrangell Mountains. Abundant Previous HitmagneticNext Hit sediments were transported to the south via the Susitna and Matanuska Valleys to Cook Inlet basin, all of which have higher amplitude (200-400 nT) Previous HitmagneticNext Hit highs than do the interior basins. The presence of Previous HitmagneticNext Hit sediments in the interior and southern basins preclude the effective use of Previous HitmagneticNext Hit analysis to determine depth to Previous HitmagneticNext Hit basement. The term "Previous HitmagneticNext Hit basement" is inappropriate in non-cratonic Alaska, where continental crust is under construction. Previous HitMagneticNext Hit analysis is useful, however, for tracking magnetite from its igneous sources to its sedimentary sinks. If carbon derived from Mesozoic and Cenozoic coal bearing strata eroded from the uplifted Alaska Range and Wrangell Mountains followed similar paths as sedimentary magnetite, then Previous HitmagneticNext Hit analysis may help locate coal bed methane and basin-centered hydrocarbons contained in Previous HitmagneticTop clastic sediments.