Structure and Stratigraphy of Western Arctic Alaska: ABSTRACT

Abstract

The geology in northwestern Alaska is a continuation of that on the east and projects westward onto the adjoining continental shelf and probably to Wrangel Island. It reflects deposition in the Arctic Alaska sedimentary basin through Jurassic time; the growth within the basin of a volcanic welt and, possibly, a continental edge in the Jurassic and an orogen in the Early Cretaceous; and filling and deformation of successor basins in the Cretaceous and Tertiary. Foreshortening of the fold belt probably exceeded 200 km (150 mi) transversely (N-S) and possibly 150 km (100 mi) laterally (W-E). The fold belt consists of several east-trending structural zones: moderately metamorphosed Paleozoic rocks with subordinate Mesozoic plutons near the south flank of the geanticline; folded, overturned, and imbricately thrust Devonian and Mississippian clastic and carbonate rocks that extend north to the mountain front in the east but merge with or plunge beneath other zones on the west; Devonian to earliest Cretaceous sedimentary and Jurassic mafic rocks stacked in folded and faulted broad thrust plates that form the northern mountains in the west and allochthons on other zones; and complexly deformed Devonian to mid-Cretaceous sedimentary and mafic rocks that underlie the foothills belt bordering the northern flank. Near the west coast, the fold belt is deflected south into the NE-tr nding Chukchi syntaxis, and then continues northwestward onto the Chukchi Shelf. A broad zone of disharmonically folded mid-Cretaceous successor-basin deposits lies north of the fold belt. As in regions on the east, older basin sediments underlying these deposits probably are relatively undisturbed and rise from depths of a few miles in the south to less than 2 mi on the shelf on the north. The sedimentary record has to be treated palinspastically, and several features seem important. The old basin was originally twice the present 300-mi width. Deposition in it was marked by Devonian and Mississippian carbonates with clastic material wedged in from a shoreline that was near the mountains and transgressed northward. The Devonian and Mississippian rocks are overlain by a blanket of chert, shale, and limestone. Northward, facies changes in the mid-Mesozoic were strong--from ophiolites, to diabase and radiolarian chert with oil shale, to chert, shale, and limestone, and to clay shale in the Jurassic and from conglomerate, to wacke, to turbidite, to quartzitic siltstone, to clay shale with shell beds, and to clay shale in the earliest Cretaceous. The onshore and offshore petroleum potential is being explored. End_of_Article - Last_Page 2508------------