Depositional Environments Of The Lower Triassic Ivishak Formation In The Northeastern Brooks Range, Alaska

Abstract

The Lower Triassic Ivishak Formation in the northeastern Brooks Range represents a progradational wave-dominated delta system. Eight distinct lithofacies were recognized based upon 27 measured sections in the Sadlerochit and Shublik Mountains and at Leffingwell and Bathtub ridges. These lithofacies record a series of progradational episodes beginning in the Kavik Shale, and continuing upward into the Ledge Sandstone Member, and the overlying Fire Creek Siltstone Member. Isopach and correlation diagrams indicate that the paleoshoreline was located in the Sadlerochit and northern Shublik Mountains area, roughly parallel to the present trend of the mountains front. The major dispersal centers were located in the Katakturuk River area of the western Sadlerockit Mountains and in the Marsh Creek area in the eastern Sadlerochit Mountains to Fire Creek area in the eastern Shublik Mountains. The Ivishak Formation contains texturally mature, very fine- to coarse-grained, light gray to light gray-blue, sublitharenite to chert arenite with an average framework: matrix:cement:porosity ratio of $\rm F\sb{75}:M\sb{<1}:C\sb{24}:P\sb1$. The Ledge Sandstone Member was derived from a recycled sedimentary provenance, with an ultimate metamorphic provenance. Compaction and late silica cementation resulted in major porosity destruction. <p>