Alluvial facies and paleosols in the Cretaceous Nanushuk formation, Kanayut River, North Slope, Alaska, Preliminary results from the 2001 field season

Abstract

Paleosols are increasingly viewed as an important, if not critical component in nonmarine sequence stratigraphic analyses where they mark interfluve sequence boundaries and provide at least qualitative information on relative rates of accommodation change within intervening alluvial strata. However, the application of detailed paleopedological analyses to nonmarine sequence stratigraphic studies is still relatively rare.This study focuses on alluvial and coastal plain deposits of the Cretaceous Nanushuk Formation exposed in outcrop along the Kanayut River south of the NPRA. During the 2001 field season, this site was logged and sampled for subsequent micromorphological, geochemical and mineralogical analyses. Preliminary observations indicate that pedogenic modification of alluvial deposits is common, however, rapid deposition of sediment and generally wet conditions resulted in a preponderance of weakly-developed and poorly-drained paleosols similar to modern Entisols, Inceptisols, Gleysols and Histosols. Sandstone and mudstone paleosols may contain a few large root traces, sometimes expressed as vertical to subhorizontal coalified structures or as surface cradle knolls, but they maintain evidence of primary stratification and cumulic development. Coalified and carbonaceous root traces, organic fragments, blocky structures and abundant siderite nodules provide further evidence of waterlogged conditions. By combining field observations, paleosols micromorphology, geochemistry and mineralogy with regional stratigraphic information, it is possible to pin-point the exact position of sequence boundaries in nonmarine rocks. Further work is planned in an attempt to better understand the regional distribution of paleosols in the Nanushuk Formation in order to better characterize significant nonmarine depositional hiatuses (sequence boundaries) and Cretaceous high latitude paleoenvironmental conditions.

Stratigraphic and reservoir quality studies of continuous core from the Wainwright #1 coalbed methane test well, Wainwright, Alaska

“…The facies composition and thickness of channel fills recognized in the Wainwright core are comparable to channel deposits recognized in other ancient deltaic successions (Dunvegan Formation of Bhattacharya and Walker, 1991; Ferron Sandstone of Ryer and Anderson, 2002;Wilcox Group of Galloway, 1968), and in outcrops of the Nanushuk Formation (McCarthy, 2003;LePain and others, 2009). Subsurface data suggest the amalgamated channels from 1,060.5 to 1,157.7 ft and 619.3 to 667 ft are part of channel belts that have regional extent in the depositional dip direction (northeast to the east; Decker, 2016 [this volume]).…”

“…The association records gradual progradation of mouth bars into quiet water interdistributary bay settings from the downstream ends of crevasse channels (Fisk and others, 1954;Coleman and others, 1964;Elliot, 1974). The vertical succession through this association closely resembles mouth bar deposits recognized in modern interdistributary bay successions of the Mississippi River (Fisk and others, 1954;Coleman and others, 1964;Coleman and Gagliano, 1965;Elliott, 1974) and in ancient deltaic successions (Elliott, 1976;Horn and others, 1978;Bhattacharya and Walker, 1991), including the Nanushuk Formation (LePain and Kirkham, 2001;McCarthy, 2003;LePain and others, 2009). Examples that include mudstone at their base and culminate in amalgamated sandstone beds record a complete progression from distal mouth bar to crevasse channel deposits ( fig.…”

Lithofacies analysis of the Wainwright #1 continuous core, western Arctic Slope, Alaska: Transition from lower to upper delta plain environments in the Albian-Cenomanian Nanushuk Formation

“…The association records gradual progradation of mouth bars into quiet water interdistributary bay settings from the downstream ends of crevasse channels (Fisk and others, 1954;Coleman and others, 1964;Elliot, 1974). The vertical succession through this association closely resembles mouth bar deposits recognized in modern interdistributary bay successions of the Mississippi River (Fisk and others, 1954;Coleman and others, 1964;Coleman and Gagliano, 1965;Elliott, 1974) and in ancient deltaic successions (Elliott, 1976;Horn and others, 1978;Bhattacharya and Walker, 1991), including the Nanushuk Formation (LePain and Kirkham, 2001;McCarthy, 2003;LePain and others, 2009). Examples that include mudstone at their base and culminate in amalgamated sandstone beds record a complete progression from distal mouth bar to crevasse channel deposits ( fig.…”

“…2006). Alluvial floodbasin deposits have been recognized in outcrops of the Nanushuk Formation south of Umiat (McCarthy, 2003;LePain and others, 2009).…”

“…Given these similarities and limitations imposed by a single core, interpretation as channel levee deposits and our ability to clearly distinguish them from mouth bar deposits is questionable. Channel levee deposits have been recognized in the Nanushuk in outcrop (LePain and Kirkham, 2001;McCarthy, 2003;LePain and others, 2009).…”