PRELIMINARY GEOLOGIC, PETROLOGIC,AND PALEONTOLOGIC RESULTS OF THE STUDY OF NANUSHUK CROUP ROCKS, NORTH SLOPE, ALASKA BY THOMAS S. AHLBRANDT , EDITOR \ GEOLOGICAL SURVEY CIRCULA~? 794 ~itedStates Department of the Interior LXIL D. ANDRUS, Secretary Geological Survey H. William Menard, Director Free on application to Branch of Distribution, U.S. Geological Survey 1200 South Eads Street, Arlington, Va. 22202 CONTENTS Page Introduction to geologic studies of the Nanushuk Group, North Slope, Alaska, by T. S. Ahlbrandt----------------------------------------------------------------------- Nanushuk Group deposition and the Late Mesozoic srrucrural evolution of the central and western Brooks Range and Arctic Slope, by C . G . Mull---------------------------------- Depositional framework and reservoir quality studies of selected Nanushuk Group outcrops, North Slope, Alaska, by T. S. Ahlbrandt, A. C. Huffman, J. E. Fox, and Subsurface studies of the Nanushuk Group, North Slope, Alaska, by K. J. Bird and J. Andrews-- A summary of reservoir characterisrics of the Nanushuk Group, Umiat test well 11, National Petroleum Reserve in Alaska, by J. E. Fox------------------------------------------------ Hydrocarbon source potential of the Nanushuk Group and the Torok Formation, a preliminary report, by L. B. Magoon and G. E. Claypool----------------------------------------------- Textural and mineralogical study of some surface and subsurface sandstones from the Nanushuk Group, western North Slope, Alaska, by S. Bartsch-Winkler----------------------- Stratigraphy and petrography of a measured section on the south limb of Barabara Syncline, North Slope, Maska, by A. C, Huffman---------------------------------------------------- Some Cretaceous plant megafossils and microfossils from the Nanushuk Group, Northern Alaska, a preliminary report, by R. A. Scott and C. J. Smiley---------------------------- Dinoflagellare and Acrirarch assemblages from the Nanushuk Group (Albian-Ceonomanian) and the Torok Formation (Albian), Umiat test well 11, National Petroleum Reserve in Alaska, northern Alaska, by E. &y------------------------------------------------------------ Dinoflagellate and acritarch assemblages from the Grandstand Formation (Middle to Upper Albian) of the Nanushuk Group, Simpaon Core Test 25, National Petroleum Reserve in Alaska, northern Alaska, by F. E. May and J. A. Stein-------------------------------------------- Cretaceous foraminifers from the North Slope of Alaska, by W. V. Sliter---------------------- ILLUSTRATIONS Page Figure 1. General North Slope index map----------------------------------------------------- 2. Generalized nomenclature and stratigraphic relationships of Lower Cretaceous sediments, western and central North Slope-----------.-.--------------------------- Index map pf structures and physiographic subdivisions of the North Slope--------- Schematic thrust sheet sequence along north flank of the Brooks Range------------- Stratigraphic nomenclature of Nanushuk Group-------------------------------------- Schematic cross-section of Nanushuk rocks, western North Slope-------------------- Selected measured sections of Nanushuk rocks-------------------------------------- Sedimentary features of Nanushuk rocks in outcr~p--------------------------------- Sandstone percent histograms of selected Nanushuk outcrop sections---------------- Index map of selected Nanushuk Group data----------------------------------------- Seismic section through Drew Point 1 well----------------------------------------- Diagrammatic stratigraphic diagram relating rocks of NPRA and Prudhoe Bay--------- Diagrammatic Cretaceous rime-stratigraphic chart for northern NPRA---------------- Cretaceous section in Drew point 1 well------------------------------------------- Directional (paleotransport) data for sediments of the Torok Formation and Nanushuk Group------------------------------------------------------------------- Log response and lithofacies in three NPRA wells---------------------------------- Isopach map including both Torok Formation and Nanushuk Group--------------------- ILLUSTRATIONS (continued) Page Nanushuk Group isopach map-------------------------------------------------------- 40 Torok Formation isopach map-------------------------------------------------------- 41 Index map of Umiat Anticline region----------------------------------------------- 43 Stratigraphic column of Umiat test well ll---------------------------------------- 44 Deltaic interpretation of Lower Cretaceous rocks in eastern NPRA------------------ 4 6 Description of core 60, Grandstand Formation, Umiat test well 11------------------ 47 Description of cores 56-58, Grandstand Formation, Umiat test well 11-------------- 45 Description of cores 52-53, Grandstand Formation, Umiat test well 11-------------- 49 Description of core 49, Killik Tongue of Chandler Formation, Umiat test well 11--- 49 Description of cores 35-38, Ninuluk Formation, Umiat test well 11----------------- 51 Porosity and permeability relationships of Cretaceous rocks, Umiat test well 11--- 53 Organic geochemistry data for Nanushuk Group and Torok Formation from the Kukpowruk type section and Kaolak No. 1 well------------------------------------- 58 Organic geochemistry data for Cretaceous rock units in Topagoruk No. 1 well and Umiat test well ll---------------------------------------------------------------- 5 9 Index map of outcrop and subsurface petrography samples---------------------------- 62 Textural properties of Nanushuk sandstones as determined petrographically---------- 63 Ternary plots of Nanushuk sandstone petrographic data------------------------------ 64 Photographs of pore-linings in sandstones of the Nanushuk Group-------------------- 68 Scanning electron microscope photographs of pore-linings in sandstones of the Nanushuk Group-------------------------------------------------------------------- Index map showing sample locations along the south limb of Barabara Syncline------- Ternary diagrams of petrographic data, Barabara Syncline, using Dickson's (1970) methods-------------------------------------------------------------------------- Ternary diagrams of petrographic data, Barabara Syncline, using ~olk's (1968) methods--------------------------------------------------------------------------- Histograms of reservoir quality parameters, Barabara Syncline---------------------- Graphic presentation of petrographic data, Barabara Syncline----------------------- Stratigraphic sequences of Mississippian to Lower Cretaceous rocks, western Index map showing plant macrofossil and microfossil. localities, Nanushuk Group, northern Hasb------------------------------------------------------------------- Stratigraphic ranges of selected plant megafossils, northern Alaska---------------- Stratigraphic occurrence and distribution of Nilssoniopteris palymorpha, northern ~aska------------------------------------------------------r------------- Index map showing location of Simpson core test 25--------------------------------- Columnar section of Grandstand Formation, Simpson core test 25--------------------- Index map showing sample and well localities studied for foraminifera1 assemblages- Distribution of foraminifers in Albian to Cenomanian interval of Umiat test Plate 1-7. Selected plant fossils of the Nanushuk Group-------------------------------------- 90-111 8-12. Selected dinoflagellates and acritarchs from Umiat test well 11------------------- 118-127 13-17. Selected dinoflagellates and acritarchs from Simpson core test 25----------------- 136-145 18. Selected foraminifers from Torok Formation and Nanushuk Group of Umiat test well ll-------------------------------------------------------------------------- 154 19. Selected foraminifers from Torok Formation and Nanushuk Group surface sections---- 156 TABLES Page Table 1. Synthesie ef resource related data gathered in 1977 outcrop studies---------------- 16 2 Selected Nanushuk outcrop and subsurface data-------------------------------------- 34 TABLES (continued) Page Organic geochemical data from outcrop and core material of Cretaceous rock units, North Slope----------------------------------------------------------------------- Clast compositions in Nanushuk Group petrographic samples-------------------------- Composition of samples from south limb of Barabara Syncline------------------------ Textural data of samples from south limb of Barabara Syncline---------------------- Uranium and thorium content of samples from south limb of Barabara Syncline-------- Ranges of dinoflagellates and acritarchs from the Nanushuk Group and Torok Formation, Umiat test well 11----------------------------------------------------- Ranges of dinoflagellates and acritarchs from the Grandstand Formation, Simpson core test 25---------------------------------------------------------------------- Foraminifer-bearing samples from the Kukpowruk type section------------------------ Foraminifer-bearing samples from the Seabee Formation in the Ninuluk Bluff section- Foraminifer-bearing samples from the Tuktu Bluff section--------------------------- INTRODUCTION TO GEOLOGIC STUDIES OF THE NANUSHUK GROUP, NORTH SLOPE, ALASKA By Thomas S. Ahlbrandt ABSTRACT Potential hydrocarbon source beds within the Nanushuk in the central North Slope are Sediments of the Nanushuk Group of early relatively less thermally mature than those in Albian to Cenomanian age are a major hydrocarbon the western area, which are relatively more play within the National Petroleum Reserve in mature