U.S. Geological Survey Digital Data Series DDS-57 STRATIGRAPHIC FRAMEWORK OF LOWER AND UPPER CRETACEOUS ROCKS IN CENTRAL AND EASTERN MONTANA By Steven M. Condon 2000 USGS Energy Resources Team Box 25046, MS939 Denver, CO 80225 U.S. Department of the Interior Bruce Babbitt, Secretary U.S. Geological Survey Charles G. Groat, Director Available from: USGS Information Services Box 25286, Building 810 Denver Federal Center Denver, CO 80225 Call: (303) 202-4200 For more information about the Stratigraphic Framework of Lower and Upper Cretaceous Rocks in Central and Eastern Montana, please contact: Steven Condon scondon@usgs.gov (303)-236-1535 U.S. Geological Survey Denver Federal Center P.O. Box 25046, MS939 Denver, CO 80225 I. INTRODUCTION INTRODUCTION This report summarizes the stratigraphic framework of Lower and Upper Cretaceous sedimentary rocks in the central and eastern part of Montana, and was written in support of U.S. Geological Survey studies of energy resources in Cretaceous rocks. The study was undertaken as a part of a larger project, under the direction of J.L. Ridgley, that investigated the occurrence of shallow biogenic gas in Upper Cretaceous rocks in north-central Montana and adjacent areas of Canada. The approach used here is to describe briefly the rock units and to show their thickness, distribution, and structural configuration using isopach maps, cross sections, and structure contour maps. In the study area, within a central foreland basin setting, most deposition of Lower and Upper Cretaceous rocks was between the lithologic end members of very coarse terrigenous clastics and the open marine chalks. With few exceptions, Cretaceous rocks in the study area consist of fine- to medium-grained sandstone, siltstone, mudstone, and shale. Other rock types, such as conglomerate and limestone are relatively rare in the section. Bentonite beds, a result of ash falls from volcanic eruptions to the west, are volumetrically insignificant, but are important marker beds through much of the Cretaceous section. Eighteen formations are described in this report; five formations of Early Cretaceous age and thirteen of Late Cretaceous age. The thickness of the entire Cretaceous section ranges between about 3,500 ft and 5,600 ft; within this range between 500 and 1,000 ft are Lower Cretaceous and the remainder are Upper Cretaceous. The entire section is thickest on the west, and thins eastward. This disk contains Portable Document Format (PDF) files which require Adobe Acrobat for viewing. Acrobat software runs on a variety of systems, and is available free of charge from Adobe (www.adobe.com). II. DISCLAIMERS This Compact Disc-Read Only Memory(CD-ROM) publication was prepared by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. Although all data and software published on this CD-ROM have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials and (or) the functioning of the software. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of this data, software, or related materials. III. SYSTEM REQUIREMENTS A. Macintosh computer (Macintosh II series with 68020 or greater processor, including all Power Macintosh computers), with MacOS 7.1.2 or later. 1. 4.5 MB application RAM, 6.5 MB recommended). 2. 8 MB of hard disk space. B. Intel personal computer (486 minimum, Pentium or Pentium Pro recommended), with Microsoft Windows 95, Windows 98, Microsoft Windows NT 4.0 with Service Pack 3 or later. 1. 8 MB application RAM minimum, 16 MB recommended. 2. 10 MB hard disk space IV. INSTRUCTIONS AND DOCUMENTATION FOR Digital Data Series 57 A. To get started: Use of this CD-ROM requires the installation of Adobe Acrobat Reader. This free software is provided on this CD-ROM and is also available from Adobe Inc. (www.adobe.com) and Apple Inc. (www.apple.com). Double-click on the ACRD4ENU.EXE icon to install Acrobat Reader 4.0. The Acrobat file ReadMe.pdf gives more information about Acrobat Reader. Help files and on-line manuals describe the software in detail; however, the following sections will help you get started. 1. Install Adobe Acrobat Reader 4.0 on your hard drive if not already installed. Refer to the read me and text files supplied with the Acrobat reader software for specific installation instructions. 2. Launch Acrobat Reader and open the "DDS57.pdf" file on the CD-ROM. 3. Hints for using Adobe Acrobat The Acrobat toolbar is located along the top of the Acrobat screen. Most of the icons in the tool bar are self-explanatory. The arrow icons move one page at a time. 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