|15 April 2014
GSA Release No. 14-27
|Alaska, USA. Image courtesy NASA.|
New GEOSPHERE Series: The St. Elias Erosion/Tectonics Project (STEEP) in Southern Alaska
Boulder, Colorado, USA – GEOSPHERE has added a new themed issue to its roster: "Neogene tectonics and climate-tectonic interactions in the southern Alaskan orogeny." Interest in Alaskan tectonics has varied over time, propelled mostly by geologic hazards. In 1964, the great Alaskan earthquake focused attention on Alaska and was a major factor in the establishment of the concept of subduction in the early days of plate tectonics.
In the 1980s, the northern Cordillera, including Alaska, was the subject of extensive study using the terrane analysis approach, which spawned a series of new tectonic syntheses. Topical studies continued in Alaska through the 1990s and into the early part of the first decade of the twenty-first century, but in smaller research groups primarily working on specific, focused studies.
Larger multidisciplinary research projects were focused in Alaska at about the time of the 2002 Denali earthquake, which occurred while a large, collaborative research group was being assembled with a goal of understanding the general problems of the Neogene tectonics of Alaska associated with the collision of the Yakutat terrane.
The St. Elias Erosion/Tectonics Project (STEEP; http://www.ig.utexas.edu/steep/) arose in large part because of increasing evidence that erosion-tectonic interactions within mountain belts were poorly understood, and southern Alaska is in an ideal setting for examining the role of glacial erosional processes in this type of interaction. Although subsequent studies indicated that the original highest estimates of glacial erosion rates were overestimated, even these revised estimates indicated that fast moving, temperate ice was capable of removing rock at rates of centimeters per year.
Since most of the world's moderate- to high-latitude mountain systems are either no longer active or are marginally active tectonically, and erosion rates are orders of magnitude lower, the southern Alaskan orogen represents a premier site for studies of the interactions between tectonic processes and glacial erosion. STEEP efforts, funded by the National Science Foundation (NSF) Continental Dynamics Program, together with other ongoing studies of Alaskan tectonics by the U.S. Geological Survey and other academic researchers, have focused attention back on Alaskan tectonics.
The next decade promises to see even more profound changes in our level of knowledge of this last frontier for geologic studies in the United States. Research reported in this GEOSPHERE themed issue was launched by members of the STEEP research group with the intent of showcasing some of the unusual data sets that were being assembled in this project.
Introduction to the New Themed Series by Terry L. Pavlis et al., Dept. of Geological Sciences, The University of Texas at El Paso, El Paso, Texas 79968, USA. Published 10 April 2014, http://dx.doi.org/10.1130/GES01023.1.
Two other 10 April postings are highlighted below and are available at http://geosphere.gsapubs.org/. Representatives of the media may obtain complimentary copies of GEOSPHERE articles by contacting Kea Giles at the address above.
Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GEOSPHERE in articles published. Contact Kea Giles for additional information or assistance.
Non-media requests for articles may be directed to GSA Sales and Service, .
Late Quaternary faulting history of the Carrizal and related faults, La Paz region, Baja California Sur, Mexico
Paul J. Umhoefer et al., School of Earth Sciences and Environmental Sustainability, Northern Arizona University, 625 S. Knoles Drive, Flagstaff, Arizona 86011, USA. Published online 10 April 2014; http://dx.doi.org/10.1130/GES00924.1. Themed issue: Origin and Evolution of the Sierra Nevada and Walker Lane.
From the abstract: The southwest margin of the Gulf of California has an array of active normal faults despite this being an oblique-divergent plate boundary with spreading centers that localized deformation along the plate boundary two to three million years ago. The Carrizal and Centenario faults form the western border fault of the Gulf of California marginal fault system within and south of La Paz Bay, and ~20 to 30 km west of the capital city of La Paz, Baja California Sur, Mexico. Geologic and geomorphic mapping, optically stimulated luminescence (OSL) geochronology, and paleoseismic investigations onshore, compressed high-intensity radar pulse (CHIRP) profiling offshore, and analysis of uplifted marine terraces in the footwall of the offshore Carrizal fault provide some of the first numerical and geometrical constraints on late Pleistocene-Holocene faulting along the Carrizal fault. The onshore Carrizal fault has ruptured with up to ~1 to 2 m of vertical displacement per event, likely producing 6.3 to 6.9 magnitude earthquakes, and at least two to three surface rupturing earthquakes have occurred since 22 thousand years ago…
Geological data extraction from LiDAR 3-D photorealistic models: A case study in an organic-rich mudstone, Eagle Ford Formation, Texas
Daniel Minisini et al., Shell International Exploration and Production Inc., 3333 Highway 6 South, Houston, Texas 77082, USA. Published online 10 April 2014; http://dx.doi.org/10.1130/GES00937.1.
From the abstract: The use of LiDAR (light detection and ranging) 3-D photorealistic outcrop models, combined with traditional sedimentological and structural field data, improves the accuracy and efficiency of qualitative and quantitative characterization of outcrops, which in turn can be used as analogs for reservoir modeling and other geologic purposes. This paper illustrates how geological data extraction from 3-D photorealistic outcrop models can be exploited, and presents some novel workflows that reduce the time needed for post-processing. The extracted data are calibrated with conventional outcrop studies and allow extensive quantitative analyses and detailed statistical examinations of the distribution, dimension, and shape of geological features that can be used to define and build geological models. We present the first statistical characterization based on LiDAR of a set of geological outcrops at centimeter resolution (bed scale) over a distance of 45 km (basin scale). These innovative methods of outcrop visualization and characterization are applied to the Eagle Ford Formation, an important unconventional hydrocarbon play in Texas. The Eagle Ford Formation consists of alternating organic-rich mudstone, limestone, and bentonites; mudstones represent the source and reservoir of the hydrocarbons, limestones control the rock’s brittleness, and bentonites provide time lines for dating and correlating sections. The presented analyses provide empirical relationships that can be applied to better understand geologic processes, to build geologic models, and to reduce uncertainties in exploration and development of hydrocarbon systems.