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Mancos Shale Landscapes: Science and Management of Black Shale Terrains

A Regional Partnership Project: U.S. Geological Survey (USGS) - Bureau of Land Management (BLM) - Bureau of Reclamation (BOR)

Photo of outcrop of Mancos Shale Formation.
Photo of Mancos Shale Formation

Project Objectives

The broad objectives of this project were (1) to use science to help define some of the issues requiring the attention of science, resource, and land-use managers who deal with black shale terrains, (2) to provide applicable, scientifically valid, information that can be used to formulate resource and land-use management policies for Mancos Shale landscapes and (3) to assure that the information provided is transportable/applicable to black shale landscapes that are not specifically studied. In some cases conflicting scientific data and interpretation caused difficulties in determining when an issue is a problem or not. For instance, there was debate about the toxic affects of selenium on fish communities in the Upper Colorado River Basin. This project or a related one strived to resolve that issue and, through on-going discussion between managers and scientists, tried to help differentiate between those issues that are truly problematic and those that are not.

In the long-term, the project contributed to the development of predictive models that can be used to evaluate black shale landscapes in terms of their economic resource potential and their environmental sensitivity. Short-term (5 year) objectives included:

  1. Maintenance and extension of the communication between project scientists and personnel (both managers and scientists) of land management agencies such as BLM, BOR, and Fish and Wildlife Service, and other stakeholders. Many of the activities were the outgrowth and continuation of a BLM-USGS cooperative project, “Developing Coordinated Science Activities in Support of Land Management in the Mancos Shale Badlands of the Gunnison Gorge National Conservation Area”.
  2. Development of a model describing the erosion of Mancos Shale. Several tasks developed the data necessary to understand (a) the processes that result in the physical and chemical erosion of the Mancos Shale and (b) the affects of changes in land use on those erosional processes. This effort resulted in the cataloging of landforms developed on the Mancos Shale in the Gunnison Gorge National Conservation Area.
  3. Documentation of the spatial distribution (background levels) of environmentally sensitive elements (ESE) and economically important elements in the Mancos Shale. The critical issues of metal and ESE sources, why elements are concentrated in some black shale sequences and not in others, the spatial and temporal distribution of elements (the geochemical framework), and the mineralogical residence of ESE were addressed in this objective, which provided much of the requisite data for the project's modeling efforts.
  4. Construction of a model describing pedogenesis of the Mancos Shale. This objective focused on examining the quantitative movement of elements during the development of soil on the Mancos Shale; asking the questions of how and in what quantities are ESE and related elements concentrated or depleted in Mancos soils.
  5. Comparison of the Mancos Shale with other black shale sequences. Understanding the genesis of black shale-hosted ore deposits and the distribution/bioavailability of potential toxicants was based on understanding the genesis of the multiple types of black shale.
  6. Investigation of the selenium toxicity on fish populations in the Upper Colorado River Basin. Current selenium levels and historic levels in fish and river sediments helped to evaluate the modern and historic affects of selenium on the health of aquatic populations of the Colorado River and its tributaries.
  7. Development of effective information transfer and visualization methodologies. Visualization of scientific information in a manner that permits the user to rapidly and effectively assimilate complex results was used not only to communicate with stakeholders but was used as a research tool for modeling landscape evolution.

Relevance & Impact

Responsible stewardship of lands is a primary goal of many federal, state, and local government agencies as well as non-government organizations (NGO) and citizen groups. In western Colorado and eastern Utah much of that land is underlain by the Cretaceous Mancos Shale. During the last few decades, land use and water-quality issues related to Mancos Landscapes have risen in prominence in the West Slope area of Colorado and parts of eastern Utah. Many immediate issues of concern to land managers are related to specific, toxicants such as selenium and salinity. Scientifically defensible information is required by land managers in order to formulate responsible land-use management policies. Responsible stewardship and assessment of mineral and energy resources is also a primary goal of many organizations, including the USGS. To those ends, understanding the processes responsible for the concentration/dispersion and spatial distribution of environmentally sensitive elements (ESE) and economically important elements in the Mancos Shale is imperative.

Such an understanding will help appropriate organizations formulate policy to alleviate problems that result in a variety of negative impacts, several of which are within the purview of legislative actions. Currently, the primer problem is the salinity of the Colorado River, which results in an annual cost of approximately 330 million dollars (U.S. Department of the Interior, 2001). Apparently more than half of the salt load originates in the Upper Colorado River Basin and a significant portion of that load can be related to Mancos Shale landscapes. Selenium, thought to originate from the Mancos Shale, has lead to the non-compliance with the Clean Water Act of portions of the Uncompahgre River and tributaries (originating in the Grand Valley) of the Colorado River, resulting in the mandate that Se loading be reduced. Additionally, the Se is suspected of being a contributing cause of reduced populations of several endangered native Colorado fish species.

Improved understanding of metal and ESE sequestration in black shale sequences will help improve National and global assessments of mineral and energy resources. Large areas of the U.S. are underlain by black shale, some of which have been exploited for energy resources and to a limited extent for mineral resources. However, new concepts on the genesis of world-class, black shale-hosted, mineral deposits coupled with this project's anticipated contribution to understanding metal sources and the processes responsible for metal sequestration will facilitate improved mineral resource assessments. Further, an increased understanding of ESE and other trace element dispersion processes and the resulting geochemical patterns will aid in mineral exploration, resource assessment, and environmental assessments of black shale landscapes.

Much of this project's work directly addressed expressed needs of USGS science programs, data/information gaps and requests for input by the Bureau of Land Management, Bureau of Reclamation, Fish and Wildlife Services, the Colorado River Basin Salinity Control Program, and the Gunnison Basin Selenium Task Force.

Outcome from the mapping portion of this project was actively used to help constrain hypotheses describing the distribution and availability of contaminants such as Se and salinity that may be stratigraphically controlled. Additionally, the preliminary mapping wa used to guide geochemical sampling tasks and to aid in the definition of flight lines for a NASA flown MASTER (multispectral mapping of surface mineralogy) mission over the Gunnison Gorge National Conservation Area (GGNCA).

Project members worked with local NGOs (on at least a monthly basis) to help understand the selenium issues related to both natural and anthropogenetic impacts on Mancos Shale landscapes. Paul von Guerard served as a consultant to the Salinity Control Forum and was a member of their ad hoc selenium committee.

Project Contact

Richard Grauch
Phone: 303-236-5551
Email: Email Richard Grauch

Mineral Resources Program
Eastern Central Western Alaska Minerals Information Crustal Geophysics and Geochemistry Spatial Data

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