Geosciences and Environmental Change Science Center
The Cenozoic Landscape Evolution of the Southern Rocky Mountains Project is a multi-year investigation funded by the National Cooperative Geologic Mapping Program. This project utilizes a combination of geologic mapping, geophysical surveys, basin modeling, and structural, neotectonic, geomorphic, volcanic, stratigraphic, and geochronologic studies to better understand the geologic landscape of the southern Rocky Mountains province.
Amy's postdoctoral research is focused on the temporal, spatial, and genetic relationships between the Platoro and Dulce dike swarms and postcaldera intrusions of the Platoro caldera complex in southern Colorado and northern New Mexico. This work will provide information about magma source(s), magma evolution and the changing stress field in relation to an evolving tectonic setting. The age range and spatial distribution of the Platoro and Dulce dike swarms and the postcaldera intrusions are ideal for assessing changes in magmatic source during the transition between convergent continental arc-related Tertiary volcanism and the extension-related magmatism associated with the Rio Grande rift. Amy will also evaluate the petrogenetic links between postcaldera intrusions of the Platoro caldera complex and regional ore deposition.
Adam's postdoctoral research is focused on Late Pleistocene and Holocene paleoclimate in the San Luis Valley of Colorado and New Mexico as recorded in the the stable and clumped isotope ratios of soil carbonates. These isotope systems record changes in precipitation and temperature through their effects on soil moisture, averaged over 10's to 100's of years. This information is important because it provides independent constraint on changes in past climate which also drove glacier advance and retreat, recorded by numerous moraine deposits in the southern Rocky Mountains, and drove the evolution of alluvial landscapes throughout the San Luis Valley.
Reading the record of past climate and tectonic variability in bedrock and detrital thermochronology
Rocks are cooled over geologic timescales as they are carried to the surface by faulting and erosion. This cooling history is recorded by certain minerals, such as apatite and zircon. Events involving extreme perturbations in temperature that occur over shorter timescales, such as the spread of wildfires or the transport and emplacement of hot fluids, may also be recorded by these minerals. Measuring these thermal histories (thermochronology) can therefore provide quantitative constraints on a host of earth processes. The radioactive decay of trace amounts of uranium and thorium in common accessory minerals produces alpha particles, the retention of which is temperature dependent and can be measured to model the thermal history of the host minerals. Sam is currently working to complete an instrument housed at the USGS in Denver that will be capable of conducting these measurements.
By collecting suites of samples on the up-thrown block of major fault systems we can relate the cooling histories measured with thermochronology to a history of slip on these faults. Sam will be applying this approach to extensional faults in the Rio Grande Rift, with a particular focus on the northern Sangre De Cristo Range, to better understand the development of this system. Unfortunately, thermochronology can't always detect variability in fault behavior that initiated since a few million years ago. However, these changes may be recorded in the morphology of landscapes influenced by faulting. As one example, the production of relief by faulting will steepen river networks that cross these faults until those rivers become so steep that they erode as quickly as faulting produces relief. By coupling models of landform evolution, analysis of landforms, and the long-term slip history revealed by thermochronology he will be able to assemble a complete history of faulting.
November 2, 2016USGS Scientific Investigations Report 2016-5126, Geologic framework, age, and lithologic characteristics of the North Park Formation in North Park, north-central Colorado by Ralph Shroba has recently been published. The report gives a geologic overview of rocks and sediments of late Oligocene and Miocene age locally preserved in and near a large intermontane basin in north-central Colorado. These rocks and sediments once formed a broad and relatively thick sedimentary apron composed chiefly of alluvial-slope deposits. Particle size and sorting data suggest that some of the fine sand, very fine sand, and silt in very fine grained sandstone and siltstone of the North Park Formation may be derived from the erosion of coeval eolian sand and loess in the Browns Park Formation that was transported across the Park Range by westerly or southwesterly winds.
October 28, 2016Project member Rich Madole is lead author of the USGS Scientific Investigations Map Geologic Map of Great Sand Dunes National Park, Colorado. This publication was created to provide the public and the National Park Service with a detailed geologic map and information about the age, origin, and evolution of the landscape of which the Great Sand Dunes National Park is a part, as well as to provide support of archeological studies that were initiated by a range fire in 2000. The Park covers an area of 437 square kilometers (or about 169 square miles), of which 98 percent is blanketed by sediment of Quaternary age, making this publication essentially a surficial geologic map.
October 17, 2016Some field trip highlights from the Geological Society of America 2016 Annual Meeting:
October 1-2, 2016Marieke Dechesne and Chris Martin (geologic consultant from Loveland, Colorado) led a fieldtrip to North Park and Middle Park, Colorado for the Joint Study Groups, a group of professional geologists from the greater Denver area. Focus of the trip was basin evolution, uplift history, and oil and gas resources of the North Park-Middle Park area.
September 8-15, 2016Ren Thompson and Kenzie Turner lead a fieldtrip for University of Oregon faculty and students in the southern Rocky Mountains of northern New Mexico and southern Colorado— an area that records Oligocene to Pleistocene continental arc to rift volcanism. Highlights and photos available on the UO-USGS 2016 Staples Trip: New Mexico and Southern Colorado blog.