Cenozoic Landscape Evolution of the Southern Rocky Mountains

Science Center Objects

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.

The southern Rocky Mountains province extends through northern New Mexico, Colorado, and southern Wyoming. This area has a diverse and protracted geologic history dominated by contractional Laramide deformation, attendant basin sedimentation, and Andean-type arc volcanism during the early Cenozoic. In contrast, the Neogene and Quaternary have been dominated by broadly distributed crustal extension and intra-arc basin formation that are concurrent with Rio Grande rifting. The geologic framework of this part of the Rocky Mountains is well mapped and characterized in some places, but emphasis in these areas is commonly placed on narrow geologic time periods or specific tectonic and orogenic episodes. Remarkably, other regions of this mountain province still have not been adequately mapped and studied to accurately define even temporally limited geologic frameworks. Moreover, linkages between past geologic and climatic processes and events, and paleo to recent landscape change have not been fully and systematically explored across the province.

In this project we explore the Cenozoic geologic history of the southern Rocky Mountains region through an integrated study of:

Geochronologic Investigations

Geophysics and Subsurface Investigation

Laramide Basin Evolution

Plio-Pleistocene Geomorphic Evolution

Tectonics

Volcanism

 

Fundamental Questions

Cenozoic Landscape Evolution of the Southern Rocky Mountains study area

Geographic Range of Proposed Project Area

Some fundamental questions that the project aims to address are:

  1. How have Neogene and younger crustal extensional strain and volcanism associated with Rio Grande rifting been transferred and distributed across the Southern Rocky Mountains?
  2. Have this strain and volcanism been influenced by earlier Laramide structures or subduction-related magmatism?
  3. How have the extensional strain, volcanism, and basin sedimentation controlled the development of landscapes defining the modern physiography of the province?
  4. How have climatically and tectonically driven events of the Neogene and Quaternary influenced establishment and integration of modern drainage patterns?

 

Significance

Many of the objectives of this project also address societal issues related to groundwater management, geothermal and traditional energy resources, and seismic hazards. The Southern Rocky Mountains encompass strategic mineral and fossil fuel reserves, agricultural resources, groundwater aquifers, and headwaters of four major intermontane river drainages that sustain and provide energy for a rapidly growing population that currently numbers more than 5 million just in Colorado alone. Linked by the through-flowing rivers (Rio Grande, Arkansas, Colorado, and Platte) along tectonic troughs of the Rio Grande rift or incised mountain valleys, the vitality of intermountain basin and Front Range communities and economies depends on a growing supply of water extracted from complex aquifers, mostly in rift-basin sediments. The groundwater is controlled by the subsurface geology, including basin aquifer thickness, buried faults and basement structure, and fault configurations at the mountain front recharge zones.

Energy resources, in the form of oil, gas, and geothermal, are found in basins or at their margins throughout the southern Rocky Mountain region. In particular, geologic controls on geothermal resources are poorly understood yet there is new impetus for the Rocky Mountain States to investigate and develop these resources.

Finally, the Rio Grande rift is still considered seismically active even though few historic earthquakes have been recorded. Evidence of large-magnitude Quaternary earthquakes with recurrence intervals of 10–140 ka suggests that these faults could be particularly dangerous. Long periods of seismic quiescence allow active fault scarps to be obscured by erosion and make them difficult to map.

Over three-quarters of the proposed study area is administered as public lands, including Rocky Mountain National Park, Great Sand Dunes National Park, Rio Grande del Norte National Park (est. 2013), Bandelier National Monument, National Forests, Bureau of Land Management lands, and US Fish and Wildlife Service wetlands areas. Each year millions of tourists and outdoor enthusiasts visit and depend on these public lands to recreate and enjoy their natural beauty and resources. Managing critical renewable and non-renewable resources, protecting wildlife and ecosystems, and providing viable recreational opportunities are reliant on understanding the underlying geologic controls on water quality and quantity, mineral deposits, fossil fuel reserves, and landscape and ecosystem stability.

 

Objectives

Cenozoic tectonics, magmatism, surface processes and landscape evolution are linked by geodynamic processes and are manifested geologically at a range of scales. The earth’s surface reflects the complex interplay of global-scale tectonic plate motions, heat flow, mantle anisotropy, crustal heterogeneity, and climate change. The impact of these forces on the earth’s diverse and spatially varying material properties results in a complex response whereby crustal geomorphic evolution can be dramatically influenced by both internal and external factors. The surface expression of tectonic faulting and folding, associated rock uplift, and construction of large volcanic edifices derived from the transient changes in lithospheric heat flow, drives a geomorphic response. This, in concert with climatic influence, can result in dramatic landscape change, including the establishment of new drainage patterns, basin sedimentation rates, and provenance history. Likewise, fault conduits influence emplacement of magma chambers in the shallow crust that, upon eruption, can alter drainage and sedimentation patterns and, in the case of large magmatic fields, influence climate. The primary geologic influences on ecosystem evolution, drainage history, water resources quantity and quality, mineral resource, oil and gas potential, and geohazards are universally linked through coupled surface processes, geomorphic evolution, and geodynamics.

 

Strategy and Approach

This project investigates the geologic framework and evolution of a broad swath of the Southern Rocky Mountains between northern New Mexico and southern Wyoming, focusing on linkages to Cenozoic landscape development. Initial project efforts concentrate on two key areas at opposite ends of the project footprint that have traditionally been viewed as having distinct, contrasting geologic styles and histories:

  • Basins and flanking ranges of the northern Rio Grande rift (northern New Mexico and southern Colorado) dominated by Neogene extensional tectonics, volcanism, and sedimentation and the North-Middle Park region (northern Colorado) dominated by Laramide contractional deformation and sedimentation.
  • The North-Middle Park region (northern Colorado) dominated by Laramide contractional deformation and sedimentation.

Early focus in these two regions builds on geologic mapping and investigations conducted on predecessor, National Cooperative Geologic Mapping Program-funded Rio Grande Basins and Colorado Headwaters Basin projects. Moreover, these initial project foci will result in detailed and comprehensive datasets to compare "end-member" tectonic influences and histories and allow opportunities to document under-recognized transitional and overprinted tectonic and magmatic signatures and attendant landscape changes. Project efforts will eventually expand to other uplifted mountain blocks and basins (or "parks") to similarly investigate and document their local geologic frameworks and their influences on landscape evolution.