AAPG Trustee Associates 38th Annual Meeting Field Trip Guide September 11, 2015 Geology of the Colorado Springs Region
Amy Luther and Tara Jonell Louisiana State University
Location map of field trip stops
Colorado road map with box showing location of map below.
Field trip stops.
Stratigraphic Column of the Colorado Springs Area (From Ross et al., 2010)
Paleogeographic setting during the Ancestral Rocky Mountains orogeny (From Abbott and Cook, 2012—Modified from Sweet and Soreghan, 2010)
Map showing the location of the two major Laramide faults in relation to the morning stops
Geologic map of the Garden of the Gods area (From Siddoway et al., 2013)
Geologic cross-section of the Garden of the Gods area (From Siddoway et al., 2013—Modified from Sterne, 2006)
Brief geologic background of the Colorado Springs Region On this fieldtrip, we will get the opportunity to explore the history of the Rocky Mountains from the Proterozoic to the present. The majority of this trip will focus on the Paleozoic and Mesozoic tectonic and depositional history. Exposures at Garden of the Gods, Red Rocks Canyon Open Space, and the Lake Pueblo State Park are amazing snapshots of two major orogenic events and the related depositional history—including in the Western Interior Seaway. We will get the opportunity to discuss all of the exciting research that continues in these areas and how these studies have implications for the structural evolution of orogenic belts both on a grain scale and a regional scale and the how the depositional systems relate to climate and oil migration. To fully appreciate the complete record of Earth’s history in the region, we will also briefly discuss the two prominent features of the Colorado Springs backdrop-the origin of the Proterozoic Pikes Peak batholith and the effects of the 2012 Waldo Canyon Fire on the region. Pikes Peak Granite One of the most striking features of the Colorado Springs landscape are the rising slopes of Pikes Peak, one of Colorado’s famous Fourteeners, or peaks rising above 14,000 ft. Pikes Peak is particularly notable in that the summit lies more than 8,000 ft above downtown Colorado Springs. All topographically high areas of Pikes Peak are part of the Pikes Peak batholith, an incrementally assembled pluton with a current exposure of ~3100 km2. The Pikes Peak batholith was emplaced from ~1.08–1.09 Ga into Proterozoic basement as part of the last, major intrusive Proterozoic episode on the southern edge of the supercontinent Rodinia. These three episodes at ~1.7 Ga, ~1.4 Ga and ~1.0 Ga, intruded successively shallower crustal levels. Pikes Peak batholith contains a suite of plutonic rocks that consists of predominant biotite-amphibole granites with smaller volumes of syenogranite, gabbroic dikes, and pegmatite veins. The batholith was constructed incrementally in three parts: the Buffalo Park, Lost Park, and Pikes Peak intrusive centers. The Ancestral Rockies Mountain Orogeny This Pennsylvanian uplift is related to the collision of North America with South America-Africa which produced the Ouachita-Marathon orogeny (Kluth and Coney, 1981). In this region, there was presumed to be ~10,000 ft of uplift caused by a combination of fault-bounded basins and basement warping (DeVoto, 1980). Suttner et al., 1984 used paleocurrent indicators to show that the granite boulders in the Fountain formation derived from nearby the NW-SE to E-W trending Ute Pass Fault during denudation of the large mountains in the area (see paleogeographic map above). Fountain formation (Atokan to Wolfcampian) is up to 1340 m thick in Garden of the Gods (Milito, 2010). This is a dominantly pebble sandstone with some boulder and cobble conglomerate. The lower 700 m of the Fountain is a maroon, muddy sandstone with massive bedding (Ross et al., 2010). This poorly sorted sandstone contains granite clasts up to 3 cm. Lying above this is a matrix-supported pebble and cobble conglomerate. There are large rip-up clasts of the maroon muddy sandstone and also contains granite boulders up to 20 cm in diameter. Sedimentary structures include load deformation and injection features. The top of the Fountain is a hummocky cross-bedded sandstone with fining-upward sequence. Marine trace fossils are also present. The Fountain formation is commonly interpreted to be an alluvial fan deposit formed at the base of the Ancestral Rocky Mountains. Recently, the base of the Fountain has been reinterpreted to be formed by
mudflows and debris flows (e.g. Ross et al., 2010). The matrix-supported cobbles and poorly-sorted sandstones are not consistent with braided river or alluvial fan deposits. The top of the Fountain is interpreted to be marine based on fossil evidence. The top of the Fountain formation also marks the waning stages of denudation and uplift during the ARM. This also marks a shift in the climate and depositional setting, as we will explore while viewing Permian Lyons Sandstone. The Lyons formation is composed of fine- to medium-grained orthoquartzites to subarkosic sandstones with clay and iron oxide matrix of an aeolian origin. The is a complex of dunes resting on alluvial plain deposits (Fountain Fm.) with near shore/deltaic facies above (Lykins Formation.) The Laramide orogeny From ~80-40 Ma, flat-slab subduction of the Farallon plate at the Western edge of North America resulted in east-west shortening as far inland as Colorado. Reactivation of older faults in the Garden of the Gods area during the Late Cretaceous to Middle Eocene created the Rocky Mountains we see today. Two large-scale Laramide age faults are present in this area—the Rampart Range fault and the Ute Fault (see location map above). The Rampart Range Fault is a north-ne striking, moderately to steeply west dipping thrust fault with minimal displacement in Garden of the Gods that increases to the N (Siddoway, 1999; Sterne, 2006). The Ute Pass fault is the range-bounding fault to the S and W of the Rampart Range fault. Uplift and related denudation youngs from N to S as the Rampart Range slipped during the Cretaceous and Tertiary, whereas slip on the Ute Pass faults occurred during the Paleocene-Eocene boundary. Both Front Range faults in this region have been interpreted to have a blind triangle zone in subsurface with a floor thrust and several backthrusts.
Stop 1: Central Garden Trail at the Garden of the Gods This trail has outcrops of the Pennsylvanian Fountain formation and the Permian Lyons formation. The exposures are all part of the steeply east dipping limb of the Front Range monocline (see geologic map and cross-section above). Recent illite geochronology suggests that the Monocline developed at ~ 57 Âą 3 Ma (Siddoway et al., 2013). The rocks we will look at are cut by a series of backthrusts that have accommodated most of the shortening of the Rampart Range fault zone, with as much ~800 m of displacement reported in the Garden of the Gods (Ross et al, 2010). 1a N. Gateway Rock: The Tower of Babel is cut by one of the backthrusts of the Rampart Range fault. We can see this by walking ~100 yards SW on a dirt path from the parking lot. Here, younger Lyons is thrust on top of the older Fountain formation. This is an anomalous younger-over-older relationship, characteristic of the proposed model for fault slip in a triangle zone as shown in the cross-section. This unique thrust geometry has been proposed for many Laramide fault zones along the Rocky Mountain front. 1b White rock: Permian Lyons formation with strong internal deformation. Iron oxides in the gray Lyons were likely removed by secondary processes, such as reduction by introduced organic matter, followed by redistribution or removal of the reduced iron compounds. Evidence that supports this hypothesis are the presence of oil and organic matter typically in the gray Lyons, the formation of authigenic ferro-sulfides (i.e., pyrite) as a result of the reduction of iron in the presence of petroleum, and there are remnants of iron oxides that do exist in the gray Lyons but are protected as inclusions in secondary quartz overgrowths. These color differences therefore can be used to locate the oil-water contact in the Lyons Formation, with an earlier contact represented by gray,
pyrite- and carbonate-bearing Lyons (old oil region) grading with depth into reddish, oxide-bearing Lyons (old water region). Subsequent Paleogene deformation during the Laramide to create the present anticlinal trap, led to devolatization and formation of bitumen residues in the gray Lyons. Structural geology of Lyons sandstone: Here we are viewing a zone that is within the relays of the fault where the lower and upper Lyons has different deformation mechanisms (Ross et al., 2010). The lower Lyons has only accommodated a small amount of strain with shear fractures and a frictional sliding deformation mechanism. The upper Lyons has accommodated a much larger amount of strain by deforming by grain fracturing and sliding mechanisms. This has resulted in compaction and permeability loss by forming numerous deformation bands. The variability of deformation has been caused by higher porosity as a consequence of hydrocarbon migration. The hydrocarbons created reducing conditions that dissolved the hematite cement and enhanced porosity. 1c Sentinal Spires: Gradational contact between Fountain Formation and the Lyons Sandstone This contact represents a change in climate and the waning tectonism in the region (Abbott and Cook, 2012). The climate becomes more arid with thin sand dunes and some rivers crossing the sandy plain. Ripple marks are visible in this outcrop. The Ancestral Rocky Mountains are no longer high peaks at this time, so the rivers draining the low hills are now low energy and only carry small particles. As we drive back to the visitor’s center, the thick piles of debris on the right side of the bus were created by slip on the Rampart Range.
Stop 2: View from Visitor’s lot The prominent ridges in the foreground are the Fort Hayes member of the Niobrara Formation, the resistant sandstone of the Dakota Group, the Lyons sandstone, and the Fountain Formation. We saw the latter two units earlier and we will see the former at stop 3. In the distance, we have a view of Pike’s Peak, the 1.09 Ga granite uplifted during the Laramide orogeny. Here, we will discuss the Proterozoic emplacement history of the large, looming batholith. If you look to the north of highway 24, we can see the extensive damage and destruction of vegetation done by huge 2012 Waldo Canyon Fire. This fire burned 28.511 square miles of the Pike National forest and 346 homes. Over 32,000 people were evacuated during this 2.5 week fire. We can discuss the effect of this fire and the >$15 million spent to control the flux of sediment now available to devastate the city during frequent flash flooding.
Stop 3: Red Rocks Canyon Open Space (RRCOS) Red Rocks Canyon has a system of trails that cross through the same section as Garden of the Gods. Although we are in the same location structurally (steep limb of the monocline), RRCOS rocks have not been cut and internally deformed by slip on the Rampart Range fault zone so primary structures are well preserved. At stop 3, we will get the chance to view and discuss the Cretaceous rocks deposited in the Western Interior Seaway (see map below) as we walk down section through two prominent ridges—the Ft. Hayes Limestone member of the Niobrara Formation with the Codell Sandstone of the Benton Group and the Dakota Sandstone. The Ft. Hayes member of the Niobrara formation is in the exposed wall looking south along strike. This is a mostly micritic limestone that contains many inoceramid fossils.
The Benton Group is interpreted to have been deposited during the largest transgression in the Western Interior Seaway. The members are Codell sandstone, Carlisle shale, Greenhorn limestone, and Graneros shale, but most members are thin and/or poorly exposed in this part of Colorado. The long wall is Codell Sandstone with Fe-concretions, beautiful ripple marks, is highly fossiliferous (shark and fish teeth, ammonites, and inoceramids) and bioturbated. We can see thin ash beds in the shaley units of the Benton Group (Milito, 2010). The next ridge we come to on the trail is the Dakota sandstone which was deposited in a regressional delta in the seaway. In the Colorado Springs area, the Dakota is fossiliferous and contains tree trunks, roots, conifer cones, pollen, ferns, and leaf imprints. There are also trace fossils related to ankylosaur and iguanadontid dinosaurs (Milito, 2010). For those who are interested, we can walk to the top of the hill and view dinosaur footprints in the Dakota formation. While we walk through these units, we can also see the angular unconformity between the Mesozoic section and the Paleogene Mesa Gravels which sit on top. This is a 10 m thick veneer that is the pediment surface and a great analog for the Fountain Formation. If time permits, we can head to the west side of the park to view undeformed Lyons and Fountain formation.
Extent of the Western Interior Seaway at ~100 Ma. (From USGS)
Cenomanian-Turonian Boundary—Lake Pueblo State Park Stop 4: GSSP Pin Here, we will view the GSSP pin. A GSSP is the Global Boundary Stratotype Section and Point that an international community agrees is the point that defines the lower boundary of a stage in the timescale. West Pueblo Lake State Park is the location of the Cenomanian-Turonian boundary (93.9 Ma) which was ratified in 2003 (Kennedy et al., 2005). As is typical of a GSSP, the boundary is based on fossils found in bed 86 of the Bridge Creek Limestone Member of the Greenhorn Limestone Formation. This limestone contains the ammonite FAD Watinoceras devonense (figure below). Bed 86 also contains the inoceramid puebloensis (figure below) and dinoflagellate. The age of the Bridge Creek Limestone is defined by bentonites that yield ages of 93 to 93.5 Ma (Kennedy et al., 2005). The unit consists of diagenetically modified limestone-marl and fossiliferous biomicrites that was deposited in Milankovitch cycles. The unit spans 10’s of 1000s of square kilometers across Kansas, New Mexico, Utah, Arizona and Colorado and was deposited in the Western Interior Seaway. The Cenomanian-Turonian boundary marks a large extinction event caused by OAEII (the second oceanic anoxic event). This is a period of high organic matter burial coupled with a high positive excursion in the carbon isotope record (see carbon isotope data below). In the Western Interior, Harries and Little (1999) reported the extinction of 79% of macro-invertebrate species and Elder (1989) of 74% of ammonoid species. Some controversy exists about the widespread significance of this extinction event (e.g. Monnet, 2009). It has also been proposed that global warming and sea level rise played a role in the local changes in the ammonoid diversity (e.g. Monnet, 2009).
Stop 5: Viewpoint of official GSSP location From this vantage point we can see the published GSSP location and the Rock Canyon anticline. On the trail, we can look for the significant ammonites and inoceramids from the Turonian (as shown in the figures below). Photographs below show the location of bed 86 in the railroad cut.
Stop 6: Liberty point The Greenhorn Formation is correlative to the Eagle Ford Formation. According to a study in West Texas (Donovan et al., 2012), the C-T boundary can be found in the K65 sequence boundary of an unnamed member of the Upper Eagle Ford Formation (see correlation below). This unit also correlates to the Ledgy Unit of Freeman (1968). In West Texas, the top of the Cenomanian is a grainstone/packstone interbedded with medium gray carbonate mudstones. The boundary is marked by enriched TOC (1-3%), U, HI, and has the positive carbon isotope (δ13C) associated with the OAEII. The Turonian rocks also show the first appearance of the microfossil Quadrum Gartneri. This boundary marks a change from a transgressive to a highstand system in West Texas.
From Monnet, 2009
Photographs of the GSSP at the base of bed 86 from the Bridge Creek Limestone-- we can view these from an overlook at stop 2. Photographs are from Kennedy et al., 2005.
Eagle Ford Group correlation diagram showing the C-T boundary. From Donovan et al., 2012
References De Voto, R.H., 1980, Pennsylvanian stratigraphy and history of Colorado, in Kent, H.C., and Porter, K.W., eds., Colorado Geology: Denver, Colorado, Rocky Mountain Association of Geologists 1980 Symposium, p. 71–101. Donovan, A.D., Staerker, T.S., Pramudito, A., Weiguo, L., Corbett, M. J., Lowery, C. M., Romero, A.M., and Gardner, R.D., 2012, The Eagle Ford outcrops of West Texas: A laboratory for understanding heterogeneities within unconventional mudstone reservoirs, GCAGS Journal, v. 1, 162-185. Elder, W.P., 1988, The paleoecology of the Cenomanian–Turonian (Cretaceous) stage boundary extinctions at Black Mesa, Arizona, Palaios, 2, pp. 24–40. Harries, P.J., and Little, C.T.S, 1999, The early Toarcian (Early Jurassic) and the Cenomanian–Turonian (Late Cretaceous) mass extinctions: similarities and contrasts, Palaeogeogr. Palaeoclimatol. Palaeoecol., 154, pp. 39–66. Kluth, C.F., and Coney, P.J., 1981, Plate tectonics of the Ancestral Rocky Mountains, Geology, v. 9, 10-15. Kennedy, W.J., Walaszczyk, I., and Cobban, W.A (2005) The Global Boundary Stratotype Section and Point for the base of the Turonian Stage of the Cretaceous: Pueblo, Colorado, U.S.A., Episodes, vol. 28, no. 2, p 93-104. Lee, M. K., & Bethke, C. M. (1994). Groundwater flow, late cementation, and petroleum accumulation in the Permian Lyons Sandstone, Denver Basin.AAPG bulletin, 78(2), 217-237. Levandowski, D. W., Kaley, M. E., Silverman, S. R., & Smalley, R. G. (1973). Cementation in Lyons Sandstone and its role in oil accumulation, Denver Basin, Colorado. AAPG Bulletin, 57(11), 2217-2244. Milito, S., 2010, A survey of fossils and geology of Red Rock Canyon Open Space, Colorado Springs, Colorado: The Mountain Geologist, v. 47, p. 1–14. Monnet, 2009, The Cenomanian–Turonian boundary mass extinction (Late Cretaceous): New insights from ammonoid biodiversity patterns of Europe, Tunisia and the Western Interior (North America), Palaeogeography, Palaeoclimatology, Palaeoecology, vol. 282, 88-104. doi:10.1016/j.palaeo.2009.08.014 Ross, M.R., Hoesch, W.A., Austin, S.A., Whitmore, J.H., and Clarey, T.L., 2010, Garden of the Gods at Colorado Springs: Paleozoic and Mesozoic sedimentation and tectonics, in Morgan, L.A., and Quane, S.L., eds., Through the Generations: Geologic and Anthropogenic Field Excursions in the Rocky Mountains from Modern to Ancient: Geological Society of America Field Guide 18, p. 77–93. Siddoway, C., Myrow, P., and Fitz-Díaz, E., 2013, Strata, structures, and enduring enigmas: A 125th Anniversary appraisal of Colorado Springs geology, in Abbott ,L.D., and Hancock, G.S., eds., Classic Concepts and New Directions: Exploring 125 Years of GSA Discoveries in the Rocky Mountain Region: Geological Society of America Field Guide 33, p. 331–356, doi:10.1130/2013.0033(13). Smith, D. R., Noblett, J., Wobus, R. A., Unruh, D., Douglass, J., Beane, R., ... & Stewart, J. (1999). Petrology and geochemistry of late-stage intrusions of the A-type, mid-Proterozoic Pikes Peak batholith (Central Colorado, USA): implications for petrogenetic models. Precambrian Research, 98(3), 271-305. Sterne, E. J., 2006, Stacked, “Evolved” Triangle Zones Along the Southeastern Flank of the Colorado Front Range, The Mountain Geologist, Vol. 43 No. 1 (January 2006), p 65-92. Suttner, L.J., Langford, R.P., and O’Connell, A.F., 1984, New interpretation of the stratigraphic relationship between the Fountain Formation and its Glen Eyrie Member, in Suttner, L.J., ed., Sedimentology of the Fountain Fan-Delta complex near Manitou Springs and Cañon City, Colorado: Society of Economic Paleontologists and Mineralogists Field Guidebook, p. 31–61. Sweet, D.E., and Soreghan, G.S., 2010, Late Paleozoic tectonics and paleogeography of the ancestral Front Range: Structural, stratigraphic, and sedimentologic evidence from the Fountain Formation (Manitou Springs, Colorado): Geological Society of America Bulletin, v. 122, p. 575–594, doi:10.1130/B26554.1.
Walker, T. R., & Harms, J. C. (1972). Eolian origin of flagstone beds, Lyons Sandstone (Permian), type area, Boulder County, Colorado. The Mountain Geologist. Wobus, R A., and Hutchinson, R. M., 1988, Proterozoic plutons and pegmatites of the Pikes Peak region, Colorado, in Geological Society of America Centennial Meeting Field Wp Guidebook: Denver, Colorado, Geological Society of America, p. 35-42.