Announcement of GSA Field Trip in Colorado, examining basement-hosted injectites, IAA constraints on Laramide deformation, and sedimentological records of environmental change
Trip Title: Strata, structures and enduring enigmas: GSA125th Anniversary appraisal of Colorado Springs geology
Dates: Oct. 31 – Nov. 1, 2013. Post-meeting trip following Annual Meeting of GSA.
Trip Leaders: Christine Siddoway & Paul Myrow / Colorado College, and Elisa Fitz Díaz / University of Michigan
Contact: [log in to unmask]
Registration information: http://community.geosociety.org/2013AnnualMeeting/Home
FIELD TRIP HIGHLIGHTS
• sedimentological records of environmental change within the Paleozoic stratigraphic succession • sediment gravity deposits and crystalline-hosted sandstone dike* array (injectites), an integrated model
• 40Ar/39Ar illite age analysis for time of major faults associated with the Front Range monocline
• structural geology of Garden of the Gods
• one-night accommodation at historic Cliff House in Manitou Springs, CO, www.thecliffhouse.com
• cost for two day trip: US$187
• Abstract submission and conference registration are at: http://community.geosociety.org/2013AnnualMeeting/Home/ .
• If you are intrigued: read more, below!
The field trip explores advances in understanding of persistent geological problems in the Colorado Springs area, in commemoration of the GSA’s 125th Anniversary Celebration, Advances in the Geosciences. The Great Unconformity is of heightened contemporary interest because of new insights into the global significance of the feature and the consequences of the effects of deep, intense chemical weathering for ocean chemistry at the time appearance of multicellular life (Peters and Gaines, 2012). Evidence of multicellular life, and of marine incursion, comes from Teichichnus and Paleophycus burrows in Sawatch Sandstone. The appearance of glauconitic tidal dune deposits (Myrow et al., 1998) due to amplification of tidal currents suggests the influence of the geometry of the transgressed landscape upon rising relative sea level and local ocean chemistry at this locality. A subsequent drop in sea level is recorded by paleokarst breccia along an unconformity surface that marks a sharp stratigraphic transition from Paleozoic carbonates to clastic rocks of the Fountain Formation, prior to onset of the Ancestral Rockies orogeny.
One of the most vexing geological issues to be examined on this trip is the mode and timing of emplacement of granite- and gneiss- hosted sandstone along the Ute Pass fault (Kost, 1984; Keller et al., 2005; Temple et al., 2007; Freedman et al. 2012; Dulin and Elmore, 2012). The sandstone dikes and tabular bodies attracted the notice of early geologists in the Front Range (Cross, 1894; Crosby, 1897) and abroad (GSBJapan, 1893), but for more than a century there has been poor means to establish the time of sandstone emplacement with certainty because the dikes consist dominantly of quartz, are devoid of fossils, were emplaced within Proterozoic crystalline rock, and are of uncertain provenance. Detrital zircon geochronology (Siddoway, unpublished) and rock magnetic characteristics, including anisotropy of magnetic susceptibility (Freedman et al., 2012), now constrain both age and emplacement mechanism.
A final problem in the Rocky Mountain foreland is the specific timing of faulting and development of monocline structures within the broad span of the Laramide orogeny. Painstaking clay mineral separation and 40Ar/39Ar illite age analysis of fault gouge (e.g. van der Pliujm et al., 2001 and 2006; Haines and van der Pluijm, 2008) offer constraints on the precise timing of Laramide fault and fold development, with acquisition of ages that may be compared to the refined lithostratigraphy of synorogenic sediments in Laramide basins (e.g. Obradovitch et al. 2002). The field trip provides context for the IAA results at Garden of the Gods Park, where segmented top-to-west reverse faults and penetrative deformation bands are now understood to be fault linkage and relay structures (Steven A.F. Smith, unpublished) that have so far been little known and poorly documented in contractional settings.
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