Field Trip

Friday, May 16, 2014
8:00 am - 7:00 pm
Bird to Hatcher Pass
Prices: Price includes insurance, guidebook, lunch, and dinner at the Hatcher Pass Lodge.
Members: $100
Non-Members: $125 (includes $25 AGS membership)
Students: $40

Financial support for students attending field trips was provided by a generous benefaction to the Alaska Geological Society on behalf of Greg Bernaski (1959-2012).


If you want to be put on a waiting list email Chad Hults - chadcph@gmail.com


Mylonitic migmatite along the Old Glenn Highway. Mafic magmatic root of the Talkeetna Arc.

Castle Mountain Fault along the Hatcher Pass Road. The Eocene Arkose Ridge Formation sandstone is sheared and deformed, causing an unstable road cut.

Late Cretaceous thin-bedded turbidites of the Valdez Group.

Mid-Cretaceous sandstone and conglomerate containing argillite, limestone, and plutonic clasts.

Basalt knocker in Early Cretaceous argillite-matrix mélange
Description: This one day field trip traverses a multi-generational Mesozoic magmatic arc from the accretionary prism to the roots of the arc. We’ll start near Bird in the accretionary prism comprised of Late Cretaceous thin-bedded turbidites of the Valdez Group. Towards Anchorage, we’ll cross the Eagle River thrust fault into an older phase of the accretionary prism, which consists of mid-Cretaceous sandstone and conglomerate around Beluga Point.  West of McHugh Creek, we cross abruptly into Early Cretaceous argillite-matrix mélange that forms the innermost part of the accretionary prism.  North of Anchorage we’ll cross the Border Ranges fault and examine Late Triassic to Early Jurassic mafic and ultramafic intrusive rocks which have been interpreted to represent the roots of the Talkeetna Arc. On our way across the flats towards Hatcher Pass, we’ll be traveling across glacial deposits of the Knik and Matanuska glaciers that subsided during the 1964 earthquake. New LIDAR images for the Matanuska Valley reveal interesting glacial and alluvial geomorphic features and scarps along the Castle Mountain fault. As we start up the road up to Hatcher Pass, we’ll stop to see the Castle Mountain fault where it separates the Paleocene-Eocene fluvial-lacustrine deposits of the Arkose Ridge Formation from the Paleocene-Eocene fluvial-alluvial fan deposits of the Chickaloon and overlying Wishbone Formations.  Snow will prevent us from reaching the pass, but when we reach the end of the road we’ll be surrounded by quartz diorite of the auriferous Late Cretaceous Willow Creek pluton, which represents a magmatic arc built on the accreted Talkeetna arc, and is time-correlative with the Late Cretaceous accretionary prism represented by the Valdez Group at the start of our trip.  We’ll cap off the trip with dinner at the scenic Hatcher Pass Lodge.
Trip Leaders: Sue Karl and Chad Hults - chadcph@gmail.com

2014 AGS
Field Trip


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