Mapping Projects in the Great Outdoors
Healy – northern foothills of the Alaska Range
The first project outside of Fairbanks takes us south to the foothills of the Alaska Range near the town of Healy. We will encounter metamorphic and young, barely lithified, sedimentary rocks, mainly conglomerate, sandstone and coal. The coherent stratigraphy and modest structural complications makes this area ideal for recognizing contacts between units, and relating 3D geology to a 2D map. We will practice drawing and interpolating geologic contacts, creating geologic cross-sections and identifying structures based on exposed and inferred geology.
Impressions from Healy
Red Rock Canyon - Central Alaska Range
30 miles south of Delta Junction along the Richardson Highway, the metamorphic and igneous rocks of Red Rock Canyon are located immediately to the south of the Denali Fault, one of the major tectonic structures in Alaska that marks the boundary between ancestral North America (Yukon-Tanana Terrane) and accreted terranes and volcanic arcs (Wrangellia Composite Terrane). Tectonic activity south of the Denali fault resulted in juxtaposition of volcanic rocks with mica schist along the Broxon Gulch Thrust, which is prominently exposed in the mapping area. We can also observe colorful hydrothermal alteration and mineralization from which the area has gotten its name.
You will learn how to use digital tools to map with the StraboSpot app and an iPad mini. With the StraboSpot data base you will create and manage your own mapping project and create a geologic map.
Impressions from Red Rock Canyon
Limestone Gap – Talkeetna Mountains
The capstone project is located in the eastern Talkeetna Mountains. Flying out of Sheep Mountain along the Glenn Highway with a small bush plane, the campsite of Limestone Gap is located on a meadow at 5000 feet elevation. For the next two and a half weeks our little camp, a cook tent and two office tents surrounded by a ring of private tents, will call this magnificent tundra landscape home.
The conditions for mapping are ideal: no need to worry about breaking trail through bush, the geology is well-exposed. The section consists of a Late Jurassic to Cretaceous mostly marine sequence, including black shales of basin origin, storm deposits, and lagoonal or non-marine calcareous clastic rocks. The section is unconformably overlain by a thick section of Tertiary basalts. Basaltic dikes related to the extrusive rocks intrude the clastic section. The sedimentary rocks are highly fossiliferous; ammonites, belemnites, and bivalves are common in parts of the section. The area is located near the eastern limits of the Castle Mountain - Caribou fault system of south-central Alaska, and the layered rocks are faulted and folded in patterns that are a challenge for students to map and explain.
Work in the area begins with measuring and describing several stratigraphic sections, defining map units, and interpreting the depositional history. The remainder of work at Limestone Gap is devoted to completing a geologic map of the 5 km x 6 km study area at a scale of 1:10,000. The structure of the area is diverse and complex, but well-defined marker units, good exposures, and easily negotiated terrain allow students to focus their efforts on locating and tracing contacts on their maps. Students must map contacts of folded and faulted units, faults, and fold axial surfaces, identify different types of faults, and evaluate whether their maps make geologic sense. The conclusion of the project involves compilation of a complete map, preparation of cross sections, interpretation of geologic history based on the mapped cross-cutting relations, and preparation of a report.
Impressions from Limestone Gap