Paleoecology and Paleoenvironment of Early Tertiary Alaskan Forests, Matanuska Valley, Alaska

Alaska map

What: This project aims to expose students to methods of paleobiological and historical analysis on a fluvio-lacustrine early Tertiary basin in south-central Alaska. The summer program will consist entirely of fieldwork, with the expectation that some laboratory analyses will be carried out through the academic year 2008-2009.

When: July 1-28, 2008

Where: After travel to the field site, we will spend 3.5 weeks in the Matanuska Valley, Alaska. Our base will be near Sutton, AK. Accommodations will be a combination of tent camping and rustic cabins. Flights should be booked into Anchorage, AK.

Who: Six Keck students. Professors David Sunderlin (Lafayette College) and Chris Williams (Franklin & Marshall College) will lead the trip.

Project Description and Goals

The middle to high latitudes appear to be particularly sensitive to climate change. How the biosphere responds and/or participates in feedback loops with this climate change is the subject of increasing attention in the Earth sciences as it has bearing on predicted future climate/biosphere interactions. As a case study for examining extra-tropical environments living at warmer climate phases in Earth’s history this project will study the Tertiary Matanuska Basin of Alaska. This basin preserves a foreland depositional sequence indicative of fluvio-lacustrine and alluvial terrestrial paleoenvironments. The lowermost unit is the Chickaloon Formation, dominated by coal-bearing and fluvial facies that preserve a diverse plant fossil record. The overlying Wishbone and Arkose Ridge units are interpreted to be higher energy terrestrial facies that indicate continued tectonic activity and the encroachment of extrabasinal depositional regimes as the basin matured (Trop et al., 2003). This Keck study focuses on the paleoenvironmental record of the Chickaloon Formation as told by the sedimentological, stratigraphic, and paleoecological record.

The project goals are to (1) obtain a detailed stratigraphic and sedimentological dataset on the depositional system of the Chickaloon Formation, (2) reconstruct the paleoclimatic history and paleoecological succession of environments in that stratigraphic context, and (3) provide field instruction and primary research experience to a motivated group of undergraduate students.

Student Projects

Figure 2. a. Wishbone Hill field site exposure.

Listed below are potential student projects within the overall project’s goal of assessing the paleoecological and paleoclimate setting of the Matanuska Basin:

  1. Characterization of the leaf and seed fossil assemblages with regard to vertical (time-transgressive) and horizontal (within forest stand) variability.
  2. Analysis of the spatial patterning and internal anatomy of fossil wood stumps and logs. The former analysis will include mapping techniques and the latter will include dendrochronology studies of plant allometry.
  3. Paleoenvironmental reconstruction of the fluvio-lacustrine stratigraphic architecture Matanuska Basin. Detailed mapping of the sedimentology and outcrop-scale stratigraphy across 1.5 km of semi-continuous lateral exposure.
  4. Detailed analysis of interbedded faunal remains within the studied section. Taxonomy, biostratigraphy, and paleoecology of gastropods, bivalves, and (if found) vertebrate remains.
  5. Biogeochemistry of fossilized amber, coalified/charcoalified(?) wood, and paleosols within the depositional environment.
  6. Investigation of wood taphonomy and preservation processes that took place in the Chickaloon sediments using a suite of analytical methods.

Field Conditions

Figure 3. Upright, in situ tree trunk in the Chickaloon Fm at Wishbone Hill. This trunk has 176 rings apparent and stands more than 2.5 meters tall. Preliminary analysis by C. Williams indicates that the wood is taxodiaceous, possibly Metasequoia. Hammer for scale. (photo D. Sunderlin)

Fieldwork for this project will be concentrated at an old coalmine (Fig. 2) exposure in Sutton, Alaska, about 1.5 hours drive north of Anchorage. Additional study of related strata may be made by raft on the Matanuska River or on foot into the Talkeetna Mountains. July weather in south-central Alaska is variable. High temperatures can range from mid 50s to high 80s (F) with lows rarely below 45 F. Rainy and misty days are common and so are active mosquito populations. Both may last for many days at a time. Black and grizzly bears are occasionally present in the field areas and, though it is unlikely, we may unwillingly encounter them. Accommodations will be mostly in tents at the field site with the occasional night in a rustic cabin setting with showers. Food preparation will take place in the field.
Alaska figure 2bAlaska figure 2cAlaska figure 3dAlaska figure 2eAlaska figure 2f

Figures 2. b. Gastropod (Campeloma?) from the Chickaloon Fm., c. Metasequoia sprig, d. Acer(?) samara or “helicopter”, e. unidentified leaf fossil, f. basin landscape reconstruction of the fluvial (Chickaloon Fm.) and alluvial (Wishbone and Arkose Ridge Fms.) depositional facies unconformably overlying the ammonoid-bearing Cretaceous marine Matanuska Fm. (a-e from D. Sunderlin, unpublished, f modified from Trop et al. 2003)

Course Preparation

Students should have completed the junior year and have had at least one course in sedimentology/stratigraphy or paleobiology/paleontology. Previous field experience in a field camp or field research setting is highly desirable. Students should be prepared for working and camping in variable weather and with biting insects. Courses in historical geology, biology, botany, organic chemistry, and/or geomorphology will be helpful.