GEOL 332 Lab 6
Mad River Slough
Methods
Pritchard (2004) studied cores in Arcata Bay. Patton (2004) also studied sediment cores in Humboldt Bay, though in southern Humboldt Bay, along Hookton Slough. If one would want to take a look at an independent data set from the same region, this would be a good candidate. A peer review article from Valentine et al. (2012) presents even more data for the entire Humboldt Bay region. All these literature sources are linked below. Please refer to Patton (2004), Pritchard (2004), and Valentine et al. (2012) for the methods used in this study.
Results
Included are the results from the laboratory. Unfortunately, the lab assistant lost track of which sample was submitted by which team. Maybe if we had paid them more money, they would have been more careful. Due to this, they have combined the results from all the analyses. For some unknown reason, the depths have been normalized to a single representative core.
Here is Figure 1 from Chad Pritchard’s HSU Geology MS thesis that shows how different vertically restricted tidal zones extend vertically (in m above two datums, NAVD88 and MTL). These three ecological zones are referred to in the diatom paleoecologic analyses plotted in the results Figure 2.
Paleoecologic Analyses
Figure 2 showsresults from the diatom paleoecologic analysis. The composite core is plotted on the left, with sedimentary materials plotted with patterns shown in the legend. On the right, the vertically restricted ecological zones are plotted on the horizontal axis and depth is plotted (cm) on the vertical axis. The horizontal axis is plotted using the Brackish Intertidal Diatom Index (BIDI; Patton, 2004; Pritchard, 2004). The depths shown in these results are composite results from both cores that were collected for this lab. We will need to look at the stratigraphic units as they match the core figures in this report. For example, the clear upper contact of the peat is at a core depth of 116 cm (this was ~96 cm in one of our cores and ~125 cm in the other core).
Age Analyses
Age results were also mixed up. Not only that, but the age results were somehow listed in a table from Pritchard (2004). They are attributed to both Valentine (1992) and Carver et al. (1992). The peat in our cores that has a clear upper contact, and an overlying blue-gray mud, is designated Sa, the Youngest Buried Soil.
References:
Patton, J. R., 2004. Late Holocene Coseismic Subsidence and Coincident Tsunamis, Southern Cascadia Subduction Zone, Hookton Slough, Wigi (Humboldt Bay), California, M.S. Thesis, Humboldt State University, College of Natural Resources, Department of Geology, 76 p.
Pritchard, C. 2004. Late Holocene Relative Sea-Level Changes, Arcata Bay, California: Evaluation of Freshwater Syncline Movement Using Coseismically Buried Soil Horizons, M.S. Thesis, Humboldt State University, College of Natural Resources, Department of Geology, 64 p.
Valentine, D. W., Keller, E. A., Carver, G. A., Li, W., Manhart, C., and Simms, A. R., 2012, Paleoseismicity of the Southern End of the Cascadia Subduction Zone, Northwestern California: BSSA, v. 102, no. 3, p. 1059-1078.
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