Sedimentology of the Catherine Creek Lane Gravels, Northeast Oregon

Adam Isaacson
Science Department, Badgley Hall, Eastern Oregon University, La Grande, OR 97850

Abstract

The ~200-foot thick Catherine Creek Lane gravel outcrop is well-weathered at the base and the degree of weathering decreases toward the top of the outcrop.  The average size of the gravels coarsens upward, reaching cobble and boulder sizes near the top of the gravels.  The average maximum projection sphericity index of the gravels is typical of stream gravels and imbrication measurements suggest a northward paleocurrent direction.  The composition of the gravels changes upward from chert-rich to plutonic rock fragment-rich to volcanic rock-rich.  The gravels may be related to former drainages of the Powder River or Catherine Creek or possibly to spillover events from Tertiary Lake Idaho.  The age of the gravels remains uncertain, although the vertical variations in the Catherine Creek Lane gravels appear to match similar variations in gravel deposition in the nearby Grande Ronde Valley between ~6.5-4 Ma, suggesting the influence of regional tectonic activity.

Introduction

The uplift of the mountains in northeast Oregon over the past 10 m.y. has caused significant changes in the drainage networks in the region.  Livingston (1928) attempted to decipher the history of the Snake River based on its tributary streams and their relation to faulting.  He hypothesized that the Powder River formerly continued northward rather than turning abruptly to the southeast and flowing toward the Snake River.  Livingston also suggested that Catherine Creek’s original channel, after leaving the main Wallowa Range, was almost due south through “The Park” into what is now the Powder River until rising fault blocks in this area diverted its waters in a northwesterly direction through High Valley to Cove, Oregon and then to its present course toward Union, Oregon.

This study focuses on an intriguing outcrop of gravels located 11.5 mi south of Union, Oregon.  These gravels, informally called the “Catherine Creek Lane gravels” in this paper, are located along Oregon Highway 203 between Catherine Creek Lane (GPS coordinates:  45°07.361’N, 117°41.950’W; Elevation:  3390 ft) and Frazier Mountain Road.  The top of the gravel unit along the road is located approximately 0.2 mi. south of milepost 12(GPS coordinates: 45°06.828’N, 117°41.521’W; Elevation:  3635 ft (Fig. 1).

Figure 1.  Outcrop map and cross-section of the portion of the Catherine Creek Lane gravels exposed above Oregon Highway 203 between Union and Medical Springs, Oregon, in section 21, T. 5 S., R. 41 E. on the Medical Springs 1:24,000 topographic map quadrangle.  A, B,C, D and E represent measured profiles along which samples were collected.

Methods

A reconnaissance of the Catherine Creek Lane gravel outcrop was conducted by Mark Ferns and Vicki McConnell (Oregon Department of Geology and Mineral Industries) and Jay Van Tassell and Tammy Dunlavey (Eastern Oregon University ) in October 2000.  The outcrop was surveyed using a Brunton compass, tape measure and Casio altimeter in April 2001 with additional measurements made during the following summer.  Topographic profiles at 5 locations along the outcrop were made using a bubble level, tape measure and surveying rod and samples were collected at intervals along these profiles.  Imbrication measurements were made of pebbles and cobbles in the well-exposed gravels near milepost 12, plotted and analyzed using the techniques described in Tucker (1982). In the lab, the sediment samples were split into subsamples using a Humboldt sample splitter and the sand was separated by wet-sieving through a 63 micron sieve.  The size, sphericity and composition of the largest cobbles in each sample were measured and the color, sorting, rounding, surface textures and composition of the sand fractions were analyzed using a Nikon binocular microscope.

Description of the Gravels

The gravel outcrop is made up mostly of gravels mixed with reddish-brown, yellowish-brown and gray sand.  The unit is well-weathered at the base and the degree of weathering decreases toward the top of the outcrop.  The average size of the gravels coarsens upward, reaching cobble and boulder sizes near the top of the gravels near milepost 12.  The sequence has an exposed thickness of ~200 ft. (Fig. 1).  No attempt was made to sample the gravel below the road level or across the creek.

The average maximum projection sphericity index of the gravels is 0.67.  This sphericity falls in the range typical of stream gravels (Folk, 1974).  The imbrication measurements range from 135°-210° with a mean direction of 181° (Fig. 2).  This suggests a paleocurrent direction to the north (1°).  An F-test suggests that the mean direction is significantly different from that of a circular distribution, but the data suggests that the distribution may be bimodal, with a pattern suggesting flow directions to the northeast and northwest (or pebbles oriented both parallel and perpendicular to the main flow direction). The gravels include volcanic rocks (basalt, andesite, dacite), plutonic rocks (tonalite, gabbro and granite) and metamorphic rocks (greenstone, metachert), plus quartz (including a 3 mm high hexagonal dipyramid of clear quartz), hornblende, muscovite, jasper, mica and other minerals.

Figure 2.  Imbrication measurements from the upper part of the Catherine Creek Lane gravels near milepost 12.  The average of the imbrication measurements (181°) indicates an overall northward paleocurrent direction, but note the hint of bimodality in the measurements.  “n” is the number of current measurements.

       There is a strong vertical variation in the composition of the gravels.  Chert (“metaquartzite”) is abundant in the lower part of the outcrop, along with iron-stained quartz and minor hornblende and other minerals.  Plutonic rock fragments are common in the middle of the outcrop and the gravels are composed almost entirely of volcanic rock fragments at the top of outcrop (Fig.3, 4).

  Figure 3.  Vertical variations in the types of gravel clasts in the Catherine Creek Lanegravel outcrop.  Note the change from gravels rich in chert near the bottom of the outcrop to plutonic rock-rich gravels in the middle to volcanic rock fragments at the top of the outcrop.  The base of the outcrop is strongly weathered, but the presence of abundant quartz suggests that it may have contained abundant granitic fragments prior to weathering.

Figure 4.  Diagram, based on the variations shown in Figure 3, showing the overall vertical variations in the percentages of chert, plutonic rock fragments (mostly tonalite) and volcanic rock fragments (basalt, andesite and dacite) in the Catherine Creek Lane gravels.

Discussion:  The Origin of the Gravels and their Age

Several possibilities exist for the origin of the Catherine Creek Lane gravels.

1.  The gravels were deposited by the tributary of Catherine Creek which is next to the gravels:  This hypothesis does not explain the abundance of chert and diorite in the gravels, which are not exposed in the drainage area above the gravels, but it could explain the volcanic rock-rich gravels in the upper part of the outcrop.

2.  The gravels were deposited along a former path of Catherine Creek:  This hypothesis is not supported by the paleoflow measurements, although there is some topographic evidence that it is possible that Catherine Creek may have flowed to the southeast of the gravel outcrop and then turned toward the northwest at a previous time.  The abundant plutonic rock fragments in the middle portion of the gravels could have come from the upper Catherine Creek drainage.  Chert and jasper are not common in the present-day Catherine Creek drainage (Vicki McConnell, 2001, personal communication), so this hypothesis would not be applicable to the lower portion of the gravels unless these represent reworking of Tertiary gravel deposits which have since been eroded from the top of the rocks in the headwaters of Catherine Creek.

3.  The gravels were deposited by spillover deposits from Lake Idaho:  Jenks and Bonnichsen (1989) suggested that Tertiary Lake Idaho, the great lake that episodically occupied the western Snake River Plain during the late Miocene and Pliocene, may have reached a current elevation of 3800 ft. and spilled over into the Powder River (Baker), Grande Ronde and Wallowa Valleys.  Since the elevation of the Catherine Creek Lane gravels is below 3800 ft. and the pass above the gravels (“The Summit”) is at 4158 ft., only a few hundred feet above the Lake Idaho shoreline level, this hypothesis would help explain the presence of rock types such as the chert, which does not come from the present drainage area, as well as the volcanic rocks, which could have been ripped out of local outcrops in the later stages of the spillover from Lake Idaho.  It is not clear why spillover would sort out the chert and granite rock types present in the gravel deposit, however.

4.  The gravels were deposited by a northwest-flowing river (The Powder River?) prior to the uplift of the fault blocks in the area of the gravel outcrop:  This would explain the abundance of metachert, which may have a source area in the Elkhorn Mountains to the south (or farther to the east), as well as the northward paleoflow direction.

       None of these hypotheses by itself appears to satisfactorily explain all of the overall vertical variations in composition in the Catherine Creek gravels, although combinations may.  Perhaps the lower, chert-rich, portions of the outcrop represent deposits of a river flowing northward from the Elkhorns or spillover from Lake Idaho, while the middle, granitic-rich, portions represent deposits from a former course of Catherine Creek established as faulting blocked the former north-flowing river as it flowed out of the Wallowa Mountains.  The upper, volcanic-rich part of the outcrop may represent local drainages after faulting diverted Catherine Creek to new course toward the Grande Ronde Valley.  It is also possible that the chert-rich gravels were derived from reworking of Late Cretaceous-Paleocene gravels in the Wallowa Mountains .

       No fossil evidence has yet been found to determine the age of the Catherine Creek Lane gravels.  Gravels in the Grande Ronde Valley (Van Tassell, Ferns, and McConnell, unpublished data) show vertical variations between ~6.5-4 Ma which are similar to those present in the Catherine Creek Lane gravels (Fig. 5).  This suggests the possibility that the Catherine Creek Lane gravels may also be ~ 6.5-4 m.y. old, assuming that the factors which caused the compositional variations in these two deposits were regional in effect.  This comparison suggests that the Catherine Creek Lane gravels may have been deposited at the end of Barrash and others (1983) tectonic stage 2 as the Grande Ronde Valley filled with gravel-rich sediment.  If valid, this would mean that gravel accumulation rates in the Catherine Creek area were less than half those at the site of the Bing’98 well in the Grande Ronde Valley.  The end of gravel deposition may have been triggered by the initiation of faulting and downdropping of the Grande Ronde Valley associated with the beginning of tectonic stage 3.

Figure 5.  Possible correlation of the vertical compositional variations in the Catherine Creek Lane gravels with those in the Grande Ronde Valley  (Van Tassell,  Ferns and McConnell, unpublished data).  This comparison suggests that the Catherine Creek Lane gravels may have been deposited during a stage of basin-filling in the Grande Ronde Valley area between ~6.5-4 Ma at the end of Barrash  and others’ (1983) tectonic stage 2, but needs to be confirmed additional age-dating.

       The top of the Catherine Creek Lane gravels is at an elevation of ~3600 ft (~1100 m), ~1600 ft (~490 m) above ~4 Ma gravels in the Grande Ronde Valley to the northwest.  If the age of the top of the Catherine Creek Lane gravels is ~ 4 Ma, as estimated, this would imply a rate of faulting of ~0.12 mm/yr over the past 4 m.y.  This faulting occurred along several faults, not just one.

       There is much work to be done to determine when and where the Catherine Creek Lane came from.  More detailed profiling and sampling of the outcrop would be useful to better understand the compositional and grain size variations in the outcrop as well as to discover any fossils which may be present.  Analysis of microfossils and more precise age-dating might help establish gravelsa link with Lake Idaho.  More imbrication measurements are needed to determine the paleoflow directions more accurately.  This would require trenching of the outcrop.  Detailed mapping of the area with the goal of determining the timing and relative rates of faulting in the area would better help us to understand the time frame we are looking at and the influence of faulting on the evolution of the drainage networks in the area through time.  With more work and a better understanding of the local geology of the area, the answer to where these deposits come from will become more evident.

Conclusions

         The ~200-foot thick Catherine Creek Lane gravel outcrop is made up mostly of gravels mixed with reddish-brown, yellowish-brown and gray sand.  The unit is well-weathered at the base and the degree of weathering decreases toward the top of the outcrop.  The average size of the gravels coarsens upward, reaching cobble and boulder sizes near the top of the gravels.

        The average maximum projection sphericity index of the gravels is 0.67, typical of stream gravels  Imbrication measurements suggest a paleocurrent direction to the north (1°). Chert (“metaquartzite”) is abundant in the lower part of the outcrop, along with iron-stained quartz and minor hornblende and other minerals.  Plutonic rock fragments are common in the middle of the outcrop and the gravels are composed almost entirely of volcanic rock fragments at the top of outcrop.

        The gravels may have been deposited by the nearby tributary of Catherine Creek; by  Catherine Creek, which may have flowed to the southeast of the gravel outcrop and then turned toward the northwest at a previous time; by spillover events from Lake Idaho; or by northwest-flowing river (The Powder River?) prior to the uplift of the fault blocks in the area of the gravel outcrop.  Combinations of these hypotheses may best explain the overall vertical variations in composition in the Catherine Creek Lane gravels.

        No fossil evidence has yet been found to determine the age of the Catherine Creek Lane gravels.  Gravels in the Grande Ronde Valley (Van Tassell, Ferns, and McConnell, unpublished data) show vertical variations between ~6.5-4 Ma which are similar to those present in the Catherine Creek Lane gravels.  This suggests the possibility that the Catherine Creek Lane gravels are valley fill deposits emplaced between ~ 6.5-4 Ma at the end of Barrash and others’ (1983) tectonic stage 2.  The end of gravel deposition may have been triggered by the initiation of faulting and downdropping of the Grande Ronde Valley associated with the beginning of tectonic stage 3.

       Much more work is needed to be done to determine where the Catherine Creek Lane gravels came from, how old they are, and how faulting influenced stream deposition in the area over time.

Acknowledgments

       The reconnaissance of the Catherine Creek Lane gravel outcrop conducted by Mark Ferns and Vicki McConnell (Oregon Department of Geology and Mineral Industries) and Jay Van Tassell and Tammy Dunlavey (Eastern Oregon University) in October 2000 helped pave the way for this study.  Jay Van Tassell helped with the fieldwork, drafted figures and edited this manuscript

References Cited

Barrash, W., Bond, J.G., Kauffman,  J.D., and Venkatakrishnan, R.,  1983, Structural evolution of the  Columbia Plateau in Washington and Oregon:  American Journal of   Science, v. 283, p. 897-935.

Folk, R.L., 1974, Petrology of  sedimentary rocks:  Austin,  Texas, Hemphill Publishing  Company, 182 p.

Jenks, M.D., and Bonnichsen, B., 1989,  Subaqueous basalt eruptions into  Pliocene Lake Idaho, Snake River  Plain, Idaho:  Guidebook to the  Geology of northern and western Idaho and surrounding area:   Idaho Geological Survey Bulletin  28, p. 17-34.

Livingston, D.C., 1928, Certain  topographic features of  northeastern Oregon and their  relation to faulting:  Journal of  Geology, v. 36, p. 694-708.

Tucker, M.E., 1982, The field  description of sedimentary rocks:  New York, The Open  University  Press, 112 p.

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