Positive river trip prognosis...could have waited until May!?

Snowpack looking fine for upcoming river trip. Check out the handy website if it is new to you.

UNLV Speaks About Argon-Argon

Here is a nice summary of the Ar-Ar analyses that surpasses anything that I was putting together. I will follow-up with Terry Spell with a discussion about the strat context of the samples.

Nevada Isotope Geochronology Laboratory - Sample Descriptions – House - NBMG

General Comments: Your samples were run as conventional furnace step heating analyses. This type of sample run produces what is referred to as an apparent age spectrum. The "apparent" derives from the fact that ages on an age spectrum plot are calculated assuming that the non-radiogenic argon (often referred to as trapped, or initial argon) is atmospheric in isotopic composition (⁴⁰Ar/³⁶Ar = 295.5). If there is excess argon in the sample (⁴⁰Ar/³⁶Ar > 295.5) then these ages will be older than the actual age of the sample. U-shaped age spectra are commonly associated with excess argon, and this is often verified by isochron analysis, which utilizes the analytical data generated during the step heating run, but makes no assumption regarding the composition of the non-radiogenic argon. Thus, isochrons can verify (or rule out) excess argon, and isochron ages are usually preferred if a statistically valid regression is obtained (as evidenced by an acceptably low MSWD value). If such a sample (U-shaped, or more generally discordant) yields no reliable isochron, the most conservative estimate of the age is that the minimum on the age spectrum is a maximum age for the sample (it could be affected by excess argon, the extent depending on the radiogenic yield). ⁴⁰Ar/³⁹Ar total gas ages are equivalent to K/Ar ages. Plateau ages are sometimes found, these are simply a segment of the age spectrum which consists of 3 or more steps, comprising >50% of the total gas released, which overlap in age at the ±2σ analytical uncertainty level. Such ages are preferred to total gas or maximum ages if obtained. However, in general an isochron age is the best estimate of the age of a sample, even if a plateau age is obtained.

OWY-36 Basalt Groundmass

The age spectrum for this sample is discordant, with both positive and negative ages which overlap 0 within uncertainties, to ages as high as ~660 ka. The total gas age is 194 ± 27 ka, and is equivalent to a conventional K-Ar age. No plateau age or isochron age was defined by these data. This sample had very low, often negative radiogenic argon (%⁴⁰Ar*) concentrations (i.e. there was no measurable ⁴⁰Ar* in two of the steps), likely reflecting both low-K contents and young age. In a case such as this there are two possible interpretations. The first is that the sample contains no excess argon and the total gas age is a reasonable estimate. Unfortunately, with no isochron the presence, or absence, of excess argon cannot be confirmed, making this interpretation somewhat tenuous. The most conservative approach is to assume that the discordance is a result of excess argon, and thus the minimum age on the age spectrum is a maximum age for the sample. In this case, since the minimum ages are actually negative, this interpretation would hold that the sample is effectively 0-age. It should be noted that in such as case as this discordance could simply result from there being very little, to no, measurable ⁴⁰Ar*, which would result in inaccurate and imprecise age determinations. Which interpretation one should choose depends somewhat on geologic relationships. Does the geology and stratigraphy support an age as old as ~194 ka?

OWY-35 Basalt Groundmass

The age spectrum for this sample is mildly discordant and U-shaped. Ages range from an initial age of ~450 ka, to a plateau segment with ages of ~250 ka, and a higher final step age of ~780 ka. The total gas age is 301 ± 24 ka. Steps 2-10 (94% of the total ³⁹Ar released) define a plateau with a younger age of 248 ± 25 ka. Steps 1-4 (49% of the total ³⁹Ar released) yield an isochron age of 179 ± 21 Ma. The isochron indicates the presence of excess argon (initial ⁴⁰Ar/³⁶Ar = 305 ± 2) in this sample. Thus, ages calculated for the age spectrum, which assume the initial argon has ⁴⁰Ar/³⁶Ar = 295.5, should be considered anomalously old. The isochron age is the most reliable for this sample. Note that the radiogenic yields are significantly higher for this sample than for the previous OWY-36 sample, thus the ages should be considered significantly more reliable.

OWY-23 Basalt Groundmass

The age spectrum for this sample is also moderately discordant and U-shaped, with ages which fall from an initial step of ~1.5 Ma to a plateau segment with ages of ~180 ka, and followed by older steps (to ~840 ka) in the final ~15% gas released. The total gas age is 292 ± 39 ka. Steps 2-7 (81% of the total ³⁹Ar released) define a plateau with a younger age of 182 ± 42 ka. Steps 2-7 also yield an imprecise isochron age of 120 ± 130 ka. The isochron does not indicate the presence of excess argon (initial ⁴⁰Ar/³⁶Ar = 298 ± 6) in this sample. Also, note that all the data points defining the isochron fall near the y-axis in a cluster (similar radiogenic yields, ), thus the y-axis intercept (initial ⁴⁰Ar/³⁶Ar ratio) is fairly well defined, whereas the x-axis intercept (age) is very poorly defined. Thus, this isochron is not useful for age determination, but does provide important information regarding excess argon, i.e. within uncertainty the sample cannot be said to contain excess argon. Other processes, such as recoil of reactor generated ³⁹Ar during irradiation, can also produce discordant age spectra for fine grained basalt groundmass samples, and this may explain this samples age spectrum in particular. Given these considerations, the plateau age should be considered the most reliable for this sample.

OWY-22 Basalt Groundmass

The age spectrum for this sample is nearly ideally flat and concordant, with the exception of higher ages in the final ~10% gas released. The total gas age is 70 ± 19 ka, and steps 1-8 (88% of the total ³⁹Ar released) define a plateau with a younger age of 38 ± 21 ka. Steps 2-5 define a valid isochron age, however, as for OWY-23 above, the data are tightly clustered at the y-axis due to similar, and low, %⁴⁰Ar* values, making this isochron useful only for confirming the composition of the initial ⁴⁰Ar/³⁶Ar ratio, which is indistinguishable from atmospheric argon. Thus, the plateau age can be considered reliable and the best estimate of the eruption age for this sample.

OWY-13 Basalt Groundmass

The age spectrum for this sample is discordant, with ages that fall, rise, and fall again with increasing %³⁹Ar released. The total gas age is 8.3 ± 0.6 Ma. Steps 3-7 (62% of the total ³⁹Ar released) define a plateau with a younger age of 7.0 ± 1.0 Ma. There was no isochron defined by these data. The discordance shown by this samples age spectrum must be considered to be potentially caused by the presence of excess argon, although this cannot be confirmed or denied since no isochron was obtained. Thus, in this case the most conservative interpretation is that the youngest age on the age spectrum (step 10, 3.6 Ma) is a maximum age for the sample.

OWY-12 Basalt Groundmass

This sample is similar to OWY-36 described above, and similar interpretations apply. The total gas age is 453 ± 94 ka. Steps 3-5 (50% of the total ³⁹Ar released) define a plateau with a younger, and imprecise, age of 173 ± 145 ka. There was no isochron defined for this sample. Note that overall the age spectrum is distinctly U-shaped. This may indicate excess argon is present in the sample and thus calculated ages may be anomalously old. This cannot be confirmed as no isochron was obtained. As for OWY-36, since several steps yield negative radiogenic yields and 0-age calculations this sample is best interpreted as being effectively 0-age, i.e. it is so young that we cannot accurately measure the accumulated ⁴⁰Ar* against the background of initial argon. The plateau age should only be used if stratigraphic constraints suggest it is accurate.

As is typical, these comments are made with little knowledge of geologic relationships and are simply interpretations of the laboratory data. Often knowledge of, e.g., stratigraphic relationships can determine which interpretation is most valid for a particular sample. The first sample above, OWY-36 is a good example of this. Feel free to call or email (best way to contact me terry.spell@unlv.edu) if you have further questions that I might assist with.

Virtual Reality on the Owyhee? Almost.

Today, Valentine's Day, was a red-letter day for mapping on the Owyhee. NBMG recently obtained some very cool software and hardware for mapping in 3-D. With the help of digital photgrammetry and several other things I only vaguely understand, it is possible to build orthorectified and georectified stereo-models in the digital domain, map on them, and then export the lines (with z-values no less) into ArcGIS. Today, my colleague Nick put me through the preliminary ropes with some Owyhee images, and I am sold. Extremely cool, and not nearly as complicated as a PG-2 plotter to set up.


I plan on fine-tuning the Owyhee map with this device before the river trip. Note, if I have time, I can also extract a very accurate longitudinal profile for the river (or any feature for that matter). Stay tuned. I can even cut cross-sections if necessary...extremely freakin' cool.

Recent article of high relevance

Check out the recent issue of Geosphere for some new insights / interpretations of lava and river interactions in Grand Canyon (with an interesting lidar application):

From Geosphere, February 2008; v. 4; no. 1; p. 183-206
History of Quaternary volcanism and lava dams in western Grand Canyon based on lidar analysis, 40Ar/39Ar dating, and field studies: Implications for flow stratigraphy, timing of volcanic events, and lava dams

Ryan Crow, Karl E. Karlstrom, William McIntosh, Lisa Peters, and Nelia Dunbar

A synthesis of the geochronology on basalt flows from the southern Uinkaret volcanic field indicates that basalts erupted within and flowed into Grand Canyon during four major episodes: 725–475 ka, 400–275 ka, 225–150 ka, and 150–75 ka. To extend the usefulness of these dates for understanding volcanic stratigraphy and lava dams in western Grand Canyon, we analyzed light detection and ranging (lidar) data to establish the elevations of the tops and bottoms of basalt-flow remnants along the river corridor. When projected onto a longitudinal river profile, these data show the original extent of now-dissected intracanyon flows and aid in correlation of flow remnants. Systematic variations in the elevation of flow bottoms across the Uinkaret fault block can be used to infer the geometry of a hanging-wall anticline that formed adjacent to the listric Toroweap fault.

The 725–475 ka volcanism was most voluminous in the area of the Toroweap fault and produced dike-cored cinder cones on both rims and within the canyon itself. Mapping suggests that a composite volcanic edifice was created by numerous flows and cinder-cone fragments that intermittently filled the canyon. Reliable 40Ar/39Ar dates were obtained from flows associated with this period of volcanism, including Lower Prospect, Upper Prospect, D-Dam, Black Ledge, and Toroweap. Large-volume eruptions helped to drive the far-traveled basalt flows (Black Ledge), which flowed down-canyon over 120 km. A second episode of volcanism, from 400 to 275 ka, was most voluminous along the Hurricane fault at river mile 187.5. This episode produced flow stacks that filled Whitmore Canyon and produced the 215-m-high Whitmore Dam, which may have also had a composite history. Basaltic river gravels on top of the Whitmore remnants have been interpreted as “outburst-flood deposit” but may alternatively represent periods when the river established itself atop the flows. Remnants near river level at miles 192 and 195, previously designated as Layered Diabase and Massive Diabase, have been shown by 40Ar/39Ar dating to be correlative with dated Whitmore flow remnants, and they help document the downriver stepped geometry of the Whitmore Dam. The ca. 200 and 100 ka flows (previously mapped as Gray Ledge) were smaller flows that entered the canyon from the north rim between river mile 181 and Whitmore Canyon (river mile 187.5); they are concordant with dates on the Whitmore Cascade as well as other cascades found along this reach.

The combined results suggest a new model for the spatial and temporal distribution of volcanism in Grand Canyon in which composite lava dams and edifices, that were generally leaky in proximal areas, were built from 725 to 475 ka near Toroweap fault and around 320 ka near Whitmore Canyon. New data on these and other episodes present a refined model for complex interactions of volcanism and fluvial processes in this classic locality. Available data suggest that the demise of these volcanic edifices may have involved either large outburst-flood events or normal fluvial deposition at times when the river was established on top of basalt flows.

Check out the interesting graphics the authors provide about lava dams:

Ar-Ar Geochron Table

Sample	Location	Total Gas	Plateau		Isochron
OWY-12	Lower Saddle Butte	452.8 ± 94.1	173.0 ± 144.8		n/a
OWY-13	Upper Saddle Butte	8.31 ± 0.62 Ma	7.03 ± 1.00		n/a
OWY-22	Upper West Crater	69.86 ± 19.15	37.60 ± 21.01		7.0 ± 8.5
OWY-23	Lower West Crater (?)	292 ± 39	182 ± 42		120 ± 130
OWY-35	Upper AM-PM	301 ± 24.3	247.6 ± 24.9		179 ± 21
OWY-36	Lower AM-PM	194 ± 27	n/a		n/a

Here is a blurb of related text I received from UNLV:

Nevada Isotope Geochronology Laboratory - Sample Descriptions

General Comments:

Isochrons are the most desirable treatment of ⁴⁰Ar/³⁹Ar data. This is because the isochron actually defines the isotopic composition of the initial argon in the sample (non-radiogenic argon). Ages calculated for an age spectrum are referred to as "apparent ages" because they are calculated assuming the initial argon is atmospheric in composition - thus, if there is excess argon (⁴⁰Ar/³⁶Ar > 295.5) the age will be overestimated. Isochrons have their measure of reliability, known as the mean square of weighted deviates (MSWD) which is a statistical goodness of fit parameter. If it is greater than a certain value (which changes depending on the number of points, see Wendt and Carl, 1991, the statistical distribution of the mean squared weighted deviation, Chem. Geol., v. 86, p. 275-285) then there is more scatter than can be explained by analytical errors and it is not a statistically valid isochron. If we provide an isochron it means that the statistical test is valid, if not then no valid isochron was obtained. Also, there are issues of number of data points defining the isochron - the more the better. Four points should be considered a bare minimum for statistical reasons, three points is getting to be a real concern. This can be understood simply by considering two points - a perfectly fit straight line can be put through any two points, so completely accidental data can have a perfect line fit. It follows that with three points there is less of a chance of an accidental line fit, but it is still a very real possibility (especially if analytical errors are fairly large), this possibility gets exponentially smaller as the number of points defining the line (isochron) goes up, thus more points = a more reliable isochron.

If there is no isochron, then a plateau age is next in preference. This is because a sample that gives ages which are analytically indistinguishable from step to step is exhibiting what is known as "ideal" behavior, which suggests it has a simple geologic history, e.g., rapid cooling as a basalt lava, followed by no reheating or alteration, both of which may produce disturbed (discordant) age spectra. A reliable plateau is 3 or more consecutive steps which are indistinguishable in age at the 2 sigma level and comprise >50% of the total ³⁹Ar released. The lack of an isochron or a plateau does not mean the sample provides no useful information, but their presence gives greater confidence in the ages obtained and requires less subjective interpretation.

Of course, you must consider that we run samples such as this "blind" in that we do not know the geologic relations of the samples, either when we analyze them, or when we provide these general interpretations. The geologic constraints must always be considered when interpreting isotopic ages; if any discrepancies arise feel free to discuss them with us, as it can in some cases make a difference in how age data are interpreted. All analytical errors are 1σ.

Map of Owyhee Geochronology Samples

Below is a map showing the locations of geochron samples from or related to our project. OSL samples in yellow; Ar-Ar (with results!) in green; Cosmo (with results) in blue; and Champion's p-mag sample sites in red. Rest assured that I will follow-up with some more info about the weakly satisfying Ar-Ar data and tell you what I have learned about it. In the meantime, enjoy the map.


View Larger Map

Landslide Dam References of Interest

Last night, I quickly compiled this reference list. Thought it may spark some interest. Using Zotero and Google Scholar, I put it together in about 15 minutes!

Adams, J. (1981). Earthquake-dammed lakes in New Zealand. Geology, 9(5), 215-219.

Alford, D., Schuster, R. L., & Reduction, I. S. F. D. (2000). Usoi Landslide Dam and Lake Sarez: An Assessment of Hazard and Risk in the Pamir Mountains, Tajikistan. United Nations.

Antognigni, M., & Volpers, R. (2002). A late Pleistocene age for the Chironico rockslide (Central Alps, Ticono, Switzerland). Bull Appl Geol, 7, 113-125.

Bovis, M. J., & Jakob, M. (2000). The July 29, 1998, debris flow and landslide dam at Capricorn Creek, Mount Meager Volcanic Complex, southern Coast Mountains, British Columbia. Canadian Journal of Earth Sciences, 37, 1321-1334.

Canuti, P., Frassoni, A., & Natale, L. (1994). Failure of the Rio Paute Landslide Dam. Landslide News International Newsletter, ISSN, 0919-5629.

Ermini, L., & Casagli, N. (2003). Prediction of the behaviour of landslide dams using a geomorphological dimensionless index. Earth Surface Processes and Landforms, 28(1), 31-47.

Gardner, J. N., Lavine, A., WoldeGabriel, G., Krier, D., Vaniman, D., Caporuscio, F., et al. (1999). Structural Geology of the Northwestern Portion of Los Alamos National Laboratory, Rio Grande Rift, New Mexico: Implications for Seismic Surface Rupture Potential from TA-3 to TA-55. LA-13589-MS, Los Alamos National Lab., NM (US).

Goff, F., Reneau, S., Rogers, M. A., Gardner, J. N., Smith, G., Broxton, D., et al. (1996). Third-day road log, from Los Alamos through the southeastern Jemez Mountains to Cochiti Pueblo and the Rio Grande. The Jemez Mountains Region. New Mexico Geological Society Field Conference Guidebook, 47, 59-97.

Hancox, G. T., & Limited, I. O. G. &. N. S. (1999). Mt Adams Rock Avalanche of 6 October 1999 and the Subsequent Formation and Breaching of a Large Landslide Dam in Poerua River, Westland, New Zealand. Institute of Geological & Nuclear Sciences.

Hancox, G. T., McSaveney, M. J., Manville, V. R., & Davies, T. R. (2005). The October 1999 Mt Adams rock avalanche and subsequent landslide dam-break flood and effects in Poerua River, Westland, New Zealand. New Zealand Journal of Geology and Geophysics, 48(4), 683–706.

Hermanns, R. L., Niedermann, S., Ivy-Ochs, S., & Kubik, P. W. (2004). Rock avalanching into a landslide-dammed lake causing multiple dam failure in Las Conchas valley (NW Argentina)—evidence from surface exposure dating and stratigraphic analyses. Landslides, 1(2), 113-122.

Hermanns, R. L., & Strecker, M. R. (1999). Structural and lithological controls on large Quaternary rock avalanches (sturzstroms) in arid northwestern Argentina. Bulletin of the Geological Society of America, 111(6), 934-948.

Huscroft, C. A., Ward, B. C., Barendregt, R. W., Jackson, L. E., & Opdyke, N. D. (2004). Pleistocene volcanic damming of Yukon River and the maximum age of the Reid Glaciation, west-central Yukon. Canadian Journal of Earth Sciences, 41(2), 151-164.

King, J., Loveday, I., & Schuster, R. L. (1989). The 1985 Bairaman landslide dam and resulting debris flow, Papua New Guinea. Quarterly Journal of Engineering Geology and Hydrogeology, 22(4), 257.

Korup, O. (2006). Rock-slope failure and the river long profile. Geology, 34(1), 45-48.

Malamud, B. D., Jordan, T. E., Alonso, R. A., Gallardo, E. F., González, R. E., & Kelley, S. A. (1996). Pleistocene Lake Lerma, Salta province, NW Argentina. Congreso Geológico Argentino, 58(1).

Meyer, W., Schuster, R. L., & Sabol, M. A. (1994). Potential for Seepage Erosion of Landslide Dam. Journal of Geotechnical Engineering, 120(7), 1211-1229.

Read, S. A. L., Beetham, R. D., & Riley, P. B. (1991). Lake Waikaremoana barrier-A large landslide dam in New Zealand. Landslide News, 54(1), 1.

Recent research on landslide dams - a literature review with special attention to New Zealand. (2002). Retrieved January 9, 2008, from http://ppg.sagepub.com/cgi/content/abstract/26/2/206

Reneau, S. L. (2000). Stream incision and terrace development in Frijoles Canyon, Bandelier National Monument, New Mexico, and the influence of lithology and climate. Geomorphology, 32(1-2), 171-193.

Reneau, S. L., & Dethier, D. P. (1996a). Pliocene and Quaternary history of the Rio Grande, White Rock Canyon and vicinity, New Mexico: New Mexico Geological Society Guidebook. 47 thField Conference, Jemez Mountains Region, 317-324.

Reneau, S. L., & Dethier, D. P. (1996b). Pliocene and Quaternary history of the Rio Grande, White Rock Canyon and vicinity, New Mexico. Jemez Mountain region: New Mexico Geological Society Guidebook, 47, 317–324.

Reneau, S. L., & Dethier, D. P. (1996). Late Pleistocene landslide-dammed lakes along the Rio Grande, White Rock Canyon, New Mexico. Geol Soc Am Bull, 108(11), 1492-1507.

Sowma-Bawcom, J. A. (1996). Breached landslide dam on the Navarro River. California Geology, 49(5), 120-128.

Trauth, M. H., Alonso, R. A., Haselton, K. R., Hermanns, R. L., & Strecker, M. R. (2000). Climate change and mass movements in the NW Argentine Andes. Earth and Planetary Science Letters, 179(2), 243-256.

Trauth, M. H., & Strecker, M. R. (1999). Formation of landslide-dammed lakes during a wet period between 40,000 and 25,000 yr BP in northwestern Argentina. Palaeogeography, Palaeoclimatology, Palaeoecology, 153(1), 277-287.

Wayne, W. J. (1999). The Alemania rockfall dam: A record of a mid-holocene earthquake and catastrophic flood in northwestern Argentina. Geomorphology, 27(3-4), 295-306.

Any Yeehows know about these slides?

Surely you read the blog over the Holidays and are busily typing up your GPS coordinates that I asked for, right? In the meantime, take a break from typing and check out the map above and the related photo in the previous post. These are some killer landslides off of Black Mesa in north central New Mexico (I flew over them twice...to and from Okla-coma). Is anyone aware of these being described in the literature? I have not looked yet. Certainly an interesting contrast to the Owyhee given the very different valley bottom morphology. However, as you go upstream the scene begins to look more familiar as you may discern below.


Here is a link to a recent map that covers a lot of landslid terrain near Los Alamos. It has a detailed approach to mapping coherent units within landslides.

http://geoinfo.nmt.edu/publications...White_Rock_preliminary_geo_rfs.pdf

Holiday Greetings Yeehows!

Against my better judgment, I am lugging the family back to Oklahoma for the Holidays. The payoff? Some incredible geology shots from the airplane! This is the most relevant sampling for this research group. Consider them my presents to you. To reciprocate, please send relevant field observations and associated GPS coordinates from the Owyhee River!!

Killer view of lava cascades into Western Grand Canyon!

Large landslides along the Rio Grande, north of Albuquerque!

Lava Butte in Google Earth

Today, I noticed an announcement that Google Earth had again updated some imagery in Oregon. Now, the Bend and Lava Butte areas are looking good (see screen snag above). The rapids formed at each lava-river interface are easily detected.

Still no improvement in the Malheur County area coverage in Google Earth. Note that at AGU I had a chance to actually interact with some Google People, and made a point out of complaining (in a friendly way) about the SE Oregon problem. No promises, but some expressions of mild concern. I did score one of those cool Google light-up balls, however. No job offer.

Cosmic Mineral Separation Directive

As Stated by Cassie Fenton:

Mineral Separate Preparation for ³He Cosmogenic samples:

STEP 1: Remove only top 4 cm of the rock (for cosmogenic samples). (If you only use the top 3 cm or top 1 cm, etc., make a note of this. It affects correction of the ³He content in the rocks.) Break the top 4 cm of the rock sample into pieces small enough to fit the crusher (generally the size of a golfball, no bigger). I use a rock hammer and chisel for this process. In some cases, for harder samples, a rock saw is needed, but rarely.

STEP 2: Make sure you clean the crusher in between samples to avoid any contamination. This includes using a dry paintbrush, a vacuum, and/or compressed air to get any/all of the previous sample out of the crusher and out of containers used to catch/transport the sample.

Always save at least one golf-ball sized hand sample of your whole rock for an archive sample. You might need this for chemical analyses etc. in the future. Start with the crusher at its widest position and throw the rock pieces in, reducing the width of the crushing gap each time until you have a variety of grain sizes. You want the majority of your sample to fall in the [250-500 μm] and [500-1000 μm] mesh range (sieve sizes in the US are labeled differently – I used to use US sizes [20-60] or so), so you just have to eye it. Grains in the [125-250] range are okay for analyses too, but makes things a bit more complicated because the grains are much smaller (i.e. handpicking this grain size is slow and tedious). There will still be pieces larger than that, up to 1 cm or so, that’s okay. You want to keep some bigger pieces in case you need to crush more in order to obtain the amount of the mineral you’re looking for. Just don’t overcrush, or you’ll end up with a lot of powder (too small!!) and not mineral grains of desirable size.

STEP 3: Sieving. Here’s a short list of sieve sizes we use:

(From Comparison Table of U.S., Tyler, Canadian, British, French, and German Standard Sieve Series)

U.S. Standard	U.S. Alternate	Tyler mesh designation
2.00 mm	10	9
1.68 mm	12	10
841 micron	20	20
420 micron	40	35
250 micron	60	60

The sieves we use are the U.S. alternate 10, 20, 40, and 60.

Set the sieves up descending in mesh size from top to bottom. (i.e. the 10 should be on the top, followed by the 20, 40 and 60, with a screen-free container (fitting the stack) at the bottom) to catch the finest part of the sample. You can either dry-sieve or wet-sieve. Both have their benefits. With dry-sieving, you don’t have to wait for the samples to dry, before moving onto the next step. Wet-sieving tends to clean the samples up, so the smaller grain sizes (<>

Either way, place your crushed sample in the top sieve and shake until you have a decent separation (Usually takes ~5 minutes). Take each container and empty it into a properly labelled bag. The labels are as follows (sample # followed by sieve size range; ex: 040609-01 [10-20]):

Clean sieves between samples, using a toothbrush and a thin tool to remove grains lodged in the screen/mesh.

STEP 4: Cleaning: Rinse the sample in a beaker and slowly pour off the dirty water until it runs fairly clear (don’t lose any sample!). Allow to dry. Oven should not be above 55º C (to minimize loss of He from crystals).

STEP 5: Magnetic Separation: I start with a hand magnet and mesh sizes [20–40] and [40-60], unless there are olivines large enough to fall in the [10-20] range, then I use that fraction as well. Often, in my basalt samples, the matrix is very iron-rich and comes off easily with a fairly strong hand magnet. If the hand magnet provides a good separate, put the magnetic material back in the sample bag and save it. Save the non-magnetic part of the sample (olivine, pyroxene, probably some plag and calcite).

Details:

1) Hand magnet: Obtain a typical hand magnet (they’re fairly weak, but work well). Dump your minerals grains on a piece of 8X11.5 paper with a clean piece of paper adjacent to it. Place a plastic baggie or weighing paper over your magnet to keep magnetic grains from sticking to the magnet, thereby decreasing contamination between samples. Run the magnet over the mineral grains, placng the magnetic grains on the empty paper, leaving the nonmagnetic grains behind. In our case, we are generally interested in olivines, pyroxenes, and feldspar. These generally stay on the nonmagnetic side, unless they have lots of inclusions or are coated with magnetic material.

If for whatever reason, the hand magnet doesn’t yield a very good separation, move on to the Frantz magnetic separator.

You can also use a Frantz if the hand magnet doesn’t work. Make sure your sample is washed before using the Frantz.

2) Frantz Magnetic separator: It is best to work with a [40-60] range on this machine, but the [20-40] range is feasible. The larger grains just tend to clog up the sample cup every now and again.

Adjust the desired angle on the ramp by turning the proper knob/wheel. I usually use an angle between 15-20 degrees tilting away from me (15 degree works best). A shallow angle tilting down to the sample collection cups also seems most productive. It allows the grains to interact with the magnet for a longer period of time, allowing for a cleaner separate. Take your clean sample fraction and pour a small amount of it into the sample cup. Turn on all appropriate switches, adjusting the strength of the magnet by increasing or decreasing the amps. I usually start with 0.25 amps, run the sample through 2-3 times. This will separate out the very magnetic material from the less magnetic material. I then switch to a higher amp (somewhere between 1.0 and 1.5) and run the magnetic fraction (when run at 0.25) through (2-3 times). This will separate off the very nonmagnetic. Then I just play around with values in between until I get a nice separate of my mineral of interest. Before changing the amps, I check each collection cup under a microscope to see which has the largest amount of my mineral of interest. These values will vary with different samples. You just have to pick and choose, use what best suits your sample.

STEP 6: Heavy liquid separation: We use lithium metatungstate with a density of 3.0 g/cc. At this density, olivines and pyroxenes (“heavies”) sink and everything you don’t want (“lights”) floats to the surface.

Here’s the address for the company we order from. We use litium metatungstate (density = 3.0). It’s water soluble, allowing for a density variation and recycling.

GEOLIQUIDS

15 E. Palatine Rd., Suite 109

Prospects Heights, Illinois 60070

1-800-827-2411

We recently ordered 3 lbs at a cost of $144/lb, I think.

Here’s a list of equipment we use to

CRU-5000 Centrifuge

50 ml polypropylene, graduated, conical centrifuge tubes with caps

3-piece Whatman filter funnel (9 cm in diameter, 200 ml volume, 17.9 cm height, Whatman no. 1950-009)

Whatman filter papers (medium-fast (1), 9 cm in diameter)

- fill the bottom of centrifuge tubes with sample grains. (Don’t fill it past the 5 ml mark). Label clearly.

- add lithium metatungstate (at a density of at least 2.95, preferably 3.0 or greater) to the 25 or 30 ml line (depends on how much sample you use and how much heavy liquid you have to work with).

- Cap and shake all the tubes

- place in centrifuge at 1.5X1000 rpm for at least 10 minutes.

- have a doer of liquid nitrogen set aside and set up funnel/filtration apparatus.

- remove tubes from centrifuge,

STEP 7: Acids: I usually use HNO3, HCl , and HF to clean up the “heavies” samples. To get rid of any secondary calcite, start with dilute (5-10%) HNO3 and your “heavies” in a beaker placed in a sonicator for 15 to 20 minutes. Then use dilute (5-10%) HCl (in sonicator 15-20 minutes). Sometimes the minerals are well-oxidized. For example, oxidized olivines tend to have an iddingsite “rind” (a red coating) around them. Sometimes HCL will get rid of this. If it doesn’t, move onto a 5% HF solution.

HF treatment: WEAR HEAVY GLOVES, A LAB COAT, AND A FACE MASK. HF is very nasty stuff. Pour your minerals into a small glass or Nalgene beaker (HF etches glass, so if you use glass beakers, set them aside after that for HF use only) and add a 5% HF solution until it submerges your minerals. Don’t use too much. It isn’t necessary to fill the beaker, just top your minerals with the solution. Place in an ultrasound for 15-20 minutes, depending on how oxidized your sample is. Check your sample regularly to make sure you don’t dissolve you minerals completely. Pour off HF into waste container, rinse your sample, and dry. Repeat as necessary, until the majority of your sample is clean (iddingsite-free).

STEP 8: Microscope check. After isolating the olivine/pyroxene, and cleaning them up with acids etc, you should have a good separate. I always check under a microscope and handpick out what looks like crappy mineral grains (grains that are still dirty, or that are obviously not oliv/pyroxene). You want the purest separate of olivine or pyroxene possible.

What the Big Boss said...

I caught up with Mike E. at AGU and asked about the grant supplement to get LiDAR. Here's what I learned:

1. The proposal should be ~5 pgs and has no formal deadline.
2. We should wait till we hear the outcome of Rose's seed proposal, since that should (hopefully) be just a few weeks away, according to Josh R.
3. We should not ask for more than $50k.
4. We need to explain in detail why we want/need the LiDAR, of course (see my posting below). I briefly described three reasons to Mike that we've batted around before: to get the 3-D shape of the valley right for hydrodynamic modeling; to get the distribution of boulder sizes remotely by subtracting bare earth from first returns -- he liked that one, Jim -- and to characterize the wavelengths of mass movements that are impinging on the channel, as this will affect the scale of potential blockages and therefore probably flood character as well. He judged these to be reasonable justifications at first pass, but we will have to substantiate the case in detail. In particular, I think we really need to demonstrate the nature and magnitude of the improvement we get in the hydrodynamic modeling if we use LiDAR rather than the 10 m DEMs. Can we feasibly try this with the Deschutes LiDAR (which Jim has) as a demonstration? Rose, what say ye? If the effects are not great relative to other sources of uncertainty in the modeling, then I think our case is weakened significantly.

5. We need to explain WHY FUNDING FOR LIDAR WAS NOT INCLUDED IN THE ORIGINAL REQUEST. I want your input on this last matter in particular. Some of the reasons for the original omission, though perhaps ultimately the most truthful, are not going to sound very persuasive in a proposal (e.g., we thought it would inflate the budget too much, or we didn't realize how much damn work all the manual surveying would be, etc.). So, let's hear some wordsmithing. Ready, set, go.

Possible LiDAR coverage request

I have taken a stab at plotting a LiDAR coverage pattern that could form the basis for grant supplement request. It's obviously tricky trying to keep the footprint shape both as simple and as small as possible while capturing the irregular pattern of the river corridor. I'm not sure we can even request a pattern as complicated as the one I've outlined here. These four polygons sum to ~208 km2 or ~51,500 acres (for some odd reason, NCALM seems to like using acres as its unit of area), which is within the range of the other NCALM requests I've seen (see, e.g., slide #26 in http://www.cuahsi.org/cyberseminars/NCALM-20050202.pdf ). Assuming a cost of about $0.75/acre, which is unreliable but is the only price info I've been able to find (see slide #24 in the .pdf above), our request would be for about $37,000. If Rose's request for 40 km2 or ~10,000 acres is funded, we can reduce the grant supplement request by about $7500. I don't know if this sum is considered reasonable for a grant supplement, but I will approach Mike Ellis at AGU and ask him. Any comments on the size/shape of this pattern?

Correlation Madness.

Thus far, I have spent 10s of hours on the map. As a consequence, the correlation diagram has evolved significantly. The colors in the snippet do not match the map yet, and some of the unit labels have changed. Also, it is likely that some units will be added and some will be dropped as the project continues. All part of my mapping process, and is often maddening to my colleagues. Nonetheless, check it out and go with the flow.

Tofu update....now much nicer (but still Tofu)

Made some decent strides on the map in THIG today. Check it out. Pretty much the most complex area I have mapped in a while. Thankfully, I don't have to parse out the bedrock.

The Hole in the Ground is Tofu

Have spent many hours mapping the Hole in the Ground area. It is total tofu. Here is the current rendition. In the process I have added some new units that make sense now that the map has progressed. So far, I have focused only on the north side of the river.

Base of Bogus Lavas

Here are three images that show the base of the Bogus lava where it sits on tilted to soupy-looking yellow sediments. These images are from the cleft. That is the spot that led me to the inference that the Bogus lavas were deposited on landslid materials--note the tilted brown stuff evident in the panorama. Everywhere I have since seen the base of the Bogus (upstream) it rests on more obviously in situ volcanic rock or flat-lying soft rocks.

Supplemental grant proposal to get LiDAR

Gang -- I'm going to follow up w/Mike Ellis on what exactly he'd like to see in a supplemental grant proposal to get LiDAR for our study reach on the Owyhee. I'd like to be armed w/a clear sense of what we want LiDAR for and w/information about the size, shape, and therefore approximate cost of the data. We have discussed the former a bit -- e.g., when Kyle was visiting Portland a couple of weeks ago -- but I'd like to solicit broader input on this matter, as the justification will be crucial. I think we need to show that LiDAR will give us essential data that we can't reasonably get any other way. As for the size of the area we want flown, I'd like to hear what you folks think. I don't know what the limitations are in terms of shape (how complex can the corridor polygon be?), but we'll probably have to do some iterating on the polygon we're going to request. My intuition is that requests larger than about $60k might raise some alarm, so we need to be judicious. Does anyone else have a sense of what constitutes a reasonable request for a grant supplement? I also asked Josh Roering (who is on the NCALM committee) when Rose will hear about the student seed project she proposed. Please post your thoughts on LiDAR justification and desired coverage here.

New Mapping Tool--Enforced Involvement?

View Larger Map

Google maps just introduced a terrain mode which is a nice way to visualize the regional setting of a map. More importantly, they also just introduced:

1. Collaborative mapping
2. kml file importation capability.

Improvement 1 allows for multiple users to edit a common, online map. The one I have included shows some key photos along the river that are useful in developing the geologic map in the office. Now that a map can be collaboratively shared, any invited mapper can post photos that they think are particularly useful for visualizing geology. In the Owyhee example, I am interested in a set of photos spread out along the entire length of the study reach (and beyond, if appropriate). All it requires is a very short amount of time to become familiar with the interface and a set of photos available somewhere online. I use Picasa Online Albums, but any program should work.

Improvement 2 allows for direct integration of data generated using Google Earth into a collaborative map. It has been possible to export kmls for some time from Google Maps, but importing has been missing. This is a huge leap.

Eventually, I will be inviting all Yeehows to post some photos that they think will help me compile the map. Please try to participate.

The Geologic Map in Progress

Here is a snippet of the map in the surprisingly complicated Lambert Rocks reach of the Owyhee River. This still needs some work, but shows some good progress. The colors don't quite match the correlation diagram I posted a while back. Will fix this eventually. I have mapped a larger area, but am having some trouble outputting the .jpg of the whole map. Yes, the labeling is bad and the landslide symbol is scaling poorly. These things will be fixed.