Welcome To My 2021 Field Office

This is my summer receptionist… a Yellowstone 2020 wolf pup of the Junction Butte pack that roams mainly in the Lamar Valley of northern Yellowstone National Park.

My geological field work lately has taken me to several areas of western Montana, so I thought I’d do a visual collage of a few of the landscapes where I’ve been working. To start with, I’ve been spending time flying drones over Tertiary exposures in southwestern Montana, Great fun and good insight into Tertiary geology. Many of my flights are focused on Eocene strata at Pipestone Springs. Along with 3 co-authors (Don Lofgren, Stephen Hasiotis, and Bill McIntosh), we have a paper on Pipestone chronostratigraphy, trace fossils, and depositional environments that is now in review. Below are a couple of drone photos from Pipestone Springs.

Pipestone Springs Eocene strata with the basal lapilli tuff (37.5 million years in age) and the upper trace fossil bed (36 million years in age) indicated. Note the person standing on the surface of the upper trace fossil bed.
A somewhat closer drone view of the upper trace fossil bed with me as pilot standing off to the right side of the photo. My drone landing pad is my friend’s political campaign sign!

My travels through a part of northwestern Montana last week put me in a very different geologic setting from southwestern Montana. Proterozoic rocks are the mainstay in this area, and they make for some spectacular landscapes. So spectacular in fact, that I’ll just do a barrage of photos from the east side of Glacier National Park…

Chief Mountain, located a few miles north of Babb, Montana, is the iconic geologic view of major thrust fault where Proterozoic rocks (Chief Mountain rocks) are pushed over Cretaceous strata (green area of this photo).
No matter how much has changed in this past year because of the pandemic, it is just astounding to me to see a sign that says the Canadian border crossing is closed. It was a heavy mix of emotions being out in the early morning to view Chief Mountain, but then to see this sign and know that we’re still all in this even a year out. Whew…
Of course, no visit to Many Glacier is complete without marveling at Grinnell Point.
One of the positive aspects of getting up very early on a spring day is the sun rise near the Many Glacier Lodge. It didn’t last long as rain clouds pushed in but what a view for a time!
And another plus to being up early in the Many Glacier area is to watch a black bear amble down the road.
Coming back south, down the Front Range of the Rockies, we got out from under the rain clouds. Once again, geologically, the rocks that comprise Dancing Lady Mountain have been thrust over younger, Cretaceous strata (basically the area in green on the photo).

In summary, this is just a quick view of a couple western Montana areas where I’ve been recently. I have to say that I’m really looking forward to more amazing places to work this field season. I may swap out my office receptionist, though.

LATE EOCENE CHRONOSTRATIGRAPHY, DEPOSITIONAL ENVIRONMENT, AND PALEOSOL-TRACE FOSSIL ASSOCIATIONS, PIPESTONE SPRINGS, SOUTHWEST MONTANA

I just received notice from the Geological Society of America (GSA) that our abstract is now accepted for the GSA 2020 annual meeting. I was very much looking forward to going to Montreal for the meeting, but like much else, it will now be virtual. Our presentation is scheduled for the session titled “D23. Recent Advances in Understanding Environmental Changes and Their Effects on Sedimentation”, which will be on Monday, 26, October 2020, beginning at 1:30 PM. And I say our abstract, because my co-authors are: Steve Hasiotis (Department of Geology, University of Kansas, Lawrence, Kansas), Don Lofgren (Raymond M. Alf Museum of Paleontology, Claremont, California,) and Bill McIntosh (New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico). We’re excited to get this abstract out in the public domain as it details the first single-crystal sanidine 40Ar/39Ar ages for the well-known vertebrate locality of Pipestone Springs in southwestern Montana. We also have other significant findings, such as newly-identified trace fossils and the presence of loessites in the Pipestone Springs section. Our paper on these findings is nearing completion, soon to be submitted to a peer-reviewed journal. Anyways, here’s our Pipestone Springs abstract:

Sanidine 40Ar/39Ar ages of lapilli tuffs and the mammalian fauna of Pipestone Springs Main Pocket provide a high-resolution chronostratigraphy of late Eocene strata in the Pipestone Springs area of southwestern Montana. Two felsic lapilli tuffs, with weighted-mean 40Ar/39Ar single crystal sanidine ages of 37.50 + 0.02 Ma and 36.00 + 0.20 Ma, occur within the basal to mid-section of the 55 m of exposed Pipestone Springs strata, whereas the upper 15 m yields a diverse and abundant assemblage of mostly small-bodied middle Chadronian mammals. The older lapilli tuff is an airfall tuff whereas the younger lapilli tuff exhibits some aeolian reworking. Loessites intercalated with paleosols dominate Pipestone Springs deposits. Andic paleosols are developed on the lapilli tuffs. Buried B cambic to weakly developed argillic horizons characterize the remaining paleosols that are also classified as andic because there is a significant component of volcanic grains mixed with identifiable non-volcanic grains in their parent material. All paleosols are extensively bioturbated, containing newly identified trace fossils likely constructed by dung beetles (Coleoptera) based on comparisons to modern and ancient traces attributed to this group. Close examination shows that the tracemakers built these structures in a helical pattern from the inside and outside by adding pelletized sediment from the base upward, such that the architectural elements resemble features of Rebuffoichnus, FeoichnusEatonichnus, and Coprinisphaera. The preserved forms likely reflect a continuum of state of completion by adults and usage by larvae and pupae, and final preservation in the paleosols. The new isotopic age constraints significantly increase the age range of the Pipestone Springs strata to include early Chadronian deposits in addition to its well-known middle Chadronian vertebrate assemblage. Recognition of loessites comprising these strata is also a new interpretation, making these deposits some of the oldest known aeolian Eocene strata in the Great Plains–Rocky Mountains region.

Pipestone Springs Main Pocket vertebrate locality (middle Chadronian).

EOCENE AND OLIGOCENE MAMMALS FROM THE GRAVELLY RANGE OF SOUTHWEST MONTANA

Our first paper on work that several of us are doing in the Gravelly Range, southwestern Montana, was just published in a special issue of Paludicola, Scientific Contributions of the Rochester Institute of Vertebrate Paleontology. This issue contains papers in honor of James Gilbert Honey, a paleontologist and stratigrapher who focused on the Cenozoic, particularly the paleontology/evolution of camels and the Paleocene’s Fort Union Formation geology and paleontology. We’re pleased to have our work included in this volume! You can find our entire paper at:

Rochester Institute of Vertebrate Paleontology – Paludicola:

Donald Lofgren, Debra Hanneman, Jackson Bibbens, Liam Gerken, Frank Hu, Anthony Runkel, Isabella Kong, Andrew Tarakji, Aspen Helgeson, Isabel Gerard, Ruoqi Li, Sihan Li, Zhihan Ji. 2020. Eocene and Oligocene mammals from the Gravelly Range of southwestern Montana. Paludicola 12: 263-297.

Our paper’s abstract is: High elevation outcrops of Tertiary strata in the Gravelly Range of southwest Montana yield late Uintan to Whitneyan vertebrates that comprise five mammalian assemblages; Rapamys Site, Black Butte Low, Teepee Mountain, Black Butte High, and Lion Mountain High. The Rapamys Site and Black Butte Low are late Uintan or early Duchesnean. Two new species are present at the Rapamys Site (the carnivore Lycophocyon tabrumi and the rodent Pareumys muffleri). Small mammalian assemblages from Teepee Mountain and Black Butte High are late Duchesnean-early Chadronian and Chadronian, respectively. The most diverse assemblage is from Lion Mountain High, which is correlative with Whitneyan faunas from Wyoming, Nebraska, and South Dakota. The Whitneyan age of the Lion Mountain High assemblage is further age constrained by an underlying tuff with a weighted mean 40Ar/39Ar age of 31.7 +- 0.02 Ma and an overlying basalt flow with a K/Ar age of 30.8 +- 0.7 Ma. Paleogeographic range extensions into Montana for Lion Mountain High taxa include Diceratherium tridactylum and Oxetocyon cuspidatus. The taxonomic composition of the combined Rapamys Site/Black Butte Low mammalian assemblage is most similar to those from southern California, rather than geographically closer assemblages found in Wyoming and Utah. Comparison of undescribed middle Eocene mammalian assemblages from southwest Montana to those from southern California will further elucidate the middle Eocene Montana-California paleobiogeographic affinity.

Our geology paper on this area is soon to follow….

Devil’s Slide and A Jumping Fox

Devil’s Slide, a part of Cinnabar Mountain, is located about 3 miles north of Yellowstone National Park’s northern boundary and about 7 miles northwest of Gardiner, Montana. The “slide” or red streak on Cinnabar Mountain is developed in Triassic red beds.

Whenever I drive to Yellowstone National Park’s northern gate, I pass by the Devil’s Slide. It seems that the slide is my gate keeper to the park, and it is always fun to see it in all our different seasons. And once again, during a chance conversation in the park, I was asked about the geology of Devil’s Slide. Because of that conversation, I thought that I’d spend some time blogging about the slide’s geology.

Devil’s Slide is a part of Cinnabar Mountain, which contains steeply-dipping to overturned Paleozoic and Mesozoic strata. Cinnabar Mountain is fault-bounded on its north side by the Gardiner Fault, a north to northeast dipping reverse fault zone. At Cinnabar Mountain’s north end, the Gardiner Fault juxtaposes Archean crystalline rock (now partly masked by Tertiary intrusive rocks and Quaternary glacial sediments as shown on geologic map snapshot below) on the fault’s northern, up-thrown side against Paleozoic strata on its down-thrown, southern side. The Paleozoic-Mesozoic strata in Cinnabar Mountain are contorted because of drag associated with the Gardiner Fault.

Cinnabar Mountain and Devil’s Slide area as a snapshot from the Geologic Map of the Gardiner 30’x60′ Quadrangle, South-Central Montana (Berg and others, 1999, Montana Bureau of Mines and Geology Open-File Report 387). Map symbols on Cinnabar Mountain are: Mm = Mississippian Madison Group, PMs = Permian-Mississippian rocks, Psh = Permian Shedhorn Sandstone, JTrs = Jurassic-Triassic rocks, Kk = Lower Cretaceous Kootenai Formation, Kmfr = Upper and Lower Cretaceous Mowry Shale through Fall River Sandstone.

According to Marius Campbell and others (1915, p. 92), “Cinnabar Mountain was named in the early days, when the bright-red streak that marks it from top to bottom was supposed to be due to the mineral cinnabar, a red ore of mercury.” (From: Guidebook of the Western United States: Part A – The Northern Pacific Route, With a Side Trip to Yellowstone Park, U.S. Geological Survey Bulletin 611). We now know that the bright red streak is not cinnabar (a brick-red form of mercury sulfide), but the area of red in Devil’s Slide is actually a set of Triassic age red beds that mark widespread continental deposition and limited marine incursions throughout the Rocky Mountain region. The red beds in this case get their color from the oxidation of iron-rich minerals contained within the rocks.

And now for the jumping fox and its association to my Devil’s Slide discussion – as I said previously in this blog, the conversation that I had with a fellow-park goer a few days ago brought about my blog on Devil’s Slide. My conversation about the slide happened while I was watching a fox hunt rodents in YNP’s Round Prairie, a gorgeous meadow near Pebble Creek Campground in the park’s northeastern area. The female fox hunted for hours that morning, and several photographers and myself were enthralled with her hunt. The light snowfall of the night before accentuated the bushy fall coat of the fox and gave the hunting scene great color contrast. Here are are few photos from the hunt:

Round Prairie fox with her gorgeous fall-winter coat.
Round Prairie fox on the hunt.
Round Prairie fox on her hunting jump.
Round Prairie fox finishing her hunting jump.

Fall Fieldwork in the Greater Yellowstone Area

Sheepeater Cliff area, Yellowstone National Park. This area is named in honor of the Shoshones who lived in this area, The name specifically comes from their use the big horn sheep – hence the name “sheepeater”. Note the columnar basalt in the cliff area which has an age of about 0.5 million years.

Doing geology field work in the greater Yellowstone area during the fall is always an adventure. This is the time that animals and birds are on the move, so it’s a good opportunity to have interesting chance encounters. In my quest to understand the Eocene thermal springs of the Gravelly Range in southwestern Montana, I’ve spent time in the Yellowstone area hiking around thermal areas. The Artists Paint Pots, located a few miles southwest of the Norris Geyser Basin, appear to be a likely analogy for the Gravelly Range thermal strata. Of particular interest is the red staining that occurs in many meters of Gravelly Range thermal deposit strata. The red stained rocks are ubiquitous in the Red Hill and Middle Springs areas.

Red Hill in the Gravelly Range, southwestern Montana, contains many meters of red-stained, thermally generated Eocene strata.
The Middle Springs area in the Gravelly Range also contains several meters of Eocene red-stained thermally-generated rocks. It’s extremely easy to confuse these rocks with the underlying red-colored Triassic Woodside Formation strata.
Red-stained thermal deposits at Artist Paint Pots.
Blood Geyser thermal pools at Artist Paint Pots, Yellowstone National Park.

The Artist Paint Pots, especially the Blood Geyser, are well known for red-colored rocks that are produced by iron oxides precipitating out of the thermal waters and staining the surrounding rocks.

As I said earlier in this blog, doing fall field work in the greater Yellowstone area usually means exciting chance encounters with various animals and birds. Some encounters are a bit more exhilarating than others, but I did manage to photo-document some in between finishing up field work for the season:

Young grizzly loading up with food (only caraway roots and mice!) in the Tom Miner Basin, Montana.

Bull moose eating on Cottonwood trees near Ennis, Montana.

Immature bald eagle near the Jefferson River, Montana.
Redtail Hawk on irrigation pipe, near Sheridan, Montana.
Trumpeter swan family resting at – ironically, Swan Lake Flats, Yellowstone National Park.
Great Horned owl giving me the evil eye…
Sandhill cranes in-flight near the Ruby Mountains, southwestern Montana.

Yellowstone To Southwest Montana Autumn Field Photo Snaps

Montana’s autumn is my favorite time of the year to do field work. Daytime temperatures are usually cool enough to encourage one to keep moving and the lighting is simply gorgeous. It is also one of the best times to visit areas in and around Yellowstone National Park (YNP) because most of the tourists have gone home. So no huge bear traffic jams or jostling for parking spots at the better known thermal spots in YNP and surrounding environs – it’s just a wonderfully introspective time for field forays. What follows are several photos that chronicle some of my fall wanderings in the greater Yellowstone area, both in terms of wildlife and geology.

Some of my favorite sightings in YNP are bison at any time of the year. But the autumn snows bring on the bison’s technique of using its head to clear snow away from any vegetative food source. The result of their snow-clearing activity is a snow-masked face.

Snow-caked face of a bison in YNP portends the winter food retrieval.

Snow-masked bison near Soda Butte Creek, YNP.

And where the snow hasn’t stacked up much, the YNP bison calmly graze and occasionally congregate on a ridge line to watch what remains of the YNP visitor traffic.

YNP bison contemplating passing vehicles.

Geological features in YNP take on new dimensions with the golden low and slanting light of autumn. I’ve spent much time re-photographing geologic features at all scales that seem to glow in this season’s light.

Tertiary sediments and Quaternary sediments/basalts of “The Narrows” cliff face adjacent to the Yellowstone River, northern YNP. Columnar basalt capped by auto-brecciated basalt makes a morel-like image for these geological units.

An early morning at -7 F on the Lamar River with steam fog resulting from the fall’s chilled air moving over water still warmed from summer.

A rodent trackway disappears into microterracettes of Palette Springs, Mammoth Hot Springs, YNP.

Microbial growth near the proximal part of Mound Springs, Mammoth Hot Springs, YNP.

The proximal end of Mound Springs abounds in various colored microbial life. It’s hard to stop photographing these features because they are so intriguing!

The lipped margin of Mound Spring’s pond facies, Mammoth Hot Springs, YNP.

The fall staging areas of sandhill cranes in southwestern Montana are mesmerizing. Staging areas are those locations where cranes annually congregate during late September into October, spend several days foraging through fields for food, and eventually continue on their migration southward from Montana to Colorado and the southwestern U.S.. The staging area that I usually go to is near Dillon, Montana, where hundreds of cranes can be viewed.

Sandhill crane interaction during their fall staging near Dillon, Montana.

Sandhill cranes doing a dance routine in the Dillon, Montana staging area.

As I said initially, it’s hard to surpass a Montana/YNP autumn!

Greater Yellowstone Area Eocene to Recent Hydrothermal Springs

The Gravelly Range spring deposits depicted in this photo are late Eocene (probably 34-36 million years in age).

Geologic field work is always fun, but especially so when it turns up something unexpected. Working on Eocene to Recent geology and vertebrate paleontology in the Gravelly Range, southwestern Montana promised to be enthralling because the volcanics, sedimentary units, and vertebrate fossils are at elevations of about 9,000 feet. But to come across extensive, unmapped calcareous spring deposits of probable Eocene age is topping off research efforts.

At this point, I’ll just say that our field team is still at work on the Tertiary spring deposits. We’ve found numerous leaf impressions including those of ginkgo, palm, metasequoia, Fagopsis (extinct member of Beech family), and alder – just to name a few. We’ve shown the plant assemblage collected to date to several paleobotanists, and, at least for age, their take is that the assemblage is probably latest Eocene in age, and bears many similarities to Florissant, Colorado fossil plant assemblages.

Palm frond impression from Gravelly Range spring deposit.

Ginkgo leaf impression from a Gravelly Range spring deposit.

Alnus cone from a Gravelly Range Spring deposit.

The spring deposits in the Gravelly Range are extensive, covering an area roughly 2 miles in length with deposits up to 120 feet in thickness. The springs are best characterized as travertine, although the spring systems’ edges contain clastic fluvial units and both the springs’ edges and pools have features such as plant impressions, root systems, and small travertine balls.

Gravelly Range Eocene spring deposit. Field backpacks in lower left corner for scale.

Because the Gravelly Range is so close to Yellowstone National Park, it is extremely interesting to compare its Eocene spring deposits to hydrothermal units at both the currently active Mammoth Hot Springs (which probably began its activity about 7,700 years ago), and to the fossil travertine found just north of Gardiner, Montana, that formed about 19.500 to 38,700 years ago (Fouke and Murphy, 2016: The Art of Yellowstone Science: Mammoth Hot Springs as a Window on the Universe).

The Gardiner travertine is fairly well exposed because it has been extensively quarried for several decades. Of interest for comparison are numerous plant impressions that occur within microterracettes. Fouke and Murphy (2016) suggest that these may be impressions of sage brush. A photo of the quarried wall with the plant impressions is shown below.

Plant impressions in Gardiner travertine. These impressions may be from sage brush. The travertine in this quarry face is estimated at about 30,000 years in age.

Other features in the Gardiner travertine, now partly covered by graffiti, include a quarry wall that shows terracettes and microterracettes that are outlined by darker lines within the travertine. These features are probably indicative of a proximal slope facies.

Gardiner travertine with its slope facies depicted well in smooth quarry face. The dark, irregular lines delineate terracettes and microterracettes.

Jumping forward in time to the extensive spring deposits of Mammoth Hot Springs (just within the northeast park boundary of Yellowstone National Park), is mind boggling. As in any comparison with rocks as old as Eocene to active deposition, one realizes how much detail is lost over time. But it is still worthwhile to try to compare spring features, so I’ll show a few photos of the Mammoth Hot Springs that may match up with various features of the fossil springs.

Branch and plant fragments in the process of becoming calcified at Mammoth Hot Springs – main terrace.

Calcified plant debris – Mammoth main terrace.

Terracettes – Mammoth main terrace, proximal slope facies.

Trees engulfed by prograding spring activity – Mammoth main terrace.

Travertine balls in small pond – Mammoth main terrace.

Suffice it to say, that the upcoming field season should be a good one, with more work to be done on the Gravelly Range spring deposits. And – it’s always fun to get a trip in to Yellowstone!

Tertiary geology and paleontology of the central Gravelly Range – a project update

The 2017 field crew working at Lazyman Hill. The strata are late Eocene (probably 34-36 million years in age) tufa deposits.

It’s time for our yearly update talk on field work and data compilation for the Tertiary geology and paleontology of the central Gravelly Range project in southwestern Montana. The Madison Ranger District in Ennis, Montana (5 Forest Service Road) will be hosting my talk on Monday, April 2nd at 10am in the Madison Ranger District conference room. We have a project permit from the US Forest Service because our project area lies within the Madison Ranger District – and the USFS District people have been really helpful with our project logistics. Thus, this is the perfect way to let them know what we did this past field season and how the whole project is coming together. The Madison District just sent their public announcement for the talk:

Dr. Hanneman and Dr. Don Lofgren, PhD (Director, Raymond M. Alf Museum of Paleontology, Claremont, CA 91711) and their team have been executing a multiyear study in the Gravelly Range near Black Butte resulting in many interesting paleontological findings right here in our own back yard.  Please join Dr. Hanneman and the Madison Ranger District for an update on this project and what they hope to unearth this year!

It’s a very intriguing project on high-elevation, mainly Eocene-Oligocene Tertiary geology and paleontology (mostly vertebrate and floral). So – anyone with an interest in this and who is in the geographic area, is welcome at the talk!

Hiking to Glacier National Park’s Grinnell Glacier

A few days ago I did the hike to Grinnell Glacier, one of the iconic glaciers in Glacier National Park. The glacier lies within the Swiftcurrent drainage area, in the northeastern part of the park. The hike, at least the way I did it, is about 11.6 miles round trip. It is possible to catch a boat ride at the Lake Josephine Boat Dock by the Many Glacier Hotel, which cuts the hike down to about 7.5 miles round trip. But – the first boat goes out at about 8.30 am, and as I didn’t want to wait around for it, I decided that adding on the extra miles for a fairly level stretch around Swiftcurrent Lake and Josephine Lake would be easy to do. It is an easy hike around the lakes and a very good warm-up for the rest of the climb to Grinnell Glacier. But –  be aware that this area is known for grizzly bear activity as I found out when I met up with a grizzly on the trail. Because I’m writing about this encounter,  it obviously ended OK, although I was glad I had bear spray readily available.

The glacier is named after George Bird Grinnell, who first explored this area during the summer of 1885. Because of bad weather, he did not actually get to the glacier during his 1885 travels. However, during the late fall of 1887, he was able to pack most of the way into the glacier by mules, and then hike the remaining distance by foot.  Although he certainly was not the first person to see the glacier, the glacier does bear his name, presumably given it by a Lieutenant John H. Beacom of the United States Army, 3rd Infantry, who accompanied him on the 1887 trip to the glacier.

It’s fun to see ripple marks in the Proterozoic rocks that outcrop along the Grinnell Glacier trail (Grinnell Lake is in the photo’s background).

Back to the hike – after about a mile from the junction of the Swiftcurrent Lake Trail with the trail coming from the North Shore of Lake Josephine boat dock, Grinnell Lake comes into view. A little further along the trail one can see Grinnell Falls dropping several hundred feet down from the headwall behind Grinnell Lake.

Grinnell Falls drops several hundred feet down from the headwall to Grinnell Lake. The Salamander Glacier can be seen in the photo’s upper right-hand corner; Gem Glacier is in the upper left-hand corner of the photo.

And – even at this distance, Salamander and Gem glaciers pop into view in the distant cirque. The hike continues along beautiful alpine meadows and even through one waterfall that cascades down the cliff adjacent to the trail. There is a rest area with pit toilets right before hiking the final switchbacks that traverse the terminal moraine to the Grinnell Glacier Overlook.

The final part of the Grinnell Glacier trail traverses the glacier’s terminal moraine.

Large boulder (Elrod’s Rock) in the Grinnell Glacier’s terminal moraine. Note the marmot atop the boulder for scale. The glacier’s terminus is now about a mile away from this boulder.

The three glaciers that once comprised the Grinnell Glacier occupy parts of a cirque developed along the area called the Garden Wall.

The cirque of the Grinnell, Salamander, and Gem glaciers.

Grinnell Glacier is still the largest of the three ice fields and covers about 152 acres. Unfortunately, this glacier is receding rapidly as the U.S.Geological Survey notes that from 1966 to 2005 it lost about 40% of its acreage. At about 5 acres, the hanging glacier called Gem Glacier, is the smallest named glacier in the park. It sits in the notch on the cliff face above the Grinnell Glacier. This glacier lost about 30 percent of its acreage from 1966 to 2005. The Salamander Glacier covers about 57 acres on a ledge off to the east side of the Grinnell Glacier. It apparently separated from the Grinnell Glacier sometime before 1929 and has undergone a 23% size reduction from 1966 to 2005.

For those interested in viewing photographs of the Grinnell Glacier from various times and viewpoints, the U.S. Geological Survey’s Repeat Photography Project has many archived photographs. This project is a documentation of glacial decline through photography and it is well worth perusing through their photo archives. Two of the earlier photographs are shown below – one from the original 1887 trek and a later view of the glacier from 1940 just to pique one’s interest.

1887 photograph of the Grinnell Glacier taken from footbridge (Lieutenant Beacon, Glacier NP. Public domain).

1887 photograph of the Grinnell Glacier taken from footbridge (Lieutenant Beacom, Glacier NP. Public domain).

Grinnell Glacier from trail 1900; Credit: F.E. Matthes, Glacier NP. Public domain.

Tertiary Geology and Paleontology in the Gravelly Range, Southwestern Montana

Lion Mountain in the Gravelly Range of southwestern Montana. This area is federal land managed by the U.S. Forest Service.

A part of my recent geological field work includes working on high elevation Tertiary strata in the Gravelly Range, southwestern Montana. The Gravelly Range is located in southwest Montana, about 10 miles southwest of Ennis, Montana. For some background on this area and what my field work is about, see an older blog that I posted at Geopostings.

So – now that one field season is done and field data compiled, both my co-worker, Don Lofgren and myself have interpreted some of our data. We recently outlined our work at the Geological Society of America’s (GSA) Rocky Mountain section meeting in Calgary. Alberta. The abstract from our session is given below as well as the poster itself in both a jpeg format and as a link to our  GSA presentation.

“Tertiary strata exposed in four high elevation areas in the south-central
Gravelly Range yield significant assemblages of Late Eocene to Oligocene
mammals. The thickest stratigraphic sections of Tertiary strata are in the
Lion Mountain-Black Butte area. The Lion Mountain section age is based
primarily on American Museum of Natural History collections; the lower
part of this section is Duchesnean-Chadronian (39-33 Ma) and the
uppermost beds are Whitneyan (32-31 Ma). Age of the basal part of the
Black Butte section is Duchesnean-Chadronian based on Harvard Museum of Comparative Zoology collections. Recent collections that include Miohippus indicate a probable Orellan age for uppermost exposures. The Tepee Mountain section is notable for abundant brontothere remains and is probably Duchesnean-Chadronian (approx. 39-33 Ma). The Rapamys site is the oldest vertebrate locality and is late Uintan to early Duchesnean (42-38 Ma) based on recently recovered specimens of RapamysProtoreodon, and Lycophocyon.

The Tertiary strata in this part of the Gravelly Range include fluvial, aeolian, and tufa deposits that are most likely mainly associated with localized Oligocene volcanism. The Lion Mountain section is about 270 meters in thickness; the lower half of the section is largely aeolian, with fluvial units comprising much of the upper section. Based upon age data, the 140 meter Black Butte section correlates to the lower 50-70 meters of the Lion Mountain section. The basal 20 meters of the Black Butte section contain some fluvial features, but much of the remaining section is largely aeolian in origin. Paleosols and extensive burrowing also occur within the Black Butte section. Stratigraphic section thickness decreases rapidly away from the Black Butte-Lion Mountain area, with section thicknesses of about 20 meters for the largely aeolian Rapamys and Tepee Mountain sections. Tufa deposits are located along the west-central edge of the Gravelly Range where they are associated with previously mapped thrust faults. Leaf imprint assemblages of Eocene-Miocene age are contained within these tufas. Strata previously mapped as Upper Cretaceous-Paleocene Beaverhead Formation are now variously reassigned to the lower Cretaceous Kootenai Formation, southwestern Montana Cenozoic Sequence 2, and diverse Quaternary units.” From: Abstract from Geological Society of America Abstracts with Programs. Vol. 49, No. 5 doi: 10.1130/abs/2017RM-293156.

The poster presented at the 2017 Rocky Mountain GSA is available below as a jpeg and at GSA as a pdf.