Holy smokes! What a day

13 November 2008. Lanjiashan, Hezheng, Gansu Province (China)

What a dramatic day; I live for days like this.

We started the day in the valley of Lanjiashan, where a thick (several hundred meters) progression of the late Miocene Liushu Formation is exposed. We were looking at the boundary between the middle Miocene and the late Miocene.

It started out smoothly, until we came to a gulch that separated a clear set of middle Miocene deposits of sandstone conglomerate and marlite on the north side, and a late Miocene-looking set of brownish red mudstone interspersed by carbonate concretion-rich silty mudstone. We did not see any faults, thus we hypothesized that a large slump obscured the true connection between the sides of the gulch.

From the middle of the valley, our leading geologist called my host advisor Dr. Qiu Zhanxiang in Beijing for consultation; "we are unsure of the true contact between the middle and late Miocene, what is the best way to proceed?". The answer we got was: "Look for index fossil species that are unique to each of the geologic ages".

Sounds easy enough, you think. Isn't that what paleontologists do anyway? Well, it's one thing to look for fossils in the well exposed rock strata on the Tibetan Plateau, where deserts and tundra dominate. However, we were in a lush valley of grasses, crop fields, and vertical cliffs. These factors make fossil prospecting impractical and dangerous.

Danger?! You might get the impression that we are daredevils for doing what we do. But today I was a conservative adventurer. The grasses are slick from the frost, and the drifting snowflakes obscure my view of the steep slope down below me. I had better take it easy so I can make it back to Beijing to continue working on my dissertation.

We spent two hours prospecting in that gulch which separated the different lithologies. Nothing major turned up except for a few small bone fragments.

After a quick lunch of cold "pancakes" and canned fish, we went down a different gulch to examine a greenish layer of laminated sandstone and marlite. Before long, our crew leader Hou Sukuan found complete elements of small vertebrates embedded within the layer.

We gathered at the same stratum, and started hacking away at exposed chunks of rock. Before we could react, we were finding small fossil bones left and right. This was indeed a fossiliferous stratum, and it is the first time in the history of the study of this basin that a group of paleontologists had discovered a micromammal site and collected from it. Most of the fossils known from this region (including all the spectacular hyena skeletons) were taken from local farmers without exact locality and geologic information. We have discovered the first confident data point in the geologic progression of the Linxia Basin.

Four hours later, we came up with a handful of small vertebrate fossils. Shi Qinqin, a Chinese graduate student of my host advisor, had found almost all of the teeth we recovered today. Among them are a few partial mandibles of tiny mammals. School children became curious and watch us from afar as they got out of school and walked through the valley to get home.

After dinner in town, I quickly photographed the best finds from today, and emailed the photos to my good friend and small mammal specialist, Dr. Li Qiang, at the Institute of Vertebrate Paleontology and Paleoanthropology. He could not wait, and called me (my cell phone service is charging the roaming rate right now) on my cell phone. Of the three main critters with known teeth, one belongs to an ancient lineage of Prosiphneus, a relatively low-crowned rodent known from th middle Miocene. The other two belonged to a small shrew and a large squirrel, respectively.

[Prospihneus-like rodent, surface view above, and side view below; scale bar lines are millimeters]

I will hand-carry the specimens back to Beijing tomorrow on my 19.5 hour train ride. This should stir up some excitement among the small mammal paleontologists in the Institute; we had little idea how the small mammal community of the Linxia Basin compared with other faunas around northern China and the plateau. The paleoenvironmental implications are extremely important because the large mammal species are preserved as spectacular fossils: what environmental conditions provided for this perservation, and what could potentially be the reasons for their extinction?

[A small shrew jaw embedded in the marlite]

[a squirrel tooth seen through a 10x hand lens in the field at the moment of discovery]

I prepare for bed, with endless possibilities to think about, and with an awe for the fascinating phenomena nature provides for the enjoyment and inspiration of naturalists.

I am very much humbled by nature (again).



(un)Happy feet!

12 November 2008. Hezheng, Gansu Province (China)

Today I am staying indoors, away from the rain. I am working on descriptions of the fossil carnivore skeletons for the public outreach program at the Hezheng Museum. Raising awareness about the natural resources in the region and promoting scientific understanding in general are two goals of the new exhibits to be installed early next year here.

A small dilemma was amplified in this cold weather: I brought two pairs of socks, one to wear until filthy, then washed; in the mean while, I would wear the spare pair until the other pair dried. It's been five days and the washed socks are still as wet as the day I washed them.

I am not one to whine constantly about the cleanliness of my attire (actually, you do not want to hear how long I have been wearing my clothes), but the lovely swampy and grassy hillsides of Hezheng made for spectacular falls down muddy slopes. Our fieldwork here is bringing back memories of my field biology days as an undergraduate.

We spent a whole day yesterday in the hills southwest of Hezheng, near Linxia Basin's edge. There we could see the basement granite in the river valley, and trace the progression of Cenozoic deposits from the early Oligocene up to the Pliocene up the mountain. boundaries between the geologic formations have been defined on layers of coarse conglomerates, which are very difficult to correlate from ridge to ridge when the vegetation obscures much of the underlying geologic features.

Our trek took us over foggy peaks, where shepherds roam and livestock dot the slopes. Every half hour we would come across a small earthen hut, which is used for shelter by the shepherds when weather turns unexpectedly. Lucky for us, there was no snow that day.

We ended the day in a small village a few mountains over from where we started. The late afternoon had already brought the chilling fog, prompting the locals to light their stoves for warmth.

On an unrelated note, I took a photo of a pair of carnivores that died together; the large hindlimbs are those of a fossil wolverine, Plesiogulo brachygnathus, whereas the little carcass on its left thigh probably belongs to that of a fossil skunk. The preparators almost got rid of the crushed skunk before realizing it was not fossil junk!



Geologists keep me honest

9 November 2008. Hezheng, Gansu Province, China

This post is for Karin.

Why do I keep talking about fossils and not so much about the geology? Because I am a biologist!

I do have a real excuse; the lithology and stratigraphy of the rich fossil deposits described in my previous post have not been worked out; I overlap with a team of students who are measuring sections in the immediate area exactly for this reason: to clarify the depositional environment and the geology of Hezheng County.

From what we know, we could at least say that all of the fossils come from yellowish to reddish mudstone, sometimes a sparse conglomeratic mudstone. The preservation differs from locality to locality; most of the deposits show signs of transport and sorting by skeletal element size. However, the deposit I visited in Hualin looked like some kind of mass death event, where many complete skeletons of animals were preserved in a catastrophic burial event.

Today was Sunday, so the museum collection was closed; after examining fossils for a whole day on Saturday, I again tagged along with the students to a geologic section adjacent to the very fossiliferous site previously discussed. No major localities are known from this valley which we measured, but it does provide some clue as to the general geology during the late Miocene of this area.

Walking up-section in the late Miocene Liushu Formation, I counted at least 30 layers of light tan mudstone rich in calcareous nodules. These layers are interspersed by deep red mudstone, representing some kind of cyclic deposition. Interestingly, as we went upsection I observed a layer of greenish mudstone overlaying the red mudstone at strange angles of contact. I hypothesized the presence of a Quaternary channel deposit in the Tertiary strata.

The student team will continue to survey the surrounding valleys, but I must continue with my museum work tomorrow; there are a couple more fossil hyena skeletons I need to measure.

[two amazing hyena skeletons in the collection of the Hezheng Museum]

From a frigid museum dormitory,