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).
Jack
