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.
From a frigid museum dormitory,
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