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Miocene Plants in Lacustrine Formation

DPS Ammonite

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I found these in a Miocene lake bed formation northeast of Phoenix, Arizona. The lake beds are deposited along with volcanic rocks and are probably part of the Chalk Canyon Formation. The lake beds have pieces of agatized plant material. Any ideas of what the plants might be? I am especially interested in the molds of a jointed plant shown in the first three photos.



Photo about 6cm high.



Detail of first photo.

Filled center of plant stem ~0.7mm. Depressed mold of stem ~ 3mm

across. Height of photo ~2.5cm.



Detail of first photo.

Center of stem ~ 1mm. Mold of stem ~3mm across. Length of stem ~5.5cm.



Bunch of stems average of 5mm across.



Cross section of above photo.




Typical stems each about 2 - 4mm across.




Possible stromatolite/algae structure.




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The plant material from the first three images reminds me of Hydrocharitaceae, maybe something close to Hydrilla.

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7 minutes ago, abyssunder said:

The plant material from the first three images reminds me of Hydrocharitaceae, maybe something close to Hydrilla.

Thanks Abyssunder. Possibly a candidate.


Here is another possibility: horsetails. 



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6 minutes ago, DPS Ammonite said:

Here is another possibility: horsetails. 

Yes, that was my first idea, but I ruled out considering the material is from a lake bed. :headscratch:

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This description from the Hualapai Limestone provides a useful explanation:


The remains of grasses, reeds, and rushes are the most abundant macrofossils found in the Hualapai Limestone Member. These can be observed as layered horizontal mats entirely replaced by limestone. Others form vertical hollow calcite tubes, having inner surfaces lined with drusy quartz and exteriors encrusted with travertine. In at least one locality (fig. 1, loc. 1) the reed stem structures have been perfectly replaced by opal, preserving the cell walls (pi. 12, figs. 1-6). Molds and casts of the plants resemble Juncus (Juncaceae, the rush family), but they have not been identified with certainty.


Some of the plant fossils with hollow stem structures look like scouring rushes (Equisetacae): these rushes are now represented only by a single genus, Equisetum (Robinson and Fernald, 1908, p. 51; Scott, 1962, p. 13). The stems usually have hollow internodes with a coating of silex, which is the zone that is normally preserved. Equisetum is a silica accumulator plant that takes silica into its system from the soil. This silica is precipitated around the cell walls in the form of plant, opal (Lovering and Engel, 1967, p. B15). When the plant dies, the silica then is either dispersed in the form of phytoliths, or, if the plant is buried before this dispersal, its opalized structure can be preserved in the rock record. The amount of silica contributed to the Hualapai Limestone Member in this manner, however, was probably minor.


text from:


Blair, W.N., Armstrong, A.K. 1979

Hualapai Limestone Member of the Muddy Creek Formation: The youngest deposit predating the Grand Canyon, southeastern Nevada and northwestern Arizona.

United States Geological Survey Professional Paper, 1111: 60 pp.  PDF LINK

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Here is some of the ends of the reeds that are about 2-3mm across:




Above photo is a detail from this photo:


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Here are some more stem end photos. Stems are 2-3mm across. They are probably not horsetails since they are not hollow in the center.



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