Posted by: paulgarner | February 13, 2010

Bees’ nests and termite mounds: rethinking problematic ichnofossils

Perhaps the most problematic ichnofossils for flood geology are those that suggest in situ organismal activity over extended time periods on particular stratigraphic horizons. Among such ichnofossils are the “bees’ nests” of the Triassic Chinle Formation and the “termite mounds” of the Jurassic Morrison Formation in the western United States (see, for example, Hasiotis 2004; Hasiotis et al 1998). I must confess that reports like these have had me scratching my head for a while. How could such ichnofossils possibly have formed during the global flood? Recently, though, I came across a couple of studies that may shed some light on these problematic features.

First of all, the termite mounds in the Morrison: a preliminary re-investigation of these structures was presented as a poster at the 58th Annual Meeting of the GSA by Roth et al (2006). They describe the mounds as complex erosion-resistant concretions, commonly cylindrical in form and about a metre across. They’re usually vertical, though rarely horizontal, and frequently branch into the surrounding bedded sandstones. Their size, morphology and petrography suggest that they’re neither fulgurites nor rhizoconcretions. However: “Thus far, we have not found a convincing termite nest architecture or termites, and this brings into question the fossil termite nest interpretation.” The authors suggest that they may be inorganic concretions that are following the pattern of the “tubes” (of organic or inorganic origin) that are abundant in the surrounding country rock. Only a poster, I know, and it would be good if a full peer-reviewed paper was forthcoming. But intriguing, nevertheless.

And then there are the nests of solitary bees and wasps found in palaeosols in the Chinle Formation. Except that’s not what they are, according to a recently published study in Palaeogeography, Palaeoclimatology, Palaeoecology. Lucas et al (2010) critically re-evaluate the ichnofossils in question and argue that they lack the diagnostic features of hymenopteran nests (e.g. flask-like shape and spiral cap). Rather, they are simple, unornamented, cylindrical burrows which they assign to Skolithos. Nor are they in palaeosols, apparently. They’re in fluvial sandstones with lateral accretion and splay features characteristic of other Chinle Group sandstone bodies. Skolithos is commonly interpreted as a dwelling trace, although I suspect that these might be escape structures generated by organisms trying to keep pace with rapid sedimentation. (Lucas et al also reinterpret alleged “colonial bees’ nests” in petrified wood in the Chinle as the larval chambers of wood-boring beetles, but those structures don’t present the same “time” problems for flood geology as bees’ nests in palaeosols, so I won’t dwell on them here).

No doubt there’ll be continued debate about the identification of these ichnofossils; these papers aren’t going to be the last word on the subject, and I’m pretty sure that Stephen Hasiotis and colleagues will have something to say in response. But these studies do serve to remind us that dogmatism in interpreting structures like these is usually unwarranted and that alternative explanations are often possible – even if we don’t know what they are yet. So next time you hear someone confidently say that this or that structure is “impossible” to explain by flood geology, remember that it might be as well to retain an open mind.

References

Hasiotis S. T. 2004. Reconnaissance of Upper Jurassic Morrison Formation ichnofossils, Rocky Mountain Region, USA: paleoenvironmental, stratigraphic, and paleoclimatic significance of terrestrial and freshwater ichnocoenoses. Sedimentary Geology, 167(3-4):177-268.

Hasiotis S. T., Dubiel R. F., Kay P. T., Demko T. M., Kowalska K., McDaniel D. 1998. Research update on hymenopteran nests and cocoons, Upper Triassic Chinle Formation, Petrified Forest National Park, Arizona, in: Santucci V. L., McClelland L. (editors), National Park Service Paleontological Research. Technical Report NPS/NRGRD/GRDTR-98/01, pp.116-121.

Lucas S. G., Minter N. J., Hunt A. P. 2010. Re-evaluation of alleged bees’ nests from the Upper Triassic of Arizona. Palaeogeography, Palaeoclimatology, Palaeoecology, 286(3-4):194-201.

Roth A. A., Zoutewelle T., Hornbacher D. 2006. Complex concretions in the Jurassic Morrison Formation. Geological Society of America Abstracts with Programs, 38(6):7.

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