June 10, 2017 | David F. Coppedge

Aliens Invade Geology

Is secular geology about to take leave of its senses, believing in unicorns? Read on.

The Geological Society of America (GSA), America’s leading geology institution, is introducing a new word: “xenoconformity.” You may have heard of a conformity (a smooth transition from one sedimentary layer to the next, without a break) and an unconformity (a break in the deposition of sediments). So what on earth is a xenoconformity? If you look up the meaning of the prefix xeno-,  the dictionary calls it “alien, strange, or unusual.” So a xenoconformity is an alien conformity, something that Galen P. Halverson links with “non-actualistic” processes (more on that word later). In his open-access article, “Introducing the Xenoconformity” for the GSA’s premier journal Geology, he reviews the usual conformities and unconformities, then defines this new kind:

Less common but arguably equally important in reconstructing geological history are surfaces that result from dramatic shifts in environmental conditions. Familiar examples are many major boundaries of the geological time scale such as the Permian-Triassic and Cretaceous-Paleogene (K-Pg) boundaries. In addition to the loss of a large number of fossil taxa, the K-Pg boundary is clearly identified by an Ir anomaly (Alvarez et al., 1980; Smit and Hertogen, 1980), a decrease in carbonate content, and a negative carbon isotope anomaly (Hsü et al., 1982). It is intuitive that state changes in paleoenvironments, as exemplified by the K-Pg boundary, occur both globally and regionally and that these changes can generate unique surfaces or transition zones that can be correlated widely. Nonetheless, while clearly understood that these stratigraphic surfaces exist, the geological lexicon lacks a term to describe them. In this issue of Geology, Carroll (p. 639) has taken the first step in correcting this semantic oversight by introducing the term xenoconformity, defined as “a stratigraphic surface or gradational interval that records a fundamental, abrupt, and persistent change in sedimentary facies across basinal to global scales.

Halverson’s article may be useful for laymen to understand terms like facies, sequence stratigraphy, and Walther’s Law, but xenoconformities are “alien” to those phenomena. He mentions geologists’ ongoing faith in uniformitarianism, but xenoconformities are alien to that Lyellian principle, too. They are usually abrupt, persistent, and often global. He mentions the Ediacaran boundary as one, the end of Snowball Earth as another, and extinction markers like the Paleocene-Eocene boundary as a third. He even speculates that the politically-correct, civilization-shaming “Anthropocene” boundary may instigate a new xenoconformity.

Now, back to those unicorns. At one point in his article, Halverson refers to one of his examples of xenoconformities to say, “It is both an exceptional chronostratigraphic marker and a cogent reminder of the importance of non-actualistic processes in shaping the stratigraphic record.” Non-actualistic? What does that mean?

Back in 2009, three geologists had some bones to pick about the terms “actualistic” and “non-actualistic”. In the book Precambrian Sedimentary Environments: A Modern Approach to Ancient Depositional Systems, their chapter, “Actualistic Versus Non-Actualistic Conditions in the Precambrian Sedimentary Record: Reappraisal of an Enduring Discussion,” they enter the discussion with a bit of indignation. It’s not often you see this kind of scorn in a scientific journal toward fellow scientists:

Actualistic models can be successfully applied to virtually all sedimentary successions preserved in the Precambrian rock record, allowing for differences in the relative rates and intensities of those processes that control weathering, erosion, transportation, deposition and lithification. As the basis for this statement, we understand actualism to be the principle that the same processes and natural laws applied in the past as those active today. This definition readily accommodates events of even catastrophic character, such as bolide impacts and tsunamis. Non-actualistic models introduce semantic problems and are of little help for understanding geological processes. A review of the English and German literature on actualism reveals that many misconceptions can arise because of the two principal meanings of the term ‘actual’: (i) real, factual; (ii) present-day. However, if the full range of possible outcomes subject to natural laws is considered, rather than just the expression of these laws as observed in present environments, all Precambrian settings can be investigated and understood by applying the actualistic approach, which is fundamental but not unique to the geological sciences. Thus, all studies involving Precambrian sedimentary rocks can be approached by means of comparisons to present-day environments. Non-actualistic models should be reserved for speculations about early Hadean environments, cosmology, religion and philosophical conjectures about ‘parallel’ worlds (such as those inhabited by unicorns).

Ouch! Better not be too hasty to say that non-actualistic processes are important in shaping the stratigraphic record. Alien unicorns might be listening from a parallel earth.

Have a fun weekend, everybody.

By the way, can you think of a sudden break in the stratigraphic record with global extent that caused a dramatic shift in environmental conditions? We can guarantee it was not caused by aliens or unicorns. Is it religious? No more so than believing in non-actualistic things. Secular geologists, you see, believe in uniformitarianism, except when they don’t. They believe things are actual, except when they are non-actual. They engage in speculation. They subscribe to the religion of xeno-geology. So there.


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