The 38th parallel lineament or chain refers to a group of 8 structures of varied impact and volcanic origin that are found in a rough line that approximates the 38th parallel in Kansas, Missouri, and Illinois. 6 objects associated with a the 38th parallel lineament are located within Missouri. The linearity of these structures was probably first observed upon by Snyder and Gerdemann or by Amstutz in 1965, but may go back farther.
The 38th Parallel chain theory is really a set of 3 competing scientific interpretations that have been competing for space in the literature over the last 50 years or so. These are:
The chain eruption and chain impact theories derive from a belief that 1) several geological items are lined up 2) the fact that they are lined up is not an accident and surpasses the bounds of random probability 3) the fact that they are lined up indicates a common origin for the objects. Whether 1 and 2 are true is debatable, and has been addressed in literature, and I will probably eventually look up the references and put them here.
The 38th parallel lineament theory, captured broadly in the work of Amstutz, 1965(a), attempted to explain a series of apparently aligned objects in terms of an underlying fault system by placing cryptovolcanic eruptions on fault intersections. A series of publications detailing the necessary locations of the fault intersections involved (often largely interpreted based on the circular evidence of the 'eruptions' they produced) emerged in the literature. Faults appeared on maps. People then went back and pointed to the maps as evidence for the faults that produced the eruptions that served as the orginal evidence for the presence of the fault intersections... and so on.
The theory evolved to say that all of the 38th parallel structures were expressions of an underlying volcanic belt associated with faulting along this line in the basement rock of the region.
A gradually emerging picture suggests, more and more strongly over time, that these structures vary substantially in both age and origin, and that their linear association is coincidental.
Igneous rocks (rocks of volcanic origin) are unusual on the Salem and Springfield plateau surfaces of the Oazrk Plateaus region, though the entire region is underlain by such rocks at reasonably shallow depths of a few thousand feet or less. The presence of igneous rocks at or near the surface of the ground, along with significant indications of violent disturbance such as breccias, shallow faulting, and regional disruption of stratigraphic patterns, set these structures apart. Both because these types of rocks are uncommon in the area and because they suggest the possibility of metal ore concentrations, any geologist working in the region would find an outcrop of such materials significant and noteable. It was this contrast with surrounding rocks that orginally put the 38th lineament structures on the map. Because they were originally poorly understood, and could not be explained in terms of clear volcanic processes, the structures were termed cryptovolcanic.
Debate about the 38th parallel lineament took on a new intensity following a fairly recent publication. Rampino and Volk, 1996, put forth a theory, after the Shoemaker-Levy 9 chain impact was observed on Jupiter, that the 8 structures located roughly along the 38th parallel in Kansas, Missouri, and Illinois might all be attributable to a chain impact of meteorites. Meteorite impacts can produce or expose igneous rock types similar to those produced by a volcano in two ways. They can either expose underlying igneous rocks when rocks at the center of the crater rebound after the impact, sometimes rising hundreds of feet above their previous depth, or the impact can actually melt substantial bodies of rock that cool and recrystallize to form rocks similar to those found in a volcanic environment. It seems that some of Missouri's structures have igneous surface material produced by these mechanisms. Nevertheless, though the crater chain theory is fun and interesting, at least one of these structures has been positively identified as volcanic in origin, meaning a broader explanation must be employed.
An opposing viewpoint (Luczaj, 1998) attempts to explain all of these structures as volcanic in origin. The confirmed presence of at least two impact strucutres and the likely confirmation of at least one more, the Weaubleau Osceolla structure, among the group, suggest that each of these structures requires independent evaluation.
Shock metamorphic features found in impact structures cannot be duplicated (or have not been found to be duplicated) in any volcanic structure, making these two lines of reasoning truly separable based on evidence. (French, 1990, 25 years of the impact-volcanic controversy - Is there anything new under the sun or inside the earth?)
While the chain impact theory as originally formulated, has been thoroughly discredited by the discovery that most of the structures involved, both within and outside of Arkansas, are not impacts. It's primary original opposing theory has been equally discredited. The structures involved do not trace any known coherent fault line, are not predominantly freatic eruptions, and are not uniformly volcanic in origin. Some question still legitimately remains regarding the possibility that two or all three of Missouri's actual impact structures may represent a binary or chain impact. Whether anyone would be asking this question if the original set of 8 structures and their mistaken interpretation had not been previously debated is open for discusion.
Evans et al., 2010, in a GSA abstract, presented a coherent evaluation of the current state of the question by pointing out that the proximity and approximate allignment of the 3 structures appears to be a statistical improbability and that, while the age of the Weaubleau structure has been constrained to approximately the Osagean-Meramecian boundary, the Decaturville and Crooked Creek structures have not yet been adequately dated. The range of time to which the ages of both of these structures has been so far constrained does not rule out contemporaneity with the Weaubleau. The detailed conodont and other fossil evidence to support this 2010 paper is reported in Miller et al. GSA abstracts on which Evans was one of several co-authors in 2006 and 2007.
In summary, while there is currently no substantial evidence in favor of the 38th parallel chain impact hypothesis, there is also no evidence solidly refuting it.
(Having visited the sites and read the literature, I will make a personal statement here that, while I lean against the 38th parallel argument on the basis of a lack of substantive data upon which to build a case, neither confirmation nor refutation would surprise me in the least.)
It is clear, at this point in history, that all of the objects involved int hese theories do not share a common origin. Although the 'lineament' theory has been thoroughly discredited, its faults (all pun intended) will probably plague us on maps for generations. It has not yet been clearly established whether two or more of the 3 known impact craters in the set are related. Although no data supporting it has yet emerged, nothing makes it impossible either. If future research into crater ages supports a common origin, a modified and substantially reduced version of the 'chain' theory may emerge from timing evidence. If this is the case, it is extremely unlikely that it will expand to involve all of the orignal structures, since several have clearly (and unrelatedly except in the broadest sense) volcanic origins.
To a significant extent, the Lineament versus Impact and Volcanic argument of the 60s and 70s reflected an underlying argument against the emerging science of impact cratering. The new impact theories in the region (which had global implications) being put forth by Dietz, Hendriks, and others, flew in the face of conventional geological understanding, and a literary backlash ensued. This took the form of increasingly elaborate interpretations based on the presence of increasingly poorly supported faults and increasingly cryptic cryptovolcanism... until the literature finally submitted to the new paradigm based on the weight of impact evidence.
The second iteration, the Chain theory, which had its heyday in the 90's was a reinterpretation of an outdated scientific literature that has no mechanism for cleaning up the spilled remnants of old debates. It was, however, again the symptom of science moving forward, and represented a watershed change in our ability to study craters. In the late 80s and 90s, we all had access to desktop computers with programs that were actually useful, and we gained the ability to do fun things with satelite views, digital models, and maps. Following the impact of comet Shoemaker-Levy 9, and given the existing literature in which the Lineament theory had been slowly beaten back by crater research, the Chain theory was almost to be expected as a reactionary 'extension ad absurdum.' In other words, it would have made good sense at the time... unless you went in to the field and looked at a lot of rocks.
This process of historical debate brought about our current toolkit for identifying and verifying craters, and led us to where we are now - a policy of 'satellite pictures and maps are nice, but ground truth is necessary.' In essence, we have said that (on Earth) an aerial view is not enough; that good impact science must be tied to the rocks - to quantifiable material evidence that can be independently verified, tested, and challenged or re-examined. After all, its science.
References and Further Reading
Amstutz, G. C. (1965), TECTONIC AND PETROGRAPHIC OBSERVATIONS ON POLYGONAL STRUCTURES IN MISSOURI. Annals of the New York Academy of Sciences, 123:876894.
Bottke, W.F., Jr., Richardson, D.C., and Love, S.G., 1997, Crater chains on Earth? Probably not: Icarus, 126, p. 470-474.
* EVANS, K.R, MILLER, J.F., and MIAO, X., 2010, Origins of the 38th parallel structures: 2010 Geological Society of America North-Central/South-Central Joint Meeting, v. 42(2), p. 91.
(In this GSA abstract, the authors nicely summarize the current status of the 38th parallel theory: Only 3 structures are impacts, the rest are apparently or definatively not. The alignment of the 3 craters is pecuiliar and intruiging, and our knowledge about impact timing for the craters neither confirms nor refutes their association with each other.)
Heyl, A. V., 1983, Some major lineaments reflecting deep-seated fracture zones in the central United States, and mineral districts related to the zones. Global Tectonics and Metallogeny, 2, p. 75-89.
Heyl, A. V., 1972, The 38th parallel lineament and its relationship to ore deposits. Economic Geology, 67, p. 879-894.
Luczaj J. (1998) Argument supporting explosive igneous activity for the origin of "cryptoexplosion" structures in the midcontinent, United States. Geology 26(4):295-298.
Luczaj was also printed in geology forum with important comments. Comments are at:
* Miller, J.F., Evans, K.R., Kurtz, V. R., Thompson, T.L.,Mulvaney, P. S., Sandberg, C. A., Repetski, J.E., Ethington, R.L., 2006, Using Conodonts and Other Fossils to Determine the Age of Missouri's 38th Parallel Structures and Some "Lost Horizons" of the Ozark Dome. (abstract)2006 Geological Society of America Philadelphia Annual Meeting, Abstracts with Programs, Vol 38, No. 7, p 184.
(Reports conodont analysis at the Weaubleau, Crooked Creek, Deacturville, and Avon sites. They constrain the Weaubleau event to the Osagean/Meramecian boundary, place the Decaturille subsequent to the Cincinnatian (Ordovician), suggest that the Crooked Creek is mid-Mississippian or later, and locate Cambrian and Early Devonian macrofossils at the Avon structure. None of these finds confirm or preclude simultaneous formation for these sites.)
Rampino M. R. and Volk T. (1996) Multiple impact events in the paleozoic: Collision with a string of comets or asteroids? Geophysical Research Letters 23(1):49-52.
Rampino, M.R., and Volk, T., 1995, Evidence for a multiple impact event on Earth in the Paleozoic; collision with a comet or asteroid string? Eos Transactions, American Geophysical Union, 76(46), p. 337-338.
Rampino M. R., Glikson A., Koeberl C., Reimold W. U. and Luczaj J. (1999) Argument supporting explosive igneous activity for the origin of "cryptoexplosion" structures in the midcontinent, United States: Comments and Reply. Geology 27(3):279-285.
Rampino, M. R., 1997, Defending the crater chain: Geotimes, 42(6), p. 4.
Re-evaluating the 38th Parallel Serial Impact Hypothesis
Spencer C. G., 2011, Roadside Geology of Missouri, Mountain Press Publishing Company, Missoula, Montana.
Snyder, F.G., and Gerdemann, P.E., 1965, Explosive igneous activity along an Illinois-Missouri-Kansas axis: American Journal of Science, 263(6), p. 465-493.
Snyder, F. G., Beveridge, T. R., Gerdemann, P. E., Hendriks, H. E., Fellows, L., 1964, Cryptovolcanic structures of south central Missouri. Guidebook, Eleventh Annual Field Trip of the Association of Missouri Geologists, 11 p.
Snyder, F.G, Gerdemann, P.E., Hendriks, H.E., Williams, J.H., Wallace, G., and Martin, J.A., 1965, Cryptoexplosive structures in Missouri: Guidebook, 1965 Annual Meeting of the Geological Society of America: Geological Survey and Water Resources Report of Investigations, 30, 73 pp.
Nice old field trip guide book.
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