ABOUT BLACK SWANS AND STRATIGRAPHY

There is a theory, known as the Black Swan theory, where an extraordinary, unexpected or extremely rare event has a disproportionate impact on our own perception. These events produce psychological biases and collateral effects when faced with the later analysis of regular versus abnormal processes. The surprise effect and its scale affect the collective perception of a higher probability of occurrence than the real one with respect to the regular processes. Given this, it is a fact that our memories are constituted mainly of extraordinary events. In the same way, we can raise the analogy and mention that throughout its history, our planet keeps in its stratigraphic record memories mainly of the extraordinary events that happened to it.

When we start to study geology, the past seems to have been a much more dangerous place than the world we know today. In the past, there were earthquakes of colossal magnitude that separated continents, meteorites that extinguished whole species in a stroke, there were floods as extensive as complete countries, there was ice everywhere and there was thaw. Patagonia was a leafy jungle that was dramatically dismantled in a few years under huge amounts of volcanic ash. It is crucial to know all this, as Harrington (1965) used to say: “the past is the key to the present”

To imagine that dangerous past of the world, I would like you to think about a catastrophic, abnormal, strange and extraordinary event. We could represent that rare event, with 8 dice and the desire to come out of a single shot eight sixes. The possibilities that this happens are extremely small (approximately 1 in 17 million). If we made about 200 pitches, the probability of throwing eight sixes at least once will remain very small, only 1 in 10,000. However, if we are persistent and throw 2,000,000 times, the probability of throwing eight sixes would increase to 63%, and if we did it 5,000,000 times, we would reach 95%. Now let's think that this rare and catastrophic geological event is represented by the dice, the throws would represent the years. If there is something that abounds in geology, it is time, and it is so much that the improbable, the rare or extraordinary, becomes probable and eventually approaches certainty. This game of probabilities and geological events was proposed by Gretener in 1967.

Although this, in a certain way, explains the conformation of the stratigraphic record from transcendent and extraordinary events, the duration of these events is another remarkable point. Referring to sedimentary processes, Sadler (1981) postulated that the duration of the geological event was inversely proportional to the deposition rate. In this way, layers of several meters are deposited in hours to days while small beds related to soil formation or pelagic sediment, represent hundreds to thousands of years of calm sedimentation.

While Sadler focused on the deposit, there were others, such as Amadeus Grabau (1913) who faced the same approach from another important stratigraphic element, the interstratal surfaces. Amadeus postulated that the time contained in these surfaces was several orders of greater magnitude than the time contained in the recorded geological event. This idea, subsequently, was in some way expressed by Harry Wheeler (1958) who graphed the geological events in a Cartesian system. He represented the relative time in the Y axis and in the X axis the space occupied by them, and in this way, he constructed one of the most powerful tools that stratigraphy has.

Finally, we can say that the stratigraphic record is composed of extraordinary geological events, instantaneous if we analyze them in a temporal context and separated by time quantities several orders of greater magnitude, represented by stratigraphic surfaces. Of all the previously exposed, we can say that on the one hand the past has the key to understand the present and on the other it takes us to raise an apocryphal law in relation to the stratigraphic registry:

"In the ocean of averages, dwarfs are drowned"

What do you think about the catastrophic events, about climate change and the future of humankind??

If you are interested in the issue, please enjoy this papers..

• Grabau A. W. 1913. Principles of Stratigraphy. New York. A. G. Seiler & Cia, 1185p.
• Gretener P. E. 1967. Significance of the rare event in geology. AAPG Bulletin; 51 (11): 2197–2206.
• Harrington, H. J. 1965. Space, things, time and events—an essay on stratigraphy, Am. Assoc. Pet. Geol. Bull. 49, 1601–1646.
• Sadler P, M. 1981. Sediment accumulation rates and the completeness of stratigraphic sections. Journal of Geology, 89, 569-684.
• Wheeler, H.E. 1958, Time stratigraphy. American Association of Petroleum Geologists, Bulletin, v. 42, p. 1047-1063