Exploration Insights September 2019 - Page 10

10 | Halliburton Landmark Exploration Insights | 11 The Drift Towards Plate Tectonic Theory From continental drift to a holistic understanding of the whole Earth system — how plate tectonics informs natural resource exploration. By: Jean-Christophe Wrobel-Daveau and Graeme Nicoll San Andreas Fault. https://en.wikipedia.org/wiki/San_Andreas_Fault#/media/File:Aerial-SanAndreas-CarrizoPlain.jpg. From simple observations of the shape of the continental margins across the Atlantic Ocean to adding the crucial evidence from stratigraphy, palaeontology, and geophysics, the theory has evolved, finally gaining wide acceptance in the late 1960s. In this article, we give an exciting historical overview of this important milestone and how it has impacted the way we conduct oil and gas exploration. We also highlight the main challenges and opportunities that lie ahead, as academia and industry continue to evolve our global understanding by linking more concepts, like mantle dynamics, climatic changes, and sea level perturbations, through plate tectonics. FROM CONTINENTAL DRIFT TO PLATE TECTONICS The Early Days was widely and often violently rejected by the wider scientific community at the time, due to the lack of better physical observations (Simmons, 2018). Wegener believed that mid-oceanic ridges were the location for the extrusion of fresh and fluid new crustal material needed to make continental drift possible. Therefore, oceanic and continental crust had to be different in nature, and had to sit on a material that had fluid properties based on his understanding of isostasy. A whole series of observations was required to confirm this hypothesis, including data on deep ocean floors and the nature of oceanic crust. More generally, the development of marine geology gave evidence for the association of seafloor spreading with mid-ocean ridges and magnetic field reversals (Figure 3), as published between 1959 and 1963 by Heezen and Tharp, Deitz, Hess, Mason, Vine and Matthews, Morley, and others. How the Theory Drifted to Become Plate Tectonics In 1927, the British geologist, Arthur Holmes, proposed a possible mechanism for Wegener’s theory of continental drift. He suggested that differential heating of the Earth’s interior, generated by the decay of uranium and other radioactive elements, caused convection in the “substratum” (the mantle, in today’s terminology), on which the continents floated (Figure 2). Convection cells would be generated that could drag continents apart, allowing new crust to rise up and form. Despite trying to propose hypothetical mechanisms for the driving forces behind his theory of continental drift, such as a centrifugal force or the change in Earth’s axis of rotation, Wegener’s theory As early as 1596, the Dutch map maker, Abraham Ortelius, suggested that the Americas were once joined to Europe and Africa, based on the observation of their matching coastlines. During the 17 th and 18 th centuries, various workers proposed similar hypotheses, but they remained speculative, due to the lack of evidence and understanding of the larger driving mechanisms behind continental separation. In 1858, a French geographer and scientist, Antonio Snider-Pellegrini, published La Création et ses mystères dévoilés (The Creation and its Mysteries Unveiled). This was a first attempt at paleogeographic reconstruction, based on observations of matching plant fossils between Europe and the United States, as well as matching fossils on all the continents (Figure 1). This reconstruction showed the continental fit across the Atlantic Ocean, and even the hypothetical position of Australia to the east of Africa. Alongside understanding geological time, the advent of plate tectonic theory in the 20 th century is arguably the most important advancement in Earth science. The establishment of the Earth’s evolution as a mobile phenomenon has fundamentally changed our understanding of the planet and revolutionized the predictive power of applied geoscience, in a similar way to what the discovery of DNA did for biology and human medicine, and the heliocentric perspective did for astronomy and space exploration. It was Alfred Wegner, widely recognized as the founding father of plate tectonics, who in 1912 introduced the theory of continental drift. He supported this idea using stratigraphic information that had recently been published about Cretaceous and Carboniferous deposits from the continents surrounding the Southern Atlantic. He showed that the continents had once been conjoined using evidence of fossil correlations, stratigraphic and mountain range patterns, and paleo-climate markers. In his book, The Origins of Continents and Oceans, first published in 1915, Wegener proposed that the continents had once formed a supercontinent (“Urkontinent” in German; “Pangea” meaning “all lands” in Greek) that started to split apart approximatively 200 Ma. Figure 1 > Reconstruction of the continental fit before the opening of the Atlantic Ocean and the present-day map (Snider-Pellegrini, 1858). (Source: https://commons.wikimedia.org/wiki/File:Antonio_Snider-Pellegrini_Opening_of_the_Atlantic.jpg).