Past Messages


Kevin Schofield, Summer 2007

schofieldWhat Price Catastrophe?

A quotation attributed to the American philosopher and historian William James Durant (1885–1981) pinned up outside a colleague’s door has been bugging me for the best part of a year now. Durant is best remembered for his 11-volume epic “The story of Civilization,” but the attributed quote takes a wry side-swipe at the significance of mankind and his civilizations in the context of the natural order of things: “Civilization exists by geological consent, subject to change without notice.

Durant’s studies in the history of civilization would have made him very aware of the painful interruptions to the steady march of “civilization” from the ancient world up to his own lifetime, with (to mention but a representative list) the eruptions of Thera (Santorini) in the early 1600s BC dealing a body-blow to the Minoan Civilization on Crete, the destruction of the Colossus at Rhodes by an earthquake in 224BC, the eruption of Vesuvius in 79AD wiping Pompeii and Herculaneum off the map, the virtual destruction of Lisbon in 1755 after a near-offshore earthquake and resultant tsunami, and, rather more immediate from his viewpoint, the eruption of Krakatoa in 1883 (which, among other superlatives, created the loudest noise in recorded history!) and the “Tunguska Event” in 1908, believed to have been the result of the collision of a smallish asteroid or cometary fragment with the earth over Siberia that resulted in the felling of some 80 million trees, but little loss of human life…although if it had come down four-and-a-half hours later on the same trajectory, it would have wiped out St Petersburg!

With modern communications, of course, one could be forgiven for thinking that we are living in The End of Days, with the eruption of Mts St Helens and Pinatubo, earthquakes demolishing city of Bam in Iran and destroying many villages in Pakistan in the last few years, the Indian Ocean Tsunami of Christmas 2004, and in the past few weeks, the earthquake in the Solomon Islands that lifted acres of coral reef several feet above sea level.

All of which, I am sure, would have fallen within the realms of possibility that Durant was thinking about when he penned his bon mot on the transient nature of man’s artifice when faced with the onslaught of nature.

But should we as geoscientists, look at things in the same way? The human experience is, after all, very transitory, and what appears to us as an event of (literally) earth-shaking magnitude seldom appears in the geological record as even a footnote, let alone a paragraph. Certainly, my geological education in the mid- to late-seventies was heavy on “The Present is the Key to the Past”, with stratigraphy being taught as a linear progression, and all thought of global cataclysm being kindly (or otherwise) dismissed as the ravings of Noachian bishops or the work of slightly unbalanced minds (those crazy Alvarez boys and their meteorite!). My undergraduate Uniformitarianism proceeded sedately to post-graduate carbonate sedimentology in the Carboniferous of Central England, where again the ideas of gradualism ruled pretty much unchallenged, and although my early years in the oil industry were punctuated with the controversies over the mega-controls on depositional systems, with the battle of wits between the structural controllers and the sea-level cyclists, again neither camp really asked us to step outside of the bounds of gradualist orthodoxy.

So if all of the above-noted philosophical and historical disasters would not disturb the Uniformitarian record as we have been taught to know and love it, and generally seem to observe it (or interpret our observations to confirm?), what is the standard for a truly catastrophic single event?

Well, in the early nineties I got my second specialist wind and discovered the whacky world of the sediment gravity flow. At first, this all seemed to match up with the general tenets of gradualism…Arnold Bouma had found the Rosetta Stone in southern France, Don Lowe tweaked it to allow for a little excess density, and we were home and dry. DSDP coring and the splendid tales of broken transatlantic telephone cables on the Grand Banks pretty much sewed it up. But then some nagging doubts crept in…cores from the deepwater Gulf of Mexico with sands tens of metres thick, seemingly deposited from individual flows, and apparently correlateable over tens of kilometres laterally…massive volumes of sediment, tricky to explain as the products of “everyday events” at the shelf-edge. Recent research by consortia in the UK at Bristol, Southampton and Leeds have taken fresh looks at Bouma’s Annot sandstones, the Marnoso Arinacea of the Central Appenines in Italy, and at long run-out events in the basins off North-East Africa, where the distal deposits of major shelf-edge collapse events can be traced over hundreds, if not thousands of square kilometres. All of these suggest that rather than deepwater basins being filled gradually by small volume flows over time, significant volumes of sediment are dumped down to the basin floor in massive events where significant portions of the continental shelf are displaced effectively instantaneously.

A fine example of this phenomenon is the Storegga Slide offshore Norway which has been extensively researched in the past decade, largely to become safe in the knowledge that the development of the Ormen Lange gas field wouldn’t set off another event…which would not be A Good Thing! In a series of retrogressive failures of the continental shelf 6000 to 8000 years ago, dumped 3500 cubic kilometres of sediment onto the Atlantic Abyssal plain and caused a tsunami estimated at 20m high across the northern Atlantic area. Sediments deposited by this tsunami have been recognized 80km inland in Scotland. Again, in terms of civilization, a pretty nasty event, but geologically, barely a whisper! Back in the Gulf of Mexico, a number of major shelf-edge collapses have been recognized in the Oligo-Miocene which between them could well have contributed thousands of cubic kilometres to the base of slope fans, including some of the reservoirs I noted above. The Oligocene Hackberry Canyon is one example, the other is the Lower Miocene “Abbeville Breakup” described by Mark Edwards (1994). These had the potential to dump hundreds of cubic kilometres into the Gulf of Mexico in very short order, and if happening today would cause devastation all around the coastline of the Gulf of Mexico, but again, geologically…hardly a footnote!

So, where am I going with this? I suppose it is really to conclude that geological events do not have to be on any sort of planetary scale to revoke the consent by which we occupy our ecological niche. The events that Durand had in mind and some of the biggest depositional events that we are able to recognise are, in the grand stratigraphic scheme, all part of the uniformitarian continuum, magnified by our very short term view of the world. And maybe that’s where we as geoscientists can play our part in the modern debates played out in the news media day after day, week after week, reminding our less long-termist brethren that human-scale tragedy is, to planet earth, all in a day’s work! I’ll be revisiting this idea in the next issue, with some thoughts on the mega news issue of the day, Global Warming…or is that Climate Change?

On a less philosophical and more “newsy” note, I’d like to draw your attention now to the fall conference season for GCSSEPM and our valued sister-organization and collaborator the GCAGS.

The GCAGS-GCSSEPM 57th Annual Convention will be held this year in Corpus Christi on October 21st to 23rd, with the theme “Exploring the Third Coast.”

The 2007 Bob F Perkins Research Conference “The Paleogene of the Gulf of Mexico and Caribbean Basins: Processes, Events, and Petroleum Systems” takes place on December 2nd to 5th 2007 here in Houston.

Look ‘em up and book ‘em people…lots of good information to be had and acquaintances to be renewed!

Edwards, M. B., 1994, Enhancing sandstone reservoir prediction by mapping erosion surfaces, Lower Miocene deltas, southwest Louisiana, Gulf Coast Basin: Gulf Coast Association of Geological Societies Transactions, v. 44, p. 205-215.