Guest “How Not to Connect the Present with the Past” by David Middleton
Alabama’s return to the sea
A paleontological site shows how life existed in an almost completely submerged Alabama – and how it could when the ocean rises.
by Jack Tamisiea
September 8, 2021
Harrell Station in Alabama, about 75 kilometers west of Montgomery and 250 kilometers inland from the Gulf of Mexico, appears to be the last place anyone would explore the ocean. But the remains of an ancient sea are crumbling out of the dusty ground, which is crumpled into white chalk women. During the Late Cretaceous Period, about 82 million years ago, high temperatures melted the polar ice caps that flooded the world’s coasts. A shallow sea known as the Mississippi Embayment spread over the southeastern United States and covered much of Alabama. Harrell Station is one of the best places to see this primeval sea.
The Harrell Station gorges are located on a belt of Cretaceous rock known as the Mooreville Chalk. Compacted over time and carved by eons of erosion, the powdered marl is made up of the crushed skeletons of microscopic algae known as coccolithophores combined with clay. When this plankton sank to the ocean floor, they buried larger sea creatures with stunning detail.
Since the 1940s, researchers have been working to exhume this fossilized premium. To this day, they keep discovering new species. Adiel Klompmaker, curator of paleontology at the Alabama Museum of Natural History, which has owned and excavated much of Harrell Station since 1991, compares the site to a Cretaceous time capsule. “We know so much about the late Cretaceous period because of Harrell Station,” he says.
[…]
This connection between the warming of the water and the rise in sea level is a problem for Klompmaker. “Harrell Station is issuing a warning,” he says. “It reminds us that sea levels can inundate huge amounts of the state of Alabama.”
This process is already underway. A combination of sinking land and a warming gulf makes Alabama one of the states most at risk from sea level rise. The ocean has risen nearly 30 centimeters in the past 50 years and has eaten away the offshore islands and coasts of the state. Some people might like having a beachfront property in northern Alabama, Klompmaker jokingly says, “but I think a lot of people would disagree.”
[…]
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It reminds me of In Search of Noah’s Ark (1976). I remember a paleontologist saying that marine fossils were found on mountain tops around the world; proved that once a great flood covered the entire surface of the earth. This is exactly how the present cannot be linked to the past. It’s not exactly geology. This is exactly how the principle of uniformitarianism is not applied. But it’s almost exactly what this aspiring young science writer did.
During the Late Cretaceous Period, about 82 million years ago, high temperatures melted the polar ice caps that flooded the world’s coasts.
Jack Tamisiea, 2020 BS Environmental Studies, minor in Narrative Structure, work on Science Writing MS
The “science writer” assumes that most of today’s Alabama was underwater during the Cretaceous Period, as melting polar ice caps were the main cause of sea level rise since the end of the last Pleistocene Ice Age.
Cretaceous sea level had nothing to do with melting polar ice caps. While there may have been some ephemeral ice sheets and glaciers during the Late Jurassic to the Early Cretaceous Period, there were no significant polar ice caps during the Mesozoic Era.
Cretaceous paleogeography was completely different from modern physical geography. Because of this, the sea level was higher, why it was so much warmer and probably the CO2 levels so much higher than it is today. Shallow seas covered much of the continental landmass. Although sea levels were much higher in the Cretaceous than they are today, today’s oceans are strangely much deeper than they were in the Cretaceous. The oceans are currently deeper than they have ever been in the last 250 million years.
The second phase of the Pangea eruption began in the early Cretaceous around 140 million years ago. Gondwana continued to break up when South America separated from Africa and opened up the South Atlantic, and India, along with Madagascar, flowed away from Antarctica and the western edge of Australia into the eastern Indian Ocean. The South Atlantic did not open up all at once, but was gradually “unpacked” from south to north. That is why the South Atlantic is wider in the south.
Other important plate tectonic events occurred during the Cretaceous Period. These include: the initiation of rifting between North America and Europe, the rotation of Iberia counterclockwise from France, the separation of India from Madagascar, the diversion of Cuba and Hispaniola from the Pacific, the rise of the Rocky Mountains, and the arrival of exotic terranos (Wrangellia , Stikinia) on the western edge of North America.
Worldwide, the climate during the Cretaceous Period, as in the Jura and Triassic, was much warmer than it is today. Dinosaurs and palm trees were present north of the Arctic Circle, as well as in Antarctica and southern Australia. Although there may have been some at the Poles in the early Cretaceous, during the Mesozoic there were no large ice caps at any time.
These mild climatic conditions were in part due to the fact that shallow sea lanes covered the continents during the Cretaceous Period. Warm water from the equatorial regions was also transported north and warmed the polar regions. These sea routes also tended to make the local climate milder, much like the modern Mediterranean, which has a positive effect on the European climate.
Flat sea routes covered the continents because the sea level was 100-200 meters higher than it is today. The higher sea levels were partly due to the formation of new cracks in the ocean basins, which, as discussed earlier in this article, pushed water towards the continents. The Cretaceous Period was also a time of rapid expansion of the sea floor. Because of their broad profile, fast-spreading mid-ocean ridges displace more water than slow-spreading mid-ocean ridges. As a result, sea levels will tend to rise during periods of rapid ocean floor expansion.
Scotese, CR, 2002, http://www.scotese.com, (PALEOMAP website). Chalk.
Most of Alabama and much of the modern Gulf Coast region were in the Gulf of Mexico during the Cretaceous Period.
Dr. William Galloway of the University of Texas Jackson School of Geosciences summarized the deposit history of the Gulf Coast / Gulf or Mexico in this mandatory paper (I have to read it because he sent me a copy of it) …
The deposition history can be generalized into seven phases: (1) Mid to late Jurassic evaporite and carbonate deposition in a wide, shallow basin restricted to an open sea basin. (2) Latest sandy clastic progression from the Jurassic Early Cretaceous Period from the northern margins. (3) Late Early Cretaceous Development of an edged carbonate shelf. (4) Mixed plastic and carbonate aggradation of the continental margins in the late Cretaceous period. (5) Resurgent paleogene clastic progression and filling in the center of the NW pelvis. (6) Miocene progression and basin filling in the central and northeastern Gulf. (7) Late Neogene climatically and eustatically influenced progression along the central edge of the Gulf. In contrast to the broad, progradational sediment wedge of the northern Gulf, the edge of Florida is a mainly aggrading carbonate platform.
Galloway, 2008.
Figure 2. From left to right: Generalized cross-section along the northern GOM region (Galloway et al., 2009), deposition phases are numbered. Relative sea level (Miller et al., 2005), atmospheric CO2 (Berner & Kothavala, 2001) and temperature anomalies (Royer et al., 2004). Click for picture.
Figure 2 clearly shows the importance of sea level cycles in the deposition history of the GOM. Also note that all source rock formations were deposited as atmospheric CO2 over 1,000 ppm and the earth was significantly warmer than it is today. Temperature and CO2 Plots have resolutions of 10 million years; they are very smooth.
A combination of sinking land and a warming gulf makes Alabama one of the states most at risk from sea level rise. The ocean has risen nearly 30 centimeters in the past 50 years and has eaten away the offshore islands and coasts of the state.
Some people might like having a beachfront property in northern Alabama, Klompmaker jokingly says, “but I think a lot of people would disagree.”
Jack Tamisiea, 2020 BS Environmental Studies, minor in Narrative Structure, work on Science Writing MS
The next NOAA tide station with a relatively long, continuous record length is Pensacola FL. The sea level has risen by about 20 cm in the last 50 years. Sea level rise is slightly higher in and around Mobile Bay; However, these stations, Dauphin Island and Mobile State Docks, are discontinuous and only go back to 1966 and 1980, respectively.
Figure 3. Sea level trend at Pensacola FL. NOAA.
Dallas County AL, where Harrell Station is located, is approximately 580 ′ above sea level. The sea level in Pensacola is rising at a rate of about 0.83 feet per 100 years. At this rate, it will be about 70,000 years before people have a chance to purchase “Northern Alabama Beach Properties”.
Alabama’s Cretaceous marine geology and modern coastal processes are in no way analogous.
References
Berner, RA and Z. Kothavala, 2001. GEOCARB III: A Revised Model of Atmospheric CO2 over Phanerozoic Time, American Journal of Science, v.301, pp.182-204, February 2001.
Galloway, William. (2008). “Chapter 15 Deposition Development of the Sedimentary Basin in the Gulf of Mexico”. Volume 5: Ed. Andrew D. Miall, The Sedimentary Basins of the United States and Canada., ISBN: 978-0-444-50425-8, Elsevier BV, pp. 505-549. (Special thanks to Dr. Gallloway for sending me a copy of this)
Galloway, William E. et al. “Gulf of Mexico.” GEO ExPro, 2009, www.geoexpro.com/articles/2009/03/gulf-of-mexico.
Miller, Kenneth & Kominz, Michelle & V. Browning, James & Wright, James & Mountain, Gregory & E. Katz, Miriam & J. Sugarman, Peter & Cramer, Benjamin & Christie-Blick, Nicholas & Pekar, S. (2005 ). “The Phanerozoic Record of Global Sea Level Change”. Science (New York, NY). 310, 1293-8. 10.1126 / science.1116412.
Royer, DL, RA Berner, IP Montanez, NJ Tabor and DJ Beerling. CO2 as the main driver of the Phanerozoic climate. GSA today, Vol. 14, No. 3. (2004), pp. 4-10
Scotese, CR, 2001. Atlas of Earth History, Volume 1, Paleogeography, PALEOMAP Project, Arlington, Texas, 52 pp.
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