(1913-1996) American Stratigrapher
Today the continents are primarily land and the ocean water covers the ocean crust. During the Paleozoic, however, much of the continental interior of North America was covered by a large shallow sea. Therefore marine sediments of this age span the entire continent. However, the sedimentation reflects several major regressions that exposed most of the continent followed by major transgressions that covered it with ocean again. This periodic rise and fall of sea level had a profound effect on the evolution of life and is the basis for our subdivision of the Paleozoic periods. The main architect of this now classic scheme is Laurence Sloss. He studied the Paleozoic stratigraphy of the United States from coast to coast in a new way. Normally, rock units are subdivided simply on the basis of rock type or lithology. Sloss was the leader in a new way to view sedimentary rocks in packages. Rock units were grouped with their neighbors into sequences to represent related depositional periods. This concept, called “sequence stratigraphy,” is now widely accepted and applied. Sloss used this concept to subdivide the sedimentary rocks of North America, which culminated in a landmark 1963 publication entitled Sequences in the Cratonic Interior of North America. Each one of these regres-sive-transgressive cycles was named based upon its best exposure, such as Tippecanoe, Kaskaskia, and others. Considering that most of life on Earth was in the oceans during this time, this draining of the continents, which served as large shelves, resulted in massive extinctions. New groups of animals would dominate during the next transgression, only to be decimated during the subsequent regression. The results of this research now appear in every historical geology textbook in the world.
The natural extension of this revolutionary research was to determine the causes and applications of these cycles. Sloss attempted to correlate the sequences with the plate tectonic events of the continental margins and the entire Earth. After all, to raise and lower sea level to such a degree required a radical change. Certainly the plate collisions with North America had an effect but the likely culprit appears to be inflation and deflation of the mid-ocean ridges, which displaced the water from the ocean basins onto the land. These inflations and deflations likely reflected the rate of spreading. The application of this work was in oil exploration. Sloss is the author of a classic 1962 paper, “Stratigraphic Models in Exploration,” in which these concepts are applied to petroleum deposits. Sloss even performed seminal research on evaporites. Laurence Sloss is one of the true pioneers of stratigraphy.
Laurence Sloss was born on August 26, 1913, in Mountain View, California, on a farm where he spent his youth. He attended Stanford University, California, and earned a bachelor of science degree in geology in 1934. He completed his graduate studies at the University of Chicago, Illinois, where he earned a Ph.D. in 1937. His first professional position was split between the Montana School of Mines in Butte, where he taught paleontology and historical geology, and the Montana State Bureau of Mines and Geology. He remained in Montana until 1947, when he joined the faculty at Northwestern University in Evanston, Illinois. He remained at Northwestern University until his retirement in 1981. Sloss was named the William Deering Professor of geology in 1971, a title he held until his retirement. Laurence Sloss died on November 2, 1996. His wife, whom he married in 1937, predeceased him; they are survived by two sons.
Laurence Sloss led a very productive career. He is an author of numerous scientific articles in international journals, professional volumes, and governmental reports. Many of these papers are benchmarks of sequence stratigraphy and the Paleozoic stratigraphy of North America. He is also an author of a highly regarded and widely adopted textbook entitled, Stratigraphy and Sedimentation, with William Krumbein. Sloss received several prestigious honors and awards for his research contributions to geology. He received the William H. Twenhofel Medal from the Society of Economic Paleontologists and Mineralogists, the Penrose Medal from the Geological Society of America, and the President’s Award from the American Association of Petroleum Geologists, among others. In honor of his work, there is now a Laurence L. Sloss Award in stratigraphy issued by the Geological Society of America on an annual basis.
Sloss was also of great service to the profession. He served numerous functions for the Geological Society of America including president and vice president. The same holds true for the Society of Economic Paleontologists and Mineralogists and the American Geological Institute, where he was also very active and served as president and vice president in each. He served on numerous panels and committees for the National Research Council and the National Science Foundation. He served in various editorial roles for the Geological Society of America Bulletin, the American Association of Petroleum Geologists Bulletin, and the Journal of Sedimentary Petrology.
