HGS General Dinner

A Chronology of Paleozoic Sea-Level Changes

Dr. Bilal Haq

 

A global synthesis of Paleozoic sequence-stratigraphic data has led to new insights into the nature, amplitude and causes of base-level changes for this Era. A “modal mean” Paleozoic sea-level curve is proposed based on “reference districts” from around the world, corroborated with data from ancillary sections. Estimating the amplitude of sea-level changes in the Paleozoic involves two separate measures: 1) The long term envelope of the sea-level changes (driven by long-term tectonic processes), and 2) the third- and higher-order eustatic sea-level changes (driven by glacial and other, unknown, processes) that can be documented widely. For the long-term envelope a consideration of the global continental flooding estimates (with epeirogenic corrections), stacked regional sea-level data, and modeling results for mean age of the oceanic crust seem to yield consistent results. For the shorter-term eustatic changes, sea-level rise and fall estimates from “reference districts” for various time slices (at localities where tectonic quiescence prevailed and thus the “modal mean” signal is more likely to be preserved) is considered the best approach. Nevertheless, accurate estimates of the magnitude of sea-level changes from stratigraphic information remain a challenge. As for the causes the shorter-term for sea-level changes, nearly 38% of the Paleozoic time suffered from some or significant glaciation and thus a glacio-eustatic cause can be invoked for those intervals. For the remaining time (when there is no known evidence of ice accumulation) the trigger for sea-level changes is as yet unknown and remains one of the major mysteries of Earth Sciences.

 

To download a large scale copy of the figure above, click here. Note the attachment is a pdf file that can be printed on a large plotter.

Dr. Bilal Haq has served as the director for Marine Geosciences Programs at National Science Foundation since 1988. He received his Ph.D. and D.Sc. degrees in marine geology from the University of Stockholm in Sweden. Before coming to NSF he carried out research at Woods Hole Oceanographic Institution in Massachusetts and Exxon Research Labs in Houston, Texas in several fields of Geosciences. He has participated in four Ocean Drilling expeditions in the Pacific, Indian and Southern Oceans, in the latter two as co-chief scientist. He has been an AAPG distinguished lecturer and a recipient of Francis Shepard medal for “excellence in marine geology”. He also received the National Science Foundation’s Antarctic medal and was elected a fellow by the American Association for the Advancement of Science in the year 2000. In 2004 he was awarded American Geophysical Union’s Ocean Sciences award for “outstanding and sustained contributions” to marine sciences. He has published extensively on a wide variety of topics, including sequence stratigraphy and global sea-level changes of the past, paleoclimatology, paleobiogeography, paleoceanography, natural gas hydrates, and global warming and its impacts on maritime economies. Dr. Haq has also held assignments with the World Bank and the White in Washington DC.

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