Isotope stratigraphy of the European Carboniferous: proxy signals for ocean chemistry, climate and tectonics

Carboniferous brachiopods from western Europe and the former USSR have been utilized as carriers of isotopic proxy signals for paleoceanography and paleoclimatology during the assemblage of Pangea. This is of particular interest, because this time interval coincides with the transition from greenhouse to icehouse conditions. The delta(18)O values (3 Ma running means) show an overall delta(18)O increase from about -7 +/- 1 parts per thousand to -3 +/- 1 parts per thousand during the Carboniferous. The rise in the delta(18)O is stepwise, with major shifts in the mid-Tournaisian and at the Visean/Serpukhovian transition. The comparable delta(13)C record shows a Tournaisian peak at 5 parts per thousand, a Visean oscillation at about 2.5 +/- 1 parts per thousand, a Serpukhovian rise of more than 3 parts per thousand, a plateau around 5 parts per thousand during the Bashkirian and Moscovian, a 4 parts per thousand drop during the Kasimovian, and another rise, of about 3 parts per thousand, during the Gzhelian. The Sr-87/Sr-86 record shows an Early Carboniferous decline from similar to 0.7083 to a mid-Visean minimum of 0.7077, followed by a rapid Serpukhovian rise to a Bashkirian and Moscovian plateau at 0.7087 and a slight decline during the Kasimovian and Gzhelian. The covariance of isotopic trends, and the coincidence with geological phenomena, indicates that the long term variations in ocean chemistry and climate may be coupled to the tectonic evolution of the earth system. The Namurian witnesses the onset of Hercynian orogeny, initiation of the main phase of Carboniferous glaciation, formation of the extensive coal deposits and the rise in Sr-87/Sr-86, delta(13)C and delta(18)O. All this suggests that a tectonically controlled climate change, resulting in cooling and increased carbon storage in the organic reservoir, was the major triggering factor for all the above phenomena. The late Carboniferous glacial episode was interrupted by a warm interval in the Stephanian. The carbon and oxygen isotope data indicate that this episode may have been restricted to the early Kasimovian, a proposition at odds with the poorly dated record of glacial deposits that are interpreted as indicating a warm climate for the entire Stephanian. In addition, the pattern of short-lived peaks in delta(13)C and delta(18)O in the Tournaisian (and possibly Visean) may be interpreted as a reflection of short-lived glacial episodes, a proposition consistent with geologic records. (C) 1999 Elsevier Science B.V. All rights reserved.