During Late Ordovician and Early Silurian times, from 450 to 428 million years ago, stromatoporoid sponges were some of the most common and abundant fossils in shallow water tropical settings of the Anticosti Basin (Gulf of St Lawrence). They formed dense, massive coralline skeletons of calcium carbonate, some up to a meter or more across, especially in reef environments, but also in deeper waters of the Anticosti shelf, down to the margins of the photic zone, where light faded.
The Anticosti Basin reveals one of the most fossiliferous carbonate sequences worldwide for rocks of this age, straddling a global mass extinction boundary, and thus revealing not only those taxa that became extinct, but also how the seas were repopulated in an equatorial setting after the mass extinction. The mass extinction has been correlated to globally cooling climates of the time, and southern hemisphere glaciation in North Africa.
This monograph describes, for the first time, the skeletal architecture of these abundant and exquisitely preserved sponges from Anticosti, and includes more than 300 skeletons selected from ca. 2000 field localities, assigned to 14 genera, of which 4 are new, and 35 stromatoporoid species, of which 18 are new. These are illustrated by 56 figures and plates and fill a major gap in our global knowledge of the reef building stromatoporoids, especially during the Early Silurian and latest Ordovician.
All materials are precisely geographically and stratigraphically defined from the Vaureal through Chicotte formations over a nearly a kilometer thick section, and their ecologic distribution plotted across shallow to deeper water facies. Oil and gas exploratory drilling in the Gulf of St Lawrence will ultimately reveal what happened in the deeper water offshore facies, not exposed on Anticosti Island itself.