Macrofossil Assemblages

The marine macrofossil assemblages of the Champlain Sea consists primarily of bryozoans, cirripeds, sponges and bivalves, whereas fresh water assemblages consist of mostly gastropods and bivalves.  Although the one species of brachiopod found in Champlain Sea sediments, Hemithyris psittacea, has stenohaline tendencies, its fossils were found in the eastern extremity of the Champlain Sea, therefore it must have tolerated slight dilutions.  

The most abundant invertebrate found in fossiliferous Champlain Sea deposits, marine and freshwater alike, are bivalves.  There are eight important marine fossil associations, groups of fossil assemblages named after the dominant species in the assemblage, and one important fresh water association.

The following table shows the names of the dominant macrofossil assemblage that characterize each association present in Champlain Sea sediments, their ages and some of their characteristics.  Ages for all macrofossils are based on C14 dating methods, except for the Mytilus edulis, whose age was inferred from the presence of associations at sites where other species have been dated.

Macrofaunal Associations




Time Range

Species Characteristics

Balanus hameri



11.3 11.1 ka 100 y

Lives in deeper. more saline and cooler waters 

Hiatella arctica



11.4 10.1 ka 100 y

Adapted several times to diluted waters

Macoma balthica



12.2 10.75 ka 100 y

Often found in biocoenosis with Mya arenaria

Lived at shallower depths

Macoma calcarea



~ 10.6 ka 100 y

(only date published)

Preferred  deeper waters

Mya arenaria



11.1 10.5 ka 100 y

Common to shoreline deposits

Thermophilic nature and extremely low δ18O values indicate shallow water habitat.

Mya truncata



~ 10.3 ka 100 y

(only date published)

Lived in typical seawater salinity levels, and therefore greater depths 

*See section on salinity for more about the relationship between salinity and depth

Mytilus edulis



11.2 10.8 ka 100 y

Adapted well to low salinity levels and temperatures

Confined to relatively diluted surface waters

Portlandia arctica



12.15 10.75 ka 100 y

Common to silty clay environments found along glacier fronts

Lived in more shallow and less saline conditions


(Fresh water)


10.25 9.75 ka 100 y



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