Carboniferous marsh foraminifera from coal- bearing strata at the Sydney basin, Nova Scotia: A new tool for identifying paralic coal-forming environments Winton G. Wightman David B. Scott Franco S. Medioli Martin R. Gibling Centre for Marine Geology, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada ABSTRACT Assemblages of agglutinated foraminifera from the Carboniferous (late Westphalian to Stephanian) coal-bearing strata of the Sydney basin, Cape Breton Island (documented for the first time in 150 yr of investigation of the Nova Scotian coal basins) indicate that deposition took place on an extensive coastal platform, not in afluviolacustrinesetting as previously suggested. The assemblages contain representatives of genera that are widely distributed in modern es- tuarine and marsh environments, allowing us to determine Carboniferous paleoenvironments with unusual confidence. Seat earths beneath several coal seams contain assemblages domi- nated by Trochammina, which suggests deposition within vegetated zones analogous to modern high-marsh environments found within the upper half of the tidal range. A coal-seam split and a coarse siltstone contain assemblages dominated by Ammobaculites and Ammotium, which indicate paleoenvironments analogous to modern low-marsh and estuarine environments. Mixed assemblages of Trochammina, Ammobaculites, and Ammotium also indicate estuarine- low-marsh depositional environments. Detailed analysis of foraminiferal biofacies assists in the recognition of marine influence during deposition of these Carboniferous rocks, and may help distinguish areas of sulfur-rich coal. The findings indicate that environmental and morpho- logical conservatism has characterized agglutinated marsh foraminifera for the past 300 m.y. INTRODUCTION Marginal marine environments of the an- cient geologic record are notoriously diffi- cult to identify, even with the use of pale- ontologicaJ criteria. Many fossil groups,  particularly those of the Paleozoic, are ex- tinct, and cannot be compared with Holo- cene taxa. Marine and fresh-water fossils  can be juxtaposed by postmortem transpor- tation or lost through dissolution. Marginal  marine settings commonly undergo pro- found, short-term changes in salinity that are  difficult to detect in the ancient record. Be- cause agglutinated foraminiferal assem- blages in modern estuarine and marsh envi- ronments are found in well-established  vertical zonations related to tidal range  (Scott and Medioli, 1980a; Scott et al., 1990,  1991), however, they are powerful tools in  the investigation of Quaternaiy marginal  marine paleoenvironments (Scott and Me- dioli, 1978, 1986). The recent discovery of  agglutinated foraminifera in close proximity  to coals in the Carboniferous Sydney basin  of Nova Scotia (Thibaudeau and Medioli,  1986; Wightman et al., 1992a, 1992b) consti- tutes the first identification of marine fossils  in 150 yr of investigation of these coalfields.  The find indicates that the coals formed in a  coastal setting rather than on flood plains far  removed from marine conditions, as previ- ously thought (Hacquebard and Donaldson,  1969; Rust et al., 1987).  Agglutinated foraminifera are widespread  in modern deltaic and coastal wetlands pe- rennially or periodically affected by marine  waters, and have been reported from many  parts of the world. They live in interdistrib- utary bays, tidal channels, marshes, and  other estuarine settings in Atlantic Canada  (Scott and Medioli, 1980a; Scott et al., 1981;  Scott and Martini, 1982), the Pacific coast of  North America (Phleger, 1967), the U.S.  Gulf Coast (Phleger, 1966; Haman, 1983;  Scott et al., 1991), South America (Scott et  al., 1990), western Greece (Scott et al.,  1979), northern Italy (Petrucci et al., 1983),  Holland (Phleger, 1970), the western Baltic  Sea (Lutze, 1968), West Africa (Debenay,  1990), and Japan (D. B. Scott, unpublished),  at latitudes of up to 54°. The principal  agglutinated genera living in marginal ma- rine environments include Ammobaculites, Trochammina, Ammotium, Miliammina, Potysaccammina, Arenoparrella, and Hap- lophragmoides. Vertical zonation of foram- iniferal species related to tidal range is well  documented, and clear faunal divisions are  present between assemblages found in  fresh-water and brackish marshes, upper  and lower saline marshes, estuaries, and  open marine settings (Scott and Medioli,  1978, 1980a, 1986; Scott et al., 1981, 1990,  1991). In general, the number of species rep- resented declines from estuarine to high- marsh environments, where salinity may fall  to 3 %c and a single species may dominate  (Murray, 1973). The number of living indi- viduals in a high-marsh environment, how- ever, may be large, and counts of 6500 spec- imens per 10 cm 3  of sediment have been  documented (Scott and Medioli, 1980b). Ag- glutinated foraminifera have a high preser- vation potential in these environments be- cause their tests are constructed from  detrital grains. They are typically the only  shelled invertebrates preserved in the fossil  record, because calcareous shells are prone  to dissolution in low-pH marsh deposits rich  in organic matter. Although agglutinated as- semblages are associated with peats and  marsh sediments, they are known only  where depositional sites have a marine  connection.  GEOLOGY, v. 21, p. 631-634, July 1993 631