Abstract The Fundy rift basin, comprising the contiguous Minas, Fundy, and Chignecto structural subbasins (Figure 1), is filled by terrestrial redbed siliciclastics, minor carbonates, and tho leiitic basalts of the Fundy Group, Newark Super group. The Minas subbasinis a shallow transtensional basin formed by left-oblique slip (Olsen and Schlische, 1990) on there activated Minas fault zone, a transform along which the Meguma and Avalon terranes were superimposed during the late Paleozoic. Outcrops of Fundy Group strata occur almost exclusively asseacliffs along the shores of the Bay of Fundy. In the Minas subbasin, a maximum of approximately 1 km of Fundy Group section is exposed along the northern and southern shores of the geographic Minas Basin and the eastern side of the Blomidon Peninsula(Figure 1). The Fundy and Chignec to subbasins are simplehalf-grabens formed when regional extension caused reactivation of Paleozoic thrusts as southeast dipping normal faults with displacement locally exceeding 10 km (With jack et al., 1995).Fundy Group strata are exposed along the Nova Scotia shore of the Bay of Fundy, forming the Fundy subbasin margin. A rider block along the faulted northwestern margin of the Fundy sub basinat Point Lepreau in New Brunswick exposes nearly2.5 km of strata. Over 3.5 km of Mesozoic strata were penetrated in the Chinampas N-37 well (Figure1) drilled offshore in the Fundy subbasin, and interpretation of seismic data suggests that thethickness of the Mesozoic section may exceed 8k min the Fundy subbasin depocenter (Brown and Grantham, 1992; Wade et al., 1996). The Chignectosubbasin is bounded to

Abstract We recognize a causal association between volcanism and lacustrine limestone precipitation in Newark Supergroup strata. Two other associations are apparent: limestone with vegetation, and limestone interlaminated with siliciclastic beds. These associations reflect the different origins of the limestone and relate to basinal hydrological parameters. Hettangian-age limestone deposits reflect an increase in carbonate production and increased rates of groundwater circulation due to the high geothermal heat flow that accompanied volcanism and rifting. Most meter-scale limestone deposits stratigraphically overlie basalt and have covarying stable-isotope compositions, indicating closed-basin conditions. Limestones with spongy to framework texture, interpreted as tufa deposits, reveal sites of sublacustrine or nearshore springs or seeps. Tufa δ 18 0 values are consistently depleted relative to meter-scale carbonates from the same basin, indicating higher temperature waters at debouching localities. Strong climatic seasonality is inferred from carbonate turbidites and euhedral calcite laminae interbedded with siliciclastic deposits. The turbidites formed when rains flushed littoral-zone carbonates into profundal depths, and euhedral calcites reflect reducing conditions in stratified lake waters associated with dry periods. Paleoclimatic differences north to south along the rift basin trend are confirmed by a 5‰ difference in δ 18 O values of meter-scale limestones. The northern Hartford and Fundy Basins have enriched values, indicating increasing aridity northward, with a resulting increase in evaporation from those rift lakes. Littoral-zone carbonates associated with plants and stromatolites contain 13 C-depleted carbon isotope signatures, reflecting organic mediation in carbonate precipitation. In contrast, profundal-zone carbonates have more uniform δ 13 C values, reflecting a greater degTee of equilibration between the atmosphere and the lake water. Newark Supergroup rift-basin limestones reflect a combination of environmental and climatic factors that increased the dissolved-load and/or bedload transportation of calcite, coupled with mechanisms such as basalt mantling, turbidite deposition, in situ precipitation, and vegetative associations, which enhanced carbonate deposition. Stable-isotope compositions help define these varied hydrogeochemical and paleoenvironmental conditions.