Modern tropical peats require continuity of precipitation for accumulation, whereas calcretes and calcic vertisols require strongly seasonal conditions. The 20-30-m-thick cyclothems of the Sydney basin, Nova Scotia, Canada, show a systematic alternation of coals and other hydromorphic paleosols with calcretes and calcic vertisols. This implies strong variation in seasonality during the duration of a cyclothem, estimated at 200 ka. In at least one cyclothem, calcic paleosols formed on an interfluve adjacent to a paleovalley cut through marine strata, suggesting that a more seasonal and probably drier climate prevailed during sea-level lowstand. The calcic paleosols are estimated to have formed during periods of 104 yr, possibly indicative of partial control by obliquity and precessional cycles.