Abstract:
Diatoms are abundant in much of the Calvert and Choptank Formations (lower to middle Miocene), and are not abundant in the Eastover Formation (upper Miocene). No significant accumulations of diatoms have been observed in the St. Marys Formation (middle and upper Miocene), Yorktown Formation (lower and middle Pliocene), and sub-Chesapeake deposits. The distribution and abundance of diatoms in the Salisbury embayment were probably affected by two main factors: availability of nutrients and dilution by deposition of terrigenous clastic sediments. Beginning during the early Miocene, massive, long-term diatom blooms may have been supported by a steady, abundant supply of silica, nitrogen, phosphorus, and other nutrients transported by upwelling cold water from northern regions. The diatom-rich, silty-sand deposits also indicate a relatively slow influx of terrigenous sediment. The paucity of diatoms in some Miocene and Pliocene deposits is primarily due to increased sedimentation resulting from tectonic uplift in the Piedmont and Appalachian source areas adjacent to the Salisbury embayment. Other factors that affect diatom abundance are environment of deposition (proximity to beach or river mouth), an increase in clastic sedimentation coincident with a sea level drop due to Antarctic glaciation, and postdepositional intrastratal solution of diatoms by circulating ground water.
