The Trow Point Bed—a deposit of Upper Permian marine oncoids, peloids and columnar stromatolites in the Zechstein of NE England

Summary An extensive thin bed of oncoids, peloids and columnar stromatolites occurs at the top of the Cycle 1 carbonate of the English Zechstein sequence in NE England; here termed the Trow Point Bed, it lies on the lower part of the basin-margin slope, basinward of a linear shelf-edge reef in the Ford Formation. The bed is generally 0.05–0.20 m thick but locally ranges to 0.60 m; it rests on an uneven surface that has a local relief of up to 15 m and slopes exceeding 35° in places. It contains a sparse marine fauna of foraminifera, ostracods and bivalves; there are only a few traces of current action and sorting, and terrigenous sediment nowhere comprises more than 2% of the bed. The Trow Point Bed is generally similar to deposits described at a comparable stratigraphical position in Germany and Poland and although environmental indications are partly mutually contradictory, it seems likely that the bed accumulated in oxic conditions on the basin floor under water perhaps 25–100 m deep.