From English - German Ding/FreeDict dictionary ver. 1.9-fd1:
topset stratum /tˈɒpsɛt stɹˈɑːtəm/
oberste Schicht
Synonyms: uppermost layer, top bed
see: layer of rock, rock layer, layer, rock stratum, stratum, rock bed, bed, rock formation, formation, rock layers, layers, rock strata, strata, rock beds, beds, rock formations, formations, superposed layer, superposed bed, outcropping bed, exposed stratum, superjacent layer, superimposed stratum, subjacent stratum, subjacent formation, sheet of rock, lamina, persistent stratum, permeable layer, permeable stratum, permeable bed, pervious stratum, pervious bed, oil storer, gas stratum, upper stratum, superstratum, upper bed, enclosing layer, substratum, subsurface layer, subsurface stratum, sublayer, underlayer, lowermost layer, basal stratum, refractive layer, refractive bed, transgressive stratum