Several peat diapirs, three to four feet high, were observed in Recent sediments of the Flevoland. The peat was deposited approximately 7,000 years ago on an eroded Pleistocene surface. Four to six feet of sediments which overlie the peat include, beginning with the oldest, Unio Clay, Young Peat, Cardium Clay, and Almere and Zuiderzee deposits. On the flanks of several elongate Pleistocene sand ridges, diapiric folds and related structures, similar to Gulf Coast structures, exist in the Recent deposits. The structures most like those of the Gulf Coast are down-to-the-basin normal faults, rim synclines, and, in one case, a central graben. These diapiric folds exist where the dip of the onlapping Recent sediments increases along the sand ridge flanks. The folds probably res lted from peat flowage down the sand ridge slopes.

The time of diapirism can be dated as about 1,000-1,500 A.D., because the overlying Zuiderzee deposits (1,600 A.D.) usually are not involved.

Although these small-scale diapirs resemble some Gulf Coast salt domes, they differ in two principal ways: (1) a shorter time for formation (500 years maximum) and (2) a negligible sedimentary overburden (four-six feet) when diapirism occurred. Nevertheless, the Flevoland diapirs suggest a possible mechanism of origin for salt diapirs on buried basement topography early in the history of the Gulf Coast geosyncline.

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