The paleohydrology of Lower Cretaceous seasonal wetlands, Isle of Wight, Southern England

The floodplain deposits of the, Wealden Group (Lower Cretaceous) of the Isl e of Wight, southern England, were formed in a seasonal wetland setting, a type of environment widespread today along higher-order tropical and subtro pical river systems but rarely identified in the geological record, The uni t consists of four main lithofacies: sheet sandstones with dinosaur footpri nt casts; green-gray mudstones with vertebrate remains, abundant lignite,:p yrite, and siderite; spectacularly color mottled mudstones with goethite an d locally pseudoanticlines; and red mudstones with pseudo-anticlines, hemat ite, and carbonate nodules, The sheet sandstones are interpreted as crevass e deposits; the green-gray mudstones were deposited in shallow ponds on the floodplain, which acted as sinks for debris released by local hoods follow ing wildfires; the mottled mudstones represent surface-water gley soils for med in seasonally waterlogged areas; and the red mudstones resemble present -day Vertisols that formed on topographically elevated areas only intermitt ently hooded, These mudstones show vertical transitions from one to another , and although they could be interpreted as components of simple catenas, t he absence of associated facies changes implies that topographic difference s were not the only control. It is proposed that these three mudstone types formed as seasonal wetland catenas, in which differences in soil drainage conditions resulted from variations in the flooding hydroperiod affecting a reas with minor relief differences, rather than drainage variability simply reflecting static topographic differences. Such seasonal wetland systems a re rarely documented in the stratigraphic record despite being a widespread environment in present-day tropical regions, and the Wealden deposits are used to identify criteria for the recognition of this important environment in the rock record. These southern English wetlands are compared with othe r Lower Cretaceous wetlands from northern Spain, enabling hydrological fact ors which controlled deposition to be recognized.