Evidence of seasonal precipitation in Pennsylvanian sediments of the Illinois basin

Statistical analysis of the temporal and spatial controls on tidal signal preservation in late-Holocene tidal rhythmites, Romney Marsh, Southeast England

“…7 Sand layer thickness from a Manor Farm (-2.21 to 0.12 m OD) and b Boulderwall Farm (0.44-1.44 m OD) sequences smoothed by 7 point moving average to highlight semiannual cycles in sand layer thickness. Notice that these longer period patterns tend towards being symmetrical, and alternately higher and lower, as anticipated from a consideration of changing tidal heights over equivalent time periods (Martino and Sanderson 1993;Kvale et al 1994, 1995, Tessier 1998. Vertical lines illustrate the bi-annual periodicity in tidal energy, hence the cores record approximately 11 years of sedimentation at Manor Farm (a) and around 3.5 years at Boulderwall Farm (b) high and low frequency patterns comparable to those recorded in the sand layer thickness data and to identify the principal harmonic components of this tidal signal as it changes through time at a particular site.…”

“…Lithostratigraphic and palaeoenvironmental evidence has already been presented which is indicative of a strong tidal control on deposition at these sites, and other work on Romney Marsh supports this conclusion regarding the back-barrier minerogenic sediments of the area (Plater 1992;Long and Hughes 1995;Spencer et al 1998;Plater et al 1999Plater et al , 2002Stupples 2002a, b;Long et al 2006). Furthermore, one of the diagnostic attributes of a tidal control on sedimentation is the presence of repetitive, nested cycles of thickening then thinning within a laminated sequence (Kvale and Archer 1991;Nio and Yang 1991;Kvale et al 1994Kvale et al , 1999 such as those described here (Figs. 5,6,7).…”

“…In addition, the symmetrical appearance of the proposed semi-annual cycles (Figs. 7,11b,c) in both smoothed sand and mud layer series is strongly indicative of a tidal control, non-tidal influences are typified by a skewing of these semi-annual cycles (Kvale et al 1994). The alternate higher and lower semi-annual peaks in the smoothed layer thickness plots, more particularly from Boulderwall, is also seen in the Dungeness tide station data at this wavelength and is typical of other sedimentary sequences in which long tidal rhythmite records have preserved semi-annual and annual periodicities (Martino and Sanderson 1993;Kvale et al 1994Kvale et al , 1995Kvale et al , 1999Tessier 1998).…”

“…7) are best explained in terms of the twice yearly cycles in tidal energy, driven by the changing alignment of earth, moon and sun, which results in the enhanced equinoctial tides twice each year (Martino and Sanderson 1993;Kvale et al 1994Kvale et al , 1999Greb and Archer 1998). Around 3.5 years sedimentation (7 semi-annual periods) are recorded in the metre-long Boulderwall Farm core whilst around 11 years are preserved in the entire 2.33 m-long Manor Farm series (Fig.…”

“…In siliciclastic intertidal systems, sands are typically laid down by the energetic flood and/or ebb currents, whilst a muddy layer accumulates under the low energy conditions around high water (Dalrymple et al 1991;Nio and Yang 1991). Alternatively, where mud dominates, well-developed silty tidal rhythmites may occur, comprised of thin, planar laminated silts with clay drapes (Kvale et al 1994;Archer 1998). Greater flow depths and longer durations of inundation lead to thicker layers, so the possibility exists for these laminated deposits to record the tidal signature associated with daily, neap-spring, lunar monthly and other cycles.…”