Holocene sea-level fluctuations inferred from the evolution of depositional environments of the southern Langebaan Lagoon salt marsh, South Africa

Abstract

A Holocene sea-level curve is constructed from the facies distribution and radiocarbon ages of sediment recovered from the distal, southern salt marsh of Langebaan Lagoon, on the southwest coast of South Africa. Calibrated radiocarbon analyses of an oyster-rich bioclastic gravel indicate that the Flandrian Transgression flooded the lagoon to 0–3 m above present-day levels by 6750 years ago (6.8 ka). Organic matter and shell material dated in distal lagoonal sediments indicate that sea level returned to present-day levels by 4.9 ka and have since remained within 61 m of present-day levels. Bleached shell and a hiatus in sedimentation suggest an approximate 1 m sea-level lowstand between 2.5 and 1.8 ka. Changes in the macrobenthos assemblage since 1.5 ka that include the loss of the oyster Ostrea atherstonei, razor clam Solen cap ensis, brown mussel Arcuatula capensis and periwinkle Oxystele variegata reflect loss of hard substrate, decreased tidal-flow velocities as reworked sands prograded into the southern lagoon and possibly cooler seasurface temperatures. Calibrated radiocarbon ages of bulk organic matter from diatom-rich, Zostera muddy quartzose sands indicate a 0.5 m sea-level highstand at 1.3 ka followed by a 0.5 m lowstand at 0.7 ka. Dating of fining-upward, organic-rich (2 wt% TOC) noncalcareous muds indicates that the present-day salt marsh has grown by aggradation (1mmy-1) and progradation since 0.7 ka.

Holocene sea level and environmental change on the west coast of South Africa: evidence from plant biomarkers, stable isotopes and pollen

“…7; 474 Miller et al 1995; Compton 2001Compton , 2006Compton , 2007. Although the thiophene data cannot serve as sea-475 level index points, they demonstrate generally good correspondence with the geomorphic evidence 476 from which Compton (2001) inferred an early to middle Holocene high stand ca. 8,000-5,500 cal yr 477 BP.…”

Holocene Relative Sea-Level Changes from Near-, Intermediate-, and Far-Field Locations

“…We also show marine and freshwater limiting data that define the lower-and upperbound of RSL, respectively [41]. We do not change the interpretation of index points from the original studies, although in one study [42] where vertical error was not specified for four index points, we assign a conservative (±1 m 2σ) error value. [46] We acknowledge that the error values of many of the index points may be underestimated, in particular because local factors that influence RSL, such as sediment compaction or tidal range change, are not considered [43].…”

“…In the far-field location of mainland southeastern Africa (e.g., South Africa, Zanzibar, Mozambique), uncertainties exist regarding the timing and amplitude of a mid-Holocene highstand [42,[142][143][144] caused primarily by continental levering [39]. Part of these uncertainties results from the large distances between field sites (e.g., South Africa to Mozambique) and the varied RSL reconstruction methods used [145].…”

“…Lagoon, South Africa [42], West Guongdong, China [166], Singapore [160], and North Queensland, Australia [181], and New South Wales, Australia [182] shown as in Fig. 3 specified time interval based on a linear transformation of f(t).…”

Evidence of Northward Limit of Sea Level Transgression in and around Central Part of Bangladesh during Holocene

“…Umitsu [2], Kudrass et al [3] and Goodbred and Kuehl [4] stated that during the mid-Holocene sea level the bay was slightly higher, the climate was warmer, and rivers of this region discharged up to two and half times more than in present times. Evidence from Japan, the Sunda Shelf, South Africa, Sri Lanka and the east-coast of India suggest that the middle Holocene transgression rose (high stand) above the present MSL in many parts of the Indo-pacific region [10][11][12][13][14][15][16][17][18][19][20]. Fixed biological indicators (oyster beds) have been used at one site on the South China Sea coast to infer the amplitude and timing of the mid-Holocene high stand which was no greater than 2 m above modern sea level at 5140 yrs BP.…”