Unclear predictions surrounding climate change, associated sea-level rise and potential impacts upon coastal
environments have placed an emphasis on the importance of sea-level change. Past sea-level fluctuations
have been measured using biological and geomorphological forms of evidence. One such biological proxy is
salt-marsh foraminifera, which have been used as a high-resolution indicator of past sea-level change, based
on the assumption that surface foraminiferal assemblages are similar in composition to buried fossil
foraminifera. In South Africa, there is ongoing research seeking to produce high-resolution records of sealevel
change, however foraminifera remain an underutilized source of proxy evidence. This research applies
salt-marsh foraminifera as precise indicators of relative sea-level change at Kariega Estuary on the Eastern
Cape coastline of South Africa. Distributions of modern foraminiferal assemblages were investigated,
revealing vertical zonation across the intertidal zone. The foraminiferal and marsh vegetation zones were in
part similar and overlapped to a certain extent, identifying three zones; high, low and tidal flats. This
suggested foraminiferal distribution is a direct function of elevation relative to tidal fluctuation. A 94 cm
core consisting of peat, sand and clay sediments was extracted from the salt marsh. A chronological
framework for the core was based on five AMS radiocarbon age determinations of both bulk sediment and
shell fragment samples placing the record within the last 1500 years Before Present (BP). The basal shell age
was a clear outlier to all bulk sediment ages, possibly as a result of shell recrystallisation. The bulk sediment
age determinations suggested two possible age reversals, potentially linked to sedimentary hiatus or
contamination. These inconsistencies in the chronology were best viewed as separate age models. The core
was analysed at a high resolution, whereby fossil foraminifera were extracted every 2 cm’s down the core. A
transfer function was applied to calculate the former elevation at which each core sample once existed, to
produce a relative sea-level reconstruction. The reconstruction was related to the age models to produce two
possible sea-level curve scenarios. Reconstructed curves from both scenarios depict a 0.5 m (±0.16 m) sealevel
highstand at 1500 cal years BP followed by a lowstand of -0.6 m (±0.03 m). Scenario One reached its
lowest recorded sea-level between 600 cal years BP and 500 cal years BP and then fluctuated below present
day levels. Scenario Two reached its lowest recorded sea-level around 1200 cal years BP, followed by low
amplitude fluctuations and a relatively stable period from 100 cal years BP till the present day. The 1500 cal
years BP highstand recorded for both scenarios correlates well with existing palaeoenvironmental literature
from the southern African coastline. Chronological limitations associated with the remainder of the record
hinder inter-comparison with previous studies. The outcomes of this research suggest that intertidal saltmarsh
foraminifera demonstrate enormous potential for the high-resolution reconstruction of relative sealevel
change in the South African context. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/10030 |
| Date | January 2013 |
| Creators | Strachan, Kate Leigh. |
| Contributors | Hill, Trevor R., Finch, Jemma M. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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