Sedimentary environments and facies of the subtropical mgeni estuary, Southeast Africa

Cooper, J. Andrew G.

doi:10.1002/gj.3350230104

Cited by 19 publications

(2 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Overwash deposits are also present within the barrier, preserved as horizontal bedding (Figure 3f). Similar features have also been found at other wave dominated barrier estuaries such as the Mgeni Estuary, Southeast Africa (Cooper, 1988). The process of sediment washover helps infill the accommodation space behind the barrier as well as facilitating its landward movement (Orford, 2004).…”

Section: Discussionmentioning

confidence: 99%

The Evolution of a Holocene Estuarine Barrier on the Coromandel Coast, New Zealand

Woods

2011

Geographical Research

View full text Add to dashboard Cite

Whitianga Harbour on the Coromandel Peninsula, North Island, New Zealand is fronted by a broad sandy barrier composed of linear beach ridges. The barrier developed through a process of rollover as sea level rose in the early Holocene with shelly sandy sediment washed inland over estuarine muds. These overwash deposits are present to 3 m below sea level in the back barrier area. Once sea level stabilised and barrier rollover had ceased the barrier continued to prograde in a series of beach ridges. The back barrier area is characterised by estuarine muds, overlain by splay and overwash deposits that are reworked by fluvial and tidal channels. The initial flooding of the estuary occurred at around 7350–7225 years cal BP, reaching modern levels by 6894–6729 years cal BP at the earliest. Infill was rapid as evidenced by estuarine species (crustaceans and bivalves) preserved in life position. From ∼6000 years BP to present, the estuary is characterised by tidal and fluvial reworking, suggesting that modern sediment inputs are bypassing the estuary.

show abstract

Section: Discussionmentioning

confidence: 99%

The Evolution of a Holocene Estuarine Barrier on the Coromandel Coast, New Zealand

Woods

2011

Geographical Research

View full text Add to dashboard Cite

show abstract

“…Each seismic facies is interpreted on the basis of similarity to other seismic stratigraphic studies of incised valley fills (e.g. Chaumillon & Weber, ; Nordfjord et al ., ; Green, ) and to known stratigraphy of contemporary estuaries on the adjacent coast (Orme, ; Cooper, , , ; Cooper et al ., ). The chaotic to steeply dipping, moderate amplitude basal fill facies of Facies 1 (Fig.…”

Section: Interpretationsmentioning

confidence: 99%

Formation and preservation of an overstepped segmented lagoon complex on a high‐energy continental shelf

Green

Cooper

Leuci³

et al. 2013

Sedimentology

View full text Add to dashboard Cite

The duration of shoreline occupation at a given sea-level, coastal response to sea-level change and the controls on preservation of various shoreline elements can be recognized by detailed examination of submerged shorelines on the continental shelf. Using bathymetric and seismic observations, this article documents the evolution and preservation of an incised valley and lithified barrier complex between À65 m and À50 m mean sea-level on a wave-dominated continental shelf. The barrier complex is preserved as a series of aeolianite or beachrock ridges backed by laterally extensive backbarrier sediments. The ridges include prograded cuspate lagoonal shoreline features similar to those found in contemporary lagoons. The incised valley trends shore-parallel behind the barrier complex and records an early phase of valley filling, followed by a phase of extensive lagoonal sedimentation beyond the margins of the incised bedrock valley. Sea-level stability at the outer barrier position (ca À65 m) enabled accumulation of a substantial coastal barrier that remained intact during a phase of subsequent slow sealevel rise to À58 m when the lagoon formed. These lagoonal sediments are stripped seawards by bay ravinement processes which caused the formation of several prograded marginal cuspate features. An abrupt rise in sea-level to À40 m, correlated with melt-water pulse 1B, enabled the preservation of thick lagoonal sediments at the top of the incised valley fill and preservation on the sea bed of the cemented core of the barriers. This situation is unique to subtropical coastlines where early diagenesis is possible. The overlying sandy sediment from the uncemented upper portion of the barriers is dispersed by ravinement, partly burying the ridges and protecting the underlying sediments. The high degree of barrier or shoreline preservation is attributed to rapid overstepping of the shoreline, early cementation in favourable climatic conditions and the protection of the barrier cores by sand sheet draping.

show abstract

Geomorphological effects of catastrophic flooding on a small subtropical Estuary

Cooper¹,

Mason

Reddering³

et al. 1990

Earth Surf Processes Landf

Self Cite

View full text Add to dashboard Cite

The Mgeni Estuary is situated on the east coast of South Africa. Tidal salinity changes commonly extend 2.5 km upstream from the mouth. The subtropical climatic regime causes seasonal flooding, the geomorphological effects of which are increased by a steep river gradient. A 120-150 year flood event during September 1987, with an estimated peak discharge of 10800 cumecs, resulted in the erosion of 1.86 x lo6 m3 of sediment from the estuary. The normal high tide volume of the estuary (0.35 x lo6 m') increased to 1.85 x lo6 m3 after the flood. The post-flood intertidal volume (tidal prism) of the estuary was 0.43 x lo6 m3 compared to 0.19 x lo6 m3 before the event.The nature and extent of erosion in the estuary was controlled by the composition of the estuary banks and bed material. Gravel and sand substrates were preferentially eroded from the estuary bed before the cohesive bank materials were undercut in sections of the estuary. Mud and fine sand were deposited on overbank areas when the flood waned and a lag of coarse sand and gravel was produced on the estuary bed. Approximately 46 per cent of the bedload sediment supplied to the estuary since 1917 was retained in the estuary until the 1987 flood. The remainder was transported through the system and into the Indian Ocean. Results show that catastrophic floods play an important role in sedimentation in small estuaries

show abstract

Sedimentary environments and facies of the subtropical mgeni estuary, Southeast Africa

Cited by 19 publications

References 17 publications

The Evolution of a Holocene Estuarine Barrier on the Coromandel Coast, New Zealand

The Evolution of a Holocene Estuarine Barrier on the Coromandel Coast, New Zealand

Formation and preservation of an overstepped segmented lagoon complex on a high‐energy continental shelf

Geomorphological effects of catastrophic flooding on a small subtropical Estuary

Contact Info

Product

Resources

About