Richards Bay is part of a back-barrier lagoon fronted by high coastal dunes on the NE, Indian Ocean coast of South Africa. In the early 1970s, a berm was constructed, dividing the original Mhlathuze Estuary into two separate systems; the Richards Bay Harbour and the new Mhlathuze Estuary. This study investigates the stratigraphic evolution of the incised valley system and bayhead delta in the Richards Bay Harbour segment. Seven seismic units (Units 1–7) were imaged. A single regionally developed sequence boundary (SB) along with two tidal ravinement surfaces (tRS1 and tRS2) were identified. Surface SB is associated with the LGM lowstand which developed when sea levels were ~ 130 m below present, until ~18,000 year BP. Cretaceous age siltstones (Unit 1) form the basement. Transgressive material overlying SB (Unit 2) reflects the filling of an incised valley located in the middle segment of a wave-dominated back-barrier system. It is overlain by a bayhead delta (Unit 3), the geometry and seismic signature of which indicate alternating periods of aggradation/progradation and backstepping. The behaviour is attributed to episodic jumps in sea-level, and is tentatively (on the basis of elevations in relation to the regional sea-level curve) linked to periods of rapidly rising sea-level (8.2 ka event and Meltwater Pulse (MWP)-1d). These intervals of rapidly rising sea-level, combined with relatively low gradient settings facilitated backstepping of the delta. Fills (Unit 4) occur within minor incisions along the delta top. These are interpreted as distributary channels that fed sediment to the seaward edge of the bayhead delta system. Elongated mounds on the seafloor (Unit 5) are interpreted as spoil from contemporary port dredging. Slump deposits (Unit 6) along the delta front are attributed to a combination of oversteepening of the delta by dredging, as well as deposition of modern sediments brought into the system by tidal currents. The system is capped by fine-grained, tidally redistributed and deposited sediments (Unit 7) which were possibly sourced from older organic material of an indeterminate source. This site is especially sensitive to episodic rates of sea-level change due to the relatively small Glacial Isostatic Adjustments (GIA) during the postglacial transgression and the flat antecedent gradients of both the subaerial unconformity and the overlying tidal ravinement.

理查兹湾是位于南非东北部、印度洋沿岸的高海岸沙丘前面的后屏障泻湖的一部分。1970 年代初期，修建了护堤，将原来的姆拉图泽河口分成两个独立的系统；理查兹湾港和新的姆拉图泽河口。本研究调查了理查兹湾港段的下切河谷系统和湾头三角洲的地层演化。对七个地震单元（单元 1-7）进行了成像。确定了一个区域发育的序列边界 (SB) 以及两个潮汐沟壑表面 (tRS1 和 tRS2)。表面 SB 与 LGM 低水位有关，该低水位在海平面低于现在约 130 m 时发展，直到约 18,000 年 BP。白垩纪粉砂岩（单元 1）形成基底。覆盖在 SB 上的海侵物质（单元 2）反映了位于波浪主导的背障系统中间段的下切谷的填充。它被海湾三角洲（第 3 单元）覆盖，其几何特征和地震特征表明了加积/进积和后退的交替周期。这种行为归因于海平面的偶发性跳跃，并且暂时（基于相对于区域海平面曲线的海拔）与海平面快速上升时期（8.2 ka 事件和融水脉冲（MWP））有关-1d)。这些快速上升的海平面间隔，加上相对较低的梯度设置，促进了三角洲的后退。填充（第 4 单元）发生在沿三角洲顶部的小切口内。这些被解释为将沉积物输送到海湾三角洲系统向海边缘的分流通道。海底细长的土墩（第 5 单元）被解释为当代港口疏浚的弃土。沿三角洲前缘的坍塌沉积物（单元 6）归因于疏浚导致三角洲过度陡峭，以及潮汐流带入系统的现代沉积物的沉积。该系统被细粒、潮汐重新分布和沉积的沉积物（第 7 单元）覆盖，这些沉积物可能来自不确定来源的较旧有机材料。