Holocene sea-level change and estuary infill in North West Nelson, central New Zealand

The sedimentary sequences found within estuaries in the north west Nelson region of central New Zealand are investigated in order to quantify the timing of the end of the Post Glacial Marine Transgression. This region has been identified as being relatively stable in terms of vertical tectonic movement during the Holocene, but is yet to yield any reconstructions of eustatic sea level. In this study, we investigate the Holocene infill of a barrier estuary (Parapara Inlet) through sedimentological analysis and radiocarbon dating of 18 vibracores up to 4.2 m in length. It is found that the estuary infilled through a combination of lateral flood tide and fluvial delta progradation as well as vertical central basin infill. The central basin infilled at a consistent rate of 0.4 mm/year in both the mid (7.0–6.0 ka) and late-Holocene (2.5–1.5 ka). By the time of early human (Maori) settlement (c. 1 ka), the estuary surface was at low intertidal elevations with sediment being transported from the fluvial to tidal delta. A discernible change in sedimentation rates could not be associated with Maori settlement; however, infill rates increased to at least 12.5 mm/year in the past 150 years due hydraulic sluicing associated with mining. The sedimentary history of Parapara Inlet is compared to nearby Whanganui Inlet, d’Urville Island and Nelson to establish the character of regional Holocene sea level movement. It is found that relative sea level reached modern elevations between 8 and 7 ka in the region. The similarity between sea level curves for the end of the post glacial marine transgression (PMT) to other tectonically stable sites in northern New Zealand suggests that this curve can now be considered a true eustatic signal for the New Zealand archipelago.

A 5700-year-old beach-ridge set at Cape Canaveral, Florida, and its implication for Holocene sea-level history in the southeastern USA

The Cape Canaveral Peninsula is the largest Holocene coastal sand deposit composed of beach ridges on the Atlantic coast of Florida. It is composed of 16 beach-ridge sets that are separated by erosional surfaces. Despite its prominence as a Holocene coastal depocenter, there are a limited amount of chronological data constraining the timing of its formation. In this study, we apply optically stimulated luminescence (OSL) dating on sand-sized quartz and radiocarbon dating on individual marine shells to develop a refined chronology of the Cape Canaveral beach-ridge plain with particular focus on constraining the depositional age of the northwesterly-most, and geographically oldest, beach-ridge set on the peninsula. We obtain an average OSL age of 5680 ± 240 years ( n = 4) for the initiation of coastal deposition at Cape Canaveral. The new ages, and the organization of beach ridges into 16 distinct sets indicates that the Cape Canaveral beach-ridge plain experienced an ~5700-year history of alternating deposition and erosion, with 75% of present-day Cape Canaveral (Beach-ridge Sets 5–16) deposited over the past 2000 years and Beach-ridge Sets 8–16 comprising 50% of the area over the past 1000 years. Because the minimum swale elevations of the ~5700-year Beach-ridge Set 1, and those of all the younger beach-ridge sets, are within several decimeters of present-day mean higher high water, we hypothesize that all the beach ridges present at Cape Canaveral could have been deposited at or within decimeters of present-day sea level. There is no evidence for Holocene “highstand” events over the past 5700 years in the published sea level curves from northeast and south Florida, which are based on subsurface estuarine foraminifera/leaf litter and mangrove peat data, respectively. This dichotomy illustrates the need to integrate both subaerial and subsurface data to produce a more realistic Holocene sea-level curve for the southeastern United States.

Depositional Setting and Cementation Pattern of Al-Mejarma Beachrocks, Saudi Arabia: A Proxy for the Late Quaternary Red Sea Coastal Evolution

This study utilizes lithofacies characteristics, petrographic, XRD, and stable isotope data of Al-Mejarma beachrocks, Red Sea, Saudi Arabia, to interpret its depositional setting, origin of cement, and coastal evolution. The beachrock is 1.15 m thick, medium to very coarse-grained sandstone with scattered granules. It shows massive to graded bedding, horizontal, ripple, and shore parallel to slightly oblique planar cross-laminations, with a remarkable absence of bioturbation. It was deposited by shore-parallel longshore currents in a relatively high-energy beach environment. The framework comprises quartz, feldspars, and lithic fragments admixed with biogenic remains of algae, mollusca, foraminifera, corals, and echinoids. They are cemented by high magnesium calcite in the form of isopachous rims and pore-filling blades, and rarely, as a meniscus bridge. The mean values of δ18OVPDB and δ13CVPDB are 0.44‰ and 3.65‰, respectively, suggesting a seawater origin for the cement. The framework composition, facies geometry, and association with back-barrier lagoon impose a deposition as a shoreface-beach barrier through two stages corresponding to the middle and late Holocene. The first stage attests landward migrating sediment accumulation and rapid marine cementation. The sediments stored offshore during the early and middle Holocene humid periods migrated landward from offshore and alongshore by onshore waves and longshore drift during the middle and late Holocene sea-level highstand. They were cemented to form beachrock and subsequently emerged as the late Holocene sea-level fell.

Supplemental Material: Late Pleistocene and early Holocene sea-level history and glacial retreat interpreted from shell-bearing marine deposits of southeastern Alaska, USA

<div>Shell-bearing strata dataset from southeastern Alaska.<br></div>