Late Quaternary history of Henderson Island, Pitcairn Group

Abstract

Henderson Island is an emergent limestone island. It rises to 33.5 m above modern sea-level (MSL) from a sea-floor depth of about 3,500 m and conforms to the pattern of an elevated atoll, although no field evidence was found pertaining to the pre-atoll volcanic history of the island. The emergence of this coral atoll can be explained by lithospheric flexure processes subsequent to the emplacement of the Pitcairn Island volcano, built by two phases of volcanism (estimated at 855 and 540 kyr by K-Ar dating). U-Th dates obtained from Henderson Island indicate that the majority of the presently visible fossil corals have an age between 404-225 kyr. Henderson Island first became emergent above MSL when sea level dropped subsequent to 380 kyr, as the period 440-380 is thought to have been characterized by sea level at least several metres above MSL in the Central Pacific. As a result Henderson Island would have become subaerially exposed from 380 kyr onwards. The uplift rate of Henderson Island is approximately 0.093-0.10 mm/yr indicating that flexure-induced uplift component above MSL commenced between 360-335 kyr, 500 kyr after the initial, and 190 kyr after the last phase of construction of the Pitcairn volcano. The time-lag following the loading of the Pitcairn volcano and the present continuation of uplift on Henderson support the theory that the lithosphere behaves in a visco-elastic manner. Field relations and U-Th dates indicate three main periods of reef development: (1) A prolific reef-building period (440-380 kyr wnit 71 and 330-300 kyr [Units 2 6' 31) dominated by large, stout branching coral colonies; (2) A shorter period of reef growth j285-275 kyr [Unit 41) dominated by well-formed large in situ coral colonies and Tridacna maxima; (3) A less prolific period of reef growth (230-215 kyr [Unit 51) dominated by platy corals enveloping the previous lithologies below 19.6 m. The absence of dateable material from the last interglacial, oxygen isotope substage ii.5 (=i;e) at Henderson Island is in marked contrast to the Late Pleistocene reefs in the southern Cook Islands where reefs of substage 5.5 age skirt older carbonate complexes. C l!)!J,i The Linnean Society of London ADDITIONAL KEY WORDS:-carbonate stratigraphylithospheric flexurefossil atollcoral reef -Pleistocenesea-level -U-series dating.

Impact of early Polynesian occupation on the land snail fauna of Henderson Island, Pitcairn group (South Pacific)

“…The earliest evidence comes from fossiliferous cave sediments in Hen-6 behind the North Beach. From its geomorphological context and from available U-Th dates, it seems likely that this cave was formed by marine processes during a late Middle Pleistocene interglacial period (Blake 1995 of a minimum of 18 species, plus one semi-terrestrial pulmonate (Melampus £avus). Like many indigenous land snails on Paci¢c islands, most of these species are small (less than 4 mm), a feature that aids natural dispersal to remote islands by aerial means (Vagvolgyi 1976;Preece 1998).…”

“…U-Th dates obtained from in situ fossil corals from Henderson span the period 404^225 kyr (Blake 1995). As mean sea level in this part of the Paci¢c is believed to have been several metres higher between 440^380 kyr ago, it is thought that Henderson would have become emergent and subaerially exposed for a period from 380 kyr.…”

“…As mean sea level in this part of the Paci¢c is believed to have been several metres higher between 440^380 kyr ago, it is thought that Henderson would have become emergent and subaerially exposed for a period from 380 kyr. The island was submerged again during the next high sea level phase at about 280 kyr, and corals of this age have been found in the fossil lagoon (Blake 1995). Subsequently, the island again became emergent, perhaps about 275 kyr.…”

The timing of sea-level high-stands during Marine Isotope Stages 7.5 and 9: Constraints from the uranium-series dating of fossil corals from Henderson Island

“…Constraining the uplift history of Henderson Island is therefore, non-trivial, requiring lithospheric flexural and isostatic rebound modelling, although a total net uplift of 55 ± 12 m since $600 ka has been estimated based on the U-series dating of fossil corals (Andersen et al, 2008). Detailed descriptions of the carbonate geomorphology of Henderson Island have been published previously (Blake, 1995;Pandolfi, 1995). Henderson Island is remotely located at the southeast margin of the Indo-Pacific subtropical belt, which makes any coral reef formation very sensitive to climatic and ecological changes (Andersen et al, 2008;Ayling et al, 2006;Benton and Spencer, 1995;Stirling et al, 2001).…”

Prehistoric Birds and Bats from the Atiahara Site, Tubuai, Austral Islands, East Polynesia

“…Evolution of flightless distinct rails has at times been rapid (for example, Porzana atra on Henderson Island, which island has only been subaerial for about 380 kyr [Blake 1995], and other examples given by Slikas et al [2002]). Many of the Gallirallus-group species were thought to have been derived from a volant ancestor like Gallirallus philippensis, for example (Steadman 2006).…”