Last interglacial reef limestones, northeastern St. Croix, US Virgin Islands—evidence of tectonic tilting and subsidence since MIS 5.5

Abstract

Most last interglacial (MIS 5.5) coral reef deposits in the Caribbean are emergent. However, in St. Croix, these are found mainly at depth, underneath Holocene material and confirmed by TIMS U-Th dated corals from eight cores through Holocene reefs. The only emergent MIS 5.5 marine deposit peaks at ?1.5 m MSL at the northwestern end of the island. The Late Pleistocene surface decreases at least 9.25 m (based on reef crest elevations) in elevation over 15 km along a 0.62 m/km eastward (alongshore) slope. Neither differential erosion nor a naturally sloping deposit is likely, thus the directional elevation decrease requires the influence of tectonic processes. Platform tilting or differential subsidence increasing in rate to the east probably operated both during and since the last interglacial and created progressively greater accommodation space for increasingly thicker overlying Holocene reefs in an eastward direction. Rates of subsidence since MIS 5.5 increase from west to east, from 0.02 mm/year to 0.1 mm/year, assuming a MIS 5.5 ?6-m sea level and ?4 m initial reef elevation. St. Croix's association with extensional shelf faulting from the northern part of the Virgin Islands Basin, the Anegada Fault to the east and the Puerto Rico Trench to the north may be significant in terms of identifying mechanisms for, or past events resulting in, directional tilting. Identification of differential elevations of MIS 5.5 reefs adds substantially to the information on Late Quaternary tectonism of the area.

Quaternary reef response to sea‐level and environmental change in the western Atlantic

“…Many detailed, reef‐derived Pleistocene sea‐level records derive from MIS 5e, centred around 125 kyr bp (e.g. Gischler, ; Hearty et al ., ; Siddall et al ., ; Toscano et al ., ; Woodroffe & Webster, ; and references therein) and suggest a complex sea‐level history for MIS 5e. Sea‐level at this time was at least 4 to 6 m higher than the Holocene highstand.…”

Effects of 2010 Hurricane Earl amidst geologic evidence for greater overwash at Anegada, British Virgin Islands

“…Dated corals elsewhere show that global sea level exceeded present levels for much of the time between 115 000 and 125 000 yr ago, and that it peaked about 124 000 yr ago in the range of 6-10 m above present levels (Kopp et al, 2009). Examples near Anegada have been reported recently from Florida (Muhs et al, 2011) and St. Croix (Toscano et al, 2012). If the dated finger coral at Anegada marks peak lastinterglacial sea level, the net land-level change at Anegada in the past 120 000 yr has been close to nil.…”

The reef platform of Martinique: Interplay between eustasy, tectonic subsidence and volcanism since Late Pleistocene

“…also proposed that Martinique was subsiding in order to explain the presence of the inner barrier around Caravelle Peninsula, similar to that of a subsiding atoll. Together with species evolution and variations in the rate of the Holocene sea level rise(Adey et al, 1977;Battistini et al, 1978;Toscano and Macintyre 2003, Toscano et al, 2011), subsidence contributed to the failure of the reef to keep up with rising sea level. Late Pleistocene to Holocene reef growth gave up at several levels, especially at -40 and -20 m MSL, and retreated to its present position along the coast.The deep patch reefs found on the Martinique platform that lie and show slope-breaks around -40 and -20 m MSL, grew on erosion surface E1 (Figure 11).…”