Potential for timing high-energy marine inundation events in the recent geological past through age-dating of reef boulders in Fiji

Geoscience Letters

Official Journal of the Asia Oceania Geosciences Society (AOGS)

Table 1 Characteristics of reef-platform carbonate boulders sampled for U:Th dating

Sample code	Place	Location	Orientation	Axis dimensions a × b × c (m)	Approx. volume¹(m³)	Approx. weight (tonnes)	Minimum flow velocity for transport²(m/s)	Sample for dating	Corrected age (years AD)	±2σ (years)	Difference in age, top to base (years)
LV1	Lavena	S16°52.395’	Inverted	4.2 × 4.0 × 1.3	21.8	30.6	>5.1	top	1513	7	157.3
		W179°53.238’						base	1670	3
LV2	Lavena	S16°52.392’	Inverted	4.0 × 2.9 × 1.0	11.6	16.2	>3.7	top	1793	3	49.4
		W179°53.251’						base	1842	2
LV4	Lavena	S16°52.382’	Right way	3.9 × 3.0 × 1.0	11.7	16.4	>2.7	top	1907	1	45.6
		W179°53.253’	up					base	1861	2
BM1	Bouma	S16°49.421’	Inverted	3.9 × 2.8 × 2.1	22.9	32.10	>5.1	top	1659	7	47.7
		W179°51.937’						base	1707	3
BM2	Bouma	S16°49.449’	Right way	3.3 × 2.3 × 1.9	14.4	20.2	>4.3	top	1763	3	24.5
		W179°51.906’	up					base	1739	2
BM3	Bouma	S16°49.438’	Inverted	3.0 × 2.4 × 1.6	11.6	16.1	>3.6	top	1809	3	27.1
		W179°51.882’						base	1836	3
BM4	Bouma	S16°49.443’	Right way	2.9 × 2.4 × 1.1	7.7	10.7	>4.4	top	1690	3	47.1
		W179°51.969’	up					base	1643	6
MK1	Matakuro	S16°51.560’	Inverted	4.7 × 3.2 × 2.7	40.6	56.9	>3.8	top	1737	2	250.9
		W179°52.731’						base	1988	1

¹Based on the rectangular, blocky boulder shapes commonly observed on Taveuni (see also [25]).
²The flow velocities (m/s) given are the minimum flows needed to set the boulders in motion as inferred from the hydrodynamic transport equations of Nandasena et al. [26]. From the growth direction of fossil corals it was possible to establish that the majority of boulders rest in an inverted position, thus the minimum flow velocity for transport by rolling (overturning) is given; it is likewise assumed that transport by rolling also occurred for those boulders now in an upright positon.
These are the largest boulders observed within the boulder fields on fringing reefs in the study area. Refer to Figure 3 for the location of the boulders.