Hydro-isostatic and tectonic influences on emergent Holocene paleoshorelines in the Mariana Islands, western Pacific Ocean

Emergent paleoreef flats and paleoshoreline notches in the Mariana Islands document the effects of a mid-Holocene highstand in regional hydro-isostati c sea level and post-mid-Holocene forearc uplift of selected islands. Globa l hydro-isostatic calculations imply for Micronesia an areally variable mag nitude of 0.6-2.7 m for the mid-Holocene highstand, relative to modern sea level, and radiocarbon ages for emergent reef flats and rubble terraces ind icate a peak during the interval 4750-2250 yrs BP. In the tectonically stab le region of Micronesia southeast of the Mariana Islands, emergences of pal eoshorelines by 1.1-2.4 m closely match hydro-isostatic expectations for ea ch island group. In the Mariana Islands, Saipan, Tinian, and southern Guam display emergent mid-Holocene paleoreef flats and paleoshoreline notches st anding 1.2-2.0 m above modern counterparts, within the range of 0.8-2.1 m e xpected from hydro-isostatic theory. With allowance for minor tectonic subs idence locally, average hydro-isostatic emergence for the Mariana Islands i s estimated as 1.8 m. Northern Guam and Rota display paleoshoreline emergen ces in excess of hydro-isostatic expectation, implying 0.8 m and 1.2 m of p ost-mid-Holocene tectonic uplift, respectively. Subduction of an oceanic se amount chain beneath the segment of the forearc belt beneath Rota and north ern Guam probably accounts for subregional tectonic uplift, and also for en hanced interplate coupling responsible for anomalous seismicity. Post-mid-H olocene drawdown in relative sea level influenced the development of attrac tive environments for human settlement, which began in the Mariana Islands c. 3500 yrs BP.