The geologic history of the southern Line Islands

Abstract

The Line Islands chain, a major bathymetric feature in the Pacific Basin, is composed of a linear series of parallel submarine ridges and volcanic edifices capped by atolls. Rocks dredged from the previously unsampled southern portion of the chain--the Caroline Island area--have been analyzed for depositional environment, biostratigraphic age, and diagenetic environment. These rocks contain Late Cretaceous and Tertiary faunas. Drilling on DSDP Legs 17 and 33 revealed that synchronous volcanic edifice building and reef development cook place in Late Cretaceous time over a distance of 1270 km along the chain. Rocks dredged from seamounts near Caroline Island contain volcanic debris and shallow-water shell debris of Late Cretaceous age. This association is evidence for the existence of a reef-bearing volcanic edifices with a minimum age of Late Cretaceous near Caroline Island. With the discovery of these seamounts, the known occurrences of Late Cretaceous, reef-capped, volcanic edifices now extend a distance of 2500 km from Kingman Reef to Caroline Island. Volcanism during middle Eocene time is documented in the southern Line Islands, where Eocene sediments were engulfed and altered by volcanic eruptions. Skeletal debris of shallow-water origin was redeposited in deep-water Paleocene. Eocene, Oligocene, Miocene, and Pliocene strata indicating that reef development was perhaps continuous throughout the Tertiary. Stable isotope geochemistry of carbonate cements indicates subsidence of the Line Islands seamounts during post-Eocene time. The synchroneity of Late Cretaceous volcanism along 2500 km of the Line Islands argues against the proposition that a single hotspot of the Hawaiian-Emperor type produced the Line Island chain. Volcanic edifices of Cretaceous age are now known to extend from the Line Islands through the Mid-Pacific Mountains to the Marshall Islands and the western margin of the Pacific Plate from Japan to the Marianas. The occurrence of both Cretaceous and Eocene volcanism in the southern Line Islands indicates similarities between the histories of the Line Islands and the Marshall Islands.