USGS · 70009987
No abstract available.
Explore connections, maps & timelines
K. N. Sachs. 1965. Removal of ash from plankton samples concentrated by ignition. https://doi.org/10.1016/0011-7471(65)91869-3
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
No abstract available.
Oceanic tholeiitic basalts were dredged from 2500 to 3000 m depth on each flank of the Amirante Ridge, 1200 km southeast of Somalia in the western Indian Ocean, by R.V. Argo in 1964. One sample, probably shed from a flow or dike in basement beneath the coralline cap, gave a wholerock K-Ar age of 82±16×10 6 years. The age is similar to those reported by others for agglomerate from Providence Reef, nearer Madagascar, and for gabbro from Chain Ridge, the southwest member of Owen Fracture Zone, nearer the Somali coast. The Amirante Cretaceous-Early Tertiary occurrence lies between the “continental” 650 × 10 6 years granites of Seychelles Archipelago and the large Precambrian “continental” block of Madagascar. Trends of major structures and distribution of the related topographic and magnetic-anomaly lineations in 7–8 × 10 6 km 2 of the surrounding Indian Ocean suggest that in addition to spreading of the seafloor from the seismically-active Mid-Indian Ocean Ridge-Carlsberg Ridge complex there has been, since mid-Mesozoic time, distributed left-lateral shear along 52°–54°E that has moved Madagascar at least 700 km south relative to Seychelles Bank. Measurements by other indicate the absolute movement of Madagascar has been southward as well. The emplacement of oceanic tholeiitic basalts at shallow depth, the development of volcanic topography between the sedimented Somali and Mascarene basins, and the existence of the faulted Amirante Trench and Ridge are consequences of the displacement.
In a collection of pelecypods from deep water off the west coast of Africa, several specimens of a new species of the foraminifer, Rosalina , are attached to the umbonal area of the bivalve. In addition, numerous attachment scars are observed on the exterior surface with interconnected penetration scars on the interior surface of the valves. It is speculated that the foraminifer made the partial or complete penetration of the clam shell in connection with its search for calcium carbonate for shell-building. From the nature of the scars on the interior of the valves, it is clear that the clam was alive, because there are mounded up shell deposits around some of the openings and others are completely sealed shut by shell material deposited by the clam.