Elemental and isotopic compositions of metalliferous and pelagic sediments from the Galapagos mounds area, data of DSDP Leg 70

Nontronite, the main metalliferous phase of the Galapagos mounds, occurs at a subsurface depth of ~2-20 m; Mn-oxide material is limited to the upper 2 m of these mounds. The nontronite forms intervals of up to a few metres thickness, consisting essentially of 100% nontronite granules, which alternate with intervals of normal pelagic sediment. The metalliferous phases represent essentially authigenic precipitates, apparently formed in the presence of upwelling basement-derived hydrothermal solutions which dissolved pre-existent pelagic sediment. Electron microprobe analyses of nontronite granules from different core samples indicate that: (1) there is little difference in major-element composition between nontronitic material from varying locations within the mounds; and (2) adjacent granules from a given sample have very similar compositions and are internally homogeneous. This indicates that the granules are composed of a single mineral of essentially constant composition, consistent with relatively uniform conditions of solution Eh and composition during nontronite formation. The Pb-isotopic composition of the nontronite and Mn-oxide sediments indicates that they were formed from solutions which contained variable proportions of basaltic Pb, introduced into pore waters by basement-derived solutions, and of normal-seawater Pb. However, the Sr-isotopic composition of these sediments is essentially indistinguishable from the value for modern seawater. On the basis of 18O/16O ratios, formation temperatures of ~20-30°C have been estimated for the nontronites. By comparison, temperatures of up to 11.5°C at 9 m depth have been directly measured within the mounds and heat flow data suggest present basement-sediment interface temperatures of 15-25°C.

Certain mounds of Arkansas and of Mississippi /

Volumes are continuously paged.

Waulsortian Mounds and reservoir potential of the Ullin limestone ("Warsaw") in Southern Illinois and adjacent areas in Kentucky /

Mode of access: Internet.

The Bessemer site, excavation of three mounds and surrounding village areas near Bessemer, Alabama,

Imprint date on verso of t.-p.: 1942.

Pre-historic mounds in Arkansas; a preliminary report on village and camp sites near the Hineman Mounds, in Ouachita County, Arkansas.

Reproduced from type-written copy.

Pre-historic mounds in Arkansas; a archaeological excavation of a pre-historic Caddo burial mound, located in Clark County, Arkansas on Mink Branch near the Hineman Mounds.

Title and text of circulating copy vary slightly from the "A" copy.

A site planning brief for Dickson Mounds Museum.

"7 Aug. 2000"--Prelim. page.