Composition of micronodules and host sediments from the Guatemala Basin

A complex of mineralogical techniques used in studies of near-surface layer hemipelagic sediments indicates that disordered todorokite and hexagonal birnessite dominate in manganese micronodules, whereas hexagonal birnessite is the main phase of micronodules from miopelagic sediments. Content of todorokite increases downward through the miopelagic sedimentary sequence; this can be reasonably explained by transformations of some other manganese minerals to todorokite. Occurrence of several manganese minerals in studied samples may reflect temporal and lateral variations in C_org content in sediments and respective local fluctuations in environmental conditions (pH, Eh, geochemical activity of Mn, etc.). Todorokite may have formed under the most anoxic conditions near the water-sediment interface.

(Table 2) Species composition of agglutinated foraminifers from the abyssal zone of the Pacific Ocean

The quantitative study of distribution and taxonomic composition of recent living and dead (without plasma) benthic foraminifers revealed three foraminiferal assemblages in bottom sediments of the Pacific Ocean at depths of 3350 to 4981 m. The assemblage dominated by epibenthic Lagenammina difflugiformis, Reophax dentaliniformis, and Saccorhiza ramose occupies slopes of underwater hills. The assemblage with a high share of infaunal Cribrostomoides subglobosum, C. nitidum, and Ammobaculites agglutinans is registered on an abyssal plateau. The assemblage with a significant proportion of large Astrorhiza and Reophax species, which are characterized by active way of life, populates gentle slopes and narrow depressions with potentially strong bottom currents.