Accretion of ferromanganese nodules that form pavement in Second Connecticut Lake, New Hampshire.

We discovered ferromanganese nodules that measure up to 46 cm in diameter with stromatolitic growth patterns in the western central near-shore portion of Second Connecticut Lake, Pittsburg, New Hampshire. They occur as four distinct morphotypes: irregular laminated convex plates that form concentric rings around a nucleating center ("domed-plate"), continuous pustular pavements that extend >10 m2 ("pustular"), nonlaminated and nonnucleated masses with pebbles scattered throughout the matrix ("lattice"), and small nonnucleated laminated structures >2 cm ("cup") in water depths between 5 and 12 m. An estimated growth rate of 26 mm/100 years was determined from oxide deposits on datable debris. X-ray fluorescence showed an elemental composition comparable with that of nodule structures in other lakes. These sedimentary structures, the first seen in any of the six New England states, are the most morphologically distinct and varied lacustrine ferromanganese nodules known so far.