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Abstract: In 2008 a unique sedimentary unit of red sandstone with abundant calcite nodules was discovered within the northeast corner of the Narragansett Basin in southeastern Massachusetts. Although the outcrop of the calcite nodules examined in this paper was destroyed in 2010, the nodules collected in 2008 were interpreted preliminarily as calcite rhizoliths representing... read morea preserved root horizon (Benner and Gardulski, 2010). The calcite nodule-rich unit lies stratigraphically below a dated rhyolite flow (Late Devonian, ~373 Ma; Thompson and Hermes, 2003) and is within the “lower portion” of the Wamsutta Formation, beneath an unconformity with the Carboniferous sedimentary rocks of the Wamsutta Formation. The outcrop area was investigated to determine whether the calcite features represent rhizoliths within a paleosol, possibly preserving an early, deeply rooted (~3m thick) plant ecosystem within a pyroclastic deposit. Petrographic analysis revealed an abundance of devitrified glass within the matrix of these samples as well as pumice and lithic fragments suggesting a volcanic origin of the deposit. Scanning electron microscopy revealed amorphous carbon fragments within all of the sample types, which supports a biogenic origin of the calcite nodules. Combining this microscopic data with stratigraphic fieldwork it was confirmed that most of the calcite nodules are preserved rhizoliths within a pyroclastic deposit from at least the Late Devonian.read less
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