Neogene crustal emersion and subsidence at the Romanche fracture zone, equatorial Atlantic

Details Neogene crustal emersion and subsidence at the Romanche fracture zone, equatorial Atlantic Neogene crustal emersion and subsidence at the Romanche fracture zone, equatorial Atlantic

Jul 1977

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977e%26psl..35..369b&link_type=abstract

Earth and Planetary Science Letters, Volume 35, Issue 3, p. 369-383.

Astronomy and Astrophysics

Astronomy

6

Scientific paper

Partly phosphatized, oolitic-biogenic limestones were recovered 950-1300 m below sea level from two sites near the crest of a transverse ridge running parallel and adjacent to the Romanche fracture valley (equatorial Atlantic). Some of the biogenic contituents of the limestones (the benthonic foraminiferal genus Amphistegina; corals of the genus Stylophora sp., scaphopods, etc.); their paleofacies assemblage (including echinoderms, gastropods, calcareous algae, etc.); and the presence of a well-developed oolitic facies, indicate that the limestones formed in very shallow water close to sea level. In addition, several features of the limestones (including the presence of stromatolite-like laminae, and dissolution features typical of subaerial diagenesis) suggest that the summit of the transverse ridge might have undergone episodes of emersion. The limestones were formed on a shallow carbonate bank at around the Miocene-Pliocene boundary, i.e., 5 +/- 1 Myr ago, as determined by the age of fossil planktonic foraminifera and corals. The transverse ridge must have subsided since that time at an average rate of 0.2 mm/yr. It is unlikely that the vertical motions of the Romanche transverse crustal block were caused solely by accreting plate margin- or mantle plume-related volcanic and/or tectonic processes. It is suggested instead that such motions are related to vertical tectonism typical of large oceanic fracture zones.

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