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Megabreccia shedding from modern, low-relief carbonate platforms, Nicaraguan Rise
Hine, A.C.; Locker, S.D.; Tedesco, L.P.; Mullins, H.T.; Hallock, P.; Belknap, D.F.; Gonzales, J.L.; Neumann, A.C.; Snyder, S.W. (1992). Megabreccia shedding from modern, low-relief carbonate platforms, Nicaraguan Rise. Geol. Soc. Am. Bull. 104(8): 928-943. hdl.handle.net/10.1130/0016-7606(1992)104<0928:MSFMLR>2.3.CO;2
In: Geological Society of America bulletin. GEOLOGICAL SOC AMER, INC: New York, N.Y.. ISSN 0016-7606, more
Peer reviewed article  

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Keyword
    Marine

Authors  Top 
  • Hine, A.C.
  • Locker, S.D.
  • Tedesco, L.P.
  • Mullins, H.T.
  • Hallock, P.
  • Belknap, D.F.
  • Gonzales, J.L.
  • Neumann, A.C.
  • Snyder, S.W.

Abstract
    Single-channel seismic reflection data from the margins of lowrelief (150-250 m, measured from edge of bank to basin) carbonate platforms on the northern Nicaraguan Rise reveal complex seismic intervals consisting of mounded, chaotic seismic facies interspersed with discontinuous, parallel/laminated seismic facies. We interpret that these intervals contain megabreccias (chaotic facies) and sandy turbidites (parallel/laminated facies). One megabreccia is exposed on the sea floor displaying an overall fan shape having individual blocks measuring nearly 300 m across and >110 m high. The source area consists of a scalloped embayment with a headwall scarp 180 m high. Reflections within the platform are sharply truncated by this escarpment. This single megabreccia is ~120 m thick and extends ~27 km along slope and ~16 km out into the basin. Other megabreccias within the basin have individual blocks measuring >400 m across.Rocks from dredge hauls are a mixture of shallow- and deep-water facies. Shallow-water facies consist of mixed, skeletal grain-stones and Halimeda packstones. Deep-water facies are massive chalks, chalks with shallow-water skeletal grains, and chalk-block breccias. This indicates that the megabreccias formed as a result of bank-margin collapse, during which the ensuing debris flow eroded into slope and basin facies, mixing rock types together. We speculate that bank-margin-collapse events, resulting in megabreccia formation, may have been seismically triggered, and we emphasize that these large-scale, mass-wasting events occurred along margins of low-relief carbonate platforms.

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