Depth and
Intensity of Bioturbation in Channel Deposits of the Mississippian-Age
Mauch Chunk Formation
Smith, Casey J.,
Fillmore,
David
L., Simpson, Edward, and Lucas, Spencer G., 2010, Depth
and Intensity of Bioturbation in Channel Deposits of the
Mississippian-Age Mauch Chunk Formation [abs]: Geological Society of
America Northeastern Section (45th Annual) and Southeastern Section
(59th Annual) Joint Meeting (13-16 March 2010).
Complex
terrestrial
communities, represented by significant
subsurficial bioturbation, are reported to have evolved in the early
Mesozoic Era. This is thought to reflect the fact that the substrate
ecospace was the last to be exploited, including depth of burrowing.
However, recent studies of the Mississippian-age middle member of the
Mauch Chunk Formation have revealed an intensely bioturbated
fine-grained sandstone preserved in an ancient channel fill. This new
information opens up for discussion the intensity and depth of
bioturbation in early (late Paleozoic) terrestrial ecosystems.
The middle member of the Mauch Chunk Formation consists of a
braided-ephemeral river deposit developed in a semiarid setting. The
bioturbation in the channel was evaluated by the application of Bedding
Plane Bioturbation Index (BPBI of Miller and Smail, 1997), a
semiquantitative scale from 1 (no bioturbation) to 5 (60% to 100%
bioturbation). The channel samples collected have a BPBI of 4 to 5. The
intense bioturbation mixes the channel sand body up to 1.6 meters in
depth. Other facies in the middle member of the Mauch Chunk Formation
have BPBIs of 2 to 3. The channel may have developed either as a single
or a multiple stage fill, and bioturbation, consisting of the trace
fossil Planolites, has homogenized any evidence of the complex fill.
The channel may have acted as a conduit, a high permeability zone that
acted as a refuge for invertebrates to survive during periods of
drought.
The Mauch Chunk channel thus indicates intensive subsurficial
bioturbation in a nonmarine setting during the Mississippian Visean
time, long before such bioturbation was thought to have occurred.
Previous failure to recognize such bioturbation in upper Paleozoic
deposits maybe due to a limited sampling of what was then a rare (but
present) phenomenon that did not become widespread until the Mesozoic.
Depth and
Intensity of Bioturbation in Channel Deposits of the Mississippian-Age
Mauch Chunk Formation 
Complex
terrestrial
communities, represented by significant
subsurficial bioturbation, are reported to have evolved in the early
Mesozoic Era. This is thought to reflect the fact that the substrate
ecospace was the last to be exploited, including depth of burrowing.
However, recent studies of the Mississippian-age middle member of the
Mauch Chunk Formation have revealed an intensely bioturbated
fine-grained sandstone preserved in an ancient channel fill. This new
information opens up for discussion the intensity and depth of
bioturbation in early (late Paleozoic) terrestrial ecosystems.