DEPOSITIONAL FRAMEWORK AND CONTROLS ON MIXED CARBONATE SILICICLASTIC GRAVITY FLOWS - PENNSYLVANIAN PERMIAN SHELF TO BASIN TRANSECT, SOUTH-WESTERN GREAT-BASIN, USA
Rp. Miller et Pl. Heller, DEPOSITIONAL FRAMEWORK AND CONTROLS ON MIXED CARBONATE SILICICLASTIC GRAVITY FLOWS - PENNSYLVANIAN PERMIAN SHELF TO BASIN TRANSECT, SOUTH-WESTERN GREAT-BASIN, USA, Sedimentology, 41(1), 1994, pp. 1-20
Mixed carbonate-siliciclastic sediment gravity flow deposits of Late P
ennsylvanian to Early Permian age are exposed in the Death Valley - Ow
ens Valley region of east-central California. The Mexican Spring unit
constitutes the upper part of the Keeler Canyon Formation and is chara
cterized by turbidites, debris flow deposits and megabreccias, all of
mixed carbonate-siliciclastic composition. The mixed composition of th
e Keeler Canyon Formation provides an opportunity to link facies archi
tecture to controls on depositional system development. Depositional r
elationships indicate that the deposits represent a non-channellized b
ase of slope carbonate apron system with inner, outer and basinal faci
es associations. These gravity flow deposits are characterized by repe
ated stacked, small scale (< 15 m) coarsening and thickening upward cy
cles with superimposed medium scale (> 100 m) coarsening and thickenin
g upward cycles. Contemporaneous outer shelf and upper slope deposits
of the Tippipah Limestone are exposed at Syncline Ridge on the Nevada
Test Site. The deposits consist of carbonate buildups directly overlai
n by cross bedded, quartz-rich sandstone and conglomerate which filled
channels that traversed across the previously existing carbonate shel
f. Detritus was transported to the west, down the upper slope by gully
systems that fed the temporally persistent base of slope apron of the
upper part of the Keeler Canyon Formation. This style of deposition d
iffers from point-sourced siliciclastic submarine fan depositional sys
tems. However, the Keeler Canyon system has lithofacies similar to som
e sandy siliciclastic turbidite systems, such as the delta-fed submari
ne ramp facies model, which is a line-sourced, shelf-fed system that i
s not supply limited. The mixed clastic apron systems of the Keeler Ca
nyon Formation differ from classical carbonate aprons in that the form
er is characterized by an abundance of sedimentary cycles. Controls on
the development of these cycles and of the facies distribution may ha
ve resulted from changes in type and rate of sediment supply, relative
sea level changes and/or tectonic events. Interpretation of the data
is focused on relative changes in sea level as the most significant co
ntrol on development of the depositional system. Relative sea level ch
anges serve two important functions: (1) they provide a mechanism for
bringing coarse siliciclastic and bioclastic grains together on the ou
ter shelf, and (2) shelf margin collapse may be initiated during relat
ive lowstands allowing for transport of the sediment to the deep basin
and development of deep basinal cycles. Therefore, an abundance of mi
xed clastic gravity flow deposits such as these in the rock record may
be an indicator of periods of high frequency changes in relative sea
level, which is a characteristic of Late Palaeozoic sea level history.