Multiple
Origins of Thin-Bedded Slope Turbidites: El Rosario
Formation, Upper Cretaceous,
Ochoa Rodriguez, Jesus Armando1,
Kelsey McNamara1,
Thinly interbedded
sandstone and mudstone in erosionally to depositionally confined slope valleys are interdigitated with conglomerate channel fills and form
meter-scale units encased within a 300m-thick mudstone succession separating
slope-valley from underlying canyon fill deposits.
Thin-bedded deposits within the valley
fill form up to 25m thick and 230m wide wedge shape bodies consisting of
25–83cm thick, fine-medium, moderate-well sorted, subangular
sandstone interbedded with 3-10cm mudstone. Sandstone
beds thin laterally from 83 to 5cm over 35m, contain climbing unidirectional
ripple cross-lamination, plane to wavy laminations commonly bracket ripples,
mudstone thicken laterally from 10cm-1m. Horizontal sand-filled burrows are
present at sandstone bed tops. Thin-bedded deposits flanking and confining
multistory slope valley channels form up to 80m thick successions that thin and
pinch out over 500m; these consist of 2-15cm thick fine sandstone beds
separated by 1-12cm thick mudstone interbeds. Sandstone
beds show the most conspicuous lateral grain size changes and contain parallel
laminations and climbing ripple cross stratification.
Thick slope mudstones encase 4-11m thick thin-bedded deposits that form a
tabular 130m-thick and >1 km wide successions. Very fine to fine, well
sorted, subrounded sandstone forms 5-25cm thick beds
showing little lateral change over 40m with plane to wavy bedded facies most common. A low diverse trace fossil assemblage
is present in both sandstone and mudstone.
Temporal and spatial controls on these
three thin-bedded facies assemblage include lateral
gradient changes related to levee height; preservation controls internal levee
thickness and sedimentation from hyperpycnal flows
for the more continuous non-associated slope valley deposits.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California