Soft-Sediment
Deformation Structures: Upper Cretaceous Lance Formation,
Alquhtani, Faisal A.1,
Frank G. Ethridge2 (1) Colorado State Universtiy,
Fort Collins, CO (2) Dept. of Geosciences Colorado State University, Fort
Collins, CO
Jonah gas field is located in the
northwestern
Soft-sediment deformation structures in
the Lance are classified into four main types following Lowe (1975), and
include fluidization structures, liquefaction structures, soft-sediment
intrusion, and soft-sediment folds. Common soft-sediment deformation structures
include Type A and B pillars (dewatering pipes), dish structures, consolidation
laminations, massive sandstones, load structures, convolute laminations and
over-steepened cross beds. Type A pillars, dish structures and consolidation
laminations are usually found together and are genetically related. Pillars are
easily mistaken for burrows. These structures are related to water escape
mechanisms and are widespread in turbidites.
Over-steepened or overturned cross beds are common in fluvial deposits. Other
soft-sediment deformation structures, while not common, have been recognized in
fluvial sands and sandstones ranging in age from Precambrian to Holocene. One
feature common to deposits with these types of soft-sediment deformation
structures and to the Lance Formation is a strongly layered sequence consisting
of interbedded sandstones and finer-grained deposits.
Similar lithofacies
and soft-sediment deformation structures are present in outcrops of the upper
Cretaceous, Laramie Formation,
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California