The processes affecting the transport and deposition of
mud in natural environments are still poorly understood, yet, understanding
these processes is important because much of the earth's surface is covered
with muddy substances, two thirds of the sedimentary rock record consist of
mudstones, mud accumulation impacts water reservoirs, harbors, and shipping lanes,
and because mudstones are an increasingly important energy resource.
From the perspective of a
sedimentologist, the need for experimental work in mudstone sedimentology comes
from the realization that many mudstones contain small-scale sedimentary structures
that can potentially provide information about depositional conditions and
history. However, as soon as one attempts to harness these features for
interpretation of environments of deposition, one realizes that there simply is
not much information available that allows us to link features observed in the
rock record to measurable sets of physical variables in modern environments.
Although one might hope to glean the required information
from studies of modern mud accumulating environments, the heterogeneity of
modern sediments makes it quite difficult to connect observed sedimentary
features and measured process variables. Thus, study under controlled
conditions in flumes and other experimental apparatuses is essential for true
improvement of our understanding of mud deposition.
can be used to obtain quantitative information about depositional and erosional
parameters, but it is of critical importance that the flume be designed in a
way that flocculated materials move under shear stress conditions that would be
reasonable in natural environments. Recent flume studies have shown that muds
can form deposits at flow velocities and shear stresses that would suffice to
transport and deposit medium grained sand. Mud suspensions are prone to flocculation
and the resulting floccules travel in bedload and form ripples that accrete
into beds. The latter finding suggests that for example many laminated shales
were deposited from currents rather than by settling from slow moving or still
water. There are many other sedimentary features in shales that can be
reproduced in flume studies.
As continued progress is being made, these will in
coming years provide a quantitative basis for shale sedimentology, as well as
offer the potential to better understand the parameters that determine the
performance of shale gas reservoirs.