Mathematical and geological approaches to minimizing the data requirements for statistical analysis of heterogeneity: summary technical progress report Page: 4 of 23
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Inference of the depositional environment of the sediments observed at the
Bosque site is based on the following three techniques: 1) comparison of the mapped
distribution of architectural elements with various alluvial/fluvial models; 2) comparison
of the sedimentary structures and faces associations observed in the faces studies with
sedimentological type models; and 3) ongoing source terrain analysis.
Results to date of this analysis suggest three possible depositional origins of the
sediments at the Bosque Site. The first hypothesis is that the Bosque site sediments are
the product of essentially overbank processes related to one or more rivers. In this
case, both the channel elements and the overbank elements are simply the result of
deposition on the floodplain following major and minor flood events, respectively. The
paleosols represent periods of non-deposition.
The second hypothesis is that the depositional environment in the vicinity of the
outcrop was characterized by perennial and ephemeral streams (possibly the confluence
of the two rivers) which combed across the alluvial plain in a series of small and large
avulsive steps. In this case, the channel elements represent axial or near-axial channel
deposits, and the clay and silt-rich elements represent the overbank deposits.
The third of the current hypotheses is that the Bosque Site sediments record
axial-tributary deposition and overbank perennial deposition. Ongoing source terrain
analysis of the channel elements at the site will help narrow down which of these
options is most likely.
Quantification of "Architectural Element" Scale Geometries
Geostatistical techniques are being used to convert the qualitative geological
information of the architectural element maps into quantitative information which can
be used to help simulate alluvial aquifer characteristics. To do this, 75 vertical transects
were drawn on the two architectural element maps. The (x,y) location of the center of
each element along the transects was then recorded. The elevation (z), element type,
and thickness of the element at each point were also recored. Standard three-
dimensional variogram and indicator variogram analysis is currently being performed on
the element-thickness data set. The results of these analyses should yield information
regarding the horizontal and vertical correlation lengths of the different architectural
elements at the Bosque Site.
Markovian Simulation Techniques
Both continuous and discrete models of random fields have been considered as a
means of synthesizing the type of geologic structure that we have encountered in the
Sierra Ladrones Formation (SLF) deposits. While continuous models can be quite
useful in describing the structure of geologic phenomena at certain scales, discrete
models are uniquely suited to the problem of describing aquifer characteristics in
geologic materials that have been deposited, eroded, or altered under abruptly changing
geologic conditions. Such abrupt changes in geologic environment are particularly
evident in the Sierra Ladrones alluvial/fluvial sediments, which appear to have been
subjected to a variety of depositional processes. Discrete stochastic models are uniquely
suited for reproducing the sharp lithologic interfaces that have been observed at the
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Mathematical and geological approaches to minimizing the data requirements for statistical analysis of heterogeneity: summary technical progress report, report, December 31, 1991; United States. (https://digital.library.unt.edu/ark:/67531/metadc683775/m1/4/: accessed April 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.