ESTIMATION OF ALLUVIAL-FILL THICKNESS IN THE MIMBRES GROUND-WATER BASIN,
NEW MEXICO, FROM INTERPRETATION OF ISOSTATIC RESIDUAL GRAVITY ANOMALIES  
(pdf file 4.9 Mb)

By Charles E. Heywood



ABSTRACT
 
The geologic structure of the Mimbres 
ground-water basin in southwest New Mexico is 
characterized by north- and northwest-trending 
structural subbasins. Sedimentation of Miocene 
and Pliocene age has filled and obscured the 
boundaries of these subbasins and formed poten-
tially productive aquifers of varied thickness. The 
location and depth of the subbasins can be esti-
mated from analysis of isostatic residual gravity 
anomalies. Density contrasts of various basement 
lithologies generate complex regional gravity 
trends, which are convolved with the gravity signal 
from the Miocene and Pliocene alluvial fill. An 
iterative scheme was used to separate these 
regional gravity trends from the alluvial-fill grav-
ity signal, which was inverted with estimated 
depth-density relations to compute the thickness 
of the alluvial fill at 1-kilometer spacing. The 
thickness estimates were constrained by explor-
atory drill-hole information, interpreted seismic-
refraction profiles, and location of bedrock lithol-
ogy from surficial geologic mapping. The result-
ing map of alluvial-fill thickness suggests large 
areas of thin alluvium that separate deep structural 
subbasins.



Abstract from Water-Resources Investigations Report 02-4007