In the southern Española basin south of Santa Fe, New Mexico,
weakly magnetic Santa Fe Group sediments of Oligocene to Pleistocene age,
which represent the primary aquifers for the region, are locally underlain
by moderately to strongly magnetic igneous and volcaniclastic rocks of
Oligocene age. Where this relationship exists, the thickness of Santa Fe
Group sediments, and thus the maximum thickness of the aquifers, can be
estimated from quantitative analysis of high-resolution aeromagnetic data.
These thickness estimates provide guidance for characterizing the ground-water
resources in between scattered water wells in this area of rapid urban
development and declining water supplies.
This report presents one such
analysis based on the two-step extended Euler method for estimating depth
to magnetic sources. The results show the general form of a north-trending
synclinal basin located between the Cerrillos Hills and Eldorado with
northward thickening of Santa Fe Group sediments. The increase in thickness
is gradual
from the erosional edge on the south to a U-shaped “Santa Fe embayment
hinge line,” north of which sediments thicken much more dramatically.
Along the north-south basin axis, Santa Fe Group sediments thicken from
300 feet (91 meters) at the hinge line near latitude 35°32'30"N
to 2,000 feet (610 meters) at the Cerrillos Road interchange at Interstate
25, north of latitude 35°36'N. The depth analysis indicates that, superimposed
on this general synclinal form, there are many local areas where the
Santa
Fe Group sediments may be thickened by a few hundred feet, presumably
due to erosional relief on the underlying Oligocene volcanic and volcaniclastic
rocks. Some larger areas of greater apparent thickening occur where the
presence of magnetic rocks directly underlying the Santa Fe Group is
uncertain.
Where magnetic rocks are absent beneath the Santa Fe Group, the thickness
cannot be estimated from the aeromagnetic data. |
