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Since Hayden's original definition of the Galisteo Formation, there has been some confusion over its upper and lower limits, age, and distribution in New Mexico. A measured section 1,100 m thick of the Galisteo in its type area east of Cerrillos provides a firm basis for recognition of the formation in other areas by enabling lithologic and biostratigraphic correlation of major Galisteo outcrops.
Steeply dipping and locally overturned strata of yellow and brown coarse-grained and pebbly sandstone dominate the lower 353 m of this section and unconformably overlie yellow and white medium to coarse-grained sandstones of the Cretaceous Mesaverde Group. Early Eocene mammals of the Cerrillos local fauna are present in red mudstones 369 to 424 m above the Mesaverde-Galisteo contact. The upper 186 m of the Cerrillos section is dominated by yellow coarse-grained and pebbly sandstones that locally contain numerous fossil logs. Latest Eocene mammals of the Tonque local fauna are present in the upper 231 m of this section. The locally conformable contact between the Galisteo Formation and the overlying Espinaso Volcanics is at a 5-m-thick transition zone of tuffaceous clay and sandstone.
Strata of the upper part of the Galisteo Formation in the Hagan basin and Rio Puerco fault zone contain mammal fossils of the Tonque local fauna and can be lithologically and biostratigraphically correlated with the Cerrillos section. Other isolated Galisteo outcrops lack fossils but can be lithologically correlated, albeit imprecisely, with the Cerrillos section. Parts of the Galisteo Formation are time equivalents of the lower Eocene San Jose Formation and the Eocene part of the Baca Formation, but lithologic and structural evidence demonstrates that the Galisteo Formation is a rock-stratigraphic unit distinct from these two formations.
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