There are two rock units in this photo. One is igneous, one is sedimentary. Can you find the contact between them? It’s somewhere along this dashed line… The Mesilla Valley Formation is Cretaceous shale with some sandstone. The Muleros Andesite (pretty much identical to the Campus Andesite you find at UTEP) is Eocene. Here’s a … Read more
These four slabs, collected at “Fossil Hill,” north of the Cristo Rey laccolith at the Chihuahua (Mexico) / Texas / New Mexico triple point, bear positively-weathering fossils of the benthic foraminiferid called Cribratina, an index fossil for the Albian age / stage: My field notebook serves as an imperfect sense of scale. Here’s the Albian … Read more
On “Border to Beltway”‘s visit to Kilbourne Hole, after we whet our appetite with Hunt’s Hole, Michael finds a xenobomb. Ernie and Boris look on with envy: A “xenobomb” is a xenolith (in this case, of mantle peridotite), slathered in a coating of lava and tossed out of a volcano in the middle of a … Read more
Check out the immense climbing ripples preserved in surge deposits at Hunt’s Hole (a maar volcanic crater in southern New Mexico) and imagine the strong currents couples with an extraordinary amount of entrained pyroclastic material.
That’s Aden Crater, a Pleistocene shield volcano in southern New Mexico. Here’s what it looks like from above (Google Maps view): I also noted the position of two nearby maar craters: Kilbourne and Hunt Holes. When you climb up to the edge of Aden and look in, you see the congealed and fractured remnants of … Read more
The laccolith of Cristo Rey, at the Chihuahua / Texas / New Mexico triple point, is host to some cool geology. It’s cored by the Campus Andesite (47 Ma, Eocene) but surrounding the intrusion are a slew of sedimentary rocks, include the Turitella-bearing limestones of the Buda Formation and the shales and sandstones of the … Read more
Kilbourne Hole is the crater of a maar volcano in southern New Mexico, just across the state line from El Paso, Texas. I went there the weekend before last with a team from El Paso Community College, led by Joshua Villalobos. This is the place where xenobombs come from! If you go to the right … Read more
The Friday fold comes from the Texas – New Mexico – Chihuahua triple point, on the flanks of Cristo Rey mountain.
Some sweet “columnar jointing” style mudcracks from an abandoned quarry in about the farthest west corner of Texas that you can get to, or maybe the southeasternmost corner of New Mexico. One of them, anyhow… Did you spot the imposter?
Callan shows off a new sample from Texas, a peridotite xenolith launched into the air from a maar volcanic eruption, slathered in a layer of basalt. With full intent to coin a neologism, he dubs it a “xenobomb.”