Tag Archives: Lepidodendron Layer

Tales From The Ranch: The Lepidodendron Layer

Fat Vulture Gulch

Out at the in-laws’ ranch, most of the available strata is former ocean bed. As such, it’s rotten with fossils, usually of crinoids, sea urchins, and other well-armored fauna. In a few very lucky areas, these have opal cores, sadly not of gemstone quality but fascinating nonetheless. The vast majority of the local rocks are very soft shale (including the now-famous Barnett Shale, which stretches all the way east to Dallas) or harder limestone, and that limestone was mined extensively as building stone since the Great Depression. However, right along the Brazos River is another formation, and it’s only accessible in one place on the ranch. That road is jokingly named “Fat Vulture Gulch,” because the combination of steepness and loose rubble promises that anybody attempting to drive it recklessly is going to become vulture food. As it is, the only way to get down it with motorized transport involves 4-wheel drive, and even then it’s a serious white-knuckle drive up or down.

Lepidodendron Layer strata

As mentioned before, most of the rocks on the ranch are oceanic in origin, but the strata that makes up Lookout Point is a bit different. This rather thick layer is otherwise only accessible from Fat Vulture Gulch, and it’s extremely different from the others above and below. Besides being much harder and more erosion-resistant than the limestone mud below it, it’s a relatively coarse conglomerate of sandstone and smooth pebbles. As the mud below it weathers away, it comes free in large slabs, most of which worked their way free before the road went in. Best of all, I gave it the informal designation “the Lepidodendron Layer”, because it’s rich with fossils of tree branches, roots, and sometimes leaves, very likely from the Carboniferous Period lycopod plant Lepidodendron.

Lepidodendron Layer - bent strata

Absolute confirmation of this formation’s origin either lie underneath the bulk of the ranch or were eroded away as the Brazos River worked its way across the desert, but those rounded pebbles give a hint as to where those Lepidodendron parts came from. At one point, while the main ranch strata is marine, a river emptied into the sea near this point, and both regular flow and the occasional flood dumped huge amounts of sand and stone over the local muds. Some of those floods transported wood from the forests along the river, and as that sunk, later floods buried it further. That river may have lasted a few hundred years, or a few thousand, but ultimately it was itself choked by rising ocean levels, and all that was left was the detritus caught in this sandstone layer.

Lepidodendron Layer - bent strata

Of particular note are some of the oddly bent slabs in the area. Since this area isn’t exactly known for its geologic uplifts, and since the material inside isn’t severely distorted by heat and pressure, the suggestion is that these slabs were deformed while they were still heavily compressed mud. Only a few show this distortion, so are we looking at alluvial deposits following an ocean slump, or did earthquakes cause a slump in the muds beneath them after they were already buried? It’s time to go back to school and find out, I think.

Lepidodendron Layer - individual slab

This slab may not have any especial scientific value, but its personal value is immeasurable. The Czarina and I spent our honeymoon on the ranch, and my first visit to Fat Vulture Gulch was during a particularly overcast and drizzly day in January. Because of the rain, a piece of turquoise showed itself atop this slab, and a couple of deft taps with a rock hammer freed it for the first time in a third of a billion years. The Czarina still has this chunk after all of this time, and one of these days, she’s going to mount it in a piece of her own jewelry. That turquoise has no real value, either, but that’s not why we still hang onto it.

Lepidodendron Layer - cliff

While it will probably outlast me, my relations, and anybody who might come across my name, the Lepidodendron Layer is doomed. As mentioned, the limestone mud below it is extremely soft, and it rapidly weathers away in every rain. West Texas doesn’t get much rain, but when it does, it comes in huge gullywasher storms, and without adequate ground cover, those gullies wash clean. Ultimately, all of the Lepidodendron Layer will end up in the Brazos, following the mud into the abyss, and those slabs will be torn apart by river, rain, freezes, and the occasional rockhound.

Fat Vulture Gulch - limestone overview

Before that happens, though, the mud needs to wash away, and Fat Vulture Gulch has a lot of it. The erosion in recent times is obvious, judging by the occasional lost tree still attempting to hang on as the mud disappears, but this is still a layer that’s at least 100 feet (30.48 meters) deep. We may be waiting for a while.

Fat Vulture Gulch - lone tree

Fat Vulture Gulch - lone tree nebari

In bonsai terminology, surface root arrangements are called nebari. This tree won’t have much but nebari before too long.