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This is a retcon of an earlier post I had. Cambrian fossils aren't something one thinks of when they think of Maryland fossil hunting, and perhaps for good reason. The Cambrian rocks of the state are poorly exposed, those few areas where they do outcrop usually being gobbled up in urban sprawl. Compared to sites elsewhere like in Utah or York, Pennsylvania, the Maryland Cambrian is also rather barren. You could probably count on both hands the number of macrospecies in the entire early and middle Cambrian section of the state. But this rarity only makes collecting in it that much more interesting! Luckily for me I'm pretty close by most of these formations, so I have a decent knowledge of the area and outcrops, but even then it took a decent amount of time researching and scouting to find a site. The most recent formation I visited was the Araby Formation. Up until the mid 20th century the Araby was considered part of the Antietam Sandstone further west in the Blue Ridge, but after some more studies done on the formation it was found that it's lithological character was distinct enough to warrant it being a separate unit. Whereas the Antietam is a white quartz sandstone (much like the Oriskany I posted about yesterday) deposited in a beach-like environment, the Araby was deposited in deeper water (compared to the Antietam) and is more a mixture of siltstones, shales, phyllites, and slates. Together with the Antietam the Araby has some of the oldest fossils in the state dating back to the early Cambrian period some 540 million years ago. This makes it the oldest formation in the Frederick Valley. For those that don't know the Frederick Valley is a predominantly limestone syncline in west central Maryland (I consider it western Maryland, but most people probably wouldn't). At it's core is the early Ordovician Grove Limestone (which has practically no fossils), and on it's flanks are the late Cambrian Frederick Limestone (fossiliferous in parts, but those parts are very rare) and finally the Araby Formation. The Araby takes up positions along the far flanks of the valley, and it's eastern boundary with the metamorphic rocks of the Westminster Terrane marks the Martic Fault (no Washingtonians you don't need to worry about a San Andrea, from what I've read the Martic has been inactive for a long, long time). Due to it's sediment type and that of the surrounding rocks, the Araby is also a minor ridge forming unit, holding up the series of hills that flank Frederick Valley's eastern edge. These hills are nicely visible from the grounds of Monocacy National Battlefield, which is also of interest for marking the site of the northernmost Confederate victory (July 9, 1864 for those who're curious) in the Civil War. This ridge forming aspect means that, although very thin and covering a very small area, the Araby Formation has multiple exposures throughout the Frederick Valley. Some of the better ones are visible along I-70 just east of it's crossing over Monocacy River (an MGS team found some trilobites there) and MD-355 as you drive through the woods before hitting Araby Church Road (I believe the namesake for the formation is actually the Araby Church). In terms of fossils the Araby is almost exclusively dominated by the trace fossil Skolithos linearis, an annelid worm burrow. Other fossils found in it, however, include echinoderms and Olenellus sp. trilobites. As another aside the Cash Smith Shale, once held as an independent formation, also has trilobites and I believe inarticulate brachiopods reported from it, however it is no longer considered an independent formation but rather a member of the Araby Formation. Almost all of my fossils were the worm burrows, still cool but for everyone's sake I won't constantly repeat what they are this time around. Image 1: The largest burrow I've found. I originally thought it was a genal spine from a trilobite due to it's size. Image 2: Cross section of a burrow, outlined by the iron oxide stain. Image 3: Another burrow, this one roughly outlined by the iron oxide. Image 4: The large tubular structure covered in iron oxide (you might be noticing a pattern here with the oxides and burrows. I can't say definitively if they're connected in some way, but oftentimes you'll find the one with the other).