Petroxestes pera bivalve borings on limestone hardground (Turkey Track Layer, Waynesville Formation, Upper Ordovician; Flat Fork, Warren County, Ohio, USA) 8 : 無料・フリー素材/写真
Petroxestes pera bivalve borings on limestone hardground (Turkey Track Layer, Waynesville Formation, Upper Ordovician; Flat Fork, Warren County, Ohio, USA) 8 / James St. John
ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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説明 | Petroxestes pera Wilson & Palmer, 1988 - bivalve borings in the Ordovician of Ohio, USA.These slit-shaped structures are borings made by fossil clams. Borings are one of many categories of trace fossils - any indirect evidence of ancient life. Other examples include burrows, tracks, trails, footprints, and bitemarks. Trace fossils, also called ichnofossils, record the behavior of ancient organisms. Traces are given Latin scientific names in the same style as living organisms or body fossils.The Petroxestes borings seen here in southwestern Ohio were made by the bivalve Corallidomus scobina. Bivalves are bilaterally symmetrical molluscs having two calcareous, asymmetrical shells (valves) - they include the clams, oysters, and scallops. In most bivalves, the two shells are mirror images of each other (the major exception is the oysters). They occur in marine, estuarine, and freshwater environments. Bivalves are also known as pelecypods and lamellibranchiates.Bivalves are sessile, benthic organisms - they occur on or below substrates. Most of them are filter-feeders, using siphons to bring in water, filter the water for tiny particles of food, then expel the used water. The majority of bivalves are infaunal - they burrow into unlithified sediments. In hard substrate environments, some forms make borings, in which the bivalve lives. Some groups are hard substrate encrusters, using a mineral cement to attach to rocks, shells, or wood.The fossil record of bivalves is Cambrian to Recent. They are especially common in the post-Paleozoic fossil record.Petroxestes borings very rarely have a bivalve body fossil still occupying the slit. The type specimen of Petroxestes pera is a boring incised into a solid, calcareous, bryozoan colony. The examples in the photo were drilled into a carbonate hardground, which is a synsedimentarily-cemented surface exposed directly on the seafloor. Some hard-substrate seafloor surfaces are composed of other rock types such as basalt, and are called rockgrounds. Many marine hardground environments were in moderately high-energy, relatively shallow water. Organisms occupying such settings frequently physically attached themselves to the hardground seafloor (= encrusters) or drilled into the substrate (= borers).Petroxestes pera borings were sometimes so abundant on ancient Cincinnatian hardgrounds that early stratigraphers called them "turkey tracks", in reference to their similarity with the footprints of living turkeys (e.g., see: www.flickr.com/photos/jsjgeology/26798916929).That the term "turkey track" referred to Petroxestes hardgrounds has been forgotten over the decades. Modern Cincinnatian geologists misidentify Trichophycus venosum-burrowed surfaces as the "turkey tracks" of old - I've seen this in the literature and in museum exhibits.The best true turkey track layer I know about is the one seen here - it's an extensive horizon at Caesar Creek State Park in Ohio. Exposures and talus blocks can be seen in the emergency spillway and along the Flat Fork trail and at creek cuts along Flat Fork itself.The only turkey track occurrences I have seen for certain are in the upper Waynesville Formation. I have also encountered this horizon, or a similar horizon, in the Waynesville Formation near Dayton, Ohio.Stratigraphy: Turkey Track Layer, upper Waynesville Formation, Richmondian Stage, upper Cincinnatian Series, upper Upper OrdovicianLocality: talus block along Flat Fork, downstream from Horseshoe Falls, Caesar Creek State Park, northeastern Warren County, southwestern Ohio, USA |
撮影日 | 2022-09-18 12:28:29 |
撮影者 | James St. John |
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