Fang et al.—Late Triassic elcanid insect fossil from North America 92(6):1028–1034
1029
Fossil location Cascade Berry Hill Virginia
North Carolina 311
Solite Quarry
N Buford
700 Eden 2 miles
Figure 1. Map showing the fossil locality. See Liutkus et al. (2010) for stratigraphic column of the Cow Branch Formation and the stratigraphic horizon of the insect layer.
The Cow Branch Formation was previously considered
Carnian in age (Olsen et al., 1991), but is now regarded as Norian (~227–208 Ma; Liutkus et al., 2010), although uncer- tainty remains (Fraser et al., 2017). At the Solite Quarry, which is located in the middle of the Dan River-Danville Basin, the upper part of the Cow Branch Formation is exposed. The exposed section of the Cow Branch Formation mainly consists of lacustrine shales, mudstones, and sandstones. The deposi- tional environment was interpreted as a deep and chemically stratified lake with an oxygenated surface layer but anoxic deep waters (Olsen et al., 1991; Fraser et al., 1996). However, recent studies by Liutkus et al. (2010) and Criscione and Grimaldi (2017) suggested that the Cow Branch Formation was deposited in a relatively shallow, saline, and alkaline lake. Exceptionally preserved fossils, including insects, plants, and vertebrates, have been found in multiple horizons of organic-rich and dolomitic black shale in the Cow Branch Formation at the Solite Quarry (Fraser et al., 1996, 2017). One fossiliferous horizon, dubbed ‘the insect layer,’ is particularly rich in insect fossils (Liutkus et al., 2010). Insects found in this layer are diverse, including members of the Blattodea, Coleoptera, Hemiptera, Diptera, Heteroptera, Thysanoptera, and Trichoptera (Fraser et al., 1996; Grimaldi et al., 2004; Blagoderov et al., 2007; Liutkus et al., 2010; Criscione and Grimaldi, 2017). The fossil described in this paper was collected from this insect layer. Plant and insect fossils in the Solite Quarry Lagerstätte are
preserved as carbonaceous compressions encrusted by silicate minerals, possibly biotite (Kearns and Orr, 2009; Muscente and Xiao, 2015). They appear silvery in color under reflected light microscopy, perhaps because of the presence of silicate
minerals. However, carbonaceous material is preserved in these fossils, and carbonaceous films constituting distinct tissues within Solite Quarry plant and insect fossils generally differ in thickness; such thickness variations may correspond to taphonomic varia- tions among anatomical features (Muscente and Xiao, 2015).
Materials and methods
The specimen was examined under reflected light microscopy and scanning electron microscopy. Interpretive drawing of wing venation pattern was based upon light and electron microscopic images, using image-editing software packages CorelDraw 12.0 and Photoshop CS6. Backscattered electron (BSE) images, secondary electron (SE) images, and EDS elemental maps of the part and counterpart were acquired at different accelerating voltages (VA) using a FEI Quanta 600F low-vacuum environ- mental scanning electron microscope (SEM) housed in the VT Institute of Critical Technology and Applied Science Nanoscale Characterization and Fabrication Laboratory (VT-ICTAS- NCFL). The SEM was equipped with a field-emission gun electron source, pole piece BSE solid state detector (SSD), BSE and SE Everhart-Thornley detector (ETD), and Bruker AXS QUANTAX 400 with a high-speed EDS silicon drift detector. The shale pieces containing the part and counterpart were trimmed to dimensions no more than 6 ×6 ×2cm so that they could fit in the sample chamber of theSEMsystem. Because this study made use of a low vacuum system, in which the sample chamber is held at a pressure (~10–2 Torr) allowing for the ionization and electrical conduction of surface charge by gases, conductive coating was not deposited on the pieces prior to
Dan river
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