Sandstone (Upper Triassic; Jordan Lake, North Carolina, USA) 6 : 無料・フリー素材/写真
Sandstone (Upper Triassic; Jordan Lake, North Carolina, USA) 6 / 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 | Channel sandstone in the Triassic of North Carolina, USA.The Newark Supergroup is a thick, geographically-widespread stratigraphic unit in eastern America. It is Late Triassic to Early Jurassic in age and represents sediments and some lava flows that filled up old rift valleys roughly paralleling the modern-day Eastern Seaboard of America. The rift basins formed in the Triassic when the ancient Pangaea supercontinent attempted to break apart, but failed. A successful breakup of Pangaea occurred during the Jurassic. Most of the basin-filling rocks are terrestrial redbeds - hematite-rich siliciclastic sedimentary rocks, such as conglomerate, sandstone, siltstone, and shale, deposited in nonmarine environments.Seen here is a sandstone outcrop along the shores of Jordan Lake, a manmade reservoir in North Carolina. In Triassic rift basin terminology, this is part of the Durham Sub-Basin of the Deep River Basin. The sedimentary rocks of this area were originally dismissed as "undifferentiated Triassic". Droughts and low water levels have exposed novel outcrops along Jordan Lake's shoreline. No formation names are available, but the rocks are part of the Chatham Group. The stratigraphic terminology used in the nearby Sanford Sub-Basin is too simple, so "lithofacies association" terminology is used instead in the Durham Sub-Basin.The rocks here are part of "lithofacies association 2", which consists of coarser-grained arkosic, micaceous sandstones with reddish-colored finer-grained sediments on top (the latter are not visible here). Some sandstones here have what appear to be fossil bone fragments, but they are really corroded basement clasts."Arkosic" refers to the common presence of potassium feldspar sediment grains. These rocks are also fairly rich in biotite mica. The sand is "immature", which generally refers to sedimentary deposits that have a high clay content, are poorly sorted, have many non-quartz minerals, and angular to subangular grain shapes.Stratigraphy: Chatham Group, Newark Supergroup, Carnian to Norian Stages, Upper TriassicLocality: shoreline outcrop along the eastern side of Jordan Lake, a little north of the Jordan Lake visitor center & south of Route 65 & west-southwest of Wilsonville, eastern Chatham County, central North Carolina, USA (35° 44’ 04.20” North latitude, 79° 01’ 07.03” West longitude)--------------------------------See info. at:en.wikipedia.org/wiki/Newark_Supergroup |
| 撮影日 | 2012-11-09 12:29:27 |
| 撮影者 | James St. John |
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