Primary Structures II GO 568 Structural Geology James S. Aber

Primary Structures in Carbonate Rocks

	Canal section in the Key Largo Limestone of Pleistocene age. A large branching coral (Acropora palmata) is shown in growth position. Section is about 3 m (10 feet) high. Key Largo Canal, Florida Keys. Photo date 12/75, © J.S. Aber.
	Cross-bedded oolitic limestone of Pleistocene age. This sediment accumulated on a shallow shoal about 125,000 years ago. Miami Oolite, Miami, Florida. Photo date 12/75, © J.S. Aber.
	Jackie Puterbaugh demonstrates a "reef" in the Frisbie Limestone Member of the Wyandotte Formation, Holliday, Kansas. Photo date 11/85, © J.S. Aber.
	Upper Cretaceous chalk (Maastrichtian) and lower Tertiary limestone (Danian) boundary in the coastal section at Stevns Klint, Denmark. Large "bank" forms are visible in the upper limestone. Photo date 5/79, © J.S. Aber.
	Overhang of bryozoan limestone (Danian) above chalk (Maastrichtian). Photo date 5/79, © J.S. Aber.
	Subtle channel with cross-bedded chalk (behind scale pole) in Arnager Kalk (upper Cretaceous) on the island of Bornholm, Denmark. Photo date 6/79, © J.S. Aber.
	Carbonate turbidites in the Dimple Formation, Marathon Basin, west Texas. Sedimentary structures are similar to clastic turbidites. Photo date 11/75, © J.S. Aber.

Fossils in Sedimentary Strata

	Fossil oreodont in Oligocene (Tertiary) alluvial strata, Toadstool Park, northwestern Nebraska. Photo date 7/80, © J.S. Aber.
	Burrow fillings, Pennsylvanian sandstone, north Texas. Photo date 3/76, © J.S. Aber.
	Burrowed top of lower Cambrian Balka Sandstone, island of Bornholm, Denmark. Photo date 6/79, © J.S. Aber.
	Burrows in lower Cambrian "Grønne Skifre" shale, island of Bornholm, Denmark. Black spots are phosphorite nodules (Bruun-Petersen 1977). Photo date 6/79, © J.S. Aber.

Primary Structures in Igneous Rocks

	Wannenköpfe scoria cone. A complete section through the cone is visible in the scoria mine. Eifel region, western Germany. Photo date 8/95, © J.S. Aber.
	Dike on side of Wannenköpfe scoria cone. Dikes formed when superheated ground water erupted through tephra deposits. Eifel region, western Germany. Photo date 8/95, © J.S. Aber.
	Growth faults in Eppelsberg scoria cone. Growth faults are caused by internal collapse during continued surficial deposition of tephra. Note people at bottom for scale. Eifel region, western Germany. Photo date 8/95, © J.S. Aber.
	Tree molds in tephra near top of Eppelsberg scoria cone, Eifel region, western Germany. Photo date 8/95, © J.S. Aber.
	Tephra rim of Leyendecker volcano. Note the evenly bedded, gently inclined layers of tephra. Eifel region, western Germany. Photo date 7/95, © J.S. Aber.
	Peridotite (olivine) xenoliths, Leyendecker volcano, Eifel region, western Germany. Photo date 7/95, © J.S. Aber.
	Niedermendiger lava flow with columnar jointing, Eifel region, western Germany. Photo date 7/95, © J.S. Aber.
	Collapsed lava flow with cave. Late Holocene eruption, 1500-2000 years old. Valley of Fires, New Mexico. Photo date 3/98, © J.S. Aber.
	Casa Grande, a thick lava cap on a stratified pile of Tertiary volcanic deposits. Notice vertical dikes on near side of hill. Big Bend National Park, west Texas. Photo date 1/78, © J.S. Aber.
	Eroded core of Tertiary volcano, known as the Elephant Tusk, Big Bend National Park, west Texas. Photo date 3/80, © J.S. Aber.
	Goemmer Butte, an eroded Tertiary volcano core, Raton Basin, near La Veta, Colorado. Photo date 6/99, © J.S. Aber.
	Spectacular columnar jointing is visible in Devils Tower, Wyoming. People at bottom are standing amid large joint blocks. Photo date 8/85, © J.S. Aber.
	West Spanish Peak with dikes, seen from Goemmer Butte, Raton Basin, near La Veta, Colorado. Dikes radiate from the peak like spokes of a wheel. Photo date 6/99, © J.S. Aber.
	Side view of the Devils Stairsteps, a Miocene dike related to West Spanish Peak, Raton Basin, near La Veta, Colorado. Photo date 6/99, © J.S. Aber.
	View along the length of the Devils Stairsteps dike, Raton Basin, near La Veta, Colorado. Photo date 6/99, © J.S. Aber.
	Crazy Horse mountain, Black Hills, South Dakota. Precambrian crystalline (gneiss) basement rocks host the gigantic sculpture in progress. Notice people standing on top. Photo date 6/97, © J.S. Aber.
	Closeup view of Crazy Horse mountain, Black Hills, South Dakota. Notice inclusions of dark (mafic) rock above the eye and nose. Photo date 6/97, © J.S. Aber.
	Felsic pegmatite (pink & white) in mafic Archean gneiss. Granite Falls, south-central Minnesota. Photo date 6/96, © J.S. Aber.

Reference

• Bruun-Petersen, J. 1977. Nedre Kambrium. In, Hansen, M. and Poulsen, V. (eds.), Geologi på Bornholm, p. 33-39. Varv Ekskursionsfører Nr. 1.

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