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Geological Society, London, Special Publications; 1996; v. 107; p. 111-126;
DOI: 10.1144/GSL.SP.1996.107.01.09
© 1996 Geological Society of London

Carbonate Buildups and Waulsortian Mud-Mounds

Biotic gradients on a homoclinal ramp: the Alamogordo Member of the Lake Valley Formation, Lower Mississippian, New Mexico, USA

David L. Jeffery & Robert J. Stanton, Jr.

Dept. of Geology & Geophysics, Texas A&M University, College Station, Texas TX 77843-3115, USA

The Lower Mississippian Alamogordo Member of the Lake Valley Formation in south-central New Mexico represents a well exposed carbonate-dominated homoclinal ramp with little evidence of sediment transport. Biotic components present and evident in thin section have distinct distributions in the level-bottom facies in relation to their shoreward and basinward ramp positions. Assemblages (I–IV) are established along the depth gradient from shallow to deep water, and are useful in palaeobathymetric interpretation; they are similar in composition to the depth-related phases recognized in Dinantian mounds by Lees & Miller (1985). The biotic assemblages shift laterally in successive beds of the Alamogordo Member, indicating variations in sea level during deposition. As a result, deepening and successive shallowing during a transgressive-regressive cycle can be tracked within the Alamogordo Member. The ramp slope is interpreted to have been of the order of 0.5°, based on the maximum depths for green and red algae having been 110m and 250m respectively. The systematic positions of several problematical taxa (Asphaltinella, Sphaerinvia, stacheiins and salebrids) are discussed.