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Paleoecology of the Alamogordo Member of the Lower Mississippian (Kinderhookian-Osagean) Lake Valley Formation, New Mexico
xiii, 189 leaves : illustrations, maps ; 28 cm.
Exposure of the Alamogordo Member of the Lake Valley Formation provides an opportunity to study ramp-mudmound paleoecology in terms of temporal and spatial changes of environmental parameters. The Member consists of 14 beds and bed sets traceable for the entire transect on the Sacramento Mountains western escarpment. The unit thins southward from 10.5m to 1.5m. The ramp is estimated to have dipped southward at 0.50 based on fossil algae distribution. The retrogradational and subsequent progradation of depth- sensitive biotic assemblages indicates accommodation increased during early deposition, and decreased during later deposition. Mounds occur in the northern 2/3 of the ramp transect in the deeper part of the photic zone. Mounds range from broad composites of laterally back-stepping subunits in shallower areas to taller, vertically stacked composites down-ramp. Mound growth and form is described in terms of several primary controlling parameters -- submarine topography, water circulation, light penetration, and accommodation fluctuations. Episodic mound growth is documented by diastems bounding mound stratal units. Mounds in shallower ramp areas grew on the margins of a broad, intra-ramp, topographic high, defined previously from facies and isopach trends in enclosing strata. Margins and irregular topography of the high are reflected by mound distribution, growth geometries, facies patterns, and facies and thickness trends of enclosing strata. Siting of mounds was controlled by local topography on and along the margins of the intra-ramp high. Mound growth began along the margin and retrograded onto the intra-ramp high, then prograded basinward. The lesser height and pronounced backstepping of shallower ramp mounds, in contrast to mounds that grew more ertically down ramp suggest that growth and overall morphology were controlled by accommodation. A new species of microproblematica occurs in a cryptic environment within the skeleton of the squamulate tabulate coral Sutherlandia from level bottom sediments. Except for this occurrence, the new microfossil is rare on the ramp, however they are common to abundant on mounds. The coral sample indicates that they may be common on mounds within cryptic habitats. It is probably allied ecologically and taxonomically with salebrids.
Issued also on microfiche from University Microfilms Inc.
Includes bibliographical references: pages 133-149.