The <Emphasis Type="Italic">Laluzia armini</Emphasis> (gen. et spec. nov.) ecosystem: understanding a deeper-water rudist lithosome from the Early Maastrichtian of Mexico |
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Authors: | Stefan Götz Simon Mitchell |
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Institution: | (1) Institute of Geosciences, University of Heidelberg, Im Neuenheimer Feld 234, 69120 Heidelberg, Germany;(2) Department of Geography and Geology, The University of the West Indies, Mona, Kingston 7, Jamaica |
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Abstract: | In the Lower Maastrichtian Cardenas Formation exposed at La Luz (State of San Luis Potosí, east-central Mexico), a shallowing-upwards
mixed-clastic-carbonate sequence is exposed. The sequence passes from marls with thin siltstones, through lower and upper
hippuritid-rudist-dominated intervals, and into a Durania-dominated interval. This succession shows an increase in grain size upwards and a progressive reworking of rudists upwards
(preserved in life position, other than in distinct tempestites, in the lower part; invariably reworked/toppled in the upper
part). Epibionts show a change from a serpulid–bryozoan assemblage in the lower sequence to a red algal–rhodolith assemblage
in the upper part. Using these data, we argue that the sequence shows a change from a low-energy, relatively deep-water, nutrient-rich
environment with low-light intensity in the lower part, to a high-energy, well-lit environment in the upper part. Two rudist
species are present: a new multifold hippuritid rudist with cellular outer shell layer, Laluzia armini, that lacks pallial canals in its free valve and has a unique myocardinal pillar arrangement, in the lower part; and Durania in the upper part. Laluzia was adapted to low-energy, low-light, soft-bottom environments that were abundant within the lower part of the sequence exposed
in the La Luz section—a very unusual environment for rudists. |
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