Complex Feed Back Loops Controlling Heterozoan Reef Development on Salt Diapirs, La Popa Basin, Mexico

Katherine Giles
New Mexico State University, Las Cruces, New Mexico ([email protected])

In the distal part of the Hidalgoan foreland basin in NE Mexico three, isolated carbonate platforms nucleated on seafloor topography created by vertically rising passive diapirs. The platforms developed in both the Late Cretaceous (Maastrichtian) and early Paleocene and are composed of heterozoan fauna dominated by coralline red algae, benthic foraminifera, sponges, and bivalves.
Carbonate facies type and architecture of each platform was distinctly influenced by the complex interplay of both short-term local conditions surrounding individual diapirs and by long-term regional conditions that affected the entire shelf. Local conditions included windward-leeward platform geomorphology, possible cold seeps at the salt-sediment interface, and halokinesis. Regional conditions included eustatic sea-level fluctuations, foreland basin tectonism, and siliciclastic sediment supply to the outer shelf via hyperpycnal flows. No single factor dominates the system, but each plays a recognizable role in the final outcome of facies type, geometry, and initiation and demise of the platform.
Platform facies are distributed asymmetrically across individual diapirs, reflecting windward versus leeward margin paleogeographic setting and differential minibasin subsidence related to salt withdrawal. Carbonate facies form the base of angular unconformity bounded carbonate/siliciclastic cycles called halokinetic sequences. The cycles reflect local variations in net diapiric-rise rates versus local sediment accumulation rates and vary in number and character between the different diapirs and between the windward and leeward margins of each diapir.
The presence of heterozoan faunal assemblages forming the platforms may be in response to high nutrient levels from local methane seeps forming at the salt-sediment interface and from continental runoff. The platforms form in the upper parts of parasequence sets developed within the transgressive systems tract (TST) of 3rd-order distal-deltaic siliciclastic depositional sequences. Hidalgoan shortening of La Popa basin formed large wavelength salt-cored detachment folds. Diapirs that lie in the hinges of folds were shortened or “squeezed” significantly more than diapirs that lie on the limbs of folds. Squeezed diapirs generated much higher and broader topographic relief and are dominated by extensive, thick, shallow water (<15m deep) sponge, red algal reef and grainstone bank facies, whereas limb diapirs contain thin, deeper water (>30m deep) silty, red algal packstone facies reflecting lower carbonate production rates in a deeper water setting.

AAPG Search and Discovery Article #90073 © 2007 AAPG Foundation Distinguished Lecturer Series 2007-2008