Differential
GPS-Mapping Reveals Lagoonal Paleorelief
of the “Layer-Cake” Latemàr Buildup, Dolomites,
Peterhänsel, Arndt1,
Gordon Schlolaut1, Ines Voigt1,
Uwe P. Baaske1, Sven O. Egenhoff2,
Maria Mutti1 (1) Universität Potsdam, Golm, Germany (2) Colorado State University, Fort Collins,
CO
Many isolated carbonate platforms display
systematic spatial facies patterns often with subconcentric belts following the contours of the buildup
margin. In modern platforms, this non-randomness in lateral facies
distribution is unequivocally related to a topographic gradient resulting from
differential growth. However, invoking a paleorelief
for ancient carbonate platforms often relies only on mapping-out facies followed by their bathymetrical interpretation.
We have used differential GPS
measurements to corroborate a conventional lateral facies
reconstruction of the cyclic lagoonal interior of the
Middle Triassic Latemàr. Individual horizons from
different stratigraphic levels were mapped down to
decimeter accuracy over extensive parts of the platform interior.
Three-dimensional visualization of these layers with PETREL software reveals
decreasing paleodepths towards a tepee belt in the backreef zone. The persistence of this paleotopographic
high throughout cyclic platform evolution argues for a higher amount of
carbonate fixation and growth in the tepee belt area likely related to sediment
trapping in tepees and inter-tepee depressions and favored by cementation and
microbial growth. It implies that despite lagoon-wide shallowing-upward
either (1) accommodation space had not been entirely filled in the lower parts
of the lagoon, or (2) relative sea level dropped and exposed the lagoon thereby
preserving the paleorelief, or (3) after filling
accommodation space, cementation processes allowed the tepee belt to build up
further into the subaerial zone. This study not only
directly measures paleotopography within a fossil
carbonate buildup but also postulates that cement-controlled tepee margins may
have the ability to grow upward beyond normal marine accommodation.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California