Sequence Stratigraphy of Carbonate Buildups Developed in an Active Tectonic/Volcanic Setting: Triassic (Late Ladinian and Carnian) of the Dolomites, Northern Italy

YOSE, LYNDON A., Johns Hopkins University, Baltimore, MD, and PETER LITTMANN, University of Tubingen, Tubingen, Germany

Late Ladinian and Carnian deposits of the Dolomites record the evolution of carbonate buildups developed during the waning phases of a major period of volcanism and strike-slip tectonics. Each separate buildup provides an independent record of eustasy, tectonism, and competing carbonate and volcaniclastic sedimentation. Palynomorphs, calibrated with ammonites, are used to correlate between buildups and provide a means for distinguishing local variations in buildup histories from regional, synchronous trends in sedimentation which may record third-order eustasy.

Although individual buildup histories vary dramatically, two depositional sequences may be recorded at a regional scale: one of late Ladinian age (early to late Longobardian) and another of late

Ladinian to middle Carnian age (late Longobardian to Cordevolian). Buildups of the first sequence developed in a complex paleogeographic-bathymetric setting of newly formed structural highs, preexisting (early to middle Ladinian) carbonate platform highs modified by middle Ladinian tectonics and volcanism, and subbasins filled to different levels with volcanogenic deposits. Consequently, the depositional framework of buildups varies tremendously from one area to the next and includes (1) buildups nucleated on tops of paleohighs and flanked by steep (20-30 degrees) talus slope systems; (2) buildups nucleated on the flanks of paleohighs with talus slopes that contain a mixture of newly produced carbonate debris and carbonate and volcaniclastic debris eroded from the emergent paleohighs; and (3) buildups flanked by low-angle (<10 degree) muddy slope systems that developed on gently inclined foundations in relatively shallow water.

A relative sea-level fall in the late Ladinian resulted in an increased supply of volcaniclastics that onlap the flanks of many buildups and/or downslope shifts in carbonate production. Buildups of the second sequence developed in response to a relative sea-level rise and are similar in diversity to those of the first sequence. Extensive buildup progradation and accretion during this phase, concomitant with mixed-carbonate/volcaniclastic basin filling and diminished tectonic activity, result in a regional suturing of the complex paleogeography developed during the middle Ladinian.

Local paleogeography, determined by the distribution of earlier platforms in addition to tectonic and volcanogenic processes, is interpreted as the primary control over buildup geometries and the variability of buildups within sequences. However, the regional extent and synchroneity of the sequences described above may record third-order eustasy.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)