Lateral discrepancies of cycle patterns in the Latemàr, Triassic, Italian Dolomites

The well-known cyclic carbonate succession of the Middle Triassic Latemàr Massif in the Italian Dolomites reveals significant lateral variability in cycle numbers in platform-interior strata. Within an interval of 60 m, a 25% increase in the number of marine flooding surfaces was detected when approaching the several-hundred-meters-wide tepee belt in the backreef area, which represents the maximum elevation of the isolated Latemàr buildup. The impact of high-frequency– low-amplitude sea-level fluctuations on this elevated zone resulted in the development of spatially restricted intermittent emergence and marine flooding surfaces bounding small-scale upward-shallowing cycles. It is postulated that these alternations of submergence and subaerial exposure have favored tepee formation. Sediment collecting in the saucer-shaped tepee megapolygons further expedited upward shallowing of small-scale cycles. Conversely, deeper parts of the lagoon remained largely unaffected by high-frequency, lowamplitude sea-level oscillations: marine flooding surfaces disappear and cycles amalgamate. It is concluded that tepee structures are generally confined to topographically elevated areas where low-amplitude sea-level fluctuations were recorded. Lateral variations in cycle stacking pattern should be commonplace in shallow carbonate buildups throughout the geological record, where paleorelief existed in the platform interior

Sea level changes versus hydrothermal diagenesis: Origin of Triassic carbonate platform cycles in the Dolomites, Italy: Discussion

In his recent paper, Blendinger (2004) presents a new and unconventional hypothesis for the formation of the Triassic Latemàr carbonate cycles. He assigned the cycles to intermittent hydrothermal influence alternating with normal marine deposition. Fluids with a composition similar to normal seawater were forced by elevated heat flow from an underlying hydrothermal field to circulate to the seafloor. These fluids are said to produce stratiform diagenetic features including tepees, and they favoured early dolomitization and the growth of cyanobacterial mats. This interpretation deviates strongly from the conventional models where these cycles are considered to be the result of relative sea-level fluctuations in a shallow-marine to subaerially exposed environment (Hardie et al., 1986, Goldhammer et al., 1987, Goldhammer et al., 1990 R.K. Goldhammer, P.A. Dunn and L.A. Hardie, Depositional cycles, composite sea-level changes, cycle stacking patterns, and the hierarchy of stratigraphic forcing: examples from Alpine Triassic platform carbonates, Geol. Soc. Amer. Bull. 102 (1990), pp. 535–562.Goldhammer et al., 1990, Goldhammer et al., 1993, Brack et al., 1996, Mundil et al., 1996, Egenhoff et al., 1999, Preto et al., 2001, Mundil et al., 2003 and Zühlke et al., 2003). We welcome this entirely new approach, as it further stimulates a discussion on the validity of criteria used to detect subaerial exposure from carbonate facies. Furthermore, it highlights the importance of microbial growth and cementation processes for the development and the geometrical maintenance of post-extinction carbonate platforms such as the Latemàr

Lateral discrepancies of cycle patterns in the Latemàr, Triassic, Italian Dolomites

The well-known cyclic carbonate succession of the Middle Triassic Latemàr Massif in the Italian Dolomites reveals\ud significant lateral variability in cycle numbers in platform-interior strata. Within an interval of 60 m, a 25% increase in the number\ud of marine flooding surfaces was detected when approaching the several-hundred-meters-wide tepee belt in the backreef area,\ud which represents the maximum elevation of the isolated Latemàr buildup. The impact of high-frequency– low-amplitude sea-level\ud fluctuations on this elevated zone resulted in the development of spatially restricted intermittent emergence and marine flooding\ud surfaces bounding small-scale upward-shallowing cycles. It is postulated that these alternations of submergence and subaerial\ud exposure have favored tepee formation. Sediment collecting in the saucer-shaped tepee megapolygons further expedited upward\ud shallowing of small-scale cycles. Conversely, deeper parts of the lagoon remained largely unaffected by high-frequency, lowamplitude\ud sea-level oscillations: marine flooding surfaces disappear and cycles amalgamate. It is concluded that tepee structures\ud are generally confined to topographically elevated areas where low-amplitude sea-level fluctuations were recorded. Lateral\ud variations in cycle stacking pattern should be commonplace in shallow carbonate buildups throughout the geological record,\ud where paleorelief existed in the platform interior