Microboring variability in bioclasts from a carbonate platform and a mixed carbonate ramp: Paleoenvironmental implications (Upper Triassic, Slovenia)
Abstract
Decompositors of both organic matter and biogenic carbonates represent important, yet overlooked organisms that significantly contribute to biogeochemical cycles within carbonate ramps and platforms. Moreover, the distribution of the microboring communities in carbonate depositional settings exhibits characteristic zonal patterns controlled by various paleoenvironmental factors, such as water dynamics, sedimentation rate and consequently the time available for colonization.
The aim of this study was to test this assumption in for the shallow-water, Upper Triassic (Carnian-Rhaetian) carbonates of the Southern Alps in Slovenia representing two different depositional carbonate environments. Both were deposited close to the northwestern margins of Neotethys in: 1) peritidal to shallow subtidal setting of mixed carbonate ramp and 2) intertidal part of a carbonate platform, or an open lagoon in a close proximity to a reef complex, both periodically affected by storms.
Microboring communities were studied from thin section combining microscopical observations with image analysis and statistical approach using shape descriptors. This represents a novel approach to the ichnofacies studies as a supplementary technique to the well-established sedimentological and microfacies analyses.
Microborings found in proximal areas of the restricted shelf are relatively small and highly circular. Even smaller microborings are typical for the more distal facies.
Additionally, they occur here far less frequently than in the proximal facies. Larger and more common microborings are found in the intertidal zone, which probably resulted from the prolonged exposure on the sea-floor close to the carbonate platform.