The presence of microbialite structures in a freshwater, dimictic mid-latitude lake and their establishment after the last ice age about 10,000 years ago is puzzling. scale) freshwater carbonate structures referred to as microbialites due to the hypothesized biological role in their formation [2]. Evidence of biological influences on carbonate precipitation within micro-stromatolitic surface nodules associated with the microbialites has been recognized using 13C isotopic biosignatures [3]. Understanding the physiochemical and biological controls on microbialite morphogenesis in Pavilion Lake could provide significant insights into the interpretation of late Proterozoic to early Paleozoic reef structures, and as such, a multi-disciplinary project is currently underway (observe Pavilion Lake Research Project (PLRP) website (http://PavilionLake.com) to meet these scientific objectives. 2. Observations 2.1. Morphology Laval [2] explained microbialite reefs oriented perpendicularly to the shoreline from depths of 5C30 m in selected regions of Pavilion Lake; however, recent Multi-Angle Swath Bathymetry (MASB) data, comprehensive pilot and video observations from manned DeepWorker submersibles and remotely operated vehicle borne video camera observations have exhibited that microbialite protection in the lake is usually more considerable than originally hypothesized [4]. They are found throughout the lake basin and on top of mounds at depths of 45C60 m [5]. The microbialites were originally categorized into three morphological groupings by depth: those found at shallow to intermediate depth of 10C15 m (Physique 1a), cone-shaped seepage structure with hollow internal conduits that open at the top of the cones at intermediate depths of about Tedizolid 20 m (Physique 1b), and artichoke-type mounds, centimeters to meters in diameter at depths ranging from 25 to 35 m (Physique 1c). The mounds found at the shallow to upper intermediate depths (<15 m) range from several centimeters to a few decimeters in height and are noted to be covered by photosynthetic microbial communities and their calcified remains. At the intermediate depth of approximately 20 m, carbonate domes approximately decimeters to meters in diameter and up to 3m in height were documented and are likely the largest structures in the lake. At the lower intermediate to deeper depths of 25C35 m, the Tedizolid morphology of the carbonates can be described as a combination of cone-shaped and leaf-like [2]. These structures are denser than those at the shallower depths and are typically 20C30 cm in height and decimeters to meters in diameter. These structures are sometimes capped by chimney like formations that range in height from 5C30 cm (e.g., Physique Rabbit Polyclonal to Thyroid Hormone Receptor alpha 1b). Physique 1 Examples of varying microbialite morphologies in Pavilion Lake. (1a) Shallow to Upper Intermediate (10C15 m). (1b) Intermediate to Lower Intermediate (about 20 m). (1c) Deep Water (25C35 m). A single internal conduit is seen in all sampled cases, running the length of these chimneys (Physique 2). These conduits are filled with fine-grained carbonate sediment. It is unclear at this time what function or environmental correlation these structures may have with groundwater inputs into Pavilion Lake. Finally, the deepest characterized carbonates were reported at depths of 30C35 m, although we now know this lower limit to be much deeper at 45C55 m [4]. Overall, the mechanical Tedizolid strength of the structures increases with depth, which may reflect a change in the relative role of biotic and non-biotic precipitation with lowering light levels. Physique 2 Internal structure of chimneys structure from sample obtained August 2007. To establish approximate ages and rates of growth more precisely, six 230Th/234U analyses were made by Laval [2] of the calcite in the lower to upper-middle parts of two whole mounds (collected from depths of 27 and 32 m) using thermal ionization mass spectrometry (TIMS), plus one bulk analysis by alpha spectrometry of the center of a third mound (collected from 32 m depth). Natural ages that ranged from 12,300 1,400 to 3,650 860 years were.