The Jurassic (Oxfordian) Smackover Formation in Little Cedar Creek Field, Alabama is composed of microbial thrombolitic buildups. Core description, petrography, SEM, and isotopic analysis were used to identify the succession of organisms, microbial carbonate deposition, and diagenesis that contributed to formation of these thrombolitic buildups. The microbial thrombolite reef facies in this study accounts for 38.5% of the total Smackover Formation. This facies was deposited 0.5 to 6.75 miles from the paleo-coastline. Today it is located 10,225 to 11,750 feet in the subsurface and contains buildups 26 to 50 feet thick. Four microfacies were defined: A- Black Renalcis-like layers, B- Digitate, C- Chaotic and D- Brown laminated centimeter-scale cycles. In most of the buildup, distinct layers of microbially precipitated micrite forms in succession. Microfacies A (Black Renalcis-like Layer) is the relatively least porous and permeable, acting as a potential barrier to flow in contrast to the other more porous microfacies.

The colloquially named leopard rock of the Holder and Laborcita formations (Late Pennsylvanian-Early Permian) is an algal/foraminiferal boundstone that occurs within a cyclic, interfingered, carbonate siliciclastic system in the Sacramento Mountains of southeastern New Mexico) and often accompanies phylloid algal mounds. This project is the first to fully characterize and evaluate the evidence that leopard rock is microbial in origin and assess the potential influence of methane seeps and deltaic organics on its genesis. Characterization of the algal-foraminiferal boundstone revealed a highly variable expression in outcrop based on geolocated photo imagery, hand samples, optical microscopy, and scanning electron microscopy (SEM) data. Leopard rock is interpreted as microbial in origin based upon all features observed in aggregate, particularly upward-oriented concentric gradational laminae and striking clusters of segmented curvilinear cylinders (~1000 nm long). Leopard rock is best described as thrombolytic. A comprehensive categorization into thrombolite types was conducted and field and analytical data were used in creating a geospatial data base. The data was evaluated spatially in ArcMap for co-occurrence, trends, and possible associations within, and between, categorizations and formations. Distribution and associations of dome (1-3 m), small coniform (< 1 m), and planar outcrop structures and thrombolite types reflect a hierarchy of complexity and prevalence that would be expected from a microbial system. An extensive multi-scale feature comparison of potential modern analogues from Australia, the Bahamas, and Canada, in conjunction with contiguous paleo-analogues, support the interpretation of a highly adaptable complex microbial ecosystem. Results were also consistent within the global chemical, biologic, and physical context at the time of deposition. Evidence for methane seep contribution support the plausibility of supplemental microbial energy sources based on modern examples and limited paleo-analogues. Stratigraphic position and a paucity of data do not support a significant role for deltaic bathymetry or organic influx in leopard rock genesis. The results of this study provide robust evidence that leopard rock is a multi-faceted complex microbial thrombolite that displays a continuum of expression not represented by one all-encompassing term and illustrates the value of multi-parameter analyses augmented across time and space using analogues and geospatial software.

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