Photgraphs of Biogenic and Chemical Structures

Wavy to crinkled laminite composed of couplets of peloidal lime grainstone(dark) and dolomite mudstone(light). The lamination is interpreted as due, in part, to the sediment trapping and binding of cyanobacterial surface mats. However, note the three depression-fills composed of fine sand-sized peloidal grainstone at left center(arrows). These are interpreted as trapped bedload and not the result of cyanobacterial trapping. Specimen from the Upper Cambrian Conococheague Limestone, western Maryland.

Continuous, isopachous mudstone laminae with radial crystal sparys separated by detrital peloidal laminae. The isopachous mudstone laminae may be very finely crystalline chemical precipitates. Stromatolite from the Cambrian Waterfowl Formation, Canmore, Alberta. Field of view approximately 2mm.

Stromatolites nucleated on flat intraclasts of planar and cross-stratified peloidal grainstone. Upper Cambrian Conococheague Limestone, western Maryland. Field of view approximately 10cm.

Dolomitic stromatolitic bioherm from the Lower Proterozoic Taltheilei Formation, Pethei Group, Northwest Territories. Coin in left center is approximately 30mm in diameter.

Bedding plane exposure of dolomitic columnar stromatolite from the Lower Proterozoic Taltheilei Formation, Pethei Group, Northwest Territories. Field of view approxiately 17inches.

Bedding plane view of burrows disrupting Upper Cambrian dolomitic mudstone from the Gatesburg Formation of central Pennsylvania. Field of view approximately 12cm.

This photograph shows an epoxy impregnated core of intertidal pond deposits from the modern carbonate tidal flats of northwest Andros Island. This completely bioturbated texture was achieved by random burrowing of rather small annelids and gastropods.

Inversely-graded pisoid bed from the tepee zone of the Permian Capitan "Reef Complex", west Texas. Lens cap about 50mm in diameter.

Nodular masses of microcrystalline gypsum(white patches) that range in shape from ovoid to rectilinear with outlines typical of vertically-oriented, bottom-grown gypsum single crystals(note the "shallow-tail" shape of some of the rectilinear forms). Clearly the microcrystalline gypsum is is pseudomorphous after large gypsum single crystals or crystal clusters. It is possible that an early diagenetic stage of dehydration of bottom-grown gypsum crystals to microcrystalline anhydrite was followed by a final rehydration of the anhydrite to microcrystalline gypsum. Dark interlayers are composed of detrital gypsum grains of granule to sand size. Miocene Solfifera Series, Sicily.