121121

Shrimp fecal pellet in pellet grainstone stained with Alizarin red S. Light curved lines within pellet are channels formed by hairs inside the shrimp's gut, now filled with calcite cement. Patterns of channels in cross section are readily identified, and can be used to ID the species responsible. Smackover Formation, shallow-marine shoal or back-barrier lagoon, 1 mm wide.

120621b

Peloid ooid grainstone with a large ooid nucleated on an intraclast containing very fine particles of quartz sand. Two generations of calcite cement mostly fill interparticle pores. Blue epoxy fills relict and dissolution pores. Field of view 1 mm, calcite is stained red. Smackover Formation, South Alabama. Images of thin rock slice viewed with a microscope.

Another view with more dissolution porosity and calcite replacing dolomite rhombs (white crystals partly replaced by red). 2.5 mm wide.

Large intraclast containing multiple ooids, which is on top of numerous small ovoid pellets (partially dolomitized; partially dedolomitized). 2.5 mm.

View with two intraclasts centered on relict pore. 2.5 mm.

052921

 

 More pictures of the Mississippian microbial reef in North Alabama.   

 

 Broken and slightly displaced spheroidal microfossil in microbial thrombolite; likely cause is compaction. Image 1 millimeter in long dimension.

040821c

 The many faces of a microbial reef. At least three distinct fabrics are visible. Scale is half a millimeter, Mississippian, Alabama.

040821b

Composite photograph of a microconchid, seen under a microscope. They look like tiny snails, but are distant relatives. This one preserves multiple wall layers, but only part of the coiled tube is preserved. The originally hollow tube is filled with coarse calcite crystals.Mississippian, Alabama, scale is 0.2 millimeters.

040721

Microscopic view of micropelletal calcite cement in a microbial reef, dense (dP) and loosely packed pellets (lP). Coarser calcite cement (C) filled in the rest of the space. This is a view of a small opening in the reef. The scale is 0.2 millimeters. North Alabama, Mississippian..

022221b

Mississippian ooid grainstone; some nuclei reveal that a reef's nearby. The two fragmentary distorted grids inside two of the ooids are encrusting microbes most common in reefs. Image 2.5 mm wide.

020521b

 

Last night I posted a high-magnification photo of part of this microconchid and the material that encrusted it (upper left). This one shows a cross-section of the entire critter, in all of its spiny glory. (The "spines" are actually ridges.) This is an encrusting organism, and you can see the dark layer at the bottom on which it grew (small white arrow).

020421c

 

 

Complex microbial crust on microconch (bottom), Mississippian, North Alabama.

020421b

 

Unidentified fossil fragment in microbial mound. The fossil is calcific and extremely porous. The matrix is sandy silty fossiliferous wackestone and microbial boundstone. Mississippian of North Alabama, scale= 200 µm, thin-section photomicrograph.

012721b

Part of a microbial carbonate mound, sand-size particles, pastel colored cement, large blobs of microbial carbonate, "T" = thrombolite (non-layered microbial carbonate), "S" = stromatolite (laminated microbial carbonate, which grew upward), "Q" = quartz sand grain, short arrow =ooid, long arrow = way up, Mississippian, North Alabama, thin-section photomicrograph, cross-polarized light, scale 0.5 mm.

012121d

Echinoderm fragment (large dark area with mottled interior like a fingerprint) with cement overgrowths (irregular extensions from the central area). Echinoderm ossicles are single crystals of calcite and they tend to be overgrown with cement in optical continuity with the original crystal. This object is photographed with crossed polarized light, and the specimen is oriented so the light canceled out the colors that would otherwise be observed. Thin-section photomicrograph, Mississippian, North Alabama, field of view 1 mm wide.

112520

 

 

Tiny spiny sphere (center), a microfossil of some kind [algal spore?] and not the first of these I've seen from this location, in microbial mound [like a reef, but lacking a rigid skeletal framework], Mississippian, North Alabama, field of view 1 mm wide, thin-section photomicrograph.

112020b

 

 

 Cross-section through microconchid embedded in microbial mound, genus and species not yet determined. Thin-section photomicrograph, field of view 1 mm wide, Mississippian of North Alabama.

101220

 

Thin-section photomicrograph of a coral-microbial boundstone unit. Crinoid ossicle (C) with internal boring (black arrow) and concentrically laminated oolitic coating (white arrow). This in turn was encrusted by a chambered organism, probably a foram (a shelled amoeba; black arrow at bottom of image).. The entire particle is encased within microbial thrombolite (dark area); former voids are filled with calcite cement (white). Mississippian of North Alabama, image 1 mm wide.

 

100520

 

 

 Thin-section photomicrograph of microbially bound skeletal grainstone filling a large void within a microbial thrombolite (not visible in this image). Particles include an ostracode (black arrow), a crinoid ossicle (Cr), and a bryozoan fragment (Br). M indicates microbial microcrystalline calcite coating binding particles together. C indicates calcite cement filling in all voids space that remained after deposition and after cessation of microbial activity. Mississippian of North Alabama, image 1 mm wide.

100420

 

Thin-section photomicrograph of microbial thrombolite (T) containing fenestrae filled with calcite cement (C). Notice microcrystalline pelletal cement (black arrow) partially lining the fenestra. The pelletal cement is encased in a coating of slightly larger cement crystals. Image 1 mm wide, Mississippian of North Alabama. Cross-polarized light.

 

100320d

 

 Thin-section photomicrograph of a fossil reef in North Alabama. The reef is composed of thrombolite ("T"), which is made by microbes. This view shows a small void that formed as the reef grew. It is now filled with particles, such as ooids ("O") and quartz sand grains ("Q"). All the spaces between the particles are filled with calcite cement ("C"). Image is 1 mm wide. Taken with crossed polarizers.

 

092920b

 

 

Fossils in microbial boundstone. Wide arrow points to a cross-section of an encrusting tube, which has popped loose from whatever it once adhered to. Narrow arrow on the left points to an inner coating on the crinoid fragment to the right of the two. Narrow arrow to the right points to an outer coating. This is difficult to see, but it is partly encrusted itself by a very thin white layer especially at the right side. Image 1 mm wide.
 

 

091120

 

Coral (lower right) encrusted by bryozoan (middle) in turn overgrown by microbial mud (dark layer) under an open void (now filled with calcite crystals (white, upper left). Mississippian, North Alabama, imaged area 2.5 mm wide.