Fossils

Polydiexodina
large benthic fusulinid

Guadalupe Mountains National Park contains the world's finest example of a fossilized reef, and it is revered among geologist around the world for its fossil record of the Permian period.  To guide you to the Park's rich fossil record, I included some pictures of fossils on this page (see below).  You can see more in the GUIDE TO THE PERMIAN REEF GEOLOGY TRAIL by Don G. Bebout and Charles Kerans, editors.  This guide was made available by the National Park Service through the Texas Bureau of Economic Geology.  Here's an exerpt from the Introduction followed by a translation.

"The Permian Reef Geology Trail in the mouth of McKittrick Canyon, Guadalupe Mountains National Park (fig. 1), traverses 610 vertical meters (2,000 ft, or 1,520 to 2,130 m [5,000 to 7,000 ft] topographic elevation) of Permian (upper Guadalupian) facies through one of the world's finest exposed examples of a rimmed carbonate platform margin. The present-day topography approximates that formed by the Capitan reef along the edge of the Delaware Basin. Encouraged by geologists from geological societies, universities, the petroleum industry, and the U.S. Geological Survey, the U.S. National Park Service constructed the Permian Reef Geology Trail (fig. 2) in the early 1980's to provide better access to the depositional facies and diagenetic features of this shelf margin..."

Google Translation (Geology to English):  This Park has some really great fossils.  To make them more accessible, a team of experts got together and did a bang-up job of contructing the Permian Reef Geology Trail and of putting all the examples and details together in one document.

If you don't want to read the Guide, here are some pictures of the some of the most striking fossils in the book.  These are not in order, but they retain the Guide's figure and trail stop numbers  (I don't think the Park Service will mind.). 

Click on the pictures to enlarge them, then click again to enlarge them.

Figure 26. Stop 14, trail and thin-section photographs: (a) inversely graded skeletal-fusulinid packstone to grainstone with the long axes of the fusulinids aligned parallel to dip of 27° to 32°, (b) plan view of steeply dipping fusulinid grainstone, fusulinids are ~2 cm long (~0.8 inch), (c) thin-section photomicrograph of inversely graded peloidal-skeletal grainstone to fusulinid-algal grainstone, the dolomitized skeletal grains (fusulinids, platy algae) are coated with isopachous fibrous cement, a thin rind of dolomite, and coarse calcite, (d) thin-section photomicrograph of fusulinid grainstone showing the isopachous fibrous cement around fusulinid grains and equant calcite cement filling most of the remaining interparticle space.

Figure 38. Outcrop and thin-section photographs of Stop 24 exposure surface (general location of figures shown in fig. 37): (a) outcrop of small columnar stromatolites with fenestral porosity (scale in cm), (b) plan view of stromatolites along floor of trail. Note that light-gray material is stromatolite and darker skeletal-peloid sediment defines unusually cylindrical intercolumnar areas (scale in cm), (c) Photomicrograph of skeletal wackestone with the large benthic fusulinid Polydiexodina; blocky spar fills intraskeletal and minor interparticle porosity, (d) outcrop photograph showing thick sheet-crack breccia related to exposure surface with Polydiexodina wackestone of figure 38c directly below the breccia (hand for scale).

Figure 30. Stop 18, fusulinids in reef, and Stop 19, pockets or neptunian dikes: (a) photomicrograph of fusulinid Polydiexodina and phylloid algal fronds, (b) outcrop photo of upright sponge and Polydiexodina (1/4 actual size), (c) outcrop expression of a neptunian dike containing large brachiopod shells (1/5 actual size), (d) photomicrograph of Tubiphytes and phylloid algal fragments encased in internal sediment and marine cement from dike site 2, (e) photomicrograph of Mizzia and other backreef skeletal grains observed at third dike or pocket in reef.

Figure 29. Stop 17, Tubiphytes and Acanthocladia in reef: (a) Tubiphytes colony (1/6 actual size), (b) branching Acanthocladia (1/2 actual size), (c) fenestellid bryozoan exposed in trail (1/4 actual size), (d) photomicrograph of Tubiphytes colony encrusted by Archaeolithoporella, (e) photomicrograph of cross section of Acanthocladia.

Figure 42. Outcrop and thin-section photographs of Stop 25 outer-shelf cycle (illustrations located on figs. 40 and 43), (a) outcrop photograph showing vertically burrowed peloid-algal packstone (b) photomicrograph of peloid-algal packstone shown in (a), (c) photomicrograph of peloid-algal packstone with well-preserved Mizzia at top of the upward-coarsening outer-shelf cycle in a downdip position with micritic coatings on larger grains, minor cloudy fibrous calcite as first-generation cement, and blocky calcite filling intraskeletal and interparticle porosity, (d) sheet-stratified pisolite packstone in lower portion of outer-shelf cycle in a more shelfward position than in a-c, (e) photomicrograph of (d) showing coarse pisolite-skeletal packstone, skeletal grains include Mizzia and mollusks, pisolites have large nuclei and relatively thin cortices, (f) outcrop photograph of pisolite grain-stone in middle of outer-shelf upward-coarsening cycle, (g) photomicrograph of (f), pisolites are similar to those of (e), interparticle porosity filled primarily by isopachous fibrous calcite, (h) outcrop view of low-angle cross-stratified skeletal grainstone at the most landward point of this cycle exposed on the trail, (i) photomicrograph of coated-grain grainstone with well-developed isopachous-fibrous calcite and blocky calcite cement. Note that the grainstone fabric is coarser grained and better sorted than the cycle-capping packstone of (c).

Figure 36. Outcrop and thin-section photographs of Stop 23 reef/outer shelf transition: (a) bedding surface showing large gastropods in skeletal packstone (scale bar in cm), (b) photomicrograph of lithoclast-skeletal-peloid packstone with pelmatozoan fragments, gastropods, various foraminifers (including Reichelina), and minor Mizzia, (c) photomicrograph of very well sorted, fine- to medium-grained, dolomitic siltstone with abundant secondary porosity resulting from feldspar dissolution and late-stage calcite cement, (d) photomicrograph of bryozoan grain-dominated packstone with quartz silt, grains rimmed by early-generation isopachous-fibrous calcite cement, and interparticle porosity filled with later clear blocky spar; (e) photomicrograph of skeletal packstone with abundant quartz silt; skeletal grains include mollusks, bryozoans, gastropods, and minor Mizzia. (early generation of cloudy isopachous-fibrous calcite shows possible corrosion prior to porosity occlusion by calcite spar); and (f) view to NE showing intense strike-parallel jointing in reef and slope portions of Yates-equivalent Capitan. Less well-developed shelf-perpendicular jointing is seen in figure 34.

Figure 25. Stop 13, trail and thin-section photographs: (a) irregular contact between sandstone and overlying lithoclastic grainstone, (b) sandstone filling in apparent growth-framework voids in Archaeolithoporella-encrusted sponge colony, (c) thin-section photomicrograph of very fine- to fine-grained, well-rounded sandstone with a dolomite matrix and kaolinite-filled molds of dissolved feldspar grains, (d) dolomitized thin-bedded, fine- to coarse-grained skeletal packstone and grainstone, (e) thin-section photomicrograph of dolomitized skeletal grainstone with skeletal grains cemented by isopachous fibrous cement, a thin rind of dolomite, and late poikilolitic calcite, (f) skeletal-lithoclast rudstone with clasts of fine-grained skeletal wackestone and the youngest occurrence on the slope of the fusulinid Polydiexodina, cemented by late-stage calcite.

Figure 27. Stop 15, basal reef: (a) typical reef boundstone with interlaminated Archaeolithoporella (dark-gray thin lines) and rust-colored botryoidal-fan cement encrusting sponges; some voids filled with internal sediment (1/4 actual size), (b) bryozoans in floor of trail (1/2 actual size), (c) cephalopod in wall of trail (1/4 actual size), (d) view looking south of reef trail showing locations of switchbacks D through F, Stops 16-19, and an approximate time line through the reef derived from plotting the youngest occurrence of the fusulinid Polydiexodina. In the reef exposures along the trail, this fusulinid has been found only west (right) of this red line.

Figure 28.  Stop 16, sponges of the Capitan reef. Photographs are almost 1/2 actual size.

Figure 21.  Stop 9, trail and thin-section photographs: (a) sponges encrusted with Archaeolithoporella standing out in relief against the undolomitized skeletal-peloidal wackestone-packstone matrix; hammer handle on right side of photo for scale, (b) reef block with large sponge fronds and Archaeolithoporella and botryoidal-fan cement, (c) thin section of Archaeolithoporella showing the characteristic irregular, concentric laminations. Stop 10, trail and thin-section photographs: (d) toe-of-slope burrowed wackestone, with 20° dip, preserved between debris flows of the slope, (e) interpreted erosional contact between the wackestone and grainstone, (f) thin section of the burrowed wackestone showing abundant peloids.

Figure 18.  Stop 7, trail and thin-section photographs: (a) stratigraphic section around Stop 7 showing the downdip thinning of intraclast packstone units (yellow) that cross the trail (dashed), amalgamation surfaces (red), and truncation of units underlying packstone (red arrows); (b) peloidal-skeletal grainstone from recessively weathered packstone and grainstone interval with mollusk fragments (M), smaller fusulinids (F), algal/foraminifer coated grains (C), peloids (P), and ostracodes (O); (c) skeletal-intraclast packstone from the middle member of the amalgamated debris flow at Stop 7 with brachiopods (B) and mud intraclasts (I).

Figure 2. Topographic map of the mouth of McKittrick Canyon showing the location of the Permian Reef Geology Trail and trail stops.

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