Thesis Images and Captions

Figure 3-5


These are images from my thesis with the corresponding figure captions. I'm in the processes of rewriting the captions so they will stand independently of the thesis text. Until then, you'll have to make due with the following (sometimes cryptic) descriptions.

Here is a map.

Figure 2-4 Wave rippled grain stones with rare cemented or microbially bound layers.

Figure 2-5 Inversely graded ooids lacking cross stratification.

Figure 2-8 Internal deformation of smooth laminae in a decimeter-diameter domal stromatolite. Scale has millimeter gradations.

Figure 2-9 Pseudoencapsulated structures. Selected laminae are outlined with pen. Current ripples above and below this layer indicate sediment transport from left to right. Scale has millimeter gradations.

Figure 2-10 Poorly preserved aragonite fan pseudomorphs in chert from the supratidal to upper intertidal lithofacies assemblage.

Figure 2-11 A) Halite casts replaced by chert (arrows). B) Chert-replaced structures that may also be pseudomorphs after another evaporite mineral.

Figure 2-13 A) Vertical section of large aragonite fan pseudomorphs. The blades of the fans are draped by sediment. Hand lens is 2 cm across. B) Domes formed by large fans like those in A draped by sediment. Their growth is consistent with a purely abiotic origin. Scale is 15 cm long.

Figure 2-14 Thin section in plane polarized light showing fibrous textures in aragonite pseudomorphs. This thin section comes from the aragonite coatings on stromatolites in Figure 2-12B.

Figure 2-16 Fenestral stratiform lithofacies with a thin layer of isopachous domes. Hand lens is 2 cm wide.

Figure 2-17 Giant stromatolite mounds that are more than 45 m long and 10 m wide from Boetsap. John Grotzinger for scale in the middle of the photograph.

Figure 2-18 The Boetsap-style lamination with abundant vertically elongate pseudomorphs that extend from the base to the top of the photograph. A fan-like geometry is developed at the base. Hand lens is 2 cm wide. (interpreted as aragonite pseudomorphs)

Figure 3-5 Plan view of cuspate microbialites to plumose structures from section EC. Supports are interconnected in a polygonal pattern. Hand lens is 2 cm.

Figure 3-6 Vertical section of plumose structures (p) overlain by a decimeter-thick bed of herringbone calcite (h) and then another layer of plumose structures. These microbialites formed individual structures that grew against each other leaving zones of interfering growth (black arrows). This bed is laterally continuous for at least 140x50 km. Hammer is 35 cm long.

Figure 3-9 Vertical section of a plumose structure growing over a protrusion consisting of a round-topped tented microbialites. Note that the support in the tented microbialite is folded, particularly at the top (small white arrows). The plumose structures grade upward into cuspate microbialites (large white arrow).

Figure 3-13 Polished slab and tracing showing irregular columnar microbialites and intervening rolled-up laminae. Herringbone calcite is indicated by "h", filmy laminated mat by "m", secondary chert by "ch", void-filling bladed and blocky calcite by a black arrow, and central supports by a white arrow. Laminae within the column are discontinuous and irregular.

Figure 3-15 Polished slab and tracing showing part of a plumose structure from the bed shown in Figure 3-9. Herringbone calcite is indicated by "h", void-filling blocky calcite by a black arrow, and a central support by a white arrow. Central supports project in a variety of directions including horizontally. Short dashes indicate areas with abundant black inclusions that define a poor lamination parallel to the overlying support. This sample consists of 90% herringbone calcite.

Figure 3-16 Plan view of a plumose structure. Note the branching pattern in the supports is similar to that in vertical sections (compare with Figure 3-15). The dark gray areas are cross sections through the inclusion-rich zones under horizontal supports.

Figure 3-17 A laterally continuous (140 x 50 km) bed of herringbone calcite with a thin layer of plumose structures in the middle (white arrow points to base of layer). This is the same bed as shown in Figure 5-3A.

Figure 3-19 Etched polished slab of a void that may have formed during gas escape from the underlying mat. Note the broken layers of mat that hang down the sides of the void and the compressed overlying laminae.

Figure 3-21 Etched polished slab of the edge of an irregular columnar microbialite (to left). Herringbone calcite (h) grew off a central support (s) and some laminated mat (m). Herringbone calcite banding is truncated against some draping laminae (white arrow), although many of the voids are also filled with herringbone calcite. It did not grow as traditional void filling cement, however, and textures indicate that it predominantly grew upward and outward from supports and draping laminated mats (growth directions indicated by black arrows). Small spherical patterns are secondary chert nodules.

Figure 3-22 Detail of the etched polished slab shown in Figure 3-13. Herringbone calcite (h) preferentially grew off the central support (s) over the laminated mat (m). Herringbone calcite grew outward from the support encasing draping laminae attached to it, but did not coat the laminae away from the support. The mat was present during herringbone calcite precipitation as demonstrated by the truncation of herringbone calcite banding against draping laminae (white arrow). Voids between draping laminated mats near the supports are filled with bladed calcite (white).

Figure 3-23 Detail of the etched polished slab shown in Figure 3-13. Herringbone calcite (h) preferentially grew off the margin of the irregular columnar microbialite over the laminated mat (m). The laminae were present during growth of the herringbone calcite as demonstrated by the encasing of some mat in the herringbone calcite (white arrow). This mat is coated by only a very thin layer of herringbone calcite and most of the void spaces filled with blocky calcite (b).



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Dawn Y. Sumner
Department of Geology
University of California
Davis, CA 95616
sumner@geology.ucdavis.edu