Kansas Geological Survey, Open-file Rept. 94-36
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Department of Geology, Kansas State University
A recently exposed surface of stromatolites (form genus Collenia) at the top of the Howe limestone in the Tuttle Creek spillway provides an opportunity for study of stromatolite features and evidence for the depositional environment. Erosion at the spillway exposed a field of columnar stromatolites (covering an area of approximately 61 x 35 m) that are generally hemispherical, club-shaped, and may coalesce, forming small bioherms (up to 140 cm in length) . The substrate for these stromatolites is a coarse, iron-stained grainstone. Many of the stromatolites are elongate in one dimension suggesting growth may have been controlled by water movement.
There appear to be four stages of development; initially oncolites and some attached stromatolites grew in shallow, turbulent water on the substrate as noted above. During growth, sedimentation was episodic and buried most of the stromatolites. A second occurrence of stromatolite growth consists of laterally linked hemispheroids that initiated on the exposed surfaces of some of the partially buried underlying stromatolites. These stromatolites produced smaller columns in a third episode possibly related to environmental stresses. Prior to the deposition of the overlying Roca Shale (a series of palaeosols), a thin sheet of probable microbial origin developed.
Given the palaeolatitude position of Kansas in the Late Palaeozoic, the internal and external morphologies of the stromatolites and associated sedimentary structures, a sabkha and associated intertidal environments is a reasonable interpretation for the uppermost part of the Howe limestone.
Stromatolites of the form genus Collenia (Shapiro, personal communication 1993) occur at the top of the Howe limestone, part of the Red Eagle Limestone; they have been described by McCrone (1963) as being composed of Osagia algae. These stromatolites have a club-like, hemispheriodal shape and occur as either solitary mounds (5 cm to 20 cm in length) or may coalesce, forming small bioherms (up to 140 cm in length). The average height of the mounds is approximately 12 cm above an undulating coarse, cross-laminated, iron-stained grainstone substrate. The Roca Shale was deposited directly over the Howe, forming a sharp contact between the units.
External form of the stromatolites is columnar, a form found extensively in middle to upper intertidal environments. This structure is attributed to the physical stresses of a wave or current dominated environment, and may be enhanced by periodic desiccation or perhaps is modified by different rates of growth during development. The mounds are elongate in a northwest-southeast direction (Fig. 3.1) suggesting growth may have been controlled by water movement. Contemporaneous stromatolites from a different locality were previously studied by McCrone (1963) and interpreted as intertidal.
Fig. 3.1 A rosette diagram demonstrates the linear orientation of the algal features. This suggests that their growth may have been controlled by water movement: wind driven currents or tidal activity.
Internal features of the stromatolites are gently convex laminations with intervals of fine grain sediment and coarse, skeletal fragments. Many of the slabbed samples from the spillway are internally vugaceous, which may be the result of leached evaporites, desiccation, or degassing of the algae during growth (Wray, 1977).
Four distinct episodes of stromatolite development can be recognized suggesting a regressive sequence (Fig. 3.2). Initially, oncoids and some attached stromatolites colonized a coarse grainstone substrate (Episode I) in a shallow subtidal to low intertidal environment. Episodic sedimentation during stromatolitic growth deposited gastropods, ostracodes, and coated and skeletal grains between and around the algal structures.
Fig. 3.2 The developmental growth of the Howe stromatolites is delineated by cartoons: (I) initially oncolites and some attached stromatolites grew in shallow, turbulent water; (II) sediment is deposited as laminations during algal growth; (III) new algal growth in the form of stromatolites; (IV) a microbial mat covers stromatolites. The Roca Shale is deposited directly on top of the mounds.
Eventually, the algae died and was buried by the sediment, or was buried and as a result died. Erosion exposed the upper parts of some of the buried, attached forms, and stromatolitic growth began once again on the exposed firm areas (Episode II).
Growth of this second episode exceeded the input of sediment, and the stromatolites coalesced into small bioherms above the coarse grained matrix. The hemispheriodal, club-like stromatolites that appear at the spillway record growth in inferred low to middle intertidal conditions.
A more columnar stromatolite growth form developed as the environment became more stressed (Episode III); sea level lowered, creating high intertidal to low supratidal conditions. Areas between the columns were filled with silt and clay size sediment.
A thin algal mat, cementing some of the hemispherical to columnar forms together, developed as the environment became even more stressed (Episode IV). Though this mat did not extend laterally across the entire spillway, it is thought to delineate a low supratidal environment of high energy. The regressive sequence ends with the development of paleosols in the Roca Shale (Miller, 1994).
Stromatolites occur in a coarse grained, iron-stained laminated matrix (varies between 15 to 22 cm thick) made up of molds of gastropod shells, ostracode valves, brachiopod shell fragments, coated, and peloidal grains. The lower part (10-12 cm thick) is laminated and appears to be cross bedded in places; both body and trace fossils are readily visible in this layer. The laminations are intermittently iron-stained (thought to have occurred during episodes of subaerial exposure or fresh water inundation) or may be a secondary oxidation process occurring after lithification.
The grainstone is chiefly composed of ostracode valves from Bairdia, Cavellina, and Cytherura (McCrone, 1963). Molds of high-spired gastropods can also be found in different intervals of the grainstone. The only brachiopod identified was Crurithyris.
During the Carboniferous, the climate was constantly in a state of flux; wet and somewhat tropical environments were rapidly replaced by arid climates (Cecil, 1990; Archer and West, 1993). Given the paleolatitude of Kansas during the Pennsylvanian Period (between 0-30 degrees), it is easy to see how such fluctuations in precipitation and temperature occurred.
The Howe limestone represents a small package of sea level regression. The unit of study (up to 30 cm thick) shows a changing trend in the palaeoecology as the sea level modified the landscape and altered ecological niches.
In the first episode of stromatolitic development, conditions thought to encompass the environment were moderately energized, high subtidal to low intertidal. Because of the moderate energy in this environment, organisms living here might be expected to have experienced minimal transportation prior to burial.
As the sea regressed, the water from within the basin became shallow and energy increased. It is presumed that the generation of gypsum molds was influenced by environmental conditions such as periodic dry spells in which desiccation was common; these crystals grew both in and on the mounds and substrate and suggest a dry climate.
Some organisms such as ostracodes: (Bairdia, Cavellina, and Cytherura) and gastropods existed (McCrone, 1963). They lived in an environment that was becoming increasingly harsh and hypersaline, and may have burrowed into the stromatolites to keep from dehydrating (Bauld, 1984). This may explain the thrombolitic (lack of laminae caused by bioturbation) texture exhibited by some of the stromatolites.
A sabkha and all of the associated environments (similar to the Recent Persian Gulf or Shark Bay and Spencer Bay, Australia) are reasonable analogs for this upper 30 cm of the Howe limestone. Typically, sabkhas occur in arid to semi-arid climates and are characterized by evaporite and hypersaline conditions and stromatolitic laminae. This interpretation is similar to that of McCrone's (1963) however the Howe is recognized here as a regressive sequence including an intertidal episode.
Archer, A. W. and West, R.R., 1993, Generalized climato-stratigraphic analyses of the exposed Permo-Pennsylvanian section of Kansas: Kansas Geological Survey Open File Report 93-24, p. 19-12 to 19-21.
Bauld, John, 1984, Microbial mats in marginal marine environments: Shark Bay, Western Australia, and Spencer Gulf, South Australia: NML Lectures in Biology, v. 3, p. 39-58.
Cecil, C.B., 1990, Paleoclimate controls on stratigraphic repetition of chemical and siliciclastic rocks: Geology, v.18, no. 6, p. 533-536.
McCrone, A.W., 1963, Paleoecology and biostratigraphy of the Red Eagle cyclothem (Lower Permian) in Kansas: Kansas Geological Survey Bulletin, v. 164, 114 p. [available online]
Miller, K.B., 1994, Tuttle Creek Lake spillway exposure: Cycle patterns and paleosol profiles, Kansas Geological Survey Open File Report 94-23, p. 26.
Shapiro, Russell Scott, 1990, Morphological Variations within a modern stromatolite field: Lee Stocking Island, Exuma Cays, Bahamas: Caribbean Marine Research Center and Humbolt State University, p. 209-219.
Wray, John L., 1977, Calcareous Algae: New York, Elsevier Scientific Publishing Company, 184 p.
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Kansas Geological Survey, Geology
Placed on web Feb. 26, 2007.
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