Carbonate deposition and facies distribution in a central Michigan marl lake

Relatively pure lacustrine carbonates referred to as marl are being deposited in Littlefield Lake, central Michigan, a hard-water lake with little terrigenous clastic influx. Thick accumulations of marl form both progradational marl benches along lake margins, and islands or lakemounts in the lake centre. Marl benches develop flat platforms up to 20 m wide in very shallow water and steeply inclined slopes, up to 30°, extending into deep water. The flat landward platform is frequently covered by algal pisoliths while the upper portion of the lakeward-sloping bottom is overgrown by Chara which in the summertime becomes thickly encrusted with low-magnesian calcite. Marl islands are flat-topped features that formed over relict highs on Pleistocene drift which underlies the lake basin. These are fringed by marl benches identical to those found along lake margins. Marl benches are composed of four units: two thin facies deposited on the shallow-water bench platform and two thicker faces deposited on the bench slope developed in moderate water depths. These in turn overlie a fifth facies deposited in deep water. A coarsening-upward sequence is developed in these sediments as a result of both mechanical sorting, and primary production of carbonate sand and gravel in shallow water. In addition to facies sequences and size grading, trends upsection of increasing carbonate content and decreasing insoluble content may serve to identify temperate-region lacustrine carbonate deposits in the rock record.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72142/1/j.1365-3091.1980.tb01164.x.pd

A quantum Peierls-Nabarro barrier

Kink dynamics in spatially discrete nonlinear Klein-Gordon systems is considered. For special choices of the substrate potential, such systems support continuous translation orbits of static kinks with no (classical) Peierls-Nabarro barrier. It is shown that these kinks experience, nevertheless, a lattice-periodic confining potential, due to purely quantum effects anaolgous to the Casimir effect of quantum field theory. The resulting ``quantum Peierls-Nabarro potential'' may be calculated in the weak coupling approximation by a simple and computationally cheap numerical algorithm, which is applied, for purposes of illustration, to a certain two-parameter family of substrates.Comment: 13 pages LaTeX, 7 figure

Geologic approaches to the determination of long-term coastal recession rates, matagorda peninsula, Texas

The degree to which human modifications in the coastal zone have increased or decreased coastal erosion rates is difficult to determine owing to the short time period for which shoreline-position data are available. This limitation is circumvented in areas where long-term recession rates can be determined from geologic data. Three such areas from Matagorda Bay have been examined to determine the temporal variation in recession rates over the past several thousand years. Preliminary results indicate that recession rates over the past century may be 30% to 40% greater than those of prehistoric time. Although additional data are needed, it is suggested that accelerated rates result from human modification of the coastal zone, and that in the future increased recession rates can be anticipated.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46765/1/254_2006_Article_BF02380504.pd

Paleolatitude distribution of Phanerozoic marine ooids and cements

Data on 493 Phanerozoic marine ooid and cement occurrences indicate that the dominance of calcite versus aragonite in tropical marine settings has changed in response to variation in atmospheric CO2 and/or oceanic temperature gradient. Holocene ooid and cement precipitation occurs over similar latitudes, with means centered around 24[deg] and 28[deg], respectively. Aragonite and calcite also display roughly comparable distributions, with average occurrences between 25[deg] and 28[deg]. Surface seawater saturation values requisite for ooid-cement carbonate precipitation are at least 3.8 ([Omega]arg) for aragonite and 3.4 ([Omega]arg) for calcite.Ancient ooid-cement occurrences vary in space and time, with depositional zones generally closer to the equator during continental emergence; greatest extent correlates with periods of maximum transgression. Aragonite formation is favored in more equatorial localities than calcite when cement-ooid distributions are narrow and continents are emergent. Similarity of latitude distribution of marine ooids, cement, and biogenic carbonate suggests that physicochemical processes that control levels of carbonate saturation were more important in predicating sites of limestone accumulation in Phanerozoic seas than biological processes related to net productivity of various carbonate platform communities. Continental position and tropical shelf area available for carbonate accumulation dictates the relative abundance of shallow water inorganic carbonate precipitates in space and time.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28586/1/0000394.pd

The peterson limestone -- early cretaceous lacustrine carbonate deposition in western wyoming and southeastern idaho

The lacustrine Peterson Limestone of western Wyoming and southeastern Idaho comprises six lithofacies throughout its 20,000 km2 aerial extent. These are: (1) calcareous sandstone and shale, (2) red nodular limestone, (3) pink sandy micrite, (4) biomicrite, (5) graded silty micrite, and (6) limestone conglomerate. The first two represent floodplain deposition and paleosols, whereas the remaining are shallow nearshore and deeper lacustrine sediments.This sequence was developed in a large fresh, hardwater lake surrounded by fluvial systems and associated flood plains in a warm temperate climate. Well-oxidized sandy terrigenous rocks, together with calcareous paleosol nodules, indicate that flood-plain deposition both preceded and was concurrent with lacustrine carbonate deposition. Micrite and biomicrite formed in deeper parts of the basin while sandy and silty carbonate accumulated in shallower lake-margin areas. Less-calcareous shale units which are interbedded with deeper-water carbonate were deposited either during rapid basin subsidence and deepening of the lake center or during periods of slower carbonate precipitation. Turbidity currents and subaqueous debris flows generated along steeper lake margins, resulted in the deposition of rhythmic layers of graded silty micrite and diamictic limestone conglomerate in the deepest part of the basin. The carbonate-rich sediments comprising these two lithofacies were originally deposited on shallow lake-margin benches and subsequently were transported downslope toward the lake center.Comparison with other carbonate-precipitating lacustrine systems indicates that this lake was not like modern playas. Although no known modern lacustrine system is precisely like Lake Peterson, the flora, fauna, composition, and distribution of facies within modern temperate-region lakes most closely resemble those of the Peterson Limestone.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23179/1/0000106.pd

Composition of the early Oligocene ocean from coral stable isotope and elemental chemistry

A sectioned and polished specimen of the coral Archohelia vicksburgensis from the early Oligocene Byram Formation (∼30 Ma) near Vicksburg, Mississippi, reveals 12 prominent annual growth bands. Stable oxygen isotopic compositions of 77 growth-band-parallel microsamples of original aragonite exhibit well-constrained fluctuations that range between −2.0 and −4.8. Variation in Δ 18 O of coral carbonate reflects seasonal variation in temperature ranging from 12 to 24 °C about a mean of 18 °C. These values are consistent with those derived from a bivalve and a fish otolith from the same unit, each using independently derived palaeotemperature equations. Mg/Ca and Sr/Ca ratios were determined for 40 additional samples spanning five of the 12 annual bands. Palaeotemperatures calculated using elemental-ratio thermometers calibrated on modern corals are consistently lower; mean temperature from Mg/Ca ratios are 12.5 ± 1 °C while those from Sr/Ca are 5.8 ± 2.2 °C. Assuming that Δ 18 O-derived temperatures are correct, relationships between temperature and elemental ratio for corals growing in today's ocean can be used to estimate Oligocene palaeoseawater Mg/Ca and Sr/Ca ratios. Calculations indicate that early Oligocene seawater Mg/Ca was ∼81% (4.2 mol mol −1 ) and Sr/Ca ∼109% (9.9 mmol mol −1 ) of modern values. Oligocene seawater with this degree of Mg depletion and Sr enrichment is in good agreement with that expected during the Palaeogene transition from ‘calcite’ to ‘aragonite’ seas. Lower Oligocene Mg/Ca probably reflects a decrease toward the present day in sea-floor hydrothermal activity and concomitant decrease in scavenging of magnesium from seawater. Elevated Sr/Ca ratio may record lesser amounts of Oligocene aragonite precipitation and a correspondingly lower flux of strontium into the sedimentary carbonate reservoir than today.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72914/1/j.1472-4677.2004.00025.x.pd

Dimensions of Sedimentary Lithotopes and Taxonomies of Fishes

The size of subgroups among larger taxonomic units, as measured by the number of taxa within them, is a metric of fundamental importance to the appreciation of causes of change in biodiversity in both time and space. Central to such evaluations is an understanding of the expected and observed variation in the numbers and sizes of groups comprising various taxonomic levels. Here we show that numbers of fish taxa within subdivisions (memberships) of any supertaxon in a Linnaean taxonomy are virtually identical to areas of patches of like sediment (lithotopes) that are distributed across various depositional surfaces. Both sedimentary surfaces and Linnaean taxonomies are closely approximated by functions that generally describe random divisions of geographic and/or shape-space. We describe a ‘broken plate’ model for taxonomic membership that is akin to Robert MacArthur’s (1957) classical ‘broken stick’ model for abundance distributions, where species abundances in an ecosystem are described by an exponential function of abundance (segment length) frequencies reflecting the random subdivision of resources. In a taxonomic context, the broken plate presumes that the amount of morphospace realized at any taxonomic level is proportional to the numbers of subtaxa of which it is comprised. A hypothetical transect across the morphospace associated with any higher taxon would comprise a ‘broken stick’, or exponential, distribution of square roots of the number of contained subtaxa. Taxonomic membership (occupied morphospace) within the higher taxon is therefore randomly partitioned among subtaxa, analogous to the sizes of fragments of the broken plate. Thus, just as the broken stick distribution is well-described using only the length of the stick and the number of segments into which it is broken, the partitioning of taxa into subtaxa within any supertaxon is random and adequately described using only the number of taxa and the number of subtaxa into which they are partitioned. Such ‘broken plate’ functions yield excellent agreement for membership partitioning among classes, orders, families, and genera of fishes. Quantification across all taxonomic levels provides several insights related to the biodiversity of this important group: (1) Membership of taxonomic groups of fishes is self-similar among all levels of Linnaean division (e.g., families per order, genera per family, species per genus) and is almost entirely independent of levels of taxonomic separation between groups being considered, with an average of seven to eight members within any taxonomic group. (2) The ‘broken plate’ representation implies that divisions within one taxonomic level are independent of all other divisions; a similar partitioning of species among genera belonging to both diverse and depauperate families supports the supposition that little ‘memory’ exists between levels of taxonomic membership. (3) Special explanations for the generation of apparently extreme polytype may be largely unnecessary; taxonomic diversities expected from the ‘broken plate’ model suggest that observed disparity in numbers of fish species comprising many clades is no greater or less than one would expect from a random fragmentation of morphospace.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/171083/1/UMMZ MP 209 Vol. 3 12.23.pdf-1Description of UMMZ MP 209 Vol. 3 12.23.pdf : Main articleSEL

Tectonic and Topographic Framework of Political Division

Boundaries between the various topographic, geologic, and socio-political entities that span the Earth’s continental surfaces are determined by a myriad of complexly interrelated natural and/or cultural factors. Areas of large river basins, of lithologic units on geologic maps, and of nations exhibit size frequency distributions that are closely approximated by density functions in which diameters of individual areas are distributed exponentially. As such, size distributions of each type of surface unit are closely modeled as randomly delimited areas. In other words, if one were to walk in a straight line across any particular continent, each step along that transect would embody some random continuous probability of passing out of a major drainage basin, or out of an area of more or less homogeneous rock type, or from one country to another. Moreover, this simple truism gives rise to area frequency distributions for large river basin or outcrop or nation area that are primarily dependent on the number of basins or outcrops or countries that exist across that particular landmass. As a consequence, the size frequencies of these areal units can be closely predicted knowing only the total area under consideration and the number of drainage basins, outcrop areas, or nations that exist within the area. The similarity between area frequencies of large river basins and rock types and nations suggests a nontrivial component of geologic influence on the partitioning of continental surfaces into major political divisions, and implies that cultural and economic factors, which serve to divide and unite political entities, do so within a geological framework.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43200/1/11004_2005_Article_1309.pd

Sr/Ca and Mg/Ca ratios in polygenetic carbonate allochems from a Michigan marl lake

Rapid accumulation of CaCO3 is occurring in Littlefield Lake, a marl lake located in central Michigan. The sediment, which is 95% CaCO3, primarily consists of eight different genetic groups of carbonate allochems. These include calcite muds, sands, algal oncoids and Chara encrustations, as well as the dominant aragonitic gastropods Valvota tricarinota. Gyraulus deflectus and Amnicola integra. and the dominant aragonitic pelecypod Sphaerium partumeium. Samples of each of these groups were analyzed for Ca, Sr and Mg. Molar Mg/Ca ratios are primarily controlled by allochem mineralogy, with calcitic forms having Mg/Ca ratios 5-10 times larger than aragonitic (shelled) forms. The Sr/Ca ratios are primarily controlled by biochemical fractionation, and are significantly lower than Sr/Ca ratios of inorganically precipitated aragonite from other settings. Partition coefficients were determined for both Sr and Mg for each carbonate allochem group and, based on comparisons with results reported by other workers, the partition coefficients determined here are generally considered `typical' or representative values for biogeneous freshwater carbonates. An analysis of variance of the data indicates that most genera and species of carbonate-secreting organisms in marl lakes have highly characteristic Sr/Ca and Mg/Ca ratios. These ratios can potentially serve as geochemical tracers in future investigations of lacustrine carbonate diagenesis. Both Sr and Mg are influenced by grain size and/or surface area, probably due to the presence of these elements in non-lattice-held (exchangeable) positions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24453/1/0000727.pd

Miocene lacustrine algal reefs--southwestern Snake River Plain, Idaho

The Hot Spring limestone is a shallow-water algal carbonate within a late Tertiary transgressive lacustrine sequence exposed in the southwestern Snake River Plain. This 5 m thick lensoid sequence crops out over an 80 km2 area that closely approximates original areal extent of nearshore carbonate accumulation. Reefal bodies consist of closely packed algal cylinders, several decimeters in height, each of which includes a dense laminated carbonate wall surrounding porous digitate carbonate that radiates outward and upward from one or more hollow tubes. These coalesce upsection into separate vertical columns several meters in diameter. Moderately well-sorted terrigenous and molluscan debris deposited between columns during growth indicates these structures were resistant to wave erosion and, therefore, were true reefs. Thick rings of littoral carbonate surrounding the upper walls of each column record the final stages of reef development.Structural attributes exhibited by these Miocene carbonate bodies are also common to a number of Tertiary and Quaternary algal buildups reported from other lacustrine settings. Although features within the Hot Spring limestone are complex in gross morphology and structural detail, both columnar reefs and algal cylinders display little variation in size, shape, or internal structure between areas of varying water depth and wave energy, thus reflecting the importance of biological processes as well as physical processes during reef development.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28624/1/0000438.pd