Geology

Facies representing eight deltaic environments are recognized in the Mansfield Formation (Pennsylvanian: Morrowan) and Dugger Formation (Pennsylvanian: Desmoinesian) of Indiana. These facies are interpreted as A) lower interdistributary bay, B) middle ...

The oldest known tidal rhythmites, identified in the Big Cottonwood Formation, Utah, are Late to Middle Proterozoic in age (800 Ma to 1.0 Ga), ˜250 to 400 m.y. older than the previously oldest known tidal rhythmites. Four tidally forced cycles and one nontidal (seasonal) cycle control lamina thickness patterns. All of these cycles are recognized in outcrop and core and

Ancient tidal periods extracted from the geologic record are useful to constrain and calibrate theoretical models of the evolution of the earth-moon system. Analysis of rocks that contain such tidal periodicities, termed cyclic rhythmites, have tended to concentrate on long series and have focused on the more obvious periods. For example, neap-spring periods have been the most widely discussed; such information can be reliably extracted from bedform thickness series measured within laterally accreted tidal bundles and vertically accreted tidal laminae.Other lunar orbital data is also encoded in cyclic rhythmites; however this additional information has been much less extensively applied to earth-moon models. Herein, short segments of well-formed cyclic rhythmites are examined to determine how reliably the various tidal periods can be extracted via harmonic analysis. Rhythmite series analyzed here exhibit well-formed neap-spring tidal periods and also exhibit a prominent fortnightly inequality or a variation in the height of successive spring tides. This inequality is related to the elliptical nature of the lunar orbit (anomalistic month) and it is demonstrated that this period can also be reliably extracted from cyclic rhythmites.Tropical periods, which reflect the changing lunar declination that occurs during a tropical month, have also been reported from cyclic rhythmites. Unlike synodic and anomalistic periods, the apparent tropical periods extracted from some cyclic rhythmites do not always accurately correspond to the expected values. In only a few cases can this period be reliably extracted from short segments of cyclic tidal-rhythmite data. This period is commonly only poorly encoded in rhythmites because: (1) it tends to be masked by higher amplitude synodic periods, and (2) it is not well expressed within predominantly semidiurnal tidal systems.Samples selected from the Proterozoic and Phanerozoic tend to be more common during specific intervals of geologic time. These intervals were characterized by glacio-eustatic flux and, in some cases, by unique continental configurations. Understanding these basic controls on rhythmite occurrences should aid in the discovery of additional examples.

RHYTHMIC SEDIMENTATION IN A MIXED TIDE AND WAVE DEPOSIT, HAZEL PATCH SANDSTONE (PENNSYLVANIAN), EASTERN KENTUCKY COAL FIELD STEPHEN F. GREB1 and ALLEN W. ARCHER2 ' Kentucky Geological Survey, University of Kentucky, Lexington ...

Recently, stacked successions of ancient tidal rhythmites have been found to preserve long records of tidal cycles. These include semidaily, daily, semimonthly, monthly, semiannual, annual and multiyear periods. Though such deposits reveal much about ancient tidal dynamics, the tidal signatures within the rhythmites can be masked or modified by basinal or nontidal effects. This paper discusses the results of an analysis of data from several different modern tidal stations. We show how actual tidal data can be abstracted to a form similar to what might ideally be preserved in the rock record, and then power spectra are calculated to yield estimates of the astronomical periods which can be compared to the current values. In this study, data from four modern tidal stations, ranging from diurnal to semidiurnal, are analyzed as both time- and event-series. A series of tests, which involve selective removal of parts of the tidal signal, are made using the modern tidal-station data. These tests were performed in order to determine to what extent the tidal signal can be degraded and still be recognized. Finally, we discuss some implications of the similarities of the modern and ancient tidal data and suggest how ancient data may be used to constrain basinal paleography and make inferences regarding ancient lunar orbital geometries.

Where individual tides deposit appreciable accumulations of sediment, cyclic tidal rhythmites can form that exhibit semimonthly tidal cyclicities. A number of modern analogs and ancient counterparts indicate the importance of such features for paleoenvironmental analyses. In this study, predicted, high-low, tidal-station data are used to simulate current speeds, which in turn are used to simulate sedimentation of tidal rhythmites. This modeling has been done to depict the patterns encoded in cyclic tidal rhythmites. In order to delineate the spectrum of different tidal regimes, the simulations are based upon a series of macrotidal, diurnal to semidiurnal tidal systems. Depending upon thresholds of relative tidal-current speed, only portions of semimonthly tidal cycles will be preserved within cyclic tidal rhythmites.

... Degree of seasonality affected styles of fluvial sedimentation and paleosol development. ... in the Central Appalachian Basin (eastern Kentucky), Eastern Interior Basin (Illinois, Indiana, western ... with the development of the late Missis-sippian and early Pennsylvanian unconformity ...

... Pacific plate, WB—Wrangle block, am—Aleutian megathrust, bbf—Bruin Bay fault, cmf—Castle Mountain fault, df—Denali fault, kl ... Mw 5.5), large-scale sediment deformation, including sand dikes formed by liquefaction, has been well documented (Youd, 1973; Lowe, 1975; Seed ...

... 8.-Analyses of silty rhythmites from Hindostan Whetstone lithofacies: A) Lamina-thickness series showing well developed neap-spring cycles and ... Analyses of silty rhythmites from Francis Creek Shale: C) Lamina-thickness series showing well developed neap-spring cy-cles ...

Fine-scale fabric within shales can be used to interpret environments of deposition. In particular, systematic variations in lamina thicknesses can be used to suggest the presence or absence of specific sedimentological controlling factors, such as tides. Herein, shale fabric is analyzed from Carboniferous coal-bearing and siliciclastic-rich formations in Indiana and Kansas. The shales exhibit well developed, normally graded lamina. Sediment grain sizes range from silt and sand at the base of the lamina up to silt and clay at the top. Computer-based optical scanning of prepared shale samples was undertaken so that the lamina thicknesses could be extracted automatically and then used for thickness-series analysis. The sands and silts tend to be very light in color because they consist of well sorted, quartz-rich sands. Conversely, the silt and clay that cap the laminae tend to be dark because of the small grain size; such fine-grained layers also contain large amounts of macerated and coalified plant material. Grain size and sedimentological differences within the laminae can be detected by optical properties and this facilitates automated image processing. Extraction of laminae thicknesses and harmonic analyses of laminae-thickness series can then be used to test the reasonability of specific environmental processes, such as tidal forcing, that were operative during the formation of these shales.

The Tonganoxie Sandstone Member of the Stranger Formation (Douglas Group, Upper Pennsylvanian, Kansas) was deposited in a funnel-shaped, northeast-southwest-trending paleovalley that was incised during the uppermost Missourian sealevel lowstand and backfilled during the subsequent transgression. Quarry exposures of the Tonganoxie near Ottawa, Kansas, include [approximately] 5 m of sheetlike, vertically accreted siltstones and sandy siltstones, bounded above and below by thin coals with upright plant fossils and paleosols. Strata range from submillimeter-thick, normally graded rhythmites to graded bedsets up to 12.5 cm thick with a vertical sedimentary structure sequence (VSS) consisting of the following intervals: (A) a basal massive to normally graded interval; (B) a parallel-laminated interval; (C) a ripple-cross-laminated interval; and (D) an interval of draped lamination. The Tonganoxie succession has many similarities to fluvial overbank/floodplain deposits: sheetlike geometry, upright plant fossils, lack of bioturbation and body fossils, dominance of silt, and a punctuated style of rapid sedimentation from suspension-laden waning currents. Analysis of stratum-thickness variations through the succession suggests that tides significantly influenced sediment deposition. A fluvial-to-estuarine transitional depositional setting is interpreted for the Tonganoxie by analogy with modern depositional settings that show similar physical and biogenic sedimentary structures, vertical sequences of sedimentary structures, and aggradation rates.

Assemblages of in situ upright stem casts, or fossil standing forests, provide information on the composition and spatial arrangement of the original plant communities they record, with minimal taphonomic bias. Stands of calamites and lycopsids are found repeatedly as fossil forests in the Late Carboniferous, while other major groups of plants are only rarely preserved in this way. The Carboniferous coal measures of Europe and North America were formed in low‐latitude, tropical environments. The ancient plant communities of these settings can be interpreted by comparison of their taxa with specific, modern tropical analogs. Here, ancient standing forests of the extinct sphenopsid Mesocalamites suckowii are compared with modern stands of the monocot Montrichardia arborescens. These modern analogs occur in the Orinoco Delta of Venezuela and the mouth of the Amazon. Montrichardia and its ancient counterparts occur in comparable clastic facies of fluvio‐deltaic and estuarine depositional systems. Although Mesocalamites and Montrichardia are very different anatomically and taxonomically, they exhibit some intriguing morphological similarities that can be linked to a common ecology. These modern and ancient taxa have evolved convergent forms of vegetative propagation that enable the plants to colonize and survive in environments characterized by very high rates of sedimentation, or episodic sedimentation events. Such environments have an unusually high potential to preserve standing forests.

Regional correlation of interbedded pelagic/hemipelagic limestones and calcareous shales of the Fort Hays Limestone Member of the Niobrara Formation confirms development of at least two levels of cyclicity. Occurrence of time-parallel rhythmically deposited beds that can be correlated over distances exceeding 800 km lends strong support to the hypothesis that these cycles were induced by Milankovitch-type climatic forcing. However, visual

Based on field observations of the preservation potential and genesis of couplets and small sequences, diastems occur within tidal flat deposits at scales of semi-tidal, daily, monthly, and yearly intervals. Thus, tidal flat deposition is riddled with more diastems of different scales than previous assumptions. Units that are apparently complete when examined at longer time scales actually contain many diastems when examined at a shorter time scale. Diastems within tidal flat deposits are generated not only by high-magnitude storm waves, which occur during typhoon seasons, but also by daily erosion produced by tides and weak waves during calm-weather seasons. The missing intervals in diastems generated by storm waves can be several days to several years. Preservation potential of storm-generated small sequences is of the order of one-third. Diastems generated by erosion, by tides, and weak waves can have spans from a semidiurnal cycle to several days. They are easily overlooked because of the low-magnitude destruction and lack of distinctive sedimentary features. Net erosion by tides and weak waves is unexpectedly increased by day-to-day processes. Alternations of sandy and muddy laminae are related to tidal rhythm, but individual laminae can be separated by a significant diastem. Documentation of erosion by tides and weak waves under normal (non-typhoon) conditions is the principal focus of this report.

... MR Gibling. Department of Earth Sciences, Dalhousie University, Halifax, NS B3H 355, Canada.DR Reid. ... Locations of modem tidal rhythmite deposition, discussed in text, include Maccan Bridge (Mc) and Truro (Tr). ... 1993), the Gulf of St. Lawrence (Wightman et al. ...