Abstract: 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 herein 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 reflects 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 dominantly 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.

Abstract: Various paleotidal periods can be extracted from analyses of cyclic tidal rhythmites, which are common in upper Carboniferous (~300 Ma) rocks of the eastern and midcontinental U.S. These periods provide details of the paleotidal regime that controlled sedimentation during deposition of the rhythmites. In addition to shorter-term diurnal/semidiurnal periods and longer-term neap-spring tidal periods, some rhythmites have unusual intermediate periods of approximately 50 hours. These intermediate periods are not readily explainable by any known completely tidal period.

It is hypothesized that this 50-hour period could be the product of a basinal resonance, or seiche. Herein, estimates are made regarding the required basin depths and widths necessary to produce a seiche of this period. These estimates are based upon paleogeographic reconstructions of the global paleocean, Panthalassa, that surrounded Pangea. These reconstructions provide basinal paleowidth estimates; subsequently paleodepths can be extrapolated from the depth-to-width relationships in modern oceans.

Combining such fine-scale tidal-rhythmite periodicities with large-scale paleogeographic information provides many useful constraints for modeling of Pangean tidal systems. Forward modeling of global tides, based upon very large-scale paleogeographic controls, when combined with reverse modeling, based upon fine-scale, detailed rhythmite-period analysis, allows detailed calibration of the paleotidal-systems response. Based upon the available fine- and large-scale information, the unusual 50-hour period that occurs within cyclic rhythmites is most likely related to a global paleocean seiche.

Abstract: Cyclical tidal rhythmites, which express neap-spring and other tidal cycles, appear to be particularly common within Carboniferous rocks of the eastern U.S. These rhythmites exhibit many similarities to a variety of modern tidal periods. In well preserved examples, it is possible to extract synodic, tropical, and anomalistic periods. Yearly periods, which probably relate to sediment supply, have also been documented from several sites.

A number of controls probably served to influence the commonality of such facies during that particular episode of geologic time. Tractive forces and astronomical periods were not significantly different; thus the extraterrestrial controls were essentially identical to those operative within modern tidal systems. Conversely, terrestrial systems exhibited several important differences. At the largest scale, global distribution of land and oceans had a major effect. During the Carboniferous, ongoing continental accretion leading to the development of Pangaea, also resulted in a globe-spanning ocean. This ocean, termed Panthallasia, would have resonated more freely with tractive forces. Therefore, it has been estimated that open-ocean tides were on the order of 50% higher. When compared to today, it would thus be expected that macrotidal coastal systems would have been significantly more common. Analysis of detailed rhythmite records from the U.S. Mid- Continent indicate periods that may relate to Panthallasian non-tidal oceanic resonance.

Sequence stratigraphic relationships could also affect the commonality of rhythmites. Rhythmite-bearing intervals within the Carboniferous are commonly related to cyclical successions of strata, or "cyclothems." These cycles can be correlated for considerable distances across the eastern U.S. Such cycles are apparently to high-magnitude, high- frequency glacio-eustatic flux that in turn was potentially controlled by Milanokovitch- type orbital variations. Within such cycles, lowstand conditions resulted in development of integrated fluvial drainage and incision of valleys of significant size into pre-existing deposits. During subsequent baselevel rise, these fluvial systems were flooded and converted into estuarine systems. When appropriate length/depth relationship were established, linear resonance and tidal amplification could occur.

Paleoclimatic and geomorphic conditions also exerted controls on rhythmite occurrences. Much of the Carboniferous of the eastern U.S. was formed in near-equatorial, low-latitude depositional systems that were within areas of moist, tropical climate. In addition, because of laterally extensive continental size and potential for large drainage basins, the fluvial systems were potentially quite large. Thus, coastal environments were characterized by large-scale tropical rivers. These rivers were not only capable of incising significant-sized valleys during lowstands, but also could have resulted in large-scale estuaries during sealevel rise. It is thought that many Carboniferous rhythmites were formed in nearly freshwater systems near the landward limits of large-scale estuaries. These ancient rhythmites exhibit many similarities in terms of periodicities, thicnesses, and sediment types to modern analogs formed in macrotidal estuaries, such as within the upper reaches of the Bay of Fundy, Canada.

Thus the combined factors of a globe-spanning ocean, high degree of glacio-eustatic flux, and large fluvio-estuarine systems probably help to explain the common occurrence of cyclical rhythmites in Carboniferous of the eastern U.S.

Similar conditions may have occurred at other times in the geological past, such as the late Proterozoic, although for rhythmites of such antiquity, the litho- and chronostratigraphic resolution is too low to allow for large-scale correlation of cycles. Paleogeographic reconstruction have suggested the occurrence of a supercontinent during this time period and rhythmites that have been described occur in stratigraphic proximity to tillites. Global tidal response and glacio-eustatic flux may have affected rhythmite occurrences during the Late Proterozoic. Thus, broad-scale similarities may exist regarding controls on Proterozoic and Carboniferous cyclical rhythmites.

Analysis of U.S. Mid-Continental rhythmites and field work in the Bay of Fundy analogs were funded by NSF grant EAR-9405123. Analysis of Proterozoic rhythmites in Utah and modeling were funded by NSF grant EAR-9316177.

Abstract: Within the cyclical Pennsylvanian-age succession of the U.S. Mid-continent, a number of Fossil Lagerstatten occur within incised valley fills (IVFs). These Lagerstatten contain a variety of well-preserved terrestrial plants, articulated fish (particularly acanthodians and xenacanths), and reptiles. Although the fossil evidence has traditionally been used to infer freshwater deposition, the IVFs were formed predominantly within fluvio-estuarine to brackish marine facies of the lowstand systems tract (LST). That is supported by widespread occurrence of acanthodian scales and xenacanth teeth in marine sediments.

The IVFs are related to the high degree of eustatic flux that characterizes cyclothems of this period. During sealevel lowstands, rivers incised drainage networks that were subsequently filled during base-level rise. Depth and lateral extent of paleovalley incision of the IVFs is defined from outcrops and wireline well logs. Core analysis indicates that estuarine facies, including cyclic tidal rhythmites, tidal bedding, and mud-draped bedforms, are common in the IVFs.

In Kansas there are both small- and large-scale IVFs. The small IVFs, such as the Hamilton and Garnett localities, have paleovalleys that are less than 1 km in width and incised less than 10 m deep. These contain a significant amount (>30%) of carbonate sediments. Their fossil flora and lack of regionally derived siliciclastics suggest that they were formed during relatively drier paleoclimates.

Conversely, large IVFs, such as those that characterize the Douglas Group of Kansas, are about 10 km in width and exhibit 10s of m of incision into older strata. The fill is dominated by distal-source siliciclastics, contains thin coals, and has estuarine lithofacies containing sideritic concretions with well-preserved fossils. The extrabasinal siliciclastics and associated coals suggest that they were formed during relatively wetter paleoclimates.

Abstract: The record of Late Carboniferous fauna in the sea cliffs of the classic Joggins section has been formative in interpreting Late Paleozoic paleoecology. Recorded are 29 taxa representing 14 invertebrate orders, including foraminifera, polychaete worms, two mollusc, and 10 arthropod orders, and a similar number of taxa from eight fish and five tetrapod orders. Hitherto unreported finds include representatives of 3 new orders: Xiphorsaurida, Scorpionida and Megasecoptera. The vertebrate ichnotaxa record, perhaps the most prolific of the pre-Permian, include 16 cm wide footprints of a previously unknown leviathan, which doubtless was the top predator at Joggins. Recent palynostratigraphy has pushed back the age of these fossil occurrences to the late Westphalian A (late Lower Pennsylvanian).

The paleoecology of this rich biota has undergone little comprehensize scrutiny in recent decades. Although the section clearly in terrestrial in origin, sedimentological, trace- and microfossil evidence suggests that the limestone and bivalve-bearing source beds of an aquatic fauna that includes xenacanth and ctenacanth sharks, ray-like fishes, limulids and spirorbids may record rising sea level within or beyond the basin. The long cherished theory that hollow lycopsid trees acted as pitfalls for blundering tetrapods is not easily reconciled with the nature of their occurrence within fossil trees. Examination of type specimens at the British Museum (Natural History) and Redpath Museum, field observation and review of Dawson's discoveries point strongly to the role of wildfire and to the hollow trunks as ecological niches.

Partial Abstract: The Middle to Late Proterozoic Big Cottonwood Formation, north-central Utah, contains the oldest known (~900 Ma) example of cyclical tidal rhythmites. Despite mild metamorphic overprinting, there is excellent preservation of sedimentary structures. The thick formation (5 km) has been previously interpreted as shallow marine, but recent work suggests deposition in a tide-influenced estuary.

Important diagnostic tidal features recognized in the Big Cottonwood Formation include: 1) heterolithic tidal rhythmites, 2) current ripples with crests rounded by backflow, 3) sigmoidal bundles, and 4) abundant, clay-draped, reactivation surfaces. Other structures which corroborate the tidal interpretation include: 1) flaser bedding, 2) mud cracks, and 3) mud-draped wave ripples.

Tidal cyclicities in the formation occur with a variety of periodicities: 1) daily (semidiurnal to diurnal), 2) semi-monthly (neap-spring) cycles, 3) monthly cycles, and 4) longer term semi-annual to annual cycles. Daily rhythms and neap-spring cyclicities are best distinguished in the black siltite facies, yielding continuous records for periods of 4-10 years. Annual cycles are best distinguished in the transitional greenish gray siltite facies of the large-scale vertical sequences. Harmonic analysis of rhythmite thicknesses provide constraints on lunar recession rates over the past 900 Ma.

Partial Abstract: Cyclic rhythmites are diagnostic features of tidal sedimentation. Cyclic rhythmites show (1) repetitive vertical thickening and thinning of alternating sandstone-shale laminae couplets, (2) a similar, repetitive number of laminae between sandstone-thickness maxima, and (3) a sinusoidal thickness distribution related to the lunar orbital cycle. Cyclic rhythmites in Pennsylvanian, shallow-water tidal facies of the eastern and mid-continent United States, typically have ranges of couplet values suggesting diurnal to semidiurnal paleotidal systems. Although numerous examples of Carboniferous cyclical rhythmites have been noted, noncyclic rhythmites, which show only partial or amalgamated neap-spring cycles, are much more common. These noncyclic rhythmites are inferred to have been deposited in tidal environments in which the rate of sediment accumulation and reworking exceeded accommodation space. At any single location, the contact between cyclic and noncyclic rhythmites marks the loss of accommodation space in that depositional sequence.

Abstract In order to better understand the original depositional environments of some Carboniferous siltstones in eastern Kansas, analysis of a potentially suitable modern analog was undertaken. Since the Carboniferous siltstones may have formed within macrotidal estuarine environments, we studied sediment accumulation upon silt-rich estuarine bars within the upper intertidal reaches of the Bay of Fundy, Nova Scotia, Canada. Data collected included current speed, water salinity, heights of the tides, and rates of sediment accumulation.

An interesting aspect in the Bay of Fundy is the high rate of silt accumulation. Over the 2-day period monitored, accumulation rates averaged about 1 cm per day. Detailed analysis of rates of accumulation indicate that most of the silt is deposited within a matter of minutes following the rising, flood tides. Although the rates of sediment accumulation are very high, the total duration of tidal immersion is relatively low. In the areas studied, high tides covered the bar for only slightly longer than 1 hour. In addition, although tidal processes control sedimentation, the waters are only of relatively low salinity and oscillate between being fresh and brackish.

Cyclical patterns of lamination thickness in the modern analog bear many similarities to the Carboniferous siltstones of Kansas. In addition, markings made within the sediment by modern organisms also exhibit many similarities to trace fossils in Kansas rocks. Thus, by comparison to the modern analog, these Kansas siltstones appear to share many similarities to the Bay of Fundy analog regarding modes of sediment accumulation and interactions of organisms within the sediment.

Analysis of U.S. Mid-Continental rhythmites and field work in the Bay of Fundy analog were funded by NSF grant EAR-9405123. (1) denotes undergraduate geology major at Kansas State University.

Abstract: Cyclic tidal rhythmites are small-scale (mm to cm) sedimentary features consisting of: (1) lamination of mud deposited during the still-stands at high and low tide, alternating with (2) coarser silt and sand deposited between flood and ebb tides, when higher flow rates where encountered. Some controversy persists regarding whether these types of rhythmites are reliable indicators of tidal environments; to date laminae-thickness periodicities have been relied upon to provide evidence of tidal controls during deposition.

At a finer scale of analysis, the use of microfabric analyses of the particle-to-particle contacts of clay within the rhythmite muds can offer an additional tool in determining their potential tidal origin. Mud laminae within suspected tidal rhythmites of both the Pennsylvanian-age Stranger Formation of eastern Kansas and the Late Precambrian-age Big Cottonwood Formation of Utah display the randomly oriented microfabric characteristic of flocculated muds. In modern settings, such fabric typifies estuarine environments. Within such estuarine settings, rapid deposition of flocculated muds would account for the high accumulation rates prediced by cyclic tidal rhythmite models. These very high sedimentation rates, which are much higher than would be allowed by Stoke's Law for clay particle settling, have previously been difficult to reconcile with the fine-grained lithology of the rhythmites. Other features, such as lack of bioturbation and biogenic microfabrics, offer additional indications of high rates of deposition within the Pennsylvanian-age cyclic tidal rhythmite.