Allen W. Archer

Daily, monthly, and yearly tidal cycles within laminated siltstones of the Mansfield Formation (Pennsylvanian) of Indiana

Whetstones (laminated siltstones) within the Mansfield Formation of Orange County, Indiana, are Lower Pennsylvanian (Morrowan) tidal deposits characterized by rhythmic laminations. Laminae thicknesses vary systematically in a vertical sequence and reflect tidal events of a mixed tidal regime. So complete is the record of tidal deposition that daily and monthly tidal cycles can be delineated. Neap-spring tides (related to the phases of the moon) and equatorial-tropical tides (related to the declination of the moon) are recognizable within the sequence.

Soft-sediment deformation produced by tides in a meizoseismic area, Turnagain Arm, Alaska

Turnagain Arm is a semidiurnal hypertidal estuary in southeastern Alaska with a recorded tidal range of 9 m. Contorted bedding and flow rolls preserved in tidal sediments within the estuary have previously been interpreted as resulting from the Mw 9.2 Great Alaskan earthquake of 1964. Horizons of flow rolls between undeformed beds in sediments and rock strata have been used to infer ancient earthquakes in other areas. Although many types of soft-sediment deformation structures can be formed by earthquakes, observations of sedimentation on tidal flats in the inner parts of Turnagain Arm in the summers of 2003 and 2004 show that a wide range of soft-sediment deformation structures, similar to those inferred to have been formed by earthquakes, can form in macrotidal estuaries in the absence of seismic shock. During sedimentation rate measurements in 2004, soft-sediment deformation structures were recorded that formed during one days tide, either in response to overpressurization of tidal flats during rapid tidal drawdown or by shear stress exerted on the bed by the passage of a 1.8 m tidal bore. Structures consisted of flow rolls, dish structures, flames, and small dewatering pipes in a bed 17 cm thick. In the future, if the flow rolls in Turnagain Arm were found in isolated outcrops across an area 11 km in length, in an estuary known to have been influenced by large-magnitude earthquakes, would they be interpreted as seismites? These examples show that caution is needed when using horizons of flow rolls to infer paleoseismicity in estuarine deposits because many of the mechanisms (tidal flux, tidal bores, slumping, flooding) that can cause deformation in rapidly deposited, unconsolidated silts and sands, are orders of magnitude more common than great earthquakes.

An Amazon-Scale Drainage System in the Early Pennsylvanian of Central North America

This study compares Morrowan conglomeratic sandstones from three basins in the central North American craton: Central Appalachian Basin (eastern Kentucky), Eastern Interior Basin (Illinois, Indiana, western Kentucky, and lateral extensions in Arkansas), and Hugoton Embayment (Kansas and Colorado) to develop realistic analogues for Morrowan fluvial systems and to compare the relative effects of tectonic subsidence, eustacy, and paleoclimate on sedimentation. Based on paleogeographic reconstruction, the paleodrainage for the Central Appalachian Basin is estimated to have ranged from

Oldest direct evidence of lunar-solar tidal forcing encoded in sedimentary rhythmites, Proterozoic Big Cottonwood Formation, central Utah

1,337,100 km^{2}

Rhythmic Sedimentation in a Mixed Tide and Wave Deposit, Hazel Patch Sandstone (Pennsylvanian), Eastern Kentucky Coal Field

to

Tidal deposits associated with low-sulfur coals, Brazil Fm. (Lower Pennsylvanian), Indiana

2,854,300 km^{2}