I. Uniqueness of record of the region

II. Terminology cyclic - any series of events or conditions which is repeated with constancy of pattern may be definable in terms of a cycle whether regular (rhythmic) or irregular in time.

• exhibits constancy of arrangements of phases (cyclic); whereas, the regularity of recurrence constitutes rhythm.
  
• A major distinction of late Paleozoic sedimentation cycles from simple alternations of rock types which may be cyclic is - the presence of far grater diversity of lithologic and paleontologic components!
• phase - each distinguishable element in a cyclic succession, each denoting a combo of physical and biological conditions
• cyclothem - deposits of a single sedimentary cycle of interrelated phases associated with a landward-and-seaward oscillation of the strandline. (Weller, 1930).
• megacyclothem - strata belonging to a group of successive sedimentary cycles which exhibit regularity of occurrence in sequence, with each cyclothem marked by distinctive characters (Moore, 1936).
  
  III. General Characteristics of late Paleozoic cyclic sedimentation.

• - recognized in upper Mississippian, Pennsylvanian and lower Permian (see overhead)
• - cycle normally consists of: (from base up) a. lower coarse clastics, often disconformable, generally sandstone b. fine materials c. coal bed d. marine sediments (shale or limestone) e. reappearance of non-marine deposits (:.regression to end cycle)
• cycles represent oscillatory shafts of strand line!

IV. Distribution: Kansas, Nebraska, Iowa, Missouri, Oklahoma (N)
Increase in clastic unit thickness to the south, particularly in Pennsylvania

• - carbonate units more widely separated by clastics to the south.
• - Southern Oklahoma a region dominated by subaerial sedimentation during late Paleozoic; whereas, shallow seas more or less persistently occupied region farther north.
• - Late Pennsylvania limestone disappear to south - several cycles units can be correlated with units in Illinois and Indiana, and these in turn with cyclic sed. farther east.

V. Specific Characteristics (see overhead)

VI. Significance of Cyclic Sedimentation

• - Oscillatory movement of strand line obvious: marine deposits, coals, plant remains, non-marine in rapid succession
• - a member of phase i.e. environments
• - least understood:
  1. variations in limestone
  2. black platy shale
• - invertebrates, fishes, land plants, high organic carbon
• - evenness of bedding, fine grain
• :. suboxic, weak currents, quiet water although shallow perhaps: marine swamp where seaweed damps wave activity.
• - units contemporaneous or diachronous?
• Why cyclothems of differing character in regularly repeated order?
• megacyclothems - sedimentary record of major seaway fluctuations on which minor advances and retreats of strand line are superposed.
• types depend on paleogeography
• since transgression spread eastward -the main marine phase of an Illinois cyclothem may correspond to the dominant marine cyclothems of Kansas megacyclothem.

VII. Periodicity of cycles.
Mid Pennsylvanian estimates:
Arizona: 352 ka (Connolly and Stanton, 1992)

Other widely separated areas with different tectonic settings and styles of sedimentation:

• 235-400 ka (Heckel, 1986)
• 330-370 ka (Algeo, 1991)
• 230-385 ka (Goldhammer, et al., 1991).
  
  Given the error margins of time scales these still fall within the upper end of the Milankovitch band!!..... eccentricty of the Earth's orbit.

To make such a inference suggests that astronomic variables were the modulators of late Paleozoic ice sheet fluctuations as during the late Pliocene-Pleistocene. Would such be the case in the Paleozoic world?

VIII. Cause.

¥Recent work has resulted in sea-level curves on the order of 60-100 meters.

¥Glacial eustasy is the only major mechanism for global sea-level changes of this magnitude and with the stated periodicity.

A. Estimates of Carboniferous ice volume and sea level response (Crowley and Baum, 1991).

• Based on application of area volume relationships developed for Quaternary ice sheets
• estimates derived for Westphalian (305Ma)
• Three estmates made with different ice extent configurations
• Ice I- 17.9 million sq. km 39.8 million cubic km
• Ice II- 27.2 million sq. km 63.9 million cubic km
• Ice III- 40.0 million sq. km 108.4 million cubic km
  
• Greatest ice in West Gondwana, Antarctica-India-Mad., Australia, Andean
• sea level influence of Ice I (once volume adjusted to a water equivalent by mult. by 91.7% and reducing the sea level equivalent by 28.4% to adjust for the isostatic effects of ice loading on continental shelves) = 45-75m
  
• For comparision these figures are for the max. Pleistocene reconstruction
  Laurentide ice sheet- 11.6 million sq. km
  East Antarctic ice sheet- 10.2 million sq. km 21.8 million sq. km
• Maximum Pleistocene global ice volume- 65.4 million sq. km.
  
  
  B. Estimates of mid-continental Pennsylvanian sea level variations between maximum regressive phase and maximum flooding surface (Klein, 1992).

• magnitude caused by glacial eustacy = 70%
• magnitude resulting from tectonic subsidence = 5-20%
• magnitude caused by long term climate change=up to15%

X. Conclusions

• 1. The continental surface in the United States was mostly just above or below sea level during the late Paleozoic. Because of the lack of relief only slight changes in sea level would produce vast regional changes in inundation or emergence.
• 2. Sedimentation was dominated by cyclic accumulation of varied clastic and calcareous deposits which may be identified over hundreds of km (including units only cm thick).
• 3. Phases of each cycle sequence record advancing and retreating environments.
• 4. Cyclic successions of different ages show divergence of expression (e.g. related to differing subsidence and sediment source rates)
• 5. Some Pennsylvanian and Permian cyclothems (esp. Kansas) have individual peculiarities of expression arranged in repeated constant order - Meglacyclothems.
• 6. Gradual subsidence resulted in maintenance of depositional surface near mean sea level.
• 7. The primary control on sea variations was glacial-eustatic. Estimates of glacial-eustatic sea level change for the Penn. is 60.0m + 15m. Locus of glaciation was in southern Gondwanland.
• 8. In the mid-continental U.S., estimates of water depth between regressive surface and maximum flooding surface exceed glacial-eustatic amount. Some 70% of depth variation is glacial eustatic, 5-20% tectonic subsidence, up to 15% long term climatic change.
• Tectonic influences: Ouachita orogenic reactivation, uplift of Ancestral Rocky Mts, reactivation of Precambrian faults).