DUDKIEWICZ, GEORGE C., Franklin and Marshall College, Lancaster, PA

ABSTRACT: Recognition of Parasequences and their Diagenesis in Cambrian Carbonates, Morgantown, PA

The Upper Cambrian Carbonates of the Conococheague Group in Morgantown, PA, were deposited as cyclic shallowing upward packages, or parasequences. There are eight lithologies present in the study area. The lithologies have been interpreted as representing supratidal, intertidal, inter/subtidal, and deeper subtidal depositional environments. The supratidal environment is characterized by mudcracks contained in micritic mud stone. The intertidal is determined by the presence of stromatolites within a bound stone and cryptalgal limestone/dolomite couplets. The intertidal to subtidal paleoenvironment is characterized by oomicrite packstones, creamy dolomite interbedded with pink dolomite, and a fine-grained, red, friable sandstone. The deeper subtidal zone contains dark grey micrite/pelmi rite and a pure greenish micrite.

Stromatolites, mudcracks, ripple marks, hummocky bedding, dolomite couplets, fenestral algal structures, and ooids are sedimentary structures present in the rocks which were used to delineate paleo-water depths. Four distinct shallowing upwards cycles are present at the Morgantown quarry. The possible forces of autocyclicity, episodic subsidence, and eustatic oscillations all provide mechanisms for the formation of such cycles. Fifth-order shallowing upward parasequences are commonly attributed to Milankovitch-driven sea level changes (Anderson & Goodwin 1982, Osleger & Read 1992), but diagenetic alteration may be useful in determining whether meteoric waters affected marine sediments during relative sea level fall.

Evidence of vadose meteoric and meteoric water diagenesis within the Conococheague Group rocks demonstrates that subarial processes affected the sediments during sea level falls.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.