Recognition of regional lithologic marker beds is accelerated by refined mechanical logging techniques and adequate drilling density. These correlative "punctuations" are considered to be geologically instantaneous, and to yield time surfaces bounding reliable

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stratigraphic units. The enclosed units represent longer intervals of time, and their lithologic gradations represent the diluted total environmental impress.

Markers represent (1) widespread, essentially contemporaneous deposition of thin lithologic components, and (2) virtually contemporaneous contact phenomena resulting from halmyrolic chemical alteration, replacement, and syngenetic emplacement proximal to the sediment-water interface during times of non-deposition. Time markers may indicate such short-interval lithologic inflictions as changes in water depth, climatic variations, migration of shoreline, and influx of suspensoids with chemical or physical character sharply differing from that of sediments within the body of the marker-bounded unit. Unit thickness of sediment deposited at any locale is dependent on sediment availability, fluxes of the scattering agent, rate of regional variation in chemical impress of depositing medium, nd amplitude of local and regional structural change.

Lithologic variations occur in any unit, but the mechanical-log characters of the units are remarkably consistent through an entire sedimentary basin. If log character of unit sequence is similar, one may consider the unit to be areally equivalent not only in duration but in simultaneity. Log character is a function of space and environment, and the time markers signal massive changes in the vertical continuity of these environmental controls.

Stratigraphic analysts are able to use these "time slices" to create isopachous and lithofacies maps of short-interval synchronous units. These maps are rigidly controlled for unit initiation, termination, and time span. Thickness variations represent a measure of competitive sedimentation resulting from an interplay of environmental factors which involve the allogens and syngens in sedimentary prisms of a marine basin. Paleontologic and sedimentologic characteristics in these geosynchronous units yield environmental and geographic patterns important in the delineation of porosity trends. Geosynchron maps permit analysis of intra-basin structural growth which influences first-phase oil migration. Time-length vacuity becomes susceptible to quantitative analysis.

If the generally accepted concepts of uniformitarian geology are approximately correct, these maps systematize haphazard lithologic patterns into geographic and time-controlled stratal units whose internal characteristics make it possible to determine rates of sedimentation, facies gradation, lateral intensities of environmental impress, origins of sediments, depth of water, distance to shore, and a host of other sedimentational variables not otherwise easily susceptible to quantification.

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