K.M. Bohacs¹, J.E. Neal¹, A.R. Carroll², D.J. Reynolds¹
(1) Exxon Production Research Co, Houston, TX
(2) University of Wisconsin, Madison, WI

Abstract: Lakes are not small oceans! —sequence stratigraphy in lacustrine basins

Contrasts among lake and marine systems make it inap-propriate to apply one unmodified marine sequence-stratigraphic model to all lake systems. The sequence-stratigraphic approach— looking at a hierarchy of rock packages bounded by various types of surfaces— works very well with lake strata. However, the expression of depositional sequences varies as a function of lake depositional system — just as shallow marine-carbonate sequences differ from shallow-marine-siliciclastic sequences. Indeed, one lacustrine model is not applicable to all lake-basin types.

Lakes differ from oceans in several significant ways, most notably: 1. Lake levels vary more widely and rapidly than sea level, hence, shoreline strata are commonly poorly developed and relatively thin. 2. Lake level and sediment supply are often closely linked in lake systems (most marine models assume no linkage). These differences strongly influence the expression of depo-sitional sequences and the occurrence, distribution, and character of hydrocarbon source, reservoir, and seal play elements. Sequence boundaries vary by lake-basin type, from non-existent or minimally developed, through extensive erosion and incised-valley formation, to large basinward shifts and widespread exposure. Flooding surfaces are enhanced as they are commonly coincident with decreased sediment supply.

Lowstand systems tracts vary from aggradational stacks of basin-floor turbidite strata to basin-center evaporites surrounded by extensive desiccation surfaces. Transgressive systems tracts vary from thick and coarse-clastic prone to thin and shale prone. Highstand systems tracts range from obliquely progradational clastic shoreline parasequences to aggradational carbonate shoreline parasequences. Recognizing these differences is essential to successful exploration and exploitation in lake basins.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana