Sequence stratigraphic reconstruction of the late Middle Devonian Geneseo Formation of NY, USA: Developing a genetic model for “Upper Devonian” unconventional targets in the Northern Appalachian Basin

Abstract

The late Middle Devonian Geneseo Formation and its lateral equivalents in the northern Appalachian Basin are significant secondary targets to the extensively explored Marcellus Sub-group. Surface to sub-surface characterization of the mudstone-dominated Geneseo Formation combines detailed observations of facies, facies associations, stratal architecture, stratal geometry, and stratal terminations, in combination with geochemical proxies to assess proximal to distal trends and enable prediction of hydrocarbon play element quality and distribution. Correlations within this mudstone-rich succession are conducted at the parasequence-scale, and incorporate detailed descriptions of four drill cores, >100 outcrops, and mapping of >500 wireline logs.The Geneseo Formation herein has been subdivided into two depositional sequences comprising three lithostratigraphic units (i.e., Lower Geneseo, Fir Tree, and Upper Geneseo members respectively). The Lower and Upper Geneseo members show systematic aggradational to progradational parasequence stacking patterns, as well as downlap‒onlap stratal terminations with underlying strata; these members represent highstand systems tracts. The Fir Tree Member occurs between the Lower and Upper Geneseo members, truncates the underlying Lower Geneseo, shows progradational‒aggradational‒retrogradational parasequence stacking patterns, and spans two systems tracts: lowstand and transgressive.Isopach maps were constructed within the high-resolution sequence-stratigraphic framework to better understand thickness trends at the landing-zone scale. Thickness variation across the basin suggests reactivation of basement structures and syndepositional faulting strongly influenced accommodation. Specifically, the N–S trending Clarendon-Linden Fault System appears to have been a western sediment barrier during Geneseo time and the primary depocenter of fine-grained clastics occurs in south-central NY in a structural low. As the Geneseo system advanced, the succession sequentially filled topographic lows from east to west (proximal to distal). Understanding the controls on reservoir quality and distribution of secondary and tertiary targets to the Marcellus can facilitate ranking and prioritization of landing-zones, as well as optimization of well placement for completion design.