253-4 Subsurface Conodont Biostratigraphy of Lower-Middle Devonian (Emsian-Middle Givetian) Grand Tower and Lingle Formations, Illinois Basin

Session: Conodonts from North America and Beyond - Honoring the Career of Dr. James E. Barrick

Presenting Author:

Authors:

Abstract:

Lower-Middle Devonian carbonate platform strata in the central and southern Illinois Basin are included in the Bailey, Backbone-Clear Creek (undifferentiated), Grand Tower and Lingle formations, overlain by Middle-Upper Devonian shales of the Blocher Member of the New Albany Shale.  Here we report results on the conodont biostratigraphy of the Grand Tower and Lingle formations penetrated by one six inch and two four-inch diameter cores housed at the Illinois State Geological Survey (ISGS).  These are the ISGS White County, and Story and Brown cores.  All were drilled in White County, southeastern Illinois and are housed at the ISGS core library in Champaign, Illinois. The Grand Tower and Lingle formations were sampled continuously in the White County core.  Ninety-three samples were taken from the Lingle and Grand Tower sections available in ISGS Brown (54) and Story (39) cores. The Blocher Member of the New Albany was sampled at and above its contact with the Lingle in the Brown and Story Cores.  All but one carbonate sample yielded conodonts, and samples from thin sandstones in the basal 1-2 m of Blocher Member (basal New Albany) did not yield conodonts.

            The Dutch Creek Member of the Grand Tower spans most of the Emsian Stage (Lower Devonian) with a fauna dominated by Latericriodus (L. nevadensis, L. alces, L. robustus). The Lower-Middle Devonian boundary is identified in the upper Dutch Creek by the first appearance (FA) of P. partitus (= partitus Zone). The overlying Haunted House Member (=un-named upper member) of the Grand Tower is entirely Eifelian age.  The Eifelian-Givetian boundary (=base hemiansatus Zone) is identified in the lower Lingle by the last appearance (LA) of Icriodus michiganus, immediately followed by the FA of I. arkonensis. The successive FAs of I. brevis and P. varcus identify the bases of the timorensis and varcus zones in the lower Lingle. The LA of I. obliquimarginatus succeeded by the FA of P. ansatus identify the ansatus Zone in the middle of the Lingle.  Samples in the Brown and Story cores from the upper Lingle at and just below the contact with the Blocher Member contain abundant conodonts including I. brevis, I difficilis, L. l. latericrescens, and P. l. linguiformis gamma morphotype, P. varcus and P r. rhenanus.  These indicate the upper Lingle and overlying Blocher are no older than ansatus Zone. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11142

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