Wednesday, September 27
The Petroleum Club of Houston
1201 Louisiana Street, 35th floor, Houston, TX
- If you valet park PCOH will provide a discount coupon, the Petroleum Club does NOT validate parking
Social 11:15 AM, Luncheon 11:30 AM- 1:00 PM
Cost: $50 pre-registered members, Emeritus, Honorary Life; $60 for non-members and ALL walk-ups;

To guarantee a seat, you must pre-register on the HGS website and pre-pay with a credit card.  You may walk up and pay at the door if extra seats are available.  Please cancel by phone or email within 24 hours before the event for a refund.  

Special Cretaceous-Stratigraphy Double Header Featuring Two Amazing Talks

Regional Sequence Stratigraphy and Facies of the Upper Cretaceous Austin Chalk in South and Central Texas and Evolution of the Maverick Basin and San Marcos Arch  

Dr. Christine Griffith, Ph.D Texas A&M University, College Station TX

A regional sequence stratigraphic framework, based on well-log correlations, outcrop and core observations, and new detailed nannofossil biostratigraphy from three wells across the San Marcos Arch, indicates that Upper Cretaceous Austin Chalk consists of three asymmetric, unconformity-bound, composite stratigraphic sequences.  Sequence boundaries are recognized in core by hardgrounds, firm grounds, and lithoclasts, overlain by transgressive glauconitic skeletal packstone beds that coincide with biostratigraphic hiatuses. Glauconitic units have distinctive character in well logs, can be widely correlated, and overlie angularly truncated beds.

The lowest sequence AC–I (upper Turonian–middle Coniacian) is very thick west of the San Marcos Arch but is almost completely truncated in the eastern study area (like the underlying Eagle Ford Group). Sequence AC–II (upper Coniacian–upper Santonian) is very thick east of the San Marcos Arch but is eroded in the center and on the west side of the arch.  Sequence AC–III (upper Santonian–lower Campanian) thins over the arch and is thicker to the east. Downdip, the Austin Chalk thins dramatically toward the relict Lower Cretaceous Edwards margin in south Texas. This geometry is interpreted as a depositional ramp, based on coincident thickening of the overlying Anacacho Formation and facies and markers within the Austin Chalk.  The ramp formed due to strong subsidence toward the Gulf of Mexico, with greater planktonic productivity updip, and non-deposition or erosion downdip. 

The stratigraphic framework in this study ties the different stratigraphic nomenclature of the major producing petroleum fields on either side of the San Marcos Arch and the outcrop.  Petroleum reservoirs occur across multiple depositional settings but typically are older west of the San Marcos Arch than to the east.  Paleogeographic maps show that water circulation between the Gulf of Mexico and the Western Interior Seaway switched from south Texas to east Texas during the Santonian. 

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Unraveling the “Eaglebine”: A Sequence Stratigraphic Framework for the Eagle Ford Group in the East Texas Basin

Speaker: Art Donovan, Texas A&M University with  P. Johnson, S. R. Gifford, M.J. Meyer, S. Dangtran, L. Evans, and M. Pope Texas A&M University: Department of Geology and Geophysics

Geochemical data indicate that the “Eaglebine Resistivity Zone” in the Southern East Texas Basin (SETB) is a Ca- and TOC-enriched mudstone.   Previous researchers had assigned and interpreted this unit as either the: 1) basal Pepper Shale, coeval to the Woodbine Freestone Delta; or 2) Maness Shale of the Washita Group, which predates the Woodbine Group.   Along the outcrop belt to the northwest, similar mudstones occur at the base of the Eagle Ford Group and overlie Al-rich and TOC/Ca-poor mudstones of the Woodbine Group.  

In order to resolve this juxtaposition in the facies succession between the outcrop belt and subsurface of the SETB, a detailed sequence stratigraphic study, including a grid of well-log cross sections,  as well as  geochemical data from key cored wells, was constructed.   This sequence stratigraphic analysis indicates that: 1) a major regional unconformity separates the Woodbine from the Eagle Ford Groups across the study area, 2) the “ Eaglebine Resistivity zone” in the SETB overlies this unconformity and correlates to the Middle to Late Cenomanian Lower Eagle Ford Formation along the outcrop belt to the west; and 3) the classic “top resistivity marker” overlies a sequence boundary. which defines the base of the Upper Eagle Ford Formation.   Across the study area, Lower Eagle Ford Ca- and TOC-enriched mudstones, unconformably overlie Al-rich, TOC-/Ca-poor, low-resistivity mudstones of the Pepper Shale (Woodbine Group/Freestone Delta), and are overlain unconformably by the Al-rich, TOC-/Ca-poor Lower Member of the Upper Eagle Ford Formation (Harris Delta).    Based on sequence stratigraphic analysis it is now clear that the bulk of the “Eaglebine” in the SETB, is actually the Eagle Ford Group.