HGS Northsiders' Luncheon - Organic-rich Woodford Shale deposits and the spread of vascular plants during the Late Devonian

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Total Seats: 64 Reserved: 1
Tuesday, March 20, 2018
Southwestern Energy
10000 Energy Dr. Houston TX
Social 11:15 AM, Luncheon 11:30 AM
Cost: $30 pre-registered members; $40 for non-members/ ALL walk-ups (Credit Cards Accepted);
$25 for Emeritus/Life/Honorary; $10 for HGS student members if pre-registered and pre-paid.

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.  Online & pre-registration closes Monday, March 19, at 5:00 a.m.

Speaker:  Carlos Molinares-Blanco
Ph.D. Student, University of Oklahoma

Organic-rich Woodford Shale deposits and the spread of vascular plants during the Late Devonian

The Late Devonian is a period characterized by the widespread accumulation of organic-rich black shale deposits in North America. The Woodford Shale in Oklahoma is a good example of these type of accumulations (Algeo et al., 2007). The Woodford is generally characterized as organic rich, black shales deposits, accumulated during the presence of anoxic/euxinic conditions, in circulation restricted and relative shallow (epicontinental) marine paleo-environments (Miceli-Romero and Philp, 2012; Slatt et al., 2012; Turner et al., 2015). It is one of the most prolific oil and gas resources in North America and it has been estimated a total of 22 billion barrels of bitumen and 16 billion barrels of saturated hydrocarbons expelled from the Woodford across the central and southern areas of Oklahoma (Comer and Hinch, 1987).

During Late Devonian vascular plants appeared on continental dry land areas as well as trees with complex root systems that are preserved on fossil record (Algeo and Scheckler 1998; 2001). The continental plants increased in size from two evolutionary innovations: The arborescence or tree-sized high and second, the development of seed habit (Fig. 1). Primitive plants include Lycopods, Cladoxylaleans and Progymnosperm trees and other plants related to the oldest vascular plants on earth, including the Archaeopteris spp, which petrified silicified tree logs are commonly well preserved on Woodford Shale outcrops in Oklahoma (Cardott and Chaplin, 1993).

Eutrophication occurs when marine (or lake) ecosystems experience an excess of nutrients that stimulates the excessive growth of primary producers creating anoxic sea bottom conditions  conducive to the accumulation of organic-rich, black shale deposits (Passey et al., 2010). Changes in the weathering processes due to the spread of vascular land plants in late Devonian has also been related to increase flux of river-borne nutrients into epicontinental seas, producing a subsequent eutrophication and oceanic-bottom anoxia (Algeo et al., 1994).

The spreading of vascular plants and the enhanced chemical and physical weathering rates are associated with a significant decline in atmospheric CO2 levels (Fig. 2) and the extinctions of corals and stromatoporoids reef-builders during that period (McGhee, 1996). The sequestration of significant atmospheric CO2 levels is also related to positive Carbon isotopic excursion events described for the Frasnian/Famennian (F/F) (Lower and Upper Kellwasser events), and the Devonian/Carboniferous (D/C) boundaries (Hangenberg event) (e.g. Walliser 1996; Joachimski et al., 2002; Saltzman 2005).

This work shows a compilation of d13C stable isotopes, biomarkers, palynology, thin sections, XRD and XRF element compositional analysis from Woodford Shale rocks cored by the Wyche-1 well, Lawrence Uplift, Pontotoc Co., Oklahoma (Slatt et al., 2012). The core is subdivided into Welden Shale and Lower, Middle and Upper Woodford intervals and nine (9) lithofacies are identified based on core, XRD, XRF and thin section analysis (Fig 3). The facies are grouped on regressive-transgressive cycles, based on Total Organic Carbon (TOC) and gamma ray contents, and ratios between continental (pollen grains) and marine algaes (tasmanites + acritachs) palynomorph assemblages.  

A series of positive isotopic Carbon excursion events identified in some samples from the Middle and Upper Woodford Shales were correlated with the Kellwasser (F/F Boundary) and Hangenberg (D/C Boundary) anoxic events (Fig 4) using temporal constraints of conodont assemblages reported from adjacent localities (Over, 1992, 2002). The permanent anoxic/euxinic sea water conditions during the accumulation of the Middle Woodford Shale, based on the presences of C40 Carotenoids and Aryl-Isoprenoid biomarker compounds (Miceli-Romero and Philp, 2012; Connock 2015), and the positive isotopic excursion events support the idea that the organic-rich, Middle Woodford Shale interval is related to the F/F anoxic event(s) described globally and possibly associated with the spreading of vascular plants during the same period.

Carlos E. Molinares Blanco is a PhD student at the University of Oklahoma in the Institute of Reservoir Characterization. He worked as South Texas development geologist for ConocoPhillips (2013-2015) focused on integrating geological, geophysical and historical production data for characterizing complex unconventional tight-gas reservoirs. He was responsible for OGIP/OOIP mapping, analyses of prospective intervals for supporting recompletion and propose new drilling locations. Prior to joining ConocoPhillips, he worked for Ecopetrol (Bogota – Colombia) as an exploration geologist for from 2007-2011. He was responsible for regional studies, prospect identification, acreage acquisition and evaluation of new ventures opportunities in offshore basins; including Guajira, Sinu and Cayos Basins (Colombia), Santos and Espiritu Santo Basins (Brazil) and projects from the Green Canyon area, Gulf of Mexico (USA). Carlos received a B.S. degree in geology (with distinction) from the Universidad Nacional de Colombia (Bogota, Colombia) in 2004, an M.Sc. in Earth Sciences from Universidad EAFIT (Medellin, Colombia) in 2007, and he also received an M.Sc. and Ben Hare outstanding thesis award by the University of Oklahoma on May 2013. Carlos is interested on unconventional reservoir characterization, particularly understanding the origin and controls on the distribution of anoxic global events, including the Selli (OAE1) and Bonarelli (OAE2) Cretaceous events, and the Late Devonian, Kellwasser and Hangenberg events. Carlos is author/coauthor of more than 20 publications and presentations on AAPG, SEG, URTEC, SIPES, HGS and GSA.



Algeo,T. J., Berner, R. A., Maynard, J. B. & Scheckler, S. E. 1995 Late Devonian oceanic anoxic events and biotic crises: rooted in the evolution of vascular land plants? GSA Today 5, 45, 64-66.

Algeo, T.J., Scheckler, S.E. and Maynard, J.B., 1998, Terrestrial-marine teleconnections in the Devonian: Links between the evolution of land plants, weathering processes, and marine anoxic events: Royal Society of London Philosophical Transactions (B): Biological Sciences, v. 353, p. 113-130.

Algeo, T.J., and S.E., Scheckler, 2001, Land plant evolution and weathering rates changes in the Devonian. Journal of Earth Science, v. 21, Supplement 1, p. 75-78.

Algeo, T.J., Lyons, T.W., Blakey, R.C., and Over, D.J., 2007, Hydrographic conditions of the Devonian-Carboniferous North American Seaway inferred from sedimentary Mo-TOC relationships: Palaeogeography Palaeoclimatology Palaeoecology, v. 256, p. 204-230

Bergman, N.M., Lenton, T.M., and Watson, A.J., 2004, COPSE: a new model of biogeochemical cycling over Phanerozoic time. American Journal of Science, v 304, p. 397-437.

Berner, R. A., and Kothavala, Z., 2001, "GEOCARB III: A revised model of atmospheric CO2 over Phanerozoic time". American Journal of Science, v. 301 (2): 182.

Cardott, B.J., and Chaplin, J.R., 1993, Guidebook for selected stops in the western Arbuckle Mountains, southern Oklahoma: Oklahoma Geological Survey Special Publication 93-3, 55 p.

March 20th, 2018 11:15 AM   through   1:00 PM
Southwestern Energy
10000 Energy Dr.
Spring, TX 77389
United States
HGS Member $ 30.00
Non-Member $ 40.00
Emeritus/Life/Honorary $ 25.00
Student $ 10.00
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contact Email ian.mcglynn@bhge.com

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