HGS General Lunch- How close is geological thought to reality? Insights about geological time, continuity, and rates of change revealed by the Holocene sequence stratigraphy of the Po-River—Adriatic-Sea system, Italy

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Wednesday, May 29
The Petroleum Club of Houston
1201 Louisiana Street, 35th floor, Houston, TX
- If you valet park we can give you a discount coupon, the Petroleum Club does NOT validate parking
Social 11:15 AM, Luncheon 11:30 AM- 1:00 PM
Cost: $35 pre-registered members; $40 for non-members/ALL walk-ups;
$35 for Emeritus/Life/Honorary; $15 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 Wednesday, May 29 at 5:00 AM

Speaker: Kevin Bohacs

How close is geological thought to reality? Insights about geological time, continuity, and rates of change revealed by the Holocene sequence stratigraphy of the Po-River—Adriatic-Sea system, Italy

Kevin M. Bohacs1, Alessandro Amorosi2, Luigi Bruno2, Bruno Campo2, Tina M. Drexler3

1 ExxonMobil Upstream Research Company (retired), now at KMBohacs GEOconsulting LLC

2 University of Bologna, Italy

3 ExxonMobil Exploration Company

 

Two fundamental questions confront a geologist when faced with a stratigraphic succession: How much time is represented by the preserved strata? and How continuous was the sediment accumulation? The vastness of geological time is largely beyond human observation and comprehension. Time spans of “just” tens to hundreds of thousands of years may become unfamiliar when moving from modern, observable, and quantifiable depositional processes to the almost incomprehensible series of moments recorded in the rock record.

We enhanced our experiential concept of time based on the chronologically well-constrained Holocene succession of the Po-Adriatic system, Italy. The parasequences of the highstand systems tract are tens of meters thick and locally constitute up to 95% of the total volume of Holocene deposits. The preserved strata, however, represent only a relatively short time interval (a few hundreds of years) and record < 10% of the total time span involved. Early Holocene (9.2 to 7.7 ky bp) transgressive shorelines retreated at a mean rate of ~10 m/y, following a stepped trajectory at the centennial scale. At the transition from aggradation to progradation (ca. 7.0 ky bp), a laterally extensive prograding deltaic body, up to 30 m thick and > 20 km long downdip, accumulated in less than 2,000 years. Both phases involved rates of change up to three orders of magnitude larger than those observed in the last two centuries.

Parasequences of similar size in the rock record are commonly interpreted to have developed at slower rates over longer temporal scales, based on coarser-resolution chronometry and the assumption that stratal thickness equals time duration. However, severe misconceptions can be generated by using the common approach that subdivides an arbitrary thickness of strata into equal parts and durations. In the Holocene succession of the Po Plain, very short periods of very rapid sedimentation alternated with long phases of non-deposition, erosion, or stratigraphic condensation, recorded at bounding surfaces of individual parasequences. The bounding surfaces represent at least 90% of the entire time span of the Holocene and are associated with distinct rock properties.

The highly fragmented nature of the sedimentary record impacts the interpretation of hierarchical stacking of parasequences, time scales of accumulation of ancient strata, and inherent rates of change of alluvial and deltaic depositional systems. We illustrate these consequences by comparing the Holocene Po-Adriatic stratigraphy to older strata, including the middle Pleistocene of the Enza River region, Italy and the Cretaceous Blackhawk and Mancos formations, Book Cliffs, Utah. All of these observations and considerations reinforce a key foundation of sequence stratigraphy: that surfaces are just as significant as the strata they bound…if not more so.

 

Kevin Bohacs Sc.D. FGSA FGS FRGS recently retired as Senior Research Scientist from ExxonMobil Upstream Research Company where he led the application of sequence stratigraphy and sedimentology to mudstones from lacustrine to deep-marine environments. He now operates KMBohacs Geoconsulting LLC. Kevin is an Eagle Scout and earned a B.Sc. (Honors) in Geology from University of Connecticut and Sc.D. in Experimental Sedimentology from Massachusetts Institute of Technology.

 

He has written more than 100 scientific contributions on the stratigraphy and sedimentology of mudstones, hydrocarbon source and reservoir rocks, and continental depositional systems (lakes, fluvial-floodplain systems, paleosols, coals, and paleoichnology). Dr. Bohacs is the co-author and editor of books on sequence stratigraphy, lacustrine hydrocarbon reservoirs, and field safety. (He is writing a second edition of the field safety book.)  He has received many best paper citations and awards (including AAPG Honorary Member and AAPG’s Berg award for outstanding research) and served as distinguished lecturer for several societies nationally and internationally. He currently serves as Secretary-Treasurer for SEPM.

He has written more than 100 scientific contributions on the stratigraphy and sedimentology of mudstones, hydrocarbon source and reservoir rocks, and continental depositional systems (lakes, fluvial-floodplain systems, paleosols, coals, and paleoichnology). Dr. Bohacs is the co-author and editor of books on sequence stratigraphy, lacustrine hydrocarbon reservoirs, and field safety. (He is writing a second edition of the field safety book.)  He has received many best paper citations and awards (including AAPG Honorary Member and AAPG’s Berg award for outstanding research) and served as distinguished lecturer for several societies nationally and internationally. He currently serves as Secretary-Treasurer for SEPM.

When
May 29th, 2019 11:15 AM   through   1:00 PM
Location
The Petroleum Club of Houston, Total Plaza Building
1201 Louisiana St
Houston, TX
United States
Event Fee(s)
Member $ 35.00
Non-Member $ 40.00
Emeritus/Honorary Life $ 35.00
Student $ 15.00
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