Modern and Fossil Bathymetric Data: Application to Exploration in the Nile Delta, Egypt

By

 Tarek M. Afifi¹, David Pocknall², Ali A. Sabour¹, Anthony Gary³, John C. Dolson¹

(1) BP Egypt, Cairo, Egypt (2) BP America Inc., Upstream Technology Group, Houston, TX (3) Energy & Geosciences Institute University of Utah, Salt lake City, UT

 Understanding depositional environment and paleobathymetric relationships of Miocene to Pleistocene sediments in the Nile Delta, Egypt is vitally important in constructing a sequence stratigraphic framework for the basin, and predicting seal and reservoir fairways. Paleobathymetric interpretations routinely use benthic foraminiferal distributional data and planktonic-to-benthic ratios as proxies for water depth. Foraminiferal (benthic and planktonic) distributional data are largely correlated to water depth and to some degree other factors (e.g., freshwater supply). Understanding the distribution of present day faunas and linking them to their fossil counterparts is the most direct method to model environmental relationships in the fossil record. A recent study of 112 piston cores collected in water depths ranging from 70 to 2863 meters in the off shore modern Nile Delta has provided local ground truth data needed to interpret water depth changes for the Miocene/Pleistocene Nile Delta.

With these modern benthic foraminiferal data as a reference the Integrated Paleontological Systems (IPS) software was used to calculate the most likely paleowater depth, and the minimum and maximum water depths for each sample. IPS produced log format output that was particularly beneficial in its ease of integration with other geoscience data - petrophyscial and geophysical. Trends (shallowing and deepening) in the paleobathymetry curve indicate significant changes in the depositional environment and enabled us to better understand the development of parasequence sets.

In addition to estimates of paleowater depth, IPS allowed analysis of faunal discontinuities (dramatic excursions) using a cosine-theta calculation that detected and helped to define stratigraphic boundaries. Discontinuities could further be classified as local or regional events or sampling artifacts by calculating separately for the benthic and planktonic components.