Sergio Andò

A detrital record of the Nile River and its catchment

This research uses analyses from Nile catchment rivers, wadis, dunes and bedrocks to constrain the geological history of NE Africa and document influences on the composition of sediment reaching the Nile delta. Our data show evolution of the North African crust, highlighting phases in the development of the Arabian–Nubian Shield and amalgamation of Gondwana in Neoproterozoic times. The Saharan Metacraton and Congo Craton in Uganda have a common history of crustal growth, with new crust formation at 3.0 – 3.5 Ga, and crustal melting at c. 2.7 Ga. The Hammamat Formation of the Arabian–Nubian Shield is locally derived and has a maximum depositional age of 635 Ma. By contrast, Phanerozoic sedimentary rocks are derived from more distant sources. The fine-grained (mud) bulk signature of the modern Nile is dominated by input from the Ethiopian Highlands, transported by the Blue Nile and Atbara rivers. Detrital zircons in the Nile trunk are predominantly derived from Phanerozoic cover rocks. Most detritus from the upstream White Nile is trapped in the Sudd marshes and contributes little to the Nile trunk. Therefore, the White Nile downstream is dominated by locally derived Phanerozoic cover. The White Nile proximal to the Gezira Fan is influenced by the fans Blue Nile signature. Supplementary material: Sample information, analytical methods and data tables are available at https://doi.org/10.6084/m9.figshare.c.3569490

A New Frontier Technique for Nano-analysis on Flooded Chalk - TERS (Tip Enhanced Raman Spectroscopy)

Understanding the chalk-fluid interactions at the sub-micron scale is one of the most challenging goals in Enhanced Oil Recovery. The grain size of newly grown minerals far below 1 micron asks for a high performing imaging: we present a new methodology using the TERS (Tip Enhanced Raman Spectroscopy), a new frontier technique that combines Raman Spectroscopy with Atomic Force Microscopy, allowing impressively high-resolution chemical analyses down to an outstanding spatial resolution (~ 20 nm). TERS permits the recognition of minerals thanks to the vibrational mode peaks that are diagnostic of composition and structure. Carbonate-group minerals are easily identified by Raman spectroscopy. First analyses allow us to state that magnesite and calcite could be identified in, respectively, ultra-long-term flooding experiments of chalk at reservoir conditions and in unflooded samples; no dolomite or high Mg-calcite have been found. Few microns squared areas have been imaged by AFM using ultra polished thin sections with a 50 nanometers step. Transmission electron microscopy has been employed to confirm the results of TERS and add dark and bright field grain-imaging to the investigations. This confirms the need for high-resolution methodology such as TERS and TEM to fully understand EOR effects at sub-micron scale.

A New Provenance Tool for the Exploration of Unconventional Plays - The Provenance and Mineralogy of Silt

Provenance analysis has traditionally focused on sandstones, which are much easier to analyse than conglomerates - which must be analysed in the field with limited tools - and mudrocks - which cannot be dealt with easily with classical optical methods. However, it is important to recognise that the silt fraction transported in suspension actually represents the majority of the sediment in large river systems and the predominant grain-size in major deltas and submarine fans, as well as in most of ancient sedimentary basins and reservoirs. Quantitative provenance analysis of silt represents a step forward in provenance studies as it provides the access to an unexplored world where detrital minerals can be easily identified and their history reconstructed. The technique can be applied to both siltstone and shale making it attractive for the hydrocarbon industry, particularly in the area of research of Unconventional Plays. This contribution is therefore intended to prove the validity and efficacy of the method and its possible application to both QPA studies and to hydrocarbon exploration. The latter is located in the onshore Mandawa basin in southern Tanzania. where hydrocarbon exploration is particularly important for the presence of huge deep-water gas fields.