This article about petrography and Petroledge was written by Ana Bárbara Sampaio da Costa (Terra & Mar, Geophysics and Geology Solutions). Endeeper gratefully acknowledges Terra & Mar, Geophysics and Geology Solutions.
The Cenomanian-Turonian passage is globally known as the largest marine transgression during the 250 Ma.
In the Potiguar Basin, northeastern Brazil, this passage occurs within the stratigraphic interval constituted by the Açu and Jandaíra formations.
A detailed petrographic analysis of this interval was executed by the description of 190 thin sections using the Petroledge® system for petrography.
The study using petrography was performed through the detailed characterization and quantification of the primary and diagenetic constituents, and pore types.
The reconstruction of the primary detrital composition supported the interpretation of the clastic provenance. The analysis of the diagenetic processes and constituents allowed identifying their impacts on the porosity, establishing paragenetic sequences, and inferring paleoenvironmental information. The identification and quantification of the different pore types made possible to reveal the relationships among the diagenetic processes and the modification of pore space.
The effective integration of petrographic data and information, made possible by use of the Petroledge® system, revealed the following:
- The predominantly siliciclastic units Açu-3 and Açu-4, from the initial phase of development of the marine transgression, provided from uplifted blocks of the plutonic basement, being affected essentially by diagenetic processes indicative of continental eodiagenesis under dry climate, including mechanical clay infiltration.
- The late phase of eustatic development (upper Açu-4 unit) is represented by the deposition of hybrid sediments, constituted by extrabasinal grains derived from the uplifted basement, carbonate and non-carbonate intrabasinal grains. Their diagenetic alterations are indicative of eodiagenetic conditions transitional between marine and meteoric.
- The deposition of the Jandaíra Fm. Characterizes the maximum of the transgression, with establishment of a carbonate platform, which sediments were affected by marine eodiagenetic processes, including intense calcite cementation.
The use of the Petroledge® software was fundamental for assuring the quality and coherence of the obtained data, allowing their effective integration with stratigraphic and sedimentologic information.