The complex case of Macaronichnus trace fossil affecting rock porosity
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Show full item recordEditorial
Nature Research
Date
2021-01-21Referencia bibliográfica
Dorador, J., Rodríguez-Tovar, F. J., & Miguez-Salas, O. (2021). The complex case of Macaronichnus trace fossil affecting rock porosity. Scientific Reports, 11(1), 1-7. [https://doi.org/10.1038/s41598-021-81687-6]
Sponsorship
EU's Horizon 2020 research and innovation program under the Marie Skodowska-Curie Grant 792314; Ministerio de Educación, Cultura y Deporte, Spain; Secretaria de Estado de I+D+I, Spain CGL2015-66835-P PID2019-104625RB-100; Junta de Andalucía B-RNM-072-UGR18 P18-RT-4074; Scientific Excellence Unit (UGR) UCE-2016-05Abstract
Bioturbation is an important factor for reservoir quality due to the modification of host rock
petrophysical properties (i.e., porosity, permeability, and connectivity). However, there is no
predictable relationship between bioturbation and its effect on rock properties, due to the variability
of the involved ichnological features. A detailed ichnological analysis is necessary to determine how
bioturbation affects petrophysical properties in a bioturbated reservoir. Traditionally, ichnological
features such as density, tiering, size, orientation, architecture, and fill, have been considered.
However, other properties have been undervalued as is the case of lining. Here, we present a detailed
study on the effects of Macaronichnus burrows, an ichnotaxon usually related to hydrocarbon
exploration due to its high concentration in rock notably affecting petrophysical properties.
Macaronichnus, a subhorizontal cylindrical burrow, is characterized by a well-defined and developed
outer rim surrounding the tube core. Our data indicates a clear zonation in porosity according to
burrow structure, with the lowest porosity in the tube core and higher values associated with the
surrounded rim. This duality is determined by the tracemaker grain selective feeding activity and the
consequent concentrated cementation. The organism concentrates the lighter minerals in the tube
core fill during feeding, favoring post-depositional cementation during diagenesis and this results in
lower porosity than the host rock. However, heavy minerals, mainly glauconite, are located in the
rim, showing higher porosity. Our results support the view that ichnological analyses are essential to
determine reservoir quality in bioturbated reservoirs, evidencing that other ichnological properties in
addition to those traditionally considered must be evaluated.