--> ABSTRACT: Numerical Reconstructions of Post-Rift Burial Diagenesis, Lower Carboniferous, Derbyshire Platform, UK, by Frazer, Miles; Hollis, Cathy ; Whitaker, Fiona; #90142 (2012)

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Numerical Reconstructions of Post-Rift Burial Diagenesis, Lower Carboniferous, Derbyshire Platform, UK

Frazer, Miles *1; Hollis, Cathy 1; Whitaker, Fiona 2
(1) Miles Frazer, University of Manchester, Harrogate, United Kingdom.
(2) Department of Earth Sciences, University of Bristol, Bristol, United Kingdom.

Identifying sources of sufficient reactive fluid volumes is a major challenge when producing conceptual models that explain observed porosity modification in the deep burial environment. The Lower Carboniferous limestone of the Derbyshire Platform, northern England, provides an opportunity to test one such conceptual model in a data-rich environment. The platform hosts economic volumes of Pb-Zn-F-Ba mineralisation and its tectono-stratigraphic and diagenetic evolution is well established. This enables construction of well-constrained numerical simulations of hydrological system development during basin evolution. We are thus, able to quantitatively explore hydrological factors that control the distribution, timing and mechanisms of burial diagenesis and mineralisation.

During the Lower Carboniferous shallow water carbonate sedimentation in northern England focussed upon fault-bounded platforms, such as Derbyshire-East Midlands shelf. This platform was bounded by more rapidly subsiding hanging-wall basins that accumulated thick successions of remobilised carbonate and siliciclastic sediments. The current conceptual model suggests that metal-enriched fluids from organic-rich, fine grained siliciclastic sediments were expelled from the basins along faults and fractures during the Variscan Orogeny in the Late Carboniferous (Hollis and Walkden, 2002).

Numerical simulations of co-evolving poro-perm, fluid pressure and flow patterns using Basin2 suggest the development of overpressures within syn-rift sediments may have developed in response to post-rift sedimentation. Immediate, compaction-driven flow caused by this overburden was limited by low permeabilities within basement and seal units. Thus, release of overpressured fluid up through platform carbonates was modulated primarily by bounding-fault activation. Overpressure history results suggest that the burial history of the Derbyshire-East Midlands shelf produces near-optimal overpressures for the given system. The simulations also provide a good match to observed paragenetic sequences and provide fluid volume estimates that will help inform future conceptual models. These simulations will also be used to design and condition future Reactive Transport Models, providing a robust method to evaluate burial diagenesis on the Derbyshire Platform.

Hollis, C and Walkden, G., 2002 Reconstructing fluid expulsion and migration north of the Variscan Orogen, Northern England. JSR, 72, 700-710

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California