Naslov
Smectite stability in alternating mudstone- sandstone facies from the Pennsylvanian Hoxbar Group (Anadarko Basin, Oklahoma)

Autori
Zanoni, G ; Šegvić, Branimir ; Coe, J ; Sweet, D

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, prošireni sažetak, znanstveni

Skup
9th Mid-European Clay Conference, MECC 2018

Mjesto i datum
Zagreb, Hrvatska, 17.09.2018. - 21.09.2018

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
clay minerals ; shale ; Anadarko Basin

Sažetak
One of the most prolific sedimentary basins in North America is the Anadarko Basin located in the central part of the United States (Oklahoma and north Texas). It is also the deepest structural and sedimentary basin in the cratonic interior of the United States, containing approximately 12 km of Cambrian through Permian sediment in its deepest portion, with a total thickness of the Pennsylvanian strata reaching 3-4 km (RASCOE, 1962). These strata are chiefly consisted of marine and non-marine shale and sandstone, presenting one of the major hydrocarbon reservoirs in the Anadarko Basin. The studied Pennsylvanian shale and sandstone belong to the Hoxbar Group, which is a thick sedimentary unit made of multiple shaley horizons interbedded with sands and, occasionally, thin limestones (RASCOE, 1962). Two cores were sampled from a depth of about 3 km. The amount of detrital clays in sandstones is usually modest, owing to hydrodynamic sorting and other depositional processes, whilst in mudstones clay minerals are abundant and are mostly inherited directly from the original sediment (e.g. CLAUER et al., 1999). Illite-smectite from the prograde diagenetic series is common in both lithologies and subtle changes in its crystal chemistry and component makeup may be considered as proxies of the continuously changing diagenetic conditions (e.g. ŚRODOŃ et al., 2000). If one assumes the uniform source of detrital clays, than the smectite evolution in such alternating series may result with (1) a similar specific composition of I-S in sandstones and adjacent mudstones, (2) lower smectite in I-S in sandstones compared to I-S of alternating mudstones, and (3) higher smectite in I-S in sandstones compared to I-S of alternating mudstones (e.g. HILLIER et al., 1996). The reasons for such dynamics are multiple and are generally related either to the differences in thermal stability of authigenic and detrital smectite or to enhanced flow rates in sandstones that promote illitization of smectite (e.g. MCKINLEY et al., 2003). This work examines the depositional environment of the Hoxbar Group along with diagenetic aspects of alternating shales and sandstones. The latter presumably exercised a major influence on the evolution of smectitic clay assemblages and, given an increasing significance of Pennsylvanian strata of the Anadarko basin in the exploration of hydrocarbons, a detailed knowledge of clay mineralogy of mudstones (shales) and associated sandstones becomes critical for predicting the distribution of high-quality reservoirs and for the exploration of their forming mechanisms. Our preliminary data shows that the average clay mineral content in sandstone of the Hoxbar Group is about 6% compared to 35% of clays in mudstone. In the latter, several generations of illite- smectite, including rectorite, dominate the clay fraction. On the other hand, clays in sandstone are illite-rich I-S with only minor rectorite component and kaolinite. This clearly shows a facies (lithology) control on clay speciation but it also points to the effect of higher permeability of sandstone or, alternatively, the impact of the circulation of hot fluids facilitating higher diagenetic rates characteristic of an open diagenetic system. Such smectite dynamics in neighboring sandstone and mudstone layers may also suggest different rates of authigenesis of smectite in analyzed rock types, which is subject to further investigation.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

POVEZANOST RADA