Berthierine from the Lower Cretaceous Clearwater Formation, Alberta, Canada

Abstract

Abstract--Berthierine occurs as pore-linings of well crystallized laths of variable thickness in oil-sands of the Clearwater Formation, Alberta, Canada. Berthierine crystallized early in diagenesis within portions of a deltaic/estuarine complex dominated by brackish to fresh water.Separates prepared using high gradient magnetic separation contain approximately equal amounts of monoclinic and orthohexagonal berthierine. Minor, but variable, quantities of inseparable, iron-rich impurities mainly consist of chamosite Ib and lib, and Fe-rich smectitic clays.Clearwater Formation berthierine has a range of chemical compositions that differ from those reported for most other berthierines. The SiO2 (27-35 wt%), Fe203 (5-8 wt%) and A1203 (16-18 wt%) contents for Clearwater Formation berthierine fall between values normally reported for berthierine and odinite. The average structural formula of five samples studied in detail is (Fe2+~.olAloszMgo.46Fe3+o28 Mn<0.m[70.43)(Si1.74A10.26)Os(OH)4, where [] represents vacancies in the octahedral sheet. The large number of vacancies in the octahedral sheet implies a di-trioctahedral character for this clay. Our results also suggest that a series of compositions can occur between ideal berthierine and odinite end-members.Berthierine has been preserved within the Clearwater Formation because temperatures during diagenesis did not exceed 70~ and perhaps also because hydrocarbon emplacement limited subsequent transformation of berthierine to other phases, such as chamosite. Intense, early diagenetic, microbial activity and/ or the strongly reducing environment created by later emplacement of hydrocarbons may be responsible for the Fe>/Fe 3+ ratio of the berthierine. Because of these conditions, this ratio may have changed since initial clay crystallization. The Clearwater Formation occurrence of grain-coating Fe-rich clays provides valuable insights into possible relationships between the Fe-serpentine minerals, odinite and berthierine, and supports an important role for these phases as precursors to the grain-coating and pore-lining Fechlorite (chamosite) that is so common in ancient sandstones, including many hydrocarbon reservoirs.

Berthierine in the Middle Jurassic sideritic rocks from southern Poland

“…Hornibrook and Longstaffe (1996) have shown that berthierine crys tal lised at a tem per a ture of 25-45°C. Accord ing to Worden and Morad (2003) and Wil son (2013) the forma tion of berthierine took place in trop i cal, off shore and deltaic en vi ron ments where iron-bear ing fresh wa ter mixed with sea wa ter.…”

“…Its chem ical com po si tion is iden ti cal to that of iron-rich leptochlorite, com monly re ferred to as chamosite. It may also be sim i lar to the com po si tion of an other iron alu mi no sili cate -odinite (Hornibrook and Longstaffe, 1996). Berthierine (like chamosite) is gen er ally con sid ered to be char ac ter is tic of ma rine de pos its (Tay lor and Curtis, 1995;Ryan and Hill ier, 2002;Tay lor et al, 2002), al though it has also been re ported in de pos its of brackish bas ins (Tay lor, 1990), in laterites (Fritz and Toth, 1997), and even in hy dro ther mal de pos its (Rivas-Sanchez et al, 2006).…”

“…The exper i ments of Hornibrook and Longstaffe (1996), car ried out on berthierine from Lower Cre ta ceous oil-bear ing sands of the Clearwater For ma tion, Al berta, Can ada, have shown that it crys tal lised from fresh or brack ish wa ters at a tem per a ture of 25-45°C in the early diagenetic stage. Berthierine can transform to chamosite at 70°C, and is com monly con sid ered its precur sor (e.g., Iijima and Matsumoto, 1982;Longstaffe and Ayalon, 1987).…”

“…Berthierine can transform to chamosite at 70°C, and is com monly con sid ered its precur sor (e.g., Iijima and Matsumoto, 1982;Longstaffe and Ayalon, 1987). Re place ment of berthierine by chamosite can thus point to a >70°C tem per a ture dur ing diagenetic al ter ation in sed i men tary rocks (Velde, 1995;Hornibrook and Longstaffe, 1996;Meunier, 2005).…”

Ocorrência de Ironstones no Devoniano da Bacia do Paraná

“…7). Acredita-se que a chamosita presente nesses arenitos seja produto de uma provável transformação isoquímica mesodiagenética da bertierina (Hornibrook & Longstaffe 1996;Morad et al 2000;Velde 2003), em temperaturas em torno de 120-160ºC (Curtis 1985).…”