Origin and Growth Mechanism of Authigenic Chlorite in Sandstones of the Lower Vicksburg Formation, South Texas

Abstract

Authigenic chlorite, occurring as grain coatings, pore fillings, and rosettes, is common in deltaic sandstones of the lower Vicksburg Formation in South Texas. Chlorite rosettes are isolated and occur late in the diagenetic history, whereas grain-coating and pore-filling chlorite occur early, predating the development of secondary porosity and the precipitation of quartz overgrowths and Fe-poor calcite. Grain-coating and pore-filling chlorite, which are interstratified with approximately 15 percent 7 Å layers, are Fe-rich with a mean Fe/ (Fe؉Mg) ratio of 0.68. Stable-isotope data (␦ 18 O averages 13.5‰ (SMOW)) indicate that the grain-coating and pore-filling chlorite began precipitating between 20؇C to 40؇C within the upper 1.8 km (6000 ft) of burial.Sandstones of the lower Vicksburg Formation were deposited in a relatively shallow deltaic environment as part of a large fluvial system draining the volcanics of Sierra Madre Occidental, Mexico and Trans Pecos, Texas. Weathering of these volcanics brought large amounts of particulate Fe to the river mouth. An increase in salinity in the distributary channel complex caused Fe flocculation and deposition. During periods of high river discharge, or when coastal currents acted to concentrate particulate Fe, large amounts of particulate Fe were deposited in the delta system. This resulted in thick layers of Fe-rich clay (odinite?) around grains. During periods of low river discharge, or when coastal currents caused wide distribution of particulate Fe, less particulate Fe was deposited. It is proposed that the grain-coating and pore-filling chlorite began forming through the transformation of an Fe-rich clay precursor in the formation-water hydropressure zone following Ostwald processes. The presence of this synsedimentary Fe-rich clay, and its recrystallization to Fe-chlorite, strongly influenced fluid flow and played a large role in developing the diagenetic heterogeneity seen in lower Vicksburg sandstones today.

Formation mechanisms and sequence response of authigenic grain-coating chlorite: evidence from the Upper Triassic Xujiahe Formation in the southern Sichuan Basin, China

“…Some researchers believe authigenic chlorite transformed from Fe-rich grain coating (Grigsby 2001;Lanson et al 2002). Billault et al (2003) thought authigenic chlorite precipitated from pore water.…”

“…As rivers flow into the ocean, ferruginous components formed flocculent precipitates and become a source of chlorite (Grigsby 2001) and filled mudstones with iron and magnesium ion-rich fluids (Hilier et al 1996). After thin section analysis, study area debris was identified mainly as sedimentary and metamorphic rock debris, with minor amounts of iron-rich volcanic rock debris.…”

“…Studies have been performed on many sedimentary formations such as the Upper Triassic Yanchang Formation in the Ordos Basin Ding et al 2013;Zhang et al 2013;Zhu et al 2015), the Upper Jurassic in the Songliao Basin (Zeng 1996), Xujiahe Formation in the Sichuan Basin Huang et al 2010;Zou et al 2013), Middle Jurassic Shaximiao Formation in the Sichuan Basin (Lü et al 2015), Jurassic Sangonghe Formation in the Junggar Basin (Xi et al 2015), Upper Cretaceous in the Santos Basin, Brazil (Bahlis and Luiz 2013), and the Lower Vicksburg Formation in Southern Texas (Grigsby 2001). However, the clastic sequences which developed grain-coating chlorite in these sedimentary basins have varying characteristics.…”

Impact of Mineralogy and Diagenesis on Reservoir Quality of the Lower Cretaceous Upper Mannville Formation (Alberta, Canada)

“…The alteration of igneous and metamorphic minerals (e.g. micas) in the sedimentary system, originated from the erosion of the mountain range westward also favoured detrital Fe-rich clay minerals precursors and chlorite formation (Grigsby, 2001). Clay rims may thus formed during eodiagenesis linked with pedogenic processes (Walker et al, 1978) as it was present in the sediment during sandstone deposition, and predates all other diagenetic phases, including compaction and detrital grains interpenetration (Fig.…”

In situ mineralogy and permeability logs from downhole measurements: Application to a case study in chlorite‐coated sandstones

“…The fractures statistics (density, orientation, size) could be determined by microresistivity high-resolution images of the walls of a borehole using, for example, the Formation MicroScanner (FMS 2 ) and the Formation MicroImage logs (FMI 2 ). Actually, it is likely that the use of highresolution logs in addition to available core data would be helpful in providing additional constraints on the a priori model used to estimate the mineralogy and its influence upon petrophysical properties of interest [e.g., Grigsby and Langford, 1996;Grigsby, 2001].…”