The Occurrence of Pedogenic Palygorskite (Attapulgite) in Saudi Arabia

Abstract--Clay mineralogy and petrography of the Early to Middle Eocene succession of the Dammam dome, Saudi Arabia, comprising the Rus and Dammam Formations, were studied using X-ray powder diffraction, light microscopy, and scanning electron microscopy. These formations consist of alternations of dolomite, dolomitic marl, claystone, and shale. The rocks were deposited and subjected to early diagenetic dolomitization in a shallow, coastal marginal basin characterized by rapid changes in salinity. Palygorskite occurs as interwoven fibrous mats forming fine laminae in shales and as coatings and porefilling and pore-bridging cements in dolomitic marls. This textural evidence suggests a direct chemical precipitation, mostly post-dating dolomitization. Magnesium concentrations in presence of dolomite was sufficient for palygorsldte precipitation; the necessary Si and AI were derived by dissolution of silicates under alkaline conditions. The maximum development of palygorskite was near the top of the Dammam Formation, which was deposited during a marine transgression in the Lutetian. The formation of palygorskite in marginal restricted basins in eastern Saudi Arabia took place during Paleocene-Middle Eocene time and was contemporaneous with similar occurrences in the Tertiary basins of West Africa.

Section: Discussionmentioning

confidence: 99%

Palygorskite in the Eocene Rocks of the Dammam Dome, Saudi Arabia

Çağatay

1990

“…Tertiary sediments appear to be the main host of palygorskite in the Middle East (Yaalon, 1955;Wiersma, 1970;Millot, 1970;Shadfan and Dixon, 1984), and Shadfan and Mashhady (1985) described shales of Tertiary age in eastern Saudi Arabia that consisted mainly of palygorskite. Elprince et al (1979) and Mashhady et al (1980) indicated also the pedogenic formation of palygorskite in some soils of Saudi Arabia.…”

Section: Introductionmentioning

confidence: 91%

Palygorskite from Tertiary Formations of Eastern Saudi Arabia

Shadfan

Mashhady

Dixon

et al. 1985

Abstract--The occurrence of palygorskite in some Tertiary sediments in eastern Saudi Arabia was studied. Mineralogical and chemical analyses were made of samples from two sections several meters thick from the Umm er Radhuma and Dammam Formations of Paleocene and Eocene periods, respectively. Layers of shales were observed within the sections of the dolomitic-calcitic limestone of the Umm er Radhuma Formation and of the dolomitic limestone of the Dammam Formation. After treatment for carbonate removal the shales consisted of more than 95% clay-size particles, most of which were <0.2-#m in size. Palygorskite was the main constituent of some of the shales, with minor amounts of gypsum, soluble salts, and carbonates. The association of gypsum and other salts with palygorskite in the shale suggests that palygorskite formed in closed-basin environments. The presence of palygorskite and the absence of other minerals in the clay fraction of the limestones also suggests that the palygorskite formed under marine conditions.

“…Where smectite is the thermodynamically favored product (Elprince et al, 1979), palygorskite should transform to smectite under natural conditions; however, under some soil ionic conditions and at pH 7 to 8, palygorskite appears to be stable. Increased solubility of AI and Si under high pH favors the transformation of palygorskite to smectite.…”

Section: Discussionmentioning

confidence: 99%

Low-Temperature Alteration of Palygorskite To Smectite

Golden

Dixon

1990

Abstract--The feasibility of transforming palygorskite from two localities to smectite hydrothermally at temperatures ranging from 22 ~ to 160"C was investigated in a series of laboratory experiments, in which alkalinity was maintained in the pH range of 11.4 to 12 by adding NaOH. The smectite formed was characterized by chemical, spectroscopic, and electron microscopic techniques. Smectite formed rapidly at > 100*C; the transformation was slow, however, at 22"C. The introduction of MgCO3 accelerated the alteration process, but changes in alkalinity at pH > 12 and the difference in elemental composition of the palygorskite samples did not significantly affect the alteration. A pressure of one atmosphere and a temperature of 22~ were sufficient for some transformation to occur within a few months, provided the alkalinity was maintained close to pH 12. X-ray powder diffraction characterization of the product indicated a smectite, and infrared spectroscopy indicated saponite. The alteration to smectite was appreciable even at room temperature, which suggests that the reaction can take place without any external heating.