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Volume 38, Number 1January/February 1987

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Glaciers in Arabia

Written by Arthur Clark
Illustrated by Michael Grimsdale
Additional photographs by Hal McClure

Glaciers in Arabia? Glaciers in what is now a vast and stony desert? No, it's not impossible. There were glaciers in Arabia - one in the vicinity of Qasim in the north-central part of the kingdom - and last year the Aramco geologist who first wrote about it came up with, well, rock-solid evidence to prove it.

According to that geologist, Hal McClure, the glacier moved across what is today's Saudi Arabia several hundred million years ago - before the world's land masses broke up into separate continents. Back then, he says, the South Pole was in Africa and the fringes of its ice cap reached into the Arabian Peninsular.

To Aramco geologists of the 1950's, this would not have been quite as startling as it seems to laymen today. While prospecting at Khasm Khatmah and Jabal Ghiran in southwestern Saudi Arabia in 1950, S.B. "Krug" Henry, one of the 1933 pioneers who launched the Aramco venture, and R. A. "Dick" Bramkamp, who became Aramco's chief geologist in 1951 (SeeAramcoWorld, May-June 1984), reported the discovery of granite boulders "... as large as three feet across (one meter)" that could not be traced to any nearby outcrop, and theorized that they had been "rafted" to the site by glaciers.

But it was not until 1977 that McClure, quite by accident, came across traces of the Qasim glaciation - and even then he wasn't at all sure what he had found.

However, investigation showed striking similarities between the curious Qasim rocks and those that showed glaciation in North Africa. Further, McClure's evidence pointed to glaciation in Arabia about 435 million years ago, near the end of the Ordovician period and roughly the same time that the giant ice sheets had scraped their way across Algeria and Libya. Excited about his discoveries, McClure contacted Columbia University geologist Rhodes W. Fairbridge, one of the first men to identify signs of glaciation in North Africa.

"Fairbridge was in Germany at the time," says McClure, "so Columbia forwarded my letter to him. He wrote back saying that he'd shown my photographs to other glacier specialists and they all agreed." He also gave McClure some advice: "Publish!" In 1978 McClure became the first of several geologists to produce papers reporting and describing glacier sites on the Arabian Peninsula.

Now McClure, while leading a party of 55 geologists on a field trip through north-central Arabia which included the site of the glacier near Qasim - 320 kilometers northwest of Riyadh (200 miles) - has ome across still further evidence that, he says, nails down his theory.

In the comfort of his office in Aramco's new Exploration and Petroleum Engineering Building, McClure answers a question about ice sheets by pointing to a fragment of stone on his windowsill: a shiny, pink-hued piece of granite with thin, finely cut parallel lines on its surface. These lines - "striations" - were inscribed in the stone, he says, when an ice sheet weighing thousands of tons ground over it on the long push into Arabia. They even show the direction in which the glacier was moving. In the case of the Qasim glaciation, the ice moved in a north-northeasterly direction from a "South Pole" then located in central Africa.

The stone's reflective sheen, called "glacial polish," was caused by long rubbing against the rock of fine clay particles in the ice - something like the effect of fine sandpaper on wood. Matched with other markings, the buffing on the stone is an important sign of glaciation.

Further evidence of glaciers includes stones marked with deeper gouges, "exotic" stones - rocks resting far from their places of origin - and deposits of poorly sorted rocks ranging in size from clay particles to boulders more than a meter across (39 inches). Another key sign is glacial tillite, or unsorted rock-debris deposits, and "chatter marks" on the edges of striation-marked boulders. These occurred when larger pieces of rock firmly frozen in the base of a moving glacier bumped over firm but brittle bedrock; instead of cutting smooth, parallel striations, they left markings "like railroad ties," McClure says.

Even more striking signs of the immense power of a glacier are "faceted" rocks: rocks with their tops neatly shaved away on the same plane by the inexorable pressure of many tons of ice studded with sharp grains of frozen clay and stone.

The evidence at the Qasim site, and at Khasm Khatmah and Jabal Ghiran, also suggests that glaciers entered what today is the Arabian Peninsula from different directions in two ice invasions, one about 435 million years ago, the other, more southerly, 280 million years ago. The continents were shifting in relation to the poles, "zigzagging here and there," says McClure, noting that nobody knows exactly what caused the continental peregrinations.

The Qasim glacier site was probably on the fringes of the polar cap, and "lobes" of ice pushed out over the barren ground like white-gloved fingers - all part of an ice field that reached across 4,000 kilometers of North Africa (2,500 miles). "Given the fact that Arabia was part of Africa until late in geological time - some 20 million years ago - it's not surprising that the giant ice sheets extended into Arabia then," McClure says.

As to the southwestern sites first investigated by Henry and Bramkamp, the evidence suggests that glaciers there also covered locations in North Yemen and Oman at the same time. McClure thinks that when ice invaded the southern reaches of Arabia - as opposed to the Qasim region - the South Pole was probably located off the east coast of Africa, possibly in present-day Antarctica. Arabia then would have been part of Africa, nearly touching the clustered land masses of Madagascar, India and Australia. A picture of the world at that time would show ice stretching from the pole in a wide ring which reached the southern edge of today's peninsula.

The power of the glacier was, in any case, enormous: in southeastern Oman, ice-carved striations on uncovered bedrock measured 30 meters wide (98 feet) and single grooves run as long as 15 meters (50 feet).

For Aramco geologists, of course, the point of such discoveries is oil, and with regard to glaciers it's the tillite that's important. Tillite, the rock debris randomly collected by ice as it moves and deposited just as randomly when it melts, can point the way to hydrocarbons. "In southern Oman," McClure says, "glacial tillites that continue from the surface into the subsurface are closely associated with hydrocarbon occurrences."

The tillite, McClure argues, couldn't have been deposited by any normal water flow. "Rivers and streams sort out rocks, rounding them and laying them down by diminishing weight and size according to the strength of the current." No, these rocks were probably "frozen in one chunk of ice and when the ice melted they just dropped as one load."

McClure, who coined the term "armored ice balls" to describe the original icy form of the stone clusters found at glacial sites, says that glacial melt has also produced unique rock formations called "dropstone laminites", which look a little like rock mattresses with large lumps in them. They occurred when large stones, released from melting blocks of ice floating on glacial lakes, fell into the soft lake bed below and depressed the sediment under them, thus permitting layers of later sediment to be "draped" over them as they were deposited. Today, erosion has sliced away sections of earth to reveal profiles of such deposits with their wrappings.

"The rocks couldn't have been brought in any other way [than by glaciers], and dropstone laminites are very good indicators of glaciation," says McClure. "There were glaciers in Arabia."

Arthur Clark covers Saudi Arabia for Aramco World magazine.

This article appeared on pages 28-33 of the January/February 1987 print edition of Saudi Aramco World.


Check the Public Affairs Digital Image Archive for January/February 1987 images.