Pleistocene glaciation in Kurdistan

Abstract. The mountains of Kurdistan are a portion of the Taurus-Zagros, mountain arc that extends through southern Turkey, northern Iraq, and southwestern Iran and separates the Anatolian-Iranian Plateaus from the Mesopotamian Lowland. The crest reaches elevations of 3000-4000 m in the segment from the Cilo Dagh area in southeastern Turkey for 250 km to the Algurd Dagh area in northern Iraq. Southeastward the crestal elevation descends to 2200-2800 m, but in the Zardeh Kuh of southern Iran it again locally reaches 4000 m. The highest part of the range is generally in the belt of metamorphic rocks. The outer ridges are formed mostly by long folds of Mesozoic limestone, giving way in the foothills to folds in sediments as young as Pliocene. Within Kurdistan the ranges are cut transversely by four major tributaries of the Tigris River, namely the Khabur, Greater Zab, Lesser Zab, and Diyala Rivers. The climate of Kurdistan is marked by winter precipitation and summer drought. The rains are brought in part by cyclonic disturbances from the Mediterranean Sea, and in part by circulation around an anticyclone centered in winter over the Arabian peninsula. The regional precipitation increases with elevation in the mountains, and ranges from about 300 mm per year in the outer foothills to more than 1000 mm in the highest part of the range in the area of the Cilo Dagh and Algurd Dagh. The precipitation reaches a maximum here not only because the mountains are high and massive but also because here the trend of the ranges shifts from east to southeast, and the storms which follow the outer flank of the range from the Mediterranean Sea eastward are forced to rise over the mountains or be diverted sharply to the southeast. Inland from the mountains on the high Anatolian and Iranian Plateaus the precipitation falls abruptly to 300-500 mm. The vegetation in Kurdistan closely reflects the climate. The lower treellne has a general elevation of 700-1000 m on the outer foothills of the mountains for most of the distance along the ranges, and follows approximately the 500 mm precipitation line. The woodland consists domln-antly of deciduous oak, locally reduced to scrub by woodcutters and goats. In addition upiper may be found generally in the upper part of the forest zone. Maple, walnut, hawthorne, almond, and ash occur with the oak at middle elevations, and pistachio and olive are found on some of the drier sites. The upper treeline on the outer ranges occurs at an elevation of about 2000 m, and is presumably limited at this elevation by the temperature (January mean about 10° C). Southeastward along the range in Iran, where the crests of the ridges are generally less than 3000 m, the forest cover extends farther inland and terminates in what may be considered an inner tree-line, where the precipitation Is about 500 mm and the elevation about 1300-1500 m. Pleistocene glacial features were studied principally in three regions, the Algurd Dagh area in Iraq, Ruwandiz River area nearby, and the Cilo Dagh area in Turkey. The ridges near Algurd Dagh reach 3000-3500 m in elevation, and are so located with respect to the drainage that extensive Pleistocene glaciers formed on the northern slopes and flowed through gaps southward down valleys tributary to the Greater Zab River to elevations as low as 1100 m. The upper portions of broad valleys were plugged with glacial debris without distinct morainic loops but with lakes and other small depressions. Small cirques with floors as low as 1500 m were found on north-facing scopes of subsidiary ridges. The Ruwandiz River, one of the major tributaries of the Greater Zab River, contains Pleistocene glaclo-fluvial gravels at least 30 m thick in terraces 40-60 m above the present river. Although fresh cirques were found on some of the ridges crossed by the Ruwandiz River, the terraces do not head in a distinct moraine complex, and it is possible that they pre-date the last major gllacial advance. The relations are complicated by the presence of deposits attributed to landsliding In the headwater region. There terraces themselves contain intercalated colluvium and soil; they are overlain by thick colluvium that may represent the last glacial phase as well as the post-glacial. Earlier Pleistocene events In this region are recorded by still higher benches of limestone breccia (with Mousterian caves) on the hill slopes as well as by a remnant of a deposit of sand and gravel and even thin layers of lacustrine silt and limestone standing 250 m above the Ruwandiz River. In the area north of Cilo Dagh in southeastern Turkev, Pleistocene glacial deposits were found along the Greater Zab River as low as 1500 m elevation. They were supplied by glaciers originating on the north side of Cilo Dagh as well as on subsidiary ridges to the north and west. The lowest Pleistocene cirques identified have an elevation of about 1800 m, but the only areas visited were actuallv in the northern part of the glaciated area, where the precipitation is less than in the main Cilo Dagh and its outer flank. Although no modern glaciers exist in the Algurd Dagh area, several small remnants were mapped by BOBEK in cirques in the Cilo Dagh. The modern snowline on shaded exposures is placed at about 3300 m. Pleistocene cirques at 2100 m in the Cilo Dagh area and at 1500 m in the Algurd Dagh area imply a Pleistocene snowline depression of 1200-1800 m, a figure much larger than the 700 m postulated by Bobek. If Pleistocene depression of the snowline is assumed to be a result of depression of temperature alone, then the mean annual temperature must have been at least 12° C lower (based on a vertical temperature gradient of about 0.7° C/100 m). Such a value is as great as that infered for central Europe, where permafrost and tundra flora and fauna were apparently widespread. For Kurdistan there are no frost features or paleontologic records to indicate such low temperatures, and it is probable that the glaciation was result of increased snowfall as well as moderately lower temperature. This conclusion applies only to the outer flank of the Kurdish mountains, which may have received greatly increased winter snowfall as Mediterranean storms were intensified on the margin of a strengthened Asiatic anticyclone. On the Anatolian and Iranian Plateaus, however, the precipitation may not necessarily have been greater, and search for reliable geologic and paleontologic evidence must be made in this region. Despite the evidence for markedly different climatic conditions in Kurdistan during the last glacial phase of the Pleistocene, there is little evidence yet that climatic change near the Pleistocene was critical in the evolution of early man from hunters to farmers and herders. The transitional stages occurred during the period about 11,000 to 9,000 years ago, and it is probable that the climatic change that brought about glacier recession had been essentially by that time. In any case, the Pleistocene climatic changes may have involved only an altitudinal shifting of the life zones within the Kurdish mountains and foothills and the Mesopotamian piedmont, and that even during the glacial period there were natural habitats suitable for the animals and plants destined to be domesticated as soon as man reached the requisite cultural level.