【摘要】：早白堊世晚期的東亞大陸具有十分獨特的拼貼式地理特點,同時遍布豐富的脊椎動物群,是恐龍種群起源和發(fā)展的搖籃。緯度溫度梯度的變化、天然地理屏障的存在、以及不同的當(dāng)?shù)丨h(huán)境條件,均可導(dǎo)致生物群的非均勻分布。因此,研究生物的種類及分布特點,可部分恢復(fù)其生存環(huán)境,為古氣候、古地理的重建提供新的視角和有力證據(jù)。爬行動物(恐龍、鱷魚及龜類)磷灰石的穩(wěn)定同位素已被用來分析及解釋古生態(tài)及古環(huán)境。本文的研究區(qū)是甘肅省酒泉市北部的北山地區(qū)(馬鬃山地區(qū)),處于天山興蒙構(gòu)造帶的西南部,構(gòu)造變形強烈且復(fù)雜,早白堊世時期處于伸展背景下,化石埋藏地以紅色陸相碎屑巖為主,為河湖相沉積。采集自研究區(qū)下白堊統(tǒng)新民堡群的恐龍、鱷魚的牙齒及龜甲等化石樣品,由于其釉質(zhì)層及甲殼部分堅硬、致密,抗風(fēng)化性強和受成巖作用影響小,可利用樣品生物磷灰石的磷酸鹽氧同位素與大氣水的氧同位素分餾關(guān)系,及大氣水氧同位素與氣溫的線性方程式,計算得出研究區(qū)全年平均氣溫(MAAT)為19±3℃,同時證明了磷酸鹽能夠很好地保存原始氧同位素信號不受后期改造;另一方面,利用標(biāo)本中碳酸鹽的碳同位素與植物葉片的碳同位素分餾關(guān)系,計算出當(dāng)?shù)刂参镱愋蜑镃3植物,再根據(jù)植物的碳同位素與降水的最小二乘回歸方程式,計算得出研究區(qū)全年平均降水(MAP)為500±200mm/yr。在氣候分帶三角圖中投圖,得到研究區(qū)早白堊世的氣候類型屬于半干旱-干燥森林、草原氣候,與前人孢粉學(xué)、沉積學(xué)研究結(jié)果一致。陸生爬行動物氧同位素值高于半水生-水生動物,后者所處水環(huán)境的溫度波動也比前者要小。植食性恐龍(禽龍、角龍類)有截然不同的碳同位素組成,表明它們的食物來源有區(qū)別,可以避免種間競爭從而相互共存。鱷魚屬于冷血動物,生存條件有嚴(yán)格的限定,研究區(qū)古緯度(35°N)的溫度恰好屬于鱷魚生存溫度的臨界點。而龜類生存條件較鱷魚寬泛,再向北仍有存活跡象。
[Abstract]:The East Asian continent in the late early Cretaceous had unique collage geographical characteristics and abundant vertebrate groups, which was the cradle of the origin and development of dinosaur population. The variation of temperature gradient of latitude, the existence of natural geographical barrier and the different local environmental conditions can lead to the inhomogeneous distribution of biota. Therefore, the study of species and distribution characteristics of organisms can partly restore their living environment and provide a new perspective and strong evidence for the reconstruction of paleoclimate and paleogeography. Stable isotopes of apatite from reptiles (dinosaurs, crocodiles and tortoises) have been used to analyze and explain paleoecology and paleoenvironment. The study area of this paper is the Beishan area in the north of Jiuquan City, Gansu Province (Madonshan area), which is located in the southwest of the Xingmeng structural belt of Tianshan Mountain. The tectonic deformation is strong and complex, and the early Cretaceous period is in the extensional setting. The fossils are mainly red continental clastic rocks, which are fluvial and lacustrine deposits. Samples of dinosaurs, crocodiles teeth and tortoise shells from the Lower Cretaceous Xinmin Fort Group in the study area were collected. Due to the hard and dense enamel layers and crustaceans, strong weathering resistance and little diagenesis, The relationship between phosphate oxygen isotope and oxygen isotope fractionation of atmospheric water, and the linear equation of oxygen isotope and temperature of atmospheric water can be used to calculate the annual average air temperature (MAAT) of the study area is 19 鹵3 鈩，

本文編號：2313413