Paleoclimate Interpretation from a Petrographic Comparison of Holocene Sands and the Fountain Formation (Pennsylvanian) in the Colorado Front Range
Paleoclimate Interpretation from a Petrographic Comparison of Holocene Sands and the Fountain Formation (Pennsylvanian) in the Colorado Front Range
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科罗拉多前缘山脉全新世砂岩和喷泉地层（宾夕法尼亚）岩相比较的古气候解释
DOI：
10.1306/212f70fe-2b24-11d7-8648000102c1865d
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发表时间：
1978
影响因子：
2
通讯作者：
L. Suttner
中科院分区：
文献类型：
--
作者：
G. Mack;L. Suttner
摘要在科罗拉多前山脉的至少四个地区，喷泉组中的碎屑石英群和来自现代河流的全新世砂存在显著的相似性，这些河流排出前寒武纪结晶岩并靠近喷泉露头。在科罗拉多斯普林斯和博尔德附近，喷泉和全新世石英群主要来自花岗岩源岩;在洛夫兰和戈尔登附近，大部分石英由变质岩提供。由于这四个地区的喷泉砂岩和全新世砂岩都来自于共同的母岩，并在相似的条件下堆积，因此，根据Young等人（1975）的方法，可以使用两种沉积物的频率百分比抵抗框架颗粒作为大小的函数的图来比较前山脉东翼的宾夕法尼亚和全新世气候。在所有四个地区，这样的比较表明，喷泉沉积在一个气候比全新世时期存在的气候要潮湿得多。潮湿的气候是一致的推断近赤道，南半球的位置在二叠纪和宾夕法尼亚州的祖先落基山脉。当温暖潮湿的东南信风从大陆中部海面吹来，沿着古老的落基山脉上升时，就会产生地形效应。降水将集中在东侧，但更干旱的条件将在对面的科罗拉多西部盛行。
ABSTRACT In at least four areas of the Colorado Front Range remarkable similarity exists in the detrital quartz populations in the Fountain Formation and Holocene sand from modern day streams draining Precambrian crystalline rocks and located close to the Fountain outcrops. Near Colorado Springs and Boulder both the Fountain and Holocene quartz populations were derived principally from granitic source rocks; in the vicinity of Loveland and Golden metamorphic rocks provided most of the quartz. Because both the Fountain sandstone and Holocene sand in these four areas came from common parent rocks and accumulated under similar conditions, plots of frequency percent resistant framework grains as a function of size for the two deposits can be used to compare Pennsylvanian and Holocene climates for he east flank of the Front Range following the approach of Young et al. (1975). In all four areas such comparisons suggest that the Fountain was deposited in a climate substantially more humid than that which has existed during the Holocene. A humid climate is consistent with the inferred near equatorial, southern hemisphere location of the Ancestral Rocky Mountains during the Permian and Pennsylvanian. An orographic effect would have been produced as warm, moist southeasterly trade winds, blowing off the mid-continent sea, ascended the Ancestral Rockies. Precipitation would have been concentrated on the east flank, but more arid conditions would have prevailed in western Colorado on the opposite flank.