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首页> 外文期刊>The Journal of Geology: a semi-quarterly magazine of geology and related sciences >Tectonic Decapitation of a Pliocene Mega-Delta on Isla Del Carmen in the Gulf of California (Mexico): And a River Ran through It
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Tectonic Decapitation of a Pliocene Mega-Delta on Isla Del Carmen in the Gulf of California (Mexico): And a River Ran through It

机译：加利福尼亚湾（墨西哥）上的卡门岛上新世大三角洲的构造斩首：一条河横冲而过

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The Tiombo conglomerate on Isla del Carmen in Baja California Sur represents a mega-delta deposited mainly during the middle Pliocene (early Piacenzian age). A cross-section with the characteristically arched profile of a fan delta is exposed in sea cliffs 60 m high that extend for 2 km along the east side of the fourth-largest island in Mexico's Gulf of California. A tidewater aspect to the delta is proven by the inclusion of fossil-rich lenses dominated by the pecten Patinopecten bakeri, which also occurs abundantly together with many other middle Pliocene fossils in the Arroyo Blanco limestone juxtaposed against the south flank of the delta construction. Inland, the conglomerate fills a broad, cross-island channel approximately 3 km(2) in area that ends with cliff exposures of a lesser thickness overlooking the Carmen Passage between Isla del Carmen and the peninsular mainland of Baja California. Based on exposures that fail to reveal the full basal contact, the combined fluvial and deltaic parts of the system are conservatively estimated to exceed 200 million m(3). This study finds that the Pliocene Tiombo Delta is massively too large for the island it now occupies and that the related distributary channels in the delta's original watershed extended to the peninsular mainland and the Sierra de la Giganta in the Loreto area. The direct implication is that the Pliocene delta suffered tectonic decapitation when a reactivated halfgraben subsided and that the Carmen Passage flooded only in later Pliocene time. A useful comparison in scale is provided through examination of the modern delta at Loreto, together with its associated watershed on the peninsular mainland. Long-term changes in El Nino Southern Oscillation cycles are appraised as an influence on regional Pliocene delta construction at several other localities along the peninsular gulf coast of Baja California.
机译：南下加利福尼亚州卡门岛上的Tiombo砾岩群是一个大型三角洲，主要沉积在上新世中期（Piacenzian早期）。扇形断面具有典型拱形轮廓的横截面暴露在60 m高的海崖中，该海崖沿墨西哥加利福尼亚湾第四大岛的东侧延伸2公里。三角洲的潮水方面得到了证明，其中包含以花胶Patinopecten bakeri为主的富含化石的晶状体，这种晶状体也与Arroyo Blanco石灰岩中许多新中新世的化石一起大量出现，并列在三角洲构造的南侧。在内陆，该集团在一条约3 km（2）的区域内填充了一条宽阔的跨岛通道，其终点是厚度较小的悬崖，可俯瞰卡门岛和下加利福尼亚州半岛大陆之间的卡门通道。基于无法揭示整个基础接触的暴露，保守估计该系统的河流和三角洲相结合的部分超过2亿平方米（3）。这项研究发现，上新世Tiombo三角洲对它现在所占据的岛屿来说太大了，并且该三角洲原始集水区中的相关分流河道扩展到了半岛大陆和洛雷托地区的Sierra de la Giganta。直接的暗示是，上新世三角洲在重新活化的半粒状岩消退时遭受了构造灭绝，而卡门通道仅在上新世以后才被淹没。通过检查洛雷托的现代三角洲及其在半岛大陆的相关分水岭，可以对规模进行有益的比较。厄尔尼诺南部涛动周期的长期变化被评估为对下加利福尼亚州半岛海湾沿岸其他几个地方的上新世三角洲构造的影响。

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