Reevaluating the process regime in the Sego Sandstone: Sedimentological and ichnological evidence for an underemphasised fluvial signature

IF 1.9 3区 地球科学 Q1 GEOLOGY
Marcello Gugliotta, Daniel S. Collins, James A. MacEachern, Narjess El Euch-El Koundi
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Abstract

Rocks of coastal to shallow-marine origin are challenging to interpret owing to the complex interplay of various depositional processes. This study reevaluates the relative roles of fluvial, tidal and wave processes in the Upper Cretaceous Sego Sandstone (and subordinately in the underlying Buck Tongue) of the Book Cliffs, USA, a well-studied ancient coastal to shallow-marine succession. Detailed sedimentological and ichnological analyses were used to interpret a previously underemphasised riverine signature, consisting of centimetre- to decimetre-thick alternations of sandstone and heterolithic beds inferred to represent flood–interflood periods of variable river discharge. Recognition of a widespread fluvial-dominated signature across the studied units better agrees with other sedimentological and regional observations in the study area, such as high sandstone–mudstone ratios, largely unidirectional and seaward-oriented palaeocurrents, and modelled weak tidal conditions in the basin. When considering all of the sedimentological, ichnological and stratigraphic observations together with its regional depositional context, the Sego Sandstone/Buck Tongue system is better explained using a mixed-energy but fluvial-dominated deltaic model. This highlights an historical over-interpretation of tidal processes and subordinate wave processes in the Sego Sandstone and likely in similar units. The widely used approach that emphasises only certain sedimentary features in discerning the process regime from analysis of rocks of inferred coastal to shallow-marine origin is unrefined and may therefore underrepresent the actual complexity of these systems.

Abstract Image

重新评价塞戈砂岩的过程机制:一个不太突出的河流特征的沉积学和技术证据
由于各种沉积过程的复杂相互作用,对海岸到浅海成因的岩石进行解释具有挑战性。本研究重新评估了美国Book Cliffs的上白垩世Sego砂岩(及其下伏的Buck Tongue)中河流、潮汐和波浪过程的相对作用,Book Cliffs是一个被充分研究的古代沿海到浅海演替过程。详细的沉积学和技术分析被用来解释以前未被强调的河流特征,包括厘米到分米厚的砂岩和异质石器床的交替,推断为代表可变河流流量的洪水-洪水间期。在整个研究单元中发现了广泛的河流主导特征,这与研究区域的其他沉积学和区域观测结果更好地吻合,例如高砂岩-泥岩比,大部分单向和向海的古洋流,以及模拟的盆地弱潮汐条件。综合考虑所有沉积学、工艺学和地层观测资料及其区域沉积背景,塞戈砂岩/巴克舌体系最好采用混合能量但河流主导的三角洲模型来解释。这突出了对Sego砂岩和类似单元的潮汐过程和从属波浪过程的历史过度解释。在从推断的海岸到浅海成因的岩石分析中,在识别过程机制时,广泛使用的方法只强调某些沉积特征,这种方法是不完善的,因此可能不足以代表这些系统的实际复杂性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
CiteScore
4.10
自引率
16.70%
发文量
42
审稿时长
16 weeks
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