Insights into glendonite formation from the upper Oligocene Sagavanirktok Formation, North Slope, Alaska

IF 2 4区 地球科学 Q1 GEOLOGY
J. Counts, Madeleine L. Vickers, M. R. Stokes, W. Spivey, Kristina F. Gardner, J. Self‐Trail, J. Gooley, Ryan J. McAleer, Aaron Jubb, D. Houseknecht, R. Lease, Neil P. Griffis, Martin Vickers, K. Śliwińska, H. Tompkins, Adam M. Hudson
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Abstract

The type locality for the upper Oligocene Nuwok Member of the Sagavanirktok Formation (Carter Creek, North Slope, Alaska, USA) contains abundant occurrence of glendonite, a pseudomorph after the calcium carbonate mineral ikaite, which typically forms in the shallow subsurface of cold marine sediments. The region during the time of Nuwok Member deposition was located at a high latitude, similar to today, and the study site is characterized by sands and silty muds interpreted here to have been deposited in coastal and shelfal marine environments. Isotopic (Sr) and biostratigraphic (foraminifera) evidence presented here refine the depositional age of the outcrop to approximately 24 Ma. Glendonites occur in two basic forms: radial clusters, commonly centered around a single larger primary crystal ( approx. 10 cm; Type A) and larger single blades generally without accessory crystals (approx. 15–25 cm; Type B). Microscopic examination revealed a sequence of multiple types of replacive calcite that formed as a direct result of ikaite transformation: Type 1 rhombohedral crystals characterized by microporous and inclusion-rich cores and concentric zones, Type 2A, composed of clear calcite that overgrew and augmented Type 1 crystals, and inclusion-rich, microcrystalline Type 2B, which formed a matrix surrounding the rhombs and commonly dominates the outer rims of glendonite specimens. Type 3 calcite precipitated as fibrous, botryoidal epitaxial cement atop previous phases and is not ikaite-derived. These phases are distributed in similar ways in all examined specimens and are consistent with several previously described glendonite occurrences around the world, despite differing diagenetic and geologic histories. Stable isotope evidence (δ13C and δ18O) suggests sourcing of glendonite carbon from both organic and methanogenic sources. Glendonites of the Nuwok Member can therefore assist in the determination of a more comprehensive ikaite transformation model, improving our understanding of glendonite formation and the sedimentological and environmental context of their occurrence. Oligocene glendonites are uncommon globally; the well-preserved occurrence described here can allow future studies to better reconstruct Arctic environmental conditions and paleoclimates during this time.
阿拉斯加北坡上新世萨加瓦尼尔克托克地层釉石形成的启示
上渐新统Sagavanirktok组Nuwok段(Carter Creek, North Slope, Alaska, USA)的类型位置富含绿榴石,这是一种继碳酸钙矿物ikaite之后的伪形态,通常形成于寒冷海洋沉积物的浅层次表层。Nuwok成员沉积时期的地区位于高纬度地区,与今天相似,研究地点的特点是沙子和粉质泥浆,在这里被解释为沉积在沿海和陆架海洋环境中。这里提出的同位素(Sr)和生物地层(有孔虫)证据将露头的沉积时代确定为大约24 Ma。绿橄榄石以两种基本形式出现:放射状簇状,通常以一个较大的原生晶体为中心。10厘米;A型)和更大的单叶片,通常没有附属晶体(大约。15 - 25厘米;镜下检查发现一系列由爱凯石转变直接形成的多种类型的替代方解石:1型方解石以微孔和富含包裹体的岩心和同心区为特征;2A型方解石由透明方解石组成,过度生长和增强了1型晶体;2B型方解石由富含包裹体的微晶组成,形成了包围方解石的基质,通常主导着绿榴石标本的外缘。3型方解石以纤维状、瓶状外延水泥的形式沉淀于前相之上,并非由岩矿衍生。尽管成岩和地质历史不同,但这些阶段在所有被检查的标本中以相似的方式分布,并且与世界各地先前描述的几处绿榴石矿床一致。稳定同位素证据(δ13C和δ18O)表明绿榴石碳的来源既有有机碳源,也有甲烷碳源。因此,Nuwok段的格兰东岩可以帮助确定一个更全面的艾克岩转化模式,提高我们对格兰东岩形成及其发生的沉积学和环境背景的理解。渐新世榴辉岩在全球并不常见;这里描述的保存完好的事件可以让未来的研究更好地重建这一时期的北极环境条件和古气候。
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来源期刊
CiteScore
3.80
自引率
5.00%
发文量
50
审稿时长
3 months
期刊介绍: The journal is broad and international in scope and welcomes contributions that further the fundamental understanding of sedimentary processes, the origin of sedimentary deposits, the workings of sedimentary systems, and the records of earth history contained within sedimentary rocks.
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