Lithostratigraphy, Tephrochronology, and Rare Earth Element Geochemistry of Fossils at the Classical Pleistocene Fossil Lake Area, South Central Oregon

Abstract

One of the most famous fossiliferous Pleistocene sites in the Pacific Northwest is Fossil Lake, Oregon. Until recently, fossil collections from the area were not stratigraphically controlled, owing to the lack of a detailed stratigraphic and chronologic framework. Our field studies reveal at least nine exposed thin rhythmic fining-upward depositional packages, most separated by disconformities. Analysis of interbedded tephras reveals that the Rye Patch Dam (∼646 ka), Dibekulewe (∼610 ka), Tulelake T64 (∼95 ka), Marble Bluff (47 ka), and Trego Hot Springs (23.2 ka) tephra layers are present in the section, indicating deposition from more than ∼646 ka to less than 23 ka, which includes both the late Irvingtonian and Rancholabrean North American land mammal ages, a much longer time span than previously believed. Bones analyzed from eight of the defined units have distinctly different rare earth element (REE) signatures. Fossils obtain REE during early diagenesis, and signatures are probably closely related to lake water compositions. REE signatures in fossils from lower packages suggest uptake from neutral pH waters. In contrast, REE signatures become increasingly heavy REE-enriched up-section, with positive Ce anomalies in the upper units. REE signatures in fossils from the upper units are very similar to waters from modern alkaline lakes, such as Lake Abert, Oregon, suggesting diagenetic uptake in increasingly alkaline and saline waters. These REE changes suggest increasing aridity up-section, a contention reinforced by the habitat preferences of the terrestrial vertebrates preserved.

Multiproxy reconstruction of the palaeoclimate and palaeoenvironment of the Middle Miocene Somosaguas site (Madrid, Spain) using herbivore dental enamel

“…5) did not show evidence of micro organisms affecting this tissue during the fossilization process and therefore it can be assumed that pristine 8 18 0P04 values have been maintained. (Elorza et al, 1999;Metzger et al, 2004;Martin et al, 2005;Trueman et al, 2006). However, the vast majority of studies deal preferentially with fossil bone that traditionally has been considered more prone to suffer diagenetic effects.…”

Alteration of the metal content in animal bones after 2.5-year experimental exposure to sediments

“…While chemical composition of the bone may be affected by some environmental and behavioral factors during life of animal or human (Balter et al 2002;Martínez-García et al 2005;Allmäe et al 2012;Martiniaková et al 2011), the concentration of metals in buried bones are usually much higher than in fresh ones, which indicates advanced post-mortem chemical alterations (Trueman 2007). Diagenetic parameters of bones, such as their chemical composition, are influenced by the environment, including the chemistry of surrounding sediment (Henderson et al 1983;Wright et al 1984;Plummer et al 1994;Johnsson 1997;Dauphin et al 1999;Trueman 1999;Pawlikowski and Niedźwiedzki 2002;Trueman et al 2003Trueman et al , 2006Martin et al 2005;Smith et al 2007;Cook and Trueman 2009;Rogers et al 2010). According to Kohn and Moses (2013), the bone acts as a sink for trace elements, causing the depletion of particular metals in the surrounding sediment.…”

Preservation of successive diagenetic stages in Middle Triassic bonebeds: Evidence from in situ trace element and strontium isotope analysis of vertebrate fossils

“…Thus, REE patterns have frequently been used to study various aspects of the fossilisation environment such as reconstruction of the palaeoenvironment, taphonomy, palaeoceanography, provenance and reworking of vertebrate remains (e.g., Wright et al, 1984Wright et al, , 1987Elderfield and Pagett, 1986;Denys et al, 1996;Girard and Albarède, 1996;Samoilov et al, 2001;Picard et al, 2002;Kemp and Trueman, 2003;Trueman et al, 2003Trueman et al, , 2005Trueman et al, , 2006Lécuyer et al, 2003Lécuyer et al, , 2004Metzger et al, 2004;Martin et al, 2005;Labs-Hochstein and MacFadden, 2006;Ounis et al, 2008;Anderson et al, 2007;Domingo et al, 2007Domingo et al, , 2009aDomingo et al, , 2009bDomingo et al, , 2011Cook and Chemical Geology 410 (2015) 108-123 Grandstaff and Terry, 2009;Kocsis et al, 2009;Iliopoulos et al, 2010;Rogers et al, 2010;Suarez et al, 2010;Patrick, 2013aPatrick, , 2013bZhao et al, 2013).…”