Provenance of Holocene beach sand in the Western Iberian margin: the use of the Kolmogorov–Smirnov test for the deciphering of sediment recycling in a modern coastal system

Abstract

Detrital zircons from Holocene beach sand and igneous zircons from the Cretaceous syenite forming Cape Sines (Western Iberian margin) were dated using laser ablation – inductively coupled plasma – mass spectrometry. The U–Pb ages obtained were used for comparison with previous radiometric data from Carboniferous greywacke, Pliocene–Pleistocene sand and Cretaceous syenite forming the sea cliff at Cape Sines and the contiguous coast. New U–Pb dating of igneous morphologically simple and complex zircons from the syenite of the Sines pluton suggests that the history of zircon crystallization was more extensive (ca 87 to 74 Ma), in contrast to the findings of previous geochronology studies (ca 76 to 74 Ma). The U–Pb ages obtained in Holocene sand revealed a wide interval, ranging from the Cretaceous to the Archean, with predominance of Cretaceous (37%), Palaeozoic (35%) and Neoproterozoic (19%) detrital‐zircon ages. The paucity of round to sub‐rounded grains seems to indicate a short transportation history for most of the Cretaceous zircons (ca 95 to 73 Ma) which are more abundant in the beach sand that was sampled south of Cape Sines. Comparative analysis using the Kolmogorov–Smirnov statistical method, analysing sub‐populations separately, suggests that the zircon populations of the Carboniferous and Cretaceous rocks forming the sea cliff were reproduced faithfully in Quaternary sand, indicating sediment recycling. The similarity of the pre‐Cretaceous ages (>ca 280 Ma) of detrital zircons found in Holocene sand, as compared with Carboniferous greywacke and Pliocene–Pleistocene sand, provides support for the hypothesis that detritus was reworked into the beach from older sedimentary rocks exposed along the sea cliff. The largest percentage of Cretaceous zircons (<ca 95 Ma) found in Holocene sand, as compared with Pliocene–Pleistocene sand (secondary recycled source), suggests that the Sines pluton was the one of the primary sources that became progressively more exposed to erosion during Quaternary uplift. This work highlights the application of the Kolmogorov–Smirnov method in comparison of zircon age populations used to identify provenance and sediment recycling in modern and ancient detrital sedimentary sequences.

Revisiting the Intermediate Sediment Repository Concept Applied to the Provenance of Zircon

“…A reference study by Sircombe [13] on the provenance of Cenozoic siliciclastic deposits from eastern Australia made emphasis on the concept of the intermediate sediment Sedimentary rocks may contain zircon grains derived from older sources that are not exposed in the provenance areas draining to the basin; thus, they pass through an intermediate sediment repository (ISR) before reaching the sink [9,13]. Comparing the detrital zircon population of siliciclastic rocks with the crystallization ages of potential protosources (i.e., the igneous or metamorphic rock [14][15][16][17] in which zircon crystallizes) or an ISR that includes grains recycled directly from protosources (first-cycle erosion) and an older ISR is crucial in provenance studies [9,13]. Nevertheless, recycling from older sedimentary deposits may be more significant than first-cycle derivation from a protosource.…”

“…The sea cliffs mostly comprise the Pliocene-Pleistocene sandstones and conglomerates of the Alvalade Basin (north of Cape Sines), the Cretaceous plutonic rock exposures of Cape Sines, and the Carboniferous metasedimentary rocks of the South Portuguese Zone (south of Cape Sines) [16,[28][29][30] (Figure 2C) that represent the uplifted pre-Mesozoic basement of southwest Iberia.…”

“…Cape Sines mostly consists of an Upper Cretaceous pluton (circa 77-74 Ma [16,37]) composed of syenite, gabbro, diorite, and mafic breccias, surrounded by the host Middle-Upper Jurassic limestones of the Alentejo Basin. Cretaceous plutonism occurred in a postrift setting that lasted throughout the rotation of the Iberia microplate and the initiation of Alpine compression [37].…”

“…The quantitative analysis presented in this study was based on a compilation of detrital zircon U-Pb ages from Holocene beach sands [16] and their potential metasedimentary and sedimentary sources [16,28,29,33,34,[39][40][41], as well as igneous zircon ages from Sines plutons [16,30]. LA-ICP-MS measurements, 90-110% concordant 206 Pb-238 U ages for grains younger than 1.0 Ga, and 207 Pb- 206 Pb ages for older grains [41] were used to compare the distinct populations of zircon U-Pb ages obtained.…”

Correlation Analysis of Sedimentary Rocks of Novohrad Block (Volynsky Megablock of Ukrainian Shield)

“…На сьогодні статистичні методи в лі-тології мають помітно менше поширення, ніж в геохімії, геофізиці, гідрогеологіїї. Серед останніх робіт досить вдалими застосуваннями цих методів є такіі: [15], в ній за допомогою критерію Колмогорова-Смірнова склад цирконів важких фракцій використаний для з'ясування походження сучасних і стародавніх уламкових осадових послідовностей; у роботі [16] застосовані аналіз голо-вних компонент і кластерний аналіз для інтерпретації каротажних даних свердловин, що були пробурені у межах Карпатського крайового прогину; у роботі [13] статистичний аналіз гранулометричного складу пісків використаний для оцінки берегової морфодинаміки; у роботі [17] перетворення Фур'є і аналіз головних компо-нент використані для дослідження форм і поверхонь піщинок флювіального, флювіогляціального і еолового походження. Автору невідомі приклади застосування кореляційного аналізу для вивчення осадового чохла того чи іншого кристалічного щита.…”