New paleomagnetic data for the Hauterivian-Aptian deposits of the Middle Volga region: A possibility of global correlation and dating of time-shifting of stratigraphic boundaries

Abstract

The aim of this project was to study the paleomagnetic stratigraphy of the Hauterivian-Aptian deposits in the Middle Volga region, namely in the areas of the Saratov, Samara, and Uliyanovsk right-hand Volga areas. Original data were obtained for the first time for the magnetic polarity of the Hauterivian and Barremian rocks of the Russian Platform. The results obtained for the Aptian rocks agree very well with the results of the previous paleomagnetic studies which had been carried out in the Uliyanovsk region earlier [Baraboshkin et al., 1999] and in the vicinities of Saratov City [Grishanov, 1984]. Based on the complex correlation of the bio-and magnetostratigraphic data for the rocks from the Middle Volga region, the North Caucasus, the North Mediterranean area, and South England, it is shown that the stage and substage boundaries of the Hauterivian, Barremian, and Aptian stages differ in terms of the absolute age from the similar boundaries in the Boreal Belt by a value of some 10 5-10 6 years, which is comparable with the duration of the Early Cretaceous ammonite zones. The diachronism of the Lower Aptian ammonite zones (Deshayesites volgensis-D. forbesi) and of the Middle Aptian Parahoplites melchioris zone in different regions. The results of this study called for a complex substantiation and tracing of the units of the General Stratigraphic Scale (GSS). The basic GSS unit must be a stage, rather than a zone, because where boundaries were traced over a large territory, the asynchronism of the boundaries between the zones is comparable with the duration of the zones, whereas in the case of a stage it is 1-2 orders of magnitude lower. Geomagnetic inversions or isotopic data can be used to test the isochronism of stratigraphic boundaries.

On Interdependence of the Paleomagnetic Field Characteristics

“…The magnetite was the main carrier of samples magnetization. Guzhikov et al [2003] the magnetization of these rocks was of orientational nature.…”

The use of sedimentary rocks to determine the intensity of the ancient geomagnetic field

“…Êðîìå òîãî, ïîñêîëüêó íå âñå îòëîaeåíèÿ ïðèãîäíû äëÿ îïðåäåëåíèé íàïðÿaeåííîñòè ãåîìàãíèòíîãî ïîëÿ, òî íà ïðåäâàðèòåëüíîì ýòàïå èññëåäîâàíèé îñóùåñòâëÿåòñÿ èõ ðàçáðàêîâêà. Êðèòåðèè, ïî êîòîðûì ïðîâîäèòñÿ îòáîð îñàäî÷íûõ îáúåêòîâ, ïðèãîäíûõ äëÿ ðåêîíñòðóêöèé ïàëåîíàïðÿaeåííîñòè, ïîñòîÿííî ñîâåðøåíñòâóþòñÿ [King et al, 1983;Tauxe, 1993;. Guzhikov et al, 2003].…”

“…Èçâåñòíû ðàçëè÷íûå ñèñòåìû òåñòèðîâàíèÿ, ïîçâîëÿþùèå ðàçëè÷àòü îñàäêè, îáëàäàþùèå ïðåèìóùåñòâåííî îðèåíòàöèîííîé ëèáî ïðåèìóùåñòâåííî õèìè÷åñêîé íàìàãíè-÷åííîñòüþ. Íàïðèìåð, ñîãëàñíî ðàáîòå [Guzhikov et al, 2003], îá îðèåíòàöèîííîé ïðèðîäå îñòàòî÷íîé íàìàãíè÷åííîñòè ñâèäåòåëüñòâóþò ñëåäóþùèå ïðèçíàêè: 1) íèçêàÿ ìåaeïëàñòîâàÿ êó÷íîñòü (äî íåñêîëüêèõ äåñÿòêîâ) è îáðàòíàÿ çàâèñèìîñòü âíóòðèïëàñòîâîé êó÷íîñòè îò ðàçìåðîâ ÷àñòèö îñàäêà, 2) íèçêèå çíà-÷åíèÿ ôàêòîðà Êåíèãñáåðãåðà ( ìåíüøå 0,1 ) , 3) íàëè÷èå îáëîìî÷íûõ çåðåí ìèíåðàëà íîñèòåëÿ îñòàòî÷íîé íàìàãíè÷åííîñòè. Ýòè òåñòû ìîãóò áûòü äîïîëíåíû.…”

“…Òåì íå ìåíåå áûëà ïðåäïðèíÿòà ïîïûòêà îïðåäåëåíèÿ äèàïàçîíà çíà÷åíèé ýòîãî êîýôôèöèåíòà äëÿ ñîâðåìåííûõ ìîðñêèõ è ïðåñíîâîäíûõ äîííûõ îòëîaeåíèé (òîíêèé ïåñîê àëåâðèòû ãðóáàÿ ãëèíà ) , îáëàäàþùèõ îðèåíòàöèîííîé íàìàãíè÷åííîñòüþ è îáðàçîâàâøèõñÿ â ðàçëè÷íûõ êëèìàòè÷åñêèõ çîíàõ. Çàêëþ÷åíèå îá îðèåíòàöèîííîé ïðèðîäå íàìàãíè÷åííîñòè ýòèõ îñàäêîâ ñäåëàíî íà îñíîâàíèè êîìïèëÿöèè òåñòîâ èç ðàáîò [Guzhikov et al, 2003;Ñòðàõîâ, 2008]: íèçêèå çíà÷åíèÿ ôàêòîðà Êåíèãñáåðãåðà, íà-ëè÷èå îáëîìî÷íûõ çåðåí ìàãíèòíûõ ìèíåðàëîâ è ïðîïîðöèîíàëüíîå (âåñó ôðàêöèé) ðàñïðåäåëåíèå çíà÷åíèé I rs ìåaeäó ôðàêöèÿìè, ïîëó÷åííûìè â ðåçóëüòàòå ãðàíóëîìåòðè÷åñêîãî àíàëèçà.  òàáë.…”

Behavior of paleointensity during the Paleogene

“…The results of separation of grains of magnetic minerals and thermomagnetic analysis suggested that terrigenic magnetite is the main carrier of the sediments magnetization (Bogachkin, 3 2004;Molostovskii et al, 2007). According to Guzhikov et al (2003) the following criteria indicate the orientational nature of the sediments' NRM and, hence, their primacy: the presence of detrital grains of ferromagnetic minerals, low values of the Königsberger factor (Q < 0.1) and low interlayer concentration of distribution of the vectors of remanent magnetization directions (k = 5 -15).…”