Remanent magnetization of oolitic ironstone beds, Hazara area, Lesser Himalayan thrust zone, Northern Pakistan: Its acquisition, timing, and paleoenvironmental implications

Abstract

Chamosite-hematite type oolitic ironstone is distributed in the Cretaceous-Tertiary (K-T) boundary zone of the Hazara area, Lesser Himalayan thrust zone, in the northwestern margin of the Indo-Pakistani subcontinent. A total of 52 oriented samples were collected from 6 beds in two open pit mines, Nathia Gali and Bagnotar. Ferromagnetic properties of the oolitic ironstone are dominated by fine-grained hematite that possesses a characteristic remanent magnetization (ChRM). The ChRM is a chemical remanent magnetization (CRM) acquired by the hematite which formed from Fe-rich initial materials (iron hydroxides) during early diagenesis of the ironstone bed. The direction of the remanent magnetization indicates that the magnetization was acquired in an equatorial region (average inclination = 2°, paleolatitude = 1°N), which is consistent with the paleoposition of the Indian subcontinent during early Paleocene time, as estimated by previous data. The initial Fe-rich sediments were deposited under anoxic conditions, probably in a non-marine or brackish environment. During early diagenesis, after development of oolitic textures, the paleoenvironment became arid, where the CRM was acquired through the conversion of amorphous hydroxides or goethite to fine-grained hematite. The paleomagnetic results reveal complicated local rotational movements of oolitic ironstone blocks about vertical axes, which might be a result of intense thrusting within the terrane after early Tertiary collision between India and Asia.

Toarcian–Kimmeridgian depositional cycles of the south-western Morondava Basin along the rifted continental margin of Madagascar

“…Sturesson et al (2000) propose that iron ooids form in a shallow turbid sea directly next to volcanism. In contrast, Yoshida et al (1998) suggest rather a non-marine or brackish environment to promote iron-ooid formation. Oxyhydroxides of iron and aluminium, silicon oxide and calcium carbonate are the main components of fossil and modern iron-ooids (Sturesson et al 2000).…”

Rock Magnetism of Late Cretaceous to Middle Eocene Strata in the Lesser Himalaya, Western Nepal: Inferences Regarding the Paleoenvironment

“…Zone I starts with a basal fluvial detritus in the form of siliceous sandstone followed by a pebbly conglomerate (Figures 2, 3), through local high-energy ephemeral channel systems derived from the adjacent highlands (not highlyelevated mountains), as a result of erosional processes, in response to active tectonics. These sediments are enriched in Fe-silicates and Fe-oxyhydroxides and some ferruginous nodules, probably showed earlier diagenetic processes under anoxic conditions (reducing conditions) developed by bacterial activities in the organic materials, and the high sulfate content possibly under brackish conditions, and occasionally under nonmarine conditions (Figure 2 and Figure 9A) (Harder, 1989;Yoshida et al, 1998;Shouyun et al, 2002). In addition, the multiple thin coal layers in zones I, II, and IIIA, with some ash and sulfur, sandwiched between greenish-gray sandstone and siltstone in zone I (Figure 2), originated from a peat swamp in a thick forest moor in a humid and marshy environment.…”

Genesis of langrial iron ore of hazara area, khyber pakhtunkhaw, parkistan

“…The Paleocene Lockhart Formation is lying above the ironstone beds and Cretaceous Kawagarh Formation (Table 1) is lying below the Ironstone beds [8,10,11] . The Hangu Formation is overlain by the Lockhart Limestone [8,10,11] . Iron beds also exist at places in the cores of both limbs of anticlines of Paleocene Lockhart Limestone.…”