Terrigenous Accumulation Rates Research Articles

A Global Reassessment of the Spatial and Temporal Expression of the Late Miocene Biogenic Bloom

AbstractThe Late Miocene Biogenic Bloom (LMBB) is a late Miocene to early Pliocene oceanographic event characterized by high accumulation rates of opal from diatoms and calcite from calcareous nannofossils and planktic foraminifera. This multi‐million year event has been recognized in sediment cores from the Pacific, Atlantic, and Indian Oceans. Based on existing studies, it is not clear whether the LMBB is a global omnipresent event, or whether it is restricted to certain regions or oceanographic environments. Moreover, the origin of this event is still widely discussed. In this study, we aim to provide a comprehensive overview of the geographical and temporal aspects of the LMBB by compiling published ocean drilling (DSDP, ODP, and IODP) records of sedimentation rates, and CaCO3, opal, and terrigenous accumulation rates that cover the late Miocene and early Pliocene interval. Our data compilation shows that manifestations of the LMBB are present in many different locations but in a very heterogeneous way. The compilation shows that the sites where the LMBB is expressed are mainly located in areas with a high productivity regime (i.e., upwelling systems). We suggest that one of the possible hypotheses to explain the onset of the LMBB could be a global increase in upwelling intensity due to an increase in wind strength or an increase in deep water formation, ramping up global thermohaline circulation.

Quaternary sedimentary regime on the Berthois Spur (Bay of Biscay)

A study of cores from the Celtic Margin shows that high terrigenous accumulation rates occurred at the end of isotopic stage 3 and during isotopic stage 2. These high rates prevailed during rapid changes from relatively warm conditions (Alesund interstadial) to maximum glacial condition. The input of terrigenous material may have culminated with the blockage of the North Sea by an ice sheet and the diversion of NW European flumes toward the Celtic Margin. The uppermost sediments are in a state of overconsolidation as the consequence of erosional processes following the episod of high sediment supply.

Accumulation Rates of Biogenous Silica and Terrigenous Detritus in Late Miocene-Early Pliocene Santa Maria Basin, California: ABSTRACT

The upper-Miocene-lower Pliocene laminated to massive diatomaceous strata of the Santa Maria basin encompass portions of the Monterey and overlying conformable to nonconformable Sisquoc Formations and record the continued accumulation of admixed siliceous (mostly diatoms) and terrigenous (silt and clay) components in a Neogene borderland basin. Lithologies, which vary from diatomite to diatomaceous mudstone, are the result of fluctuations in slope-accumulating silica and terrigenous debris. Bulk accumulation rates, as well as silica and terrigenous component accumulation rates, were calculated for four measured sections using accurate stratal thicknesses, absolute ages, rock compositions, and bulk densities. Bulk accumulation rates range from less than 20 to greater than 70 mg/cm/sup 2//year and are comparable to bulk accumulation rates in the present-day Santa Barbara basin and Gulf o f California. Silica accumulation rates (20-30 mg/cm/sup 2//year) suggest that sedimentation took place beneath productive waters and they exceed those encountered in other high-productivity oceanic areas, such as the Bering Sea and Peruvian coastal waters. Relatively high terrigenous accumulation rates (18-35 mg/cm/sup 2//year) reflect the dilution of these high-productivity waters by continentally derived detritus. Comparison of calculated accumulation rates with rates determined for similarly aged strata of the Santa Barbara basin reveals that silica and terrigenousmore » debris were accumulating at higher rates within the Santa Maria basin. These differences are due to the complex interplay of tectonics and oceanographics and to the proximity of the basins relative to the strandline.« less