Calcareous nannofossil biostratigraphy from a 15-km transect (Cocos plate to Caribbean plate) across the Middle America Trench, Nicoya Peninsula, Costa Rica

Content Provider	Semantic Scholar
Author	Muza, Jay Phillip
Copyright Year	2001
Abstract	Three Pleistocene, five Pliocene, and thirteen late and middle Miocene calcareous nannofossil datums have been identified in the Leg 170 cored sequences collected from a transect across the Middle America Trench off the Nicoya Peninsula. Although some nannofossil zones could not be delineated, particularly in the Pliocene and upper Miocene, there appears to be a complete or very nearly complete Pleistocene through lower Miocene section at Sites 1039 and 1040. The oldest assemblages, observed at Site 1039 and 1040, are latest early Miocene in age (nannofossil Zone NN4). These assemblages are associated with gabbro intrusions into the basal sediments (one contact metamorphic hornfels sample contains relict nannofossils), indicating an age for the intrusion event of between 15.6 and 18.2 Ma at both Sites 1039 and 1040. Reference Site 1039, located on the Cocos plate, provides the best-preserved sequence of sediments of late Pleistocene to latest early Miocene age. The sediments cored in the prism sections at Sites 1040, 1041, 1042, and 1043 all indicate that the age of nannofossil assemblages in the prism sediments, including the toe, wedge, and apron, are all Pleistocene with a considerable amount of upper Miocene reworking. A period of low sediment accumulation rates (~5.3 m/m.y.) is recorded for Pliocene and upper Miocene sediments at Sites 1039, 1040, 1Muza, J.P., 2000. Calcareous nannofossil biostratigraphy from a 15km transect (Cocos plate to Caribbean plate) across the Middle America Trench, Nicoya Peninsula, Costa Rica. In Silver, E.A., Kimura, G., and Shipley, T.H. (Eds.), Proc. ODP, Sci. Results, 170, 1–63 [Online]. Available from World Wide Web: . [Cited YYYY-MM-DD] 2Department of Physical Sciences (Oceanography), Broward Community College Central Campus, Davie FL 33314, USA. jmuza@broward.cc.fl.us Initial receipt: 8 December 1999 Accepted: 7 August 2000 Web publication: 1 November 2000 Ms 170SR-008 J.P. MUZA CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY 2 and 1043. Pliocene calcareous nannofossil assemblages characteristic of the ~2.5to 3.75-m.y. time interval (nannofossil Zones NN16 and equivalent nannofossil Subzones CN12b and CN12a) were not resolved at any site. Nannofossil Zones NN15, NN14, NN13, and NN12 (early late Pliocene to early Pliocene) could not be resolved at any site either because of the absence of marker species. Within the Miocene at Sites 1039 and 1040, nannofossil Zones NN10–NN6 were difficult to differentiate because of the absence of several species that define the zonal boundaries. These intervals, where the nannofossil zones have not been resolved or are partially resolved, are primarily composed of carbonate ooze deposited during an ~8.5-m.y. (2.5–11 Ma) low sediment accumulation rate time interval. The absence of many of the marker species is attributed to warmer water conditions during those periods. Many of the same marker species are absent in the sediments recovered from nearby Deep Sea Drilling Project Site 155 in the Panama Basin. INTRODUCTION Subduction of oceanic lithosphere, with its blanket of biogenous and terrigenous sediments, is an essential part of the global pathway by which the solid earth is recycled. This part of the cycle is also the least documented and, therefore, the least understood, in terms of the mass balance between subducting oceanic lithosphere, the portion of the lithosphere that descends into the mantle, and the portion that emerges elsewhere (Kimura, Silver, Blum, et al., 1997). Part of the subducted lithosphere may be accreted to or may underplate the overriding plate, released through pore water kinetics and chemistry and ultimately ejected or released as volcanic solids, liquids, and gases or emplaced as magma plutons. An understanding of the nature of this recycling—particularly the amounts and rates at which the lithosphere is underplated or accreted—is important to understanding the processes of earthquake generation at subduction zones (Kimura, Silver, Blum, et al., 1997). In addition, determining the mass balance of carbonate material that enters the subduction zone and leaves as carbon dioxide and other carbon compounds is important in aiding our understanding of the complex cycle of carbon dioxide in our atmosphere, biosphere, and lithosphere and the impacts to trends in global temperatures. To this end, Ocean Drilling Program (ODP) Leg 170 drilled and cored oceanic lithosphere in a transect across the Middle America Trench, off of the Nicoya Peninsula, Costa Rica (Fig. F1). A comprehensive investigation has been undertaken to arrive at an understanding of the fate of subducted materials. One study of importance to this endeavor is the derivation of accurately age-dated fossils from the Leg 170 cores. PURPOSE The purpose of this study is to synthesize and provide as accurate and precise age-depth models as possible, utilizing calcareous nannofossils for age determination, for all of the cores recovered during ODP Leg 170 seaward of the Costa Rican Nicoya Peninsula on the subducted margin. Comprehensive calcareous nannofossil species range and distribution charts have been constructed from all the sites cored during Leg 170 from which the age-depth models have been synthesized. Garza Carillo Tamarindo
File Format	PDF HTM / HTML
DOI	10.2973/odp.proc.sr.170.008.2000
Alternate Webpage(s)	http://www-odp.tamu.edu/publications/170_SR/VOLUME/CHAPTERS/SR170_05.PDF
Alternate Webpage(s)	https://doi.org/10.2973/odp.proc.sr.170.008.2000
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article