About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 66 (1982)

Issue: 10. (October)

First Page: 1700

Last Page: 1700

Title: Sedimentology and Paleolimnology of Miocene Peace Valley Formation, Ridge Basin, Central Transverse Range, California: ABSTRACT

Author(s): Paul R. Smith

Article Type: Meeting abstract

Abstract:

The Peace Valley Formation of Miocene age occupies the axis of an asymmetrical trough in southern California known as the Ridge basin. Sandstone tongues of the Ridge Route Formation extend across the basin and separate the Peace Valley Formation into five members: the Paradise Ranch, Osito Canyon, Cereza Peak, and Posey Canyon Shale Members and the Alamos Canyon Siltstone Member.

The Paradise Ranch shale is a relatively deep freshwater facies, which was deposited in an anoxic lake that possibly was deeper than 65 to 80 ft (20 to 25 m). This unit consists of clay shale with interbedded turbidites, which form upward-thickening depositional lobes.

The Osito Canyon and Cereza Peak shales are shallow freshwater facies. Claystone is the dominant lithology in this extensively bioturbated facies. Deltaic distributary-channel and channel-levee deposits occur in this facies. Wave ripples, ostracodes, and bioturbation suggest deposition in an oxic lake. The sediment accumulation rate for this facies is from 11.1 to 11.7 ft/1,000 years (3.1 to 3.3 m/1,000 years), which is more than twice that of the deep freshwater facies 5.1 ft/1,000 years (1.4 m/1,000 years).

The Posey Canyon Shale and Alamos Canyon Siltstone are deep, brackish-water facies. The absence of insect burrows, mammal tracks, wave ripples, and mudcrack casts suggests that the lake was deeper than wave base or seasonal exposure, which may indicate depths from 65 to 80 ft (20 to 25 m). Dolostone, analcime-rich shale, clay shale, and claystone, as well as debris-flow and turbidite deposits, occur in this facies. Ridge Basin Lake was probably chemically stratified during accumulation of the deep brackish-water facies. The change from shallow freshwater to deep brackish-water deposition probably reflects a change from a hydrologically open to a closed basin.

Vitrinite reflectance indicates that, although the vertical composite thickness of the Peace Valley Formation exceeds 5 mi (8 km), the vertical thickness never exceeded 2.5 mi (4 km) at any given location.

End_of_Article - Last_Page 1700------------

Copyright 1997 American Association of Petroleum Geologists