Geology of the Interandine Basin of Cuenca, Ecuador

Abstract

The region which forms the subject of this paper is in the southern part of the Republic of Ecuador (Fig. 1) in the Provinces known as Canar and Azuay, and is situated between the two principal cordilleras of the Andes at an elevation of about 8,500 feet above sea-level.

The stratigraphical paleontology of the Tertiary non-marine sediments of Ecuador

“…The paleontology is completely revised. The early stratigraphy (Sheppard, 1934;Fiddle, in Fiddle and Palmer, 1941) was somewhat confused as it was not appreciated that the so-called "Cuenca Shales" were a hybrid deposit, with the similar lithologies of the Loyola, Guapan, and Mangan formations not stratigraphically distinguished. The correct sequence was first recognized by Erazo (1957) and this has been adopted, with minor nomenclatural changes, by subsequent authors.…”

“…It was only the Biblian Anticline outcrop which was known to Sheppard (1934) and Fiddle and Palmer (1941). However, the fossiliferous horizon within the "Biblian Sandstone and Conglomerate" locality of the above authors, exposed on the flanks of the small anticline (377,990) between Biblian and 2 The Giron Basin is separated from the Cuenca Basin by a blanket of Pleistocene volcanic deposits.…”

“…-Only a very sparse fauna has been collected from this formation. The fossiliferous Biblian Sandstone and Conglomerate locality of Sheppard (1934) and Fiddle and Palmer (1941) is the basal bed of the Loyola Formation and is fully discussed below. The author has found a thin shell bed composed almost entirely of Doryssa bihliana (Marshall and Bowles), but with rare Diplodon giiaranianus biblianus (Marshall and Bowles) in the uppermost part of the Biblian Formation at only two localities near El Valle (250, 757; 278, 780) (loc.…”

“…The Cuenca White Shales of Sheppard (1934) were defined as occurring between the Biblian Sandstones and Conglomerates, and the Azogues Sandstone. By this definition they are synonymous with the Loyola Formation, but, from an examination of Sheppard's Fig.…”

“…Liddle (in Liddle and Palmer, 1941:22) also included the shales and coal of what is now known as the Mangan Formation in the Cuenca Shales. Additionally, the fossiliferous "Biblian Sandstone and Conglomerate" locality of Sheppard (1934) and Liddle and Palmer (1941) at the classic anticlinal section between Biblian and Azogues, is in fact the overstepping basal bed of the Loyola Formation. Erazo (1957:13-14) was the first to recognize much of the confusion, but no new names were given to the revised strata.…”