Grails/Hibernate error "sequence does not exist" on hibernate_sequence

I am using Grails and connected my app to an Oracle db. When I try to create an object (via the corresponding view in the app front-end) I get this error:

Hibernate: select hibernate_sequence.nextval from dual | Error 2014-03-10 12:03:14,596 [http-bio-8080-exec-5] ERROR util.JDBCExceptionReporter - ORA-02289: sequence does not exist

Of course, adding this manually to the db fixed the issue:

CREATE SEQUENCE hibernate_sequence START WITH 1 INCREMENT BY 1;

But I am wondering why I needed to manually create that seq in the db and why Hibernate couldn't create it automatically. Any idea? Any way I can set Hibernate to create it on its own?

Thanks.

This is my DataSource.groovy, set up with a sand-box db:

dataSource {
    pooled = true
    driverClassName = "oracle.jdbc.OracleDriver"

    dialect = "org.hibernate.dialect.Oracle10gDialect"
    dbCreate = "update" 
    url = "jdbc:oracle:thin:@localhost:1521/ORCL"
    username = <user>
    password = <psw>

    logSql = true

    properties {
        validationQuery="select 1 from dual"
        testWhileIdle=true
        timeBetweenEvictionRunsMillis=60000
    }

}
hibernate {
    cache.use_second_level_cache = true
    cache.use_query_cache = false
    cache.region.factory_class = 'net.sf.ehcache.hibernate.EhCacheRegionFactory'
}